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ENGINEERING AND MODELING OF COMPATIBILIZED BIO-
BASED POLYMER BLENDS USING REACTIVE EXTRUSION

presented by

GUOREN CHENG

has been accepted towards fulﬁllment
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ENGINEERING AND MODELING OF COMPATIBILIZED BIO-BASED
POLYMER BLENDS USING REACTIVE EXTRUSION

By

Guoren Cheng

A DISSERTATION
Submitted to
Michigan State University

In partial fulﬁllment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of Chemical Engineering and Material Science

2006

ABSTRACT

ENGINEERING AND MODELING OF COMPATIBILIZED BIO-BASED
POLYMER BLENDS USING REACTIVE EXTRUSION

By
Guoren Cheng

Two bio-based polymers, cellulose acetate (CA) and starch, were selected in this
study to prepare compatibilized polymer blends. These blends were prepared by adding a
reactive copolymer—poly (styrene-co-maleic anhydride (SMA)), generating graft
copolymer of a CA-SMA or a Starch-SMA copolymer in situ by reactive extrusion to act
as compatibilizer. In order to improve the compatibility of the blends, different grades of
SMA having various molecular weights and various maleic anhydride contents were
studied.

The grafting reaction (e.g. reactant concentration, temperature and catalyst
concentrations), morphology and the mechanical properties of CA/SMA blends were
investigated under both solution and melt conditions. We observed that a third order
kinetic model of the grafting reaction parameters gave adequate ﬁt and could be used to
describe the compatibility of the blends under different reaction conditions. The
morphology and the mechanical properties of CA/SMA blends having different
compositions were also studied. Our results indicate that it is possible to prepare
compatible CA/SMA blends having high tensile properties and good moisture resistance,
which should make such blends suitable for a wide range of commercial applications.
Furthermore, the preparation process itself was studied and optimized. Our results
indicate that if the blends contain more than 15 wt% high molecular SMA, the extrusion

proceeds smoothly without the need to add any plasticizer. Generally, the tensile strength

was inversely proportional to the SMA content and the highest tensile strength was
obtained when a minimum amount of SMA was used.

The relationship between the morphology of the blends and the extent of grafting
reactivity was also studied. In the melt, the phase dispersion affects the grafting reaction
via increasing the interface area while the grafting reaction affects the phase dispersion
by reducing the interfacial tension. Additionally, shear rate, interfacial tension,
temperature and composition as well as the injection molding conditions further impact
the compatibility of the blends and were used to optimize the injection process.

In starch/SMA blend, the addition of glycerol as a plasticizer greatly improves the
processability due to grafting of glycerol onto SMA as well as additional cross-linking
between starch, SMA and glycerol. This modiﬁed starch/SMA blend was blended with
poly (butylene adipate-co-terephthalate) (Ecoﬂex) and the resulting compatible blend was
blown into ﬁlms. Such blends of Ecoflex and modiﬁed starch exhibit good mechanical
properties, excellent processability, low cost (compared with Ecoﬂex and starch blend),
and are biodegradable.

In the last part of this thesis, vinyltrimethoxysilane was used as a grafting agent to
prepare organic-inorganic hybrids based on Ecoflex and Magnesium Silicate Hydroxide
(Tale). The graﬁing reactions of this silane were studied in relation to the mechanic

properties of the blends.

Cepyright by
GUOREN CHENG

2006

Dedicated to

My parents and my wife

ACKNOWLEDGEMENTS

I would ﬁrst like to thank Dr. Ramani Narayan, my thesis advisor, guide and
mentor. His resolute support and exemplary guidance helped me attain my academic and
professional goals. I would also like to acknowledge the advice and support offered by
my committee: Dr. Andre Lee, Dr. Ilsoon Lee, and Dr. Gregory Baker. Special thanks are
to Dr. Andre Lee for reviewing theoretical parts of my thesis and a lot of suggestions. A
special word of thanks should go to Ken Farrniner and Dr. Dan Graiver, for their great
ideas and encouragement. Ken also spent time reviewing my writing. I wish to
acknowledge all my group members for their help: Laura Fisher Patrick, Sunder
Balakrishnan, Madhu Srinivasan, Yogaraj Umesh Nabar, Weipeng Liu, Chisa, Brookes,
Alison C. Fowlks and more.

I would like specially thank my wife, Hui Zhang, for her unselﬁsh support and
encouragement all the time, this work would not be possible without the help and support
from my wife. Although I have mentioned only a few names, there are many more
people who have helped me in this venture and I would like to extend my appreciation to

all the other people who I may have left out.

vi

TABLE OF CONTENTS

LIST OF TABLES .......................................................................................................... xi
LIST OF FIGURES ......................................................................................................... xii
TABLE OF ABBREVIATIONS .................................................................. xv
Chapter 1: INTRODUCTION ............................................................................................. 1
1.1 RATIONALE .......................................................................................................... 1
1.2 PROPOSED GOALS .............................................................................................. 6
1.3 SPECIFIC OBJECTIVES ....................................................................................... 6
1.3.1 Problem Statement ...................................................................................... 6
1.3.2 Objectives of this research .......................................................................... 8

1.4 Organization of the Thesis ...................................................................................... 9

Chapter 2: STUDY OF THE GRAFTING REACTION OF CELLULOSE

ACETATE AND STYRENE MALEIC ANHYDRIDE IN SOLUTION ........................ 10
2.1 INTRODUCTION ................................................................................................ 10
2.2 EXPERIMENTAL ................................................................................................ 11

2.2.1 Materials ....................................................................................................... 1 1
2.2.2 Grafting reaction ........................................................................................... 14
2.2.3 Soxhlet extraction ......................................................................................... 14
2.3 THEORETICAL STUDY ................................................................................. 14
2.4 RESULTS AND ANALYSIS ............................................................................... 19
2.4.1 The SMA grafting conversion vs. time at different CA/SMA232
concentrations ........................................................................................................... 19
2.4.2 The SMA grafting conversion vs. the concentration of DMAP ................... 21

vii

2.4.3 The SMA grafting conversion vs. temperature ............................................. 22
2.4.4 The SMA grafting conversion vs. MA content in SMA ............................... 23
2.4.5 Calculate reaction constant K0 from the SMA conversion value in solution 24
2.5 CONCLUSIONS ................................................................................................... 25

Chapter 3: STUDY OF THE GRAFTING REACTIVITY AND PROPERTIES OF
CA/SMA POLYMER BLENDS PREPARED BY REACTIVE EXTRUSION... . ...26

3.1 INTRODUCTION ................................................................................................ 26
3.2 EXPERIMENTAL ................................................................................................ 27
3.2.1 Materials ........................................................................................................ 27
3.2.2 Reactive extrusion of CA/SMA ..................................................................... 28
3.2.3 Soxhlet extraction and Fourier transformed infrared spectroscopy test ........ 30
3.2.4 Injection mold ................................................................................................ 31
3.2.5 Tensile properties test ................................................................ 32
3.2.6 Izod impact test ........................................................................ 32
3.2.7 Moisture absorption test .............................................................. 32
3.3 RESULTS AND ANALYSIS ............................................................................... 33
3.3.1 Grafting reaction results ................................................................................. 33
3.3.2 Properties of CA/SMA blend ......................................................................... 38
3.4 CONCLUSIONS ................................................................................................... 41
Chapter 4: COMPATIBILIZATION STUDY OF CA/SMA BLEND ............................. 43
4.1 INTRODUCTION ................................................................................................ 43
4.1.1 Polymer Blend .......................................................................................... 43
4.1 .2 Compatibilization ...................................................................................... 46

viii

4.1.3 Theoretical study of compatibilization ..................................................... 48

4.2 EXPERIMENTAL ................................................................................................ 49
4.2.1 Transmission Electron Microscopy(TEM) ............................................... 49
4.3 RESULTS AND ANALYSIS ............................................................................... 49
4.4 THEORETICAL STUDY ..................................................................................... 55
4.4.1 The disperse phase droplet breakup under shear rate ............................... 55
4.4.2 The effect of compatibilizer on the interfacial tension ............................. 58

4.4.3 The morphology of in situ compatibilized CA/SMA in reactive
extrusion... ................................................................................................................ 59

4.5 CONCLUSIONS ................................................................................................... 68

Chapter 5: STUDY OF THE GRAFTING REACTION BETWEEN THERMOPLASTIC

STARCH AND SMA VIA REACTIVE EXTRUSION ................................................... 69
5.1 INTRODUCTION ................................................................................................ 69
5.1.1 Starch and thermoplastic starch ................................................................ 69
5.1.2 Starch and biodegradable polyester blends ............................................... 70
5.1.3 Modiﬁed starch to improve its compatibility with biodegradable polyesters
....................................................................................... 72

5.2 EXPERIMENTAL ................................................................................................ 73
5.2.1 Materials and Equipment .......................................................................... 73
5.2.2 Synthesis of TPS/SMA graft copolymers by reactive extrusion .............. 75
5.2.3 Soxhlet extraction of TPS/SMA grafting co-polymer .............................. 77
5.2.4 Blending Ecoﬂex with TPS/SMA by extrusion process ........................... 78
5.2.5 Fourier Transformed Infrared Spectroscopy ............................................. 78
5.2.6 Blowing Film ............................................................................................ 79

ix

5.2.7 Mechanical Property Determination ......................................................... 79

5.3 RESULTS AND ANALYSIS ............................................................................... 80
5.3.1 Soxhlet extraction and FTIR results ......................................................... 80
5.3.2 Mechanical properties of Ecoﬂex and TPS/SMA blends ......................... 85

5.4 CONCLUSIONS ................................................................................................... 85

Chapter 6: PREPARING COMPATIBLE ORGANIC-INORGANIC HYBRID BLENDS

BY REACTIVE EXTRUSION ......................................................................................... 87
6.1 INTRODUCTION ................................................................................................ 87
6.2 EXPERIMENTAL ................................................................................................ 90

6.2. 1 Materials ................................................................................................... 90
6.2.2 Reactive extrusion ..................................................................................... 92
6.2.3 Soxhlet extraction and FTIR test .............................................................. 94
6.2.4 Blowing ﬁlms ............................................................................................ 95
6.3 RESULTS AND ANALYSIS ............................................................................... 96
6.3.1 Soxhlet extraction and FTIR results ......................................................... 96
6.4.2 Mechanical properties of Ecoﬂex-silane-talc blends .............................. 102
6.4 CONCLUSIONS ................................................................................................. 105

Chapter 7: CONCLUSIONS AND RECOMMEND WORKS ....................................... 107
7.1 CONCLUSIONS ................................................................................................. 107
7.2 RECOMMEND WORKS ................................................................................... 109

7.2.1 Theoretical expectation of the polymer blend properties ....................... 109
7.2.2 Compatibilizing biodegradable polyesters .............................................. 1 10
REFERENCES ............................................................................................................... 112

LIST OF TABLES

 

 

 

Table 2-1: f SM A vs. reaction time at different CA/SMA concentrations* -------- 20
Table 2-2: f SMA vs. DMAP concentrations* 22
Table 2-3: f SM A vs. temperatures* 23
Table 2-4: f SMA vs. MA content* 24
Table 3-1: SMA grafting conversion in CA/SMA blends 34

 

Table 3-2: The properties and phenomena comparison between compatibilized
and incompatibilized CA/SMA233 (70/30) 39

 

Table 3-3: Mechanical properties of CA/SMA blend at different compositions - 39

Table 3-4: The tensile properties of CA/SMA/DMAP (70/30/001) at different
injection conditions 41

 

Table 4-1: Dispersed phase size of CA/SMA232 at different pass 57

 

Table 4-2: The SMA particle size of cast ﬁlm at different grafting conversion -- 63

Table 5-1: Blown Film Processing Conditions for Ecoﬂex—TPS/SMA blend ---- 79

 

Table 5-2: TPS/SMA soxhlet extraction results 80
Table 5-3: The mechanical properties of Ecoﬂex and TPS/SMA blend ---------- 85

Table 6-1: Blown Film Processing Conditions for Ecoﬂex-silane-talc blends --- 95

 

Table 6-2: The Soxhlet extraction data for Ecoflex/Talc blends 96

Table 6-3: Tensile Properties (Machine Direction) of blown ﬁlms derived from
the PBAT—silane-talc blends 104

 

Table 6-4: Tensile Properties (Transverse Direction) of blown films derived from
the PBAT-silane-talc blends 105

 

xi

Figure 1-1:
Figure 2-1:
Figure 2-2:
Figure 2-3:
Figure 2-4:
Figure 2-5:
Figure 2-6:
Figure 2-7:
Figure 2—8:
Figure 2-9:
Figure 3-1:
Figure 3-2:
Figure 3-3:
Figure 3-4:
Figure 4-1:
Figure 4-2:
Figure 4-3:
Figure 4-4:
Figure 4-5:
Figure 4-6:

Figure 4-7:

LIST OF FIGUREURES

 

 

 

 

 

 

 

 

 

Global carbon cycling 3
Cellulose acetate (DS=2.5) 12
Poly (styrene-co- maleic anhydride) SMA232 12
Grafting reaction between CA and SMA232 13
f SM A vs. time ﬁtting curve at 8 g/ 100ml concentration 20
f SMA vs. time ﬁtting curve at 1 1g/100ml concentration 21
f SM A vs. time ﬁtting curve at 14g/ 100ml concentration 21
f éM A vs. DMAP concentration ﬁtting curve 22
ln(1/f§MA) vs. l/T ﬁtting curve 23
f SMA vs. MA contents fitting curve 24

 

Screw conﬁguration used for the synthesis of CA-SMA copolymers -- 29
FTIR spectrum of CA/ SMA3000P blend after extraction --------------- 35

FTIR spectrum of CA/SMA232/DMAP (50/50/005) after extraction - 36

 

 

 

 

FTIR spectrum of CA/SMA232 (70/30) after extraction 36
Effect of composition and viscosity on phase morphology -------------- 46
TEM of CA/SMA232 (70/30) after 1 extrusion pass 50
TEM of CA/SMA232 (70/30) after 2 extrusion passes 50
TEM of CA/SMA232 (70/30) after 3 extrusion passes 51

TEM of CA/SMA232/DMAP (70/30/0.01) after 1 extrusion pass ------ 51
TEM of CA/SMA232/DMAP (70/30/0.05) after 3 extrusion passes --- 52

TEM of CA/SMA232/DMAP (70/30/0.1) after 3 extrusion passes ----- 52

xii

Figure 4-8: TEM of CA/SMA332 (70/30) after 1 extrusion pass 53

 

Figure 4-9: TEM of CA/SMA332/DMAP (70/30/0.01) after 1 extrusion pass ------ 53

Figure 4-10: Number average diameter of SMA (pm) in CA/ SMA blend ---------- 54

 

 

Figure 4-11: In vs. extrusion passes of CA/SMA232 57

C

Figure 4-12: The TEM picture of CA/SMA232 cast ﬁlm at different grafting
conversions 62

 

Figure 4-13: The ﬁtting line of SMA phase diameter vs. 1/ f ’SMA (cast ﬁlms) ------ 64
Figure 4-14: SMA phase size vs. time for CA/SMA232/DMAP (70/30/0.01) ------ 67

Figure 4-15: SMA conversion vs. time for CA/SMA232/DMAP (70/30/0.01) ----- 67

 

 

 

 

 

 

 

 

 

 

Figure 5-1: Structure of amylose 69
Figure 5-2: Structure of amylopectin 70
Figure 5-3: Starch reaction with half-esters of dicarboxylic acids 72
Figure 5-4: Structure of SMAIOOOP 74
Figure 5-5: Structure of SMA3000P 74
Figure 5-6: Structure of Ecoﬂex 74
Figure 5-7: Grafting reaction between starch and SMA 76
Figure 5-8: Grafting reaction between SMA and glycerol 76
Figure 5-9: Cross-linking between starch, SMA and glycerol 77
Figure 5-10: Extracted out material weight vs. SMA content 81

Figure 5-11: FTIR of TPS and TPS/SMA(2.5%wt) after extraction(thimble) ------- 83
Figure 5-12: FTIR of TPS/SMA (5, 10 ,20wt%) after extraction(thimble) ---------- 84
Figure 5-13: FTIR of material extracted out form TPS/SMA (10%wt) (solvent) --- 84

Figure 6-1: 2,5-dimethyl-2,5-di-(tert-butylperoxy) hexane (lupersol 101) ----------- 91

xiii

 

Figure 6-2: Structure of Vinyl-trimethoxysialne 91

 

 

 

 

 

 

Figure 6-3: Structure of vinyl-methyl-dimethoxysilane 91
Figure 6—4: Proposed structure sketch of Talc 92
Figure 6-5: Proposed reaction structure of Ecoﬂex and Silane 93
Figure 6-6: Proposed crosslink between Ecoﬂex, silane and talc 95
Figure 6-7: FTIR spectrum of talc 97
Figure 6-8: FTIR spectrum of Ecoﬂex 98

Figure 6-9: FTIR spectrum of Ecoﬂex/silane/talc after extraction (in thimble) vs.
talc- 99

 

Figure 6-10: FTIR spectrum of extracted material from Ecoﬂex/silane/talc
(solution) (side and center part) 100

 

Figure 6-11: FTIR spectrum of extracted material from
Ecoﬂex/Silane/talc(solution) comparing with Ecoﬂex 101

 

Figure 6-12: FTIR spectrum of Ecoflex/silane subtracted by Ecoflex 102

 

xiv

TABLE OF ABBREVIATIONS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WEFT ;
CA Cellulose acetate i
SMA Poly (styrene-co-maleic anhydride)
Ecoflex Poly (butylene adipate—co—terephthalate)
Talc Magnesium Silicate Hydroxide
T PCL Poly (e-caprolactone) I
PLA Poly (lactic acid) I
I PHE Poly (hydroxyester)
7 PHEE Poly (hydroxyesterether) A
; DOP Dioctylphthalate i
l DEP __ Diethylphthalate
T,m Melting Temperature
Chapter 2
l MA Maleic anhydride
; l
DS Degree of substitution F
l
H; Weight average molecular weight II
I 5
l M n Number average molecular weight
T Tg - Glass transition temperature
I DMAP 4-Dimethy1aminopyridine

 

XV

 

 

 

N,N:Dimethylformamide

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

f SMA Weight grafting conversion of SMA

M ,- Molecular weight of ith SMA chain

C i Mole concentration of the ith SMA chain after reaction

Cl.O Initial mole concentration of the ith SMA chain

aung Fraction of un-grafted SMA chains that have the same
chance to graft compared to the grafted chains
VS Fraction of interfacial volume in total volume between
two phases

V0 Volume of the solution

N Number of SMA droplet

S k Surface area of kth droplet
; 5k Depth of the interfacial penetration of kth droplet
J
I
I E Average SMA droplet radius
l K 0 Reaction constant
L
[ E Activation energy
i R’ Gas constannt
i
l T Reaction temperature
I
E C.0H Concentration of OH group
C.MA Concentration of MA group
i C DMAP Concentration of DMAP

 

xvi

w,_s__....__q__——_w_...r._ —.__5 ﬂ W._.___~A_

 

Initial mole concentration of SMA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PDI Polydispersity index
f §MA Modiﬁed SMA grafting conversion
Chapter 3
L/D Length to diameter ratio of extruder
D Diameter of extruder
FTIR Fourier transformed infrared spectroscopy
Chapter 4
AG," Gibbs energy of mixing
V A Actual volume of polymer A
VB Actual volume of polymer B
(If A Volume fraction of polymer A I
I
I ¢ B Volume fraction of polymer B J
I B A B Binary interaction energy I
I 17A Molar volume of polymer A I
I _ I.
I VB Molar volume of polymer B I
I A17," Mixing enthalpy at unit volume
I AS," Mixing entropy at unit volume i
I P Properties of polymer blend ‘
I PA Properties of polymer A “It
I

 

4%..-- «W__4 .. .. ._ __________.._. _._____ ..___.__ , . .___ _ -7 - -__—._—..

