A microscopic investigation of the surfaces of Kraft Pulp...

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A microscopic investigation of the surfaces of

Kraft Pulp papermaking fibres

Morag Weller, Chemistry,

McGill University, Montreal

September 2008

A thesis submitted to McGill University in partial fulfilment of the requirements

of the degree of Masters in Chemistry

© Morag Weller 2008

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Contents

Abstract Page 3

Abstract Page 4

Introduction Page 5

Chapter 1 Page 13

Comments on the interpretation of XPS (ESCA)

spectra of lignocelluslosic surfaces.

Chapter 2 Page 36

An atomic force microscopy investigation into the

physical properties of pulp fibre surfaces.

Chapter 3 Page 51

Transcrsytallisation of polypropylene at surfaces

of unbleached Kraft Pulp fibres.

Conclusion Page 66

Acknowledgements Page 67

References Page 69

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Abstract

To maintain its innovative and competitive edge the forestry sector is

focused on conducting research into more efficient ways of manufacturing

current products and generating new markets for by-products and

technologies. It is the surface of pulp fibres which are of fundamental

importance to the pulp and paper industry. A better understanding of the

chemistry and morphology of Kraft pulp fibres is the primary motivation for

this Master’s thesis study.

Through this work, we will show that simple and straight applications of

newer technologies (X-ray photoelectron spectroscopy, Atomic Force

microscopy, Optical Microscopy and Differential Scanning Calorimetry) could

be employed by the pulp and paper industry to determine the surface

chemistry of Kraft Pulp fibres (and therefore other lignocellulosic fibres). The

effect that variability in the surface composition of such fibres has on

industrial applications is commented on.

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Abstract

Pour maintenir son avantage innovateur et concurrentiel, le secteur de

sylviculture est concentré sur la recherché dans des manières plus efficaces

de produire des produits et des marchés courants pour des sous-produits et

des technologies. C’est l’extérieure des fibres de pâte qui est d’importance

fondamentale pour l’industrie de pâte et papier. Une meilleure

compréhension de la chimie et de la morphologie des fibres de pâte Kraft est

le raisonnement primaire pour cette thèse de maîtrise.

Dons çe recherche nous démontrons que des applications simple et

directes de nouvelles technologies (spectroscopie de photoélectron de rayon

X, microscopie atomique de force, microscopie optique, analyse entalbique

différentiel) peuvent être utilisés par l’industrie de pâte et papier pour

déterminer la composition extérieure des fibres de pâte Kraft (et donc d’autre

fibres lignocellulosique.) L’effect de la variabilité en composition extérieure

sur des applications industrielles sera aussi étudié.

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Introduction

The forestry sector in Canada is valued at $80 billion per annum, with

the pulp and paper industry making up approximately 40%. With the majority

of pulp and paper products destined for export markets it is the largest single

contribution to Canada’s balance of payments. The industry is also one of

the biggest and most high-tech employers in the country. Innovation and

continued development are of utmost importance if the industry is to maintain

its position as a dominant force in the global market. Industry directed

research within Canadian universities on subjects related to Pulp and Paper

is vast and varied, ranging from engineering paper mill solutions to bioactive

paper initiatives.

Cellulose is the most abundant organic substance occurring in nature.

Cellulose imparts the strength to wood and it is the cellulose in pulp fibres

that is the key to papermaking. It is the cellulose that provides the strength of

the individual fibres and it is the cellulose that forms the drying induced

bonding between the fibres in the sheet of paper. The useful properties of

paper result from the mechanical and surface properties of cellulose and the

interactions of cellulose and water. It is the surface of pulp fibres which are of

fundamental importance to the pulp and paper industry and this is the primary

motivation for this study.

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Wood is composed of cellulose, lignin, hemicellulose and extractives.

The relative ratio of the components varies between species and position

within the tree. Cellulose is a linear crystalline polymer of glucose units, as

depicted in Figure 1. It is the main structural component of plants, and the

most important component of papermaking. Lignin is a complex phenolic

cross-linked polymer network based on substituted phenylpropane units

bonded predominantly with ether linkages (Figure 2). Hemicelluloses are

polymers containing two or more sugar units often in the form of acetyl esters

or methyl ethers. They are often branched and are seldom crystalline.

Extractives are a wide variety of small molecules found in small amount in

wood.

Figure 1: Cellulose.

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Figure 2: Structural model of softwood lignin.1

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It is the wall of the fibre that is of particular interest in papermaking, as

this is where the fibre-fibre bonds that create paper occur. The location and

organization of the four wood components within the layer structure of the

wood fibre wall is well known (Figure 3). Cellulose is present as microfibrils of

extended cellulose chains, 10-30 µm in diameter and very long. These

microfibrils are oriented at different angles to the fibre long axis in each of the

fibre layers. Most of the cellulose is in the S2 layer, which makes up 70-90%

of the fibre wall thickness. The microfibrils are arranged spirally at an angle

between 0° and 30° to the fibre axis. In the S1 layer (10-20% of the wall

thickness) the fibril angle is higher, 50° to 70° and in the S3 layer

(approximately 10% of the wall thickness) the angle is even greater, 60° to

90°. However, in the thin primary wall the microfibrils are randomly oriented.

The lignin content of the fibre wall is also spread over the layers. The primary

wall is 70% lignin, although as it is very thin it contains just 10% of the total

lignin content. The S2 layer by contrast consists of 20% lignin but due to its

thickness contains 50% of the total lignin content of the fibre wall. The

hemicelluloses are intimately mixed with the other wood components

throughout the fibre wall and are in the same proportions as the cellulose, i.e.

most in the S2 layer and least in the primary layer. The extractives are found

in the parenchyma, in the resins canals, in the vessels and in the heartwood.

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Figure 3: A generic wood fibre model diagram2 showing the orientation and

location of the main components in the fibre wall.

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As a result of extensive research conducted by the global Pulp and

Paper industry for over a century, a branch of science with its own language

has developed. By many paper-making is still regarded as an art rather than

an exact science.

Due to its abundance in the Boreal Forest and its superior fibre quality

Black Spruce (Picea mariana) is the main wood source in Quebec. It is the

main source of newsprint papermaking fibres. Pulping may be defined as the

treatment of wood by chemical and/or mechanical means to produce a fibrous

material suitable for papermaking. The aim of pulping is to liberate the fibres

from the wood incurring as little damage as possible. The most widely

employed chemical pulping process is Kraft pulping. This is a sulphate

process, in which basic media are used to facilitate the removal of lignin from

the wood chips. H-factor and Kappa number are terms which are often used

to describe pulps.

