SURFACE MODIFICATION STUDIES OF POLYPROPYLENE USING

ULTRAVIOLET RADIATION AND OZONE

by

Liam Francis MacManus

Department of Chemistry

Submitted in partial fulfillment of the requirements for the degree of

Master of Science

Faculty of Graduate Studies The University of Western Ontario

London, Ontario January 1998

O Liam F. MacManus 1998

National Library Bibliothéque nationale du Canada

Acquisitions and Acquisitions et Bibliographie Services senrices bibliographiques

395 Wellington Street 395. nie Wellington OttawaON K I A M OFtawaON KlAON4 Canada CaMda

The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loaq distri-bute or sell reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/nlm, de

reproduction sur papier ou sur format électronique.

The author retains ownership of the L'auteur conserve la propriété du copyright in tbis thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation.

Abstract

Chemical reactions of the d a c e of polypropylene (PP) in the presence of various

combinations of ultraviolet light and ozone gas (UVO) conditions were studied. Exposure

of the polymer suface was carried out in a laboratory scale W O reactor where the followuig

parameten codd be varied: ozone concentration, wavelength of W radiation, pulsing of the

W larnps, the treatment distance between the PP and the larnps, and water vapour

concentration. Modification of the energy of the PP surface was followed using advancing

and receding contact angle measurements. Two spectroscopie techniques, X-ray

Photoelectron Speceoscopy ( X P S ) and Attenuated Total Reflectance Fourier Transform

b e d Spectroscopy (Am-FTR), were used to rnonitor changes in the surface chernistry

of the polymer.

Oxidation of the PP surface is proposed to occur through two altemate mechanisms:

(1) insertion of an O ('D) atom to form ether linkages, or (2) hydrogen abstraction by O ('P),

followed either by crosslinking or by reaction with oxygen species to form carbonyl and/or

carboxyl functional groups. It was found that reaction (1) dominates initially, but that its rate

is reduced by the formation of products from reaction (2). It appears that the ether functionai

groups produced by reaction (1) are primarily responsible for increased surface energy.

Carbonyl, carboxyl, and hydroxyl groups appear to have little additional effect on surface

energy; it is proposed that these groups are strongly involved in intni-molecular hydrogen

bonding, thereby decreasing their availability to contribute to increased surface energy. High

energy UV radiation was found to play ody a rninor role in the surface modification of PP.

Of the range of ozone concentrations studied, no clear relationship appean to exist between

iii

ozone concentration and rate of modification of the surface; thus, the concentration of ozone

does not affect the relative concentrations of the products of the competing reactions.

Increased surface oxidation and decreased contact angles were observed when the lamp-to-

sample distance was minimized. The presence of water vapour during UV0 treatment was

found to lead to greater oxygen uptake after short term treatments, but did not resdt in

increased surface energy.

Acknowled~ementg

1 would like to thank Dr. Stewart McIntyre for his mtiring support and guidance

throughout this work 1 would also Like to thank Ms. Mary Jane Walzak for al1 of her help,

suggestions and support. Thanks to Surface Science Western and the Department of

Chemistry for the financial support for this work. To ail of the staff at Surface Science

Westem 1 would like to express deep thanks for their help and support., technical and

otherwise, whenever needed. Thanks as well to my fetlow graduate and undergraduate

students at SSW and in the Department of Chemistry for providing diversions apart from

academia Finally, many thanks to my family and fnends for their constant support

throughout my time in graduate school.

Table of Contents

* . . . Certificate of Examination ................................................................................................... il

... .............................................................................................................................. Absmct 111

.............................................................................................................. Acknowledgements Y

Table of Contents ................................................................................................................ vi

List of Figures ..................................................................................................................... ix

. . ..................................................................................................................... List of TabIes XI

CHAPTER 1 - Introduction ................................................................................................. 1

. . ............................................................................................. 1 . 1 Objectives of thesis 1

............................................................................... 1.2 General Review and Theory 1

1.2.1 Surface Chemisû-y and Polymers ................................................................ 1

1 2 .2 Polymer Surface Modification ........................ .... ........................................ 6

........................................................................................... 1 2 . 3 Polypropylene 12

1 2.4 W O Processes and gas phase reactions .................................................. -1 3

1.3.5 Reactions with the polypropylene surface ................................................ 17

1.3 Research to be undertaken ............................................................................... 2 5

........................................................................................................ 1 -4 References 27

..................................................................................... CHAPTER 2 - Experirnental 3 t

................................................................. 2.1 Surface Anal ytical Techniques . 1

....................................................................... 2.1.1 Contact Angle Goniomeîry 3 1

. . 2.1.1 . 1 Pnnciples ........................................................................................ 3 1

.................................................................................. 2.1 . 1.2 Experimental 34

2.1.2 X-ray Photoelectron S pectroscopy .......................................................... -34

...... .................... . 2 I .2.1 Principles .. -34

2.1 2.2 Experirnentai ........ ...... ........... +5

2.1.3 Attenuated Total Reflectance Fourier Trziforrn Infiared Spectroscopy .................. .. ................................................................. 52

2.1 -3 -2 Experimentai ........................ ., 63

2.2 Polypropylene .................................................................................................. 63

......................................................................................................... 2.3 Apparatus 64

..................................................... 2.3-1 UV0 Reactor ......................................

......................................................... 2.3 -2 Ozone concentration measurements 73

? ? 2.3.3 Gas inlets .................................................................................................. 76

Experimental ...................................................................... 7 6

................... .*..*.............--..--..--.-----.......*..............*.. 2.3.3 -2 Results .............. 78

2.5 References .............. .,. .............................................................................. 8 2

.............................................. CHAPTER 3 - Reactions with UV0 .................................... 84

............................................................................ .................. 3.1 Introduction ,. 85

............................. 3.2 Effects of irradiation bandwidth and ozone concentration 87

............................................................................................ 3 2 . 1 Experimental 87

.................................................................................. 3.3 W Pulsing experiments 95

3.3.1 Expenmental ............................................................................................. 95

vii

3.3.2 Results and Discussion ................................. .. .................................... 96

3.4 Sample distance fkom lamps .......................................................................... 102

......................................................................................... 3.4.1 Experimental -1 O5

3.4.2 Results and Discussion ......................................................................... 105

9 . 3.3 Effects of water vapour .................................................................................. 108

........................................................................................... 3 S.1 Experimentai 108

3 S.2 Results and Discussion ......................... ,.,. ............................ 108

3.6 Surface chernis - ........................................................................................... 110

3.6.1 High resolution carbon 1s XPS spectra .................................................. 110

3.6.2 ATR-FTIR spec tra. ................................................................................. 120

..................................................................................................... 3 -7 References 1 37

................................................................................... . CHAPTER 4 Final Discussion 3 8

............................................................................................. 4.1 Final Discussion 138

...................................................................................................... 4.2 References 144

.................................................................................................................................. Vita 145

viii

List of Fiares

.............................................................................. Figure 1.1 : Structure of polypropylene -12

Figure 1.2. Possible geometric orientations for polypropylene .......................................... 12

Figure 1.3. Absorption spectra for ozone. 0.. and molecular oxygen. O2 ........................ 16

Figure 1.4: Possible reactions with the PP surface . (a) hydrogen abstraction by O (;P). (b) reaction with molecuiar oxygen. (c) M e r oxidation to produce ketone and ester functionality ............................. 20

Figure 1.5: Possible reactions with the PP surface . (a) O (ID) insertion. (b) reaction of molecular oxygen at an allylic . . carbon position. (c) ozonolysis reaction ........... ... ............................................. 22

Figure 2.1 : Contact angle measurements ........................................................................... 32

Figure 2.2. Photoemission process for a carbon 1 s electron ............. .. ........................... 36

Figure 2.3: X P S survey scans . (a) untreated PP. (b) treated PP (IO minutes U V 0 treatment) ............................... 39

Figure 2.4: High Resolution carbon 1 s spectra . ............................... (a) untreated PP. (b) treated PP (1 0 minutes UV0 treatment) 42

Figure 2.5. X-ray photoelectron spectrometer schematic diagram ........................ .. ........ 47

Figure 2.6: (a) measured high resolution carbon 1s spectnim of a 10 minute ............................... UWO. + ozone treatment. (b) MEM deconvoluted spectnim 51

Figure 2.7. Typicai stretching and bending vibrations for a methylene group .................. 54

Figure 2.8: (a) Typical stretching and bending vibrations for a methyl group. (b) Stretching vibrations and changes in dipole moment ....................................... 56

Figure 2.9. ATR-FTIR spectm of untreated PP .............................................................. 58

Figure 2.10. ATR-FTIR schematic diagram ...................................................................... 62

Figure 2.1 1 : Diagram of the UV0 reactor at SS W ........................................................... .66

Figure 2.12: Emission spectra for the ozone-producing and -decomposing sets of UV lamps ...... ..... ................................................................................................ 69

Figure 2.13: Ozone concentration venus time, during operation of either the hard- or soft-UV larnps ......................................................................................... ..72

Figure 2.14: Ozone concentration venus time, during constant or pulsed operation ................................................................... of the (a) hard- and @) soft- W larnps 75

Figure 2.15: Ozone aansmissometer schematic diagram ................................................... 77

Figure 2.16: Results for gas d e t experiments. (a) 0:C ratio, (b) contact angle measurements.. ...... .... ..... .., ................................................................................ 80

Figure 3.1 : Contact angle measurements for samples treated with a hard- or sofi-W/02 + 0; (1000 sccm 02) treatment regime at three di fferent ozone concen~tions.. ............................................................................. 9 1

Figure 3.2: Results fkom UV pulsing experiments using the hard-UV source. .......... ........*.......... .......... (a) 0:C ratio da& (b) contact angle measurements ,.,, .... 98

Figure 3.3: Results fiom W pulsing experiments using the soft-UV source. (a) 0:C ratio data (b) contact angle rneasurements ........................................ 100

Figure 3.4: % transmission of UV to the polymer surface ............................................... 104

Figure 3.5: 0:C ratio and contact angle data obtained fkom sample distance experiments .......................................................................................................... 1 07

Figure 3.6: High resolution carbon 1 s spectra of two and ten minute hard-üV treated samples, before and afier washing ........................................................... 1 14

Figure 3.7: High resolution carbon 1 s spectra of two and ten minute soft-W treated samples. before and after washing ........................................................... 1 16

Figure 3.8: High resolution carbon 1s spectra of two and ten minute hard-üV treated samples, veated with and without supplementai water vapour ................ 1 18

Figure 3.9: ATR-FTIR spectra of the O-H stretching band region: (1) untreated BOPP sample, (2) two minute hard-Wlwashed sample,

......... (3) two minute hard- W with supplemental water vapoudwashed sample 1 24

Figure 3.10:ATR-FTIR spectra: (a) Ountreated BOPP, Q two minute hard-W/washed sample; (b) results of s p e c d nibtraction of Q fiom O, showing an absorbance band at 1067 cm" ............................. .....,..... ...................................................... 126

Figure 3.1 1 : ATR-FTIR spectra of the C=O stretching band region: (1) untreated BOPP sample, (2) two minute hard-W/washed sample, (3) two minute hard-UV with supplemental water vapoudwashed sample ........ -129

Figure 3.12: ATR-FTiR spectra for 10 minute UVOhid O,-concentration treated samples. C=O stretching region: (a) hard-UV treated, (b) sofi-UV treated.. ...... - 1 32

Figure 3.13: ATR-FTIR spectra for 10 minute hard-UV/supplemental water vapour treated sample, C=O stretching region ..................................................... 136

List of Table

..................... Table 2.1 : Carbon 1 s chernical shifb fiom 285.0 ev ., ................................ 49

.................................................................................... Table 2.2. UV0 treatment regimes 70

Table 3.1 : Contact angle results for ozone concentration and irradiation bandwidth experimen ts .......................................................................................... 88

Table 3.2: XPS results for ozone concentration and irradiation bandwidth ........................................................................................................... experiments 9 3

.................................. Table 3.3. Expenmental results for sample distance experiments 105

...................................................... Table 3.4. XPS results for water vapour experiments 109

....................................... Table 3.5. Contact angle results for water vapour experiments 109

................ Table 3.6. Areas obtained from peak-fitted hi& resolution carbon 1s spectra 111

Table 3 -7: IR spectral band assignments .......................................................................... 121

Table 3.8: Results from band-ratio analysis of ATR-FTIR spectra of hard- ............. and soft-UV 10 minute treated samples at the mid ozone concentration 130

Table 3.9: Results from band-ratio analysis of ATR-FTIR spectra, for samples ........................................... treated with and without supplemental water vapour 134

HAPTER 1 - Introduction

1.1 Obiectives of thesis

There has been extensive past research in the area of polymer surface modification,

including studies on the UV0 surface modification of polypropylene (PP). The common

goal of the majority of these studies has been related to increasing the water-wettability of

the naturally inert polymer surface. While UV0 has been recognized as a possible

alternative for the modification of polymer surfaces, there h a not been much effort to

optimize the treatment parameten for a rapid and extensive surface modification by UV0

treatment. One of the objectives of this midy was to identi@ the optimal parameters for the

W O surface treatment of PP. This was done by examining the effects, on the treatment, of

ozone concentration, wavelength of W used, UV larnpto-sample distance, and the presence

of water vapour. The second objective of this çhidy was to try and elucidate the mechanism

of surface modification by W O treatment., by identifying the most active species during the

treatments and to identify the role of the W light in the modification, other than producing

reactive gaseous species. The third objective of this work aims to relate the chemical

functionalization of the surface to its increased wettability. There has been work done in the

past with respect to objectives two and three; it is hoped that the results of this research will

make a usehl contribution to the general understanding in these areas.

1.2 General Review and Theorv

1.2.1 Surface Chemistry and Polymers

As an introduction to the work undertaken in this project, it is necessary to begin with

a discussion of the k e energy of surfaces, and the hydrophobicity/hydrophilicity, or the

wettability, of surfaces, and how these thermodynamic concepts apply to polymer systems.

Only a very basic overview of the fundamental ideas of s d a c e thermodynamics will be

presented here. For a full treatment of the physical chemistry of surfaces, Adamson (') should

be consulted. More information on surface chemistry, and how it relates to surface

wettability and polymer systems, can also be f o n d in papers by a number of authon ('4!

Al1 surfaces possess a s d a c e fiee energy, or surface tension. Surface tension refers

to the revenible work required to create a unît area of surface at constant temperature,

volume, and chernical potential, or the Gibbs energy change upon creating a surface of area

dA:

where y is the surface tension, or surface fiee energy. Therefore, work must be done (or

energy m u t be supplied) to add molecules to the surface fiom the interior of the matenal.

Mathematically, the t e n s s d a c e fke energy and surface tension are equivaient, and c m be

used interchangeably. Surface tension is the term originally useci, and came from the idea

that a liquid surface has a surface 'skin', arising from an imbaiance of molecular forces at

the liquid-air interface. When dealing with two matenals, the term "interfaciai fiee energy"

can be used, also an equivalent term to both surface fiee energy and surface tension.

Surface free energy can be subdivided into component fiee energies:

where y* is the surface k e energy component due to London dispersion, or van der Waal's.

forces, arising from the effects of oscillating temporary dipoles; yP is the surface fkee energy

due to dipole-dipole forces; y" is the surface fke energy due to dipole-induced dipole

forces; and y* is the Surface free energy due to hydrogen-bonding forces (? Equation 1.2 c m

be compressed into the surface energy components arising from dispersion forces, yd, and

that arising h m the sum of al1 of the polar forces, or polar acid-base interactions, y":

For example. the surface energy contribution from polar forces will be zero for a non-polar

solid, such as the polymer poIy(teaafluoroethylene) (Teflon). ï h e surface free energy will

be a resdt of dispersive forces only. Similarly, for a non-polar liquid, such as an alkane, the

surface eneru will be due to the dispersive forces component only.

Hydrogen bonding is one of the components of the polar forces contributing to the

surface fiee energy of a material, or the interfacial f k e energy between materials. For

example, hydrogen-bonding can occur between a carbonyl group (Lewis base) and the

hydrogen atom of a hydroxy 1 group (Lewis acid) (? A liquid or solid having both Lewis acid

and Lewis base character is called a bipolar material, one having neither characteristic is

called an apolar material, and a material having one or the other characteristic is called

monopolar. Hence, water is a bipolar liquid, and a saturated alkane is an apolar liquid.

Similarly, a polymer consisting of saturated hydrocarbon chahs, such as PP, is an apolar

solid.

A material's hydrophobicity or hydrophilicity is detemiined by the extent of Lewis

acid and Lewis base character it possesses. Hence, a hydrophilic surface is more desirable

than a hydrophobie one when developing, for example, an adhesive bond between a surface

and an aqueous-based coûting. The fiee energy of adhesion is defined as the free energy

change per unit area when two unlike bodies are reversibly brought together, or the negative

104 of the work of adhesion:

where AG is the free energy change, y is the surface energy or interfaciai energy, W is the

work of adhesion. and the subscripts 1 and 2 refer to the two bodies involved. Adhesion can

be more simply defmed as "the mechanical resistance to separation of a system of bonded

materials" ? The extent of adhesion will also be affected by surface roughness - actual

mechanical adhesion between two bodies can be affected either positively or negatively by

surface roughness. For more details on surface roughness efTects, references 1. 7, and 8

should be consulted.

The most hy dro pho bic materials are saturated hydrocarbons, and fluorocarbons.

These materiais will not form hydrogen bonds, as they possess little to no Lewis acid/base

character. The surface energy of these materials is due completely to dispersion forces. A

surface will be hydrophilic on account of the presence of Lewis acid groups, or Lewis base

groups, or both, since they will be able to form hydrogen bonds with water. This idea can

be extended to the surfaces of polyrneric solids. For example, a polymer surface containing

ether groups should have more hydrophilic character than a saturated hydrocarbon polymer

surface such as PP. ïherefore. the pol ymer surface containing Lewis acid/base character

should be hydrophilic, or water-wettable.

However, polymer chahs are not static structures, and they will reonent themselves

via macromolecular motions to a form of low surface fiee energy. This is due to a

thermodynamic driving force to minimize the surface free energy (9! Air is a low-energy

medium, so higher-energy surface species, such as ether groups, are not in a

themodynamically stable situation when in contact with air.

will occur, bringing lower-energy groups to the surface.

If possible, chah conformation

This explains the low water-

wettability, or hydrophobicity, of polymer surfaces that possess Lewis acid/base character.

Using contact angle measurements, x-ray photoelectron spectroscopy, and secondary ion

mass spectrumetry, Ochiello et. al. ( Io' studied the interaction of an oxidized polypropy lene

surface with air and water. The authors concluded that when in contact with air, the polymer

reonented the polar groups away fiom the polymerlair interface. When in contact with water,

polar groups remained at the polymerlwater interface. This is a requirement of surface

thermodynarnics: that rearrangement of surface region molecules occurs when possible, such

that the surface which is presented to the air has the lowest possible surface fiee energy ( I l ) .