:xvii

 

 

Properties of polymer—B

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WA Weight fractions of polymer A
”’3 Weight fractions of polymer B
APE (w) Excess term of properties

Ca Capillary number

77", Polymer matrix viscosity

7 Shear rate

R Radius of disperse phase size

0' Interfacial tension
l
I t Processing time
E
I Cac Critical Capillary Number

RC Radius of disperse phase size at critical state I
“T f A constant of droplet breakup rate I

(I5 Volume fraction of the dispersed phase
Pc Probability that collision of the particles will be followed I
I by their fusion I
l xi Ratio of the viscosities of the dispersed phase and matrix I
c Concentration of the compatibilizer i
i I
I k A constant of interfacial tension change with
. compatibilizer concentration

as Interfacial tension under saturate compatibilizer
' concentration
I C0,,,_,,,,, Mole concentration of half-ester bonds

F Volume flow rate in the extruder

xviii

 

 

 

 

 

 

 

 

 

 

I res Extruder residence time L
I I
I I
I 00 Interfacial tension without compatibilizer I
l :
RCS Radius of disperse phase droplet at critical state under I
saturate compatibilizer I
I RC0 Radius of disperse phase droplet at critical state with out
I compatibilizer
I Chapter 5
I TPS Thermoplastic Starch i
I
I Chapter 6
PBS Poly(butylene succinate)

 

 

Lupersol 101

2,5-Bis(tert-butylperoxy)—2,5 dimethylhexane

 

VTMOS

Vinyl-trimethoxysilane

 

 

VMDMOS

 

vinyl-methyl-dimethoxysilane

xix

Chapter 1. INTRODUCTION

1.1 RATIONALE

Plastics play a very important role in today’s life. While plastics are convenient,
strong, light-weight, inexpensive and easily processable, they are not readily broken
down in the environment. This is of particular concern when plastics are used in single-
use disposable packaging and consumer goods. It causes a serious issue of environmental
pollution. Another important concern of plastics is that most general plastics are
petrochemical-based and, hence, are derived from a non-renewable resource. Thus, two
concepts: bio-based and biodegradable are introduced into new products design. The
impacts of raw material resources and the disposal of end products must be factored into
the design phase of any new products. This has opened up new market opportunities for
developing biodegradable and bio-based products from annually renewable resources as
the next generation of sustainable materials that meets ecological and economic
requirements (1 — 5).

The advantage of using annually renewable biomass as the feedstock for the
production of polymers, chemicals and fuel, needs to be understood from a global carbon
cycle basis. Crude oil is pumped out of the ground and is made into gasoline, diesel and a
variety of synthetic materials by the chemical industry. These polymers, chemicals and

fuels are used by manufacturers, cars and trucks, which upon their disposal and

decomposition release C02 into the atmosphere. The problem is that this release of CO;

takes only a few years whereby plants and trees capture C02 through photosynthesis and

fossilized it over geological timeframes (millions of years). Consequently, the
geological carbon cycling process for petrochemical feedstock is out of balance leading
to unsustainable development (Figurel -l). Thus, it is desirable to use annually renewable

crops like corn, soy and wheat as the carbon source for polymers, chemicals and fuels.

This approach will ensure that the rate of C02 capture by photosynthesis is equal to that

of CO; release by burning and decomposition. It is important to note that although the

Kyoto Protocols hasn’t been ratiﬁed by the US, Sustainable development is our
responsibility to society. Furthermore, if we manage our biomass resources effectively by

ensuring that we plant more biomass than we utilize, we can begin to reverse the carbon
dioxide rate equation and move toward a net balance between C02 ﬁxation/sequestration

and release.

GLOBAL CARBON CYCLING
THE ECO DRIVER

 

C02 : Biomass/Organic matter

I

 

[Bio-chemical Industry I

   

 

 

 

 

 

 

 

1- 10 yrs 1 >106 years
311mm? : Fossil Resources
emrca S etroleu Natural as
& Fuels Chemical industry (p m, g )
Renewable Carbon Green Materials
COz , & Biomass & Products

 

 

Figure 1-1 Global carbon cycling

Environmental regulations, societal concerns, and a growing environmental
awareness throughout the world have triggered a paradigm shift in industry to develop
products and processes compatible with the environment. In this regard, there is an
interest in developing and evaluating materials based on recyclable, natural and
degradable polymers. These include natural polymers like starch, cellulose and proteins,
or synthetic biodegradable polymers like poly (s—caprolactone) (PCL), poly (D, L, or DL-
lactide) (PLA), poly (butylene adipate-co-terephthalate) (PBAT), poly (hydroxy esters)
(PHE), poly (hydroxy ester ethers) (PHEE) and their modiﬁed versions. Biodegradable
plastics derived from these polymers are currently being used in a variety of applications
ranging from packaging ﬁlms, cutlery items (spoons, knives, forks etc.), biodegradable

packaging foams and more.

Although bio-based and biodegradable polymers have been commercialized for
over 20 years. this niche market is beset with a variety of roadblocks led by high prices
and poor processability. Indeed, natural polymers such as starch, cellulose and proteins.
are widely available and are generally comparable in cost to petrochemical based
polymer, however, their processability is much poorer. Synthetic biodegradable
polymers, on the other hand, have good processability but they are much higher in price.
A practical way to reduce the cost and improve the processability is by blending.
Blending has emerged as a major tool to obtain new polymeric materials with desired
properties by mixing two or more existing polymers. The study of polymer blends has
therefore developed rapidly in recent years (6-10). Blends of synthetic, biodegradable
polymers with low cost, environmentally ﬁ'iendly ﬁllers or natural products were
previously prepared and studied from polymers like PCL, PLA and PBAT that were
blended with starch, calcium carbonate or tale (1 1-15). Unfortunately, simple mixing
leads to poor blends due to incompatibility. Thus, it is necessary to add a compatiblizing
agent in order to improve the preparation process as well as enhance the physical
properties of the blends. Processing natural polymers and their derivatives by adding a
plasticizer or using a reactive process are described in the literature as common methods
to process polymers to form bio-based polymer blends (16-20).

Extruders are traditionally used to transform a solid plastic into a uniform melt for
delivery to the next stage of processing. Various physical processes, such as
devolatilization and blending, have also been carried out in extruders. During the last
three decades, the direction of polymer R&D has been changing gradually from pursuing

new polymers to ﬁlling some of the performance gaps in the diversity of existing plastic

materials via modifying, reactive blending, reinforcing and other methods that improve
properties. Using extruders as continuous ﬂow reactors to modify polymers (enhancing
thermal properties, improving mechanical or adhesive properties via introducing certain
chemical changes) is termed as “Reactive Extrusion” (20 — 30). More speciﬁcally,
reactive extrusion refers to the process of conducting chemical reactions during the melt
extrusion process. Discrete processes can be carried out in speciﬁc modular segments of a
twin-screw extruder, whose screw conﬁguration can be tailored to meet the desired
objective. The reaction needs to be achieved within the residence times available in
extrusion operations. Advantages of using extruders to conduct reactions are listed below:

0 Fast and continuous process

- Solvent free melt process

0 Control over residence time

0 Integration of other extrusion ‘streams’ along with the polymerization process

0 Efﬁcient devolatilization capability through the vent port

0 Modular in design; easy to scale up
Interest in environmentally ﬁiendly materials has stimulated fast development of
biodegradable packaging ﬁhns and foams. However the study of bio-based engineering
plastics is rare. Glasser, Wolfgang G (31) discussed converting woody biomass into a
variety of thermoplastic and thermosetting materials, and into regenerated ﬁber and
hydrogel products ; Grafting by copolymerization of e-caprolactone and lactic acid onto
cellulose diacetate at the residual hydroxyl positions to obtain thermoplastic was studied
by Teramoto, Yoshikuni et.al (32); A bio-composite using cellulose acetate and natural

ﬁber (coconut, ramie) with triacetine (TA) as a plasticizer were combined in a melting

process by Lee, Sang Hwan and his co-workers(33).

1.2 PROPOSED GOALS

The target of this study is to prepare compatible bio-based polymer blends by
blending natural polymers (cellulose acetate(CA), starch) with synthetic polymers that
have a high number of functional groups (styrene maleic anhydride copolymer(SMA)).
Grafting SMA onto CA to form grafting co-polymers, which act as compatibilizers, can
be done in situ by reactive extrusion. The graft co-polymer improves the properties of the
CA/SMA bio-based polymer blends by reducing the interfacial tension and improving the
phase dispersion. Possible target applications of these bio-based polymer blends are in
structural materials such as, automobile parts, furniture and tools. The study further deals
with improvement of the mechanical properties; cost reduction, and the optimization of
process conditions and components.

This study also focuses on improving the compatibilization of bio-based polymers
with synthetic biodegradable polymers by reactive blending. The goal is to prepare
materials with good properties and to lower the cost associated with bio-based or
biodegradable materials. Speciﬁcally, the target application for a thermoplastic starch and
SMA blend is biodegradable packaging ﬁlms. Such compositions were prepared by
grafting thermoplastic starch and SMA onto biodegradable polyester. The blends thus

prepared can be used as low cost biodegradable materials.

1.3 SPECIFIC OBJECTIVES

1.3.] Problem Statement

Cellulose esters are one important family of modiﬁed natural polymers. Cellulose
acetate is of particular commercial importance. Cellulose acetate is used as a sustainable
material in many areas and products (e.g. textiles and ﬁbers, spectacle frames, tools
handles) due to its toughness and high gloss. However it has a very narrow processing
window due to the close proximity of its melting temperature to its decomposition
temperature. Between 28 and 44% phthalate ester plasticizer (e.g. DOP and DEP) is
added to enable processing. Unfortunately adding a plasticizer reduces the mechanical
properties and in the case of phthalate ester plasticizers can have detrimental health
effects. Such plasticizers are suspected cancer causing materials and are prohibited by
European Union and California legislation.

Starch, an anhydroglucose polymer derived from plants, offers a structural
platform for the manufacture of sustainable, biodegradable packaging material. Starch
granules, however, exhibit hydrophilic properties and strong inter-molecular associations
via hydrogen bonding due to the hydroxyl groups on the granule surface. The strong

hydrogen bonding association and crystallization lead to poor thermal processing because

the melting temperature (Tm) is higher than the thermal decomposition temperature.

Thus, degradation sets in before thermal melting. The process prOperties of plasticized
starch are also very poor. It is also incompatible with biodegradable synthetic polymers
due to its strong intermolecular associations.

Adding inorganic ﬁller to synthetic biodegradable polymer can lower the cost.
However, simply adding inorganic ﬁller signiﬁcantly reduces the tensile properties of the

blend due to incompatibility.

1.3.2 Objectives of this study

I. In CA processing, use synthetic polymers in place of monomeric plasticizer,
eliminate leaching, improve processing window and reduce environmental consequence.

H. Improve the compatibility of CA and synthetic polymer by choosing
functionalized synthetic polymer (Styrene maleic anhydride (SMA)) and proper catalyst
to introduce grafting reaction between the components in reactive extrusion, generating
in-situ grafting copolymer as the compatibilizer.

111. Study factors affecting the reactivity and phase dispersion of CA/SMA
polymer blend, optimize the mechanical properties by changing the component contents
and injection molding conditions. The fonowing detail objectives are included:

A. Study the reactive kinetics of cellulose acetate and SMA in solution

B. Study the grafting reaction in the reactive extruder

C. Analyze the relationship between compatibility and the reactivity

D. Maximize the bio-based component without affecting the process
properties
E. Optimize the mechanical properties by changing the process conditions

IV. Prepare a starch semi-ester by reactive extrusion of thermoplastic starch and
SMA, improve the compatibility of thermoplastic starch and a commercialized
biodegradable synthetic polyester (Poly (butylene adipate-co—terephthalate)) (Ecoﬂex),
and improve the mechanical and biodegradable properties of the blend blown ﬁhns.

V. Prepare organic-inorganic hybrid polymer blends (Ecoﬂex/Talc) which apply
to blown ﬁlm, introduce a functional silane as a grafting agent in this organic-inorganic

blend to improve the compatibility and tensile properties.

1.4 ORGANIZATION OF THE THESIS

The thesis is composed of seven chapters, each of which individually addresses
the work that has been done in relation to the speciﬁc objectives outlined below.

Chapter 2 deals with the CA/SMA grafting reaction in DMF solution. The
grafting conversion of SMA at different time, concentration, temperature and MA content
are measured, analyzed and compared with a theoretical analysis.

Chapter 3 describes the preparation of CA/SMA polymer blends by reactive
extrusion and characterizes the grafting reaction in melt conditions. Different SMA
compositions and different grades of SMA were used. This chapter also deals with the
studies of properties and processing conditions.

Chapter 4 studies the phase dispersion of CA/SMA polymer blends in a reactive
extrusion process. The relationship between grafting reaction and phase dispersion are
characterized by experimental and theoretical methods.

Chapter 5 discusses the preparation of thermoplastic starch and SMA grafting
polymer blends. The grafting reactivities at different amounts of SMA are characterized.
One such polymer blend is mixed with a biodegradable plastic (Ecoﬂex) and the blown
ﬁlm process is characterized.

Chapter 6 introduces a method to prepare biodegradable, organic-incrganic
hybrid blend. Here, the biodegradable polyester (e. g. Ecoﬂex) and an inorganic ﬁller (e. g.
talc) are mixed using a functional silane as the grafting agent. The mixture is blown into
ﬁlms and the tensile properties are studied.

The conclusions and recommendations for future work are discussed in chapter 7.

Chapter 2. STUDY OF THE GRAFTING REACTION OF CELLULOSE
ACETATE AND STYRENE-MALEIC ANHYDRIDE IN SOLUTION

2.1 . INTRODUCTION

Grafting reactions provide a method for preparing new polymeric materials with
desirable and improved properties. Grafting a monomer or a mixture of monomers onto
the backbone of an existing polymer for the purpose of improving various properties has
been done by free radical, anionic, cationic or a condensation mechanism (34-3 8). Most
graft polymerization processes, irrespective of the initiation process, produce mixtures of
graft copolymers, and homo-polymers

Grafting a monomer or a functionalized polymer (ex. styrene, acrylamide,
caprolactone, nylon66) onto cellulose or cellulose acetate has been studied in solvent or
by extrusion processes (39-43). The availability of more functionalized and/or modiﬁed
polymers provides new opportunities for the production of graft copolymers and their
alloys by coupling two reactive polymers. Maleic anhydride (MA) -modiﬁed polyoleﬁns
and random copolymers of maleic anhydride with some vinyl monomers are one family
of reactive polymers (44-45). The reactivity is provided by the anhydride. Extensive work
has been done on grafting anhydride groups on one polymer and amine groups on another
polymer to form compatibilized blends via reactive extrusion (46). Polymers containing
hydroxyl groups are another family of reactive polymers. The reaction between the

anhydride and the hydroxyl is another choice for the production of graft copolymers to

10

form compatibilized blends. Many natural polymers and their derivatives are an
important source of hydroxyl-bearing reactive polymers.

Cellulose acetate (Degree of substitution (DS): 2.45) is one of the most
commercially important cellulose derivatives. It is a tough material with excellent optical
clarity. However, it is well known that cellulose acetate has poor dimensional stability
under high humidity and at elevated temperature. Additionally, this polymer is relatively
expensive, it is characterized by a very limited compatibility with other synthetic
polymers, and it requires high processing temperature.

Styrene-maleic anhydride copolymer has gained attention because it is
commercially available. The grafting reaction between CA and SMA can add new
properties to cellulose acetate by forming compatibilized blends and the incorporation of

hydrophobic SMA can help further improve the dimensional stability of CA.

2.2 EXPERIMENTAL

2.2.1 Materials

 

Cellulose Acetate (DS: 2.45, 717,, .- 103,000, M, .- 46,000, Tg=187°c, Tm=232
0C) was provided by Eastman Chemical Company. High Molecular weight Styrene

maleic anhydride random copolymers (SMA132: 4.75 wt % maleic anhydride, m :

274,000, H; .- 136,000; SMA232: 7.08 wt % maleic anhydride, Ill—W .- 249,000, IT, :

 

126,000; SMA332: 12.2% maleic anhydride, 717;:193000, M, .- 100,000) were

provided by Nova Chemical Company. The structural units of CA and SMA232 are

shown in FigureZ-l and Figure2-2 . The catalyst 4-Dimethylaminopyridine (DMAP),

11

solvents anhydrous grade N,N-Dimethylformamide (DMF, 99%) and Toluene

(anhydrous) were purchased from Sigma-Aldrich, Inc.

    
 

crizococn3

    

COCH
H3COCO 3 CHon

Figure 2-1 Cellulose acetate (DS=2.5)

MOO

O

O

Figure 2-2 Poly (styrene-co-maleic anhydride) SMA232

In this study the grafting reaction of CA with SMA happens between the hydroxyl
and anhydride groups in the presence of catalyst to form a half ester (Figure 2-3). In this
particular polymers system, each polymer has a large number of reactive groups available
for interactions: 85 hydroxyls on CA and 90 anhydrides on SMA232 as can be calculated

from the number average molecular weights of these polymers.