The Kraft pulping process was invented by a German chemist, Dahl in

1879. The advantage of this process over existing methods was a much

faster delignification; this resulted in stronger pulps as the reduction in

cooking times corresponded to a reduction in carbohydrate degradation. It is

a full chemical pulping method that uses sodium hydroxide and sodium

sulphide in highly basic pH at temperatures of 160°C – 180°C to dissolve the

lignin from the wood.3

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As pulping apparatus and conditions can vary substantially the term H-

factor is employed to compare pulp cooks in a meaningful manner. The H-

factor is a Kraft pulping variable that combines the cooking temperature and

time into a single variable that indicates the extent of the reaction. The rate of

delignification approximately doubles for an increase in temperature of 8°C.

For example a cook of 1.5 hours at 170°C corresponds to 0.75 hours at

178°C or 3 hours at 162°C.3

The Kappa number is a measure of the lignin content of the pulp; the

higher the Kappa number, the higher the lignin content. The measurement is

based on the rapid oxidation of lignin (but not carbohydrate) by acid

permanganate at room temperature. It is defined as the number of millilitres

of 0.1M potassium permanganate consumed by one gram of pulp in 0.5N

sulphuric acid after ten minutes at 25°C under conditions such that one half of

the permanganate remain unreacted.3

Most applications of cellulosic fibres depend on the detailed surface

chemistry and morphology of the soft, often wet lignocellulosic surface.

Electron Spectroscopy for Chemical Analysis (ESCA or XPS) provides a

sensitive way to measure the surface composition of pulp fibres and paper.

Atomic Force Microscopy (AFM) facilitates the measurement of physical

properties on the surface under ambient papermaking conditions.

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X-ray photoelectron spectroscopy (XPS), was first

developed by Siegbahn in 1967.4 The technique of photoelectron

spectroscopy measures the ionisation energies of molecules

when electrons are ejected from different orbitals and uses the

information to infer the orbital energies.

The energy of the incident photon is so great that the electrons are

ejected from the inner cores of the atom. The core ionisation energies are

characteristic of the individual atom rather than the molecule; giving lines

which are characteristic of the element rather than the compound. Whilst it is

largely true that the core ionisation energies are unaffected by bond

formation, small shifts can be detected and interpreted in terms of the

environments of the atoms. The shape of each peak and the binding energy

can be slightly altered by the chemical state of the emitting atom therefore

XPS can provide chemical bonding information.

XPS, also known as Electron Spectroscopy for Chemical Analysis

(ESCA) has been widely applied to the technologically important problem of

assessing the surface composition of lignocellulosic materials. The surface

compositions of solid wood products, pulps, paper and board are critical to

their end use performance. However, the materials are chemically and

morphologically complex and it is difficult to determine the amounts of

cellulose, hemicelluloses, lignin, extractives and additives at the surface of

these materials.

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Atomic force microscopy (AFM) was first introduced by Binning, Quate

and Gerber in 1986.5 Its success has led to the development of a family of

techniques based on the same principle grouped under the name scanning

force microscopy. These techniques have been applied to a variety of

research fields, including pulp and paper research.

One of the advantages to pulp and paper research is the fact that AFM

can be operated in both air and liquid environments. Consequently the

conditions of industrial papermaking can be replicated microscopically in the

laboratory. AFM has been used to study the topography of wood derived

samples, both wet and dry.6-30 The mechanism for AFM also facilitates the

measurement of physical properties on pulp samples.18,20,31-33

Combining the techniques of AFM and XPS to investigate the surface

of newsprint quality Kraft pulp fibres is the focus of this work.

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Chapter 1

Comments on the interpretation of XPS (ESCA) spectra of lignocellulosic

surfaces

INTRODUCTION

X-ray photoelectron spectroscopy (XPS), was first

developed by Siegbahn in 1967.4 The technique of photoelectron

spectroscopy measures the ionisation energies of molecules

when electrons are ejected from different orbitals and uses the

information to infer the orbital energies.

The principle of the conservation of energy states that the

total energy in any system is constant. Therefore, energy wil l be

conserved when a photon ionises a sample; the energy of the

incident photon, must be equal to the sum of the ionisation

energy of the sample and the kinetic energy of the ejected

electron, the photoelectron. An incoming photon carries energy,

a binding energy is required to remove an electron from the

orbital and the difference appears as the kinetic energy of the

electron (Figure 4). As the ejected electron cannot escape

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except from a few nanometres from the surface, this technique is

mainly l imited to the study of surfaces.

Figure 4: Schematic of the principle involved in XPS.

1s

Ene

rgy

Valence

2s

2p

K.E. = hν - Eb

hν

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The energy of the incident photon is so great that the electrons are

ejected from the inner cores of the atom. The core ionisation energies are

characteristic of the individual atom rather than the molecule; giving lines

which are characteristic of the element rather than the compound. Whilst it is

largely true that the core ionisation energies are unaffected by bond

formation, small shifts can be detected and interpreted in terms of the

environments of the atoms. The shape of each peak and the binding energy

can be slightly altered by the chemical state of the emitting atom therefore

XPS can provide chemical bonding information.

Nomenclature Approximate shift relative to C(1s) binding energy of 285 eV

C1

-1 ↔ 1

C2

1 ↔ 2.5

C3

2 ↔ 4

C4

3.5 ↔ 6

Table 1: A list of the chemical shifts that are present within the C (1s) peak.

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For example, the C (1s) peak in the XPS spectra of carbon (Figure 5)

can be broken down into four components, each one representing the

different possible carbon environments, as listed in Table 1. The C (1s) peak

itself is centred at 285eV. Any carbons atoms that are not bonded to any

oxygen atoms (C1) will show up between 284eV and 286eV. A carbon atom

bonded to one oxygen atom (C2) will have a slightly different electronic

configuration compared to that of a carbon atom bonded to other carbon

atoms only. The C2 peak to located between +1eV and +2.5eV of the centre

point. As the number of oxygen atoms bonded to the carbon increases the

corresponding peak moves further up field.34

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Figure 5: A typical C (1s) peak in XPS. The peak has been deconvoluted

into the four different carbon environments.

Binding Energy (eV)

Inte

nsit

y

C1

C2

C3

C4

285

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XPS, also known as Electron Spectroscopy for Chemical Analysis

(ESCA) has been widely applied to the technologically important problem of

assessing the surface composition of lignocellulosic materials. The surface

compositions of solid wood products, pulps, paper and board are critical to

their end use performance. However, the materials are chemically and

morphologically complex and it is difficult to determine the amounts of

cellulose, hemicelluloses, lignin, extractives and additives at the surface of

these materials.

