Reducing the water absorption of thermoplastic starch ... · The overall objective of this thesis...

Reducing the water absorption of thermoplastic starch

processed by extrusion

by

Philip Oakley

A thesis submitted in conformity with the requirements

for the degree of Master of Applied Science

Graduate Department of Chemical Engineering and Applied Chemistry

University of Toronto

© Copyright by Philip Oakley 2010

ii

Reducing the water absorption of thermoplastic starch processed by extrusion

Master of Applied Science 2010

Philip Oakley

Graduate Department of Chemical Engineering and Applied Chemistry

University of Toronto

Abstract

Novel plastics that are biodegradable, environmentally benign, and made from renewable natural resources are currently being researched as alternatives to traditional petroleum-based plastics. One such plastic, thermoplastic starch (TPS) is produced from starch processed at high temperatures in the presence of plasticizers, such as water and glycerol. However, because of its hydrophilic nature, TPS exhibits poor mechanical properties when exposed to environmental conditions, such as rain or humidity. The overall objective of this thesis was to produce a thermoplastic starch based material with low water absorption that may be used to replace petroleum-based plastics. Three different methods for reducing water absorption were investigated, including the following: extrusion of starch with hydrophobic polymers, starch modifying chemicals, and citric acid/sorbitol as plasticizers. It was found that all methods reduced the water absorption of TPS. TPS blended with polyethylene and sorbitol/glycerol plasticized starch samples exhibited the lowest water absorption of all samples tested.

iii

Acknowledgements

Firstly, I would like to acknowledge the support and guidance provided by my

supervisor, Dr. Mohini Sain. I’d also like to acknowledge the members of Dr. Sain’s

research group for the training and help they provided throughout the completing of this

thesis. Thank you to Casco Inc. for generously supplying the cornstarch used for the

experiments in this thesis. Finally, I thank my parents for their continual support of my

education.

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TABLE OF CONTENTS

Abstract ............................................................................................................................ii

Acknowledgements ......................................................................................................... iii

TABLE OF CONTENTS ..................................................................................................iv

LIST OF TABLES ........................................................................................................... vii

LIST OF FIGURES .......................................................................................................... x

Chapter 1 : Introduction and Literature Review ............................................................... 1

1.1 Introduction ............................................................................................................ 1

1.2 Literature Review ................................................................................................... 2

1.2.1 Starch .............................................................................................................. 2

1.2.2 Thermoplastic starch ....................................................................................... 5

1.2.3 Water absorption ............................................................................................. 9

1.2.4 Reducing TPS water absorption .................................................................... 12

1.3 Problem Statement .............................................................................................. 15

1.4 Objective .............................................................................................................. 16

1.4.1 Specific Objectives ........................................................................................ 17

1.5 Research Approach ............................................................................................. 17

1.6 References ........................................................................................................... 19

Chapter 2 : Extrusion of starch with paper sizing agents ............................................... 21

2.1 Introduction .......................................................................................................... 21

2.2 Experimental ........................................................................................................ 23

2.2.1 Materials ........................................................................................................ 23

2.2.2 Plasticization .................................................................................................. 24

2.2.3 SEM ............................................................................................................... 24

2.2.4 Water Absorption ........................................................................................... 25

2.3 Results and Discussion ........................................................................................ 25

2.3.1 SEM ............................................................................................................... 25


2.4 Conclusions ......................................................................................................... 29

2.5 References ........................................................................................................... 30

Chapter 3 : Extrusion of starch with maleated polyethylene, green polyethylene, and green polyethylene compatibilized with maleic anhydride ............................................. 31

v

3.1 Introduction .......................................................................................................... 31

3.2 Experimental ........................................................................................................ 33

3.2.1 Materials ........................................................................................................ 33

3.2.2 Plasticization .................................................................................................. 33

3.2.3 FTIR ............................................................................................................... 34

3.2.4 SEM ............................................................................................................... 34

3.2.5 TGA ............................................................................................................... 34



3.3.1 FTIR ............................................................................................................... 35

3.3.2 SEM ............................................................................................................... 36

3.3.3 TGA ............................................................................................................... 39


3.4 Conclusions ......................................................................................................... 46

3.5 References ........................................................................................................... 47

Chapter 4 : Extrusion of starch with beeswax, paraffin wax, and paraffin wax compatibilized with maleic anhydride ............................................................................ 48

4.1 Introduction .......................................................................................................... 48

4.2 Experimental ........................................................................................................ 49

4.2.1 Materials ........................................................................................................ 49

4.2.2 Plasticization .................................................................................................. 50

4.2.3 FTIR ............................................................................................................... 50

4.2.4 SEM ............................................................................................................... 50

4.2.5 TGA ............................................................................................................... 50



4.3.1 Plasticization .................................................................................................. 51

4.3.2 FTIR ............................................................................................................... 51

4.3.3 SEM ............................................................................................................... 52

4.3.4 TGA ............................................................................................................... 53


4.4 Conclusions ......................................................................................................... 60

4.5 References ........................................................................................................... 61

vi

Chapter 5 : Extrusion of citric acid/glycerol and sorbitol/glycerol co-plasticized starch . 62

5.1 Introduction .......................................................................................................... 62

5.2 Experimental ........................................................................................................ 63

5.2.1 Materials ........................................................................................................ 63

5.2.2 Plasticization .................................................................................................. 64

5.2.3 SEM ............................................................................................................... 64


5.2.5 Mechanical Testing ........................................................................................ 64


5.3.1 Plasticization .................................................................................................. 65

5.3.2 SEM ............................................................................................................... 65


5.3.4 Mechanical Testing ........................................................................................ 68

5.4 Conclusions ......................................................................................................... 70

5.5 References ........................................................................................................... 71

Chapter 6 : Conclusions and Recommendations .......................................................... 72

6.1 References ........................................................................................................... 73

Appendix A : Chapter 2 Data and Statistics .................................................................. 74

A.1 Water Absorption Data ........................................................................................ 74

A.2 Statistical Analysis ............................................................................................... 76

Appendix B : Chapter 3 Data and Statistics .................................................................. 78

B.1 Water Absorption Data ........................................................................................ 78

B.2 Statistical Analysis ............................................................................................... 85

Appendix C : Chapter 4 Data and Statistics .................................................................. 86

C.1 Water Absorption Data ........................................................................................ 86

C.2 Statistical Analysis ............................................................................................... 90

Appendix D : Chapter 5 Data and Statistics .................................................................. 91

D.1 Water Absorption Data ........................................................................................ 91

D.2 Mechanical Testing Data ..................................................................................... 92

D.3 Statistical Analysis ............................................................................................... 94

vii

LIST OF TABLES

Table 1.1: Water uptake at equilibrium in plasticized maize starch. .............................. 14

Table 1.2: Technical substitution potential of bioplastics. .............................................. 15

Table 1.3: Commercial starch plastic producers. .......................................................... 16

Table 2.1: Used symbols and corresponding sample compositions. ............................. 24

Table 2.2: Temperature profile used for extrusion. ........................................................ 24


Table 3.2: Temperature profile used for extrusion. ........................................................ 34

Table 3.3: Data from derivative TGA curves. ................................................................ 42


Table 4.2: Data from derivative TGA curves. ................................................................ 57


Table 5.2: Mechanical properties of TPS blends and pure polymers with literature values for comparison. .................................................................................................. 70

Table A.1: Water absorption weight data for TPS sample. ............................................ 74

Table A.2: Calculated water absorption values for TPS sample. ................................... 74

Table A.3: Water absorption weight data for AKD sample. ........................................... 75

Table A.4: Calculated water absorption values for AKD sample. .................................. 75

Table A.5: Water absorption weight data for BSO sample. ........................................... 75

Table A.6: Calculated water absorption values for BSO sample. .................................. 76

Table A.7: Average water absorption values with confidence limits. ............................. 77

Table B.1: Water absorption weight data for TPS sample. ............................................ 78

Table B.2: Calculated water absorption values for TPS sample. ................................... 78

Table B.3: Water absorption weight data for 5GPE sample. ......................................... 79

Table B.4: Calculated water absorption values for 5GPE sample. ................................ 79

Table B.5: Water absorption weight data for 10GPE sample. ....................................... 79

Table B.6: Calculated water absorption values for 10GPE sample. .............................. 80

Table B.7: Water absorption weight data for 20GPE sample. ....................................... 80

Table B.8: Calculated water absorption values for 20GPE sample. .............................. 80

Table B.9: Water absorption weight data for 5MGPE sample. ...................................... 81

Table B.10: Calculated water absorption values for 5MGPE sample. ........................... 81

Table B.11: Water absorption weight data for 10MGPE sample. .................................. 81

Table B.12: Calculated water absorption values for 10MGPE sample. ......................... 82

viii

Table B.13: Water absorption weight data for 20MGPE sample. .................................. 82

Table B.14: Calculated water absorption values for 20MGPE sample. ......................... 82

Table B.15: Water absorption weight data for 5MPE sample. ....................................... 83

Table B.16: Calculated water absorption values for 5MPE sample. .............................. 83

Table B.17: Water absorption weight data for 10MPE sample. ..................................... 83

Table B.18: Calculated water absorption values for 10MPE sample. ............................ 84

Table B.19: Water absorption weight data for 20MPE sample. ..................................... 84

Table B.20: Calculated water absorption values for 20MPE sample. ............................ 84

Table B.21: Average water absorption values with confidence limits. ........................... 85

Table C.1: Water absorption weight data for 5BW sample. ........................................... 86

Table C.2: Calculated water absorption values for 5BW sample. .................................. 86

Table C.3: Water absorption weight data for 10BW sample. ......................................... 87

Table C.4: Calculated water absorption values for 10BW sample. ................................ 87

Table C.5: Water absorption weight data for 5PW sample. ........................................... 87

Table C.6: Calculated water absorption values for 5PW sample. .................................. 88

Table C.7: Water absorption weight data for 10PW sample. ......................................... 88

Table C.8: Calculated water absorption values for 10PW sample. ................................ 88

Table C.9: Water absorption weight data for 5MPW sample. ........................................ 89

Table C.10: Calculated water absorption values for 5MPW sample. ............................. 89

Table C.11: Water absorption weight data for 10MPW sample. .................................... 89

Table C.12: Calculated water absorption values for 10MPW sample. ........................... 90

Table C.13: Average water absorption values with confidence limits. ........................... 90

Table D.1: Water absorption weight data for 20SOR sample. ....................................... 91

Table D.2: Calculated water absorption values for 20SOR sample. .............................. 91

Table D.3: Water absorption weight data for SORBLEND sample. ............................... 92

Table D.4: Calculated water absorption values for SORBLEND sample. ...................... 92

Table D.5: Mechanical testing data for TPS sample. .................................................... 92

Table D.6: Mechanical testing data for MPE sample. .................................................... 93

Table D.7: Mechanical testing data for 20SOR sample. ................................................ 93

Table D.8: Mechanical testing data for SORBLEND sample. ........................................ 93

Table D.9: Average water absorption values with confidence limits. ............................. 94

Table D.10: Average max stress values with confidence limits. .................................... 94

Table D.11: Average modulus values with confidence limits. ........................................ 94

ix

Table D.12: Average elongation values with confidence limits. ..................................... 95

x

LIST OF FIGURES

Figure 1.1: The Carbon cycle of biodegradable polymers. .............................................. 2

Figure 1.2: Structure of the amylose polymer. ................................................................. 3

Figure 1.3: Structure of the amylopectin polymer. ........................................................... 3

Figure 1.4: Helical structure of α-amylose molecule. ....................................................... 4

Figure 1.5: SEM image of potato starch granules. .......................................................... 5

Figure 1.6: SEM Images (2500x magnification) of tapioca starch at the temperature (oC) below each image. .......................................................................................................... 6

Figure 1.7: Tg of TPS as a function of plasticizer content and type. ................................ 7

Figure 1.8: Strain at break versus water content, W, for various plasticized starches. .... 8

Figure 1.9: Twin-screw extruder used for compounding starch. ...................................... 9

Figure 1.10: Strength (a), strain at break (b), and elastic modulus (c), versus water absorbed for TPS. ......................................................................................................... 11

Figure 1.11: Starch modification reactions. ................................................................... 12

Figure 1.12: Chemical structure of (a) glycerol, (b) xylitol, (c) sorbitol, (d) maltitol. ....... 14

Figure 2.1: Chemical reaction of ASAs with starch. ...................................................... 22

Figure 2.2: Chemical reaction of AKD with starch. ........................................................ 22

Figure 2.3: Chemical structure of styrene/butyl acrylate copolymer. ............................. 23

Figure 2.4: SEM images of extruded samples at 200X magnification: (a) ASA (b) AKD (c) TPS (d) BSO ............................................................................................................ 26

Figure 2.5: Water absorption profile for AKD, BSO, and TPS samples. ........................ 27

Figure 2.6: Water absorption at equilibrium for the TPS and BSO samples with 95% confidence intervals....................................................................................................... 27

Figure 2.7: Water absorption at 10 days for the TPS and AKD samples with 95% confidence intervals....................................................................................................... 28

Figure 3.1: Reaction of MAH with PE initiated by DCP or BPO. .................................... 32

Figure 3.2: Reaction of maleated PE with starch. ......................................................... 32

Figure 3.3: FTIR spectrum for GPE and MGPE. ........................................................... 35

Figure 3.4: SEM image of TPS sample. ........................................................................ 36

Figure 3.5: SEM images of extruded samples: (a) 5GPE, (b) 10GPE, (c) 20GPE ........ 37

Figure 3.6: SEM images of extruded samples: (a) 5MGPE, (b) 10MGPE, (c) 20MGPE 37

Figure 3.7: SEM images of MPE samples: (a) 5MPE (b) 10MPE (c) 20MPE ................ 38

Figure 3.8: TGA curves for pure GPE, TPS, and blends of TPS/GPE. ......................... 39

Figure 3.9: TGA curves for pure MGPE, TPS, and blends of TPS/MGPE..................... 40

xi

Figure 3.10: TGA curves for pure MPE, TPS, and blends of TPS/MPE. ....................... 40

Figure 3.11: Derivative TGA curves for pure GPE, TPS, and blends of TPS/GPE. ....... 41

Figure 3.12: Derivative TGA curves for pure MGPE, TPS, and blends of TPS/MGPE. . 41

Figure 3.13: Derivative TGA curves for pure MPE, TPS, and blends of TPS/MPE. ...... 42

Figure 3.14: Water absorption at equilibrium for MGPE samples with 95% confidence intervals. ........................................................................................................................ 44

Figure 3.15: Water absorption at equilibrium for GPE samples with 95% confidence intervals. ........................................................................................................................ 45

Figure 3.16: Water absorption at equilibrium for MPE samples with 95% confidence intervals. ........................................................................................................................ 45

Figure 4.1: Reaction scheme for grafting maleic anhydride onto paraffin wax. ............. 49

Figure 4.2: FTIR spectrum for PW and MPW. ............................................................... 51

Figure 4.3: SEM images of extruded samples: (a) 5BW (b) 10BW ............................... 52

Figure 4.4: SEM images of extruded samples: (a) 5PW (b) 10PW (c) 5MPW (d) 10MPW ...................................................................................................................................... 53

Figure 4.5: TGA curves for pure BW, TPS, and blends of TPS/BW. ............................. 54

Figure 4.6: TGA curves for pure PW, TPS, and blends of TPS/PW. ............................. 54

Figure 4.7: TGA curves for pure MPW, TPS, and blends of TPS/MPW. ....................... 55

Figure 4.8: Derivative TGA curves for pure BW, TPS, and blends of TPS/BW. ............ 55

Figure 4.9: Derivative TGA curves for pure PW, TPS, and blends of TPS/PW. ............ 56

Figure 4.10: Derivative TGA curves for pure MPW, TPS, and blends of TPS/MPW. .... 56

Figure 4.11: Water absorption at equilibrium for BW samples with 95% confidence intervals. ........................................................................................................................ 58

Figure 4.12: Water absorption at equilibrium for PW samples with 95% confidence intervals. ........................................................................................................................ 59

Figure 4.13: Water absorption at equilibrium for MPW samples with 95% confidence intervals. ........................................................................................................................ 59

Figure 5.1: Reaction scheme of citric acid with starch................................................... 63

Figure 5.2: SEM images of extruded samples: (a) 20CA (b) 30CA (c) 45CA ................ 66

Figure 5.3: SEM images of extruded samples: (a) 20SOR (b) 30SOR (c) 45SOR (d) SORBLEND .................................................................................................................. 67

Figure 5.4: Water absorption at equilibrium for sorbitol plasticized samples with 95% confidence intervals....................................................................................................... 68

Figure 5.5: Stress-strain curves for extruded samples. ................................................. 69

1

Chapter 1 : Introduction and Literature Review

1.1 Introduction

Over the past century the petroleum-based polymer industry has grown rapidly by

creating materials that are cheap, easy to transform, hydrophobic, and biologically inert.