12

 

poly(styrene-co-maleic anhydride) 0

cnzococn3 “30000

. O o
o

OCOCHs CHZOH

    
   
   

H3COCO

Cellulose acetate

CHZOCOCH3 H3COCO

 

CA-SMA grafted copolymer

Figure 2-3 Grafting reaction between CA and SMA232

l3

2.2.2 Grafting reaction

Grafting reactions were carried out in DMF solution in a glass batch reactor with
stirring. Cellulose acetate was vacuum dried overnight at 90-100°C. The DMAP catalyst
was added after the polymer solution reached a stable temperature and the reaction was
allowed to proceed for hours at this temperature. The solutions were then cooled to room
temperature and the product was precipitated by washing with large excess (three-times
by volume) of water. The precipitate was further washed with excess of hot water to
remove residual DMF and any traces of the catalyst. The precipitates were then dried at
room temperature overnight and then at 50°C under full vacuum. Each sample was
weighed and kept under dry conditions. This procedure was used for different polymer
concentrations, temperature, catalyst amounts and grades of SMA (with different MA

content).

2.2.3 Soxhlet extraction

Information on the grafting conversion of SMA (wt %) was obtained by soxhlet
extraction with toluene for 48 hrs. Elemental analysis of the extractable material
(obtained by C,H,N elemental analysis) showed the presence of less than 2% of CA in the
extractable fraction. Therefore, only free SMA was extracted. Percentage conversion of

SMA was obtained from the mass balance.

2.3 THEORETICAL STUDY

The grafting conversion of SMA can be written as:

14

MiCi
fSMA =1’(—;_6)SMA (2-1)

zMiCi

f SMA is the weight grafting conversion of SMA

M ,- is the molecular weight of ith SMA chain

. . .th . .
C, rs the mole concentration of the 1 SMA chain after reaction

. . . . . .th .
C 1'0 rs the 1mt1al mole concentration of the 1 SMA chain

Thus, the SMA conversion rate can be written as:

ZMiaCi
afSMA =___( 5,

)
at ZM,C,-O SMA

 

(2-2)

.th . .
In the Batch reactor, the 1 SMA charn conversron rate can be expressed as:

(ea) _( aungMiCi
— SMA "
at ZMiCiO "(l—dung)ZMiCi

 

)SMA Vs rMA (2-3)

am is the fraction of un-grafted SMA chains that have the same probability to

aungMiCi

0 is the
ZMiCi ’(1-aung)ZMiCi

 

graft compared to the grafted chains, and

coefﬁcient of the consumption of ith SMA chain in the grafting reaction.
N
VS = 281.51. /V0 (24)
k=l

Vs is the fraction of interfacial volume in total volume between two phases

V0 is the total volume of the solution

N is the total numbers of SMA droplet

15

S k is the surface area of kth droplet

6k is the depth of the interfacial penetration of kth droplet

We assume that 5k does not change with the size of the droplet as it is only
related to free volumes and the interfacial tension.

Thus, at a given volume fraction of SMA,

V, cc l/R (25)

where, R is the average SMA droplet radius.

rM A is the reaction rate of MA functional group in SMA and it can be written as:

(3C_ 1
I‘M/4 1‘ — at/WA z KO eXP(— E/R T)Cv—OH C—MA CDMAP (2-6)

 

K 0 is the reaction constant

E is the activation energy
R ' is the gas constant

T is the reaction temperature

CO” is the concentration of OH group
CM; is the concentration of MA group

C DMA p is the concentration of DMAP

Substituting equation 2-3 into equation 2-2, we get:

2
_5fSMA = aungZMi Ci

)SMA VerA (2-7)
at (ZMiCiO - (1 - aung)ZMiCi)ZMiCio

l6

When the grafting reaction is performed at low concentrations in solution, SMA
polymer chains are “stretched” and all the reactive groups have similar probability to
react.

(1 =1 and V5 is a constant.

ung

Thus, we can simplify equation 2-7 and rewrite it as in equation 2-8.

-0fsm :( XMiZCz‘
6’ (ZMiCiO)

 

 

2 )SMA Vs rMA (2-8)

The weight average molecular weight M W and the number average molecular

weight M n can be written as:

—— _ XMIZCI
MW - ZMici (2'9)
M—nzm (2-10)

2c.
And the polydispersity index (PDI) can be expressed as:
PDle—w/M—n (2-11)
Equation 2-8 can be modiﬁed to equation 2-12 from equations 2-1, 2-9, 2-10, 2-

ll;

17

 

 

2
_5fSM.4 :( ZMi Ci

)SMA VerA
6’ (ZMiCiO)2

.2 .
_(ZMi Ci
(ZMiCi0)2
444741—ISMn/(ZMICioiismI/am (2-12)
M— M 0
=((1—f )x W x W
SMA M 0 (ZMiCio/ZCiO)XZCiO

W
M 101)]0
w X 0 )SMA VerA
0 C

W

 

)SMA Vs r MA

 

 

 

)SMA Vs " MA

 

=((1—fSMA)><

 

In the CA-SMA232 grafting reactions, the consumption of -0H and —MA groups
are negligible since the average grafted linkage is less than 2.5 even when the SMA
grafting conversion goes to 80% as was shown by a theoretical study done by Nie, Li
(47). Accordingly, Nie concluded from the molecular weight measurement results of
SMA232, that the molecular weight distribution is very close to the Schulz distribution,
and the FBI is 1.98. From this distribution, we can draw the relationship between the
change of the weight average molecular weight and the graft conversion of SMA as

shown in equation 2-13.

M
(=——E—‘)SMA = (1 - f SMA )0'5 (2-13)
MWO

Then, we solve the differential equation 2-12 with these initial conditions:

f SMA = 0 at t = O, and we get equation 2-14.

0
_ PD] ,
(1 ’fSMA) 0'5 -1= C0 K0 eXP(- E/R T)C—0H C—MACDMAP Vst (2-14)

 

18

Finally, by setting f éMA = (l — f SM A)“ —1 the modiﬁed SMA grafting
conversion is given by equation 2-15:

, _ PDI° ,
fSMA : (1 — farm) 05 ‘1 = C0 K0 exP("' E/R T)C—0H C-MACDMAP Vst (2'15)

 

C—MA
C0

 

In this equation, the term is a constant related to a speciﬁc SMA grade.

2.4 RESULTS AND ANALYSIS
2.4.1 The SMA grafting conversion vs. time at different CA/SMA232 concentrations
The grafting rate of SMA232 was studied in three different polymer

concentrations under constant temperature and ﬁxed catalyst concentration. From the

ﬁtting curves we can see that f .i‘MA is linearly proportional to the reaction time for all

. . . . 2
three concentratrons. It rs further observed that at high polymer concentrations, the R
value of the trend line decreased. Apparently, at higher concentration aung is not equal

to 1 and, therefore a variable coefﬁcient must be considered under these conditions.
We can also observe that the slopes of each ﬁtted line (at l4g/ 100ml, 11 g/ 100m]
and 8g/ 100ml) are also linearly proportional to the polymer concentration as predicted

from equation 2-15.

19

Table 2-1 f SM .1 vs. reaction time at different CA/SMA concentrations*

 

 

 

 

 

 

 

 

 

 

8g/100m1DMF llg/100ml DMF 14g/100m1DMF
time fsw fs'MA time fsim fSMA time fSMA fs'MA
hrs % hrs % hrs %
0.5 0.27 0.17 0.5 0.3 0.20 1 0.33 0.22
l 0.4 0.29 1 0.45 0.35 2 0.46 0.36
1.5 0.51 0.43 1.5 0.56 0.51 3 0.54 0.47
2 0.58 0.54 2 0.66 0.71 4.5 0.63 0.64
2.5 0.64 0.67 2.5 0.74 0.96 5.9 0.72 0.89
3 0.69 0.80

 

 

 

 

 

 

 

 

 

*CA.'SMA232=I:I, DMAP=0.5g/100ml, T=110 0C

modiﬁed SMA conversion

Figure2-4 f 5M A vs. time fitting curve at 8g/100ml concentration

0.8 -
0.6 r
0.4 r—
0.2 r

 

    

8g/100ml

y = 0.2708x

time

20

R2 = 0.9908

(hrS)

 

IIg/IOOmI

    

 

 

:

.9 1.2 I

g l H y = 0.3666x

> 2 _

§ 0.8 P R —0.9874

g 0.6 ~

3 0.4 ~

£5

E 0.2 '-

E 0 1 1 1 L 1 J
0 05 1 L5 2 25 3

time (hrs)

Figure2-5 f 35M A vs. time ﬁtting curve at 11g/100ml concentration

    

 

14g/100ml
g I r y=0.1523x
9:5 03 I R2=0.9625
t:
8 06 _
< ‘ l
E 0.4
"U l
0.)
SE 0.2 I 0
“O
O
E O 1 _,1 L 1 1 I 1
0 1 2 3 4 5 6 7

ﬁnn(hm)

Figure2-6 f S'M A vs. time fitting curve at 14g/100m1 concentration

2.4.2 The SMA grafting conversion vs. the concentration of DMAP
Using a constant polymer concentration of 1 lg/ 1 00m] the grafting reaction was

studied under four different DMAP concentrations. It is apparent from Figure 2-7

that f S'M A is a linear function of DMAP concentrations conﬁrming a third order reaction

21

kinetics. Furthermore, it is apparent that when the DMAP concentration approaches zero,
f §M A becomes a very small negative number indicating that without a catalyst the
grafting reaction does not occur. This dependence on the catalyst will also be conﬁrmed
under melting conditions.

Table 2-2 f SMA vs. DMAP concentrations*

 

 

 

 

 

 

DMAP concentration f SMA fsMA
g/100ml %
0.135 0.34 0.23
0.27 0.51 0.43
0.45 0.66 0.71
0.54 0.73 0.92

 

 

 

 

 

*CA:SMA232=1:I, [lg/100ml, T=1100C, t=2hrs

y = 1.6825x- 0.012
R2 = 0.9924

    

0.9 ~
0.8 r
0.7 r
0.6 r
0.5 2
0.4 r-
0.3 h
0.2 r
0.1 r
0 1 1 1 1 1 J

0 0.1 0.2 0.3 0.4 0.5 0.6
DMAP content (g/ 100ml)

modiﬁed SMA conversion

 

 

Figure2-7 f 3',” A vs. DMAP concentration fitting curve

2.4.3 The SMA grafting conversion vs. temperature
The SMA grafting conversion as a function of temperatures was also studied

while keeping all other variables constant. The data indicate that the relationship between

22

modiﬁed grafting conversion and reaction temperature follows Arrhenius law and the

average activation energy can be calculated to be : E = 1556710 / Kmol

Table 2-3 f SMA vs. temperatures*

 

T T l/T fSMA ngA '“(1/ fS'MA)

 

C K 1/K %

 

91 364 0.0027 0.43 0.32 0.489

 

100 373 0.00268 0.58 0.54 0.265

 

110 383 0.00261 0.66 0.71 0.146

 

 

 

 

 

 

 

 

125 398 0.00251 0.73 0.92 0.034

 

0.600

0.500

0.400 r

0.300

-Ln(f'SMA)

0.200

0.100

0.000

*CA .‘SMA232=1.'I, [lg/100ml, DMAP=0.5g/100ml, t=2hrs

 

41

0.0025 0.0026 0.0026 0.0027 0.0027 0.0028 0.0028

l/T (l/K)

Figure2-8 ln(1/ f §MA) vs. III fitting curve

2.4.4 The SMA grafting conversion vs. MA content in SMA

As discussed before,

 

is only related to the grade of SMA, more particularly, to the
0

MA content in SMA. Here, SMA132 and SMA232 with different MA contents were

used. It is expected ac

cording to equation 2-15 that f 8MA will be a linear function of MA

contents as shown in Figure 2-9.

23

Table 2-4 f SMA vs. MA content*

 

SMA grade MA% f S... fs'm
%
SMA132 4.74% 0.56 0.51
SMA232 7.08% 0.66 0.71

 

 

 

 

 

 

 

 

 

*CA:SMA=1:I, [lg/100ml, T=1100C, t=2hrs, DMAP=0.5g/100ml

0.8 r y = 0.1029x

07 * R2 =0.9979
0.6 ~-

0.5 r
0.4 L
0.3 r
0.2 r
0.1 *

 

modiﬁed SMA conversion

 

MA wto/o

F igure2-9 [gm vs. MA contents ﬁtting curve

2.4.5 Calculate reaction constant K0 from the SMA conversion value in solution
The reaction constant (K0) can be calculated from equation 2-15 using the following
conditions: T=1000C, t = 2hrs, CA/SMA232=I:I, solution concentration of 11g/100m1,
and DMAP concentration of 0.5g/100m1. At f SMA =0.58 we can assume a dilute solution
conditions, so, Vs=1.

Thus, using Equation 2-15:

0
, —0.5 PD] ,
fSMA =(1—fSMA) -1= C0 K0 BXP(- E/R T)C—0HC—MACDMAP Vst

 

24

0 —- —4
C =5.5g/100mI+M,,(SMA) =5.5x10 mol/L
C_0H =5.5g/100ml+A7n(CA) x N—OH =0.102m01/L , N—OH is the number of

—OH groups in the CA chain with a given number average molecular weight.

C_MA = C0 x N_MA = 0.0495mol/L, N_MA is the number of—MA groups in

the SMA chain with a given number average molecular weight.

CDMAP =0.5g/100ml +Mn(DMAP) =0.0409mol/L

T=373.15 K
t=120 min

We can calculate K0 from the equation 2-15:

KO =1.1951.2 /moI2 min
2.5 CONCLUSIONS
The CA/SMA grafting reaction in dilute solutions can adequately be described by

equation 2-15. Our data clearly indicate that the modiﬁed SMA conversion [33W is

proportional to the CA concentration as predicted. Furthermore, grafting reaction is also
linearly proportional to the MA content of SMA and the catalyst. Finally, the results
show that the relationship between the reaction constant and the temperature follows
Arrhenius Law, with an activation energy of 15,567 K] / Kmol .

However, it should be noted that as the polymers concentration is increased, some
phase separation can occur, which will then impact the effective reaction volume and the

probability of the un-grafted chain and the grafted chain to react.

25

Chapter 3. STUDY OF THE GRAFTING REACTIVITY AND
PROPERTIES OF CA/SMA POLYMER BLENDS
PREPARED BY REACTIVE EXTRUSION

3.1 INTRODUCTION

Grafting provides a method to improve the compatibility of polymer blends to
achieve desirable properties. It is based on the formation of compatibilizer at the interface
between the two polymers phases (48). Maleic anhydride (MA) has been widely used as
one such compatibilizer because it has two distinct functional groups; an anhydride group
that can undergo a condensation reaction with polymers containing amine or alcohol
groups and a double bond, which can be copolymerized onto the backbone of polymers
such as styrene, ethylene and propylene (49-52). From an environmental concerns point
of view and sustainable development considerations, it is preferable to use natural
polymers such as starch, cellulose and their derivatives (53). Many natural products and
their derivatives (after chemical modiﬁcation) are an important source of hydroxyl-
bearing reactive polymers, but their processing and mechanical properties are often poor.
Grafting a functional synthetic polymer with maleic anhydride groups onto natural
polymers provides an important method of improving the properties of a natural polymer
while meeting environmental requirements (54, 55).

Cellulose acetate is one of the commercially available cellulose derivatives. It is a
tough material with excellent optical clarity, however, due to its poor processability high

concentrations of plasticizer is necessary during processing. Although grafting synthetic

26

polymers such as styrene or acrylamide onto cellulose or cellulose acetate has been
studied in the past, these studies show that the reactivity of the grafted polymers is poor
and their properties have not improved signiﬁcantly (56-60). Grafting SMA onto CA in
DMF solution using DMAP as catalyst was studied by Nie, Li (61). Who showed that
with a proper catalyst, high SMA grafting conversion could be obtained.

In this study, an extruder was used as a continuous flow reactor to perform in situ
the grafting reactions and blending simultaneously. Such continuous process is
advantageous over reactions in dilute solutions as it provides good mixing, excellent
temperature control and obvious economic beneﬁts (62). As is shown below, it was
apparent that successful grafting greatly improved the processability, enhanced the
mechanical properties and improved the water resistance of the modiﬁed CA polymers.
These improvements were realized only when DMAP catalyst was present. In the
absence of the catalyst, almost no grafting reaction occurred and no signiﬁcant changes

were observed in the properties.

3.2 EXPERIMENTAL

3.2.] Materials

Cellulose Acetate (DS: 2.45, ”MT, .- 103,000, 114—, .- 46,000, Tg=187°c, Tm=232

0C) was provided by Eastman Chemical Company. High molecular weight Styrene

 

maleic anhydride random copolymers ( SMA232: 7.08 wt % maleic anhydride, M w .°

 

249,000, M: .- 126,000; Tm=232 °C ,SMA332: 12.2% maleic anhydride, MW .-193,000,

M n : 100,000, Tm=232 0C) was provided by Nova Chemical Company; low molecular

27

weight SMA(SMA3000P, 25 mol% maleic anhydride, X]; .-9,500, B; .- 3,800,
Tg=125°C) was supplied by Sartomer Company Inc. The catalyst, 4-

Dimethylaminopyridine (DMAP) was purchased from Sigma-Aldrich, Inc. Dioctyl
phthalate (DOP) was provided by Spectrum Chemical Mfg. Corp., and ethyl acetate was

purchased from EMD Chemical Inc.

3.2.2 Reactive extrusion of CA/SMA
All the extrusions were run in a Century ZSK-30 twin screw extruder. This
equipment consists of an extruder driver with a speed control gearbox; a twin-screw, co-

rotating screw with a screw diameter of 30 mm and an L/D (Length to Diameter ratio) of

40, fed by accurate single-screw feeders. CA was dried in a ventilated oven at 100 0C for

24 hr. prior to feeding it into the extruder. The catalyst, DMAP, was dispersed in CA at a
ratio of 1000:] (CAzDMAP) and the mixture was then crushed using a mortar and a
pestle until a uniform mixture was obtained. This master batch was then mixed with the
balance of the CA powder and the required amount of SMA resin.

The screw conﬁguration used (Figure 3-1) is divided into 3 sections; section 1 of
12.5D distance followed by section 2 of 15.5D distance and ﬁnally section 3 with 12D

distance. The vent port was kept open to remove vapor and catalyst.

28

 

‘1‘" .. 1 1 ‘ It - 1 “ _ " 1‘9 - 1‘ v 1., J .' .1, ‘J

.' ‘ - g ‘u k l\ . \ '1‘. ‘3'. 1“ ‘2‘ '..

i I _ ‘ i \. k, I ‘1 1‘ ‘ .