The XPS method on solids gives, in essence the elemental composition

of a thin surface layer.4 An introduction to the method as applied to paper

surfaces was first given by Dorris and Gray.35 They measured the XPS

spectra for filter paper and samples of bleached Kraft and sulphite papers,

and for isolated lignins. The results were interpreted in terms of the ratio of

oxygen atoms to carbon atoms, (No/Nc), in the surface region, and the

observed chemical shifts of the carbon 1s XPS peaks.

Under suitable circumstances, the experimental XPS oxygen-carbon

ratio and the components of the carbon 1s peak after deconvolution35,36 may

be used to estimate the surface composition in terms of the individual wood

components. For example, lignin and especially extractives should have

much lower (No/Nc) values than cellulose, which has 5 oxygen atoms for

every 6 carbon atoms. This approach was quantified by Dorris and Gray to

estimate how much lignin was on the surface of hand-sheets made from

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mechanical pulps.37 This required careful extraction of the sheets to remove

resin and fatty acids from the sheet surface. In principal, XPS can also

quantify the surface extractives content; an attempt using stearic acid as a

model has been reported,34 but in general quantification of extractive

coverage is difficult.

The XPS method has been applied to a range of pulp and paper

samples25,26,38-40, but there have been continuing questions regarding both

the reproducibility of XPS measurements on lignocellulosics, and the validity

of interpretations. Recently, the results of a set of XPS measurements in four

laboratories in Scandinavia and Canada on identical paper samples have

been reported.41 The overall findings were that the experimental results were

in reasonable accord, providing care is taken to avoid or correct for carbon-

rich contaminants on cellulose-rich surfaces. However, methods of

interpretation in terms of surface lignin and extractives used by different

laboratories gave somewhat scattered results.28

The initial interpretation of XPS data in terms of surface composition

involved several problems. In contrast to most previously studied surfaces,

fibrous lignocellulosic surfaces were rough and chemically heterogeneous,

both across the paper surface and in the depth direction. The only XPS

observables were the ratio of oxygen atoms to carbon atoms, and the

deconvolution of the carbon peak into components with different chemical

shifts resulting from the numbers of oxygen atoms that were attached to the

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carbon atoms. Interpretation of this data in terms of the molecular

composition of the surface layer sampled by XPS required a number of

assumptions.

Thus, to interpret the XPS atomic composition data in terms of the

proportion of carbohydrates (cellulose and hemicellulose) and lignin content

of the surface layer, the following assumptions were employed or implied.35

The samples contained only carbohydrate and lignin. Wood extractives were

presumed to have been removed by suitable solvent treatments.

(i) The composition of the analysed volume of material close to the

surface was uniform.

(ii) The polysaccharide component of the surface layer (cellulose +

hemicellulose) was represented by the empirical composition, C6O5 ,

molar mass, 162.1.

(iii) The empirical formula for the lignin component was that for

Freudenberg lignin, namely C9.92O3.32 , with a molar mass of 183.5.

Dorris and Gray chose this model for lignin as it seemed an

appropriate approximation for the lignin in mechanical pulp.

To relate the observed oxygen carbon ratio, No/Nc, to the surface

composition, it was assumed that there were S anhydroglucose or sugar units

and L lignin phenylpropane segments per unit volume in the (uniform) volume

sampled by XPS at the surface of the fibres. Hence, from the empirical

formulae for S and L, the number of oxygen and carbon atoms in this volume

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were No = 5S + 3.32L and Nc = 6S + 9.92L, respectively. The segment mole

fraction of lignin in the surface, SL, was thus L/(L + S). From the empirical

formulae for S and L, the value for SL was derived in terms of the measured

No/Nc.

(1)

The weight fraction of lignin, WL, may be calculated from the segment mole

fraction and the molar masses of the segments:

(2)

A typical value for No/Nc for an extracted thermomechanical pulp sheet

was 0.56, giving a lignin weight fraction in the surface of 0.45, a value that

was somewhat higher than the bulk value.35

Since these early experiments, XPS has been applied to a variety of

lignocellulosic materials. For Kraft pulp fibres, a different way of interpreting

the No/Nc values,42 first suggested by Ström and Carlsson43 has been widely

accepted. For an extracted pulp, the surface coverage of lignin was taken as:

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(3)

where (NO/NC)Pulp sample is the measured oxygen/carbon atom ratio of the pulp

under study, (NO/NC)Lignin-free pulp is the measured oxygen/carbon atom ratio of

an appropriate lignin-free (fully-bleached) pulp measured under the same

conditions as the sample, and (NO/NC)Lignin is the corresponding value for a

sample of lignin. The resultant value for , the surface coverage of lignin,

is a dimensionless quantity that varies linearly with (NO/NC)Pulp sample and is

independent of the oxygen-carbon values for lignin and carbohydrate.

Recently, Li and Reeve44 took issue with the use of Equation 3,

pointing out, correctly, that the assumption of a linear relationship between

lignin content and (NO/NC)Pulp sample cannot be correct for simple algebraic

reasons. They provided a generalized form of the approach of Dorris and

Gray, where appropriate empirical formulae for the lignin and polysaccharide

components of the fibre may be used to estimate the surface lignin. For

carbohydrate formula CmOn and lignin CxOy, the segment mole fraction and

weight fractions of surface lignin given by Li and Reeve are44

(4)

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(5)

where and

This is not just a question of (very real) experimental problems such as

sample contamination or decomposition. The major discrepancy between

surface lignin contents calculated from Eq.2 and from Eq.3 occurs at low

lignin contents44 precisely the region where the effects of sample

contamination or degradation are most evident.

In this chapter, we consider these methods used to convert XPS

measurements of relative atomic composition to amounts of cellulose, lignin

and other components in the surface, and try to clarify the reasons for the

apparent discrepancies.

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EXPERIMENTAL

Black spruce chips, selected for uniformity (Paprican, Pointe-Claire)

were pulped under typical Kraft conditions (Active alkali – 18%, Sulphidity –

30%, Temp - 172oC, time to temperature - 90mins, Liquor/wood – 4.5:1, H-

factors – 1065, 1260, 1510, 1760 and 2050). Five pulp samples of

decreasing kappa numbers3,44 were obtained, ranging from a moderately high

value to a low value. The pH of 13 at the end of the cook was high enough to

avoid re-precipitation of dissolved lignin onto the fibre surfaces. For ESCA

analysis, two small hand-sheets were made from each sample. The hand-

sheets were extracted with acetone, air dried and pairs of the sheets were

placed between Whatman filter papers. The inside contacting faces of the

pulp sheets were used for XPS analysis. Two Whatman filter papers were

treated in the same manner and their surface composition was analyzed

along with the pulp samples.