However, several decades of using and disposing of non-biodegradable plastic has

caused an accumulation of plastic waste in landfills, polluted maritime environments,

and contributed to the depletion of our limited reserves of fossil fuels1. One alternative

to disposing these plastics in landfills is burning them for energy production. However,

this merely moves pollution from ground level into the atmosphere in the form of carbon

dioxide and other gases. Recycling also has the problem of being energy intensive and

requiring selective sorting out and cleaning of waste plastic2. A better alternative is to

minimize the quantities of non-degradable plastics used by substituting them with

biodegradable plastics.

Biodegradable plastics are often made from renewable natural polymers, such as

starch, proteins, and cellulose. In contrast to petroleum-based plastics, these so called

bioplastics do not drain our limited supply of fossil-based resources and have a small

carbon footprint. However, the most attractive feature of bioplastics is their total

biodegradability. As a result, they fit in perfectly well with our ecosystems and have a

closed loop carbon cycle where no waste is generated3. This principle is demonstrated

below in Figure 1.1 where plant material is processed into plastic which later degrades

and may form new plant material.

Starch has attracted attention as a suitable material for the production of biodegradable

plastics due to its natural abundance and low cost4,5. Starch is a renewable biomaterial;

therefore, it may be used to produce plastics without depleting fossil fuel resources

when sustainable (or carbon neutral) farming techniques are used. Plasticized starch or

2

thermoplastic starch (TPS) is prepared under specific extrusion conditions and in the

presence of plasticizers, such as glycerol and water6,7,8,9. However, four problems

hinder TPS from becoming a commonly used plastic, including the following10:

1. hydrophilic nature of TPS and poor water resistance

2. deterioration of mechanical properties upon exposure to environmental

conditions like humidity

3. brittleness in the absence of suitable plasticizers

4. soft and weak nature in the presence of some plasticizers

Figure 1.1: The Carbon cycle of biodegradable polymers3.

1.2 Literature Review

1.2.1 Starch

Starch is a polymer which occurs widely in plants11. It is produced during photosynthesis

and functions as the principal polysaccharide reserve material12. The principle crops

used for production of starch include potatoes, corn, and rice11. In all of these plants,

starch is deposited in the form of complex structures called granules, with varying

shapes and sizes depending on the botanical origin.

3

1.2.1.1 Chemistry

The two main constituents of starch granules are the polysaccharides amylopectin and

amylose. Both of these polymers are composed of repeating units of α-D-glucose. The

major component of most starches is amylopectin and it constitutes about 70% of the

polysaccharide content13. The structure of amylose and amylopectin are shown below in

Figure 1.2 and Figure 1.3, respectively.

Figure 1.2: Structure of the amylose polymer14

.

Figure 1.3: Structure of the amylopectin polymer14

.

Amylose is essentially a linear molecule consisting of α-1,4-linkages between glucose

monomers. The polymer strands of α-amylose in starch adopt a helical structure (shown

below in Figure 1.4) similar to that found in nucleic acids. Typical chain lengths for α-

amylose units are approximately 1000 monomer units11.

4

Figure 1.4: Helical structure of α-amylose molecule15

.

The second polymer in starch, amylopectin, is an extensively branched macromolecule.

Like amylose, the glucose units are connected through α-1,4-linkages. The difference

between amylose and amylopectin is that at irregular intervals there are branch points

where a secondary polysaccharide chain is connected to the main chain by α-1,6-

linkages.

Each starch molecule has two important functional groups. The OH group is susceptible

to substitution reactions and has a high affinity for water, causing much of the problem

of water absorption in TPS. Also, the C-O-C bond is susceptible to chain breakage11. A

number of chemical reactions with these two groups have been studied in the literature.

These reactions have a number of purposes, such as increasing the hydrophobicity of

starch16.

1.2.1.2 Physical structure

Amylose and amylopectin in starch are organized into granules as alternating semi-

crystalline and amorphous layers. As revealed by SEM studies17, starch granules are

smooth with a spherical or ellipsoid shape. The granule surface is smooth with only

5

minor ripples and bumps at the nanometer scale. SEM images of potato starch granules

are shown below in Figure 1.5.

Figure 1.5: SEM image of potato starch granules17

.

Starch granules consist of both semi-crystalline and amorphous phases. The semi-

crystalline regions are composed of double helices formed by short amylopectin

branches and the amorphous regions are composed of amylose and non-ordered

amylopectin branches18.

1.2.2 Thermoplastic starch

Thermoplastic starch (TPS) is the material produced when starch is heated in the

presence of plasticizers. It is a plastic material with poor elongation and high tensile

strength properties19.

1.2.2.1 Plasticization of starch

Starch plasticization is a three stage process during which the following events take

place20:

1. Plasticizers are absorbed by starch granules and form hydrogen bonds with amylose

and non-ordered amylopectin. This facilitates increased amylose and amylopectin

mobility in the amorphous regions. Amylose and amylopectin rearrange, forming new

intermolecular interactions.

3. Amylose and amylopectin become more mobile and lose their intermolecular

interactions and granular structure when heat and shearing forces are applied. Energy

absorbed by the granules melts their crystallite structures and facilitates the formation of

new bonds among starch and plasticizers. SEM images of this process are shown

6

below in Figure 1.6. Starch restructured in this way acquires flowing properties close to

thermoplastics such as polyethylene and polypropylene.

Figure 1.6: SEM Images (2500x magnification) of tapioca starch at the temperature (oC) below each image

20.

4. A thermoplastic material is formed as starch is cooled back below the melting

temperature of the starch crystallites. Starch chains re-associate and a new crystalline

order is created, different from the original granule structures. The re-organizing of

amylose molecules is rapid due to the greater mobility of amylose molecules compared

to amylopectin molecules. On the other hand, the restructuring of amylopectin

molecules proceeds slowly over several days. The final material contains amorphous

regions as well as crystalline regions.

1.2.2.2 Plasticizers

Plasticizers are required to form hydrogen bonds with amylose and amylopectin chains

during the plasticization of starch. This increases amylose and amylopectin chain

mobility which in turn lowers the melting temperature of starch. Therefore, plasticizers

are used in order to process starch into a thermoplastic material at a temperature below

its degradation temperature, but above its melting temperature21. Glycerol is the most

7

common plasticizer used for starch, but many others have been studied. Other common

plasticizers include the following: xylitol22, sorbitol22, maltitol22, urea23, formamide23, and

sugars24.

Figure 1.7: Tg of TPS as a function of plasticizer content and type19

.

The amount and type of plasticizer used influence the properties of TPS, such as its

water absorption (discussed later), glass transition temperature (Tg), and modulus25.

Shown above in Figure 1.7 is the relationship between Tg and plasticizer amount and

type. In general, an increase in the concentration of plasticizer results in a lower Tg

because more plasticizer groups are available to bond with starch, thus increasing

starch chain mobility. However, the intensity of this decrease is dependent on the nature

of the plasticizer used19. A general rule is that the glass transition temperature

decreases as molecular weight decreases because smaller molecules are better able to

penetrate the starch granule structure, promoting amylose and amylopectin chain

mobility22.

8

1.2.2.3 Role of water during plasticization

Plasticization of starch is aided by water in addition to other plasticizers. In a study by

Hulleman et al.26, it was found that as the amount of water added to a starch/glycerol

mixture increased, polysaccharides increasingly migrated out of the starch granules

during plasticization. Due to this larger fraction of non-granular and interacting

polysaccharides, the material became more deformable without losing coherence. This

affected the strain at break, as shown below in Figure 1.8.

Figure 1.8: Strain at break versus water content, W, for various plasticized starches26

.

However, above specific water contents the strain at break started to decrease because

the interaction or entanglement of polysaccharides is limited at relatively high water

contents. The formation of an even more coherent polysaccharide system is hindered,

possibly due to the formation of inter and intramolecular contacts within granules,

instead of the formation of a non-granular polysaccharide network26.

1.2.2.4 Plasticization by extrusion

Starch may be plasticized using small scale laboratory methods such as solution

casting; however, plasticization of starch by extrusion is a more realistic approach to the

industrial preparation of TPS. Extrusion is the method of choice for producing TPS in

large quantities; therefore, it was the method used in this thesis. Shown below in Figure

1.9 is a diagram of a twin-screw extruder used for processing starch into TPS.

9

Figure 1.9: Twin-screw extruder used for compounding starch27

.

Starch, plasticizers, and other additives are placed in the hopper – from where they are

fed into the barrel of the extruder. The heat and shear required to plasticize starch

granules are supplied by external heaters and by the compression and shearing action

of the screws, respectively. As starch is pushed through the barrel of the extruder it

restructures into a free-flowing material until it emerges from the die and is cooled back

below the melting temperature. The material that emerges from the die is TPS and will

ideally contain no intact or unplasticized starch granules.

1.2.3 Water absorption

1.2.3.1 Theory

Water absorption in TPS is a diffusion process driven by a concentration gradient and

complicated by swelling of the material. Water molecules in the air present as humidity

or rain will diffuse into a hydrophilic polymer such as TPS to produce a swollen material.

Dissolution of the material is prevented if the bonding between neighbouring polymer

molecules is strong as a result of crosslinking or hydrogen bonding. Swelling of the

material continues until the forces due to swelling of the polymer balance the osmotic

pressure. The polymer swelling required to accommodate water absorbed from the

surface is initially constricted by the internal glassy material. This causes compressive

forces to build up in the plane of the sample surface, and initial swelling occurs

predominantly perpendicular to the surface resulting in a thickness increase without a

corresponding increase in the longitudinal dimension28.

10

An experiment by Russo, et al. 29 was conducted in order to determine which theoretical

model of diffusion applies to the case of water diffusion into TPS. They found that a

Fickian diffusion model accounting for polymer swelling described their data most

accurately. Therefore, Fick’s law of diffusion, shown below in equation (1.1), may be

used to model water absorption by TPS.

(1.1)

Where C is water concentration, t is time, D is the diffusion coefficient, and x is the path

length. In the study by Russo, et al. 29, the best fit to the experimental data could only be

made by applying an exponential dependence on water concentration. Therefore, the

diffusion coefficient is modeled by equation (1.2).

(1.2)

Where C is the concentration at a point, C0 is the concentration at the surface, and D0

and A are constants. The swelling during water absorption was taken into account by

modifying the diffusion coefficient and rescaling the linear distances. The new equation

for the diffusion coefficient is equation (1.3).

(1.3)

Where S∞ is the degree of swelling calculated as the maximum thickness of the sample

at full swelling divided by the initial thickness of the polymer. By combining equation

(1.3) with equation (1.1), a model for water absorption in TPS was produced, shown in

equation (1.4).

[

]

(1.4)

11

Water absorbed by TPS over time is a function of all terms on the right side of equation

(1.4). The parameters which are a function of TPS material properties and thus may be

engineered are D0, S∞, and x. However, S∞, the amount of swelling must be close to

zero for all applications; therefore, it was not considered an engineer-able variable

parameter. Also, the method by which the path length, x, is varied involves adding clay

or nanoparticles that have a detrimental effect on the strain at break of TPS30.

Therefore, this method was not investigated. Lowering the diffusion constant, D0, by

modifying the material properties of TPS was examined in this thesis.

1.2.3.2 Water absorption effects on mechanical properties

Water absorption in TPS promotes two separate processes – an increase in

plasticization, and an increase in crystallinity known as retrogradation. Absorbed water

behaves as a plasticizer just as it does during the granule melting process and leads to

a decrease in Tg and hence an increase in the strain at break (Figure 1.10b). However,

the increase in crystallinity accompanied by this causes a decrease in strength (Figure

1.10a) and modulus (Figure 1.10c) 30 because the crystalline regions are less efficient

than the amorphous regions at transferring stresses between polymer chains22.

Figure 1.10: Strength (a), strain at break (b), and elastic modulus (c), versus water absorbed for TPS30

.

12

These immediate detrimental effects on the mechanical properties of TPS are a

hindrance to its commercialization as a commodity plastic. For TPS to be widely used in

many applications it must be water resistant and able to maintain its mechanical

properties over a long period of time.

1.2.4 Reducing TPS water absorption

1.2.4.1 Chemical modification of starch

Starch may be modified via many different chemical reactions, as shown below in

Figure 1.11. Modified starches are the products of glucosidic bond cleavage (acid

modification to dextrins), forming new functional groups (carbonyl group formation

during oxidation), substitution of free available hydroxyl groups (by etherification or

esterification), and bridging of molecular chains by cross-linking reactions16. By

replacing OH groups or cross-linking starch molecules, chemical modification reduces

the diffusion coefficient and hence water absorption of TPS.

Figure 1.11: Starch modification reactions16

.

13

1.2.4.2 Blending with hydrophobic polymers

Some authors have tried to improve the water resistance of TPS by melt-blending

starch with hydrophobic polymers such as poly(e-caprolactone)31, cellulose acetate32,

poly(butylene adipate-co-terephthalate)33, polylactides34 and polyethylene35. When a

hydrophobic polymer is blended with a hydrophilic polymer, the diffusion coefficient for

the blend is lower than that for the hydrophilic component. Therefore, the blend will be

more water resistant than the hydrophilic component alone. A theoretical explanation for

this observation is provided by analysis of the equation for the diffusion coefficient of

miscible polymer blends, shown below as equation (1.5)36.

(1.5)

and are the respective volume fractions and D1 and D2 are the respective

diffusion coefficients of polymer 1 and 2 in the blend. ΔE12 is a measure of the

thermodynamic interaction energy of the blend and is given by equation (1.6).