The generally accepted method of obtaining surface energy information is by classical

means: by rneasuruig the contact angle that a drop of probe liquid makes with a surface.

Contact angle measurements are extremely surface sensitive, probing the outermost

monolayen of a surface "? The larger the surface energy, the smaller the contact angle the

probe liquid will make with that surface. The contact angle is a measurement of the ratio of

surface free energies at the interfaces of three phases (or the interfacial free energies):

surface-& ( y 3 (or the solid surface tension), liquid-air (y,J (or the liquid surface tension),

and surface-liquid ( y 3 (or the interfacial tension, or the interfacial free energy). A

manipulation of Young's equation (' '- ". 14' shows this ratio to be equal to the cosine of the

contact angle (0) at the junction of the three interfaces:

Using Young's equation requires the assumption that the solid surface of interest is

%6 chemically homogeneuus, smooth or flat at an atomic scale, and rigid. It must dso be

assumed that the solid does not react with the probe liquid, or its vapour, and that no

dissolution of the solid in the probe liquid occurs 16).

A value for the fiee energy of a surface can be determined experimentally by

measuring the contact angles of two to three probe liquids, that differ in their polar

characteristics. Meanrring the contact angle of non-polar and polar probe liquids ailows the

determination of the dispersive and polar components, respectively, to the surface fkee energy

? Due to the extensive assumptions required for the use of Young's equation, there has

been much controversy concerning the use of contact angle measurements as an accurate

method to determine specific surface energies (? Obtaining an absolute experimental value

for a specific surface energy can be dificult; it is much easier to get values for changes in

sudace energy (? In any case. changes in surface energy are of more interest when studying

the effects of polymer surface modification. as opposed to obtaining specific surface fiee

energy values. When using the same probe liquid, and testing samples diRering in, for

example, the amount of W O treatrnent, a decrease in contact angle is indicative of an

increase in surface Gree energy.

1.2.2 Polymer Surface Modification

Polymer w has increased greatly in recent years in diverse industries such as the

automohve, biomedical, aerospace, and hi&-technology industries, as well as for consumer

products such as packaging and containers. This increased usage is due to the desirable

physical and chernicd bulk properties of polymers, such as high strength-to-weight ratio, and

chernical and moisture resistance. Unfortunately, these excellent bulk properties extend to

surface regions, resulting in an inert, hydrophobie, very low energy surface. This leads to

problems with adhesion for applications that require binding of two different polymer

systems, or the binding of polymer and metal surfaces. It also creates wetting problems for

paints, inks, and other surface coatings.

While maintaining the bulk properties of a polymer, its outemost surface chemistry

may be aitered through a variety of high energy chemical processes. Ideally, this would

d t in a more water-weîtable surface. due to the incorporation of polar functional groups,

such as hydroxyl or carboxylic acid groups, capable of acidmase interactions. This modified

surface is more likely to form chemical and physical adhesive bonds with prospective

aqueous-based paints, inks, and coatings. Surface modification processes available for use

include: chernical m e n t ('j), corona discharge treatment ( l ' . 14- "- 'O), flame treatment ("-"),

plasma mtrnent '="', ozone treatment '>), and ultraviolet lightlozone gas (WO) treatment

( S 3 . 4 )

Chernical surface treatments have been used in the past. Lee et. al. ( 1 3 ) studied the

oxidation of poiypropylene (PP) film by exposure to chrorniurn (VI) oxide in acetic

acidacetic anhydride solution, hoping to selectively oxidize the tertiary carbon to a tertiary

alcohol. Instead, they detected the development of hydroxyl, ester, ketone, and olefin

fûnctionality. Increased wettability was obtained, but the authors also discovered the loss

of the oxidized material with continued exposure to the reactive solution. Polymer surface

treatment by exposing the s d a c e to lithium-based reagents in tetrahydrofuran (ïHF)/heptane

solution has also ken studied (35! This type of treatment results in the incorporation of the

a b 1 group of the lithium reagent into the polymer surface. Subsequent reaction steps can

lead to the incorporation of sudace hydroxyl and carboxyl groups 06! There are three main

reasons why this type of surface modification is not commonly used currently: the loss of

~ 0 8 newly oxidized polymer surface can occur due to overexposure to the reactive solution; the

treatment consists of mu1 tiple steps, making it inconvenient for possible industrial

applications; and this type of treatment also leads to the production of organic wastes, an

undesirable situation due to environmental and health concem.

Corona discharge plasma matment fmt appeared as a surface modification process

in the 1950's ('? It is used for the in-line high speed treatment of polyolefin fiims, and is one

of the most fiequently used surface modification techniques. The process involves the

passing of a film between two electrodes, through a region of electrical discharge (usually

at radiofrequencies). In the coron% there are ions, electrons, excited neutrals (molecules,

fiagrnents, and atoms), and photons. Al1 of these species possess suflicient energy to transfer

to the polymer surface to f o m radicals. which may then react rapidly with oxygen to form

an oxygen-hctionalized surface ('? It is a very fast and effective method of surface

oxidation, resulting in a consistent layer of oxidized material at the polymer surface. It is also

a cheap method. as it can be carried out at atmospheric pressure. The main disadvantage to

corona discharge plasma treatment is its inability to treat three-dimensional objects. Bnggs

et. al. studied the effects of corona discharge treatment of poly(ethy1ene terephthalate)

(PET). The authors exposed their samples to the corona for up to 40 seconds, and noted

considerable increases in wettability and surface oxidation &er only 10 seconds of matment

Similar results were obtained by Strobel et. al. ('", who studied the corona treatment of PET

and PP.

Flame treatment is another surface modification technique that first appeared in the

1950's Like corona treatment, it was fint developed to irnprove the wettability and

adhesive properties of polyolefin films. Today, it is used more fiequently to modify

109 paperboard materials, and thicker polyolefin materials, such as rnoulded car bumpers. The

technique involves exposure of the material's sdace directiy to a flame, which contains

many reactive radicals, ions. and other intermediates. Therefore, flame treatment is not

suitable for thermaily sensitive materiais, the extent of sürface modification is difficult to

control, and overtreatment can lead to surface damage.

Glow discharge plasma surface treamient is a process that has undergone extensive

study since its introduction about 20 years ago. It can be used as a s d a c e modification

method resulting in either surface oxidation or surface etching, depending on the type of

plasma discharge ("). Microwave plasma discharges contain electronicaily excited atoms and

molecules and are used to achieve both oxidation of the poiyrner surface and increased

surface wettability. Exposure to radio fiequency plasma discharge results in the etching of

a polymer surface. Foerch et. al. '=' studied the microwave oxygen plasma discharge

treatment of polyethylene (PE). detecting significant oxidation after less than 0.02 seconds.

Ochiello et. al. (26' studied the oxygen plasma treatment of PP, detecting the introduction of

carbon-oxygen functionality to the surface region, as well as an irnprovement in surface

wettability. Glow discharge plasma treatment requins a moderate vacuum environment (1 -

10 Pa), so it is a process easily carried out on a laboratory scale, but is not easily reproduced

on an industrial scale due to cost and complexity. Therefore, there are limited incentives for

mod industries to replace surface treatments such as corona or Barne treatment with plasma

treatrnent, even with the rapid treatment times possible with plasma treatment, and its

potential for high-speed in-line film treatment "?

Reactions using a combination of ultraviolet Light 0 and ozone gas were originally

used for the cleaning of silicon and other semiconductor surfaces pnor to processing. Vig

110 has published a review of past studies in this area ("). McIntyre e t al. studied the use of

UVIozone treatrnent for the removal of organic contminants fiom gold and silicon dioxide

surfaces of complex geometry. Ultraviolet light/ozone gas (WO) treatment has since been

studied as a polymer surface modification technique. The technique relies on UV light

produced by lamps. such as low pressure mercury vapour lamps, and ozone gas produced by

W-induced reactions ancilor supplied by a separate ozone generator. Peeling et. al. studied

the effects of ozone alone on both polystyrene and PE surfaces, as well as the combined

effects of UV0 on PE surfaces 30' . The authors concluded that the combined treatment

results in a more extensive and rapid oxidation han that obtained by ozone alone. Gongjian

e t al. ('') studied the W O surface modification of PE and PP samples in the f o m of films,

sheet, and fibers. Carbon-oxygen functionality in the f o m of ether, ketone, and carboxyl

groups were detected d e r 40 minutes of treatxnent. Increased wettability was detected &er

approximately 10 minutes of treatment. Walzak et. al. (") studied the UV0 treatments of PP

and PET films, obtaining increased wettabilities and surface oxidation with both polyrners

after treatrnent times of only three minutes. This was the first UV0 surface modification

midy to add supplemental ozone. from an extemal ozone generator, to the W O treatment.

Lane and Hourston '43' have published a review of polymer surface modification

treatments and various studies on these treatments. Currently, excited state gas-phase surface

modification processes (corona, flame, plasma, ozone, and W O ) are receiving the most

attention, with corona treatment king used most fiequently in industriai applications. Each

of these treatment techniques has its own advantages and disadvantages, with respect to cost

and extent of surface modification. Strobel et. al. published a comparative snidy of these five

surface modification techniques using each treatment technique separately to treat the

surfaces of PET and PP. Flarne treatment most readily yielded a wettable surface, closest to

the sdace region at the shallowest depth; corona and plasma treatments seemed to result in

a deeper treatment. These three treatment techniques resulted in extensive surface

modification on the order of seconds. The W O treatments studied resulted in the deepest

treatment, but required longer treatment tirnes to produce significant levels of modification.

However, W O treatments seem to have some advantages over other processes. The process

can be can-ied out at atmospheric pressure, with simple and inexpensive equipment, which

can then be operated safely by non-technicd personnel. The treatment is applicable to three-

dimensional objects, as well as therrnally sensitive materials which could be darnaged by

flame or corona treamients. L a d y , W O treatment of polymer surfaces requires no chernical

reagents other than compressed gas, and it produces no polluting waste byproducts, other

than ozone gas, which is relatively easily converted to oxygen. Therefore, U V 0 treatments

seem to be a promising alternative for a polyrner surface modification technique, at least

under some circumstances.

1.2.3 Poiypropylene

Polypropylene is prepared nom the rnonomer, propylene, which is obtained as a

gasoline refming byproduct. Its structure is show in Figure 1.1 :

Figure 1 . 1 : Stmcture of polypropylene

There are three possible geometrical orientations, or structures, for the PP chain: isotactic,

syndiotactic. and atactic. These structures are depicted in Figure 1 -1.

Figure 1.2: Possible geometric orientations for polypropylene

Isotactic

S yndiotactic

Atactic

113 An isotactic structure has al1 of the methyl (CH,-) groups on the same side of the chah,

whereas syndiotactic structures have al of the methyl groups alternathg h m one side of the

chain to the other. An atactic structure has the methyl groups positioned in a random order

on either side of the chain. When the correct Ziegler-Natta catalyst is used, predominantly

isotactic PP can be produced. Due to its regular structure, isotactic PP chains will stack and

orient well, and will be significantly crystalline, resuiting in its excellent bulk properties (see

below). Hence. most commercial PP produced is isotactic PP.

Isotactic polypropylene has a high melting point (208"C), which facilitates its

sterilization. Its hi@y crynalline nature gives it stiffness, hardness and tende strength. It

is chemical resistant, moisture resistant, and stable to heat and light. Polypropylene is used

in appliances. housewares, packaging, larninates, cassette holders, pipes, rnonofilaments,

storage tanks, and in the automotive industry (").

1.2.4 W O Processes and gas phase reactions

As stated in the previous section, UV0 treatments have been used in the past for

surface cleaning, and more recently has been studied as a polymer surface modification

method. The combination of W light and ozone gas resuits in the production of reactive

oxygen species, the major reactive ones being ozone itself, atomic oxygen, and singlet

rnolecular oxygen ('?

The formation and decomposition of ozone in the presence of UV light has been the

subject of many studies, primarily due to interest in atmospheric chemistry, as well as in

waste management technoîogy. Atmospheric chemical reactions of particular interest are

those involving the decrease in high altitude ozone concentration and the corresponding

increase in damaging UV reaching the earth's surface. Baulch et. al. have published an

114 extensive lia of kinetic and photochernical rate parameters of gas-phase reactions of the

middle atmosphere for the purposes of modeiiing. Bolton et. al. have performed midies

on the photodegradation of pollutants in air, using an advanced oxidation process (AOP)

involvuig high energy W light and ozone gas. Products fkom the photolysis of ozone react

with, and hence degrade, the pollutant in the low temperature process, producing oniy CO,

and H,O. Undesirable byproducts of incineration, such as NO, (x=1,2) and CO, are not

produced by the process.

Absorption spectra for ozone and molecular oxygen are shown in Figure 1.3 (4?

Photolysis of ozone occm as it absorbs strongly in the 200-300 nrn (2000-3000 A) W light

region to fom atomic oxygen and molecular oxygen:

O, ('A) + hv (253.7 nrn) - O ('D) + O2 ('A, or 'ZJ (1 -6)

O (ID) is a very reactive f o m of atomic oxygen and is therefore shortlived. It reacts

(45-48) subsequently with gaseous species present, such as rnolecular oxygen and ozone :

(i) O (ID) + O, - O (3P) + OZ ( ' C i ) kZg8 = 4.0 x IO*'' cm3 moiecuie-' s-' (1.7)

(ii) O (ID) + O, - O? + 2 0 (,P) km = 2.4 x 1 O-'' cm3 molecde" s-' (1 -8 )

Any water vapour present may react with O (ID) to produce hydroxyl radicals ("):

H,O + O (ID) - 2 *OH (1.9)

Ozone may be produced via a sequence of reactions. Molecular oxygen absorbs

1 84.9 nm W light to forrn excited-state molecular oxygen:

0, ('Ci) + hv (184.9 nrn) - O,' ('2;) (1.10)

This excited-state rnolecular oxygen overlaps with the repulsive O,' ('DJ electronic state,

which allows the transition fiom the higher energy electronic state to the lower energy

repulsive state:

Figure 1.3: Absorption spectra for ozone, O,, and molecular oxygen, O?.

0; (32J - O**

which can then dissociate to form two ground-state oxygen atoms:

02* - 20 OP) (1-12)

The O (3P) atoms can then react with molecular oxygen to form ozone:

O ( j ~ ) + O2 ()Ci) - O, (1.13)

The quantum yield for al1 of the reaction pathways combined is 0.5, meaning that for every

NO photons of light, one ozone molecule is generated

1.2.5 Reactions with the polypropylene surface

Several gaseous species are created during W O treatments which may react with the

surface of PP. These include rnolecular oxygen, atomic oxygen and ozone. The most

reactive species should be atornic oxygen, present as either O ('P) and O ( D). Atomic

oxygen is a potent oxidizing agent that may react with the PP surface in differing ways,

depending upon its form. In a study on the UV0 treatment of PP, Rabek et. al. (") concluded

that a simultaneous attack of molecular oxygen, ozone and atomic oxygen was responsible

for the surface modification of PP. They also described the possible mechanisms of reaction

of these species with the pol ymer surface. Ki11 et. al. "O' studied the air-plasma surface

modification of polyethylene. In this paper, the authors also monitored the species present

in the gas-phase with absorption and emission spectroscopies in an attempt to identify the

species responsible for the surface modification. They concluded that the dominant species

was dependent on the flow rate conditions of the experiment; O ('P) was important at high

flow rates, whereas species other than O ('P), such as O (ID), played more of a role in the

modification at lower flow rates. The authors also included possible mechanisms of reaction

of atomic oxygen with the polymer surface. In another shidy, PP surface modification by

JI8 oxygen glow-discharge plasma m e n t was investigated ('? Similar to the work of Küi e t

al., the authon attempted to isolate the effects of particular gas-phase species on the

modification. They concluded that singlet molecular oxygen does contribute to the surface

modification, but only after longer treatment times. They suggested that this was b e c a w

singlet molecular oxygen reacts with carbon-carbon double bonds. There should be little

unsaturation in PP, leading to a slow reaction rate of molecular oxygen with the PP surface.

The authoa also concluded that the presence of atornic oxygen sped up the process, resdting

in appreciable surface oxidation a e r shorter periods of treatment.

In Figures 1.4 and 1.5, some of the possible reactions with the surface of PP are

depicted. O OP) will abstract hydrogen atoms fiom carbon atoms of the polymer chain, h m

either a secondary or tertiary carbon, producing a radical carbon (Figure 1.4(a)). Hydrogen

abstraction nom a primary carbon is not likely to occur due to the instability of a primary

carbon radical. Foilowing hydrogen abstraction, several things rnay occur. Any hydroxyl

radicals present rnay combine with a radical carbon to form a hydroxyl group, or they rnay

abstract a hydrogen atom to form an alkene unit. Molecular oxygen may react with the

radical chain, fomiing a peroxy unit, which rnay then abstract a hydrogen atom from a

neighbouring chain to f o m a hydroperoxide unit (Figure 1.4(b)). Further oxidation of

hydroxyl, peroxy, and hydroperoxide groups rnay occur, producing ketone and/or ester

groups (Figure 1.4(c)). Crosslinking of polymer chains rnay occur, if radical chains or

peroxy units corne into contact.

O (ID) will react with the polymer chain in an entkly different way than will O (p).

Instead of abstracting hydrogen to form a radical chah, O ('D) will m c t by insertion into the

chain. O (ID) rnay insert into C-H bonds, to form hydroxyl groups, or into C-C bonds, to

Figure 1.4: Possible reactions with the PP surface. (a) hydrogen abstraction by O OP), (b)

reaction with molecular oxygen. (c) M e r oxidation to produce ketone and ester

functionality.

Figure 1.5: Possible reactions with the PP surface. (a) O (ID) insertion, @) reaction of

molecuiar oxygen at an allylic carbon position, (c) ozonolysis reaction.

I CH3

molozonide

1 \ - *CH CH- \

ozonide CH3

123 f o m ether groups. O (ID) does not possess the appropriate symmetry, or electron parïty, to

engage in an abstraction reaction, as O ('P) does not possess the appropnate symmetry to

engage in an insertion reaction O (ID) C-H insertion may occur, resulting in primary,

secondary, and tertiary alcohol (hydroxyl) groups (Figure 1.5(a)). O (ID) C-C insertion can

also occur, producing ether groups (Figure 1.5(a)). Dihydroxy units may also form, due to

a second C-H insertion at a secondary carbon. The reactions depicted in Figure 1 S(a) are

coilision limited; under nomai conditions, deactivation of O (ID) by collision with Nz or O,

wiii occur about ten times for each tirne that the reactions in Figure 1.5(a) occur. Thus, O

(ID) would not normally survive more than about 100 collisions. It must therefore be

generated very close to the surface for the surface reactions to occur. Further oxidation of

hydroxyl and ether groups may occur resdting in ketone and ester functionality (Figure

1.4(c)).