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Figure 3-1 Screw conﬁguration used for the synthesis of CA—SMA copolymers

The temperatures in the extruder zones were set up to reach the required melting
temperature of CA and SMA. For all mixtures the temperature proﬁle during the
extrusion was set at 15/145/200/235/245/250/250/250/255/245/235°C from the feed
throat to the die, with a melt temperature of 235°C-246°C. The feeder for mixture
material was set to between .50-2.20. This setting was calibrated tol4.7-l6.0 lb/hr for
different mixtures required to maintain the main motor torque at 50-60%. The screw
speed was maintained at 150 rpm.

The CA/SMA232 blends with various percentage of SMA (30/70, 50/50, 70/30,
85/20, 85/ 15) were processed by extrusion. When the SMA content decreased, the torque
and the melting pressure increased due to the very high viscosity of CA Thus, the feed

rate was reduced in order to maintain a constant torque. At 10wt% SMA, the melting

29

pressure became very high and the extruder was shut off automatically due to blockage at
the die.

CA/SMA blends with a ratio of 70/30 were processed for different grades of SMA
(ex. SMA3000P, SMA232, SMA332) and different amounts of catalyst (0.01%, 0.05%,
0.1%). The catalyst concentration did not signiﬁcantly affect the extrusion process. When
CA/SMA3000P was processed, the melting pressure and torque were very high leading to
the very weak and brittle materials due to poor mixing. When 20% DOP (wt% of CA)
was added the pressure and torque dropped and mixing improved signiﬁcantly.

The extrudate was cooled by water, pelletized into resin and dried in a ventilated

oven at 70 0C for 24 hrs.

3.2.3 Soxhlet extraction and Fourier transformed infrared spectroscopy (FTIR) test

The CA/SMA polymer blend to be tested was grounded into a powder. The
powder was Soxhlet extracted with ethyl acetate as the solvent for 48 hrs. When pure CA
was Soxhlet extracted under identical conditions, less than 2% were extracted.

The conversion of SMA grafted onto CA was calculated by the mass balance.

The materials which remained in the thimble and casts made from the extracted
solution were analyzed by F TIR to conﬁrm the grafting reaction.

FTIR analysis: For solid materials, a 1% sample was mixed with 99% KBr
powder and pressed using a pellet maker to a ﬁne transparent disk. This disk was directly
put into the sample holder in the FTIR to obtain the spectrum. A background scan was
obtained with the pure KBr pellet and this spectrum was subtracted from the sample

spectrum in order to eliminate interference from atmospheric moisture and C02.

30

FTIR of all the extracted materials were obtained by ﬁrst solvent casting thin
ﬁlms of the samples and then placing these ﬁlms directly in the sample chamber to obtain

the FTIR spectrum.

3.2.4 Injection mold

The reacted blends were injection molded into tensile bars (ASTM D638 type 1)
using a Cincinnati Milacron injection molder. The zone temperature proﬁle, pressure,
shot velocity and mold temperature was changed to study their effects on the tensile

properties. The general set is shown below.

Temperature proﬁle: (All temperatures are in 0F)

 

 

 

Nozzle Zone 1 Zone 2 Zone 3 Mold
Set 500 490 480 480 150
Temperature
Actual 501 490 480 480 150
temperature

 

 

 

 

 

 

 

 

The pressure setting proﬁle was:
Fill pressure: 1300 psi

Hold pressure: 1000 psi

Pack pressure: 1200 psi

Timer conditions:

Inject high: 5 sec

Pack: 3 sec

31

Hold: 2 sec

Cooling: 35 sec
Extruder delay: 16 sec
Open dwell: 1 sec
Shot size: 1.0 in

Shot velocity: 2.0 in/s
Cushion: 0.25 in

Transfer position: 0.5 in

3.2.5 Tensile properties test
The tensile properties (e. g. tensile strength, elongation, Young’s modulus) were

tested in a UTS machine following the ASTM D638 standard. The tensile bars were

conditioned at 50%RH, 23°C for 40hrs. The cross head speed was set at 0.2 in/min, the

load cell capacity was 1000 lbs. At least 5 specimens were tested for each sample.

3.2.6 Izod impact test
The tensile bars were cut into 2.4 x 0.5 x0.125 inches. A TMI notch cutter and

impact tester were used in notching and Izod impact test following the ASTM D256A

standard.

3.2.7 Moisture absorption test

The ground CA/SMA232/DMAP (70/30/0.01) and CA/SMA232 (70/30) polymer

blend powders were dried in a ventilated oven at 100 0C for 24 hrs, 10g of each blend

32

powder was put in a desiccator (diameter 30 cm) for 24 hrs, which was adjusted to 90%

relative humidity by ﬁlling with saturated barium chloride solution at 25 0C. After

equilibrium moisture was achieved, the powder was weighed again.

3.3 RESULTS AND ANALYSIS
3.3.1 Grafting reaction results
The SMA grafting conversion is calculated from the mass balance of the Soxhlet

extraction data, the results are shown in Table 3-1.

33

Table 3-1 SMA grafting conversion in CA/SMA blends

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Materials(weight percentage) SMA conversion

CA/SMA3000P/DMAP(70/30/0.01) 39.4%
CA/DOP/SMA3000P/DMAP(56/14/30/0.01) >46.7%
CA/SMA232/DMAP(30/70/0.01) 32.3%
CA/SMA232/DMAP(50/50/0.01) 41.3%
CA/SMA232/DMAP(70/30/0.01) 68.%
CA/SMA232/DMAP(80/20/0.01) 32.3%
CA/SMA232/DMAP(85/15/0.01) 23.8%
CA/SMA232(70/30) 7%
CA/SMA332/DMAP(20/80/0.01) 21.8%
CA/SMA332/DMAP(30/70/0.01) 32.5%
CA/SMA332/DMAP(50/50/0.01) 41.9%
CA/SMA332/DMAP(50/50/0.05) 77.7%
CA/SMA332/DMAP(70/30/0.01) 54.2%
CA/SMA332/DMAP(85/15/0.01) 26.2%
CA/SMA332(30/70) 0.0%

 

 

 

The FTIR results are shown in Figure 3-2, Figure 3-3 and Figure 3-4.

Figure 3-2 shows pure CA, the material remaining in the thimble, and the ﬁlm
cast from the extracted solution of the CA/SMA3000P/DMAP (70/30/0.01) blend.

Figure 3-3 shows the FTIR spectrum of the material remaining in the thimble

from the extraction of CA/SMA232/DMAP (50/50/0.01) blend.

34

Figure 3-4 shows the F TIR spectrum of the material remaining in the thimble

form the extraction of CA/SMA232 (70/30) blend compared with pure CA.

 

 

 

 

 

_ CA/SMA3000P/DMAP
, g . , ., . . .. _ Grafted SMA=39.4°/o
(LHUIU‘sk ‘\kLttllk
12‘ - Material disloved in solvent
_ - Material remained 1n thimble 173 1
‘ 1275
1'— r‘ 1073
. l
0.8— l
8 ‘ F.
g "‘ 703
.e 1
g 0.6-
..o ..
N d ‘ ‘
0.4-
0.2- ‘
4
04 1.-" 9"
. l . - . l . . . . I . . . . I . . . . I . . . . l . . . . I . . . . l .
4000 3500 3000 2500 2000 1500 1000 500

cm-1

Figure 3-2 FTIR spectrum of CA/ SMA3000P blend after extraction

35

absorbance

absorbance

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

L75 T - Cellulose Acetate
: C A ISM A332 IDM AP(50 ,50 [0.05) - Material remain in thimble after extraction
1 5__‘ Grafted SMA%=77.7%
1.25; 111050
: A 1226 i ,"g/
I. l
, .1
.1 :1
l—: ‘ 699
f 1754'”
075—:
2 1602
0.5-9
l
0.25-E
0“?
l"'*l""l""1""l""l""l""l'
4000 3 500 3000 2500 2000 1500 1000 500
cm]
Figure 3-3 FI‘IR spectrum of CA/SMA232/DMAP (50/50/0.05) after extraction
CA/SMA232(70/30) after extraction
1 Grafted SMA=7°/o
* - Cellulose Acetate
1-2'4 - Material remain 111 lllllllltiC c
_ g; '3 §
.. l‘ ""
1- '9'
.. j‘ I
.. h /
0.8- l i/
0.6-1
1
0.4—
0.2‘
1
0—
.l...r]....l...-r...f[....l-...l..4'.
4000 3500 3000 2500 2000 1 500 l 000 500

cm-l

Figure 3-4 FTIR spectrum of CA/SMA232 (70/30) after extraction

36

The Soxhlet extraction data indicate a very low grafting reaction in the absence of
the catalyst.

The Soxhlet extraction data also show that adding catalyst improves the reaction
signiﬁcantly. Adding a plasticizer to the CA/SMA3000P blend increases the conversion
of SMA since it improves the processability of the blend, reduces the matrix phase
viscosity, increases the SMA phase dispersion, and increases the reactivity.

The phase dispersion effects on grafting can also be observed by comparing the
composition of CA/SMA232 at 70/30, 80/20 and 85/ 15 proportions. The SMA
conversion dr0ps due to poor processability and lower phase dispersion. However, when
the SMA content increases from 30% to 50% and then 70%, SMA grafting conversion is
reduced due to a lower concentration of CA in the blend.

Furthermore, when more DMAP is added, higher grafting conversion of SMA is
observed comparing with a composition of CA/SMA332 (50/50) at 0.01% and 0.05%
DMAP respectively.

It is observed that SMA332 has a better compatibility with CA because than the
other grades of SMA used. Apparently, SMA332 has a closer viscosity and solubility
parameter to CA. Since the original compatibility affects the SMA phase size, it further
affects the grafting reactivity. Under the same conditions, CA/SMA332 has a higher
grafting conversion than CA/SMA232 except at the 70/30 blend level.

It is observed from the F TIR data (Figure 3-2 ) of a sample composition of

CA/SMA3000P/DMAP (70/30/0.01) aﬁer Soxhlet extraction, that it still contain the

benzene group (around 700 cm.1 ), the ester C=O group (peak frequency that was shifted

37

from 1754.7 cm-lto 1731.1 cm'l) and greatly lower content of the hydroxyl group

(around 3500 cm.I ). Similar results are also observed from Figure 3-3.

All these results indicate that SMA has been grafted onto CA. We can only

observe the most signiﬁcant anhydride peak (1778 cm']) and benzene group peak (700

cm-]) from the FTIR of the cast ﬁlm prepared from extracted solution. It is apparent that

only free SMA and a very few short chain CA which were grafted onto SMA have been
extracted.

In the samples with lower grafting (CA/SMA232 without catalyst) we cannot
identify the benzene group (Figure 3-4), the shift of the ester C=O group is small, and the
hydroxyl group peak value has almost the same intensity. It is apparent from these data
that the grafting conversion was very low in the CA/SMA232 blend without catalyst and

that almost all the free SMA232 was extracted.

3.3.2 Properties of CA/SMA blend

3.3.2.1 Properties test results

The tensile properties and Izod impact strength of highly grafted CA/SMA232
(70/30/0.01) blend at different content SMA and a lower grafted CA/SMA232 (70/30)
sample were tested and are compared in Table 3-2.

Table 3-3 shows the mechanical properties for the different compositions of

CA/SMA.

38

Table 3-2 The properties and phenomena comparison between compatibilized and

incompatibilized CA/SMA233/DMAP (70/30)

 

 

 

 

 

 

 

 

 

 

 

properties CA/SMA232/DMAP CA/SMA232

Graft percent >60% <7%

Tensile strength 9800 psi 6400psi

Tensile strength (after 2 month) 9700psi 5900psi

Tensile modulus 480 kpsi 560 kpsi

Tensile modulus (after 2 month) 480 kpsi 480 kpsi

Elongation 2.52% 1.22%

Moisture absorption 0.7% 2.97%

(at 90% RH, 24hrs)

Acetone solution(10g/100m1) Uniform solution, a layer of CA
gray color precipitated in bottom

after 24 hr

 

 

Table 3-3 Mechanical properties of CA/SMA blend at different compositions

 

 

 

 

 

 

 

 

 

 

 

Materials Tensile Moudulus Elongation Izod impact
strength strength_
psi (kpsi) (°/o) ft.lb/in
CA/SMA232(70/30) 6400i400 560i20 1.21i0.13 O.31i0.05
CA/SMA232/DMAP(50/50/0.01 5500:1350 480i40 1.191017 0.86:t0.05
CA/SMA232/DMAP(70/30/0.01 9600i450 470i30 2.52i0.26 1.472t0.10
CA/SMA232/DMAP(85/15/0.01 12500i900 7002520 2.81i0.21 2.12i0.09
CA/SMA332/DMAP(70/30/0.01 9200i420 470i10 2.31i0.24 1.23:1:0.15
SMA232* 7100 500 1.8
SMA332* 7500 540 1.7
CA(p1asticized)* 3840-7540 220-320 16-25 2.6-6.59

 

 

 

 

 

 

*data was provided by the producer

39

 

These results show that in a CA/SMA blend without the catalyst, the grafting
between CA and SMA is very low yielding an incompatible blend with very poor
mechanical properties. When the catalyst DMAP is added, the mechanical properties of
the blends are greatly improved indicating high grafting reactions. Also, the moisture
absorption is reduced signiﬁcantly due to the grafting reaction. The grafted polymer
blend can form a clear uniform solution in acetone compared with the un-grafted polymer
blend which does not yields a clear solution at these concentrations. This is because the
grafted CA-SMA copolymer acts as a compatibilizer to form a strong interfacial adhesion
between two incompatible polymers, thus, improving the mechanical properties and the
moisture resistance. The CA/SMA blend with higher CA content gives higher mechanical
properties due to CA having higher mechanical properties. The grafted polymer blend has

higher properties than plasticized CA and pure SMA (properties given by the supplier).

3.3.2.2 Injection mold conditions studying results

The effects of injection molding conditions on the tensile properties are analyzed
by unbalanced Fractional Factor Design Analysis using an SAS program. The four
factors: ﬁll pressure (A), set temperature (B), shot velocity (C) and mold temperature (D)

were studied in this design.

40

Table 3-4 The tensile properties of CA/SMA/DMAP (70/30/0.01) at different

injection conditions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sample Fill Nozzle Shot Mold Tensile Tensile Elongation
pressure temperature velocity temperature strengt Modulus (%)
(psi) (0,.) (imsec) (0F, h(psi) (kpsi)
1 1300 518 1.5 100 8300 520 1.76
2 1300 518 1.5 100 9040 480 2.17
3 1300 490 1 100 8660 480 2.05
4 1000 490 0.5 130 8500 430 2.11
5 1000 490 0.5 130 8380 430 2.15
6 1000 490 0.5 100 9100 470 2.31
7 1000 490 0.5 100 8350 470 2.06
8 1000 490 2 130 10500 450 2.97
9 1000 490 2 130 9900 450 2.69

 

The results show that the Shot velocity (factor C) and the Mold temperature

(factor D) have signiﬁcant effects on tensile strength and elongation. At a higher mold

temperature and higher shot velocity, the tensile strength and the elongation are much

higher. Apparently, the higher shot velocity and higher mold temperature make the

polymer blend cooling more uniformly and the residual stress is reduced under these

conditions. The Fill Pressure (factors A) and the Nozzle temperature (factor B) do not

have signiﬁcant effects on the tensile strength, tensile modulus or the elongation at break.

The interaction of the Shot velocity (factor C) and the Mold temperature (factor D) has a

signiﬁcant effect on the tensile modulus but no signiﬁcant effect on the tensile modulus.

3.4 CONCLUSIONS

41

 

It is concluded that high grafting reaction of SMA onto CA can be obtained only
when a catalyst (DMAP) is present. Without this catalyst, the grafting reactivity of
CA/SMA blends is very low and incompatible CA/SMA blends with very poor
mechanical properties are produced.

The grafting reaction improves the phase dispersion due to reduced interfacial
tension and increased interfacial adhesion between the two phases. The mechanical
properties of these compatible blends are improved and are comparable to glass ﬁber
reinforced ABS and other engineering thermoplastics. These high mechanical properties
make CA/SMA polymer blends useful, sustainable materials.

At speciﬁed grade SMA and catalyst concentration and temperature, the SMA
conversion is affected by two factors: the proportion of CA/SMA and its processability.
In the case of CA/SMA3000P blend, adding plasticizer can improve the reactivity of the
blend by reducing the viscosity of the CA phase. The highest mechanical properties were
observed at 15% SMA, which is the highest CA content processable without plasticizer.

The injection molding conditions were studied in order to optimize the tensile
properties of the CA/SMA blends. A lower ﬁll time and a higher mold temperature can

improve the tensile properties due to uniform cooling.

42

Chapter 4: COMPATIBILIZATION STUDY OF CA/SMA BLEND

4.1 INTRODUCTION
4.1.] Polymer Blend

The development of new multiphase polymeric materials often involves the
blending of two or more polymers. The combination of the favorable properties of
different polymers is usually the goal of blending. In polymer blends the required
properties can be easily achieved by the careful selection of the component polymers and
their blend ratios (63, 64).

Polymer blends can be broadly classiﬁed into three types: miscible blends,
immiscible but compatible blends, and incompatible blends. When the free energy of
mixing is negative the blend is a miscible blend. According to Flory-Huggins’s theory,
the free energy for mixing of two polymers A and B in the homogenous state can be

expressed as:

VA +VB VA VB

 

1 (4-1)

AGm: Gibbs free energy of mixing
V A , VB : actual volume of polymer A and B
(15 A , ¢B : volume fraction of polymer A and B

B A B : binary interaction energy

43

17A , I73 : molar volume of polymer A and B

A17," = BAB¢A ¢B , Aﬁm is mixing enthalpy at unit volume

 

— l l — . . . .
AS m = —R[¢Al7n¢A + ¢Bl7n¢8 ], AS m 18 mlxmg entropy at unit volume.
A B

In miscible blends, this miscibility of the two polymers results in a single glass
transition temperature (T g) for the blend, which is composition dependent, as per the Fox-

Flory theory. The Fox relationship for a two-component blend (65) is explained in

equation as follows:

Lzﬂﬁhwi (4-2)

T8 T8 A T8 8

Here T g A and T g3 are the glass transition temperatures of the polymer A and B,

and w A and WE are the weight fractions of polymer A and B in the blend respectively.

