é
“5‘35“

’3

3341.
2.

.u

A" uunmt

4 .

and

 

 

 

 

 

 

 

 

77427.63
\

This is to certify that the

thesis entitled

DESIGN AND ENGINEERING OF ECO-FRIENDLY BIOCOMPOSITES
FROM HEMP FIBER AND LOW COST NOVEL SOY PROTEIN BASED
BIOPLASTICS

presented by

David D. Hokens

has been accepted towards fulfillment
of the requirements for

M.S. degree in Materials Séience

 

 

5% WW {QM/(L,

Major professor a

 

Date 112/344 1/

07639 MS U is an Affirmative Action/Equal Opportunity Institution

 

 

LIBRARY
Michigan State
University

 

 

 

PLACE IN RETURN Box to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6/01 cJClFiC/DateDuepes-sz

DESIGN AND ENGINEERING OF ECO-FRIENDLY
BIOCOMPOSITES FROM HEMP FIBER AND LOW COST NOVEL
SOY PROTEIN BASED BIOPLASTICS

By

David D. Hokens

A THESIS

Submitted to
Michigan State University
In partial fulfillment of the requirements
For the degree of

MASTER OF SCIENCE
Department of Material Science Engineering

2002

ABSTRACT

DESIGN AND ENGINEERING OF ECO-FRIENDLY BIOCOMPOSITES FROM
HEMP FIBER AND LOW COST NOVEL SOY PROTEIN BASED BIOPLASTICS

By

David D. Hokens

The study of developing new structural materials from non-petroleum
based materials is investigated with a focus on developing materials from soy
protein. A biocomposite material is formed through reinforcement with hemp
fiber. This investigation explores processing effects, effect of surface treatment
of reinforcing fibers, and environmental effects on the composite material. The
development of a biobased material is presented as well as the effects of

processing and optimization of the process parameters.

TABLE OF CONTENTS

List of Figures ................................................................................ iv

List of Tables ................................................................................. v

Chapter1

Introduction .................................................................................. 1
1.1) Research Goal/Problem Statement .................................... 1
1.2) Motivation for research ..................................................... 1
1 3) Soy background ............................................................. 2
1.4) Fiber ............................................................................ 5

Chapter 2

Literature review ............................................................................ 11
2.1) Soy plastics .................................................................... 11
2.2) Natural fibers .................................................................. 24
2.3) Biocomposites ................................................................ 29

Chapter 3

Experimental procedure ................................................................... 33
3.1) Extrusion of soy concentrate plastics ................................... 33
3.2) Extrusion of composite materials ......................................... 37
3.3) Fiber treatment and preparation .......................................... 38
3.4) Injection molding ............................................................. 39
3.5) Material property measurement ......................................... 41
3.6) Data evaluation .............................................................. 43

Chapter 4

Results and discussion .................................................................... 45
4.1) Soy concentrate plastics/composites ................................... 45

Chapter 5

Conclusions .................................................................................. 75
5.1) Conclusions ................................................................... 75

Chapter 6

Research Recommendations ............................................................ 78

6.1 ) Recommendations .................................................................... 78

BIBLIOGRAPHY ............................................................................ 80

iii

List of Figures

Figure 1.1 Constituents of soybean on a percent basis .......................... 3
Figure 1.2 Description of natural fiber source ....................................... 7
Figure 1.3 Classification of natural fibers ............................................. 9
Figure 2.1 The twenty amino acids .................................................... 14

Figure 2.2 Effect of plasticizer on modulus and elongation to failure
of the soy polymer14 ........................................................................ 18

Figure 2.3 Structure of lignin and cellulose, base materials of natural

fibers. .......................................................................................... 26
Figure 3.1 Schematic of W&P ZSK twin-screw extruder .......................... 34
Figure 3.2 Barrel of W&P ZSK-30 twin-screw extruder ........................... 35
Figure 3.3 MSU/CMSC extrusion screw configuration ........................... 35
Figure 3.4 MSU/CMSC diagram of screw configuration .......................... 36
Figure 3.5 Extruder schematic for addition of fiber to soy plastic .............. 38
Figure 3.6 Schematic of Cincinnati Milacron Injection Molder .................. 40
Figure 3.7 Schematic stress strain curve ............................................ 42

Figure 3.8 Schematic of apparatus used to weigh immersed hemp fiber....44
Figure 4.1 Effect of initial moisture content on final material properties...... 46

Figure 4.2 Change in stress-stain behavior as a function of moisture

content ......................................................................................... 46
Figure 4.3 FTIR of glycerol and residue on desicator ............................. 47
Figure 4.4 TGA of soy concentrate plastic .......................................... 49