(1.6)

Edb, Ed1, and Ed2 are the activation energies of the blend and the two unblended

components. Solving equation (1.5) for Db gives equation (1.7).

(1.7)

Therefore, the diffusion coefficient and hence water absorption of the polymer blend is

dependent on the weight fraction of TPS, weight fraction of hydrophobic polymer, the

thermodynamic interaction energy between TPS and the hydrophobic polymer, and their

respective diffusion coefficients. As the weight fraction of TPS decreases in the blend,

so too will the diffusion coefficient and water absorbed since the hydrophobic polymer

will have a lower diffusion coefficient than TPS.

1.2.4.3 Plasticizer Choice

Plasticizer type has an influence on water absorption in TPS since it is largely

responsible for its material properties, including the diffusion coefficient. In a study by

14

Mathew and Dufresne22 it was found that for the commonly used group of polyol

plasticizers, a continuous decrease in water uptake and diffusion coefficient was

observed as molecular weight increased (shown below in Table 1.1). An explanation for

this was proposed based on the chemical structure of the plasticizers, shown below in

Figure 1.12. The amount of end hydroxyl groups is greater for the low molecular weight

compounds and these groups have an affinity for and are more accessible to water22.

Figure 1.12: Chemical structure of (a) glycerol, (b) xylitol, (c) sorbitol, (d) maltitol22

.

Table 1.1: Water uptake at equilibrium in plasticized maize starch22

.

Plasticizer Diffusion Coefficient

(cm2/sx108)

Equilibrium Water Absorption

(%)

Xylitol 14.6 42

Sorbitol 10.1 40

Maltitol 7.0 27

15

1.3 Problem Statement

Water absorption in thermoplastic starch causes deterioration of its strength properties,

limiting its applications in any environment exposed to humidity or water. In a survey of

bioplastic industry experts, shown below in Table 1.2, starch based plastics were found

to have the lowest technical substitution potential for petroleum-based plastics37.

Technical substitution potential refers to the ability of a novel plastic to replace the

common petroleum-based plastics, based solely on material properties. Therefore,

starch based plastics currently do not have strong enough material properties to replace

petroleum-based plastics in a wide array of applications. The most problematic material

property of starch plastics – their tendency to absorb water from their surroundings –

must be minimized in order to increase their technical substitution potential.

Table 1.2: Technical substitution potential of bioplastics37

.

Industry currently minimizes water absorption and improves mechanical properties of

starch plastics by blending with hydrophobic polymers. As shown below in Table 1.3,

almost every commercially available starch plastic is a blend with other polymers, with

the exceptions of partially fermented starch from Solanyl and starch composites from

PaperFoam38. However, these commercial products are included in the low technical

substitution estimate above. Therefore, their material properties are not ideal for

substituting petroleum-based plastics. Novel starch based plastics with better material

16

properties than the currently available products must be prepared and studied if starch

plastics are to replace petroleum-based plastics to a high degree.

Table 1.3: Commercial starch plastic producers38

.

1.4 Objective

The overall objective of this thesis was to produce a thermoplastic starch based material

with low water absorption that may be used to replace petroleum-based plastics.

17

1.4.1 Specific Objectives

The specific objectives for this thesis were the following:

1. Reduce water absorption in TPS by chemical modification with paper sizing

agents.

2. Reduce water absorption in TPS by blending with the hydrophobic polymers

polyethylene, paraffin wax, and beeswax.

3. Reduce water absorption in TPS by using sorbitol and citric acid as plasticizers.

1.5 Research Approach

Chemical modification of starch has been well studied in the literature and many

hydrophobicity increasing reactions are known16. However, none of the current starch

based plastics on the market make use of hydrophobicity increasing chemical

reactions38. Also, many literature studies on starch chemical modification make use of

TPS preparation methods, such as solution casting, which are unsuitable to industrial

scale plastic production. Therefore, an experiment was undertaken in Chapter 2 of this

thesis with the objective of reducing the water absorption of TPS by extruding starch

with paper sizing agents – chemicals known to increase starch hydrophobicity.

Blending TPS with hydrophobic polymers is performed to improve TPS properties in

most of the commercially available starch plastics. However, some new plastics are

commercially available that have not been blended with TPS, such as green

polyethylene. Therefore, in Chapter 3 green polyethylene was blended with starch in

order to reduce water absorption. Also, waxes are commonly used to reduce water

absorption in wood products, but have not been blended with TPS. Therefore, in

Chapter 4 paraffin wax and beeswax were blended with starch in order to reduce water

absorption.

Plasticizers used in the preparation of TPS have an effect on material properties, such

as water absorption. Sorbitol has been shown to produce TPS with lower water

absorption than glycerol plasticized TPS. Also, citric acid has been used as a plasticizer

18

for TPS, but water absorption tests have not been published. Therefore, in Chapter 5

sorbitol and citric acid were used as plasticizers for starch in order to reduce water

absorption.

19

1.6 References

1. Showmura, R.S. (1990). Second International Conference of Marine Debris. US Department of Commerce, Honolulu. 2. Rouilly, A. and L. Rigal (2002). Agro-materials: a bibliographic review. Polymer Reviews. 42:4, 441-479. 3. Tharanathan, R.N. (2003). Biodegradable films and composite coatings: past, present and future. Trends in Food Science & Technology. 14, 71-78. 4. Gross, R. A. and B. Kalra. (2002). Biodegradable polymers for the environment. Science. 297, 803-807. 5. Reddy, C.S.K., Ghai, R. and V.C. Kalia. (2003). Polyhydroxyalkanoates: an overview. Bioresource Technology. 87, 137-146. 6. de Graff, R.A., Karman, A.P. and L. Janssen. (2003). Material properties and glass transition temperatures of different thermoplastic starches after extrusion processing. Starch. 55, 80-86. 7. Forssell, P., Mikkilä, J., Suortti, T., Seppäl, J. and K. Poutanen. (1996). Plasticization of barley starch with glycerol and water. Journal of Macromolecular Science, Part A. 33: 5, 703-715. 8. Shogren, R.L., Fanta, G.F. and W.M. Doane. (1993). Development of starch based plastics – a re-examination of selected polymer systems in historical perspective. Starch. 45:8, 276-280. 9. R.F.T. Stepto. (2003). The processing of starch as a thermoplastic. Macromolecular Symposium. 201, 203-212. 10. Kalambur, S. and S. Rivzi. (2006). An overview of starch-based plastic blends from reactive extrusion. Journal of Plastic Film and Sheeting. 22:39, 39-58. 11. R., Chandra and R. Rustgi. (1998). Biodegradable Polymers. Progress in Polymer Science. 23, 1273-1335. 12. H. Cornell. (2003). Starch in food; structure, function, and applications. Woodhead Publishing Limited, CRC Press. 211-240. 13. A. M. Donald. (2003). Starch in food; structure, function, and applications. Woodhead Publishing Limited, CRC Press. 156-184. 14. Royal Society of Chemistry. (2008). Carbohydrates. Available at http://www.rsc.org/education/teachers/learnnet/cfb/carbohydrates.htm. Accessed on July 5, 2010. 15. T. A. Newton. (2003). Glucanes containing alpha – glycosidic linkages. Available at http://www.biologie.uni-hamburg.de/b-online/e17/17b.htm. Accessed on July 5, 2010. 16. R. N. Tharanathan. (2005). Starch – value addition by modification. Critical reviews in Food Science and Nutrition. 45, 371-384. 17. Glaring, M.A., Koch, C.B. and A. Blennow. (2006). Genotype-specific special distribution of starch molecules in the starch granule: a combined clsm and sem approach. Biomacromolecules. 7:8, 2310-2320. 18. Ray, S.S. and M. Bousmina. (2005). Biodegradable polymers and their layered silicate nanocomposites: in greening the 21st century materials world. Progress in Materials Science. 50, 962-1079. 19. Lourdin, D., Coignard, L., Bizot, H. and P. Colonna. (1997). Influence of equilibrium relative humidity and plasticizer concentration on the water content and glass transition of starch materials. Polymer. 38:21, 5401-5406.

20

20. Ratnayake, W.S. and D.S. Jackson. (2007). A new insight into the gelatinization process of native starches. Carbohydrate Polymers. 67, 511-529. 21. R.F.T. Stepto. (2000). Thermoplastic Starch. Macromolecular Symposia. 152, 73-82. 22. Mathew, A.P. and A. Dufresne. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules. 3, 1101-1108. 23. Ma, X. and J. Yu. (2004). The plasticizers containing amide groups for thermoplastic starch. Carbohydrate Polymers. 57, 197-203. 24. Barrett, A., Kaletunc, G., Rosenburg, S. and K. Breslauer. (1995). The effect of sucrose on the structure, mechanical strength and thermal properties of corn extrudates. Carbohydrate Polymers. 26, 261-269. 25. Da Roz, A.L., Carvalho, A.J.F., Gandini, A. and A.A.S. Curvelo. (2006). The effect of plasticizers on thermoplastic starch compositions obtained by melt processing. Carbohydrate Polymers. 63, 417-424. 26. Hulleman, S.H.D., Janssen, F.H.P. and H. Feil. (1998). The role of water during plasticization of native starches. Polymer. 39:10, 2043-2048. 27. AIPMA. (Year Unknown). Plastic Process. Available at: http://www.aipma.net/info/plasticprocess.htm. Accessed July 20, 2010. 28. Thomas, N.L. and A.H. Windle. (1981). Diffusion mechanics of the system pmma-methanol. Polymer. 22:5, 627-639. 29. M.A.L. Russo, et al. (2007). A study of water diffusion into a high-amylose starch blend: the effect of moisture content and temperature. Biomacromolecules. 8, 296-301. 30. N. Lilichenko, et al. (2008). A biodegradable polymer nanocomposite: mechanical and barrier properties. Mechanics of Composite Materials. 44:1, 45-56. 31. Averous, L., Moro, L., Dole, P. and C. Fringant. (2000). Properties of thermoplastic blends: starch–polycaprolactone. Polymer. 41, 4157-4167. 32. R.L. Shogren. (1996). Preparation, thermal properties, and extrusion of high-amylose starch acetates. Carbohydrate Polymers. 29:1, 57-62. 33. Nabar, Y., Raquez, J.M., Dubois, P. and R. Narayan. (2005). Production of starch foams by twin-screw extrusion: effect of maleated poly(butylene adipate-co-terephthalate) as a compatibilizer. Biomacromolecules. 6, 807-817. 34. Dubois, P. and R. Narayan. (2003). Biodegradable compositions by reactive processing of aliphatic polyester/polysaccharide blends. Macromolecular Symposium. 198, 233-243. 35. Shujun, W., Jiugao, Y. and Y. Jinglin. (2005). Preparation and characterization of compatible thermoplastic starch/polyethylene blends. Polymer Degradation and Stability. 87, 395-401. 36. D.R. Paul. (1984). Gas transport in homogenous multicomponent polymers. Journal of Membrane Science. 18, 75-86. 37. Shen, L., Worrell, E. and M. Patel. (2010). Present and future development in plastics from biomass. Biofuels, Bioproducts and Biorefining. 4, 25-40. 38. Shen L., Haufe, J. and M. Patel. (2009). Product overview and market projection of emerging biobased plastics. Copernicus Institute for Sustainable Development and Innovation, Utrecht University, Netherlands. Report No: NWS-E-2009-32.

21

Chapter 2 : Extrusion of starch with paper sizing agents

2.1 Introduction

Chemical modifications to starch are often carried out for a variety of reasons, including

increasing its hydrophobicity. A group of chemicals known as sizing agents are used to

hydrophobically modify the starch applied to paper in a procedure known as paper

sizing. In this procedure, cellulose paper fibres are covered with a thin film of starch

modified by a sizing agent, creating a water repellent surface. Reactions between starch

and sizing agents have been well studied and are generally carried out at alkaline

conditions and moderate temperatures1,2. However, little is known about how these

chemicals affect the water absorption and mechanical properties of thermoplastic starch

processed by high temperature extrusion at neutral pH.

Styrene maleic anhydride (SMA) is the only paper sizing agent to have been extruded

with starch and reported in the literature3,4,5. In a study by Vaidya and Bhattacharya4,

starch was successfully extruded and reacted with SMA at neutral pH. TPS/SMA blends

showed improved water resistance over TPS; however, a significant drop in tensile

strength was observed in a high humidity environment. Different paper sizing agents

were examined in this chapter. Alkenyl succinic anhydride (ASA), alkyl ketene dimer

(AKD), and a styrene/butyl acrylate copolymer (BSO) were studied.

ASAs react with the OH groups of starch by an esterification reaction, as shown below

in Figure 2.1. The length of the alkenyl group ultimately determines the extent of

hydrophobic character in the modified starch, with longer chains increasing

hydrophobicity more than shorter chains6.

22

Figure 2.1: Chemical reaction of ASAs with starch2.

The reaction of starch with ASA is generally carried out in aqueous medium and under

alkaline conditions. A study of the modification of starch with ASA found the optimal

reaction conditions to be pH 8.5-9, 23oC, and 5% ASA concentration. Previous studies

on the ASA modification of starch use a solution casting method to prepare films7;

therefore, the effects of high temperature extrusion on this reaction are unknown.

AKD is another common commercial chemical used for paper sizing and is classified as

non-hazardous1. It has a reactive β-lactone functionality that can react with hydroxyl or

amino groups under mild reaction conditions. The reaction scheme whereby AKD

replaces an OH group on a starch glucose unit is shown below in Figure 2.2.

Figure 2.2: Chemical reaction of AKD with starch1.

The reaction between AKD and starch may be enzyme catalyzed or performed under

alkaline conditions with or without the use of a solvent. It is generally carried out at pH

8-8.6 at a temperature of 90-120oC. The effect of carrying this reaction out in an

extruder at higher temperatures is currently unknown, as AKD has only been used to

modify starch in a batch reaction8.

23

Basoplast (BSO) is a polymeric paper sizing agent consisting of a styrene/butyl acrylate

copolymer9. The structure of this chemical is shown below in Figure 2.3.

Figure 2.3: Chemical structure of styrene/butyl acrylate copolymer.

Butyl acrylate reacts with starch through a graft copolymerization reaction10; however

the reaction mechanism for Basoplast paper sizing is unknown due to a lack of

information provided by the manufacturer.

The objective of this chapter was to reduce the water absorption of TPS by chemical

modification with ASA, AKD, and BSO. Reactions between these chemicals and starch

were carried out at neutral pH in an extruder, despite having maximum efficiencies in

alkaline solution. The rationale behind this decision was to minimize energy use and

eliminate unit operations such as batch reaction, filtration, and drying of starch that

would be required were the reaction to take place outside of an extruder in alkaline

solution. By performing the reaction inside an extruder, the plasticization of starch and

reaction with sizing agent are accomplished in a single step.

2.2 Experimental

2.2.1 Materials

Industrial grade cornstarch (11% moisture) was obtained from Casco Inc. (Cardinal,

ON). Glycerol was purchased from ACP Chemicals Inc. (Montreal, QC). ASA was

purchased in the form of Eka SA 220 from Akzo Nobel (Amsterdam, NL). AKD was

purchased from Hercules Inc. (Wilmington, DE) as Hercon 115 and Basoplast 400 DS

was obtained from BASF Corporation (Ludwigshafen, Germany).