The mechanical properties of miscible blend can be predicted by the equation:

P = WAPA + WBPB (4-3)

P , PA , P8 is the properties of polymer blend, polymer A and polymer B
respectively.

Due to the low combinatorial entropy of mixing of high molecular weight
polymers, the miscible polymer blends can only be attained when there are some kind of
speciﬁc intermolecular interactions, such as hydrogen bonding and n-bonding, so that
mixing enthalpies are negative (exothermal). But most of the binary polymer blends are
not thermodynamically miscible giving rise to a two-phase system which is mostly
characterized by coarse and unstable phase morphology and poor interfacial adhesion

between the phases. This strongly affects the mechanical/physical properties of the

44

ﬁnished product. The interaction between the polymer pairs at the molecular level has
been deﬁned by the term “compatibility”. Compatibility is treated as a relative term and

can be deﬁned by a compatibility number as explained in the following equation.

NC = (Experimental Probe size)/ (Domain sizes of phases)

The experimental probe size can be taken as the scale of resolution of an
instrumental technique. The domain size is the average dimension of the dispersed phase
in the blend. Thus, when N c —> oo , the system is compatible and when N c ——) 0 , the
system is incompatible (66, 67, 68).

Most incompatible blends show phase separation. The phases, however, vary in
amount, size, sharpness of their interfaces, and degree of continuity. The type of
morphology depends upon several factors, the most important being the composition and
the viscosities of each component.

Figure 4-1 shows the effect of those two parameters on the morphology of the
blend. The component, which is in higher proportion or is less viscous, tends to form the

continuous phase (69).

45

 

   
   
 

Continuous
Phase of B

Viscosity ratio
A/B

Continuous
Phase of A

 

 

 

Volume ratio A/B

Figure 4-1 Effect of composition and viscosity on phase morphology

4.1.2. Compatibilization
Simple blending of immiscible blends does not generally give a material with
desired characteristics because of the high interfacial tension existing between the two
phases.
In general, the properties of two component polymer mixtures can be described

by the equation:
P = wAPA + wBPB + APE(w) (4-4)

In equation 4-4, APE (w) is an excess term, which is dependent on the

composition under consideration. The compatibilization achieved results in positive

46

values of APE (w) , which means that the properties of the polymer combination are better

than the volume arithmetic average of the constituents’ properties (70). There are various
routes for obtaining this effect of compatibilization.

Compatibilization is most often based on the use of suitable block or graft
copolymers which are located at the interface between the phases of an immiscible blend
and act as an emulsifying agent. In the past, much attention has been paid to the synthesis
of block and graft copolymers as potential compatibilizers which were subsequently
added to an immiscible blend. However, this strategy cannot be applied for all kinds of
blends and, moreover, the synthesis is most often very expensive. For these reasons, most
current interest is now directed to a method called 'reactive' compatibilization. This is
based on the in situ formation of a block or graft copolymer at the interface between the
blend phases as a result of chemical reactions during melt-mixing. In most cases, the two
components of a binary blend do not have the appropriate reactive groups for the
formation of a copolymer at the interface and, as a consequence, functionalization is
required. Functionalization of the blend components is a widely applied strategy for
reactive compatibilization. In recent years, research has been performed to realize
ﬁmctionalization of different types of polymers and to obtain insight into the reactivity of
different functional groups and hence to obtain the desired compatibilization effect (71).
Another method of reactive compatibilization is based on the addition of a reactive
polymer to the blend as a third component. It is necessary that this reactive polymer is
miscible with one of the blend components and reactive with the other blend component.
A reactive polymer which fulﬁls these conditions can only be found for a limited number

of binary blends.

47

Recently, increasing efforts have been directed towards in situ compatibilization
of immiscible polymer blends by reactive extrusion (72-77). Instead of synthesizing the
compatibilizers in a separate step, these are created in situ during extrusion through
interfacial reactions between the respective functionalized polymers. From a
technological point of view, a one-step reactive extrusion process is easier to control for
cost-effective generation of compatible blends from initially immiscible polymers. In
this study, CA-SMA grafting copolymer was synthesized in situ by reactive extrusion and

acted as a compatibilizer of the CA/SMA blend.

4.1.3. Theoretical study of compatibilization

The morphology of polymer blends and their interrelations with compatibilizers
has been mostly studied experimentally (78, 79, 80), and less attention has been paid to
the theoretical analysis of the phase structure development at mixing. Tang and Huang
(81) tried to describe the effect of a compatibilizer on the size of dispersed droplets in
polymer blends, but only the droplet break was studied in their work. This approach is
justiﬁed only for blends containing very small fractions of the dispersed phase due to
coalescence. Milner and Xi (82) considered the effect of a compatibilizer on both
breakup and coalescence of dispersed droplets and draw a conclusion that the
compatibilizer decreases the interfacial tension slightly and does not affect the breakup of
the droplets. This conclusion is in strong disagreement with the experimental results of
other studies. Recently, the balance of breakup and coalescence of dispersed droplets in
polymer blends containing a compatibilizer was analyzed by I. Fortelny and A. Zivny

(83). The formula for dispersed droplet size in the steady state was drawn in assumed

48

interfacial copolymer states. I. Aravind et.al describe a simple theoretical analysis of an
ethylene—polypropylene-diene terpolymer (EPDM)/poly(trimethylene terephalate) system
using poly(ethylene-co-propylene-co-maleic anhydride) (EPM)-g-MA as compatibilizer
and compared it with experimental results (84).

In this study, the compatibilizer CA-SMA was generated in situ. The
concentration of compatibilizer is determined by the grafting reactivity. The grafting
reactivity was affected by phase dispersion. On the other hand, the phase dispersion was
improved by the grafting co-polymer generated in situ. A formula was derived between

disperse phase size and reactivity and further used to explain the experimental results.

4.2 EXPERIMENTAL
4.2.1 Transmission Electron Microscopy (TEM)

Morphology of CA/SMA blend was examined by TEM with samples that were
freshly fractured. Samples with thickness of the 90-150 nm were prepared using a 3 mm
MICRO STAR diamond knife. The samples were examined by A JEOL 100CX TEM at
very short time (around 15 seconds) under 10 KV potential. Since the contrast between
CA and SMA phase is high, no staining is required. The number average particle size was
calculated. The TEM was done on the CA/SMA232 blends under different extrusion
passes, different catalyst amounts (0, 0.01%, 0.05%, 0.1%) and varied CA/SMA332
blends. The TEM pictures and the comparison of SMA particle size are shown in the

following ﬁgures. The section is perpendicular to the ﬂow direction for all TEM pictures.

4.2 RESULTS AND ANALYSIS

49

The TEM pictures of CA/SMA blend at various passes, catalyst amounts and SMA
grades are shown in Figure 4-2 to Figure 4-9. The lighter area is CA phase due to the loss

of material in the CA phase under the electron beam. The darker area is the SMA phase.

 

Figure 4-3 TEM of CA/SMA232(70/30) after 2 extrusion passes

50

 

Figure 4-4 TEM of CA/SMA232 (70/30) after 3 extrusion passes

 

Figure 4-5 TEM of CA/SMA232/DMAP (70/30/0.01) after 1 extrusion pass

51

 

Figure 4-7 TEM of CA/SMA232/DMAP (70/30/0.1) after 3 extrusion passes

52

 

Figure 4-8 TEM of CA/SMA332 (70/30) after 1 extrusion pass

 

Figure 4-9 TEM of CA/SMA332/DMAP (70/30/0.01) after 1 extrusion pass

53

The number average diameter of the SMA droplet was measured and calculated

from the TEM picture, the results are shown in Figure 4-10.

 

 

 

 

 

 

 

 

g SMA droplet diarnter in CA/SMA(70/30) blend
E 4 ” I 1 extrusion pass
§ 3- 5 I 2 extrusion passrun
o 3
g 2 5 D 3 extrusion pass
'6 .
g 2
{:3 1. 5
8. 1
< 0. 5
5 0
3
0‘

Figure 4-10 Number average diameter of SMA (pm) in CA/ SMA blend

From the results we can see the SMA phase size in the CA/SMA232 blend
became smaller with increased extrusion passes. In Figure 4-2, Figure 4-3 and Figure 4-4,
the size reduction from 1 extrusion pass to 2 extrusion passes is much sharper than the
reduction from 2 extrusion passes to 3 extrusion passes. The data show that the phase
dispersion was improved signiﬁcantly after increased initial mixing time, but when the
phase size reached a speciﬁc level, additional mixing had little effect.

When the catalyst was added more grafting occurred and the phase dispersion

improved. This can be observed by comparing Figure 4-2 and Figure 4-5 for

54

CA/SMA232 blend, and comparing Figure 4-8 and Figure 4-9 for CA/SMA332 blend.
This is caused by the grafting reaction generated CA-SMA co-polymer at the interface
and consequent reduction in the interfacial tension resulting in improved phase
dispersion. When Figure 4-6 and Figure 4-7 are compared it can be seen that higher
catalyst content gave higher phase dispersion due to higher grafting conversion.

It can also be seen that the phase dispersion in the CA/SMA332 blend is improved
compared with that of the CA/SMA232 blend, due to the increased MA content of
SMA332. The lower molecular weight and the higher MA content make it more

compatible with CA because its solubility parameter is closer to that of CA.

4.4 THEORETICAL STUDY
4.4.1 The disperse phase droplet breakup under shear rate

Morphology analysis for in-situ forming grafting copolymer used as
compatibilizer has not been studied before. In the ﬁrst step, we will analyze the breakup
of dispersed droplets under shear rate in the extruder without considering coalescence.

The Capillary number was introduced by Taylor (98) as:

Ca = ”m% (45)

Where 7]", is the matrix viscosity, 7 is the shear rate, R is radius of disperse

phase size, 0' is interfacial tension.

The droplet breakup rate was expressed by the Equation 4-6 (83):
dR
- (Tit-)6 = f (Ca - Cae )1? (4-6)

Where f is a function of rheological property of the matrix and dispersed phase.

55

Cac is critical Capillary Number, which is the value the breakup stopped

We assume at the critical Capillary Number, the droplet size is at steady state RC,

and

Cac = "m 77% (4-7)

Then we rearrange equation 4-6 as:

fnmr

 

dR
- (Elb - R(R - Re) (4-8)

We solve the equation for CA/SMA blend at a constant composition using the
following assumptions:

Cac is only dependant on the blend system.

7 is a constant at a speciﬁed process condition

0' does not change without grafting reaction

R—Rc 0'

ln

At t = 00, R 2 RC. RC was measured from CA/SMA blend cast ﬁlm from the dilute

solution, the value is 1.14 pm.

In CA/SMA232 system without catalyst, the experimental results are shown in

Table 4-1, the curve of In

 

vs. extrusion passes is drawn in Figure 4-11.

C

56

Table 4-1 Dispersed phase size of CA/SMA232 at different passes

 

 

 

 

Sample # Passes Phase size(diameter, pm)
1 1 2.88
2 2 2.36
3 3 2.32

 

 

 

 

 

function of dispersed particle size vs
extrusion passes

    

 

 

4.5 — 2-
4 R — 0.9348 9
A35
13 3
Cr.
5% 2.5
g 2
51.50
1-
0.5 r
O 1 J
1 2 3
passes

 

Figure 4-11 ln vs. extrusion passes of CA/SMA232

C

The curve is close to a straight line showing that the assumptions are reasonable

and M is close to a constant. It also indicates that the effect of coalescence is
0'

insigniﬁcant and the droplet breakup dominated in the extrusion process. But in the 3rd

extrusion pass, the radius of dispersed phase droplet is larger than we predicted from the

57

data. This is caused by the onset of coalescence when the phase size approaches the
critical size.
When the volume fraction of dispersed phase is increased, the action of

coalescence must be taken into account. The rate of coalescence can be written as (83):
dR 4 .
(_“‘)c :_7¢PCR (4'10)
dt 7:

Where 7 is shear rate, ¢ is volume fraction of the dispersed phase, Pc is the
probability that collision of the particles will be followed by their fusion. It is a function

of o and R, and can be expressed as (83):

9Ca2R2
8h,2(1+3C/2)'

 

PC = exp{— (4-11)

Where ,1 = 7],, /77m is the ratio of the viscosities of the dispersed phase and matrix,
C is a function of the mobility of the interface, Ca is capillary number, h, is speciﬁc

distance between two disperse phase droplets fusion. The critical dispersed phase size
can be solved by the following Equation 4-12. At this state, the rate of breakup and rate

of coalescence are equal.
dR dR
— — = — 4-12
( dtlb ( dt)c ( )

The phenomenon of coalescence has not been studied in detail in this work.

4.4.2 The effect of compatibilizer on the interfacial tension
The compatibilizer reduced the interfacial tension, and then improved the phase
dispersion. The relation of interfacial tension and the compatibilizer concentration can be

expressed as:

58

_d_"=k(e_e,) (4-13)
do

Where c is the concentration of the compatibilizer

k is a constant related to the chemical properties of the compatibilizer

as is interfacial tension under saturate compatibilizer concentration

In the CA/SMA blend system, the concentration of semi-ester OH-MA was used

as concentration of compatibilizer, then:

-—d0'
J—O'S

 

= kdc = deOH—MA (4-14)

We solve the differential equation using the initial condition,

0200 at 6:0 toget:
0' = as + (00 — Us ) ex13(_kCOH—-MA ) (4‘15)

Here both a and Comm are function of time.

4.4.3 The morphology of in situ compatibilized CA/SMA in reactive extrusion

In the CA/SMA blend system, the compatibilizer (grafting copolymer) was
generated in situ during reactive extrusion. The grafting copolymer reduced the
interfacial tension between the two phases, which increased the dispersed phase (SMA
phase) droplet breakup speed. The droplet breakup gave more interfacial area (reaction
area) to improve the rate of generation of grafting copolymer.

The reactive extruder can be modeled as a PFR reactor, so the OH-MA generating

rate can expressed as:

FdCO/l -— MA =

E
dV I[SI<0 exp( ,7. )C—OH C—MA CDMAP (4‘16)

R__

59

Where F is a CA/SMA polymer blend volume ﬂow rate in the extruder, V is the

total volume of the extruder, and V5 is coefﬁcient of effective reaction volume and is a
function of the SMA phase size: VS 0C %,

Since F was set to a constant in the extrusion, equation 4-16 can be rearranged
using the extrusion residence time tm :

tres = V/F, we got:

dC _ — E
-—£gt—A1A— = Vs K 0 exP(-RT]—")C"0H C—MA CDMAP (4‘17)

Substitute equation 4-14 by equation 4-17:

—d0'

o—as

 

- E
= deOH—MA = k Vs K 0 ”NEW—0H C—MA CDMAPdt (4-18)

When it is solved as before we get:
I
0 = Us + (0 0 — 0 s ) “1’6ij 5 K 0 eXP(1;—,1;:)C—0H C—MACDMAPdt) (4-19)
0
By substituting equation 4-19 to 4-8, the droplet break can be rewritten as
dR ’ —E
~ (1)6 = ﬁlm/MR "— Re)/(Os + (00 - Us)eXP(-k£ 'VsKO exP(ﬁ)C—0HC—MACDMAPdt»
(4-20)
Here Vs is a function of R; RC is a function of o.
For CA/SMA blending in reactive extrusion, the following assumptions are used
to solve the differential equation 4-20:

1) The dispersed phase size is much larger than the critical size, so droplet

breakup dominates in the extrusion, thus the action of coalescence is negligible.

60

2) For a speciﬁed blend system (ex. CA/SMA232/DMAP), f is only a
function of rheological property of the matrix and dispersed phase, we can assume the

grafting does not change the rheological property signiﬁcantly, so f is a constant.

3) RC is only a function of concentration of compatibilizer for a speciﬁc

system. It can be written as:

k,
RC oc———— (C0H~MA $0)
COH—MA

Where k’ is a constant.
4) For a speciﬁed CA/SMA system, the concentration of -0H, -MA group
and catalyst DMAP are constants due to the reacted group is less than 3% even when

the grafting conversion of SMA is about 90%.

5) In equation 4-13, k and as is a constant for the CA-SMA grafting

copolymer compatibilizer.

We use the data of CA/SMA without catalyst to solve out the value of 00 .

R R
ln———1——ln 2

my: Ri—Rao Rz—Rco
00 ’Rcotres

 

(421)

We assume the critical Capillary number Co, is a constant for a speciﬁed system,
so we can drive:

77m WCO : 77m Wes
00 Us

 

(422)

Then,

as = O'ORCS /Rc0 (4-23)

61

The RC values at different compatibilizer concentrations can be attained by

measuring the phase size in the solvent cast ﬁlms of a speciﬁed grafting conversion

polymer blend. SEM pictures of four CA/SMA blend cast ﬁlms at different SMA grafting

conversion are shown in Figure 4-12.

3‘ '.

f‘

' ”illiivlfwfi ‘

'4 . ‘ v.-.‘
E} . .1_
.\ ‘1 -

1‘

is an: as its: ~

p

.r

J

 

*bar length is 1 micron
Figure 4-12 the TEM picture of CA/SMA232 cast ﬁlm at different grafting

conversions

(a) fSMA = 0-26 (b) fSMA = 0-39 (C) fSMA = 0-51 (d) fSMA = 0-74

62

Table 4-2 The SMA particle size of cast ﬁlm at different grafting conversion

 

 

 

 

 

fSMA fSMA 1/ f SMA particle diameter(um)
0.29 0.19 5.35 0.18
0.36 0.25 4.00 0.15
0.51 0.43 2.33 0.09
0.74 0.96 1.04 0.06

 

 

 

 

 

 

According to equation 2-15, the concentration of the grafting bond MA-OH is
proportional to the value f ’SMA. The relationship of particle size and the modiﬁed grafting

conversion was drawn in Figure 4-13. From the ﬁgure we can draw the following

formula:

R, = 0.01405 + 0.01445/ ngA (f’SMA ¢ 0) (4-24)

This also conﬁrms the assumption that the critical phase size is inversely

proportional to the concentration of the grafting bonds.

63

Critical phase size at rifferent grafting conwrsion

0.20 ~ y = 0. 02891 + 0.0281

0-13 “ R" = 0. 9909
0.16 ~

0. 14 ~
0.12 r
0. 10 ~
0.08 r
0.06 ~
004 ~
0.02 -
0.00 ‘ 1 ‘ ‘ ‘ '
0.00 1.00 2.00 3.00 4.00 5.00 6.00

 
  
 

O

   

 

SMA droplet diameter (micron:

 

l/modiﬁed SMA conversion

Figure 4-13 Fit of SMA phase diameter (pm) vs. I/ ﬂew (cast ﬁlms)

Here the state f 'SMA=2.2 (which few/4:09 is the highest grafting conversion we

can attain) was used as saturate compatibilizer concentration.