As stated above, molecular oxygen may react at carbon radical sites, producing

peroxy units (figure 1.40)). This is the case for ground-state molecular oxygen. It may also

react at any allylic carbon positions, resulting in hydroperoxide functionality, although this

will be a slow reaction (Figure 1.5(b)) '*". The extent of unsaturation should be minimal for

untreated PP, but may develop during W O treatment. Normand et. al. suggea that excited-

state molecular oxygen (0, ('AJ) rnay react at sites of unsaturation, producing radicals which

may then react M e r with hydroxyl radicals or 4 ('? Rabek et. al. '49', however, suggest

that reaction of O, ('A,) =<th the PP surface does not occur.

Ozone is proposed to react with the polymer chah at any C-C double bonds, by an

ozonolysis reaction (Figure 1 .S(f)). As mentioned above when discussing reaction with

molecular oxygen, the extent of unsaturation should be minimal for untreated PP, but may

develop during W O treatment. Ozone attack on a C-C double bond leads to the formation

of a molozonide, which subsequently decomposes to form an ozonide. Under oxidizing

conditions, the ozonide should b e n t into ketone and carboxylic acid groups (under

reducing conditions, aldehydes should form) (? Rabek et. al. suggest that ozone may also

react with the unsanirated chah by hydrogen abstraction. leading to radical formation (49),

which can then react M e r as shown in Figures 1.4 (a) and (b).

Chain scission products, also known as low molecular weight oxidized material

(LMWOM), rnay fonn after extended oxidation. Strobel et. al. ')*) investigated the formation

of LMWOM during the corona treatment of PP, concluding that afler a threshold level of

oxidation is reached, continued treatment results in chain scission and the production of

LMWOM. LMWOM will be unattached material on the polymer surface, not bonded to the

surface of the polymer, and may be water-soluble. From their subsequent analyses, Strobel

et. al. suggested that LMWOM may actually enhance adhesion between the polymer d a c e

and adherants. Its presence will cornplicate the interpretation of contact angle data, however,

if a polar liquid. such as water or an alcohol, is used as the probe liquid. In a study by

Peeling et. al. (53', W O treated PET was found to have less LMWOM on the surface than

corona-discharge treated PET. shown by less of an increase in the contact angle upon

washing for the UV0 ireated PET. The authors attributed this to lower chain scission

resulting fiom photooxidation compared to corona discharge treatment. Hill et. aI. ('*)

pexformed a washing study of the UV0 treated surface of PP and PET, concluding that

LMWOM formation cm resuit fiorn continued UV0 treatrnent. This water-soluble material

is also readily washed off with ultrafiltered, deionized water, resulting in a loss of surface

oxygen and increased contact angles.

1.3 Researcb to be undertaken

In pursuit of the goals of this thesis, several experiments were completed. Ozone

concentration may be a limiting factor in W O treatment - more ozone may result in more

atomic oxygen, but it may also hinder the production of atomic oxygen close to the polymer

surface. Therefore. in one set of experiments the effects of different ozone concentrations

on UV0 treatment were midied. Two types of low pressure mercury vapour W lamps were

available for UV0 treatment, one set transmitting both 185 and 254 nrn U V , the other

transmitting solely 254 nm W. Separate treatments with either of the two sets of lamps

were camied out, in order to determine the effects of the differing wavelengths of W on the

surface modification of PP. In another set of experiments, the ozone concentration in the gas

fed into the reactor was kept constant while the W lights were pulsed on and off, in aîtempts

to detemine the roles of UV light and atomic oxygedozone in the process. The effects of

lampto-sample distance, or the W intensity at the surface, were also investigated by treating

PP at different distances from the UV lamps. Finally, experiments were carried out to

determine the effects of supplemental water vapour on the surface modification of PP.

Contact angle goniometry has been shown to be a usehl surface energy and

wettability probe of the uppermost monolayers of a solid, so was used to monitor the changes

in wettability of W O treated PP sampies. To probe elemental compositions and the

functionalization of the PP surface, X-ray Photoelectron Spectroscopy (XPS), and Fourier

Transform Infrared Spectroscopy (FTIR), were used. XPS has been s h o w to be useN in

monitoring the changes in oxygen concentration upon polymer surface oxidation, providing

elemental and chernical state information up to a depth of 10 nm. FTIR techniques have

been successfully used to monitor fùnctional group formation in a polymer system, providing

the changes are at depths of the order of one Pm.

A.W. Adamson. Phvsical Chemi of Surfaces. John Wiley and Sons, New York, 1990.

K.L. Mittal (Ed.), "Contact Ande. Wettablitv and Adhesiorf'. VSP, 1993.

M. Strobel, C. Lyons, K.L. M i d (Eds.), "Plasma Surface Modification of Pofvmers". VSP, 1994.

K.L. Minal (Ed.), "Polymer Sudace Modification: Relevance to Adhesion". VSP, 1996.

RJ. Good, in: 'Contact Anele. Wettability and Adhesion". K.L. Mittal (Ed.), VSP, 1993.

E.M. Liston, L. Martinu, M.R. Wertheimer, in: "Plasma Surface Modification of Pol~men". M. Strobel, C. Lyons, K.L. Mittal (Eds.), VSP, 1994.

J.D. Eick, R-J. Good, A. W. Neumann, Journal of Colloid and Interface Science, v. 53, n. 2, 1975.

R.E. Johnson, R.H. Dettre, in: Contact Anele. Wettability. and Adhesio~. editor F.M. Fowkes, Advances in Chemistry Senes, v. 43, pp. 112-135, Arnencan Chernicai Society, Washington, DC, 1964.

1. Noda, in: "Contact Anele. Wettability and Adhesiorf'. K.L. Mittal (Ed.), VSP, 1993.

E. Ochiello, M. Morra, G. Morini, F. Garbassi, P. Humphrey, Journal of Applied Polymer Science, v.42, pp. 55 1-559, 199 1.

D. Briggs, D.G. Rance, CR. Kendall, AR. Blythe, Polymer, v.2 1, pp. 895-900, 1980.

M.J. Walzak, S. Flynn, R. Foerch, J.M. Hill, E. Karbashewski, A. Lin, M. Strobel, Journal of Adhesion Science und Technology, v.9 n.9, pp. 1229-1 248, 1995.

K.W. Lee, T.J. McCarthy, Marrornolecules, 11-21, pp. 309-3 13, 1988.

J. Adelsky, Tappi, v.72. pp. 18 1-1 84, 1989.

J.D. Eick, R.J. Good, A. W. Neumann, Journal of Colloid and Interface Science, v. 53, n. 2, 1975.

K. Grundke, in: "Polvmer Surface Modification: ReIevance to Adhesio~". K.L. Mittal (Ed.), VSP, 1996.

M. Sû-obel, C.S. Lyons, J.M. Strobel, RS. Kapam, J o m u l ofAdhesion Science mid Technology, v. 6 n. 4, pp. 429-443, 1992.

L.J. Gerenser, J.F. Ehan, M.G. Mason, J.M. Pochan, Polyrner, v. 26, pp. 1 162-1 166, 1985.

J.M. Strobel, M. Strobel, CS. Lyons, C. Dunatov, S.J. Perron, Journal ofAdhesion Science and Technology, v. 5 n. 2, pp. 1 19- 130, 199 1.

D. Briggs, D.M.Brewis, M.B. Konieczko, J o u m l of Materials Science, v. 14, pp. 1344- 1348, 1979.

F. Garbassi, E. Ochiello, F. Polato. Journnl of Muterials Science, v. 22, pp. 207-21 1, 1987.

1. Sutherland, D.M. Brewis, R J. Heath, E. Sheng, Surface and Interface Analysis, v. 1 7, pp. 507-5 1 O, 199 1.

E. Papirer, D.Y. Wu, J. Schultz, Journal of Adhesion Science und Technology, v. 7, pp. 343-362, 1993.

R. Foerch, G. Kill, M. J. Walzak, Journal of Adhesion Science and Technology, v. 7 n. 10, pp. 1077-1 089, 1993.

E. Ochiello, M. Morra, G. Morini, F. Garbassi, P. Humphrey , Journal of Applied P o h e r Science, v.42, pp. 55 1-559, 199 1.

F. Garbassi, M. Morra, E. Occhiello, L. Barino, R. Scordarnaglia, Surface and Interface Analysis, v. 14, pp. 585-589, 1989.

M. Morra, E. Occhiello, F. Garbassi, Journal of Colloid and Interface Science, v. 132 n. 2, pp. 504-508, 1989.

J. Peeling, M.S. Jazzar, D.T. Clark, Jownal of PoIymer Science: P o h e r Chemisfry Edirion. v. 20, pp. 1 797- 1805, 1 982.

J. Peeling, D.T. Clark, Journul of Polymer Science: Polymer Chernishy Mition, v.21, pp. 2047-2055, 1983.

M.J. Walzak, S. Flynn, R Foerch, J.M. Hill, E. Karbashewski, A. Lin, M. Strobel, Journal of Adhesion Science and Technology, v.9 n.9, pp. 1 229- 1248, 1995.

J.M. Hill, E. Karbashewski, A. Lin, M. Strobel, M.J. Wal* Journal ofA#zesion Science and Technology, v. 9 n. 12, pp. 1575- 159 1, 1995.

B. Gongjian, W. Yunxuan, H. Xingzhou, Journal of AppZied P o h e r Science, v. 60, pp. 2397-2407, 1996.

N.S. McIntyre, M.J. Waizak, Modern PZasrics, March 1995.

P. Nowak, M.Sc. thesis, U.W.O., 1995.

T.G. Bee, E.M. Cross, A.J. Dias, K W . Lee, M.S. Shoichet, T.J. McCarthy, in: "Contact Angle. Wettabilitv and Adhesion". K.L. Mittal (Ed.), VSP, 1993.

M. Strobel, M.J. Walzak, J.M. Hill, A. Lin, E. Karbashewski, C.S. Lyons, Journal of Adhesion Science and Technology, v.9, pp. 365-3 83, 1 995.

M. Strobel, C. Dunatov, J.M. Sîrobel, C.S. Lyons, S.J. Perron, M.C. Morgen, Jou171aZ of Adhesion Science and Technology, v. 3 n. 5, pp. 32 1-335, 1989.

M. Strobel, MC. Branch, M. Ulsh, RS. Kapaun, S. Kirk, C S . Lyons, Journal of Adhesion Science and Technology, v. 10 n. 6, pp. 5 15-539, 1996.

G. Kill. M.Sc. thesis, U. W.O. 1994.

J.R. Vig, Journal of Vacuum Science and Technology, A3(3), pp. 1027-1034, 1985.

N.S. Mclntyre, R.D. Davidson, T.L. Walzak, R. Williston, M. Westcott, A. Pekarsky, Jourml of Vacuum Science and Technology, A9(3), pp. 1355- 1 359, 1 99 1.

J.M. Lane, D.J. Hourston, Progress in Orgmic Coarings, v. 2 1, pp. 269-284, 1993.

V.R. Gowariber, N.V. Viswanathan, J. Sreedhar. Polyner Science. John Wiley and Sons, New York, pp. 21 5-21 6, 1986.

D.L. Baulch, RA. Cox, P.J. Crutzen, R.F. Hampson Jr., I.A. Kerr, J. Troe, R.T. Watson, "Evaluated Kinetic and Photochernical Data for Atmosphenc Chemisv ; S u ~ ~ l e m e n t r, Jourml of Physical Chemistry Reference Data, v. 1 1 n. 2, 1982.

J.R. Bolton, A.S. Amiri, J.A. Buckley, R Notarfonzo, S. Cater, presentation at: " 8 7 ~ . . . and Exhibition. A r gnd Waste Managgnent", 1994.

J.G. Calvert, J.N. Pitts, Jr., Photochemistry, John Wiley and Sons, New York, pp. 205-209, 1966.

. . 130

48. B. Duron, in: Handbook of Ozone Technolom and Ap licatrort, R G. Füce and A. Netzer (Eds), v. 1 , pp. 77-84, A m Arbor Science, Ann Arbor, 1982.

49. J.F.RabekJ.Lucki,B.Ranby,Y.Watanak,B.J.Qu,in: ChernicalReactionson Polymers. pp. 187-200, Amencan Chernical Society, Washington, DC, 1988.

50. G. K U , D.K. Hunter, N.S. McIntyre, JowmI of Polymer Science, Part A: Polymer Chernistry, v. 34, pp. 2299-23 10, 1996.

5 1 . F. Normand, J. Marec, P. Leprince, A. Granier, Materials Science and Engineering, v. A139, pp. 103-109, 1991.

52. S. Ege. Orrcanic Cherni-. second edition. D.C Heath and Company, U.S.A., 1989.

53. J. Peeling, G. C o w d , M.S. J m T Jourml of Polymer Science: PoZymer Chemistry Edition, v. 22, pp. 4 19-428, 1984.

CHAPTER 2 - EXPERIMENTAL

2.1 Surface Analytical Techniaues

2.1.1 Contact Angle Goniometry

2.1.1.1 Principles

As described in Section 1.2.1, contact angle measurements can be used as a measure

of surface fiee energy. When studying the effects of polymer surface modification, changes

in contact angle values between samples treated under differing conditions can be attributed

to changes in surface energy or surface roughness. Contact angle measurements have been

used in many studies to probe the changes in wettability of polymer surfaces "-"!

The procedure used for this work was the sessile drop method. This measures the

profile of a drop of the probe liquid, placed on the sample surface using a syringe. For this

measurement, a microscope objective is used which is fitted with a goniorneter lem with

angles indicated. The contact angle is measured tangentid to the edge of the &op where it

contacts the sample surface (Figure 2.1).

The contact angles of static sessile drops of probe liquid can be measured, as well as

those of advancing and receding drops of a probe liquid. A static drop refers to a stationary

drop of probe liquid on the sample surface. Advancing and receding contact angles are

measured while increasing or decreasing the size of the &op with the syringe until it

advances or recedes across the surface (Figure 2.1). Measurement of a static &op gives a

contact angle value between the values for the advancing and receding contact angle, usually

closer to the advancing angle, and is not as useful a measurement (").

Advancing and receding contact angles give a measure of different surface energy

charactenstics. The resis ting element to wetting will be hydropho bic surface regions.

Sample Surface

Advancing Receding

Figure 2.1 : Contact angle measurements

333 Therefore, an advancing contact angle measurement is indicative of the unmodified, lower-

energy, hydrophobie portions of the surface. The receding contact angle measmes the ability

of the surface to stay wetted and hydrophilic, or higher-energy, surface regions will

determine its value. Any hydrophilic regions on the d a c e of PP wili be a result of surface

modification, therefore, receding contact angle measurements are more indicative of the

overall surface modification of the polymer surface (?

Contact angle hysteresis refers to the difference between the advancing and receding

contact angles for a d a c e . Hysteresis is a result of the d a c e failing "to meet the ideality

conditions" required for use of Young's equation ("). Surface roughness is one of the causes

of hysteresis effects, as is inhomogeneity of the sample surface ('? Walzak et. ai., in work

on UV0 surface modification of PP and PET, obtained surface topographical features having

dimensions less than 100 nm - such surface topography effects should not significantly affect

contact angle measurements ( ? Since the treatment techniques used in that study were

similar to those used for this project, that assumption was made, and al1 changes in contact

angle were attributed to changes in surface energy due to changes in surface chemistry.

The presence of water-soluble LMWOM will affect the results when using water as

the probe liquid. For highly soluble LMWOM, dissolution is likely to occur in the probe

liquid and thus alter the localized surface tension of the probe liquid. The LMWOM may

also have differing surface energy characteristics than the insoluble, underlying rnaterial that

is still achially attached to the polymer "). Although this complicates the interpretation of

the contact angle results, wettability trends with modification can still be identified.

Measuring the contact angle before and &er water washing of the surface also overcomes

this problem, as well as indicates the effect of LMWOM on the surface wettability.

2.1.1.2 Experimental

For this study, a Rame-Hart contact angle goniorneter was used, with de-ionized,

ultra-filtered water as the probe liquid. An assurnption made while taking measurements,

and when comparing the results, was that the probe liquid remained pure during

measurement. This is not a completely accurate assumption, as some dissolution of

LMWOM is likely to occur. A highly water-wettable surface (hydrophilic), will give the

lowest contact angle results. A surface of low water-wettability (hydrophilic), will give

higher contact angle results. By increasing and d e c ~ a s h g the size of the drop with the

syringe, the advancing and receding contact angles were measured as the drop advanced or

receded across the surface. Measurements were taken at multiple spots (three to five) on each

sarnple. Variability in contact angle measurements results kom operator error and actuai

differences in surface energy between samples. Typical error associated with the

measurement of advancing and receding contact angles is 13 O ( I l . Data variability greater

thao this can be attributed to actual surface energy differences when comparing samples.

2.1.2 X-ray Photoelectron Spectroscopy

2.1.2.1 Principles

X-ray photoelectron spectroscopy (X I 'S ) , or electron spectroscopy for chemical

analysis (ESCA), is a non-destructive surface analysis t~hn ique that c m provide both

elemental and chemical state information about the surface and near-surface region of a

material. XPS has been used extensively in studies of polymers and polymer surface

modification ('"3. 17-19)

XPS uses the photoelectric effect, the emission of photoelectrons upon bombardrnent

by x-rays. The photoelectric effect establishes a relationship between the khetic energy (EJ

of an ejected photoelectron and the energy of the exciting x-ray photon beam (hv):

hv is the known incident bearn energy, is the work function of the spectrorneter, and the

kinetic energy of the ejected photoelectrons is measured by the spectrometer. The binding

energies of the photoelectrons are then deterrnined. The binding energy cm be viewed as the

difference in energy between the initial and fmal states of an atom following emission of a

photoelectron. Bhding energies are characteristic for each element and the chemicai

environment of that element.

When a materiai is irradiated with a monoenergetic, focussed beam of x-rays from

an Ai-Ka (hv=1486.6 ev) source, the incident photons penetrate the material to a depth of

up to one micrometer. This causes photoelectrons to be ejected from core electron levels of

elements present within this volume. Shown in Figure 2.2 is the photoemission process for

a carbon 1 s electron. If an atom lies too deep below the surface, emitted photoelectrons will

undergo inelastic collisions with other atorns preventing their escape from the solid. If an

atom is located within a short distance fiom the surface, emitted photoelectrons have much

greater probability of escaping fiom the surface and being detected by the spectrometer (*O*

*'). For this reason, XPS is a surface-sensitive technique, providing sample information for

depths up to ten nanometea. Only those emitted photoelectrons having enough kinetic

energy to escape fiom surface or near-surface regiow will contribute to the spectnun.