The ESCA measurements were performed with a Kratos Ultra electron

spectrometer (Kratos Analytical) using monochromatic Al Kα X-ray source (15

kV, 15 mA). The low-resolution survey scans were taken with a 1 eV step

and 160 eV analyzer pass energy; high-resolution spectra were taken with a

0.1 eV step and 40 eV analyzer pass energy. The collected data was

analyzed using Vision software version 2.1.3 and CASA XPS version 2.3.

The analysis area was less than 1mm2 and measurements were taken at two

different locations on the each of the touching faces of the hand-sheets.

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RESULTS AND DISCUSSION

The bulk lignin contents of the five unbleached softwood Kraft samples,

expressed as Kappa numbers (see introduction), are listed in Table 2, along

with the results of the XPS elemental analysis of the surface of the samples.

The only XPS observables in this work are the ratio of oxygen atoms to

carbon atoms, and the deconvolution of the carbon peak into components

with different chemical shifts resulting from the numbers of oxygen atoms that

were attached to the carbon atoms.

The No/Nc value of 0.83 for cellulose is seldom observed experimentally,

presumably due to the presence on the surface of carbon rich contaminant,

degradation, etc. This is illustrated in Figure 6, which shows typical C(1s)

XPS spectra for a pure cellulose sample, including the carbon contamination

and for a lignocellulosic sample. Ideally, the contamination should be

minimized by taking the precautions outlined elsewhere.41 However the

conditions for absolute XPS measurements of atom ratios are difficult to

achieve, and many publications use explicit or implicit calibration against a

pure cellulose surface such as filter paper or low-yield bleached pulp. Thus

Equation 3 assumes a linear relationship between lignin content and (NO/NC),

with the zero lignin content assigned to the measured value of (NO/NC) for a

pure cellulose sample.

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Figure 6: C(1s) spectra for a lignocellulosic hand-sheet (left) and a pure

cellulose hand-sheet.

We propose the following way to correct for the excess carbon signal

observed in a series of XPS samples containing only lignin and carbohydrate

components, where a pure cellulose sample has been run under identical

conditions as the unknown lignocellulosics. The basic assumption is that the

excess carbon signal which results in the value less than 5/6 for (NO/NC) for

the pure cellulose sample is in the same proportion to the total signal (NO +

NC) for the unknown samples, measured under the same spectrometer

conditions.

(6)

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Writing the excess carbon signal (~ the C1 contribution) due to the

contaminating carbon as NC*, we first wish to estimate its value relative to the

total XPS signal, NC*/(NC + NO) from the measured oxygen to carbon

ratio,(NO/NC) for pure cellulose.

The following abbreviations are convenient. We write;

(NO/NC)Cellulose, theoretical = CT

(NO/NC)Cellulose, measured = CM

(NO/NC)Pulp, measured = PM

(NO/NC)Pulp, corrected = PC

This preserves the usual convention of reporting the ratios of XPS signals for

individual elements.

The measured oxygen to carbon atom ratio for cellulose contains an

added contribution from the contaminant carbon:

(7)

After some algebra,

(8)

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We then assume that the value for NC*/(NC + NO), obtained as above from the

experimental value for cellulose filter paper and Equation 8 will be the

approximate value of NC* /(NC + NO) for pulp samples measured at the same

time as the cellulose standard.

In order to correct for the unwanted contribution from the excess

carbon, NC*, the corrected value for the oxygen to carbon ratio for a pulp

sample is given by,

(9)

Again, after some algebra,

(10)

or, rearranging,

(11)

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Combining (9) and (11) and forgetting about abbreviations:

(12)

from which the corrected oxygen to carbon ratio for the pulp sample,

(NO/NC)Pulp, corrected can easily be evaluated. The (NO/NC)corrected values for the

five Kraft pulps along with the corresponding surface lignin content (Wt%

surface lignin) are shown in Table 2.

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Kappa

number

Wt% bulk lignin

(0.147 x kappa)

NO/NC

measured

(XPS)

NO/NC

corrected

(from Eqn 13)

Wt%

surface lignin

45 6.5 0.631 0.715 17.5

37 5.4 0.651 0.738 13.9

32 4.7 0.670 0.762 10.3

25 3.6 0.681 0.775 7.8

21 3.1 0.699 0.797 5.2

Table 2: XPS measurements of surface lignin content for softwood Kraft

pulps.

The surfaces of these pulps appear to be richer in lignin than the bulk

this is in agreement with many previous measurements. There is an as

expected decrease in the weight fraction of lignin content with decreasing

Kappa number, for both measured and corrected values. Li and Reeve noted

that the correct empirical formula for lignin should be chosen when

interpreting XPS spectra.44 Table 3 shows the corrected weight fraction

percentage of lignin calculated using the empirical formula for Freudenberg

lignin model, and also for a residual Kraft lignin with a molar mass of 189.46

and an empirical formula of C9H8.64O2.99S0.07(OCH3)0.73.45 In this case, the

final results are virtually identical for both formulae.

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Kappa

Number

Wt% surface

lignin

Residual Kraft

Softwood lignin

Wt% surface

lignin

Freudenberg

lignin

45 17.4 17.5

37 13.9 13.9

35 10.3 10.4

25 7.8 7.8

21 5.1 5.2

Table 3 : The calculated weight fraction percentage of surface lignin in five

different Kappa number Black spruce pulp hand-sheets.

The solvent extraction conditions also play a significant role in the

determination of excess carbon signal, and should be duly noted when

reporting XPS results. Table 4 shows the effect of different extraction

solvents and conditions on the same pulp fibre.

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Wt% surface lignin (Freudenberg) Extraction conditions

Acetone DCM

3% 70°C 11.6 13.8

3% 35°C 21.3 32.6

0.3% 50°C 15.7 15.0

Table 4: The weight fraction percentage of a Black Spruce Kraft pulp with

Kappa number 45 subjected to different extraction conditions.

Interpretation of the measured XPS data according to Equations 1 and

Equation 2 gave higher values for the weight fraction of surface lignin. These

values are based on the assumption that a pure cellulose surface gives a

No/Nc value of 0.83, as follows from the atom ratio of 5/6, and that the

empirical formula of lignin is given by the value accepted for Freudenberg

lignin in wood (C9.92O3.32). The higher values obtained highlight the

importance of correctly accounting for contamination and sample

degradation.

The experimental results for an inter-laboratory comparison of XPS

data for a range of pulps 41 were also re-examined in light of this suggested

method. The "corrected" (No/Nc)cor values were calculated and used, to give

a “corrected” weight fraction percentage of surface lignin and are listed in

Table 5. This data, calculated for each lab's results, gave quite good overall

agreement, with fairly clear assumptions in arriving at the results.