RCS=0.0206 pm.
RC0 was measured in the cast ﬁlm of un-grafted CA/SMA blends. the value is

1.14pm.

Using by these data, we can simplify the equation 4-21 as:

fnm7: 1.816 (4_25)
00 RcOtres

The equation 4-20 can be simpliﬁed by using the above results and assumptions:

 

”515 _1.816R(R-RC) RC, __1_r£,_ _’C' _
(dt)6- /( +(1 R )exp( ‘71:» (426)

RcO’ res RcO c0

Here C’ is a constant related with copolymer generating rate and chemical

properties of the copolymer in the blend system. We assume at critical phase size under

64

 

 

saturated compatibilizer concentration, the polymer blend is perfectly mixed, and the

effective volume parameter equals 1.

V, =l,at R=RCS

Then VS = RC5 /R

So we can drive the formula for C’

C'=kKoRa “pig—ﬂap” C—MACDMAP (4-27)

We can calculate the grafting conversion for CA/SMA232/DMAP (wt%,

70/30/0.01) in the extrusion process by equation 2-15.

 

0
, _ PDI ,
fSMA =(1-fSMA) 0'5 *1: C0 K0 eXP(- E/R Tlc—OHC—MACDMAP Vst (2-15)

The initial concentration of SMA in the CA/SMA melting blend is:

0 ,— ._
C =WSMA xpCA/SMA TM’WSMA) :WSMA x1'14kg/LTM”(SMA) =0.0027moI/L

WSM A is the weight percentage of SMA, pCA/ SMA is the density of the polymer
blend in melting condition, 117 n( S M A) is the number average molecular weight of SMA.

The concentration of —OH group can be written as:

C_0H =pCA +ll7n(CA) x N__0H =1.20kg/L +117,,(CA)x N_0H =2.217mol/L

PCA is the density of the CA in melting condition, 117,, (CA) is the number average

molecular weight of CA. MO}; is the number of —OH groups in a CA chain which has the

number average molecular weight.

The concentration of —MA group can be expressed as:

C—MA : IDS/rm + MINSMA) x N-—MA : 1.08kg /L “i“ Malawi) X N—MA : 0'972m01/L

65‘

PSM A is the density of the SMA in melting condition, MM, is the number of —

MA groups in a SMA chain which has the number average molecular weight.

At 250 0C, we assume the concentration of DMAP vapor distributed in the void
volume of the polymer blend is much larger than the concentration of DMAP vapor
penetrated into the polymer matrix in the melting condition. We can, therefore, neglect

the DMAP penetrated into the polymer matrix. According to the measurement of the

expansion ratio between room temperature and melting condition, the expansion ratio is:

rex = (17ml, — I760“ ) / 17mg], is about 0.008, where 17mg], is the speciﬁc volume of

CA/SMA polymer blend in melting condition, and I760“, is the speciﬁc volume of
CA/SMA polymer blend in room temperature under high pressure (1300psi). We assume
the expanded volume is close to the void volume in the melting condition.

CW, = wt%DMAPx1.14kg/L + Mam, + r_ = 0.117mol/L

er

T= 523.15 K (250°C)
t = tres=4 min

From the equation 2-15 and 4-26, we can apply numerical method to integrate the
value of dispersed phase size and SMA grafting conversion by ﬁtting the k value and use

the following initial conditions:
R=R0=2mm , fSMA =0 At 1:0

The SMA phase size and grafting conversion vs. time are shown in Figure 4-14

and Figure 4-15.

66

-— —I N
Ut O UI O

O

_ SMA particle radius (micron)

Dispersed phase size vs.time

 

 

1 1

0 l 2 3 4 5

tin: (min)

Figure 4-14 SMA phase size vs. time for CA/SMA232/DMAP (70/30/0.01)

SMA conversion

0.45
0.4
0.35
0.3
0.25
0.2
0. 15
0. l
0.05

SMA grafting conversion change with time

 

 

time (rrrin)

Figure 4-15 SMA conversion vs. time for CA/SMA232/DMAP (70/30/0.01)

When we set the k value to equate the simulation result of SMA droplet radius to

that of the measuring value (0.505 pm), the simulation SMA grafting conversion result is

67

42% and the measuring value is 68%. The difference is derived from the approximations
in the assumptions that were made.
4.5 CONCLUSIONS
1. It is reasonable to describe the relationship between phase dispersion and
grafting conversion in reactive extrusion of polymer blend by using equation 4-26,
the grafting reaction generates a co-polymer acting as a compatibilizer, reduces

interfacial tension, and hence improves the droplet breakup rate.

2. From the theoretical study of phase dispersion and the experimental study,
we draw the same conclusions for the relationships between dispersed phase size and
grafting conversion. Without reaction, the phase size was reduced with more
extrusion runs. When the phase size is close to the critical size, coalescence begins.
At the critical size, the breakup rate and the coalescence rate are in balance, and the
droplet stabilized. When catalyst is added, the grafting copolymer is formed during
reactive extrusion. This copolymer can reduce the interfacial tension and further
reduce the critical size of the blend system. In the CA/SMA blend system, the
relationship between the critical size and concentration of OH-MA bonds (which can

be expressed by f gMA) is inversely proportional. Hence the grafting reaction can

improve the droplet breakup speed and shift the balance of critical state to a small

phase size.

3. Theoretical study shows that in-situ generation of compatibilizer is an
effective way to compatibilize polymer blends due to increased reactivity during
phase dispersion, and subsequent grafting of copolymers to improve the phase

dispersion.

68

Chapter 5: STUDY OF THE GRAFTING REACTION BETWEEN

THERMOPLASTIC STARCH AND SMA VIA REACTIVE EXTRUSION

5.1 INTRODUCTION
5.1.1 Starch and thermoplastic starch

Starch is the second most abundant carbohydrate in plants after cellulose. It is the
major storage component of polysaccharide in plants. Principal sources of commercial
starch are maize (corn), potato, wheat and cassava (86). Starch is an anhydroglucose
polymer and consists of two distinct molecules: amylose and amylopectin which both

contain a-D-glucose units. Amylose is a linear or sparsely branched polymer with a
molecular weight in the range of 105 to 106 g/mol linked primarily by a1 —> 4 glucosidic

linkages (Figure 5-1). The chains form a spiral-shaped single or double helix (87).

CHZOH

.\‘\ 0
o H
O CHZOH .
0
HO
0 OH
HO *

Figure 5-1 Structure of amylose

69

In contrast, amylopectin is a highly branched polymer with a molecular weight of

107 to 109 g/mol. Amylopectin also contains a1 —> 4 glucosidic linkages, but in addition

it has al —> 6 glucosidic branching points which occurs every 25-30 glucose units.

Figure 5-2 shows the structure of amylopectin.

CHZOH
O
* OH
CHZOH
. O HO
\‘\ /0
O OH
H20
0
HO
O OH
HO .

Figure 5-2 Structure of amylopectin

Thermoplastic starch (TPS) is described as a substantially amorphous starch. TPS
is produced from granular starch by employing heat and mechanical energy in the
presence of several plasticizers, which do not evaporate substantially during processing at
high temperature and pressure. Some common plasticizers used are glycerol, ethylene
glycol and polyols. Plasticization of starch in an extruder using a plasticizer breaks the
hydrogen bonds and disrupts the granular crystalline structure. It further releases the

amorphous polymer chains with al ——> 4 and or] —> 6 linkages.

5.1.2 Starch and biodegradable polyester blends

70

Due to the biodegradable nature of starch, many researchers have attempted to
incorporate starch into a variety of materials in order to improve the environmental
desirability and reduce the cost of such materials. Starch may be added as an inert ﬁller
(88, 89), typically in its native, unmodified, state, which is generally a water insoluble,
granular material. Ramsay et al. (90) studied blends of granular starch with Poly (HB-co-
HV). The inclusion of 25-wt% of a granular starch was reported to result in a
composition with a tensile strength of about 60% that of the original. The authors
acknowledged that the use of unmodiﬁed granular starch as a particulate ﬁller did not
offer any appreciable reinforcement due to the poor adhesion at the polymer granule
interface. In such cases, the starch granules will normally behave as any other solid
particulate ﬁller and will not improve the mechanical properties of the resulting material.
The thermodynamic incompatibility between starch and synthetic polymers leads to the
poor performance properties of these blends.

Alternatively, starch that has been plasticized dried, and then ground into a
powder may also be added as particulate ﬁller. Examples of patents that disclose the
manufacture of “destructurized starch” and blends of “destructurized starch” and other
polymers include US. Patent 4,673,438 to Wittwer et al.; US. Patent 4,095,054 to Lay et
al.; US. Patent 5,256,711 to Tokiwa et al.; US. Patent 5,275,774 to Bahr et al.; US.
Patent 5,382,611 and US. Patent 5,405,564 to Step et al. Lately, there have been
considerable publications on the use of thermoplastic starch (TPS) as a component in
multi-phase blends (91 -95).

Although many researchers have attempted to discover the “perfect”

starch/polymer blend that would yield an environmental polymer, the desired mechanical

71

 

 

properties and comparatively low cost are difﬁcult to achieve. One drawback is that most
of the polymers and other mixtures are more expensive than starch, which tends to
increase the cost of such polymer blends compared to starch melts. Another drawback is
that such starch/polymer blends lead to poor performance properties due to the

thermodynamic incompatibility between the starch and the polymer.

5.1.3. Modiﬁed starch to improve its compatibility with biodegradable polyesters
Reaction with cyclic dibasic acid anhydrides such as succinic anhydride yields
starch esters (96). The same chemistry could be carried out with maleic anhydride to
yield the maleate half ester. The reaction schemes are depicted below in Figure 5-3.
Treatment of a starch suspension with a cyclic dicarboxylic acid anhydride containing a

hydrophobic substituted group yields products with emulsion stabilizing properties (97).

O
R—CH—‘(O 0H" ll ll - +
Starch—OH + ——>Starch—O-—C-—CH2— —IH—C—O Na

H iC—<: pH=8

Figure 5-3 Starch reaction with half-esters of dicarboxylic acids

While all of the above work is related to the production of starch esters in batch
systems, starches can be acylated during extrusion with cyclic anhydrides in the presence
of carbonate buffers to yield the corresponding starch esters. Tomasik et a1. (98) reacted
corn starches in extruders containing varying amounts of moisture (18, 20 and 30%) with

succinic, maleic and phthalic anhydrides. A carbonate buffer, to either pH 8 or pH 9, was

72

added during extrusion. It was demonstrated that extrusion of starch with cyclic
anhydrides in an alkaline medium presents a facile method for preparation of anionic
starches with hydrophobic base character.

In this study, starch was reacted with low molecular weight, high MA content
SMA, in a twin-screw, co-rotating, extruder in the presence of glycerol as plasticizer. The
grafting between starch and SMA, glycerol, and SMA and the cross-linking among
starch, SMA and glycerol were observed. The TPS/SMA grafting blend was further
blended with a biodegradable polyester,r Ecoﬁex, a polymer designed for blown-ﬁlm

applications, in the melt phase.

5.2 EXPERIMENTAL
5.2.1 Materials and Equipment

Granular starch was obtained from Cargill, grade SMP 1100, un-modiﬁed com-
starch with equilibrium moisture content of about 12 wt%. Ecoflex polyester [poly
(butylene adipate-co-terephthalate)] was obtained from BASF. Anhydrous glycerol

[2136-03], 99.9% assay was obtained from J .T. Baker. Low molecular weight SMA
(SMA3000P, 25 mol% maleic anhydride, Mw:9,500, Mn: 3,800, Tg=125 OC;
SMA1000P, 50 mol% maleic anhydride, Mw:4,5 00, Mn: 2,000, Tg=155 0C; ) was

supplied by Sartomer Company Inc, the catalyst 4-dimethylaminopyridine (DMAP) were
purchased from Sigma-Aldrich Inc. The structure of SMA1000P and SMA3000P and

Ecoﬂex are show in Figure 5-4, Figure 5-5 and Figure 5-6 respectively. Un-modiﬁed

corn starch was dried in a vacuum oven at 1200C for 48 hrs to reduce the moisture to less

73

than 1wt%. Ecoﬂex was dried at 700C for 24 hrs in a ventilated oven. All other materials

were used as obtained.

Figure 5-5 Structure of SMA3000P

0 0
a O i
lo/WOMO/W MY
0 0

Figure 5-6 Structure of Ecoﬂex

A twin-screw, co-rotating CENTURY extruder having a length: diameter ratio
(L/D) of 40:1 and a screw diameter of 30 mm was used for the plasticization as well as

the grafting reaction and blending. The extruder was electrically heated and was cooled

74

using circulating water. The screw elements needed for the screw conﬁguration were also
obtained from CENTURY. The auxiliary equipment includes a water bath to cool the

extrudate and a pelletizer to cut the extruded strand into small pellets.

5.2.2 Synthesis of TPS/SMA graft copolymers by reactive extrusion

The synthesis of TPS/SMA graft copolymers was accomplished in a twin-screw
co-rotating CENTURY extruder using DMAP as a catalyst. Glycerol at 20 wt% (based on
TPS) is added as a plasticizer in the extrusion. About 2.5, 5, 10, 20wt% SMAIOOOP was
mixed with starch before feeding. The catalyst DMAP at 0.01wt% percent was ground to
a ﬁne powder with 10g starch, and then mixed with 100g starch, ﬁnally it was mixed with

the balance of the starch. The mixed starch, SMA and DMAP was fed through the main

extruder feeder, and the glycerol was heated to 70°C and pumped into a separate feed
port. The material was collected in an aluminum pan and ground into powder, then stored
in a ventilated oven at 700C. The extrusion temperature proﬁle was set as
15/95/ 145/ 155/ 160/165/ 165/ 165/ 160/150 0C. For comparison, pure TPS (20%wt

glycerol) and TPS/SMA (2.5wt% SMA) without DMAP was also made. The proposed
reaction structures for starch and SMA, glycerol and SMA, and cross-linking of starch,
SMA and glycerol are shown in Figure 5-7, Figure 5-8 and Figure 5-9.

SMA3000P was applied in the same conditions to compare the results.

75

CHZOH

\[~ 0
O 0” CHZOH
0
HO 0 OH

HO ,,

 

 

Starch
CHZOH
. O
> +0 OH
HO

   

HO ,

Starch-SMA grafting copolymer

Figure 5-7 Grafting reaction between starch and SMA

 

Glycerol SMA-Glycerol

Figure 5-8 Grafting reaction between SMA and glycerol

76

CHZOH
.\‘\ o
o H
O CHZOH

HO
0 OH +

H0

t

 

 

 

 

Starch
OH
SMA-glycerol
CH20H ‘
.+ 0
o H \
0 CH2
0
HO
O OH

HO

Starch-SMA-Glycerol coploymer

Figure 5-9 Cross-linking between starch, SMA and glycerol

5.2.3 Soxhlet extraction of TPS/SMA grafting co-polymer
The graft TPS/SMA copolymer powder was extracted using acetone. For

comparison, TPS was also extracted with acetone. Approximately 10 grams of the sample

77

was accurately weighed into a cellulose extraction thimble (33 mm x 94 mm) and placed
into the Soxhlet extractor. The extraction was run for 24 hours. After extraction, the
thimble together with the sample were removed and dried to constant weight. A mass
balance and FTIR analysis were completed for the remaining contents in the thimble and

a cast ﬁlm sample was obtained from the extracted solution.

5.2.4 Blending Ecoﬂex with TPS/SMA by extrusion process
The synthesis of Ecoﬂex-TPS/SMA graft copolymers was accomplished in the

twin-screw co-rotating CENTURY extruder. The polymer blend TPS/SMA was oven

dried overnight at 700C, ground to a ﬁne powder, and fed using an external feeder to the

feed port of the extruder. Ecoﬂex was dried in an oven at 700C to remove moisture and

fed through the main feeder. The feeder rates were adjusted to obtain a ratio of 70:30
Ecoﬂex: TPS/SMA. The temperature proﬁle was set at the same processing temperature
proﬁle used for blending TPS/SMA. The vent port was kept open to remove steam. The

extruded strand was cooled using a water bath and pelletized in line. The pellets were

dried in an oven overnight at 70°C before being blown into a ﬁlm.

5.2.5 Fourier Transformed Infrared Spectroscopy

FTIR analysis was conducted on samples of TPS and TPS/SMA graft copolymers
using a Perkin Elmer spectrophotometer. The TPS/SMA copolymer was extracted using
acetone in a Soxhlet extraction unit, dried and ground to a ﬁne powder. 1% extracted
TPS/SMA was mixed with 99% KBr powder and pressed using a pellet maker to a ﬁne

transparent disk. This disk was put directly into the sample holder to obtain the spectrum.

78

A background scan was also conducted with just the KBr pellet, which was subtracted
from the total spectrum to obtain the sample spectrum. Films obtained by solvent casting

were directly placed into the sample chamber to obtain the FTIR spectrum.

5.2.6 Blowing Film

Films of the Ecoflex-TPS/SMA blend are made using a Killion single-screw
blown ﬁlm unit. The screw diameter was 25.4 mm with an L: D ratio of 25:1. The die
inner diameter was 50.8 mm with a die gap size of 1.5 mm. The blown ﬁlm processing
conditions are shown in table 5-1.

Table 5-1: Blown Film Processing Conditions for Ecoﬂex-TPS/SMA blend

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Die 3 Die 2 Die 1 Adaptor Clamp Ring Zone 3 Zone 2 Zone 1
Set (0F) 70 330 350 360 360 360 360 315
Actual (01:) 78 330 350 357 358 338 360 315
Melt (OF) 328
Screw Speed (RPM) 17.0
FPM (ft/min) 8.5
Pressure (psi) 1890

 

 

 

 

5.2.7 Mechanical Property Determination
Tensile properties of the ﬁlms were determined using INSTRON Mechanical

Testing Equipment ﬁtted with a 100 lb. load cell. The crosshead speed was set at 1 inch

79

per minute. Rectangular ﬁlm samples, 4”><1”, were conditioned at 230C and 50%

Relative Humidity for 40 hours before being tested according the ASTM D-882 standard.

5.3 RESULTS AND ANALYSIS
5.3.] Soxhlet extraction and FTIR result

The TPS/SMA blends Soxhlet extraction results are shown in table 5-2. Here TPS
was made using 80% starch and 20% glycerol. In all these samples, 0.01% DMAP was
added as catalyst except where noted. Sample #5 was a blend of pure starch and SMA
with no added glycerol.