For non-conductive insulating samples, photoemission of core-level and secondary

electrons h m the sample leaves a net positive charge on the surface. This causes peaks in

XPS spectra to shift to higher binding energies than their charactenstic values. If non-

ejected photoelectron

x-ray photons \ \ \

Figure 2.2: Photoemission process for a carbon I s electron

uniform charging (differential charging) occurs across the sample surface, peak shifling is

usually accompanied by asymmetric peak broadening ancUor spli thg. This c m make

qualitative and quantitative spectral assignments di ficult and unreliable. For XPS analysis

of po 1 ymer films. there are two fiequent1 y used solutions to combat the charging problem ('*!

One is to cast the polymer of interest ont0 a rneral substrate, resulting in a thin film on a

conductive surface. The second method of overcoming charging problems is to use a low-

energy ( 5 15 eV) electron flood gun, in conjunction with a fine wire rnesh suspended

approximately one mm above the sarnple surface '"'. Each element having charactenstic binding energies enables the determination of

surface elemental composition by XPS. Binding energies can also provide chemical state

information of a given element. due to differences in binding energies beiween atoms of the

sarne element in different chemical environments or states. These core-level binding energy

differences between atoms of the sarne elernent are cdfed the "chemical shift". If an atom

is involved in an oxidative bond (as in a carbon-oxygen bond), the nuclear attraction is

unaffected, but the repulsion forces acting on the remaining electrons are decreased. Ail

core-levels are then lowered with respect to the Fermi level and the binding energies of

electrons in these core levels increase "'). The presence of electron-withdrawing groups in

an oxidative bond \siIl not be the only cause of a decrease in electronic charge of a particular

atom. Chernical shifts reflect changes in oxidation state, coordination. nature of ligands, and

iattice sites.

XPS specm are plots of intensity of emitted photoelectrons versus binding energy.

XPS survey scans, or broad scans, are shown in Figure 2.3 (a) for an unmated PP sample and

in Figure 2.3(b) for a treated PP sample (10 minutes W O treatment). Labelled in Figure

Figure 2.3: XPS s w e y scans. (a) untreated PP, (b) aeated PP (10 minutes UV0 matment).

1 O00 800 600 400

Binding energy (ev)

1000 800 600 400 200 O

Binding energy (ev)

2.3(b) are two sharp peaks which result from photoemission nom the 1s core-levels of

carbon and oxygen. The rising background towards higher binding energy is a result of

emitted photoelectrons losing energy during inelastic scattering within the sarnple.

S w e y scans can be used for the quantitative determination of surface elemental

composition. The elemental compositions in a sample are proportional to the area under the

core electron peaks in an X P S survey scan. Photoelectron peak intensities will Vary between

elements due to difiering photoionization cross-sections arnong elements and diffenng

sampling depths for different kinetic energies. The relationship used in the quantification

of elemental composition by the instrumentai software is:

where A, is the integrated peak area, is atomic concentration, q is the photoionization

cross-section, A is the inelastic mean fiee path of the photoelectron (or attenuation length),

and K incorporates instrumental factors such as photon flux. analyzer geometry, and

instrumental transmission "-". By integrating the area under the carbon 1 s and oxygen 1s

peaks in the survey scans. multiplying these values by the corresponding cross-section and

mean free path, and normalking the resulting values to 100%, the relative carbon and oxygen

atomic percentage can be obtained.

High resolution spectra are collected fiom a 10 to 20 ev window, containing a

characteristic peak of the element of interest High resolution carbon 1s spectra of untreated

PP and treated PP (10 minutes W O treatment) are shown in Figure 2.4(a) and 2.4(b). The

O bserved spectral resolution ( AE) (the full peak-width at ha1 f-maximum height, or F WHM)

obtainable by an x-ray photoelectron spectrometer is a combination of contributions fkom the

Figure 2.4: High resolution carbon 1s spectra. (a) untreated PP, (b) treated PP ( 1 O minutes

UV0 treatment).

Binding energy (ev)

292 290 388 286 284 282

Binding energy (ev)

.143 linewidth of the x-ray source (AEJ, the spectrometer resolution (& ), and the inherent

linewidth (lifetime) of the core-hole (AEJ used for measurernent (24):

AE = (AE: + AE: + &,yn (2.3)

Hence. the measured specuum represents a convolution of the original photoemission

process and contributions fiom the instrument "":

where d(E) is the measured spectrum. s(E) is the 'me' photoelectron spectnim. r(E) is the

resolution function of the spectrometer, and (8 represents circular convolution. Iris-entd

contributions result in broadened rneasured spectra, therefore obscuring fine spectral detail.

This makes the identification of peaks chemically shifted by fractions of eV dificult. The

Maximum Entropy Method (MEM) is a peak deconvolution procedure that c m be used in

an effort to obtain the ' m e ' photoelectron spectrum that would be obtained by a perfectly

resolving spectrometer. The method has been s h o w to be effective in deconvoluting high-

resolution spectra, resdting in resolution enhancements up to 50% MEM has become

an attractive deconvolution method due to advances in persona1 computer processing

technology; spectra can typically be processed in iess than 15 minutes (25*26).

The mathematics of MEM have been described in detail by Splinter and Mclntyre

("), so only a bnef introduction will be presented here. The basis of MEM is the

quantification of the uncertainty of a probability distribution:

as the "idomational entropy" (?

In ail fields of science, entropy is a measure of the arnount of disorder. High levels of

entropy are genemlly favoured (Le. chernical reactions will proceed spontaneously towards

a final state of higher entmpy than the initial state). In ternis of information, entropy should

be viewed as an inverse measure of information, i.e. "a shape possessing greater entropy is

less informative than one with less entropy" (? The "principle of maximum entropy" ("'

states that inferences should be drawn fiom the probability distribution which has maximum

uncertainty (entropy) c6! Therefore, with MEM, it is necessary to search for the signal with

the maximum entropy (uncertainty) subject to the known information. The informational

entropy, H, becomes the function descnbing the instrumental contributions to the spectnim,

and is used to deconvolute the 'me' spectnim fiom the measured spectnun. H is maximized

to ensure that the weighted sum of squared errors, a', is consistent with the uncertainty in

the data to ensure that the calculated specûum does not depart from the experimental mean

by more than one standard deviation "'?

Here u is the noise variance and N is the number of data points in the spectnim. The entropy

fùnctional, H, is extended to include al1 positive additive distributions to obtain the solution

for maximum entropy (26!

H = - 2 [ S , i = l

where mi is a defadt modei to which the estimate collapses in the absence of constrauits.

This form of entropy is invariant under a change of coordinate system and the distribution

does not require normalization ('? The deconvolution problem is now fonnulated as:

so that Q2 = N

2.1.2.2 Experimental

For this midy, N o different Surface Science SSX-100 ESCA Spectrometen were

used. The instments differed in their resolution and sample size capabilities. Both

instruments make use of an Al-Ka x-ray source, and a concentric hemispherical analyzer

(CHA), for measuring the kinetic energy of the photoelectrons ejected fiom the sample

(Figure 2.5). The x-ray source, sample, analyzer, and detector are held within a vacuum

chamber at or near ultra-high vacuum (UHV) conditions (s 10" Pa). For introduction into

the system, the sample was placed into an introduction chamber which is purnped down to

approximately 2 x 104 Pa by a turbomolecular pump. UHV conditions in the main XPS

charnbers are maintained by ion pumps. UHV is required for two reasons: the fint is that

residual gas molecules present in the analysis chamber will impede analysis by interacting

with photoelectrons through inelastic collisions and preventing them fiom reaching the

analyzer. ï h e second reason is to maintain sample surface cleanliness during analysis.

The emitied photoelectrons are retarded to a fixed pass energy prior to entering the

analyzer. The choice of pass energy affects the resolution of the instrument and the number

Figure 2.5: X-ray photoelectron spectrometer schematic diagram.

apoue AEJ-x

/

4 '48 of photoelectrons analyzed. The lowest pass energy will result in the highest energy

resolution, but lowest counts. and vice versa. The focus of the monochrornatized x-ray beam

can also be change4 to a specific analysis spot size. The smallest spot size d l result in the

best resolution, but will lead to low counts [?

Survey scan spectra were collected using a spot size of 600 p m and a resolution

setting of 4, which corresponds to a pass energy of 150 ev. The resolution function width

of the instrument at these settjngs is 1.55 ev. High resolution spectra were collected at spot

size 300 Pm. resolution setting of 3. which corresponds to a pass energy of 50 ev. The

resolution function width of the instrument at these settings is 0.64 ev (? Al1 spectra were

collected using an electron take-off angle of 3 7 O. The electron flood gunkcreen technique

was used to compensate for surface charging (?

EIemental compositions were detemiined by integrating peak areas fiom collected

survey scans. The arnount of surface oxidation was expressed as the ratio of the oxygen to

carbon atornic percentages (0:C ratio). High-resolution carbon 1 s spectm were analyzed by

a regimented peak-fitting procedure used for each individual spectra. Spectra were

referenced to 285.0 0.1 eV. the binding energy attributed to carbon 1 s electron. Spectra

were peak-fitted with peak-fitting software which uses a least-squares fitting algorithm with

a Shirley background subtraction, Gaussian-Lorentnan peak shapes, and aiIows constraints

to be placed on peak position (binding energy), height, and width. Peak-fitting requires

knowledge of the material under investigation, so that an acceptable mathematical peak-fit

with an achial physicaVchemica1 basis is obtained (In. Collected spectra were fitted with

80% Gaussian - 20% Lorentzian peak profiles. "Goodness-of-fit" was measured

qualitatively by a x2-value supplied by the software. Constraints were placed on peak

-3 89 position, width and height as necessary to optimize the x2-value. Peak position was

constrained closely using literature values for carbon 1 s chemical shifts (Table 2.1) (?

Figure 2.4(b) depicts a hi&-resoiution carbon 1s spectnim with peak-fitting and chemical

shifts indicated.

Table 2.1 : Carbon 1 s chemical shifts fiom 285.0 ev

MEM specaal deconvoIution was carried out on several sets of data using an

algorithm coded in the MATLAB" language on a Pentiurn-based PC. An exarnple is shown

in Figure 2.6, a collected high resolution carbon 1s spectrum of a 10 minute W/02 + ozone

treatment, and the accompanying deconvoluted spectrum. Identical peak positions were used

for fitting the two spectra The original spectrum was fitted using peak widhs of 1.25 ev for

the main aliphatic carbon 1s peak (285.0 I 0.1 eV), and 1.20 ev for the chemical shift peaks,

producing a f-value of 6.7. The deconvoluted spectrurn was fitted using peak widths of

1.10 ev for al1 the peaks. producing a x'-value of 5.4. The lower x'-value indicated a better

fit for the deconvoluted spectrum, and the spectnun was indeed sharpened at specific binding

energies where peaks were assigned. Unfortmately, the resolution enhancements obtained

were not of the order of 50%. so the sharpening obtained was insuficient to hlly resolve

spectral features as hoped. and MEM treatment of M e r data was abandoned. However,

the procedure was useful in providing an indication of the validity of peak positions used in

M e r fitting.

C-O c=c=o C=O O-C=O

Figure 2.6: (a) rneasured high resolution carbon 1s spectrum of a 10 minute W I O , + ozone

treatrnent (b) MEM deconvoluted spectnun.

Binding energy (ev)

288 286

Binduig energy (ev)

2.13 Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy

2.13.1 Principles

AU molecules possess a number of energy levels corresponding to different possible

vibrational states. The spacing between these levels corresponds to the energy of the

radiation in the infrzlred region of the electromagnetic spectnim. Infkred (IR) radiation

refers to that part of the electromagnetic s p e c t . between the visible and microwave

regions, in the range 10 000 to, 100 wavenumbers (cm-') (one to 100 pm). The mid-IR

region, between 4000 to 600 cm-' (2.5 to 15.0 pm), is of the most interest when studying an

organic system "9'. If radiation having equivalent enerw to the difference in energy between

molecular vibrational levels irnpinges upon a molecule, the radiation is absorbed and the

energy converted into molecular vibrational energy, as well as rotational energy. The

absorbed energy is evennially released as heat. Different functionai groups, or bonds, absorb

at different fiequencies, comesponding to certain vibrations typical of those functional

groups. Two main modes of vibration are possible: stretching vibrations, which produce

changes in bond lengths. and bending vibrations, which produce changes in bond angle. The

stretching fiequency of a bond is dependent on the masses of the atoms involved in the bond

and on the strength of the bond. For example, triple bonds will absorb at higher fkequencies

than wili double or single bonds. Both stretching and bending vibrations may be

symmetrical or assymetncal. Shown in Figure 2.7 and 2.8 (a) are typical stretching and

bending vibrations for a methylene SOUP, and a methyl group, respectively, with each

vibration occurring at characteristic fiequencies. If a particular rnolecular vibration

corresponds to a change in dipole moment, a strong IR absorption will result. During

vibrations in which little or no change in dipole moment occurs, the resultant absorption is

Figure 2.7: Typical stretching and bending vibrations for a methylene group.

Figure 2.8: (a) Typicai stretching and bending vibrations for a methyl group; (b) Stretching

vibrations and changes in dipole moment.

weak or absent altogether. Shown in Figure 2.8 (b) is the difference between a C=O

stretching vibration and a C=C stretching vibration. Since a C=û stretching vibration resuits

in a change in dipole moment, a strong absoption will result. Stretching of the non-polar

C=C bond does not affect its dipole moment, resulting in a weak IR absorption (30!

In Figure 2.9, an IR spectrum of untreated PP is shown. Indicated are absorbances

due to C-H stretching and bending vibrations. The hct iona l group region refers to the

range 4000-1 300 cm". The major hquencies typical of hct ional groups occur here, so this

region is w f u l for quick determination of the presence or absence of hinctionaiity. The

fmgerprint region refers to the range 1300-600 cm-'. Bands in this region are harder to

specifically assign as they are afected by the molecular structure as a whole. This region is

used for comparing spectra of unknown samples with known reference spectm

Infrared spectroscopy has been practiced since the late 180Ois, when the

instrumentation available consisted of primitive spectrometers. Since the 19401s, commercial

spectrorneters have been available. Early spectrometers w d sequences of pnsms and

gratings to disperse the incident infraed (IR) radiation upon a scanning slit mechanism.

Thus. a selected fiequency mnge was incident upon the sarnple and the detector. This system

suffered fiom low sensitivity because not al1 of the available energy falls upon the slits, or

the subseguent sarnple and detector (?

The development of the Fourier transform IR spectrometer resulted in greater

sensitivity in the practice of IR specroscopy because it allows detection of al1 frequencies

simultaneously. At the heart of this system is the Michelson interferorneter, where the

incident IR bearn is split by a potassium bromide (KBr) beamsplitter. Haif of the beam is

transmitted to a moving minor, the other half is reflected to a stationary &or. Both barns

C-H stretc hing

Lir 4 : fmgerprint regio s

4000 3500 3000 2500 2000 1500 1 O00

Wavenurnber (cm-')

Figure 2.9: ATR-FTIR spectnun of untreated PP.

recombine after king reflected back to the bearnsplitter. Here it is split again, causing half

the beam to travel to the detector, and the other half to travel back to the IR source. The

result is an interferogram, a plot of IR intensity versus optical path difference. The

interferogram is converted to a fiequency spectrum through Fourier transfomi caiculations

(37.3)

Early IR spectroscopy technique was predominantly transmission, or absorbance. IR

spectroscopy. In transmission IR spectroscopy, the IR beam passes through the sample and

the trammittance of the IR radiation is rneasured. Trammittance (T) is the ratio of the

amount of transmitted light (1) to the amount of incident light (I,):

I T = - (2.1 0 ) 4

Trammittance is related to the absorbance (A) in the following way (and hence Beer's Law):

A = - log T = &bc (2.1 1)

where c is the extinction coefficient b is the path Iength of the sample ceII, and c is the

sample concentration.

Surface IR spectroscopy has k e n practiced since the 1940's "'), consishg largely of

the shidy of adsorbed materials using transmission IR spectroscopy. Although transmission

IR spectroscopy is an excellent method of obtaining chernical information, it is not a highly

surface sensitive technique. as the incident bearn passes completely through the sample. For

increased surface sensitivity, diffise reflectance IR spectmscopy @RIFTS), grazing angle

reflection-absorption IR spectroscopy (RAIRS), and attenuated total reflectance (ATR) ( a h

known as multiple intemal reflectance, MIR) IR spectroscopy methods were developed,

enabling the surface studies of adsorbates on metal, semiconductor, and catalytic surfaces,

the study of thin films ("), and the study of polyrner surfaces and coatings ('. 12. ").

When using the DRIFTS technique, the sample is ground and mixed with a materid

that acts as a non-absorbing matrix. Dilution of the sarnple in a non-absorbing ma&

increases the proportion of the infrared beam that is diffisely reflected by the sample. IR

radiation incident upon the sample will result in two types of reflected energy : specular and

diffuse reflectance. Specular reflectance refers to IR radiation that is reflected directly off

the sample surface, and is not absorbed by the sample. Diffuse reflectance refers to the

radiation which penetrates the sample and then re-emerges, with some of the incident IR

energy being absorbed. Sample dilution and mixing in the the non-absorbing matrix must

be extensive to rninimize the arnount of specular reflectance to obtain desirable quantitative

precision "'? Therefore, aithough DRIFTS may be a suitable technique for the surface

analysis of some irregular surfaces or coatings, it is not an acceptable method for the anaiysis

of the surface modification of pol ymer films.

Grazing angle RAIRS is a type of extemal reflectance spectroscopy, providing a non-

destructive method for anaiyzing surfaces or coatings requiring no sample preparation. The

technique does require the analyte of interen k ing attached to a reflective surface. "Grazing

angle" refers to the IR bearn's angle of incidence, between 60 to 85 O relative to the surface

normal. It is the technique of choice for sub-micron films, because of the shallower sampling

depth. For thicker films, between 0.5 and 20 Pm in thickness, near-normal RAIRS (in which

the angle of incidence of the IR beam is between 10 to 60") is an appropriate technique

because of the greater sampling depth ''? At the angles of incidence used in grazing angle

RAIRS, the electromagnetic field in the plane containing the incident and reflected radiation

is greatly increased, resuiting in an increase in sensitivity. The incident radiation aiso

consists of s- and ppolarized components: the s-polanzed component is perpendicular to the

plane containhg the incident and reflected radiation, whereas the p-polarized component is

in the same plane as the incident and reflected radiation. At the grazing angle, the s-

polarized component approaches zero. while the p-polarized component is comparitively

large. This results in onl y ppolarized radiation king absorbed and only surface bonds with

dipoles in the ppolarized plane absorbing the infiami radiation (3? Therefore, grazing angle

RAIRS can be used for molecular orientation studies. Although grazing angle RAIRS is a

wfûl surface IR technique. it is unsuitable for the anaiytical requirements of this study since

it requires a reflective surface.

Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) has

k e n used in polymer s d a c e modification studies VA 12). In ATR-FTIR, the sample is kept

in contact with a crystal pnsm surface. such as a zinc selenide or germanium crystai (Figure

2.10). IR radiation enters the crystal at an angle which causes the radiation to be totally

internaily reflected. This intemal reflectance creates an 'evanescent wave' which extends

beyond the crystal's surface into the sample. In regions of the IR specmim where the sample

absorbs, the evanescent wave will be attenuated. The depth of penetration of the evanescent

wave into the sample (and. therefore, the depth of analysis) is af3ected by the rehctive index

of the crystal prism (n,), the rehctive index of the sample (na, the contact pressure between

the crystai and sample surfaces. and the wavelength of the incident beam ('* When using

a germanium crystal (n, = 4) for ATR-FTIR analysis of PP,(n = 1.55), the depth of

penetration is 1 -04 pm at 650 cm-', 0.40 Fm at 1666 cm", and 0.17 pm at 4000 cm-'. When

using a zinc selenide crystal (n, = 2.4) for ATR-FTR analysis of PP, at 1666 cm" the depth

of penetration is 1.38 pm (j6!

45 degrees d

t IR beam Ge crystal

Io

Figure 2.10: ATR-FTIR schematic diagrarn

2.1.3.2 Experimen ta1

For this study, a Bruker Instruments ES-55 FTIR spectrometer with a S pectra-Tech

ATR at tachent was used, with a germanium ATR crystal. The crystal face was washed

between samples with methanol and allowed to air-dry. The contact pressure between

sample and crystal was constant for each sample. A new background was collected between

samples, which is then automatically ratioed with subsequent collected IR absorbance

spectra.

Spectra were compared through the identification of specific bands. some of which

were identified through peak-fining, and by using the band-ratio analysis technique.

Absorbante in the 1900 to 1500 cm-' region is due to carbon-oxygen double bond stretching,

so the appearance of peaks in this region is indicative of surface oxidation. The band-ratio

technique involves dividing the integrated area of peaks in this 1900 to 1500 cm-' region by

the integrated area of a reference peak. This technique compensates for any differences

between samples due to differing sarnple sises or differing arnounts of contact between

sarnple and crystal. The reference peak used was in the 1530 to 1410 cm-' region, an

absorbance due to methyl and methylene bending modes. This region was chosen because

it should be unaffected by the surface modification, and is of a sufkiently close wavelength

to the peaks of interest so that sampling depths are similar (*? Untreated PP gave a band ratio

of approximately 0.023 * 0.015; an increase fiom that indicates an absorbance due to the

presence of carbon-oxygen double bond stretching. Band-ratio analysis has an error of

M.02-0.03 uni& '*'. 2.2 Polypropylene

The polymer used for the majority of this study was a welltharacterizcd

polypropylene (hereaffer refen-ed to as PP) nIm used in previous studies (' --'), and supplied

by 3M. This fih was a thermally extmded, biaxiaily oriented PP (BOPP) with a thickness

of 0.03 mm. It was produced fiom a homopolymer resin (M, = 1.9 x 1 Os, polydispenity =

0.6) containing 500-1000 ppm each of an inorganic acid scavenger and a high-molecular-

weight phenolic anti-oxidant. The film was produced on a tenter-fkme film line and

quenched at 45 O C pior to orientation. The machine-direction draw ratio was 5 -2: 1 and the

transverse-direction draw ratio was 9: I "'. A second sample of PP was used in preliminary work: a 'semi-crystalline' PP (SCPP)

film of 0.04 mm thickness. purchased fiom Goodfellow Corporation. This sarnple of PP was

a cast polymer film, and thus was considered to be less crystalline than would be an oriented

polymer film "?

2.3 A~paratus

2.3.1 üVO Reactor

The reactor used for this study is a small prototype chamber, built for the purpose of

treating threedimensionai objects (Figure 2.1 1). It consists of a cylindricai, stainless steel

d-, equipped with an O-ring sealable door at one end. At the other end of the reactor are

various O-ring sealable inlets. These are used to introduce gases into the reactor, for the

power supply connections for the UV lamps, as well as for the mounting of a themocouple

to monitor reactor temperature. The gas supplied to the interior of the reactor was extra-dry

compressed air (dew-point = -65 OC), or medical-grade cornpressed oxygen. the flow rate of

which was controlled by an MKS mass-flow controller, with a maximum flow rate capacity

of 2000 sccm (standard cubic centimetres per minute, or mL/min). This gas-flow was nin

h u g h an exterior ozone generator, in which ozone is created as the gas fiows through an

Figure 2.1 1: Diagram of the U V 0 reactor at SSW.

Cage

7

Ozone 1 1 Detector 1

Ozone inlet O Ozone ; Generator

Compressed Flow -- cd Meter i l

Gas 1

361 electrical discharge, to supply the main quantity of ozone to the reactor interior. For

reactions involving water vapour, a separate extra-dry compressed air line was bubbled

through a vacuum flask containing deionized, dtrafiltered water, to supply water vapour to

the reactor interior. The Bow rate of this second gas line was controlled with a simple bubble

meter with a maximum flow rate capacity of five rnL/min.

A steel cylindrical cage fits inside the reactor, to the outside of which the polymer

film samples were fastened. The distance of the film to the lamps was aitered using foil-

covered cardboard spacers. These spacers made it possible to have the PP sarnples at a

distance of 0.5. 1 .O, and 1.5 cm fiom the larnps.

The reactor intenor is Iined with a bank of custom-made low-pressure mercury

vapour arc lamps. The radiation intensity of the 253.7 nm line produced by the lamps is 12-

15 mW/cm2 at a distance of one inch fiom the lamps There are two sets of lamps lining

the reactor wall. One set of lamps is made of pure clear fused silica, which transrnits dl

mercury W ernissions, including the two strong W lines at 184.9 and 253.7 nm. The

second set of larnps is made of specially processed clear fused silica which blocks the

transmission of the 184.9 nrn ozone-producing W line. Figure 2.12 shows the emission

spectra for the two sets of lamps In the following text, the ozone-decomposing lamps

will be refemd to as the sofi-UV lamps and the ozone-producing larnps (those passing both

the 184.9 and 253.7 nrn strong lines) will be referred to as the hard-UV lamps.

Different -ment regimes are therefore possible with the reactor setup (Table 2.2).

The different treatment regimes result in varying concentrations of ozone in the reactor, and

varying amounts of surface modification. The W/air + ozone treatment was chosen

initially, due to past studies indicating it resulted in the most rapid and extensive suface

Figure 2.12: Ernission spectra for the ozone-producing and -decomposing sets of larnps.

Table 2.2: W O treatment regimes

Treatment regime

I Ozone only I off I on I

W lamps Ozone generator

W/(air or 03

W/(air or O,J + ozone

modification (''. For Iater experirnents, a W/02 + ozone treatment regime was adopted, to

obtain higher ozone concentrations.

Treatments can also be modified by varying the ozone concentration in the reactor.

This can be done by altering the gas-flow rate, by pulsing the W lamps, or by choosing

either set of W lamps. "Pulsing" the lamps refers to activating and deactivating the larnps

at reguiar time intervals.

In Figure 2.13, a plot of ozone concentration vesus time is s h o w , comparing the

arnounts of ozone present in the reactor when using either the hard-UV or soft-UV lamps,

at a constant oxygen flow rate. The f k t two minutes consisted of an 'equilibration' period

(t = O to 2 minutes), during which the reactor was charged with ozone from the extemal

ozone generator. m e r two minutes, the lamps were activated (t = 2 minutes). Before larnp

excitation, the ozone concentration in the charnber increases. The ozone concentration

reached a maximum (-8.0 x 10" molecules 03/cm3) after approximately one minute of lamp

operation for either set of larnps, after which it begins to decrease - d e r this one minute

period, the rate of ozone buildup is exceeded by the rate of ozone reaction in the charnber.

In the presence of the hard-UV larnps. the ozone concentration decreases sharply to about

half the maximum concentration, after appmxirnately seven minutes. In the case of the %fi-

UV Iarnp exposure, there is a minor decrease in the ozone concentration before it begins

on

on

off

on

Figure 2.13: Ozone concentration venus time, during operation of either the hard-W or soft-

W larnps.

A soft U V

I

Tirne (min)

373 to increase again. This decrease is probably the result of the rapid reaction of atomic oxygen

with the charnber walls which leads to a corresponding decrease in ozone concentration.

Figure 2.14 compares the ozone present in the reactor during constant versus pulsed

operation of the hard- and sofi-UV larnps (lamps manually pulsed on and off, every 30

seconds), at a constant air-flow rate. Pulsing the hard-W lamps resulted in a constant ozone

concentration of approxirnately 8.0 x 1 016 molecules/cm3, while constant operation of these

larnps resdted in the steady decline of ozone (Figure 2.14 (a)). Pulsing the soft-UV lamps

resulted in a slight increase in ozone concentration, whereas constant operation of these

larnps resdted in a slight decline followed by increasing ozone concentrations (Figure 2.14

(b)).

Treatments of PP film samples were normally carried out in the following manner:

(i) with the sample fmed to the outer wall of the cage, the reactor was sealed at room

temperature;

(ii) with gas flowing, the ozone generator was tumed on and lefi on for an equilibration

period of two minutes, to 'charge' the reactor with ozone;

(iii) at two minutes, actual treatment time was started;

(iv) d e r the desired treatment time, the sample was removed and wrapped in aluminum foil;

(v) the sample surface was then analyzed.

Deionized, dtrafïltered water was used for al1 sarnple washing. The wash procedure

consisted of pouring 50 ml of water over the treated sample surface and lening the sample

air dry.

2.3.2 Ozone concentration measurements

The concentration of ozone was monitored with a Resonance Ltd. UVTRANS2

Figure 2.14: Ozone concentration versus t h e . during constant or pulsed operation of the (a)

hard- and (b) soft-UV lamps.

-, 1 --a-- constant W 1

Time (min)

- pulsed UV -0- constant UV

Time (min)

176; mode1 ozone transrnissometer mounted at the exit end of the reactor. Monitoring the ozone

concentration in situ, inside the reactor, would be the rnost desirable position for making

accurate ozone concentration measurements. Taking measurements at the exit end of the

reactor is acceptable for acquiring an idea of the amount of ozone present in, and flowing

through, the reactor. It is also an acceptable measurement position for making cornparisons

between different treatment regirnes.

The transrnissometer unit employed a 253.7 MI W light-producing larnp and fibre

optic cables (Figure 2.15). Ozone exiting the reactor passes through a junction and absorbs

some of the transrnitted 253.7 nm light (13. The remaining light travels back to the detector

unit (I). The ozone concentration cm be caiculated ( I l 0%) using the digital display value

fiom the detector (arnount of transmitted light), the absorption coefficient (a) for ozone (1.2

x 1 O-" cm2), and Beer's Law 'j9':

where A is absorbance, T is transmittance, IJI is the ratio of incident Iight to transmitted

light, b is the pathlength in centimetres. and c is concentration.

23.3 Gas inlets

23.3.1 Experimen ta1

Two different ozone inlet confi~gurations were tested for two reasons:

(i) to determine the effect of the distance b e ~ n the sample and the gas idet, and hence the

effect of the transit time of ozone, and other reactive gas species, to the sample;

(ii) to optimize the treatrnent.

Inlet one simply fastened to the back of the reactor, for the gas to diffuse on its own through

Reactor gas outlet

To furnehood

/ log (I,,/I) =abc 1

Figure 2-15: Ozone transmissometer schematic diagrarn

318

the reactor intenor. Inlet two passed through the reactor inlet, into the reactor dong the cage

beside the üV light source. and had holes drilled dong its length (dubbed the 'ozone

sprinkler') (Figure 2.1 1 ). In this way, the gas was delivered into the reactor intenor, directly

above the polymer sample.

Sarnples of SCPP were treated with the UV/air + ozone treatrnent regime (1 000 sccm

air, quartz Iamps) with both inlet setups (three SCPP samples each per seîup), for treatrnent

times of 1,2. and 4 minutes. Sample size and sample placement inside the reactor was kept

constant. XPS s w e y scan spectra of the treated sarnples were collected. from two analysis

areas per sample. Advancing and receding contact angles were rneasured of the treated

samples, kom three to five areas per sample.

2.3.3.2 Results

The XPS and contact angle data are shown in Figure 2. 16 (a) and (b), respectively.

The 0:C values obtained from each X P S survey scan (two per sample) are plotted. Averages

for the contact angles obtained for each sarnple are aiso ploaed. The general trends observed

were that the O C ratios increased with increasing exposure time. and both the advancing and

receding contact angles decreased with increasing exposure time. These were the trends

expected and correlate with past studies on the UV0 surface modification of PP ('- ". Slightly

higher 0:C ratios and lower contact angles were obtained compared to a similar study on the

UV0 surface modification of PP (9!

Also shown in the plots in Figure 2.16 are the mean values and error bars. The XPS

data showed an error of no more than k0.02, and the contact angle data showed an error of

no more than 15 O . This reproducibilty also correlated with well past studies (' . ' . '). The

contact angle values obtained for sarnples treated with the first inlet setup indicated the

Figure 2.16: Results for gas inlet experiments. (a) 0 :C ratio, @) contact angle

measurements. Mean values are represented by white data points.

inlet two (sprinkler) + inlet one

1 2 3 4 exposure time (min)

1 2 3 4

exposure time (min)

381 largest arnount of error, this infreased error was amibuteci to operator inexperience and error,

and were still within acceptable limits.

Both the XPS and contact angle data indicated that the inlet delivering the ozonated

air closest to the sample resulted in a more extensive surface modification. 0 : C levels

increased to higher levels for samples treated with the ozone sprinkler inlet. Both the

advancing and receding contact angles decreased to lower levels for samples treated with the

ozone sprinkler inlet. This indicated that the ozone sprinkler setup was the optimal reactor

setup for the W O treatment of PP. It also indicated that there was an effect of transit time

on the reaction. suggesting that the closer to the polymer surface the ozone is supplied the

less tirne reactive gaseous species will have to be inactivated and will react with the polymer

itself.

M.J. Walzak, S. Flynn, R Foerch, J.M. Hill, E. Karbashewski, A. Lin, M. Strobel, Journal of Adhesion Science and Technology, v.9 n.9, pp. 1229-1 248, 1995.

J.M. Hill. E. Karbashewski, A. Lin, M. Strobel, M.J. Walzak, Journal ofAdhesion Science and Technology, v. 9 n. 12, pp. 1 575- 1 59 1, 1 995.

M. Strobel. C .S. L yons. J.M. S trobel, R.S . Kapaun, Journal of Adhesion Science and Technologv, v. 6 n. 4. pp. 429-443. 1992.

M. Strobel, C. Dunatov, J.M. Strobel, C.S. Lyons, S.J. Perron, M.C. Morgen, J o u d ofAdhesion Science and Technology, v. 3 n. 5, pp. 321-335, 1989.

J.M. Strobel. M. Strobel, C.S. Lyons? C. Dunatov, S.J. Perron, Journal ofAdhesion Science and Technology, v. 5 n. 2, pp. 1 1 9- 1 30, 1 99 1 .

F. Nomand, J. Marec, P. Leprince, A. Granier, Materials Science and Engineering, v. Al39, pp. 103-109, 1991.

J.F. Rabek, J. Lucki, B. Ranby, Y. Watanabe, B.J. Qu, in: Chemical Reactions on Polyrners. pp. 187-200, Amencan Chemical Society, Washington, DC, 1988.

M. Strobel, M.J. Walzak, J.M. Hill, A. Lin, E. Karbashewski, C.S. Lyons, Journal of Adhesion Science and Technology, v.9, pp. 365-383, 1995.

B. Gongjian, W. Yumuan, H. Xingzhou, Journal of Applied Polymer Science, v. 60, pp. 2397-2407, 1996.

E. Ochiello. M. Morra, G. Marini, F. Garbassi, P. Humphrey. Journal cfAppZied Polqrner Science. v.42, pp. 55 1-559, 199 1.

L.J. Gerenser, J.F. Elrnan, M.G. Mason, J.M. Pochan, Polymer, v. 26, pp. 1 162-1 166, 1985.

K. W. Lee, T.J. McCarthy, Macrornolecules, v.2 1, pp. 309-3 1 3, 1988.

D. Briggs, D.G. Rance, C.R. Kendall, A.R. Blythe, Polymer, v.21, pp. 895-900, 1980.

R.J. Good, in: "Contact m e . Wettabilitv - and Adhesiorf7. K.L. Mittal (Ed.), VSP, 1993.

M. Morra, E. OcchielIo, F. Garbassi, Advances in CoZZoid and Interface Science, v. 32, pp. 79- 1 16, 1990.

RE. Johnson, RH. Dettre, in: Contact Angle, Wettability, and Adhesion. editor F.M. Fowkes. Advances in Chemistry Senes, v. 43, pp. 1 1 2- 135. Amencan Chernical Society, Washington, DC, 1964.

D. Briggs. G. Beamson, Analytical Chemistry, v. 64, pp. 1 729- 1736, 1992.

G. Bearnson. D. Bnggs. Hieh Resolution XPS of Organic Polvmeq. John Wiley and Sons, New York 1992.

G. Kill, D.H. Hunter. N.S. McIntyre, Journal ofPolymer Science. Part A: Polymer Chemimy. v. 34. pp. 2299-23 10, 1996.

D. Briggs. M.P. Seah. Practical Surface Analvsis Vol. 1. John Wiley, New York, I W O .

S. Kaliaguine. in: "Recent Advances and New Horizons in Zeolite Science and Technology." H. Chon, S. 1. Woo, S. E. Park (Eds), Studies in Surface Science and Catalysis. v. 102, Elsevier Science, 1996.

C.E. Bryson III, Surface Science, v. 189/190, pp. 50 1-509, 1987.

T.L. Barr. Modern ESCA: The Princi~les and Practice of X-rav Photoelectron S~ectrosco~v. Pg. 71, CRC Press, Florida, 1994.

P. Spevack. Ph.D. thesis, U.W.O., 1993.

S.J. Splinter, N.S. McIntyre, Surface and Interface Analysis, submitted, 1997.

A.R. Pratt. N.S. McIntyre, S.J. Splinter, in press. 1997.