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Laboratory &

sample

No/Nc

measured

No/Nc

corrected

Wt % surface

lignin

corrected

Åbo Akademi University, Finland

TMP 0.66 0.66 26.7

UBK 0.78 0.78 7.6

ECF 0.81 0.81 3.3

Helsinki University of Technology, Finland

TMP 0.61 0.71 19.2

UBK 0.70 0.82 2.4

ECF 0.71 0.83 0.7

Chalmers University of Technology, Sweden

TMP 0.67 0.69 22.4

UBK 0.76 0.79 7.8

ECF 0.81 0.83 0.4

Universite de Québec à Trois-Rivieres, Canada

TMP 0.59 0.67 25.1

UBK 0.68 0.78 7.9

ECF 0.70 0.81 4.4

Interlab

TMP 0.63 0.68 23.8

UBK 0.73 0.79 6.4

ECF 0.76 0.83 1.6 Table 5: Attempt to summarize data for surface lignin, together with

recalculated data for weight % lignin, assuming uniform surface, and also

scaling O/C data to correct for lignin-rich contamination assuming that

measured O/C data for filter paper may be linearly scaled to expected values

for filter paper (O/C =0.83). TMP = Spruce Thermomechanical Pulp, UBK =

Unbleached Birch Kraft Pulp, ECF = Elemental Chlorine Free Bleached Birch

Kraft Pulp.

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CONCLUSION

We have suggested a simple method which may be used, with a high

degree of confidence (through the use of a pure cellulose reference and a few

logical assumptions), to convert XPS measurements of relative atomic

composition to amounts of cellulose, lignin and other components in the surface.

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Chapter 2

An atomic force microscopy investigation into the physical properties of

pulp fibre surfaces.

INTRODUCTION

Atomic force microscopy (AFM) was first introduced by Binning, Quate and

Gerber in 1986.5 Its success has led to the development of a family of

techniques based on the same principle grouped under the name scanning force

microscopies. These techniques have been applied to a variety of research

fields, including pulp and paper research.

One of the advantages to pulp and paper research is the fact that AFM

can be operated in both air and liquid environments. Consequently the

conditions of industrial papermaking can be replicated microscopically in the

laboratory. AFM has been used to study the topography of wood derived

samples, both wet and dry.6-27,29,30,46 The mechanism for AFM also facilitates the

measurement of physical properties on pulp samples.18,20,31-33

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The topographical imaging ability of AFM has been used to investigate

many surface properties of pulp fibres. Physical features such as surface

roughness,12,29 the existence and orientation of fibrils in the primary and

secondary cell wall,14 how extractives are located and adsorbed on the surface of

fibres and model surfaces,22 the effect of surface treatments,9,10,38 and the effect

of beating16 were acquired.8,11,13,46

There is another dimension to the challenge of obtaining accurate physical

measurements at the individual pulp fibre level. Wood is a very heterogeneous

material and this is evident even at the single pulp fibre level. There is a high

amount of variability in the properties of individual pulp fibres and the non-

uniformity of the pulping process.47 The processing conditions the fibres are

subjected to prior to any physical property measurements also plays an important

role. Bawden and Kibblewhite noted that the first drying the pulp fibre undergoes

causes the greatest change in fibre dimensions,48 and that this is not completely

reversed upon rewetting. Therefore, a large variability in the physical properties

obtained by the same method can be expected if the fibres are treated by

different pulping processing. The properties of never-dried, dried, and rewetted

fibres are also very different. There is even a vast range of modulus/flexibility

values in fibres derived from the same wood source depending on whether it

underwent a chemical or mechanical pulping process.49

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AFM has been perceived by many as a revolution in micro and nano scale

science. As with all techniques it has disadvantages and limitations. It is

theoretically possible to obtain atomic resolution on crystalline surfaces, and the

instrument can perform in a wide range of sample conditions. The practicalities

of achieving good quality and reproducible results are not always so easy. AFM

can produce force-distance curves between the tip and sample surfaces

approaching each other from distances of microns to nanometres, which can be

used to measure van der Waals,, double layer and, electrostatic forces.

From force-distance curves, indentation modulus values have been

calculated for many different materials. Unfortunately, many of the quoted values

have uncertainties arising from a lack of calibration of key components, such as

the use of manufacturers' nominal value for the cantilever spring constant and tip

radius, or the assumption of an incorrect model for calculation the modulus.50

Clifford and Seah50 found that these uncertainties could be as much as 40% for

homopolymers. With heterogeneous materials the uncertainties can be expected

to be even greater. The direct measurement of elastic modulus requires the

calibration of all the factors involved including the cantilever spring constant, the

tip radius, the tip shape and the piezoelectric scanner movement in the z

direction. The result is an accurate, traceable value for the indentation modulus

of the material.50

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A few groups have applied AFM force-distance measurements to the

problem of finding the modulus of a pulp fibre in the hope of understanding more

about fibre-fibre bonding.18,51-53 Other methods have also been investigated.

Zadorecki et al incorporated bleached unbeaten pulp fibres into a polyester

composite and calculated the modulus of the fibres from the modulus of the

composite and matrix.54 Page et al used the stress-strain curve taken directly

from individual dry fibres to calculate the axial and transverse modulus.55 Hartler

and Nyren also employed a technique using an individual fibre to obtain a load-

deformation curve from which the transverse modulus was determined.56 Wild et

al built a fibre compression instrument consisting of micro hammer and anvil set-

up and defined the modulus in such terms as to eliminate as much variation as

possible between the fibres.57 Tchepel et al used a single-fibre fatigue cell to

apply force and measure elongation and then deduce elasticity.58 Orso et al

employed standard beam theory to directly calculate the modulus of wood cell

wall in their focussed ion beam method.59

Previous work within Dr. Grays group by Furuta31 & Pang32 used AFM to

probe the surface properties of pulp fibres. They found that some of the complex

changes in the fibre properties could be directly observed in aqueous media by

AFM force-distance curves. The shape of the force-distance curve infers the

changes in fibre properties caused by the beating process, the higher the level of

beating the more readily compressible the surface of the wet fibre is. The levels

of fibrillation at different areas of the same fibre and the effect of salt solution on

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fibrillation is also very apparent form the corresponding force-distance curve.

Nilsson et al measured the surface stiffness of wet Kraft fibres from the force-

distance curves and used it to estimate the apparent local modulus of elasticity of

the fibre.53 Chhabra et al18 also determined the modulus from the force-distance

curves, the force-distance curve was converted into a load-depth plot using

Hook’s Law and then Sneddon’s equation was used to find the modulus. In this

case the tip was model as a conical indenter and the fibres were modelled as

purely elastic. Nanoindentation was used by Gindl et al on natural and

regenerated cellulose. They concluded that using nanoindentation absolute

values for modulus could only be applied to isotropic materials (regenerated

cellulose) and the values obtained for anisotropic materials (wood pulp fibres)

were relative values and valid only for comparison.52

In this chapter, we report on the use of AFM as a method of investigating

the surface properties of Kraft pulp paper-making fibres.