Figure 4.5 Baseline material properties of the soy concentrate plastic ...... 50

iv

Figure 4.6 Effect of extended drying on soy plastic material properties..... 51

Figure 4.7 Effect of change in rpm ..................................................... 52
Figure 4.8 Effect addition of fiber on soy plastic ................................... 53
Figure 4.9 Impact energy of soy plastic and composites ........................ 55
Figure 4.10 Rule of mixtures for composite properties ........................... 57
Figure 4.11 Illustration of fracture of soy plastic tensile coupon ............... 57
Figure 4.12 End view, schematic of fractured tensile coupon .................. 58

Figure 4.13 SEM of ductile fracture initiation site of soy plastic; 100x........ 58
Figure 4.14 100x brittle fracture area of tensile failed specimen ............... 59

Figure 4.15 1000x ductile initiation fracture area of tensile failed
specimen ...................................................................................... 59

Figure 4.16 1000x brittle fracture area of tensile failed specimen ............. 60

Figure 4.17 15wt% Alkali treated hemp in SCP6, tensile failure surface,
400x ............................................................................................. 61

Figure 4.18 15wt% Alkali treated hemp in SCP6, tensile failure surface,
1000x ........................................................................................... 62

Figure 4.19 15wt% raw hemp in SCP6, tensile failure surface, 1000x ....... 62

Figure 4.20 15wt% raw hemp in SCP6, tensile failure surface, 300x .......... 63
Figure 4.21 Schematic of alkali treatment of natural fiber ........................ 64
Figure 4.22 1000x raw hemp fiber ...................................................... 64
Figure 4.23 1000x alkali treated hemp fiber ......................................... 65
Figure 4.24 Effect of moisture on soy plastic with 15% raw hemp ............ 66

Figure 4.25 Change in stress-strain behavior of alkali fiber composite
with aging ..................................................................................... 66

Figure 4.26 Effect of moisture on soy plastic with 15% raw hemp ............ 67

Figure 4.27 Change in stress-strain behavior of raw fiber composite

with aging ..................................................................................... 67
Figure 4.28 Tensile fracture surface of 15wt% raw fiber in soy plastic,

tested 30 days after composition, 300x ............................................... 68
Figure 4.29 Tensile fracture surface of 15wt% raw fiber in soy plastic,

tested 30 days after composition, 1000x .............................................. 68
Figure 4.30 Tensile fracture surface of 15wt% alkali treated fiber in soy
plastic, tested 30 days after composition, 300x .................................... 69
Figure 4.31 Tensile fracture surface of 15wt% alkali treated fiber in soy
plastic, tested 30 days after composition, 1000x ................................... 69
Figure 4.32 Schematic of melt flow filling part cavity.20 .......................... 71

Figure 4.33 An example of a glass filled polypropylene injection-molded
part, longitudinal cross-section20 ......................................................... 71

Figure 4.34 An example of a glass filled polypropylene injection-molded
part, transverse cross-section.20 ........................................................ 72

Figure 4.35 Surface of dog bone sample scp6 with 15wt% raw hemp
fiber 100x, some fibers highlighted in black ......................................... 72

Figure 4.36 Optical micrograph of fibers in bulk of a injection molded

dog bone 15wt% raw hemp fiber 100x, some fibers highlighted in black,
longitudinal cross-section ................................................................ 73

vi

List of Tables

Table 1.1 Price and percentage of soy protein sources .......................... 2

Table 1.2 Properties of various fibers ................................................. 10
Table 3.1 Breakdown of soy polymer components ................................ 33
Table 3.2 Temperature profiles of extrusion runs ................................... 34
Table 3.3 Explanation of MSU/CMSC screw configuration ....................... 36
Table 4.1 Breakdown of plastic and composite components .................... 74

vii

Chapter 1
Introduction
1.1) Research Goal/Problem Statement

Develop a biobased composite material for structural applications.
1.2) Motivation for research

The increase in the world’s population as well as the development of a
global community have attributed to an increase in C02 emissions. As new
technologies are developed to answer the demands from consumers for more
products that are less expensive, the ecological impact of this increased
consumption of durable goods is beginning to be felt and are requiring solutions
to mitigate these potential problems.