24

2.2.2 Plasticization

Starch, glycerol, and any additives were mixed with a high speed kitchen mixer for

30min. The compositions of four samples prepared are listed below in Table 2.1.

Table 2.1: Used symbols and corresponding sample compositions.

Weight Proportion

Sample Starch Glycerol Additive

TPS 100 42 N/A

ASA 100 42 15% Eka SA 220

AKD 100 42 15% Hercon 115

BSO 100 42 15% Basoplast 400DS

Starch mixtures were compounded using a twin screw extruder, the ONYX TEC-25/40,

supplied by ONYX P.M. Inc. (Toronto, ON, Canada). The extruder had a screw diameter

of 25mm and L/D ratio of 40; screw speed was 125RPM and feeder speed was 12RPM.

The temperature profile along the extruder barrel (from feed zone to die) is shown below

in Table 2.2.

Table 2.2: Temperature profile used for extrusion.

Zone 1 2 3 4 5 6 7 8 9 10

Temperature (oC)

135 145 145 150 150 160 160 165 165 155

Plastic emerged from the extruder out of a circular die and was reduced to small

fragments using the rotating knife on the ONYX TEC-25/40.

2.2.3 SEM

Specimens were fractured with a knife and the exposed surfaces were observed with a

JEOL JSM-840 scanning electron microscope (Tokyo, Japan). All surfaces were coated

with gold to avoid charging under the electron beam. The electron gun voltage was set

at 15 kV. The micrographs of samples were taken at magnifications of 200 to identify

cracks, holes and other changes on the surface of the samples.

25

2.2.4 Water Absorption

Water absorption (WA) of each sample was measured by first preparing 2x2sqinch thin

film specimens using a model ARG-450 hydraulic press supplied by Dieffenbacher N.A.

Inc. (Windsor, ON). Samples were pressed for 4min at 160oC and 500kPa, cut into

square specimens, and dried overnight in a desiccator. Dried specimens were placed in

a desiccator containing distilled water at room temperature (23oC, 100% RH) and

weighed every 24h. WA of each specimen was calculated by the following equation:

(1)

where Wa is the weight of the specimen at a specific time interval and W i is the initial dry

weight of the specimen. Equilibrium was assumed to be reached when the difference

between successive WA values was less than 1%. The result of each sample

represents the average of five specimens.

2.3 Results and Discussion

2.3.1 SEM

Images for all extruded samples at 200X magnification are shown below in Figure 2.4.

The TPS, BSO, and AKD samples have smooth surfaces with some roughness caused

by the physical slicing of the samples in preparation for SEM and some starch granules

remaining unplasticized. The image for the TPS sample is similar to images from

previous studies which show smooth surfaces with some roughness or pits caused by

unplasticized granules11. The ASA sample image in Figure 2.4b shows only partially

melted granules. This indicates that complete plasticization of starch was prevented by

the addition of 15% ASA in the form of Eka SA 220. This is a novel finding since

previous studies have modified TPS with ASA after plasticization by dipping samples

into an ASA solution7. In this experiment, it appeared that modification of starch with

ASA prior to plasticization had the effect of hindering the plasticization of starch. A

possible explanation for this result is that ASA reacted with starch, replacing hydroxyl

groups with hydrocarbon chains. This modified starch was then less capable of forming

hydrogen bonds with glycerol through its hydroxyl groups. Therefore, the plasticization

26

of starch was hindered because glycerol was less capable of aiding in starch polymer

chain mobility through hydrogen bonding.

Figure 2.4: SEM images of extruded samples at 200X magnification: (a) ASA (b) AKD (c) TPS (d) BSO


Shown below in Figure 2.5 are the water absorption profiles for the AKD, BSO, and TPS

samples (data in Appendix A). An ASA sample was not prepared because the extruded

material was very brittle due to incomplete starch plasticization. TPS and modified TPS

samples typically demonstrate the water absorption phenomenon shown below,

whereby the samples absorb water quickly during the first days immersed in a high

humidity environment. Then the rate of water absorption slows until equilibrium is

reached – at which point the samples stop absorbing more water12. The AKD sample

absorbed less water than both the TPS and BSO samples; however, the specimens fell

apart after 10 days, before equilibrium was reached. Also, there was no significant

27

difference in water absorption between the BSO and TPS samples. These results are

discussed further in the sections below.

Figure 2.5: Water absorption profile for AKD, BSO, and TPS samples.

2.3.2.1 BSO

Figure 2.6: Water absorption at equilibrium for the TPS and BSO samples with 95% confidence intervals.

Shown above in Figure 2.6 are the water absorption results at equilibrium for the BSO

sample with TPS as a reference. The absorption value for TPS (46%) is comparable to

0

10

20

30

40

50

60

0 5 10 15 20 25

Wa

ter

Ab

so

rpti

on

(%

)

Time (days)

AKD

BSO

TPS

0

10

20

30

40

50

60

TPS BSOEq

. W

ate

r A

bs

orp

tio

n (

%)

Sample

28

the literature values which range from 46-62%12,14, depending on starch type and

glycerol content. There was no significant difference in water absorption between the

BSO and TPS samples. A possible explanation for this observation is that Basoplast did

not react with starch under the conditions of this experiment. Therefore, starch was not

hydrophobically modified and the water absorption for the TPS and BSO samples was

equal. Additional experiments must be undertaken in order to determine the reaction

mechanism for Basoplast with starch and the optimal conditions for this reaction. Once

this is known, another experiment may be designed to produce Basoplast modified

TPS.

2.3.2.2 AKD

Figure 2.7: Water absorption at 10 days for the TPS and AKD samples with 95% confidence intervals.

Shown above in Figure 2.7 are the water absorption results for the AKD sample with

TPS as a reference. The AKD sample absorbed less water (35%) than the TPS sample

(48%) with 95% confidence (calculated by t-test; see Appendix A). However, the AKD

sample fell apart after 10 days, before equilibrium was reached. This suggests that the

strength of the AKD reacted sample was lower than the TPS sample, especially under

high relative humidity conditions. These observations are corroborated by a previous

study that showed the tensile strength of cornstarch films was reduced and the

hydrophobicity increased with the addition of AKD13. Therefore, AKD modified TPS

0

10

20

30

40

50

60

TPS AKDWate

r A

bso

rpti

on

, 10d

(%

)

Sample

29

prepared by extrusion exhibits similar water absorption and strength properties as AKD

modified TPS prepared by solution casting.

2.4 Conclusions

An experiment was conducted in order to reduce the water absorption of TPS by

chemical modification with ASA, AKD, and BSO. A large number of unplasticized starch

granules were visible in SEM images of the ASA sample; therefore, ASA inhibited

starch plasticization. Water absorption for the BSO and TPS samples was statistically

equal at 46%. Starch extruded with AKD absorbed 35% water compared with 48% for

the TPS sample after 10 days. However, the strength of the AKD sample was low under

high humidity, and the specimens fell apart before an equilibrium water absorption value

was reached.

30

2.5 References

1. El-Tahlawy, K., Venditti, R. and J. Pawlak. (2008). Effect of alkyl ketene dimer reacted starch on the properties of starch microcellular foam using a solvent exchange technique. Carbohydrate Polymers. 73, 133-142. 2. Angellier, H., Molina-Boisseau, S., Belgacem, M.N. and A. Dufresne. (2005). Surface chemical modification of waxy maize starch nanocrystals. Langmuir. 21, 2425-2433. 3. Bhattacharya, M., Vaidya, U.R., Zhanc, D. and R. Narayan. (1995). Properties of starch and synthetic polymers containing anhydride groups. II. effect of amylopectin to amylose ratio in starch. Journal of Applied Polymer Science. 57, 539-554. 4. Vaidya, U.R. and M. Bhattacharya. (1994). Properties of blends of starch and synthetic polymers containing anhydride groups. Journal of Applied Polymer Science. 52: 617-628. 5. Seethamraju, K., Bhattacharya, M., Vaidya, U.R. and R.G. Fulcher. (1994). Rheology and morphology of starch/synthetic polymer blends. Rheologica Acta. 33, 553-567. 6. Jeon, Y., Viswanathan, A. and R.A. Gross. (1999). Studies of starch esterification: reactions with alkenyl-succinates in aqueous slurry systems. Starch. 51, 90-93. 7. L. Ren et al. (2010). Influence of surface esterification with alkenyl succinic anhydrides on mechanical properties of corn starch films. Carbohydrate Polymers. In Press. 8. Qiao, L., Gu, Q. and H.N. Cheng. (2006). Enzyme-catalyzed synthesis of hydrophobically modified starch. Carbohydrate Polymers. 66, 135-140. 9. R.V. Lauzon. (2002). Method for preparing aqueous size composition. US Patent No. 6,414,055 B1. 10. Athawale, V.D. and S.C. Rathi. (1999). Graft polymerization: starch as a model substrate. Polymer Reviews. 39: 3, 445-480. 11. Mathew, A.P. and A. Dufresne. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules. 3, 1101-1108. 12. Yu, J., Wang, N. and X. Ma. (2005). The effects of citric acid on the properties of thermoplastic starch plasticized by glycerol. Starch. 57, 494-504. 13. Li, X., Shen, Y., Li, G. and X. Lai. (2010). Preparation and properties of hydrophobic starch based biodegradable composite films. Polymeric Materials Science and Engineering. 26:5, 155-157. 14. Mathew, A.P. and A. Dufresne. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules. 3, 1101-1108.

31

Chapter 3 : Extrusion of starch with maleated polyethylene, green

polyethylene, and green polyethylene compatibilized with maleic

anhydride

3.1 Introduction

Some authors have tried to improve the water resistance of TPS by melt-blending

starch with hydrophobic polymers, while maintaining the biodegradability of the overall

product. Hydrophobic and biodegradable polymers such as poly(e-caprolactone)1,

cellulose acetate2, poly(butylene adipate-co-terephthalate)3, and polylactides4 have

shown to be valuable candidates for melt-blending with TPS; however, use of these

biodegradable polymers in commercial applications is restricted by their relatively high

cost and poor mechanical properties compared to commodity plastics such as

polyethylene (PE) and polypropylene. Melt blending of starch with non-biodegradable

polymers such as PE is a good way of improving TPS properties, but PE contents must

be kept low to ensure biodegradability of the blend5. A new form of PE, called green

polyethylene, has recently become available on the market. It is produced from the

renewable material sugarcane; therefore, it seems to be a suitable material to melt-

blend with starch from a marketing (‘green’ materials) and environmental perspective.

Developing melt-blends with satisfactory properties depends on the ability to generate a

small dispersed phase size with strong interfacial adhesion, thereby improving the

stress transfer between the component phases6. This is accomplished by using a

compatibilizer that reacts with the hydroxyl groups of starch to form covalent bonds,

providing interfacial adhesion7. Common compatibilizers used in starch mixtures are

ethyleneeacrylic acid (EAA), maleic anhydride (MAH), and ethylene vinyl alcohol (EVA).

MAH is the most suitable of these compatibilizers because EVA is hydrophilic and the

moisture it attracts is detrimental to TPS’s mechanical properties. Also, a large amount

of EAA is required for compatibilization which becomes costly8. The reactions whereby

MAH reacts with PE to form maleated PE which then reacts with starch are shown

below in Figure 3.1 and Figure 3.2, respectively.

32

Figure 3.1: Reaction of MAH with PE initiated by DCP or BPO5.

Figure 3.2: Reaction of maleated PE with starch5.

Reactive extrusion is the simplest and most cost effective method for carrying out this

two-step reaction. It is a process whereby the reactions in Figure 3.1 and Figure 3.2 are

carried out in a single step at high temperature using an extruder. Combining these two

reactions into a single step eliminates the need for two separate extrusion steps and

therefore reduces energy use and processing costs9. Previous authors have studied the

extrusion of starch with PE and found that blends containing MAH showed higher

tensile strength, elongation at break, and thermal stability than those of blends without

MAH8. However, these authors did not compare extruded starch/PE/MAH with

starch/maleated PE blends and water absorption tests were not conducted.

33

The objective of this chapter was to reduce water absorption in TPS by blending with

polyethylene. PE was melt blended with starch in three different ways, including the

following: reactive extrusion of green polyethylene and starch facilitated by MAH and

DCP, melt blending of green polyethylene and starch by extrusion, and melt blending of

maleated polyethylene and starch by extrusion.

3.2 Experimental

3.2.1 Materials


ON). Glycerol was purchased from ACP Chemicals Inc. (Montreal, QC). Green

polyethylene DA-5800 (GPE) was supplied by Braskem S.A (Sao Paulo, Brazil) and

maleated polyethylene (MPE) by Arkema Inc. (Philadelphia, PA). Maleic anhydride

(MAH) and dicumyl peroxide (DCP) were purchased from Sigma-Aldrich (Oakville, ON).


Starch, glycerol, and water were mixed with a high speed kitchen mixer for 30min. MPE

or GPE, MA, and DCP were added and mixed for an additional 10min. Compositions of

the ten samples prepared are listed below in Table 3.1.


Weight Proportion

Sample Starch Glycerol Water GPE MPE MAH DCP

TPS 100 45 30 0 0 0 0

5GPE 100 45 30 5 0 0 0

10GPE 100 45 30 10 0 0 0

20GPE 100 45 30 20 0 0 0

5MGPE 100 45 30 5 0 0.05 0.005

10MGPE 100 45 30 10 0 0.1 0.01

20MGPE 100 45 30 20 0 0.2 0.02

5MPE 100 45 30 0 5 0 0

10MPE 100 45 30 0 10 0 0

20MPE 100 45 30 0 20 0 0

34

The temperature profile along the extruder barrel (from feed zone to die) is shown below

in Table 3.2. Other extrusion parameters were the same as previously described, see

section 2.2.2.

Table 3.2: Temperature profile used for extrusion.

Zone 1 2 3 4 5 6 7 8 9 10

Temperature (oC)

155 155 155 160 160 160 160 165 170 180

3.2.3 FTIR

An experiment was conducted in order to determine if maleic anhydride reacted with

green polyethylene. GPE was extruded separately at the same processing conditions

and in the presence of MAH and DCP. The extrudate was purified to remove any

unreacted MAH and the purification method was as follows: dissolution of PE in xylene

followed by precipitation in acetone.

3.2.4 SEM

Testing was the same as the previous experiments; see section 2.2.3.

3.2.5 TGA

The thermal properties of the blends were measured with a TGA Q500 type thermal

analyzer purchased from TA Instruments (New Castle, DE). Sample weight varied from

1 to 5 mg. Samples were heated on a platinum pan from ambient temperature to 600°C

at a heating rate of 15°C/min. Results shown for each sample are from a single

measurement. Derivatives of TGA thermograms were obtained using TA Instruments

Universal Analysis software.



35


3.3.1 FTIR

Maleic anhydride, after grafting onto PE, exists in the form of succinic anhydride. In

FTIR spectra the presence of 5 membered anhydride rings, such as succinic anhydride

is shown by a peak in the area of 1790cm-1. If any unreacted MAH remains after the

purification it is shown by the peak at 698cm-1, attributed to the C=C bond in MAH8.

Figure 3.3: FTIR spectrum for GPE and MGPE.