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EXPERIMENTAL

Black spruce chips, selected for uniformity (Paprican, Pointe-Claire) were

pulped under typical Kraft conditions (Active alkali – 18%, Sulphidity – 30%,

Temp - 172oC, time to temperature - 90mins, Liquor/wood – 4.5:1, H-factors –

1065, 1260, 1510, 1760 and 2050). Five pulp samples of decreasing kappa

numbers3,44 were obtained, ranging from a moderately high value to a low value.

The pH of 13 at the end of the cook was high enough to avoid reprecipitation of

dissolved lignin onto the fibre surfaces.

AFM measurements were made with a MFP-3D instrument from Asylum

Research (Santa Barbara, CA). Never-dried Kraft pulp fibres were secured to a

glass microscope slide with a temperature sensitive adhesive then immersed

completely in deionised water. The actual spring constant of the tip (Olympus

Biolever) was calculated prior to each experiment. Measurements were never

taken on the same spot in order to prevent damage to the fibre, to prevent

inaccurate force measurements being taken and to simulate the force felt by

another fibre in the bonding process. AFM topographies were obtained on dried

fibres in both contact and tapping modes. Individual fibres were placed on a

clean glass microscope slide and allowed to dry under ambient conditions. The

topographies were scanned perpendicular to the fibre axis.

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The bulk lignin contents, expressed as Kappa number (see Introduction)

and the corresponding surface lignin content, from ESCA analysis are listed in

Table 6.

Kappa number

Wt% bulk lignin (0.147 x kappa)

Wt% surface lignin

45 6.5 17.5

37 5.4 13.9

32 4.7 10.3

25 3.6 7.8

21 3.1 5.2

Table 6: The Kappa numbers with corresponding bulk and surface lignin

contents of the five Black Spruce Kraft pulp fibres under study.

An AFM topography (deflection image in contact mode) of a typical dried

Black Spruce Kraft Pulp fibre is shown in Figure 1. The resolution of the AFM

imaging mode allows the ordering of the cellulose microfibrils around the pits and

within the S2 layer to be observed. The variation in surface structure of a Kraft

pulp fibre can be clearly seen. Although a large amount of information is

obtainable with AFM on dry Kraft fibres it does not accurately mimic the

conditions of the papermaking process.

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Figure 7: An AFM contact mode deflection topography of a typical dried Black

Spruce Kraft pulp fibre. The scanning direction is perpendicular to the fibre axis.

The bulk of the papermaking process is carried out in water. AFM has the

capability to acquire a variety of measurements in a liquid environment.

Therefore, the physical properties of wet Kraft pulp papermaking fibres can be

obtained. Several force-distance curves on never-dried pulp fibres were

obtained under water. Typical curves for the two extremes in pulping are shown

in Figure 8 and Figure 9.

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Figure 8: Typical deflection-distance curves for the two extremes in pulping

conditions. The red curve is the Kraft pulp with kappa number 45 and the blue

curve is the Kraft pulp with kappa number 21.

A lot of information can be inferred from the data collected by AFM.

Figure 8 shows the deflection of the cantilever as the tip is moved closer to the

sample and through into the contact region. In this case the “contact point” is

taken as the Burnham contact point,60 defined as the point when a repulsive

force is first detected by the cantilever. Overlaying the curves, defined in this

manner, the slope of the contact region to be clearly observed; the steeper the

slope of the contact region the harder that surface. From Figure 8 it appears that

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Kraft pulp 45 (red curve) is a harder surface than Kraft pulp 21 (blue curve). This

shows that the high lignin content fibre is more rigid than the fibre from which

most of the lignin has been removed by pulping.

Figure 9: Typical force-distance curves for the two extremes in pulping

conditions. The red curve is the Kraft pulp with kappa number 45 and the blue

curve is the Kraft pulp with kappa number 21.

Figure 9, in contrast to Figure 8, shows the force-distance curves, where

the force is determined from the deflection data and the actual tip spring

constant. The “contact point” in this case is calculated from the linear portions of

the curves. By overlaying the two pulping conditions curves it can be seen that

the pulp with less surface lignin (Kraft Pulp 21, blue) experiences a repulsive

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force between the tip at a distance around 10 times greater from the “true”

surface than the higher surface lignin content pulp (Kraft 45, red).

The earlier onset of the repulsive force observed as the AFM tip

approaches the Kraft 21 fibre is ascribed to surface fibrillation. The microfibrils

and the surface of the fibre are negatively charged due to the presence of some

carboxyl groups introduced during pulping, so mutual electrostatic repulsion

causes the microfibril tails extend away from the surface into the aqueous media,

where they interact the tip. The distance at which the AFM tip starts to sense the

repulsive force can be considered as an indication to the effective length of

dangling microfibrils. The higher the fibrillation, the greater the repulsive force.

From Goring’s Interrupted Lamella model61 it is evident that as lignin is

removed from the fibre, the fibre becomes more compressible. The results from

the AFM measurements are in agreement with this.

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Figure 10: Values for moduli of Kraft pulps with different lignin contents,

calculated by the method suggested by Nilsson.53

The data collected from the force-distance was used to calculate the

apparent modulus for all five Kraft pulps. The results are shown on Figure 10.

The average results is in agreement with the value calculated by Nilsson et al.53

The large range in apparent moduli for all five Kappa numbered pulps accurately

reflects the extent of variation found on the surface of pulp fibres. With such

diversity on the surface the sample population size must also be taken into

account.

0.000

0.500

1.000

1.500

2.000

2.500

20.00

25.00

30.00

35.00

40.00

45.00 Kappa

Number

Mod

ulus

(M

Pa)

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Pulp fibre Deformation Modulus Reference:

Crystalline Cellulose I Axial tensile 128 GPa Sakurada et al62

Kraft – dry In fibril direction 77 GPa Page et al55

Kraft – dry Transverse to fibril direction 8.8 GPa Page et al55

Kraft – dry Transverse compressibility 0.9 GPa Hartler and

Nyren56

Kraft – wet unbeaten

Transverse compressibility 0.56 GPa Hartler and

Nyren56

Kraft – wet beaten

Transverse compressibility 0.44 GPa Hartler and

Nyren56

Kraft – wet AFM Transverse microcompressibility 0.013 GPa Nilsson et al53

TCF bleached – wet

AFM Transverse microcompressibility 0.007 GPa Nilsson et al53

Kraft in composite Tensile of composite 16.1 GPa Zadorecki et al54

Kraft Tangent modulus 0.007 GPa Wild et al57

Spruce wood cell Standard Beam theory 28 GPa Orso et al59

Table 7: Some examples of moduli obtained for wood pulp fibres.