C. E. Shannon. Bell System Tech. J., 27,379, 1948.

E. T. Jaynes, Phys. Rev., 106,620, 1957.

R.M. Silverstein, G.C. Bassler, T.C. Momll, "Spectrometric Identification of Or~an ic Compounds." John Wiley and Sons, New York, 198 1.

S. Ege. Qrganic Chemistry. second edition. D.C Heath and Company, U.S.A., 1989.

P. Hollins. in: Surface Science Techniques. Pergamon, pp. 57-66, 1994.

D.A. Skoog, J.J. Leary, Principles of I~trumenta1 Anal~sb. Saunders College Publishing. pp. 252-288.

33. M. Cartwight. Fourier Methods for mathemahcians. scientists. and enoineen. Ellis Horwood Limited, Chichester, England, 1990.

34. P.R. Griffiths, K.W. Van Every, N.A. Wright, in: Chernical. Biolo~ical. and Industrial A~plications of infrared Spectroscopy. pp. 253-276, 1985.

35. P. Blais. C.J. Carlsson, D.M. Wiles, Journal of Polymer Science: Part A-1, v. 10, pp. 1077- 1092, 1972.

36. S pec tra-Tec h ATR-FTIR attachrnent instructional manual.

37. Goodfellow Corporation, persona1 communication.

38. BHK Inc. W larnp manufacturer, personal communication.

3 9. Resonance Lirnited Mode1 WTRANS2 ozone transmissometer instrument rnanud, 1993.

HAPTER 3 - Reactions with UV0

3.1 Introduction

The following is a brief description of each experiment completed during this

research project, accompanied by the rationale behind eac h experiment.

Irradiation bandwidth: Treatrnents with either the hard- (A,,, < 250 nm) or soft-W (A,,,

> 250 nm) lamps may result in a different PP surface modification, due to the involvement

of differing U V wavelengths. The differences in the surface modification obtained by UV0

treatments of PP samples, when using either of the two sets of larnps, were thus investigated

using contact angle measurements, XPS, and ATR-FTiR spectroscopy.

Ozone concentration: An increased ozone concentration in the reactor should result in an

increased arnount of reactive atomic oxygen produced fiom ozone photolysis. This should

increase the initial rate of attack on the surface and this, in turn, may result in an increased

rate of modification of the surface. An increased ozone concentration may also result,

however, in the absorption of 254 nm UV before it reaches the surface, thereby lessening the

extent of surface modification. The differences in the surface modification obtained by UV0

treatrnents of BOPP samples using different ozone concentrations were thus investigated

using contact angle measurements, XPS, and ATR-FTIR spectroscopy to measure the effects.

UV pulsing experiments: In an attempt to separate the effects of the presence of omne only

and the combined effects of UV and omne on the surface modification, experiments were

conducted in which either hard- or sofi-UV illumination was pulsed during treatment. This

should provide an indication of the role of W itself on the surface modification, as well as

the separate roles of atomic oxygen and omne. Samples of BOPP were treated to alternathg

periods of combined W and ozone exposure, and periods of ozone exposure by itself". XPS

186 and contact angle meanirements were used to follow the surface changes that resulted fkom

these pulsed treatments.

Sample distance from Iamps: A decrease in the distance between the sarnple and the lamps

would be expected to increase the intensity of the W radiation incident upon the sample

surface. This increased UV-intensity might be expected to increase surface oxidative

changes due to one or more mechanisms. Increased UV-intensity at the surface would be

expected to lead to photolysis of ozone at a point which is closer to the polymer surface,

resulting in the availability of more atomic oxygen closer to the surface. Also, increased

UV-intensity at the surface might cause increased activation of the polymer surface itseif.

The quantitative difference in the surface modification obtained by W O treatrnents of PP

sarnples at different lamp-to-sarnple distances was thus investigated using XPS and contact

angle measurements.

Effects of water vapour: The effects of increased concentrations of water vapour were

examined by introducing a flow of water vapour into the reactor during treatrnent. Water

would be expected to lose a hydrogen to any O ('D) present, producing hydroxyl radicals.

Provided there is O (ID) present, additional water should result in the production of hydroxyl

radicais, which may then react with the PP surface. The effects of additional water vapour

on the W O treatment of BOPP were examined by contact angle measurements, XPS, and

ATR-FTIR.

Surface Chemistry: The results of the above experiments were investigated primarily

through quantitative analysis of contact angles and XPS atomic ratios. XPS high resolution

carbon 1s spectra and IR spectra were also collected to obtain information on mechanisms

responsible for the surface modification.

3.2 Effects of irradiation bandwidth and ozone concentration

The aim of this expairnent was to detemiine the effects of irradiation bandwidth and

varying ozone concentration on the surface modification of BOPP. The W lamp used

during W O treatment wïii determine which wavelengths of W are present. Either the hard-

(A,,, < 250 nm) or sof t-W (LI, > 250 nrn) lamps can be used, and the results may Vary

between the two treatments.

Photolysis of ozone produces atornic oxgyen, die species believed to play the major

role in the surface modification of PP when using a UWair + O, treatment regime (').

Increasing the ozone concentration during U V 0 treatment may result in the increased

production of atomic oxygen. The amount of ozone added to the reactor can be controlled

with the extemal ozone genentor.

3.2.1 Experimental

Samples of BOPP were treated with either a hard- or soft-W/Oz + O, (1000 sccm

02) treatrnent regime, at a distance of 0.5 cm from the larnps, at three different ozone

concentrations (low - 1 .O x 1 016 molecules ozone/cm3, rnid - 2.0 x 10 l6 molecules ozondcm

high - 8.0 x 1016 molecules ozonekd) . Gas-flow was set at 1000 sccm. Three samples

were treated per treatment regime. Contact angle rneasurements, XPS survey scans, and

ATR-FTIR spectra were collected.

3.2.2 Results and Discussion

The advancing and receding contact angle results are show in Table 3.1. These

reported values are averages of the three to five measurernents taken per sample. Figure 3.1

depicts the changes in contact angle for exposure to hard- or sof t-W with the three O,-

concentrations, for both unwashed and washed samples. The standard deviation of al1 the

3 88. Table 3.1: Contact angle resdts for ozone concentration and irradiation bandwidth experiments

[O31 (molecules/cm3)

(*lm)

1.0 x 1016

2.0 x 10t6

8.0 x 10t6

1.0 x I O t 6

2.0 x 10t6

8.0 x 10t6

Exposure time (min)

I

2

5

1

2

5

10

1

2

5

10

I

2

5

1

2

5

1 O

1

2

5

10

Advancing contact angle

unwashed

95

82

75

1 03

88

73

68

95

88

82

74

9 1

8 1

74

97

87

78

76

92

86

77

70

Receding contact (*3 O)

washed

95

88

84

1 03

90

79

78

97

92

86

83

93

86

83

96

88

83

84

90

87

84

84

angIe

unwashed

53

47

45

63

46

36

34

54

49

48

46

50

43

42

55

47

39

41

50

45

44

41

(k3 O )

washec

54

48

48

66

46

40

44

56

50

50

50

5 1

45

42

56

47

40

44

50

45

45

45

measurements taken was always less than *3 O , the error associated with the contact angle

tec b ique ( '1.

The data in Figure 3.1 showed the expected trend of decreasing contact angles with

increasing exposure tirne. Focussing on data for the washed samples, afler one minute of

treatment, the low and hi& ozone concentrations resulted in the lowest contact angles. Sofi-

UV treatment resulted in lower contact angles than hard-UV treatment, with the mid and

high ozone concentrations. There was linle difference in the contact angle results between

hard- and soft-W for the low omne concentration &er one minute of treatment. M e r two

minutes of treatment, the contact angles are very similar for a11 ozone concentrations and for

both W sources. Treating for longer than two minute periods resulted in only rninor m e r

decreases in the contact angle, compared to the decreases after one and two minute

treatments, although the mid ozone concentration treatment resulted in a further decrease in

contact angle by about 10". There was littie difference in the resuits of hard- or soft- W

treatment after five and 10 minutes, aithough mid ozone concentration/hard-LJV treatment

resulted in slightly lower contact angles d e r five and 10 minutes of treatment. Comparing

unwashed and washed data, there were increases in contact angle upon washing f ie r five and

ten minutes of treatment, indicating that LMWOM species were being washed from the

surface. For the rnost part, the contact angle values obtained in this snidy were within five

degrees of those obtained by Walzak et. al. ( ') with their hard-W/ozone treatrnents of PP

using a different reactor and an ozone concentration of approximately 1 .O x 10" molecules

0Jcm3. An exception to this was that the values obtained in this study &er one minute of

soft- W treatment were about 10" lower.

Figure 3.1 : Contact angle measurements for samples treated with a hard- or sofi-W/Oz + O,

(1000 sccm O?) treatment regime at three different ozone concentrations.

Contact angle (degrees) Contact angle (degrees) Contact angle (degrees)

192 There appears to be no significant effect of ozone concentration on the contact angle

results, at least within the range of ozone concentrations studied here. This somewhat

nirprising result is perhaps due to the compensating effects of UV transmission and atomic

oxygen formation. The % transmission of 184.9 nm W to the polymer surface will not Vary

as the ozone concentration is changed fiom the low to high Ievels; even at the high ozone

concentration. oxygen accounts for 99% of the gas fed into the reactor. However, the %

transmission of the 253.7 nm UV will vary fkom 94 to 62% as the ozone concentration is

raised fiom the low to high Ievels. Higher transmission of the lower energy W to the

d a c e would result in the production of more atornic oxygen close to the surface, but more

ozone would result in increased arnounts of atomic oxygen altogether. Of the ozone

concentrations explored here, the low and high levels seem to produce the more wettable

surface after one minute of treatment; however, the lowest receding contact angle values

appear to corne from the mid ozone concentration after five minutes of treatment.

It appears fiom these contact angle results that the 184.9 nm U V plays a negligible

role in the UV0 surface modification process. Afier one minute of treaunent, soft-W

treatment actually resulted in lower contact angle values, suggesting that the presence of

184.9 nm W when using the hard-W source is detrimental to obtaining a higher energy

d a c e during short term treatments. After extended treatment of five and 10 minutes, hard-

UV exposure seems to lead to a slightly higher energy surface when using the mid ozone

concentration, but d e r washing, the samples exhibited comparable surface wettabilities

between hard- and soft-UV treated samples. This M e r suggests that the higher energy UV

plays a negligible role in the activation process.

Analysis of the XPS s w e y scans of samples treated at the mid O,-concentration gave

the 0:C ratio data s h o w in Table 3.2,

Table 3.2: XPS results for ozone concentration and irradiation bandwidth experiments

As expected, the 0:C ratio increased with increasing exposure tirne. Washing resulted in a

decrease in the 0:C ratio only for the samples treated for 10 minutes; this indicates that

LMWOM species are forming only afier the longer treatrnent times. Walzak et. al. ( l ) used

an ozone concentration of 1 .O x 10" molec~leS/cm~ in their studies of UV0 treated PP, an

order of magnitude more ozone than used in this study. They obtained 0:C ratios of

approximately 0.10 and 0.14 &er two and ten minutes of treatment, respectively. As

mentioned previously, however. their contact angle findings were similar to those described

here. This suggests that increased ozone concentrations would Iead to more oxggen uptake,

but this additional oxygen is not effective at providing an increase in wettability. The

additional oxidation could also be at depths not probed by contact angle measurements. The

difference in 0 : C ratio between hard- and soft-UV exposure for both two and 10 minute

treatrnent was not significant; this is M e r evidence of the minimal role that 184.9 nrn W

plays in the W O surface modification process.

As noted previously, the contact angle values did not decrease substantially after

W source

Hard-UV

Soft-UV

Ozone concentration

(moIecdes/cm3) (* 1 0%)

2.0 x 1 016

2.0 x 1016

Exposure time (min)

2

10

2

10

O C ratio unwashed

0.01 3 * 0.00 1 0.075 * 0.01 1 0.0 15 * 0.003 0.068 * 0.028

0:C ratio washed

0.01 3 k 0.007

0.048 0.005

0.0 14 0.003

0.041 * 0.003

treatrnent times of longer than two minutes, at any of the three O,-concentrations, when

using either hard- or soft-W. Ten minutes of treatment actually resulted in an increase in

the 0:C ratio fkom that obtained after two minutes of treatment, without a further significant

decrease in receding contact angle. This result correlates with the findings of WaIzak et. ai.

(') - the advancing and receding contact angle had decreased to minimum values f i e r

approximately two minutes of treatment, whereas the 0:C ratio continued to increase.

Groups that are effective at improving the wettability of the polymer surface are introduced

during the f h t hvo minutes of treatment - the additional surface oxygen uptake is apparently

composed of groups that are ineffective at increasing the surface energy of the polymer.

Further, modification occurring may be oxidation at depths not probed by contact angle

measurernents. This additional oxygen uptake may also be LMWOM that is water-soluble

and hence dissolves in the contact angle probe liquid. The presence of LMWOM is

supported by the decrease in 0:C ratio and the increase in contact angles after washing.

Further discussion of the surface chemistry is presented in Section 3.6.

The 0:C ratio for washed samples that were treated for ten minutes was still greater

than the 0 :C ratio obtained for samples treated for only two minutes - without M e r

decreases in contact angle. This is a M e r indication that the additional oxygen

functiondity obtained with longer term treatrnents is not effective at increasing surface

energy. A possible esplanation is that initidy oxidized areas would be more susceptible to

M e r oxidation; this would result in a localized patchy oxidation which would result in

higher 0:C ratios. but may not lead to substantial decreases in contact angle, as would a more

homogeneous surface oxidation.

3 3 1JV P u l s i n ~ treatments

The aim of this experiment was to attempt to elucidate the role and importance of

UV, and the wavelength of UV, atomic oxygen, and ozone on the UV0 surface modification

of PP. The data obtained from the irradiation bandwidth expenments indicated that 184.9

nm UV played a negligible role in the surface modification of BOPP. In Figure 2.13, graphs

of ozone concentration verjus Ume are s h o w depicting the amount of ozone present at the

rûactor outlet when the W source is pulsed on and off every 30 seconds. Pulsing the hard-

W larnps (A,,, c 250 nm) resulted in a relatively constant ozone concentration, whereas

constant operation of these lamps resulted in the steady decline of ozone (Figure 2.13 (a)).

Pulsing of the sofi-UV larnps (Ami, > 250 nrn) also resulted in a relatively constant ozone

concentration; constant operation of these lamps resulted initially in a slight decline in ozone

concentration, followed by an increase after about five minutes (Figure 2.13 (b)). Pulsing

either set of UV lamps resulted in virtually identical ozone concentrations. The sole

difference between the treatments of PP using either set of larnps, then, is the absence of the

184.9 nm üV for the pulsed soft-UV treatment.

33.1 Experimen ta1

Samples of BOPP were treated with the UVIair + O, treatrnent regime, pulsing the

lamps on and offevery 30 seconds. Hard- or soft-UV lamps were used with an air-flow rate

of 1000 sccm. For each sample treatment, &er the initial two minute equilibration period

of exclusively ozonated-air exposure, the treatment was stopped after half-minute intervals

and a sample removed. In this way, samples were obtained after every ha1 f-minute interval,

up to and including 5 minutes of pulsed treatrnent. For example, a sample treated for 1.5

minutes with this treatment regime, had been exposed to the two minute equilibration pend,

j s-6. followed by a half-minute of W O exposure, a half-minute of ozonated air exposure without

UV, then a final hdf-minute of W O exposure. Each treatment was carried out on two

separate BOPP samples. X P S s w e y spectra of two areas on each of the treated samples

were collected. Advancing and receding contact angles were measured at three diflerent

areas on the treated samples.

3.3.2 Results and Discussion

The data obtahed frorn XPS survey scans and contact angle measurements are shown

in Figure 3.2 for samples treated using hard-UV, and in Figure 3.3 for samples treated using

soft-W. The data points plotted are the statisticd means of al1 measurements taken per

sarnple; error bars shown represent one standard deviation.

For the samples treated using soft-W, the 0:C ratio and contact angles showed

steplike changes. Both the 0:C ratio and contact angles changed during the first three UV0

cycles. The 0:C ratio increased and the contact angles decreased during these cycles; these

changes would be expected to correlate if the oxygen functionality being formed caused

increased water-wettability of the surface.

For samples treated using hard-UV, both the O:C ratio and contact angle data also

exhibited steplike changes with increasing exposure time. However, after this initial W O

cycle, the 0 : C ratio appeared to change primarily during the ozone-only exposures, while

the receding contact angle changed during UV0 exposure. This continued up to the end of

the third ozonesnly cycle. The clifference in trends between the 0 : C ratio and contact angle

changes during the first three minutes of pulsed exposure suggests that the separate cycles

are changing the surface but in different ways. W O treatment during this period Ieads to

the production of hydrophilic functional groups at the polymer surface, shown by the

Figure 3.2: Results fkom W pulsing experiments using the hard-UV source.

(a) 0:C ratio data, (b) contact angle measurernents.

exposure time (min)

exposure tirne (min)

Figure 3.3: Results fiom W pulsing experiments using the sofi- W source.

(a) 0:C ratio data (b) contact angle measurements.

exposure time (min)

exposure time (min)

! 01 decreases in contact angle. However. most of the change in 0 :C ratio occurred d u ~ g the

ozone-only cycle. This could suggest that the XPS 0 : C measurements during this period

could involve oxygen fbnctionalities which do not contribute to improved contact angles.

These could be fomed by a process which diffen significantly f?om that involved during

UV0 cycles.

A cornparison of hard- and sofi-UV exposures shows linle difference in the extent

to which advancing or receding contact angle is reduced in the fkst three W O cycles. This

suggests that the higher energy UV line at 1 84.9 nrn. present during hard- W exposure. plays

no additional role in the usehl modification of the BOPP surface, either through activation

of the d a c e or through additional mechanism for atomic oxygen production. Also, under

sofi-W irradiation, changes to the 0:C ratio and contact angles only occur during W O

cycles; ozone-only cycles have no effect on surface energy or composition. However, in the

case of hard-W exposure, an increase in the 0:C ratio is noted during early ozone-only

cycles. This suggests that the higher energy üV line does lead to the creation of additional

reactive species which remain present during al1 or part of the ozone-only cycle, resulting in

additional surface changes during these cycles. These additional changes, however, do not

lead to a more wettable surface.

Surfaces reacted under pulsed-UV conditions were significantly less modified than

those which had k e n exposed to constant UV conditions (Section 3.2). The reason for this

is that. when the W is turned off, the equilibrium concentrations of O (ID) and O ( P)

change; the ratio of concentrations of O CP)IO (ID) increases as O (ID) decays to O (3P). O

('P) is responsible for crosslinking, and thus the decrease in surface reactivi ty .