Consumption of energy and generation of disposable goods based on
fossil fuels have raised concerns over their ecological impact. Fossil fuel based
materials also have associated issues; first there is the problem of having a large
amount of non-biodegradable plastic waste. Second incineration of these
materials leads to a large release of 002. With the world’s oil reserves
decreasing, the rising dependence on fossil fuels raises concerns. What will
happen when the reserves run dry? Steps need to be taken to reduce the
ramifications of fossil fuel dependence to minimize societal impacts when the
reserves run low. The flow of disposable goods will decrease with increasing
price until the use of petroleum-based materials is not economical. The same
increase in prices of energy and fuel will take place unless there is an alternative

technology to replace the dependence on fossil fuel.

The awareness of decreasing oil reserves has raised the questions: What
are the potential alternatives? Where and what are the potential new sources for
durable goods materials? Universities and government research labs are now
beginning to explore replacement materials for the manufacture of durable
goods.

1.3) Soy background

This study is focused on finding sustainable, inexpensive materials that
will be useful for structural applications. One possible solution is composite
materials derived from biobased resources. This study investigates combining a
soy plastic as a polymer matrix with a bio-fiber for reinforcement to produce a
structural biocomposite. There are a number of synthetic biodegradable
polymers that are derived from fossil fuels, although they tend to be high priced
and of limited usefulness as a structural material. Soy protein has been shown to
be processable into a biobased plastic. Soy protein comes from the soybean,
which is made up of about 38% protein. The abundance of soybeans in the US.
allows for an ample opportunity to process soy protein into useful materials and

find a suitable replacement to fossil fuel derived products.

Protein . Percenta
flour 0.15 52

concentrate 0.77 65
isolate 1 .50 90

Table 1.1 Price and percentage of soy protein sources.

 

II’TSUDIUDIE

 
   

carbohydrates
M ' t A h 15%
013 ure, 3 . . \\\ '
other WEED Pg?”
0
14% *

on.
13%

Soluble
carbohydrates
15%

Figure 1.1 Constituents of soybean on a percent basis.

Soy plastic is based on polymerizing soy proteins, which are readily
available in nature. Proteins are large macromolecules that are composed of
amino acids. Soybean protein is composed primarily of two different proteins:
glycinin, with a molecular weight in the range of 330,000 to 360,000 D and
conglycinin, which have a molecular weight of 180,000 to 200,000 D. The
glycinin protein is composed of 12 primary subunits each with a molecular weight
in the range of 20,000 to 37,000 D. The conglycinin protein is composed of three
primary subunits with molecular weights in the ranges of 57,000 to 83,000 D.
These proteins are polymers of amino acids, pre-polymers of the large polymer
chain that they will form. This limits the number of molecular structures, which
can be formed from this source, and consequently the mechanical properties of
the soy plastic.

The presence of these large, naturally occurring protein molecules gives

rise to a unique opportunity to engineer these molecules and create new

materials. The prospect of crosslinking protein is a complex task. The task of
modeling the molecular interactions, and verifying what occurs during
crosslinking is difficult at the molecular level. An alternative process is to conduct
structure-processing-property studies based on physico-mechanical property
measurements to gain insight into the soy plastic. Higher modulus and strength
can be related to the degree of cross-linking and molecular interaction.

There is published information on the properties of soy protein, such as
the degradation temperature of each protein, or the percentage of each protein
that makes up the total soy concentration of the soybean. However much of this
research has been focused on determining how the protein works as a nutrient
and has been studied for food science purposes.

Soy protein is readily available from a number of grain processing
companies in various forms: soy isolate, soy concentrate, and soy flour. The
difference between these soy variations is the percentage of protein. The
isolated protein is approximately 90% pure, the concentrate is about 65% and the
flour is about 50% soy protein. The isolate and concentrate are processed using
an acid-base extraction to remove the protein from the carbohydrate fraction as
well as the soybean oil. The soy flour however, is soybean that is de-hulled,
ground, and the oil is removed to produce the defatted soy flour. From these raw
materials the processing of the proteins begins in order to produce a soy protein
polymer. However, there is a large difference in price between the three different

materials, largely due to the difference in processing.

There are also differences in the soy product. Soy protein is capable of
reacting with itself and crosslinking, however it is very stiff and very brittle, and
has little strength. Addition of plasticizers to the soy protein allows it to become
more flexible and have increased strength. However the increased strength
comes as a trade off, a reduction in modulus. Commonly used plasticizers for
modification of the soy protein are glycerol, ethylene glycol and water.

The products in this niche market that these materials will compete with
are on the order of twenty or thirty cents a pound. The raw soy protein is not this
inexpensive by itself. The addition of wheat starch, as an inexpensive filler aids
in plasticizing the proteins, and reduces the cost of the end product. Soy
polymers have been used for applications such as biodegradable soy adhesives
for making particleboard. Moisture absorption of the soy protein plays a role in
potential applications as well. When exposed to moisture the adhesive
properties are lost.