Shown above in Figure 3.3 are the spectra for unreacted green polyethylene and green

polyethylene extruded with MAH and DCP. In the reacted sample, a peak at 1790cm-1

caused by the asymmetrical stretching vibration bond of anhydride groups is present.

This verified the fact that MAH grafted onto GPE in the presence of DCP, and may be

used as compatibilizer in TPS/GPE blends during extrusion. The spectrum for the

unreacted GPE shows no peaks at 1790cm-1 and 698cm-1. This indicates that there are

no anhydride groups in the sample, as expected.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

05001000150020002500300035004000

Ab

so

rba

nc

e U

nit

s

Wavenumber (cm-1)

MGPE

GPE

698cm-1 1790cm-1

36

3.3.2 SEM

Figure 3.4: SEM image of TPS sample.

Shown above in Figure 3.4 is the SEM image for the TPS sample at 100X

magnification. The sample has a smooth surface with some roughness caused by the

physical slicing of the sample in preparation for SEM and some starch granules

remaining unplasticized. The image for the TPS sample is similar to images from

previous studies which show smooth surfaces with some roughness or pits caused by

unplasticized granules10.

Shown below in Figure 3.5 are SEM images of the GPE samples. Some starch particles

remained unplasticized and were removed from the surface of the blends during the

fracture of the specimen, leaving some pits in the fracture surface. These pits are most

clearly visible at 500X magnification in Figure 3.5b. There appears to be phase

separation between starch and GPE in all samples and this is most clearly visible at a

higher GPE content, in Figure 3.5c. Therefore, interfacial adhesion between TPS and

GPE was poor, since a continuous phase was not formed. This result was expected

because PE and starch are structurally dissimilar polymers known to form incompatible

blends5.

37

Figure 3.5: SEM images of extruded samples: (a) 5GPE, (b) 10GPE, (c) 20GPE

Figure 3.6: SEM images of extruded samples: (a) 5MGPE, (b) 10MGPE, (c) 20MGPE

38

Shown above in Figure 3.6 are SEM images of the MGPE samples. As with the GPE

samples, some starch particles remained unplasticized and are visible in the images,

especially in Figure 3.6c. This may be caused by GPE interfering with starch

plasticization during extrusion and could be remedied by feeding GPE from a side

feeder at a later stage on the extruder. In this way, starch will plasticize in the earlier

stages without interference from GPE. With the addition of MAH, TPS and GPE

combined a continuous phase in which the phase interface between TPS and GPE

disappeared. This result shows that the morphology of the blends with MAH was

improved due to the increased compatibility between TPS and GPE.

Figure 3.7: SEM images of MPE samples: (a) 5MPE (b) 10MPE (c) 20MPE

Shown above in Figure 3.7 are SEM images of the MPE samples. Again, some starch

particles remained unplasticized likely from MPE interference as explained above. TPS

and MPE combined in a mostly continuous phase as with the MGPE samples. Again,

this was a result of maleic anhydride improving the compatibility between TPS and PE.

39

3.3.3 TGA

TGA curves for all PE/TPS samples are shown below in Figure 3.8, Figure 3.9, and

Figure 3.10 with PE and TPS as references. In the case of all GPE, MGPE, and MPE

samples, there were three well defined shifts in the TGA curve. First, at around 100oC,

water evaporation and unreacted MAH sublimation (in the case of MGPE) caused the

initial weight loss. Weight loss continued gradually as water continued to evaporate

along with glycerol (starting at 150oC). A second major shift occurred from 300oC to

350oC where the thermal degradation of starch occurred. Finally, the third shift was a

result of PE degradation beginning at 450oC.

Figure 3.8: TGA curves for pure GPE, TPS, and blends of TPS/GPE.

40

Figure 3.9: TGA curves for pure MGPE, TPS, and blends of TPS/MGPE.

Figure 3.10: TGA curves for pure MPE, TPS, and blends of TPS/MPE.

Derivative TGA curves for all PE/TPS samples are shown below in Figure 3.11, Figure

3.12, and Figure 3.13 with PE and TPS as references.

41

Figure 3.11: Derivative TGA curves for pure GPE, TPS, and blends of TPS/GPE.

Figure 3.12: Derivative TGA curves for pure MGPE, TPS, and blends of TPS/MGPE.

42

Figure 3.13: Derivative TGA curves for pure MPE, TPS, and blends of TPS/MPE.

Shown below in Table 3.3 are the data extracted from the derivative TGA curves for all

pure polymers and TPS blends tested.

Table 3.3: Data from derivative TGA curves.

Sample T5% (oC)

Starch Tmax (oC)

PE Tmax (oC)

TPS 182 329 N/A

GPE 337 N/A 388

MGPE 304 N/A 381

MPE 435 N/A 476

5GPE 128 328 470

10GPE 143 330 480

20GPE 123 328 482

5MGPE 97 330 480

10MGPE 163 326 482

20MGPE 199 328 488

5MPE 139 326 482

10MPE 139 326 480

20MPE 145 324 478

43

T5%, the temperature corresponding to 5% weight loss of the sample showed no

discernable trend with respect to amount or type of PE for the GPE and MPE samples.

However, for the MGPE samples the T5% values increased with the amount of PE,

indicating an increase in stability of the blends. Perhaps this trend was not seen for the

GPE and MPE samples because these blends were not as compatible; therefore,

increasing the amount of PE in these samples did not further increase the stability of the

blends because the PE portion was not strongly associated with the less thermally

stable starch portion.

Starch Tmax and PE Tmax values shown above in Table 3.3 correspond to the maximum

rate of degradation for starch and PE, respectively. There was no trend evident in the

starch Tmax values for the blended samples, which all have a Tmax value close to that of

TPS. Therefore, it does not appear that any significant starch degradation occurred in

all three types of TPS/PE blends. PE Tmax values for the MPE blended samples are

similar to the value for pure MPE, indicating no PE degradation occurred.

An interesting phenomenon was observed in the derivative TGA curves for the GPE and

MGPE blended samples. The derivative TGA curves for pure GPE and MGPE displayed

a wide degradation temperature range as a result of the composition of GPE. GPE is a

branched co-polymer of ethene and butane and since it is produced from a natural

source the chain length and branching amount vary considerably, resulting in a wide

range of degradation temperatures. However, in the case of the GPE and MGPE

samples blended with TPS, the degradation temperature range was reduced and shifted

to approximately 480oC from 380oC. One possible explanation is that starch char

remaining in the sample absorbed heat and limited heat transfer to PE, thus increasing

the temperature at which PE degraded.

44


Results from the water absorption testing at 100% RH and room temperature for all PE

samples are shown below in Figure 3.14, Figure 3.15, and Figure 3.16. Raw data and

confidence interval calculations are contained in Appendix B. TPS is shown as a

reference on the plots and the value for TPS water absorption (66%) is comparable to

the literature value (62%) for glycerol plasticized (50wt%) TPS10. Adding polyethylene

had the effect of significantly reducing water absorption below the value of TPS for all

PE samples. This result is explained by the theory for a polymer blend that predicts the

diffusion coefficient and water absorption of a hydrophilic polymer will be reduced when

blended with a hydrophobic polymer (equation 1.7). Also, the water absorption value for

all samples decreased as the amount of PE increased from 5% to 20%, except for the

GMPE sample (discussed below). Again, this observation is explained by equation (1.7)

which predicts the diffusion coefficient and water absorption of a polymer blend will

decrease as the weight fraction of hydrophobic polymer increases.

Figure 3.14: Water absorption at equilibrium for MGPE samples with 95% confidence intervals.

The MGPE samples displayed higher water absorption than the GPE and MPE

samples. A number of possible explanations exist for this observation. It is known that

MAH causes starch destruction at high temperatures8; however, no evidence of starch

destruction was found in the TGA results. Another possible explanation is that MGPE

0

10

20

30

40

50

60

70

80

TPS 5MGPE 10MGPE 20MGPE

Eq

. W

ate

r A

bs

orp

tio

n (

%)

Sample

45

interfered with starch plasticization during extrusion, leaving pits and unplasticized

granules where water can pass through. Evidence for this explanation is provided by the

SEM images which contain more unplasticized granules for the MGPE samples than the

MPE and GPE samples. Also, it is possible that MAH bonded with starch, preventing

starch plasticization. This effect was the most pronounced in the 20MGPE sample since

more PE and MAH was available to interfere with starch plasticization and this may

explain why the 20MGPE sample had higher water absorption than the 10MGPE

sample.

Figure 3.15: Water absorption at equilibrium for GPE samples with 95% confidence intervals.

Figure 3.16: Water absorption at equilibrium for MPE samples with 95% confidence intervals.

0

10

20

30

40

50

60

70

80

TPS 5GPE 10GPE 20GPE

Eq

. W

ate

r A

bs

orp

tio

n

(%)

Sample

0

10

20

30

40

50

60

70

80

TPS 5MPE 10MPE 20MPE

Eq

. W

ate

r A

bs

orp

tio

n

(%)

Sample

46

The MPE samples displayed the lowest average water absorption of all three sample

types tested. These samples exhibited better plasticization and thus lower water

absorption than the MGPE samples. Also, the MPE samples showed better interfacial

adhesion than the GPE samples. Therefore, their water absorption was lower since the

diffusion coefficient equation for polymer blends (equation 1.7) contains a term for the

activation energy (related to interfacial adhesion) of the blend. When the activation

energy of the blend is reduced, the interfacial adhesion and water resistivity will

improve.

3.4 Conclusions

An experiment was conducted in order to determine which method of melt blending TPS

with PE (reactive extrusion of GPE and TPS facilitated by MAH and DCP, melt blending

of GPE and TPS by extrusion, and melt blending of MPE and TPS by extrusion) was the

most effective at reducing water absorption. It was found that all methods reduced the

water absorption of TPS significantly. However, the GPE/TPS samples showed poor

interfacial adhesion and the MGPE/TPS samples had higher water absorption due to

some starch remaining unplasticized.

47

3.5 References

1. Averous, L., Moro, L., Dole, P. and C. Fringant. (2000). Properties of thermoplastic blends: starch–polycaprolactone. Polymer. 41, 4157-4167. 2. R.L. Shogren. (1996). Preparation, thermal properties, and extrusion of high-amylose starch acetates. Carbohydrate Polymers. 29:1, 57-62. 3. Nabar, Y., Raquez, J.M., Dubois, P. and R. Narayan. (2005). Production of starch foams by twin-screw extrusion: effect of maleated poly(butylene adipate-co-terephthalate) as a compatibilizer. Biomacromolecules. 6, 807-817. 4. Dubois, P. and R. Narayan. (2003). Biodegradable compositions by reactive processing of aliphatic polyester/polysaccharide blends. Macromolecular Symposium. 198, 233-243. 5. Kalambur, S. and S. Rivzi. (2006). An overview of starch-based plastic blends from reactive extrusion. Journal of Plastic Film and Sheeting. 22:39, 39-58. 6. Barlow, J.W. and D. R. Paul. (1984). Mechanical compatibilization of immiscible blends. Polymer Engineering and Science. 24:8, 525-534. 7. J.M. Raquez et al. (2008). Maleated thermoplastic starch by reactive extrusion. Carbohydrate Polymers. 74, 159-169. 8. Shujun, W., Jiugao, Y. and Y. Jinglin. (2005). Preparation and characterization of compatible thermoplastic starch/polyethylene blends. Polymer Degradation and Stability. 87, 395-401. 9. J.M. Raquez et al. (2006). Biodegradable materials by reactive extrusion: from catalyzed polymerization to functionalization and blend compatibilization. C. R. Chimie. 9, 1370-1379. 10. Mathew, A.P. and A. Dufresne. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules. 3, 1101-1108.

48

Chapter 4 : Extrusion of starch with beeswax, paraffin wax, and

paraffin wax compatibilized with maleic anhydride

4.1 Introduction

Waxes are hydrophobic organic compounds often used for waterproofing purposes in

applications such as wax paper and wood composites1. However, melt-blending of

waxes with TPS has not been investigated in the literature, despite the existence of

research into melt-blending TPS with other hydrophobic polymers, such as

poly(butylene adipate-co-terephthalate)2, and polylactides3, polyethylene4, etc. This

chapter investigates the potential for two common waxes, paraffin wax and beeswax, to

be melt-blended with TPS in order to improve its water resistance.

Beeswax is a natural, hydrophobic, and biodegradable wax produced in the beehive by

honey bees. The chemical nature of beeswax is basically lipoid, with the major

components being 14% hydrocarbons, 35% monoesters, 3% diesters, and 12% free

acids5. Previous studies on melt-blending esters with TPS have found that the mixtures

are immiscible; however, they form compatible blends as a result of the hydrogen

bonding interaction between the ester carbonyl group and the OH groups on starch6.

Therefore, beeswax may form a compatible blend with TPS as a result of hydrogen

bonding interaction and compatibilizers such as maleic anhydride (MAH) are not

required.

Paraffin wax is a petroleum derived wax composed of a mixture of alkanes ranging from

20 to 40 carbon chain-length. In order to improve the compatibility between starch and

paraffin wax, a compatibilizer such as MAH must be used when they are melt-blended.

The maleation reaction of paraffin wax has been studied in the literature7 and is shown

below in Figure 4.1. Once the MAH group is attached, the maleated paraffin wax will

react with starch in a similar fashion to maleated polyethylene, as shown in Chapter 3,

Figure 3.2.

49

Figure 4.1: Reaction scheme for grafting maleic anhydride onto paraffin wax7.

In this chapter, beeswax was melt-blended with starch by extrusion. Also, paraffin wax

was melt-blended with starch in two different ways, including reactive extrusion with

starch facilitated by MAH and DCP, and melt blending with starch by extrusion. The

objective of this chapter was to determine which type of wax (paraffin or beeswax) and

which method of melt blending starch/paraffin wax most effectively reduces the water

absorption of TPS.

4.2 Experimental

4.2.1 Materials


ON). Glycerol was purchased from ACP Chemicals Inc. (Montreal, QC). Beeswax (BW),

paraffin wax (PW, Tm = 80-90oC), maleic anhydride (MAH), and dicumyl peroxide (DCP)

were purchased from Sigma-Aldrich (Oakville, ON).

50


Starch and glycerol were mixed with a high speed kitchen mixer for 30min. BW or PW

or PW, MAH, and DCP were added and mixed for an additional 10min. The

compositions of ten samples prepared are listed below in Table 4.1.


Weight Proportion

Sample Starch Glycerol Water BW PW MAH DCP

TPS 100 45 30 0 0 0 0

5BW 100 45 30 5 0 0 0

10BW 100 45 30 10 0 0 0

20BW 100 45 30 20 0 0 0

5PW 100 45 30 0 5 0 0

10PW 100 45 30 0 10 0 0

20PW 100 45 30 0 20 0 0

5MPW 100 45 30 0 5 0.05 0.005

10MPW 100 45 30 0 10 0.1 0.01

20MPW 100 45 30 0 20 0.2 0.02

Extrusion parameters and conditions were the same as the previous experiment, see

section 3.2.2.

4.2.3 FTIR

An experiment was conducted in order to determine if maleic anhydride reacted with

paraffin wax. Paraffin wax was extruded separately at the same processing conditions

and in the presence of MAH and DCP. The extrudate was purified to remove any

unreacted MA and the purification method was as follows: dissolution of PW in boiling

water for 10min, followed by vacuum filtration.