3.4 Sam~le distance from l a m ~ s

Altering the W O treatment distance between the sample and the lamps should have

an effect on the extent of surface modification. A more highly oxidized, higher-energy

surface should be obtaîned as the distance between the sample and the Iarnps is decreased.

This would be exhibited by higher 0:C ratios and lower contact angles as the treatment

distance is decreased. The effect of changes in lampto-sample distance may be artributable

to a combination of increased surface activation by UV and/or increased reaction of gas-

species with the surface as they are created near the surface. However, it was shown in the

UV-pulsing experiments that surface activation effects do not appear to be important in the

process.

In a vacuum, the intensity of radiation incident upon a surface decreases as the

inverse square of the distance for a point light source. For a linear larnp source, if the

distance between the surface and the lamp is less than the length of the larnp, the inadiance

should decrease almost linearly with increasing distance from the surface. In the presence

of absorbing species, such as molecular oxygen and ozone, the intensity of radiation incident

upon a surface will be decreased even m e r . At ozone concentrations of approximately 3.0

x 1 016 r n ~ l e ~ ~ I e s / ~ m ~ , the % transmission of both 184.9 nm and 253.7 nm W radiation is

shown in Figure 3.4 to increase linearly with decreasing lampto-sample distance. Increased

transmission of 253.7 nm W to the surface will lead to the formation of reactive species

closer to the surface. Atomic oxygen is the main reactive species when using the W l a i r +

O, treatment regime; because it is a very reactive, shortlived species it may be inactivated

before it cm react with the polymer surface. Decreasing the lampto-sample distance should

facilitate its reaction with the polymer surface before its inactivation and, hence, result in a

Figure 3.4: % transmission of UV to the polymer surface.

higher degree of surface modification.

Samples of BOPP were treated with a hard-UVlair + O, treatment regime (1 000 sccm

air) for 5 minute periods at UV lamp-to-sample distances of 0.5, 1 .O, and 1.5 cm (three

samples per distance) and ozone concentrations of approximatel y 3 .O x 1 Olb molecules/cm3.

XPS s w e y spectra of two areas on each of the treated samples were collected. Advancing

and receding contact angles were rneasured at three different areas of the treated samples.

3.4.2 Results and Discussion

The XPS data and contact angle measurements are shown in Table 3.3.

Table 3 -3 : Experimental results for sample distance experiments

A graphical representation of the 0:C ratio and contact angle data is shown in Figure 3.5.

Distance fkom lamps

(cm>

The 0 : C ratio changed linearly with increased lamp-to-sample distance, as did the contact

angle. In fact, a comparable increase occurred between the 0:C ratio and the increase in

0:C Ratio

transmission of 253.7 nrn UV to the surface, as show in Figure 3.4. Therefore, the changes

in lamp-to-sample distance seem to primarily affect the formation of atomic oxygen closer

Advancing contact angle

(f3 O)

to the surface as the intensity of 253.7 nm W incident upon the surface increases.

Receding contact angle

(*3 O 1

Figure 3.5: 0:C ratio and contact angle data obtained from sample distance experiments.

0.4 0.6 0.8 1 .O 1.2 1.4 1.6

Distance fiom lamps (cm)

&. ' 0 8 - 3.5 Effects of water vaDour

Excess humidity during W O treatment is a factor that has not been investigated

previously for U V 0 treatment of PP, aithough Strobel et. al. studied the effects of different

humidities on the corona treatment of PP (?

The presence of water vapour during UV0 treatments may result in the production

of hydroxyl radicals, as O (ID) is capable of abstracting hydrogen atorns fkom water

molecules (see section 1.2.4). These hydroxyl radicais may then combine with carbon

radicals to form hydroxyl groups. or abstract hydrogen atoms fkom the polyrner chain to form

radicals or alkene uni& (see section 1.2.5). The concentration of hydroxyl groups must be

suficiently high for the formatior! of hydroxyl groups to occur before these groups are

consumed by abstraction reactions. The aim of this experiment was to detemine the effects

of the presence of water vapour on the W O surface modification process.

3.5.1 Experirneotal

Samples of BOPP were treated with a hard-UV/Oz + Q (1000 sccm Q ) + H Qg,

treatment regime at a distance of 0.5 cm fiom the lamps. for 2 and 10 minute periods (2

samples per treatment tirne) using an ozone concentration of approximately 2.0 x 1016

molecules ozone/cm3. Advancing and receding contact angles were measured, before and

d e r washing the treated samples with ultrafiltered, deionized water. XPS survey scans and

ATR-FTIR spectra were collected, before and d e r washing the treated samples with

ultrafiltered, deionized water.

3.5.2 ResuIts and Discussion

The data obtained fiom analysis of the XPS survey scans collected of samples treated

under hard-UV with supplemental water vapour is shown in Table 3.4. Included for

109 cornparison are the r d t s for samples treated under hard-UV without supplemental water

vapour.

Table 3.4: XPS results for water vapour experirnents

without 1 I I I I I

Treatment

UV0 with

M e r two minutes of treatment. the treatments which included supplemental water vapour

resulted in 0:C ratios that were slightly larger than for those samples treated without

Expowe t h e (min)

2

supplemental water vapour. After 10 minutes of treatment, the 0:C ratios were sirnilar for

samples treated with and without supplemental water vapou.. There was no decrease in the

0:C ratio unwashed

0.025 k 0.008

0:C ratio upon washing the surfaces of the samples treated for two minutes. The 0 : C ratio

0 : C ratio washed

0.02 1 * 0.0 1 O

of the 1 0 minute treated samples decreased upon washing .

The contact angle measurements of the treated samples are shown in Table 3 S.

Table 3.5: Contact angle results for water vapour experiments

Treatment Receding contact angle (*3 O)

Exposure time (min)

7

unwashed

5 1

50

46

34

Advancing contact angle (*3 O)

UV0 with

H2OW r

U V 0 without

H20w

washed

55

53

46

44

unwashed washed

90

82

90

78

2

10

85

73

2

10

88

68

110 The advancing contact angles obtained were similar for the two types of treatment. The

receding contact angles for samples treated with supplemental water vapour were higher than

for those samples treated without nipplemental water vapour, afler both two and 10 minutes

of treatment.

More oxygen uptake occurred as a result of short-term W O treatment wîth

supplemental water vapour. The higher O:C ratios obtained by this treatment may be due

to the additional reaction of hydroxyl radicais with the surface. These hydroxyl radicals

would be produced by reaction of atomic oxygen with water vapour molecules. Despite

obtaining higher 0 :C ratios for samples W O treated with supplemental water vapour, there

was no improvement in the contact angles. In fact, the contact angles for these samples were

higher than for those sarnples treated without supplemental water vapour. Although higher

oxygen uptake was observed, the wettability of the polymer was not improved. This may

be due to the same effect noticed in the results of Section 3.1 - that the additional oxidation

is not in the form of groups that are effective in increasing the wettability of the polymer.

After ten minutes of treatment, the 0:C ratio is similar for either treatment, whereas the

contact angle remains Iower for those sarnples treated without supplemental water vapour.

Again, the functionality of the sarnple treated without supplemental water vapour seems to

be more effective in providing the more wettable surface.

3.6 Surface Chemistv

3.6.1 High-resolution carbon 1s XPS spectra

High-resolution carbon 1s spectra were collected of several treated sarnples in order

to elucidate the chernical structure of the oxidized functionality, as well as the mechanism(s)

of the surface oxidation. Collected spectra were peak-fitted as descnbed in section 2.1.2.2.

I l B . Relative areas for dl o f the peaks of the coilected and peak-fitted spectm are shown in Table

3.6.

Table 3.6: Areas obtained fiom peak-fitted high resolution carbon 1 s spectra.

Treatment Carbon (1 s) Binding Energy ( * 0.1 eV) (% area in brackets)

Peak 3 Peak 4 Peak 5 (C-O) (C=O) (O-C=O)

- - -

286.5 287.9 289.2 (3.6) (0.7) (0.5)

286.4 288.0 289.3 (2.8) (0.7) (0.3)

286.5 287.9 289.3 (6.7) (2.7) (2 -2)

286.4 287.9 289.3 (4.6) (1 .O) (0.7)

(C-C) (C*-C=O) Pehk I As received

2 minutes unwashed

2 minutes washed

W / O I + Oj, hard-UV,

2 x IOi6 molecules 03/cm3

10 minutes unwashed

10 minutes washed

2 minutes unwashed

2 minutes washed

W/02 + 03, soft-UV,

2 x 10t6 molecules 0Jcm3

10 minutes unwashed

10 minutes washed

- -

W/02 +O, + H2Ow

hard-UV 2 x 1016 molecules

03/cm3

2 minutes unwashed

10 minutes unwashed

I l 2 Spectra s h o w were those obtained during studies of the effects of ozone concentration,

irradiation bandwidth, and high humidi ty . In particular, high resolution carbon I s spectra

(Figures 3.6 and 3.7) were collected of samples treated for two and 10 minutes at the mid 0,-

concentration using hard- or sofi-UV, both before and f i e r washing. For the high humidity

experiments. high resolution carbon 1s spectm were collected of samples treated for two and

10 minutes at the mid O,-concentration using hard-UV, with and without supplemental water

vapour. These spectra are shown in Figure 3.8.

In al1 of the specna peak 1 was futed at 285.0 eV. the binding energy characteristic

of a long chain. aliphatic carbon (C,H2,,) (? Peak 2 varies from 285.4 to 285.5 eV and is

representative of the aliphatic carbon alpha to carbonylic or carboxylic carbons ( C * - C e )

"). Peak 2 undergoes a small shift due to the inductive effects of the neighbouring carbon.

Peak 3 varies fiom 286.4 to 286.5 eV; its binding energies could be representative of ether

(C-O-C) and/or hydroxyl (C-OH) carbons "1. Peak 4 varies from 287.8 to 288.0 eV with

binding energies representative of carbonyl (C=O) carbons andor carbons singly bonded to

two oxygen atoms (O-C-O) (? Peak 5 varies from 289.1 to 289.3 eV, binding energies

representative of carboxylic carbons (O-C=O) of esters and/or carboxylic acids; not found

in this range are carbonate carbons or diester carbons ('1.

AAer shon term W O treatment, surface oxidation was clearly evident in the form

of C-O groups; only small amounts of carbonylic and carboxylic functionalities were

observed. XPS concentration measurements allow us to to infer the presence of ether

linkages. The O C ratio after two minutes of W O exposure was 0.0 14 * 0.005. The ratio

of C-O/C h m the carbon 1 s spectra was 0.025 2 0.005. This indicates that most C-O bonds

occur as ether linkages, rather than as hydroxyl groups.

Figure 3.6: High resolution carbon 1s specm of two and ten minute hard-üV treated

samples, before and after washing.

(a) hard- W two minutes

. i

(b) hard-W ten minutes

288 286 284 282

Binding energy (ev)

Figure 3.7: High resolution carbon 1 s spectra of two and ten minute soft- W treated samples,

before and after washing.

(a) soft-W two minutes

(b) sofi-W ten minutes g

288 286 284 282

Binding energy (ev)

Figure 3.8: High resolution carbon 1s specha of two and ten minute CTVO treated sarnples,

treated with and without supplementd water vapour.

(a) hard-UV two minutes unwashed

(b) hard- W ten minutes unwashed

288 286 284

Binding energy (ev)

L '19 The oxy gen nuictionali ties O btained b y di ffering treatments were very similar,

although the sample treated under soft-UV showed a slightly greater arnount of ether

functionality (C-O-C) than the hard-W treated sample. The sample treated with

supplementai water vapour under hard-UV showed sirnilar functionalities to the sample

treated under hard-W without supplemental water vapour, except for slightly higher

carbonyl fimctionality. The higher 0:C ratios obtained for the water vapour-treated samples

suggest that some of the C-O functionality was in the form of hydroxyl groups; this may

explain the less wettable surface of the samples treated for two minutes with supplementai

water vapour. The samples that were washed showed a loss of this functiondity upon

washing. Negligible decreases occurred in the amount of carbonyl and carboxyl constituents.

After 10 minutes of treatment. the development of ether, carbonyl, and carboxyl

functionalities was evident for al1 treatments. The sample treated under sof t -W showed the

greatest developrnent of oxygen functionality. There was a decrease in t5e arnount of oxygen

functionality after washing for both the samples treated under hard- or sofi-UV. Arnounts

of ether constituents decreased, as did carbonyl and carboxyl constituents. The sarnples

treated under hard-UV showed the greatest loss of oxygen functionality after washing,

showing a decrease in the amount of ether and, especially, carbonyl and carboxyl

constituents. Supplemental water vapour seemed to have little effect on the hctionalization

afler long term treatments. Concentrations of ether, carbony 1, and carboxy 1 constituents were

virtually identical for the sarnples treated with or without supplementai water vapour.

The high concentration of ether fimctionality fiorn short term treatment may result

from an O (ID) insertion reaction. By contrast, reaction with O ( P) would have involved

hydrogen abstraction and resulted in other products. Lengthier treatments resulted in the

1 4

developrnent of more highly oxidized constituents, in the f o m of carbonyl and carboxyl

groups. Ether. carbonyl, and carboxyl constituents dl increase with continued treatment.

Preferential attack at already oxidized sites, as opposed to the formation of fiesh ether

groups, would be expected but the development of al1 of the oxygen functionalities seemed

to occur at similar rates afier long term treatments.

Upon washing the surfaces of samples that were treated for two minutes. the relative

concentration of C-O functionality declined more than those of carbonyl or carboxyl

constituents. This is contraq to the expected result - that the more highly oxidized forms of

carbon would constitute some LMWOM species and hence tend to be water-soluble and

easily lost upon washing. The formation of carbonyl and carboxyl functionality should lead

to more chain scission, decreasing chain length and forming water-soluble LMWOM. The

obsenred trend suggests that C-O groups were indeed part of unattached, water-soluble

surface chains and were washed f?om the surface. A substantial loss of carbonyl and

carboxyl constituents was evident upon washing the surfaces of samples treated for 10

minutes.

3.6.2 ATR-FTIR spectra

Exarnination of ATR-FTIR spectra c m provide surface chernical information for

cornparison with the information gathered fiom XPS spectra. As descnbed in Section

2.1.3.2, an indication of surface oxidation can be obtained fiom the intensity ratio between

bands in the 1900 to 1530 cm'' region, which are charactenstic of C=O stretching, to those

in the 1530 to 14 10 cm-' region, absorbances due to methyl and methylene bending modes.

This is somewhat comparable to the 0 : C ratio obtained through the analysis of XPS survey

scans. Further. throuszh a detailed ~eak-fittine of bands in the 1900 to 1 SOO cm-' reeion. and

!21' analysis of other regions of the spectnim, it is possible to obtain M e r chemicd information

to that obtained by XPS.

Table 3.7 is a list of characteristic fiequencies for fûnctional groups of concem in this

study (4 ''. Table 3.7: IR spectral band assignrnents.

Hydroxyl (C-OH) 1 O-H stretching 1 3500-2500 1

Functional group

1 O-H bending 1 1420-1330 1 1 C-O stretching 1 1260-1100 1

Type of vibration

--

O-H stretching

Wavenumber

(cm-')

Carboxylic acid (COOH) 1 C-O stretching 1 1320-1210 1 I

- --

C=O stretching 7- 1760-1710 1 Ester (C-(C=O)O) 1 C=O stretching (aliphatic) 1 1750- 1735 1

1 C=O stretching (conjugated) 1 1 730- 1 7 1 5 1

1 C-C-O stretching 1 1064-1031 1 C-C(=O)-O stretching

aldehyde (HC=O) 1 C=O stretching (aliphatic) 1 1740- 1 720 1

1210-1 163

1 C=O stretching (conjugated) 1 1685-1 580 1 ketone (C=O)

Ether (C-O-C) 1 stretc hing 1 1150-1085 1 -

Vinyl ether (C=C-O-C) 1 assymetric stretching 1 Ï % 7 2 0 0 1

C=O stretching (conjugated)

C=O stretching (aliphatic)

1 symmetric stretching 1 1075-1020 1

17 10-1 685

1745-1715

Most of the spectral changes detected in this study occurred in the 1900-1 500 cm-' region;

!22 in this region, changes to carbonyl and carboql groups were found. However. some

additional information on other groups was found in the 3500-3000 cm*' and the 1200-900

cm-' regions.

In Figure 3.9, the 3500-3000 cm-' region is shown for three samples: an untreated

BOPP simple, and samples treated for NO minutes uith hard-UVO, both with and without

supplemental water vapour. The broad band fiom 3300-3 100 cm-' is likely due to O-H

stretching, probably indicating the presence of some surface hydration even on the untreated

BOPP surface. No oxygen was obsenred in the XPS s p e c t m of untreated BOPP: this

suggests that the O-H stretch observed in the FTIR spectnim results fiom a weakly

chemisorbed aqueous species on the surface which is pumped off in the XPS vacuum. Tbere

appears to be more than one type of O-H stretch occurring, indicated by two small bands

arnidst the broad band at approximately 3200 and 3 150 cm-'. These two different bands may

be attrïbuted to different types of hydrogen-bond% both intemolecular and intramolecular,

which will result in different O-H stretching fiequencies (*). It appears fiom the spectra that

two minutes of W O treatrnent. with or without supplemental water vapour, changes the

character of these chemisorbed species. changing the nature of the hydrogen-bonding. For

samples treated for 10 minutes, hydroxyl stretching bands were detected but their presence

was very inconsistent.

In the 1200-900 cm" region, computer subiraction of spectra for a two minute hard-

UV0 treated sample and untreated BOPP in the C-O stretching region reveded a band at

1067 cm-' (Figure 3.10). This band may be due to C-O stretching in ether groups, which

would support the conclusions drawn previously about ether group formation, derived from

analysis of the XPS data. The band is particularly within the symmetric stretching region

Figure 3.9: ATR-FTIR spectra of the O-H strerching band region:

( 1 ) untreated BOPP sample. (2) two minute hard-UV/washed sample, (3) two minute hard-

üV with supplemental water vapour/washed sample.

1 1 I

O-H stretching region

(1) untreated BOPP- Il 1 \

Figure 3.1 0: ATR-FTIR spectra:

(a) Shritreated BOPP, @ two minute hard-UVIwashed sample;

(b) results of spectral subtraction of Q fiom S. showing an absorbance band at 1067 cm-'.

127 for vinyl ethers. Vinyl ethers rnay form d e r the initial insertion due to hydrogen abstraction

Eom the carbon adjacent to the ether carbon; this may be a favourable abstraction reaction

due to the electron withdrawing effects of the ether carbon.