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The results of work conducted in this field are summarised in Table 7.

There are discrepancies in the moduli obtained by different means and the

processing conditions the fibre under question is subjected to also heavily

influences the modulus.

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CONCLUSION

It has been shown that although AFM is a great technique for providing

physical property information on a wide variety of surfaces and under different

environmental conditions, it is not suitable for measuring the modulus of wood

pulp fibres. The heterogeneous nature of wood pulp fibres would require a very

large sample population of measurements to reach valid conclusions as to the

effects of fibre source and pulping conditions. For the pulp and paper industry,

the valuable surface property information sought from wood pulp fibres is better

served by bulk methods.

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Chapter 3

Transcrystallisation of Polypropylene at the surfaces of Unbleached Kraft

Pulp Fibres

INTRODUCTION

For many years cellulose has been incorporated into synthetic polymer

composites in a variety of markets ranging from packaging to automotive

applications. Cellulose from wood sources is of increasing interest as it has a

very low cost per unit volume, is ‘green’ and can often match or improves upon

the mechanical and physical properties of existing reinforcing agents.63

Transcrystallisation is the preferential nucleation of polymer melts at

crystalline surfaces. The term often refers to enhanced nucleation of spherulitic

growth along fibres, typically observed for polymers such as isotactic

polypropylene. If the nucleation density is high the resultant spherulites crowd

together, producing a ‘transcrystalline’ layer in contact with the surface.63,64

Some time ago, a transcrystalline layer was observed at the surface of natural

Cellulose I fibres, but not at regenerated or mercerized (Cellulose II) surfaces.64

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Care is necessary in interpreting surface effects, as a transcrystalline morphology

can also be generated by shear at surfaces in the crystallising melt.65

Subsequent work on transcrystallisation of isotactic polypropylene (i-PP)

at cellulosic surfaces has focused on the nature of the cellulose surface and the

effect on composite performance. The presence of sizing agents on bleached

Kraft, ramie and microcrystalline cellulose surfaces inhibited

transcrystallisation.66 The transcrystallinity at Cellulose I surfaces was also

inhibited by esterification yet the effect was enhanced by beating.67 Fibres

treated with celllulase increased the nucleating ability of the i-PP/cellulose fibre

composite (matrix.)68 The presences of a transcrystalline layer improved

interfacial shear transfer between i-PP and cotton fibres.69 A thorough study of i-

PP transcrystallisation at flax fibre surfaces also showed enhanced interfacial

properties.70 In general, the higher the Cellulose I content at the fibre-melt

interface, the greater the transcrystalline layer observed, although there is one

report of transcrystallisation at a Cellulose II surface of NaOH-treated milled

woodpulp.68

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The reason why Cellulose I is a preferential nucleation site for isotactic

polypropylene is not fully understood. Felix and Gatenholm suggested that the

preferential nucleation occurs because in the helix of isotactic polypropylene the

distance between two methyl groups with the same spatial arrangement is

approximately the same length as the linear distance between glucosidic

oxygens in cellulose.69 This gives a good match of interaction sites and hence

nucleation occurs more readily.

In this chapter, we examine the effect of pulp lignin content on the amount

of transcrystalline morphology generated at Kraft fibre surfaces.

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EXPERIMENTAL

Black spruce chips, selected for uniformity (Paprican, Pointe-Claire) were

pulped under typical Kraft conditions (Active alkali – 18%, Sulphidity – 30%,

Temp - 172oC, time to temperature - 90mins, Liquor/wood – 4.5:1, H-factors –

1065, 1260, 1510, 1760 and 2050). Five pulp samples of decreasing kappa

numbers3 were obtained, ranging from a moderately high value to a low value.

Isotactic polypropylene (i-PP) pellets (Nominal Mn, 67,000,Mw 250,000)

were purchased from Sigma-Aldrich. Thin (~200 µm) polypropylene discs were

prepared by melting single pellets of i-PP between microscope slides on a Kofler

hot bench (Reichert) at ~200oC. A fibre of the Kappa number under study was

placed on the melt, a second layer of i-PP was laid over the fibre and a

microscope cover slip was then placed on top. The samples were melted at

~200oC for a few minutes, then transferred rapidly to a Mettler FP82 hot stage

set at 136oC, and viewed with a Nikon Microphot-FXA polarized light microscope.

Images were captured with a Nikon Coolpix 990 digital camera.

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Differential Scanning Calorimetry measurements of i-PP/pulp fibre

composites were performed under nitrogen on a TA Instruments DSC Q1000.

The samples were melted at a rate of 10°C min-1 to 200°C and maintained at this

temperature for 5 minutes in order to eliminate any thermal history. The sample

was cooled to 80°C at a rate of 5°C min-1 and then the heating procedure

repeated. In each experiment there was a pure i-PP sample in the reference

pan, which was the same weight as the i-PP/pulp fibre composite under study.

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Crystalline polypropylene is birefringent and therefore easy to observe

with a polarising microscope. The transcrystalline layer growth along several

Kraft pulp fibres in isotactic polypropylene was observed. After a few minutes

spherulitic growth could be detected along the fibre where few spherulites were

apparent in the bulk. As the spherulites on the fibre grow they impinge upon their

neighbours and form a transcrystalline layer around the fibre. The fibre becomes

completely encased in the transcrystalline layer long before the bulk is fully

crystalline. This effect is clearly shown in Figure 11; the rapid development of a

crystalline layer around the fibre contrasts with the lack of normal spherulites in

the bulk of the sample, indicating enhanced nucleation at the fibre surface.

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Figure 11: Transcrystallisation layer growth about a Kraft pulp fibre (Kappa

number 45) at a) 0 minutes, b) 2 minutes, c) 4 minutes, d) 6 minutes, e) 8

minutes, f) 10 minutes, g) 12 minutes, h) 14 minutes, i) 16 minutes.

The bulk lignin (calculated from Kappa numbers) and surface lignin (from

XPS measurements in chapter 2 of this thesis) of the five unbleached softwood

Kraft samples are listed in Table 8. The main difference between the five

different Kappa number pulps is the number of nucleation sites after a short

period at 136°C. Figure 12 shows growth of transcrystalline layer at the surfaces

of a low Kappa number Kraft fibre and a high Kappa number Kraft fibre.

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Kappa number Wt% bulk lignin

(0.147 x kappa) Wt% surface lignin

45 6.5 17.5

37 5.4 13.9

32 4.7 10.3

25 3.6 7.8

21 3.1 5.2

Table 8: Bulk and surface lignin (as calculated in chapter 2 of this thesis)

contents of the Kraft Pulp samples.