4.2.4 SEM


4.2.5 TGA

Testing was the same as the previous experiment; see section 3.2.5.

51





During the extrusion of starch with wax at 20% concentration, wax leaked from the

extruder at the vacuum ports and side feeder port. At the temperatures used for

extrusion, the viscosity of wax is very low; therefore, it leaked from any point on the

extruder open to the atmosphere. This was not a problem for the 5% and 10% wax

samples so the characterization was completed for those samples.

4.3.2 FTIR

Maleic anhydride, after grafting onto the polymer, exists in the form of succinic

anhydride. In FTIR spectra the presence of 5 membered anhydride rings, such as

succinic anhydride is shown by a peak in the area of 1790cm-1. If any unreacted MAH

remains after the purification it is shown by the peak at 698cm-1, attributed to the C=C

bond in MAH.

Figure 4.2: FTIR spectrum for PW and MPW.

Shown above in Figure 4.2 are the spectra for unreacted paraffin wax and maleated

paraffin wax. The spectrum for the unreacted wax shows no peaks at 1790cm-1 and

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

01000200030004000

Ab

so

rba

nc

e U

nit

s

Wavenumber (cm-1)

PW

MPW1790cm-1 698cm-1

52

698cm-1. This indicates that there was no succinic anhydride or maleic anhydride in the

sample, as expected. The spectrum for reacted wax shown above contains a peak at

1790cm-1 and no peak at 698 cm-1. This indicates that MAH grafted onto the wax in the

form of succinic anhydride and any excess MAH was successfully removed by

purification.

4.3.3 SEM

Figure 4.3: SEM images of extruded samples: (a) 5BW (b) 10BW

Shown above in Figure 4.3 are SEM images of the BW samples. Some starch particles

remained unplasticized and were removed from the surface of the blends during the

fracture of the specimen, leaving some pits in the fracture surface (visible in Figure

4.3a). Therefore, BW may have interfered with starch plasticization in the same way PE

did in Chapter 3. There appears to be phase separation between TPS and BW in both

samples and this is most clearly visible at a higher BW content, in Figure 4.3b.

Therefore, interfacial adhesion between TPS and BW was poor, since a continuous

phase was not formed. A compatibilizer may be required in order to improve the

interfacial adhesion between BW and TPS, and hence the morphology.

53

Figure 4.4: SEM images of extruded samples: (a) 5PW (b) 10PW (c) 5MPW (d) 10MPW

Shown above in Figure 4.4 are SEM images of the PW and MPW samples. Some

starch particles remained unplasticized and are visible in the images which may be

caused by wax interfering with starch plasticization during extrusion. Also, cracks

caused by retrogradation or damage by the electron beam are visible in all samples. It

appears that TPS and wax combined in a continuous phase with no interface visible in

both the PW and MPW samples. Therefore, adding MAH as a compatibilizer does not

have an effect on the morphology of the blends.

4.3.4 TGA

TGA curves for all wax/TPS samples are shown below in Figure 4.5, Figure 4.6, and

Figure 4.7 with wax and TPS as references. In the case of all BW, PW, and MPW

samples, there were two well defined shifts in the TGA curve. First, at around 100oC,

water evaporation caused the initial weight loss. Weight loss continued gradually as

water continued to evaporate along with glycerol (starting at 150oC), and then wax (at

54

150-200oC). A second major shift occurred from 300oC to 350oC where the thermal

degradation of starch occurred.

Figure 4.5: TGA curves for pure BW, TPS, and blends of TPS/BW.

Figure 4.6: TGA curves for pure PW, TPS, and blends of TPS/PW.

55

Figure 4.7: TGA curves for pure MPW, TPS, and blends of TPS/MPW.

Derivative TGA curves for all wax/TPS samples are shown below in Figure 4.8, Figure

4.9, Figure 4.10 and with wax and TPS as references.

Figure 4.8: Derivative TGA curves for pure BW, TPS, and blends of TPS/BW.

56

Figure 4.9: Derivative TGA curves for pure PW, TPS, and blends of TPS/PW.

Figure 4.10: Derivative TGA curves for pure MPW, TPS, and blends of TPS/MPW.

Shown below in Table 4.2 are the data extracted from the derivative TGA curves for all

pure polymers and TPS blends tested.

57

Table 4.2: Data from derivative TGA curves.

Sample T5% (oC)

Starch Tmax (oC)

Wax Tmax (oC)

TPS 182 329 N/A

BW 235 N/A 372

PW 179 N/A 232

MPW 209 N/A 260

5BW 157 332 N/A

10BW 151 332 N/A

5PW 159 328 N/A

10PW 179 328 N/A

5MPW 176 328 N/A

10MPW 167 328 N/A

T5%, the temperature corresponding to 5% weight loss of the sample was greater for the

PW and MPW blends than the BW blends, despite the values for pure PW and MPW

being lower than that of BW. This indicates that these samples were more stable than

the BW samples because they form more compatible blends with TPS, as shown in the

SEM images. There was no trend evident in the starch Tmax values for the blended

samples, which all have a Tmax value close to that of TPS. Therefore, it does not appear

that any significant starch degradation occurred in the BW, PW, or MPW samples. It

was not possible to analyze wax Tmax values because of degradation overlapping with

TPS.


Shown below in are Figure 4.11, Figure 4.12, and Figure 4.13 are the water absorption

results for all TPS/wax blended samples with TPS as a reference. Raw data and

confidence interval calculations are contained in Appendix C. The value for TPS water

absorption (66%) is comparable to the literature value (62%) for glycerol plasticized

(50wt%) TPS8.

58

Figure 4.11: Water absorption at equilibrium for BW samples with 95% confidence intervals.

Shown above in Figure 4.11 are the water absorption results for TPS blended with

beeswax. The average water absorption values decrease when beeswax is added to

TPS and continue to decrease as the concentration of beeswax increases from 5 to

10%. This result is explained by the diffusion coefficient theory for polymer blends

(equation 1.7) which predicts the water absorption for a hydrophilic polymer will

decrease when a hydrophobic polymer is added and when the concentration of that

hydrophobic polymer increases. However, the reduction in water absorption is not

statistically significant for either the 5BW or 10BW sample. This may be a result of the

sample preparation method used. When the samples were pressed at high temperature,

some of the wax migrated out of the samples because of its low viscosity. Therefore,

the water absorption of the extruded blends may be lower than the values reported here

for the hot pressed samples.

0

10

20

30

40

50

60

70

80

TPS 5BW 10BWEq

. W

ate

r A

bs

orp

tio

n (

%)

Sample

59

Figure 4.12: Water absorption at equilibrium for PW samples with 95% confidence intervals.

Figure 4.13: Water absorption at equilibrium for MPW samples with 95% confidence intervals.

Shown above in Figure 4.12 and Figure 4.13 are the water absorption results for TPS

blended with paraffin wax and paraffin wax with MAH, respectively. The average water

absorption values decrease when paraffin wax is added to TPS as explained by the

diffusion coefficient theory for polymer blends (equation 1.7). Contrary to the BW

samples, the reduction in water absorption is statistically significant for both the PW and

MPW samples. This indicates that paraffin wax more effectively reduces water

0

10

20

30

40

50

60

70

80

TPS 5PW 10PW

Eq

. W

ate

r A

bs

orp

tio

n (

%)

Sample

0

10

20

30

40

50

60

70

80

TPS 5MPW 10MPWEq

. W

ate

r A

bs

orp

tio

n (

%)

Sample

60

absorption in TPS. An explanation for this comes from the chemical structures of

paraffin wax and beeswax. Paraffin wax contains only hydrocarbon chains, whereas

beeswax contains water attracting groups such as esters. Therefore, beeswax and its

blends with TPS will be more hydrophilic than paraffin wax and its blends with TPS.

The water absorption values for all PW and MPW samples are statistically equal with

95% confidence. Therefore, using MAH as a compatibilizer had no effect on the water

absorption of the blends since paraffin wax formed a compatible blend with TPS when

no compatibilizer was used. Also, increasing the concentration of wax from 5 to 10% did

not reduce the water absorption of the samples. Again, this may be a result of the

sample preparation method used or loss of wax during extrusion.

4.4 Conclusions

An experiment was conducted in order to determine whether beeswax or paraffin wax

(with and without MAH) most effectively reduced water absorption when melt-blended

with TPS. It was found that paraffin wax blends with TPS absorbed less water than

beeswax blends due to paraffin wax’s greater hydrophobicity than beeswax. Also, the

use of MAH as a compatibilizer between paraffin wax and TPS did not improve the

morphology or water absorption. Wax loss from openings on the extruder became a

problem for greater than 10% wax content samples. Additionally, the 10% wax content

samples showed no significant improvement in water absorption values compared with

5% wax content samples.

61

4.5 References

1. Kamke, F.A. and T.R. Miller. (2006). Enhancing composite durability using resins and waxes – a review. Wood Protection Conference. New Orleans, LA. 2. Nabar, Y., Raquez, J.M., Dubois, P. and R. Narayan. (2005). Production of starch foams by twin-screw extrusion: effect of maleated poly(butylene adipate-co-terephthalate) as a compatibilizer. Biomacromolecules. 6, 807-817. 3. Dubois, P. and R. Narayan. (2003). Biodegradable compositions by reactive processing of aliphatic polyester/polysaccharide blends. Macromolecular Symposium. 198, 233-243. 4. Shujun, W., Jiugao, Y. and Y. Jinglin. (2005). Preparation and characterization of compatible thermoplastic starch/polyethylene blends. Polymer Degradation and Stability. 87, 395-401. 5. J.J. Jiminez et al. (2004). Quality assurance of commercial beeswax. Part I. Gas chromatography – electron impact ionization mass spectrometry of hydrocarbons and monoesters. Journal of Chromatography A. 1024: 147-154. 6. B.Y. Shin et al. (2004). Rheological, mechanical and biodegradation studies on blends of thermoplastic starch and polycaprolactone. Polymer Engineering and Science. 44:8, 1429-1438. 7. Krump, H., Alexy, P. and A.S. Luyt. (2005). Preparation of a maleated fischer-tropsch paraffin wax and ftir analysis of grafted maleic anhydride. Polymer Testing. 24, 129-135. 8. Mathew, A.P. and A. Dufresne. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules. 3, 1101-1108.

62

Chapter 5 : Extrusion of citric acid/glycerol and sorbitol/glycerol co-

plasticized starch

5.1 Introduction

Plasticizers are essential for processing starch into a thermoplastic material and have

an effect on material properties such as water resistivity, glass transition temperature,

strength, and elongation. Glycerol is the most common plasticizer used for starch;

however, it contains a high amount of end hydroxyl groups, making glycerol plasticized

starch very hydrophilic. Alternative plasticizers such as xylitol1, sorbitol1, maltitol1, urea2,

formamide2, and sugars3 have been studied in order to improve water resistivity and

other material properties of TPS. In this chapter, sorbitol and citric acid were

investigated as alternative plasticizers to glycerol.

Sorbitol is a biodegradable sugar alcohol commonly used as a sugar substitute and has

been studied as a plasticizer for starch. Sorbitol plasticized starch was found to have

reduced water absorption and greater tensile strength compared with glycerol

plasticized starch. However, at high relative humidity a significant drop in tensile

strength properties was observed4. Therefore, in this chapter sorbitol plasticized starch

was blended with polyethylene and paraffin wax in order to improve its strength

properties at a high relative humidity.

Citric acid is a natural and biodegradable organic acid found in a variety of fruits and

vegetables. It is commonly used to impart hydrophobicity to starch by a cross-linking

reaction, shown below in Figure 5.1. Yu et al.5 studied the properties of glycerol

plasticized TPS modified by citric acid and found that the addition of a small amount

(0.6-3% w/w starch) of citric acid improved the water resistance of TPS at a high relative

humidity.

63

Figure 5.1: Reaction scheme of citric acid with starch6.

Citric acid has also been added to starch as plasticizer (up to 40% w/w starch) in

glycerol/citric acid co-plasticized TPS7. It forms hydrogen bonds with starch molecules

and in the same way as polyols. However, the effect of adding a high percentage of

citric acid on the water absorption and tensile properties of TPS is currently unknown.

In this chapter, starch was plasticized with glycerol, sorbitol, citric acid, and mixtures of

these plasticizers. Also, a blend of glycerol/sorbitol plasticized starch with hydrophobic

polymers (polyethylene and paraffin wax) was prepared. The objective of this chapter

was to determine which plasticizer was most capable of reducing water absorption in

TPS.

5.2 Experimental

5.2.1 Materials


ON). Glycerol was purchased from ACP Chemicals Inc. (Montreal, QC) and maleated

64

polyethylene (MPE) from Arkema Inc. (Philadelphia, PA). Paraffin wax (PW) and sorbitol

(SOR) were purchased from Sigma-Aldrich (Oakville, ON) and citric acid (CA) from

Caledon Labs (Georgetown, ON).


Starch, water, and plasticizers were mixed with a high speed kitchen mixer for 30min.

Where citric acid and/or sorbitol were used, they were first dissolved in the water. When

BW and MPE were added, they were mixed in for an additional 10min. The

compositions of ten samples prepared are listed below in Table 5.1.


Weight Proportion

Sample Starch Glycerol Water CA SOR MPE PW

TPS 100 45 30 0 0 0 0

20SOR 100 25 30 0 20 0 0

30SOR 100 15 30 0 30 0 0

45SOR 100 0 30 0 45 0 0

20CA 100 25 30 20 0 0 0

30CA 100 15 30 30 0 0 0

45CA 100 0 30 45 0 0 0

SORBLEND 100 20 30 0 20 5 5

Extrusion parameters and conditions were the same as the previous experiment, see

section 3.2.2.

5.2.3 SEM




5.2.5 Mechanical Testing

The mechanical behaviour of the TPS samples was analyzed according to ASTM D-638

using an Instron 3367 testing machine in tensile mode, with a load cell of 1kN capacity.

Thin film specimens were prepared by hot pressing for 4min at 160oC and 500kPa using

65

a model ARG-450 hydraulic press supplied by Dieffenbacher N.A. Inc. (Windsor, ON).

Next, the specimens were cut using a die machined to the specifications for type V

samples in ASTM D-638. Samples were conditioned at 0% relative humidity for 48h.

The gap between pneumatic jaws at the start of each test was adjusted to 25mm and all

samples were strained at 2.5mm/min. The average values of the Young’s modulus,

strength, and elongation at break were calculated from at least 5 measurements.



Samples TPS, 20SOR, 20CA, and SORBLEND were plasticized well in the extruder at

the conditions listed in the experimental section above. However, it was only possible to

extrude the other samples at very high temperatures (~200oC). This was due to a

number of reasons. Firstly, citric acid and sorbitol have been shown to be less effective

plasticizers than glycerol because they have less OH groups per unit weight. Therefore,

the samples were not as well plasticized and did not flow as well in the extruder and the

temperature was increased to reduce their viscosity. At these temperatures, starch

degradation was a problem and most of the extruded plastic was burned. For this and

reason, the samples 30SOR, 45SOR, 30CA, and 45CA were not tested for water

absorption and mechanical properties.