In the C=O stretching region from 1900-1 500 cm-', two minute UV0 treatments had

little effect on the absorbante due to C=O stretching (Figure 3.1 1 ). This agrees with the XPS

data - the 0 : C ratios for these samples were very 10% and the high resolution spectra showed

only srnail peaks for carbonyl and carboxyl groups. For the hard UVO/H,O treated sarnple,

new weak bands appeared at approximately 1820 and 1600 cm-' and the band at

approximately 1705 cm-' increased in intensity. The first two bands are not in ranges

associated with functionalities which may be present in this system, and cannot be explained.

The latter band is in the fiequency region of aidehyde and ketone C=O stretchg, suggesthg

the presence of small concentrations of C=O fimctionality on this sarnple. This agrees with

the XPS data, since slightly higher 0 :C ratios were found for samples treated with

supplemental water vapour. and the high resolution spectra showed slightly more carbonyl

functionality .

Band ratio analysis was carried out on ATR-FTIR spectra by calculating a ratio

between bands in the 1 900- 1 5 3 0 cm*' region, C=O stretching bands, to those in the 1 5 3 0-

1410 cm" region, absorbantes due to methyl and rnethylene bending modes. As described

in Section 2.1.3.2, these bands were chosen because of the obvious change in the 1900- 1 500

cm-' region upon modification and the presurned stability of the bending modes in the 1530-

141 0 cm" region. Band ratio analysis was performed on spectra collected for sarnples treated

for 10 minutes with hard- or sofi-UV at the rnid ozone concentration. The calculated band-

ratios are shown in Table 3.8.

Figure 3.1 1 : ATR-FTIR spectra of the C=O stretching band region:

( 1 ) untreated BOPP sample, (2) two minute hard-Uvlwashed sampie, (3) two minute hard-

UV with supplemental water vapour/washed sample.

8 J Y O

C=O stretching region (1) untreated BOPP

i5- (3) 2 min WO/H,O 0-

1

1700 Wavenumber cm''

! 30 Table 3.8: Results fiom band-ratio analysis of ATR-FTIR spectra of hard- and soft-W 10 minute treated samples at the mid ozone concentration.

1 W source 1 IR Band-ratio 1

The band-ratio results corroborate the 0:C results obtained fiom the analysis of XPS survey

scans: similar oxidation was detected for samples treated using hard- or sofi-W. The band-

ratios decreased upon washing, an indication of a loss of LMWOM species fiom the sample

surface, which also agrees wîth the XPS fmdings. Since ATR-FTIR analysis, in general,

results in a deeper depth of analysis. this suggests that dissolution of oxidized species is

occming even at IR sampling depths, within pores in the polymer rnauix.

In Figure 3.12 (a), the ATR-FTIR spectnim for the hard-W 10 minute treated

sample at the mid ozone concentration is shown. This spectnim showed absorbances at

1785, 1750, and 17 10 cm-'. which suggests the presence of carboxylic acid, ester, and

aldehyde or ketone hinctionality, respectively. This C=O stretching region deconvolution

allows M e r characterization of the carbonyl and carboxyl groups observed by the high

resolution XPS scans. The spectnim for the washed sample (not shown) was reduced in

intensity, but had a similar shape to that for the unwashed sarnple. Therefore, washing did

not appear to change the nature of the carbonyl and carboxyl species present, suggesting that

they are of equal solubility.

In Figure 3.12 (b), ATR-FTIR spectm are shown for samples treated for 10 minutes

with soft-W at the mid O,-concentration. The unwashed sample showed C=O stretching

Figure 3.12: ATR-ETIR spectra for I O minute UVO/mid O ,-concentration treated sarnples,

C=O stretching region: (a) hard-UV treated, (b) soft-W treated.

133 absorbances at 1785, 1746. 17 12, 168 1. and 1634 cm-', m o a likely due to carboxylic acid,

ester, and aliphatic and conjugated aldehyde or ketone functionalities, respectively. Again,

Fl IR analysis allows m e r characterization of the carbonyl and carboxyl groups detected

by high resoiution XPS. The washed sample showed similar peaks but at a decreased

intensity (not shown). The hi& resolution carbon 1s X P S scans for these samples showed

slight differences in the oxidation obtained by using either hard- or sofi-UV - slightly higher

concentrations of carbon-oxygen functionalities were obtained with the soft-UV treatment,

and more of this functionality was retained after washing the so fi-UV treated sample. More

extensive oxidation was evident in the ATR-FTIR spectra for the sof t -W treatment,

especially in the form of different aidehydeketone groups ( 1 7 1 5- 1 6 10 cm-'). Peak 4 in the

high resolution carbon 1 s spectra for the sofi-W treatment. due to C=O functionality, also

contributed a greater percentage ara for the sofi-UV treated sample, M e r suggestion of

more extensive aldehyde and/or ketone formation under soft-UV treatment.

Band ratio analysis was also perfonned on spectra collected for samples treated for

two and 10 minutes with hard-W at the rnid O,-concentration with supplemental water

vapour. These calculated band-ratios are shown in Table 3.9, along with the results for

samples treated without supplemental water vapour. Washing the samples treated for two

minutes did not result in clear dif'fkrences in the calculated band ratios between before and

&er washing. AAer 10 minutes of treatrnent, the samples treated with supplernental water

vapour gave a much higher band ratio value than the samples treated without supplemental

water vapour. The band ratios decreased after washing the surfaces of the samples treated

for 10 minutes.

In Figure 3.13, the ATR-FTIR specûum for the 10 minute hard-UVfsupplemental

Table 3.9: Results h m band-ratio analysis of ATR-FTIR spectra, for samples treated with and without supplernental water vapour.

Exposure time IR Band-ratio (min)

washed

water vapour treated sample is s h o w . The peaks are at 1785. 1743. 1710, 1666 cm*',

suggesting the presence of carboxylic acid. ester, aldehyde and ketone functionalities,

respectively. M e r washing, the weak low wavenumber peak disappeared, leaving peaks at

1793. 1749. and 1709 cm-', al1 at decreased intensities compared to the unwashed sample

(not shown). F ï R analysis allows the characterization of the carbonyl and carboxyl

functionality detected by high resolution XPS as carboxylic acid. ester, aldehyde and ketone

fhctionalities. Comparing these spectra to those obtained for samples treated under hard-

UV without supplemental water vapour (Figure 3.12) indicates that the functionalities

obtained with either treatment were quite similar, although the extent of C=O

functionalization was slightly higher for those samples treated with supplemental water

vapour. This corroborates the findings obtained h m anaiysis of the high resolution carbon

1 s spectra for these samples (Figure 3.8 (b)); that similar oxidation was obtained after ten

minutes of treatment, with or without the addition of water vapow to the treatment.

Figure 3.13 : ATR-FTIR spectra for 1 0 minute hard-UV/supplementai water vapour treated

sample, C=O stretching region.

1 . M.J. Walzak, S. Flynn. R. Foerck J.M. Hill, E. Karbashewski, A. Lin, M. Strobel, Journal of Adhesion Science and Technology, v.9 n.9, pp. 1 229- 1 248, 1 995.

2. M. Strobel. C. Dunatov, J.M. Strobel, CS. Lyons, S J. Perron, M.C. Morgen, Journal of Adhesion Science and Technology, v. 3 n. 5, pp. 32 1-335, 1989.

3. G. Beamson. D. Briggs. Hieh Resolution XPS of Orpanic Polvme~. John Wiley and Sons. New York, 1992.

4. R.M. Silverstein, G.C. Bassler. T.C. Morrill, "Swftrometric identification of Organic Com~ounds." John Wiley and Sons, New York, 198 1 .

5 - D. Lin-Vien. N.B. Colthup, W.G. Fateley, J.G. Grasselli, "The Handbook of Infrared and Raman Characteristic Frequencies of Orrranic Molecules." Acadernic Press Inc., San Diego. 199 1 .

CHAPTER 4 - Final Discussion

4.1 Final Discussion

Several conclusions can be drawn from an examination of the experimental results

gathered in this snidy. From the constant photolysis of ozone occurring, there must be O

(ID) present. It is a very shortlived species, but since it is being constantly produced, its

reaction with the polyrner may occur. O (ID) wi11 insert into the polyrner chah to form ether

linkages. X P S analysis of short-term treated polyrner surfaces suggests the presence of ether

groups: this suggests that the pnmary reaction during the initial stages of the UV0 process

should then be this insertion reaction resulting in ether groups.

The correlation of contact angle rneasurements and XPS spectroscopie data indicates

that ether functional groups are primarily responsible for changes in surface energy. Short

term treatments resulted in BOPP surfaces which exhibited ether functionality and greater

wettability; further treatment resulted in increased relative concentrations of other functional

groups without accompanying further decreases in contact angle. In most previous studies

of W O surface modification, as xell as plasma and corona surface modification,

improvements in surface wetting have k e n implicitly ascribed to the fonnation of hydroxyl,

carbonyl, and carboxyl functionalities; the possible effects of ether functionality have been

largely ignored. However, there is evidence that, in bulk compounds, ether groups can lead

to increased polyrner surface energies (') and surface hydrophilicit$*. ') . Ether groups

incorporated into a.lkylsiloxane monolaprs have also been shown to be as wettable as ester

groups in similar complexes ('). In this snidy, the more polar carbonyl, carboxyl, and

hydroxyl groups were not found to Iead to surfaces which exhibit increased surface energies;

this may be due to these more polar groups k i n g involved in intrarnolecular hydrogen-

?.

bonding, and therefore less susceptible to interaction with water. 39

For ether formation to occur. O (ID) must insert into the polymer chah. However,

O ('P) is also present during treatrnent as it is a decay product of O (ID) and a dissociation

product of excited state molecular oxygen (see Section 1.2.4). When the W light is not

present as in the pulsed experiments, O ('P) becomes the dominant species (O (ID) decays

away faster and is not being reformed) and a different reaction with the polymer surface

occurs: hydrogen abstraction by O ('P) becomes the primary reaction and results in f?ee

radical sites (reactions invohing Oj and O2 will ais0 occur during these 'dark' periods, but

these are known to occur at much slower rates than reaction with atomic oxygen). These

radical sites can either react with oxygen species present or combine with other radical sites

to create crosslinking in the polper . Crosslinking is likely to decrease the reactivity of the

polyrner to atomic oxygen. This explains the lower modification levels obtained by the

pulsed-UV exposures, compared to the constant-UV exposures; during ozone-oniy cycles,

O ('P) was the dominant reactive species and thus led to more extensive crosslinking and a

less modified surface. This sarne effect may explain the "leveling-off' of the PP surface

modification even wiih constant UV-irradiation. The O ('P) present gradually increases the

extent of crosslinking and thus reduces the reactivity of the surface. I t appearç, then, that the

surface modification obtained is determined by the concentration ratio of O (ID) to O ('P).

Further evidence that both types of atomic oxygen must be present is the appearance of

functionalities such as vinyl ethers in the IR spectra. O OP) may be expected to abstract a

hydrogen atom preferentially fiom the carbon bonded to the ether oxygen.

For water-vapour ûeated samples, increased oxidation was detected compared to

samples treated in dry U V 0 conditions. However, the contact angles were higher than those

Z 40, obtained for samples treated without supplemental water vapour. Water vapour will react

with O (ID) to f o m hydroxyl radicais, which can then combine with carbon radical sites

formed from hydrogen abstraction by O (jP). This reaction with water vapour should

dUninish the concentration of O (ID) available for insertion thereby decreasing the amount

of ether groups being formed. The concentration of C-O îunctionalities fiom high resolution

XPS analysis and the higher 0:C ratio for these simples sugests that there is more hydroxyl

than ether functionaiity on these surfaces. Additionai carbonyl fiinctionality was also found

on these surfaces. The lower surface energy for these samples suggests that hydroxyl groups,

like carbonyl and carboxyl groups, do not contribute to improved wetting. Again. this is

likely the result of intrarnolecular hydrogen bonding.

A very rough approximation can be made of the concentration of ether groups on the

treated PP surface. After a two minute UV0 exposure, the atomic concentration of C-O-C

goups fiom hi& resolution XPS analysis was approximately 3% (0:C ratio of 0.0 14 from

survey scan analysis). If we assume that an individual polymer chain might be 0.5 to 1.0 nm

in thickness, then the XPS carbon 1s signal would corne from a depth representing 3-6

polymer chah thicknesses @ased on the inelastic mean free path of a 1 keV graphitic carbon

1 s photoelectron in graphite being approximately 3 nm) Y If d l of the ether groups were

attached to the outermost polymer chain, then the percent of carbon sites functionalized in

that outermost chah could be very roughly estimated at between 10 to 20%, which in any

case is still a low percent of functionalization. This selective oxidation may be the result of

the competing crosslinking reaction, which would reduce the surface reactivity of the

polymer. As a result, both hydrophilic and hydrophobie sites will exist on the surface, giving

rise to the large hysteresis observed in the advancing and receding contact angle

measurements.

The relative reactivities of methylene and methyl carbons of the polymer chah to the

W O reaction is of interest. The teaiary methylene carbon of PP might be expected to be

more reactive than the primary methyl carbon. To determine if the presence of methyl

groups had a substantial effect. some additional UV0 treatments were conducted with linear

low density polyethylene (LLDPE). Samples were exposed to W O conditions at an ozone

concentration of approximateiy 8.0 1016 molecules/cm3 at 0.5 cm fiorn the lamps for one

and two minutes. Advancing and receding contact angle measurements of the treated

surfaces were not significantly different from the resdts obtained for BOPP shown in Table

3.1 and Figure 3.1. This suggests that the differing reactivities of the primary and tertiary

carbon sites had little effect on the outcome of UV0 treatment. This may be due to the

complexities of the reaction created by the cornpetition between O (ID) and O ('P) attack.

It has dso k e n shown that the shorter wavelength, U V plays a negligible role in the

surface modification. Treatrnents which included the 184.9 nm W showed comparable

results to those treatments that did not include this higher energy W, either as a constant or

pdsed-UV irradiation. This suggests that UV-activated surfaces are not major contributors

to the modification. It also lends further support to the theory regarding the major role that

O (ID) insertion plays in the initial stages of the UV0 modification process.

Of the range of ozone concentrations examined in this study, no concentration was

found to be optimal. This is because the rate and extent of reaction, as measured by the

contact angle, is not determined by the concentration of O (ID), from ozone photolysis, but

by the ratio of O (ID) to O CP). Waizak et. aV6) w d an order of magnitude more ozone

than used in this work, and obtained more highly oxidized surfaces that were of similar

! 42 surface energy to those obtained here. This suggests that higher ozone concentrations will

lead to a more oxidized surface, but moa of the oxidized material is either LMWOM species

which is not attached to the polymer irself, or is deep enough as to not directly enhance the

wettability of the polymer surface. It may be that increasing the concentration of O (ID)

relative to O (jP) would result in additional surface modification.

The information gathered fiom XPS analysis of the various PP samples in this study

showed the usefulness of this spectroscopie technique for the examination of surfaces. Even

after Iow levels of surface o'ridation were created. XPS allowed the detection of this surface

oxidation. High resolution carbon 1s spectra also allowed the characterization and

measurement of three carbon-oxygen functionalities resultuig nom UV0 surface treatment.

Unfortunately, the resolution of the XPS instrument limited our ability to distinguish

between various carbon-oq-gen fünctionalities separated by less than 0.2 electron volts, even

after MEM data treaûnent,

ATR-FTIR analysis of the various PP samples examined in this study allowed more

extensive characterization of surface oxidation, but only after long term UV0 treatment.

Short term effects, although mongly detectable by XPS methods, were not extensive enough

to be strongly detectable by the less surface sensitive IR technique. However, the more

detailed characterization of surface functional groups of samples treated for longer exposure

times helped to cornborate the findings of the X P S analysis, and to more closely identifi

carbonyl- and carboxyl-based functional groups.

From the results of the experimental work carried out in this study, it can be

concluded that W O treatment presents a viable alternative to other polymer surface

modification techniques. Aithough the reaction times required to obtain a modified surface

C j 4 3 were not of the order of seconds - as for treatments such as corona, flame, or plasma - it has

been shown that W O treatment c m produce an oxidized surface of increased surface energy

in a fairly short time, on the order of two minutes. This rnight preclude the use of W O

treatment for a hi&-speed, continuous sample treatment, but the technique could be used for

a batch-wise type of application, especially for three-dimensional objects. The production

of LMWOM species on the surface during treatrnent may pose a problem in actual

application of UV0 treatrnent. although washing of the treated surface with water seemed

to remove water-soluble LMWOM species leaving behind a surface which still exhibited

increased surface energy. Therefore. a surface which could provide a reliable base for

adhesion remained, even afier washing the surface. It is also thought by some researchers

in the field that water-soluble LMWOM species rnay act as a reliable base for printing

applications, so its presence on the surface may be a positive result of the treatment. Optimal

conditions for W O surface treatment require the surface to be treated in close proximity to

the UV lamps and to the ozone outlet. The presence of humidity appears to be detrimental

to the surface treatrnent, leading to less hydrophilic surfaces. Thus, highly dry conditions

may improve the contact angle results. The lack of importance of 184.9 nrn UV during UV0

treatment is a useful result for two reasons: use of lamps which do not transmit the high

energy, skindamaging W would be safer for personnel operating W O systems, and lamps

encased in g l a s would present a lower cost option than lamps encased in quartz.

1. J. Brandnip, E.H. Immergut (Eds.), Polvmer Handbook, Wiley, New York, 1989.

2. K. Holmberg, K. Bergstrom, C. Brink, E. Osterberg, F. Tiberg, J.M. Harris, in: "Contact Annle. Wettability and Adhesiorf'. K.L. Mittal (Ed.). VSP, 1993.

3 D.G.Walton,P.P.Soo.A.M.Mayes,S.J.S.Allgor,J.T.Fujii.L.G.Gnffith.J.F. Ankner. H. Kaiser. J. Johansson, G.D. Smith, J.G. Barker, S.K. Satija,

Macrornolecules. v. 30. pp. 6947-6956. 1997.

4. M.K. Chaudhq. in: "Contact Ande. Wettability and Adhesion". K.L. Mittai (Ed.), VSP, 1993.

5 . S. Tanuma, C . J. Powell. D. R. Penn. Suflace Interface Analysis. v. 1 7 , pg - 9 1 1 , 1 99 1 .

6. M.J. Walzak, S. Flynn, R Foerch. J.M. Hill, E. Karbashewski, A. Lin. M. Strobel, Journal of Adhesion Science and Technology, v.9 n.9, pp. 1229- 1248. 1995.

IMAGE EVALUATION TEST TARGET (QA-3)

APPLIED ii IMAGE. lrrc - = 1653 East Main Street - -. - - Rochester. NY 14609 USA -- -- - - Phone: 716/4û2-0300 -- -- - - Fax: 716/28&5989

O 1993. W i e d Image. lm.. All Rights Reseived