Table 5-2 TPS/SMA soxhlet extraction results

 

 

 

 

 

 

 

 

 

sample weight SMA in weight

SP SMA content weight loss sample loss/SMA
g 8 g

0 2.5%SMA1000P* 10.0083 0.7203 0.2441 2.887

1 2.5%SMA1000P 10.008 0.8996 0.2441 3.685

2 4.76%SMA1000P 9.49 0.4928 0.4519 1.091

3 10%SMA1000P 10.0455 0.2218 1.0036 0.221

4 20%SMA1000P 9.9763 0.0761 1.9953 0.038

5 50%SMA1000P** 10.0233 4.6095 5.01 17 0.92

6 0%SMA1000P 10.6146 0.5429 0

 

 

 

 

 

 

 

 

*No DMAP was added in this sample.

“Pure corn starch without glycerol was used in this SP#5

80

The extraction results are expressed graphically in Figure 5-10. The weight of

extracted material based on a 10g sample vs. SMA content is shown.

Extracted material weight vs . SMA content

Eextracted out material weigh
percent (%)

 

 

0 5 10 15 20 25
SMA (wt%)

Figure5-10 Extracted material weight vs. SMA content

In the Soxhlet extraction of pure TPS with acetone, about 25% glycerol was
extracted. Another solvent, THF, was also tested. Using THF about 14% glycerol was
extracted. Acetone was, therefore, used in this study.

From the Soxhlet extraction results, it is clear that at 2.5wt% SMA1000P, without
DMAP, almost all of the SMAIOOOP and about 25% of the glycerol has been extracted.
With DMAP more material has been extracted. This is due to the faster reaction between
SMA and glycerol compared with that of SMA and starch. The SMA/ glycerol grafted
material can also be extracted. At this SMA level, the reaction between SMA and starch
or cross linking between starch/SMA/ glycerol is rare, thus the extracted material is

greater than the original SMA content. From FTIR results no ester C=O stretch peak,

81

 

 

around 1730cm'l , is observed in the Soxhlet residue. However, the C=O peak is

observed in the cast ﬁlm produced from the extraction solvent.

When the SMA content increases to 5%, the grafting reaction between starch and
SMA occurs, but the grafting between SMA and glycerol still dominates, thus the
extracted material is still greater than the original SMA amount. At 5% SMA content, the
ester C=O stretch peak can be observed from both FTIRs (the material in the thimble and
in the solvent). When the SMA content increases to 10%, most SMA and SMA/ glycerol
is grafted onto starch, resulting in only a small amount of SMA/glycerol (about 22 wt%

of original SMA) being extracted. The ester C=O peak becomes more signiﬁcant, and the

OH group peak around 3400 cm.1 is smaller. When the SMA content increases to 20%,

very few materials are extracted. Almost all SMA and SMA/ glycerol are grafted onto the

starch backbone. From the FTIR, we can observe un-reacted maleic anhydride at

l775cm'1 and l730cm'1. The FTIR results are shown in Figure 5-11, Figure 5-12 and

Figure 5-13. Catalyst was added in all TPS/SMA blends shown in these ﬁgures.

From the extraction results, it can be observed that about 25% of free glycerol can
be extracted with acetone. Free SMA and SMA/ glycerol grafted co-polymer can also be
extracted. Pure starch, SMA and SMA/glycerol which grafted onto starch remain in the
thimble.

Without DMAP, almost no grafting reaction occurs. This can be observed from
the sample TPS/SMA (2.5% SMA) without catalyst, the weight loss is equal to the sum

of the weight loss in pure TPS and the SMA weight in this sample.

82

With DMAP as a catalyst, the reaction of SMA with glycerol occurs ﬁrst to form
SMA/ glycerol grafting copolymer. When the SMA concentration increases, the grafting
reaction between starch and SMA; starch and SMA/glycerol occurs.

At 20wt% SMA, all SMA, SMA/ glycerol is grafted onto the starch back-bone and
almost nothing can be extracted with acetone. However, without glycerol as a plasticizer,
the grafting conversion of SMA 1000P in the starch/ SMAIOOOP/DMAP (50/50/0.01)
blend is very low. This is due to the high viscosity of the starch phase in the absence of

plasticizer and consequent poor dispersion of the SMA phase.

FTIR of TPS/SMA blends
_ TPS (material remian in thimble)

1.2- -~ ll’.\ s’.‘~.:\1lwil’t"“~‘i 35"

 

absorbance

 

 

ﬁ ff V’T

. I - . . . l . . . . I 4 . . . I. . . . I . . . . l . . . . l .
4000 3500 3000 2500 2000 l 500 l 000 500
cm-1

Figure 5-11 FTIR of TPS and TPS/SMA (2.5%wt) after extraction (thimble)

83

absorbance

absorbance

FTIR for TPS/SMA blends

 

   

 

 

 

“ , (materail remain in thimble)
i - TPS, S.\l.~\lii(liil’ [).\-1AP(U5 5 0.0l)
12— 2 1'“\l\\l\‘llll'll’l‘\\l\l’l‘-ltlllill.'ill
c on e
- TPS/SMAIOOOP/DMAP (80/20/0.0l) ‘2 g g
.- ‘1 .
~ g N to In c: a V
q . as no h r o
. m 7
0.8— g :3, «‘3. l i _
i b r~ 7 ;
c—r :- — i 'I
O
0.6— g
.. N
0.4‘ i ,/
l
0.2—
0_ L" \
-I.ﬁT.I.r.I. .-I..T.I-4..I. r.I..T.I.
4000 3 500 3000 2500 2000 l 500 l 000 500
cm-1

Figure 5-12 FTIR of TPS/SMA (5, 10 ,20wt%) after extraction(thimble)

 

 

 

l
‘ (material disolved in solvent) 3
" c N
.. "‘ gs
1‘ b
0.8-
0.6—
0.4—
0.2-—
0—
'l""l""l""l'"Fl*"'l""l' -
4000 3500 3000 2500 2000 l 500 1000
cm-1

Figure 5-13 FTIR of material extracted from TPS/SMA (10%wt) (solvent)

84

5.3.2 Mechanical properties of Ecoﬂex and TPS/SMA blends

The TPS/SMA grafting co-polyrner with 20wt% SMAIOOOP was used to blend
with Ecoﬂex at 30/70 wt% ratio to blow ﬁlm. Compared with the Ecoflex/TPS/MA
(70/30/1) blend, the modulus and the machine direction tensile strength improved, but the
elongation and transverse direction tensile strength decreased. The properties are poor
compared with Ecoflex and an inorganic ﬁller blend (see chapter 6). The mechanical data

are shown in Table 5-3:

Table 5-3 The mechanical properties of Ecoﬂex and TPS/SMA blend

 

 

 

 

 

 

 

tensile
material Direction elogation modulus
strength
psi % psi
Ecoﬂex+TPS/SMA MD 1120 i 30 200 i 20 9440 i 1000
70/30 CD 550 :1; 20 110 d: 15 7920 i 140
Ecoﬂex+TPS+MA* MD 980 500 6000
70/29/1 CD 900 350 5000

 

 

 

 

 

 

 

* Data form the other group member ’5 work

5.4 CONCLUSIONS
1. The grafting reaction between starch, SMA and glycerol occurs with

DMAP as a catalyst under reactive extrusion conditions.

85

 

2. At lower SMA concentrations (less than 5%), the reaction between

glycerol and SMA dominates.

3. With increased SMA concentration, the reaction between starch and SMA,

and starch and SMA/ glycerol copolymer increases signiﬁcantly.

4. At 20wt% SMA, almost all SMA and glycerol are grafted or cross-linked

onto starch.

5. Grafting SMA onto starch improves the compatibility between Ecoﬂex
and starch to a lesser extent. At higher grafting conversion, the intermolecular
attraction between starch, glycerol and SMA becomes stronger thus reducing the

compatibility of TPS/SMA and Ecoﬂex.

86

 

 

Chapter 6: PREPARING COMPATIBLE ORGANIC-INORGANIC

HYBRID BLENDS BY REACTIVE EXTRUSION

6.1 INTRODUCTION
The main drawback of synthetic biodegradable polymers is their high cost.
Adding natural and inorganic ﬁllers such as starch, cellulose, CaCO3, and Talc to reduce

the cost has been studied widely. In order to improve the properties of these blends by

 

improving their compatibility, most researchers attempt to graft functionalized groups
onto the biodegradable polymer backbones and then react with the ﬁller to generate the
co-polymer as the compatibilizer. Typically, functional groups such as isocyanate, amine,
anhydride, carboxylic acid, epoxide and oxazoline are introduced through a fast reactive
extrusion process, and then combined using their suitably reactive ﬁrnctionalities, such as
hydroxyl—isocyanate, amine-anhydride, amine-epoxide, arnine-lactam, amine-carboxylic ‘
acid and amine-oxazoline (99). Maleic anhydride was ﬁrst used as a monomer to graft
onto non-biodegradable polymers such as polyethylene, polypropylene and other

polymers (100, 101) to form a functional group. Earlier results from research conducted

 

by Bhattacharya and co-workers (102 — 112) on maleation of biodegradable polymers

such as PCL, PBSA, poly(buty1ene succinate) (PBS) and Eastar Bio® co-polyester;

Narayan and co-workers (113, 114) on maleation of PLA, indicated that blends of

anhydride functional polymers and starch as a natural ﬁller could lead to products with

87

useful ﬁnal properties. Such functionalization of polymer matrices can reduce the
interfacial tension, strengthen interfacial adhesion, and minimize coalescence (115).
Reactive extrusion techniques have proved to be an effective way to introduce a variety
of functional groups onto the surface of natural polymers (116, 117).

Recently, BASF has marketed a novel biodegradable poly (butylene adipate-co-

terephthalate) trademarked Ecoflex® (118). This aliphatic-aromatic (co)polyester is

 

prepared by condensation polymerization from adipic acid, 1,4-butanediol, and more P"
l

especially terephthalic acid (aromatic ring), designed to reinforce the co-polyester l

structure. Combination of these biodegradable polymers with cheap inorganic ﬁllers such

as Talc also provides a useful way of reducing the cost, and optimizing the properties of a

biodegradable thermoplastic polyesters (119 — 121).

Developing a melt-blend with satisfactory overall physico-mechanical behavior
will depend on the ability to control interfacial tension in order to generate a small-
disperse phase size and strong interfacial adhesion. It is of prime importance to achieve
high-performance mechanical properties in the ﬁnal material.

In this respect, our study aims at reactive melt-blending of Ecoﬂex with a natural
ﬁller through the reactive extrusion process with the ultimate objective of producing

blown ﬁlms with enhanced mechanical properties, In this study, Talc was utilized as the

 

natural ﬁller. Although the basal surface of Tale is composed of a chemically inert
magnesium silicate layer, its lateral surface exhibits some hydroxyl functionality. The
Ecoflex backbone was reactively modiﬁed through free-radical grafting of vinyl-
trimethoxysilane or vinyl-methyl- dimethoxysilane. Further, the objective of this study

was to chemically react the methoxy (alkoxy) groups of the silane with the hydroxyl

88

group of the ﬁller to provide better ﬁller-matrix adhesion and/or a tough, cross-linked
matrix with improved mechanical properties and water repellency. Silane-polyester graft
copolymers can be melt cast or blown into transparent ﬁlms with applications in the areas
of lawn and leaf compost bags, agricultural mulch ﬁlms, trash bags, regular carry out
retail bags, food packaging etc. US Patent 3,646,155 issued to Scott (122) relates to the
cross-linking of polyethylene materials using an organofunctional silane as a cross-
linking agent, which is grafted on to the polymer using a peroxide catalyst. The process
as described in the patent also leads to a reduction in melt ﬂow of the polymer leading to
difﬁculties in processability in normal equipment and a signiﬁcant reduction in
elongation compared with the base material. Other US patents similar to the above work
are US 4,117,195 (123), US 4,413,066 (124), US 4,514,539 (125), US 5,773,145 (126).

The use of trifunctional silanes in enhancing the mechanical properties of
therrnoset materials has been discussed in the Japanese Patent Application 2003221446
(127); the main intention, however, was to produce highly cross-linked networks. The
invention did not relate to the manufacture of ﬁlms, and also the mechanism of
modiﬁcation was the condensation reaction of end groups, and not a peroxide aided route
as discussed in the present work. Laminates using silane-grafted polypropylene and liquid
crystal polyesters were discussed in the Japanese patent application 2001239539 (128).
Production of ﬁbers from waste polyesters and glass ﬁbers is discussed in the Japanese
patent application 2001040528 (129) — but the silane used as a coupling agent operated
via a condensation mechanism and not by the peroxide route.

Thermoplastic polyurethanes have been modiﬁed using silane grafting agents

(130). Their technique, however, was to use a condensation type reaction between an

89

*-

 

isocyanate grafting agent and an amino functional silane rather than a free radical
peroxide induced grafting which was the aim of the present work. Similar work is
reported in the literature (131) where the authors have grafted a vinylsilane on to a
silicone rubber using an organic peroxide catalyst to improve compatibility with
polyurethane.

DE 10111992 (132) discusses the use of silane grafting on to polyoleﬁns to make
compatibilized blends with polyesters in the presence of a silane coupling agent. But in E
the invention, the focus was on grafting the polyoleﬁn and not the polyester with the
organosilane. Furthermore the work did not mention ﬁlms, and was concerned only with

the manufacture of threads.

 

This present study deals with the improvement of the physico-mechanical
properties of these silane-grafted ﬁlled polyester ﬁlms by improving the compatibility
between the ﬁller and the polyester. This graft co-polymer helps achieve the afore-
mentioned objective by providing blends in a one-step extrusion process to give ﬁlms
with enhanced tensile strengths up to 6000 psi. The grafting reaction and the mechanical
k

properties of the blown ﬁlms are discussed in this chapter.

6.2 EXPERIMENTAL

6.2.1 Materials

 

Ecoﬂex FBX 7011 was purchased from BASF Corporation, 2,5-Bis(tert-
butylperoxy)-2,5 dimethylhexane (Lupersol 101) was provided by Sigma-Aldrich
Chemical Company (Milwaukee, WI) and used as received. Talc having a particle size of

ca. 6 pm under the trade name Luzenac 20MO0S was provided by Luzenac Europe, and

90

dried at 120°C overnight before use. Vinyl-trimethoxysilane (VTMOS) and vinyl-
methyl-dimethoxysilane (VMDMOS) were purchased from Gelest, Inc.
Dichloromethane was provided by EMA chemicals Inc. The structure of Lupersol 101,
VTMOS, VMDMOS and proposed structure of Talc are shown in Figures 6-1, 6-2, 6-3

and 6-4.

0

\\‘c>

 

2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane
Figure 6-1 structure of 2,5-Bis(tert-butylperoxy)-2,5 dimethylhexane (lupersol

101)

CH
146% 2

“3C l 0
Si/ \
\O/ \0 CH3

/

H3C

Figure 6-2 Structure of Vinyl-trimethoxysilane

 

orb
Hcrﬁég
H3C l O
\\ //,su::: ‘\\‘cri
(3 (xi, 3

91

Figure 6-3 Structure of vinyl-methyl-dimethoxysilane

/
\0
”“1

Figure 6-4 Proposed structure sketch of Talc

 

6.2.2 Reactive extrusion g
700g of PBAT was hand-mixed with 0.05/0.1/0.2 wt% Lupersol(of PBAT) as a
free radical initiator, 0.5/1/2 wt% (of PBAT) VTMOS/VMDMOS, and 300g of Tale, in
that order, and fed together to a Century ZSK-30 co-rotating twin screw extruder at a feed
rate of approximately 150 g/min. The screw diameter was 30 mm, with a length-to—
diameter ratio of 40: 1. Barrel and die temperatures were maintained by means of ten
electrical/cooling devices as described heretofore. The screw speed was 150 rpm

resulting in a mean time residence of about 4-5 minutes. The temperature proﬁle was set

as 15/90/ 135/ 160/ l 70/ 175/ 1 75/ l 75/ 165/ 160 0C from the feeder barrel to the die. The

 

strand was extruded through a single oriﬁce die having a nozzle opening of 2.7 mm in
diameter, cooled in a water-bath, and pelletized downstream. The supposed grafting
reaction between Ecoﬂex, vinyl-trimethoxysilane and Tale is shown in Figures 6-5 and 6-

6. Side reactions such as crosslinking of silane will also occur.

92

To study the grafting reaction between Ecoﬂex and silane, Ecoﬂex with 1wt%
vinyl-trimethoxylsialne and O.1wt% Lupersol was extruded by itself at the same
temperature proﬁle. In comparison with pure Ecoﬂex the torque increased by about 20%

at the same feed rate.

0 O
I. O
+OWOMO/W W;
O O

CH
He/ 2

+ H3C l O
\o/S'<o \CH

/

H30

lon/VVW

C/:>Sli2\0 /CH3

CH3

lupersol 101

Figure 6-5 Proposed reaction structure of Ecoﬂex and Silane

93

O 2
‘1”
CH
O\ , 3
H3C/ O/SI\O/
CH3
HO\ HO\
. O _ Q
o/S|'/ \S/I/ \Mg
+ M/ 0 o\ /
o | l
O\ /0
Mg
0 O
OW O O Y
HZC
\CI3H2
O
HO /\Sl/0\\Si/o\
0 / M9 + H3C—OH
M/ O O\ /
o (I) ‘
0
\Mg/

Figure 6-6 Proposed crosslink between Ecoﬂex, silane and Talc

6.2.3 Soxhlet extraction and FTIR test

For comparison, Ecoﬂex/Talc (70/30) and Ecoﬂex/Talc/VTMOS/Lupersol

(70/30/1/0.1) blends were dried in a vacuum oven at 70°C for 24hrs, and Soxhlet

extracted with dichloromethane for 24 hrs. Both the material remaining in the thimble

94

 

 

and that extracted in the solvent were analyzed by F TIR. To investigate the grafting
reaction between Ecoﬂex and silane, the Ecoflex/silane/lupersol blend was also analyzed

by FTIR.