5.3.2 SEM

Images for the citric acid/glycerol and sorbitol/glycerol plasticized samples are shown

below in Figure 5.2 and Figure 5.3, respectively. The 20CA, 20SOR, 30CA, and 30SOR

samples have smooth surfaces with some unplasticized granules visible. These images

are similar to images from previous studies for glycerol plasticized starch1. Therefore,

both citric acid and sorbitol were effective plasticizers when combined with glycerol in

the proportions tested. However, starch particles remained mostly unplasticized when

only citric acid or sorbitol was used as plasticizer, as shown in Figure 5.2c and Figure

5.3c. Starch was not fully plasticized in these samples because both sorbitol and citric

acid are less effective plasticizers than glycerol. They are less effective because they

have less OH groups per unit mass than glycerol and some of these groups are less

66

accessible because of their chemical structure. Therefore, complete plasticization of

starch was not possible with 45% citric acid or sorbitol used as plasticizers.

Sorbitol/glycerol plasticized starch was extruded with paraffin wax and maleated

polyethylene in order to determine how well it melt-blended with hydrophobic polymers.

A SEM image of the extruded sample is shown below in Figure 5.3d. The sample

surface was smooth with no unplasticized starch particles visible. Also, there was no

phase separation visible; therefore, the blend appears to be compatible. The image is

similar to those from compatible blends of glycerol plasticized starch and polyethylene8.

Figure 5.2: SEM images of extruded samples: (a) 20CA (b) 30CA (c) 45CA

67

Figure 5.3: SEM images of extruded samples: (a) 20SOR (b) 30SOR (c) 45SOR (d) SORBLEND


One citric acid plasticized sample was prepared for water absorption testing, 20CA.

After 48 hours all specimens turned into a paste that could not be removed from trays in

the desiccator in order to take weight measurements. Previous studies show that both

the tensile strength of TPS and the molecular weight of starch decrease as the

percentage of citric acid increases7. For these samples with a high percentage of citric

acid, it is likely that starch polymer-polymer interactions were weakened by chain

shortening. Placing the samples in a high relative humidity environment further reduced

the strength of the samples to the point where they were no longer able to remain

coherent.

Shown below in Figure 5.4 are the water absorption results for the sorbitol/glycerol

plasticized samples with glycerol plasticized TPS as a reference. Raw data and

confidence interval calculations are contained in Appendix D. The value for TPS water

68

absorption (66%) is comparable to the literature value (62%) for glycerol plasticized

(50wt%) TPS4. The glycerol/sorbitol co-plasticized sample, 20SOR, exhibits lower water

absorption (50%) than the TPS sample. An explanation for this was proposed in the

literature based on the chemical structure of polyol plasticizers. The amount of end

hydroxyl groups is greater for glycerol than sorbitol and these groups have an affinity for

and are more accessible to water4. Therefore, the water absorption of glycerol

plasticized starch will be greater than that of sorbitol or sorbitol/glycerol plasticized

starch.

Figure 5.4: Water absorption at equilibrium for sorbitol plasticized samples with 95% confidence intervals.

Adding paraffin wax and polyethylene had the effect of further reducing water

absorption to 39% in glycerol/sorbitol co-plasticized starch. This result was explained by

the theory for a polymer blend that predicts the diffusion coefficient and water

absorption of a hydrophilic polymer will reduced when blended with a hydrophobic

polymer (equation 1.7).

5.3.4 Mechanical Testing

Shown below in Figure 5.5 are the stress-strain curves for the TPS, 20SOR, and

SORBLEND samples. The data obtained from these curves is summarized below in

Table 5.2 and found in Appendix D. The TPS sample exhibits high elongation (εb) with

0

10

20

30

40

50

60

70

80

TPS 20SOR SORBLENDEq

. W

ate

r A

bso

rpti

on

(%

)

Sample

69

low tensile strength (σmax) and modulus (E). On the other hand, the 20SOR and

SORBLEND samples exhibit high tensile strength and modulus with low elongation. The

increase in brittleness and strength of the 20SOR and SORBLEND samples was likely

due to the increase in Tg for sorbitol plasticized starch compared with glycerol

plasticized starch1.

Figure 5.5: Stress-strain curves for extruded samples.

As shown below in Table 5.2, the results obtained for the TPS sample correspond

reasonably well with published literature values. Literature values are not available for

glycerol/sorbitol co-plasticized starch and its mixtures with hydrophobic polymers;

however, it has been previously demonstrated that sorbitol plasticized starch has

greater strength, modulus, and lower elongation than glycerol plasticized starch1.

Therefore, the results shown here are in agreement with previous studies.

TPS

20SOR

SORBLEND

0

4

8

12

16

20

0 10 20 30 40 50 60 70 80 90

Str

ess (

MP

a)

Strain (%)

70

Table 5.2: Mechanical properties of TPS blends and pure polymers with literature values for comparison.

Sample σmax

(MPa)

Lit. σmax

(MPa)

E

(MPa)

Lit. E

(MPa)

εb

(%)

Lit. εb

(%)

TPS 2.70±0.73 4.81±0.35 26.4±8.8 381 73.2±7.9 85±165

20SOR 17.3±2.5 N/A 663±166 N/A 13.5±6.4 N/A

SORBLEND 12.5±1.3 N/A 619±127 N/A 11.4±4.6 N/A

MPE 23.7±1.6 N/A 897±87 N/A 168 N/A

PW N/A 0.7699 N/A N/A N/A 1.158

The SORBLEND sample exhibits slightly reduced properties when compared with the

20SOR sample. This may be caused by two reasons. The first is that blending with MPE

and PW will reduce the strength of the blend by the rule of mixtures10, since their

average strength is less than that of 20SOR. Secondly, adding these polymers may

interfere with starch plasticization during extrusion, as discussed previously in Chapter

3.

5.4 Conclusions

An experiment was conducted in order to determine whether sorbitol and/or citric acid

were effective in reducing the water absorption of TPS. It was found that citric

acid/glycerol co-plasticized starch samples lost their coherence when placed in high

humidity conditions due to starch degradation by citric acid. Glycerol/sorbitol co-

plasticized starch had significantly lower water absorption than glycerol plasticized

starch, 50% compared with 66%. By adding a small amount of hydrophobic polymers,

polyethylene and paraffin wax, the water absorption was further reduced to 39%. Also,

the strength and modulus of TPS was improved by plasticizing with sorbitol, however

the elongation at break was reduced.

71

5.5 References

1. Mathew, A.P. and A. Dufresne. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules. 3, 1101-1108. 2. Ma, X. and J. Yu. (2004). The plasticizers containing amide groups for thermoplastic starch. Carbohydrate Polymers. 57, 197-203. 3. Barrett, A., Kaletunc, G., Rosenburg, S. and K. Breslauer. (1995). The effect of sucrose on the structure, mechanical strength and thermal properties of corn extrudates. Carbohydrate Polymers. 26, 261-269. 4. Mathew, A.P. and A. Dufresne. (2002). Plasticized waxy maize starch: effect of polyols and relative humidity on material properties. Biomacromolecules. 3, 1101-1108. 5. Yu, J., Wang, N. and X. Ma. (2005). The effects of citric acid on the properties of thermoplastic starch plasticized by glycerol. Starch. 57, 494-504. 6. R. N. Tharanathan. (2005). Starch – value addition by modification. Critical reviews in Food Science and Nutrition. 45, 371-384. 7. R. Shi et al. (2007). Characterization of citric acid/glycerol co-plasticized thermoplastic starch by melt blending. Carbohydrate Polymers. 69: 748-755. 8. Shujun, W., Jiugao, Y. and Y. Jinglin. (2005). Preparation and characterization of compatible thermoplastic starch/polyethylene blends. Polymer Degradation and Stability. 87, 395-401. 9. Asadchii, O., Votlokhin, B., Bogdanov, N., and V. Gladyshev. (1979). Determination of tensile strength of paraffin waxes. Chemistry and Technology of Fuels and Oils. 15:10, 768-770. 10. M. Alger. (1997). Polymer science dictionary. Chapman & Hall, London, UK.

72

Chapter 6 : Conclusions and Recommendations

In summary, the major conclusions of this research thesis were the following:

1. 15% ASA inhibited starch plasticization. The 15% BSO sample did not reduce water

absorption compared with the control TPS sample. The 15% AKD sample absorbed

35% water compared with 48% for the TPS control sample after 10 days.

2. TPS plasticized with 45% glycerol absorbed 66% water at equilibrium in 100% RH.

3. TPS with 20% green PE, green PE with MAH, and maleated PE absorbed 42%,

52%, and 39% water, respectively.

4. TPS with 5% paraffin and maleated paraffin wax absorbed 54% and 56% water,

respectively. TPS with beeswax did not reduce water absorption below 66%.

5. Citric acid plasticized TPS samples lost all strength when placed in 100% RH. 20%

sorbitol plasticized TPS had 50% water absorption. 20% sorbitol plasticized TPS

with 5% polyethylene and 5% paraffin wax absorbed 39% water.

Recommendations based on the conclusions of this thesis include the following:

1. Investigate TPS blends with green polyethylene at higher percentages of green

polyethylene than used in this thesis. These blends may have lower water

absorption and stronger mechanical properties.

2. Investigate novel plasticizers for starch which are capable of producing TPS with low

water absorption.

3. Investigate novel applications for TPS such as drug delivery1, tissue engineering1,

electroactive polymers2, shape memory polymers3, and solid polymer electrolytes4.

73

6.1 References

1. E. Piskin. (2002). Biodegradable polymers in medicine. In G. Scott (Ed.), Degradable polymers: principles and applications. Dordrecht: Kluwer. 2. Finkenstadt, V. L., and J.L. Willett. (2004). Electroactive materials composed of starch. Journal of Polymers and the Environment. 12:2, 43-46. 3. Vechambre, C., Chaunier, L., and D. Lourdin. (2010). A novel shape-memory material based on potato starch. Macromolecular Material and Engineering. 295, 115-122. 4. Ma, X., Yu, J., and K. He. (2006). Thermoplastic starch plasticized by glycerol as solid polymer electrolytes. Macromolecular Materials Engineering. 291, 1407-1413.

74

Appendix A : Chapter 2 Data and Statistics

A.1 Water Absorption Data

The weight data and calculated water absorption values for all samples in Chapter 2 are

shown in the tables below.

Table A.1: Water absorption weight data for TPS sample.

Weight (g) at specified time (days)

Specimen 0d 1.1d 2d 4d 6d 10d 14d 24d

1 1.0562 1.3390 1.4554 1.5698 1.5590 1.5820 1.5512 1.5445

2 1.3850 1.7658 1.8326 2.0376 2.0120 2.0545 1.9965 2.0288

3 1.7988 2.2295 2.3365 2.6242 2.6440 2.6813 2.6488 2.6472

4 1.7461 2.1825 2.3086 2.5636 2.5352 2.6005 2.5489 2.5592

5 1.1854 1.4678 1.5271 1.6320 1.7128 1.7313 1.7152 1.7007

Table A.2: Calculated water absorption values for TPS sample.

Water absorption (%) at specified time (days)


1 0 26.775 37.795 48.627 47.604 49.782 46.866 46.231

2 0 27.494 32.317 47.119 45.270 48.339 44.151 46.483

3 0 23.943 29.892 45.886 46.986 49.060 47.253 47.164

4 0 24.992 32.214 46.818 45.192 48.931 45.976 46.566

5 0 23.823 28.825 37.675 44.491 46.051 44.693 43.470

75

Table A.3: Water absorption weight data for AKD sample.


Specimen 0d 1.1d 2d 4d 6d 10d

1 1.0552 Specimen Lost

2 1.2671 1.6423 1.7026 1.6326 1.7379 1.6892

3 1.6348 2.0332 2.1531 2.2803 2.3652 2.2684

4 1.4123 1.7686 1.8592 1.9153 2.0036 1.9164

5 1.3804 1.6707 1.7572 1.8864 1.9314 1.8013

Table A.4: Calculated water absorption values for AKD sample.


Specimen 0d 1.1d 2d 4d 6d 10d

1 0 Specimen Lost

2 0 29.610 34.369 28.845 37.155 33.312

3 0 24.369 31.704 39.484 44.678 38.757

4 0 25.228 31.643 35.615 41.867 35.693

5 0 21.030 27.296 36.656 39.915 30.491

Table A.5: Water absorption weight data for BSO sample.



1 1.4237 1.8101 1.9825 2.0921 2.1144 2.0950 2.0647 2.0681

2 2.0920 2.8027 2.7638 3.0673 3.1095 3.0900 3.0580 3.0617

3 2.1582 2.7301 2.8344 3.0407 3.1620 3.1464 3.1061 3.1298

4 2.2286 2.8714 2.9549 3.2272 3.2643 3.2590 3.2141 3.2407

5 2.1949 2.7471 3.0012 3.1298 3.2306 3.2179 3.1918 3.2029

76

Table A.6: Calculated water absorption values for BSO sample.



1 0 27.140 39.249 46.948 48.514 47.151 45.023 45.262

2 0 33.972 32.112 46.620 48.637 47.705 46.175 46.352

3 0 26.498 31.331 40.890 46.510 45.788 43.920 45.019

4 0 28.843 32.589 44.808 46.473 46.235 44.220 45.414

5 0 25.158 36.735 42.594 47.186 46.608 45.418 45.924

A.2 Statistical Analysis

Calculating the average water absorption at equilibrium and its confidence interval:

The TPS sample is used for this sample calculation. Calculating the mean

∑

Calculating the variance

∑

[

]

Calculating the confidence interval

√

√

77

Where ν = n-1 = 4, α=0.05 for 95% confidence and values of the student t distribution were obtained from: http://www.statsoft.com/textbook/distribution-tables/

√

√

This represents the 95% confidence interval on the mean water absorption for the TPS sample. The confidence intervals for all other samples were calculated and are shown in the table below.

Table A.7: Average water absorption values with confidence limits.

Sample Average Water Absorption (%)

Lower CL (%)

Upper CL (%)

TPS 45.983 44.188

47.778

AKD 34.563 28.974

40.152

BSO 45.594 44.926

46.262

78

Appendix B : Chapter 3 Data and Statistics

B.1 Water Absorption Data



Table B.1: Water absorption weight data for TPS sample.


Specimen 0d 0.9d 5d 6d 10d

1 1.43 2.04 2.37 2.36 2.36

2 1.60 2.41 2.80 2.76 2.75

3 1.20 1.69 1.99 1.97 1.95

4 1.58 2.26 2.65 2.63 2.65

5 1.55 2.21 2.61 2.57 2.56

Table B.2: Calculated water absorption values for TPS sample.



1 0 42.7 65.7 65.0 65.0

2 0 50.6 75.0 72.5 71.9

3 0 40.8 65.8 64.2 62.5

4 0 43.0 67.7 66.5 67.7

5 0 42.6 68.4 65.8 65.2

79

Table B.3: Water absorption weight data for 5GPE sample.


Specimen 0d 1d 2d 4d 8.1d

1 1.80 2.26 2.47 2.67 2.66

2 1.82 2.31 2.48 2.70 2.68

3 1.63 2.07 2.23 2.42 2.40

4 2.43 3.04 3.26 3.64 3.61

5 2.60 3.30 3.58 3.94 3.90

Table B.4: Calculated water absorption values for 5GPE sample.