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Figure 12: Transcrystallisation along Kraft pulp fibres with Kappa number 45

(left) and Kappa number 25 (right). The scale bar corresponds to 200µm.

Even at the early stages of the crystallisation, nucleation along the fibre

with less lignin and hemicellulose (Kappa number 25, Figure 12, right) is dense.

The amount of nucleation along the higher Kappa number fibre (Figure 12, left) at

6 minutes closely resembles the lower Kappa number fibre at 4 minutes.

The fibres with higher Kappa numbers take longer to obtain the same

amount of nucleation sites. Note that the presence of the fibre does not alter the

growth rate of the spherulites but rather changes the onset of nucleation. All

fibres are fully covered in a transcrystalline layer before normal bulk spherulitic

growth is significant. The diameter of the encapsulating transcrystalline layer at a

given time interval may be taken as a rough indication of the nucleating tendency

of the fibre. This is shown in Figure 13.

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Figure 13: Plot of the mean transcrystalline layer thickness along a Kraft Pulp

fibre. (Kraft pulp kappa number 21, blue diamonds and Kraft pulp kappa number

45, pink squares.)

It has been shown that natural cellulose fibres appear to lower the degree

of super-cooling necessary to induce crystallisation. Thus the heat evolved on

crystallisation near the fibres should be detectable at slightly higher temperatures

than the heat of crystallisation for a melt containing no fibres. Likewise, a fibre

with a higher Cellulose I surface content should have a heat of crystallisation that

is detectable at slightly higher temperatures than a fibre with more lignin and

hemicellulose on the surface.

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Figure 14: DSC curve comparison for the heat of crystallisation of i-PP in contact

with Kraft fibres, prepared by the two extremes of pulping (Kraft pulp kappa

number 21, red curve and Kraft pulp kappa number 45, green curve.)

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Figure 14 shows the Dynamic Scanning Calorimetry curves for the two

extremes in pulping conditions. Kraft pulp 21 (Figure 14, red curve) has a

surface lignin content of 5.2% and the Kraft pulp 45 (Figure 14, green curve) has

a surface lignin content of 17.5%. From the above curves it is hard to clearly see

what the difference in heats of crystallisation actually is. Air is commonly used as

the reference material in DSC experiments, in our experiments i-PP was used as

the reference. This allows us to evaluate the effect of the transcrystallisation

layer around the Kraft pulp fibre.

Figure 15: Differential of the DSC curve comparison for the heat of crystallisation

of i-PP in contact with Kraft fibres, prepared by the two extremes of pulping( Kraft

pulp kappa number 21, red curve and Kraft pulp kappa number 45, green curve.)

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If we take the differential of the curves in Figure 14 with respect to

temperature we can observe the differences between the two curves more easily.

This is shown in Figure 15. The heat of crystallisation associated with the

transcrystalline layer around the Kraft pulp 21 fibre (Figure 15, red curve, surface

lignin content 5.2%) is first detected at 125°C. Three degrees lower, the

transcrystalline layer around the Kraft pulp 45 fibre (Figure 15, green curve,

surface lignin content 17.5%) appears. As the Kraft pulp 21 fibre has a lower

surface lignin content and hence higher surface Cellulose I content it would be

expected to induce crystallisation at a slightly higher temperature than the Kraft

pulp fibre with a lower amount of Cellulose I on the surface.

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CONCLUSION

The rate of transcrystalline layer growth along a fibre is dependent upon

the surface chemistry of that fibre. The greater the amount of Cellulose I on the

fibre surfaces the faster the transcrystalline layer forms. The transcrystalline

layer is always completed before crystallisation in the bulk melt. As the size of

the transcrystalline layer is constant at one spherulite diameter, the physical

properties of the i-PP/pulp fibre composite should be unaffected by the subtle

variation of the surface chemistry on the Kraft pulp fibres.

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Conclusion

Through this work we have shown that simple and straight forward means

may be employed to determine the surface chemistry of Kraft Pulp fibres (and

therefore other lignocellulosic fibres) and the effects that variability in surface

composition has on industrial applications for lignocellulosic fibres. We have also

highlighted the challenges of quantifying a naturally highly heterogeneous

material.

It has been shown that although AFM is a great technique for providing

physical property information on a wide variety of surfaces and under different

environmental conditions, the heterogeneous nature of wood pulp fibres would

require a very large number of measurements to reach valid conclusions as to

the effects of fibre source and pulping conditions. The relative atomic

composition of the amounts of cellulose, lignin and other components in the

surface of a lignocellulosic fibre can be confidently obtained through the use of

XPS and straight forward algebra. The rate of transcrystalline layer growth along

a Kraft pulp fibre is governed by the subtle variation in surface chemistry of the

fibre. The size of the transcrystalline layer is constant at one spherulite diameter,

therefore the physical properties of an i-PP/pulp fibre composite should be

unaffected by this variability in surface chemistry.

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Acknowledgements

The author wishes to express her thanks to the following; without their

contributions, though all differing in magnitude and prowess, this project would

not have been the adventure that it was.

To the project supervisor, Dr. Derek G. Gray for his advice, support and

guidance throughout the duration of this project and beyond. For allowing me the

freedom to foster my true talents and encouraging me in seeking opportunities to

fully utilise them.

For their technical expertise I am indebted to Nilgun Ulkem primarily for

her expertise in pulping but also for her friendship and understanding and Agnes

Lejeune (Université du Québec à Trois-Rivières) for her talents in running XPS

on paper samples.

My thanks to the members of the Gray research group who cultivated a

creative environment in which problems were halved, shoulders were cried on

and shoes were bought, especially to Tiffany Abitbol and Emily Dawn

Cranston. My friendship with Emily would not have flourished had fate not

placed us both in the Gray group, for that I and my family are eternally grateful.

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A debt of gratitude is owed to the Third Floor Tea Club; the institution it

has become and its members past, present and future. No glory is so great and

no failure so bad that it cannot be made better with cake.

The staff, faculty and students at the Pulp and Paper Research Centre,

McGill University, who made my time among them a most pleasant experience. I

would especially like to thank Colleen McNamee, for always lending her ear

generously and her never ending supply of chocolate.

My husband, John for his unfoundering belief in me, his unequivocal

support and his immaculate timing with a glass of wine and a bar of chocolate.

My parents and extended family who never doubted I would succeed and never

stopped telling me how proud they were of all I accomplished. I am indebted to

Jenny Warrington the original and the best supportive friend.

The most important thanks go to Amy Megan Weller and Jack Peter

Weller for putting it all into perspective.

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A microscopic investigation of the surfaces of Kraft Pulp...

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