6.2.4 Blowing ﬁlms

The reactively modiﬁed Ecoﬂex-Talc composites were extruded into ﬁlms using a
Killion single-screw blown ﬁlm unit. The screw diameter was 25.4 mm with a length-to- F
diameter ratio of 25:1. The die inner diameter was 50.8 mm with a die gap size of 1.5
mm. The blown ﬁlm processing conditions are shown in Table 6-1. The screw speed was

maintained at 15 rpm. Blown ﬁlm processing was carried out at a pressure of ~ 2500 psi,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

F»
with a melt temperature around 150°C. '
Table 6-1: Blown Film Processing Conditions for Ecoflex-silane-Talc blends
Die 3 Die 2 Die 1 Adaptor Clamp Ring Zone 3 Zone 2 Zone 1
Set (0F) 75 280 300 310 310 330 330 315
Actual (0F) 78 281 300 311 310 318 330 315 I
O E
Melt ( F) 302

 

Screw Speed (RPM) 15

 

FPM (ft/min) 7.8

 

Pressure (psi) 2580

 

 

 

 

95

6.3 RESULTS AND ANALYSIS
6.3.1 Soxhlet extraction and FTIR results

The Soxhlet extraction results are shown in table 6-2. In the Ecoﬂex/Talc blend,
almost 100% Ecoﬂex was extracted. There is no grafting in the Ecoﬂex/Talc blend and

the extraction is complete since F TIR analysis shows that the material remaining in the

thimble is pure Talc. There are two signiﬁcant peaks at 1009 cm.1 and 670 cm.1 for Talc

(Figure 6-7), the peak at 1009 cm'I is assigned as Si-O-Si stretch and 670 cm.1 is

assigned as Si-O-Mg stretch. d'Espinose de la Caillerie et al. displayed the same FTIR

results for Talc (133).

Table 6-2 The Soxhlet extraction data for Ecoflex/Talc blends

Extracted data of ecoﬂex/talc with/without vinyltrimethoxysilane

 

 

 

 

 

 

 

 

. . Ecoﬂex
materials matenal a ftin
samples weight (g) rearnian in extracted gr g
thimble (g) out (g) percentage
(%)
Ecoﬂex/Talc (70/30) 1.851 0.5437 1.3066 -0.01
Ecoﬂex/talc/silane/lupersol (69/30/1/0.1) 1.9281 1.1883 0.7391 0.45

 

96

 

 

 

05% “1C FTIR of Talc

.o .o
W h
1 11111111111 111

670

absorbance
llJLlllll 111

.o
N
l

LllLLll

.9
l

 

 

l
\R
C

I

.1

4 I

4 —-.'/
O _ _L_ “Ah“ Mm-

‘

 

 

ﬁ' 7 f 1' T

. l . . . . l . . . . I . . . . l . . . . l . . . . l . , . 1 I .
4000 3500 3000 2500 2000 1500 1000 500
cm-1

Figure 6-7 FTIR spectrum of Talc

The material extracted by the solvent in the Ecoﬂex/Talc blend is pure Ecoﬂex.

This has been conﬁrmed by FTIR. The FTIR of Ecoﬂex is shown in Figure 6-8. The ester

C=O and C-0 stretch, -CH2- group, and para-substituted benzene group can be identiﬁed

at 1710 cm“, 1268(1103-1164) cm“, 2953 cm-iand 728 cm".

97

 

 

 

 

 

 

 

 

 

 

1 FTIR of Ecoﬂex
— Ecoﬂex
0.6—;
i 1710 728
0.5 —_
i 1268
.4—.
o 0 : 1103
U .
E: '3
".3 :
3 0.3“.
.o 1
N .:
1018
02—: r
i 1465
0.1 -: 2953
0.3 wJL V J
.3.
.‘ v I v Y r v I ‘Vi 171 f T Y ‘1 f r T v v v v I v r r V l v v V v I r v v Y I v
4000 3500 3000 2500 2000 1 500 1000 500
cm-1 E,

Figure 6-8 FTIR spectrum of Ecoﬂex

In the Ecoﬂex/Talc/VTMOS/Lupersol blends, only about 55 wt% Ecoﬂex was
extracted. The FTIR of the material remaining in the thimble shows Ecoﬂex -Ta1c
grafting copolymers were generated. The FTIR results for the material remaining in the

thimble compared to pure Ecoﬂex is shown in Figure 6-9. In this ﬁgure, we can observe

the Si-O-Si peak shiﬁ from 1009 cm.1 to 968 cm'1 combined with the ester C-O stretch

 

and Si-O-Mg peak at 667 cm.1 from Talc. The ester C=O peak at 1715 cm'l, para-

substituted benzene peak at 729 cm'land the —CH2- peak around 2950 chfrom Ecoﬂex

can also be identiﬁed clearly.

98

FT IR of Ecoﬂex/talc/VTMOS/lupersol(69/30/l /0.1)

'I ..It
- Material remian in thimble aﬁer extraction
0.7

0.6

0.5

0.4

absorbance

 

0.3

 

 

0.2

=3676

0.1

     

 

 

 

 

 

‘7 ﬂ W Y ﬁ’ 1

. l I I . . I . . I . I . A I
4000 3500 3000 2500 2000
cm-1

V’ ‘r

I I .
1500

Figure 6-9 FI‘ IR spectrum of Ecoflex/silane/Talc after extraction (in thimble) vs.

Talc

The cast ﬁlm made from the extracted solution shows us some interesting results.
It is a clear ﬁlm at the edges and opaque in the center. The FTIRs of the edge of the ﬁlm

and the center of the ﬁlm are shown in Figure 6-10. Figure 6-11 shows the FTIR results
for the center of the cast ﬁlm compared to pure Ecoﬂex in the 600 cm'1 t01050 cm-l

range.

The FTIR results show that the edge of the ﬁlm is identical to pure Ecoﬂex, but in

the center there are two strong peaks at 794 cm'land 1015 cmil. Hjertberg, T. et al. in

their study on cross-linking of copolymers of ethylene and vinyltrimethoxysilane pointed

99

 

 

out that wave number around 800 cm.1 is the peak for the —Si-OCH3 group and 1030

cm.1 is the peak for the —Si-O-Si- stretch (134).

The F TIR results conﬁrm that the grafting reaction between Ecoﬂex and vinyl-
trimethoxysilane generates the grafting copolymer, and the —Si-O-Si- group shows that
the reaction between the -Si-O-CH3 groups of vinyl-trimethoxysilane to form an —Si-O-

Si- structure can also occur.

FTl R of material extracted form Ecoﬂex/ta

 

 

 

 

 

 

 

 

 

 

 

.1
- Side part of solution cast ﬁlm
- Center part of solution cast ﬁlm
1015 794
0-8‘ 1712
. 726
J
0.6—
8 -
g
_o .1
2;
'8
0.4—
0.2—
- 2963
04 A M J
II.f..I.frI....I....I....I-...I. 4
4000 3500 3000 2500 2000 1500 1000

cm-1

Figure 6-10 FTIR spectrum of extracted material from Ecoﬂex/silanefTalc (solution)
(edge and center)

100

 

 

FTIR of d Ecoﬂex/Talc/VTMOS/Lupersol compare to pure Ecoﬂex

 

 

 

— - Extracted material form blend (in sloution)
-Ec0ﬂex
1015
0.8— 794
L M
0.6—
Q)
E’- ‘ 726
+3 4
8 .
'8
0.4-
« 5:"
0.2-
I
O—
? rﬁ I‘T II....I...II....I....I...Irﬁ...IITﬁ.I,
1050 1000 950 900 850 800 750 700 650 600

cm-1

Figure 6-11 FTIR spectrum of extracted material from Ecoflex/Silanel'l‘alc(solution)
comparing with Ecoflex

For further conﬁrmation the reaction between silane and Ecoﬂex, FTIR was also
studied for an Ecoﬂex/Silane/lupersol (99: 1 20.1 at weight) blend. The spectrum of the

blend subtracted from the spectrum of pure Ecofelx in the 1050-600'l range is shown in

 

‘1.

Figure 6-12. The peak at 1018 and 796 can be clearly identiﬁed although the silane

concentration is low (1 wt °/o).

101

FTIR spectrum of Ecoﬂex/VTMOS/Lupersol (99/1/0.1)
substracted by pure Ecoﬂex at speciﬁc area
- SilaneEcoﬂcx-Ecoﬂex

~j 1085

003—j 726
1018

absorbance
o
o
x)
I

 

796

O": W—

 

 

 

 

ﬁvv vrvv v‘r

'l""l' l I 'l'"‘l""l""l""l""l'
1050 1000 950 900 850 800 750 700 650 600

cm-1

Figure 6—12 FTIR spectrum of Ecoﬂex/silane substracted by Ecoﬂex

6.3.2 Mechanical properties of Ecoﬂex-silane—Talc blends

Tables 6-3 and 6-4 show the tensile properties in the machine and transverse
directions respectively for blown ﬁlms derived from the in situ silane-modified PBAT-
Talc composites, and the simple PBAT-Talc melt-blend.

Using VTMOS (Entries 2 — 6, Table 6-3), it was observed that tensile strengths
higher than 5000 psi in the machine direction could be achieved in some formulations
(Entries 2 & 5, Table 6—3) with elongations at break of 300 —— 350%.

Tensile strengths greater than 4000 psi and break elongations in the range of 150

— 300% were obtained from the remaining formulations (Entries 3, 4, & 6, Table 6-3).

Thus, higher mechanical properties were obtained using lower concentrations of the free-

radical initiator as well as of VTMOS. This is probably due to the fact that low levels of

102

 

 

branching would have occurred within the polyester chains due to the presence of the
peroxide. Also, the free-radically grafted silane would have induced low levels of
branching. The branching in the polyester matrix due to the silane could be due to curing
of the methoxy groups with other methoxy groups from the grafted silane as well as
curing of the grafted methoxy groups with the lateral hydroxyl groups possessed by the
Tale ﬁller. This branching would effectively improve the tensile strength of the resulting
composite but result in a decrease in elongations at break due to the formation of a
network between the polyester and the ﬁller (which would restrict the elongation of the
polymer chains). Higher levels of peroxide or VTMOS would lead to increased branching

(or possibly cross-linking) restricting the elongations at break to very low values (150 —

 

300%).

VMDMOS was used in order to reduce the branching due to the silane within the
polyester chains, and to form a more ﬂexible network with improved tensile strengths as
well as elongations. VMDMOS is, however, more expensive than VTMOS, and thus not
economically feasible. The tensile strengths of the composites obtained using VMDMOS
were approximately 4300 psi, with break elongations in the range of 430 — 480% (Entries I
7 — 8, Table 6-3).

The tensile properties of the ﬁlms in the transverse direction displayed a similar

 

trend to those in the machine direction (Table 6-4). 3‘

103

Table 6-3 Tensile Properties (Machine Direction) of blown films derived from the

PBAT-silane—Talc blends

 

% Free Type and (% Young’s Yield Tensile Break

Entry Radical Amount of modulus Stress Stress Elongation

 

 

Initiator Silane) (psi) (psi) (psi) (%)
1 - - 1 7000 1 840 2060 600
2 0.1 VTMOS (0.5) 56850 5800 5800 300
3 0.1 VTMOS (1.0) 54850 4600 4700 230
4 0.1 VTMOS (2.0) 50840 4000 4340 160
5 0.05 VTMOS (1.0) 47000 5100 5100 340
6 0.2 VTMOS (1.0) 49300 4300 4300 270
7 0.1 VMDMOS (1.0) 48000 4250 4300 470
8 0.1 VMDMOS (2.0) 49700 4250 4300 420

 

14

104

Table 6-4 Tensile Properties (Transverse Direction) of blown ﬁlms derived from the

PBAT-silane-Talc blends

 

% Free Type and (% Young’s Yield Tensile Break

 

 

Entry Radical Amount of modulus Stress Stress Elongation

Initiator Silane) (psi) (psi) (psi) (%)
1 - - 17200 1400 1500 300
2 0.1 VTMOS (0.5) 50700 3300 3300 270
3 0.1 VTMOS (1.0) 57300 3700 3800 200
4 0.1 VTMOS (2.0) 51600 3200 3300 160
5 0.05 VTMOS (1.0) 47600 3000 3000 170
6 0.2 VTMOS (1.0) 52200 3650 4000 280
7 0.1 VMDMOS (1.0) 51600 3500 3500 430
8 0.1 VMDMOS (2.0) 53600 3700 3800 390

6.4 CONCLUSIONS

1. The grafting reaction between silane functionalized Ecoﬂex and Talc was
characterized by Soxhlet extraction and conﬁrmed by F TIR.

2. The grafting reaction improves the tensile strength and Young’s modulus of the
organic-inorganic hybrid blend with a corresponding decrease in elongation. The

crosslink agents vinyl-trimethoxsilane or vinyl-methyl-dimethoxysilane can be reacted

105

 

‘Tf

 

with Ecoflex and Talc to form a grafting copolymer and improve the compatibility of

Ecoflex and Talc with resulting improvement in mechanical properties.
3. The reaction mechanism between Ecoﬂex, silane and Tale is complicated and

more work needs to be done to analyze the relationship between the mechanical

properties and the compositions of silane and Lupersol.

106

 

 

shaft“.- . '

Chapter 7: CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK

7.1 CONCLUSIONS

Using bio-based polymeric materials has a positive affect on the environment.

The main drawback of bio-based polymers is their poor processability and hydrophilicity
and the main factor affecting the marketability of synthetic biodegradable polymers is
their higher cost. The addition of cheap ﬁllers will signiﬁcantly reduce the cost but
physical and processing properties are signiﬁcantly impaired.

Compatilization is a process that improves the interfacial interaction in polymer
phases by reducing the interfacial tension, improving the phase dispersion and reducing
the phase separation and hence improving the properties of the polymer blend. In this
study, compatiblizing a CA/SMA or an organic-inorganic hybrid blend by introducing
chemical reactions between the components has proved to be an effective way to achieve
acceptable price and usable properties.

In a CA/SMA bio-based blend the high grafting conversion of SMA was obtained
by adding an appropriate catalyst both in solution and reactive extrusion reactions. SMA
grafting conversion was characterized by Soxhlet extraction and conﬁrmed by F TIR
analysis. A third order reaction was demonstrated by experimental data. The reaction

constant and activation energy were also derived from the experimental data.

107

 

 

CA can be easily processed without any added plasticizer by reactive blending
high molecular weight SMA (15wt% or higher). The grafting copolymer generated in-situ
acts as a compatibilizer to improve the phase dispersion by reducing the interfacial
tension thereby improving the mechanical properties. Compatiblized CA/SMA blends
with mechanical properties equivalent to commercial engineering plastics (glass ﬁber
reinforced ABS, glass ﬁber reinforced Nylon 66) were obtained by a one-step reactive
extrusion process.

Injection molding conditions were also studied to optimize the tensile properties
of the CA/SMA blend. Higher shot velocities and higher mold temperatures can improve

the tensile properties due to uniform cooling and should result in better properties for the

 

CA/SMA blends.

The process of CA/SMA compatibilization was also simulated using the model
deduced in this work by applying reasonable assumptions and approximations. The
simulation results are in agreement with the experimental data. Introducing a grafting
reaction to generate a copolymer acting as a compatibilizer improves the phase
dispersion. On other hand, better phase dispersion generates more reacted areas, thus l
improving the grafting rate. The mutually positive effect between phase dispersion and

grafting reaction make the CA/SMA grafting system compatibilization rapid.

 

Adding the inorganic ﬁller Talc to synthetic biodegradable polymer Ecoﬂex can J
reduce the cost, improve the Young’s modulus, improve barrier properties and improve
the blown ﬁlm process by reducing tackiness.

The use of vinyl-trimethoxysilane or vinyl-methyl-trimethoxysilane as a coupling

agent improves the tensile strength by 100%-200% and Young’s modulus by more than

108

200% due to the formation of chemical bonds between Ecoﬂex, VTMOS or VMTMOS
and Tale. A lower cost, higher property biodegradable polymer blend is achieved for
blown ﬁlm applications.

This study aimed at processing compatible blends by introducing grafting
reactions between the components proved to be an effective method to achieve the
desired properties and to reduce cost thus making it more feasible to use bio-based or

biodegradable polymeric materials.

7.2 RECOMMEND FUTURE WORK
7.2.1 Theoretical expectations for polymer blend properties

In this study, the relationship of phase dispersion and such factors as component
composition, interfacial tension, compatibilizer concentration, and shear rate have been
characterized and modeled. The theoretical analysis results are close to the experimental
results obtained. Theoretical anticipation of the properties of polymer blends will
provide valuable insights into the design of a polymer blend with desired properties.

In a miscible polymer blend, the properties can be readily predicted by calculating
their volume/weight average properties of the blended polymers. However, most polymer
blends are immiscible. To anticipate immiscible polymer blend properties is much more
complicated and most studies have been concentrated in the experimental area.

A general model to calculate average molecular weight of the copolymer formed
between two poly-disperse reactive polymers has been generated by Lie-Ding Shiau (135)
based on Flory’s assumptions. J ose.S., et.a1 (136) have done the theoretical analysis of

the tensile properties of Polyamide 12 and polypropylene blend with or without

109

 

 

compatibilizer using Nielsen’s ﬁrst power law model, Nielsen’s two-third power law
model and the Nicolais—Narkis model. Nielsen’s ﬁrst power law model was found to be
the best ﬁt with the experimental data.

To estimate the properties of polymer blends by using its components properties,
processing conditions and their microstructures will be a crucial challenge in the study of

polymer blends.

7.2.2 Compatibilizing biodegradable polyesters
In the biodegradable polymer family we still focus on developing new products

with lower cost and good properties. Recently several studies on blends of existing

 

biodegradable polymers were done (137-139). Poly (lactic acid) (PLA) has been
commercialized by Natureworks on a large scale (140,000 ton/year). PLA is a completely
bio-based and biodegradable polymer with comparable price to petrochemical-based
polymers. The application perspectives of PLA are exciting in the biodegradable ﬁeld.
However, PLA has some drawbacks such as low deﬂection temperature, low melting
strength (difficult to blow ﬁlm), and slow crystallization (requiring long cycle time in a
molding). To improve these shortages, blending PLA with other biodegradable polyesters

has been studied widely (140-142). The crystallization time can be shortened by adding a

 

nucleating agent, but none of these workers show that the deﬂection temperature and i
melting strength were improved signiﬁcantly.

To introduce a new blend of PLA with a high deﬂection temperature and good
melting strength for blown ﬁlm will dramatically improve the application of PLA and

capitalize on its lower price, higher tensile strength and good processability. To blend

110

Ecoﬂex with PLA by introducing functional silane as the crosslink agent has been tried.
Both the melt strength and deﬂection temperatures of PLA can be improved at low
additive levels. The blend can be used for blown ﬁlm when more than 70% Ecoﬂex is
added. To lower the content of Ecoﬂex and investigation of other biodegradable

polymers to achieve the object will be very interesting ﬁrture work.

111

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