1 0 25.6 37.2 48.3 47.8

2 0 26.9 36.3 48.4 47.3

3 0 27.0 36.8 48.5 47.2

4 0 25.1 34.2 49.8 48.6

5 0 26.9 37.7 51.5 50.0




1 1.84 2.33 2.57 2.76 2.74

2 1.78 2.26 2.46 2.63 2.62

3 1.46 1.95 2.01 2.18 2.15

4 1.70 2.22 2.32 2.51 2.48

5 1.81 2.37 2.54 2.65 2.66

80




1 0 26.6 39.7 50.0 48.9

2 0 27.0 38.2 47.8 47.2

3 0 33.6 37.7 49.3 47.3

4 0 30.6 36.5 47.6 45.9

5 0 30.9 40.3 46.4 47.0




1 2.26 2.82 3.10 3.24 3.21

2 1.94 2.43 2.71 2.77 2.74

3 1.63 2.08 2.27 2.37 2.30

4 1.92 2.36 2.62 2.76 2.71

5 1.87 2.31 2.63 2.68 2.67




1 0 24.8 37.2 43.4 42.0

2 0 25.3 39.7 42.8 41.2

3 0 27.6 39.3 45.4 41.1

4 0 22.9 36.5 43.8 41.1

5 0 23.5 40.6 43.3 42.8

81

Table B.9: Water absorption weight data for 5MGPE sample.


Specimen 0d 1d 1.9d 4d 5d

1 1.47 1.92 2.09 2.33 2.32

2 1.25 1.68 1.84 1.98 1.99

3 1.39 1.87 2.09 2.23 2.22

4 1.22 1.60 1.72 1.89 1.91

5 1.85 2.48 2.74 2.89 2.87

Table B.10: Calculated water absorption values for 5MGPE sample.



1 0 30.6 42.2 58.5 57.8

2 0 34.4 47.2 58.4 59.2

3 0 34.5 50.4 60.4 59.7

4 0 31.1 41.0 54.9 56.6

5 0 34.1 48.1 56.2 55.1




1 1.20 1.51 1.71 1.81 1.81

2 1.27 1.67 1.78 1.92 1.92

3 1.46 1.91 2.13 2.25 2.25

4 1.18 1.57 1.63 1.74 1.76

5 1.43 1.87 2.03 2.15 2.14

82




1 0 25.8 42.5 50.8 50.8

2 0 31.5 40.2 51.2 51.2

3 0 30.8 45.9 54.1 54.1

4 0 33.1 38.1 47.5 49.2

5 0 30.8 42.0 50.3 49.7



Specimen 0d 1d 1.9d 4d 5d 10d

1 1.30 1.71 1.88 2.05 2.02 2.01

2 1.54 2.03 2.20 2.38 2.36 2.41

3 1.36 1.72 1.91 2.12 2.08 2.10

4 1.17 1.50 1.58 1.73 1.73 1.76

5 1.19 1.50 1.62 1.81 1.78 1.81



Specimen 0d 1d 1.9d 4d 5d 10d

1 0 31.5 44.6 57.7 55.4 54.6

2 0 31.8 42.9 54.5 53.2 56.5

3 0 26.5 40.4 55.9 52.9 54.4

4 0 28.2 35.0 47.9 47.9 50.4

5 0 26.1 36.1 52.1 49.6 52.1

83

Table B.15: Water absorption weight data for 5MPE sample.


Specimen 0d 9d 16d 17d

1 2.64 3.90 3.90 3.91

2 2.46 3.70 3.69 3.69

3 2.21 3.39 3.39 3.39

4 2.37 3.59 3.59 3.59

5 2.58 3.86 3.85 3.84

Table B.16: Calculated water absorption values for 5MPE sample.



1 0 47.7 47.7 48.1

2 0 50.4 50.4 50.4

3 0 53.4 53.4 53.4

4 0 51.5 51.5 51.5

5 0 49.6 49.2 48.8




1 2.76 4.05 4.02 4.00

2 2.31 3.44 3.41 3.40

3 2.19 3.24 3.24 3.25

4 2.72 3.97 3.97 3.97

5 2.37 3.39 3.38 3.38

84




1 0 46.7 45.7 44.9

2 0 48.9 47.6 47.2

3 0 47.9 47.9 48.4

4 0 46.0 46.0 46.0

5 0 43.0 42.6 42.6




1 2.58 3.58 3.56 3.56

2 2.05 2.82 2.84 2.84

3 2.07 2.95 2.91 2.90

4 2.49 3.49 3.46 3.45

5 2.56 3.60 3.56 3.55




1 0 38.8 38.0 38.0

2 0 37.6 38.5 38.5

3 0 42.5 40.6 40.1

4 0 40.2 39.0 38.6

5 0 40.6 39.1 38.7

85

B.2 Statistical Analysis

Confidence intervals on the mean water absorption for all samples were calculated and

are shown in the tables below. Please see Appendix A for a sample calculation.

Table B.21: Average water absorption values with confidence limits.

Sample Eq. Water Absorption (%)

Lower CL (%)

Upper CL (%)

TPS 66.7 62.3 71.2

5GPE 48.1 46.7 49.6

10GPE 47.2 45.8 48.5

20GPE 41.6 40.7 42.5

5MGPE 57.6 55.3 60.0

10MGPE 50.9 48.5 53.3

20MGPE 51.8 47.9 55.6

5MAPE 50.3 47.7 52.9

10MAPE 45.8 43.0 48.5

20MAPE 38.7 37.7 39.7

86

Appendix C : Chapter 4 Data and Statistics

C.1 Water Absorption Data


shown in the tables below. Specimens in bold were considered outliers and

subsequently dropped from the average water absorption and confidence interval

calculations.

Table C.1: Water absorption weight data for 5BW sample.



1 2.28 3.82 3.78 3.76

2 1.96 3.29 3.24 3.23

3 2.03 3.69 3.64 3.62

4 1.96 3.21 3.17 3.15

5 2.27 3.77 3.7 3.7

Table C.2: Calculated water absorption values for 5BW sample.



1 0 67.5 65.8 64.9

2 0 67.9 65.3 64.8

3 0 81.8 79.3 78.3

4 0 63.8 61.7 60.7

5 0 66.1 63.0 63.0

87

Table C.3: Water absorption weight data for 10BW sample.



1 2.13 3.43 3.40 3.39

2 2.06 3.39 3.36 3.36

3 2.39 3.87 3.85 3.83

4 2.30 3.63 3.60 3.59

5 2.29 3.64 3.62 3.62

Table C.4: Calculated water absorption values for 10BW sample.



1 0 61.0 59.6 59.2

2 0 64.6 63.1 63.1

3 0 61.9 61.1 60.3

4 0 57.8 56.5 56.1

5 0 59.0 58.1 58.1

Table C.5: Water absorption weight data for 5PW sample.


Specimen 0d 1.4d 2.4d 3.4d 4.5d 5.5d 10d

1 1.40 1.94 2.07 2.16 2.16 2.15 2.15

2 1.43 2.02 2.22 2.26 2.26 2.25 2.25

3 1.14 1.59 1.71 1.74 1.74 1.74 1.74

4 1.24 1.79 1.93 1.91 1.92 1.91 1.91

5 1.04 1.42 1.58 1.59 1.56 1.55 1.55

88

Table C.6: Calculated water absorption values for 5PW sample.



1 0 38.6 47.9 54.3 54.3 53.6 53.6

2 0 41.3 55.2 58.0 58.0 57.3 57.3

3 0 39.5 50.0 52.6 52.6 52.6 52.6

4 0 44.4 55.6 54.0 54.8 54.0 54.0

5 0 36.5 51.9 52.9 50.0 49.0 49.0

Table C.7: Water absorption weight data for 10PW sample.


Specimen 0d 1.4d 2.4d 3.4d 4.5d

1 1.27 1.68 1.96 2.00 2.01

2 1.25 1.71 1.90 1.94 1.94

3 1.21 1.57 1.89 1.89 1.91

4 1.37 1.74 2.11 2.15 2.13

5 1.36 Sample Lost

Table C.8: Calculated water absorption values for 10PW sample.


Specimen 0d 1.4d 2.4d 3.4d 4.5d

1 0 32.3 54.3 57.5 58.3

2 0 36.8 52.0 55.2 55.2

3 0 29.8 56.2 56.2 57.9

4 0 27.0 54.0 56.9 55.5

5 0 Sample Lost

89

Table C.9: Water absorption weight data for 5MPW sample.



1 1.02 1.45 1.52 1.61 1.62 1.62 1.62

2 1.37 1.95 2.12 2.20 2.18 2.19 2.19

3 1.21 1.59 1.79 1.85 1.85 1.85 1.85

4 1.84 2.78 2.76 2.76 2.80 2.82 2.82

5 1.17 1.68 1.89 1.78 1.74 1.73 1.72

Table C.10: Calculated water absorption values for 5MPW sample.



1 0 42.2 49.0 57.8 58.8 58.8 58.8

2 0 42.3 54.7 60.6 59.1 59.9 59.9

3 0 31.4 47.9 52.9 52.9 52.9 52.9

4 0 51.1 50.0 50.0 52.2 53.3 53.3

5 0 43.6 61.5 52.1 48.7 47.9 47.0

Table C.11: Water absorption weight data for 10MPW sample.



1 1.07 1.45 1.57 1.65 1.68 1.67 1.67

2 1.28 1.76 1.89 2.00 1.98 1.99 1.99

3 1.60 2.30 2.40 2.41 2.55 2.52 2.52

4 1.31 1.87 1.88 1.92 1.97 1.98 1.98

5 1.49 2.09 2.22 2.31 2.24 2.25 2.25

90

Table C.12: Calculated water absorption values for 10MPW sample.



1 0 35.5 46.7 54.2 57.0 56.1 56.1

2 0 37.5 47.7 56.3 54.7 55.5 55.5

3 0 43.8 50.0 50.6 59.4 57.5 57.5

4 0 42.7 43.5 46.6 50.4 51.1 51.1

5 0 40.3 49.0 55.0 50.3 51.0 51.0

C.2 Statistical Analysis



Table C.13: Average water absorption values with confidence limits.


Lower CL (%)

Upper CL (%)

TPS 66.7 62.3 71.2

5PW 54.3 51.5 57.2

10PW 56.6 54.5 58.8

5MPW 56.2 51.1 61.2

10MPW 54.2 50.5 57.9

5BW 63.3 60.6 66.0

10BW 59.3 56.0 62.5

91

Appendix D : Chapter 5 Data and Statistics

D.1 Water Absorption Data



Table D.1: Water absorption weight data for 20SOR sample.



1 1.84 2.81 2.82 2.79

2 2.01 3.09 3.07 3.06

3 1.94 2.92 2.90 2.89

4 2.08 3.08 3.08 3.07

5 2.00 3.07 3.05 3.03

Table D.2: Calculated water absorption values for 20SOR sample.



1 0 52.7 53.3 51.6

2 0 53.7 52.7 52.2

3 0 50.5 49.5 49.0

4 0 48.1 48.1 47.6

5 0 53.5 52.5 51.5

92

Table D.3: Water absorption weight data for SORBLEND sample.



1 2.60 3.52 3.71 3.64 3.63

2 2.32 3.18 3.34 3.28 3.27

3 2.16 2.85 3.05 3.00 2.98

4 2.70 3.61 3.83 3.77 3.75

5 2.35 3.22 3.38 3.31 3.31

Table D.4: Calculated water absorption values for SORBLEND sample.



1 0 35.4 42.7 40.0 39.6

2 0 37.1 44.0 41.4 40.9

3 0 31.9 41.2 38.9 38.0

4 0 33.7 41.9 39.6 38.9

5 0 37.0 43.8 40.9 40.9

D.2 Mechanical Testing Data

Shown in the tables below is the mechanical testing data for all samples.

Table D.5: Mechanical testing data for TPS sample.

Specimen Max Load

(N)

Max Stress

(MPa)

Modulus

(GPa)

Max Displacement

(mm)

Elongation

(%)

1 5.94 3.47 3.45E-02 18.4 73.9

2 4.37 2.97 2.88E-02 17.2 68.8

3 4.38 2.75 2.59E-02 16.3 65.5

4 3.13 2.32 1.51E-02 20.5 82.2

5 3.11 1.95 2.78E-02 18.8 75.4

93

Table D.6: Mechanical testing data for MPE sample.

Specimen Max Load

(N)

Max Stress

(MPa)

Modulus

(GPa)

Max Displacement

(mm)

Elongation

(%)

1 31.1 25.3 0.985 N/A N/A

2 34.7 23.1 0.936 N/A N/A

3 33.6 23.3 0.803 N/A N/A

4 34.4 22.0 0.857 N/A N/A

5 32.9 24.4 0.903 42.0 168

*NOTE: Only one sample was elongated to break due to time constraints.

Table D.7: Mechanical testing data for 20SOR sample.

Specimen Max Load

(N)

Max Stress

(MPa)

Modulus

(GPa)

Max Displacement

(mm)

Elongation

(%)

1 30.3 15.5 0.722 2.82 11.2

2 42.6 19.2 0.650 5.04 20.1

3 35.6 17.7 0.773 2.75 11.0

4 7.83 3.52 0.529 1.22 4.91

5 36.9 16.6 0.505 2.82 11.3

Table D.8: Mechanical testing data for SORBLEND sample.

Specimen Max Load

(N)

Max Stress

(MPa)

Modulus

(GPa)

Max Displacement

(mm)

Elongation

(%)

1 40.9 12.1 0.562 1.74 6.96

2 41.7 13.9 0.792 2.62 10.5

3 41.2 12.9 0.618 3.74 14.9

4 33.5 11.0 0.592 2.27 9.08

5 41.7 12.5 0.529 3.84 15.3

94

D.3 Statistical Analysis



Table D.9: Average water absorption values with confidence limits.


Lower CL (%)

Upper CL (%)

TPS 66.7 62.3 71.2

20SOR 50.4 47.9 52.9

SORBLEND 39.7 38.1 41.2

Confidence intervals for mechanical testing data were calculated for max stress,

modulus, and elongation in the same way as for the water absorption values and are

shown in the tables below. Again, see Appendix A for a sample calculation.

Table D.10: Average max stress values with confidence limits.

Sample Avg. Max Stress (MPa)

Lower CL (%)

Upper CL (%)

TPS 2.70 1.96 3.42

MPE 23.6 22.1 25.2

20SOR 17.3 14.8 19.7

SORBLEND 12.5 11.2 13.8

Table D.11: Average modulus values with confidence limits.

Sample Avg. Modulus (GPa)

Lower CL (%)

Upper CL (%)

TPS 2.64E-02 1.76E-02 3.52E-02

MPE 0.897 0.810 0.984

20SOR 0.663 0.497 0.829

SORBLEND 0.619 0.491 0.746

95

Table D.12: Average elongation values with confidence limits.

Sample Avg. Elongation (%)

Lower CL (%)

Upper CL (%)

TPS 73.2 65.2 81.1

MPE 168 N/A N/A

20SOR 13.4 7.06 19.8

SORBLEND 11.3 6.80 15.9

Reducing the water absorption of thermoplastic starch ... · The overall objective of this thesis...

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