The focus of developing a biocomposite is to develop a material that is
composed of soy plastic and a natural fiber reinforcement.

1.4) Fiber

A composite is a complex material, in which two or more distinct
structurally complementary substances are combined to produce a composite
material with structural or functional properties not present in any individual
component. Examples of composites are wood or fiberglass. Composite
materials have been in existence since biblical times. However, the use of

synthetic reinforcing fibers such as glass or carbon with petroleum-based plastics

is a relatively new development. Fiber reinforcement of plastics has created high
strength, low weight materials that have been used in many different industries.
Aerospace industries have used composites for creating lighter aircraft. The
automotive industry has used composites in applications from exterior body parts
to under the hood applications. The lightweight and corrosion resistance of
polymer-reinforced materials has been beneficial for these applications.

There are many different types of reinforcements to add to polymer
matrixes that improve the performance of the polymer. For different applications
different fillers or reinforcements can be very beneficial. They can decrease the
cost of the material and potentially increase the performance of the composite.

In an effort to decrease material sensitivity to temperature, it may be appropriate
to blend a material with a ceramic filler, such as alumina to calcium carbonate.

Carbon and glass fibers are very common synthetic fibers. Carbon fibers
are very good for high stiffness, high strength, low density, high temperature
applications, where performance is the overlying goal and cost is not. Glass fiber
is very commonly used in a whole host of applications from car bodies to shower
paneling. Glass is probably one of the most widely used fibers for reinforcement,
with strength between 2 and 3.5 GPa and a modulus of 70 GPa.

For the sake of improving the properties of the soy polymer that is being
focused on in this study and keeping in line with the focus of making a material
that is agro-based the choice for a reinforcement was to choose a natural fiber,

hemp in this case, which has a modulus of 55GPa and a strength of 0.6GPa.

Leaf fiber comes from
the plant leaf.

 

Fruit fiber comes from
the fruit of the plant.

 

 

Bast fiber comes from around
the stalk of the plant.

 

Figure 1.2 Description of natural fiber source.

Figure 1.1 illustrates a typical plant structure and the location of each type
of fiber. One of the most common natural fibers is cotton, a fruit fiber. Leaf fibers
that are considered possible reinforcements include henequen (sisal) and
pineapple leaf fiber. The third type of natural fiber is the bast fibers, which come
from around the stem of the plant. Common bast fibers are hemp, flax, kenaf,
wheat straw, and corn.

Natural fibers have been used in different applications from clothing to
adobe. Research has recently pushed the envelope into finding materials that
are less disruptive to the environment. Natural fiber composites first came of-age
when lumber manufacturers starting looking for applications of sawdust and
discarded wood chips. The invention of Orientated Stand Board (OSB) was
basically an application of waste wood fiber. When wood chips were held

together with an adhesive the end product became a viable source of building

materials and brought about the introduction of biocomposties. Wood fiber
paved the way as the first cellulose fiber to be incorporated into a polymer matrix.
Cellulose fiber as a reinforcement from trees is a by-product of the lumber
industry and secondly the growth cycle of a tree is on the order of 30 years. The
use of trees as a source for fibers is not practical since there are more valuable
uses for trees.

Natural fibers from non-woody plants are very attractive as alternative
sources for cellulose fibers. Agriculture refuse such as corn stubble and wheat
straw are attractive commodities in that the wood fiber is attractive; it is currently
a waste product in the effort to produce corn and wheat. Research is under way
to attempt to use these waste materials as fiber reinforcements in polymers.
Although the potential for these fibers is high there is still a great deal of work to
do before they are proven.

Research efforts are also being placed into developing natural grasses as
a fiber source. All of the above mentioned sources are perennial crops that have
90 to 120 day growth cycles that improve their availability.

Hemp, Kenaf, Flax, Henequen, and Cotton are established fibers that
have an active crop base for production that are grown solely as a source for
fiber and oil. Cotton fiber has been investigated for reinforcement, as there is a
lot of waste fabric that could be used as an acceptable source of reinforcement in
composites. Flax fiber has been produced for years as the source of linseed oil,

which is used for many applications. Hemp, Kenaf and Henequen fibers each

also have traditional applications as well but new interest has been found of late
in these fibers for composite applications.

Bast fibers such as the hemp and kenaf are very stiff fibers and when
incorporated into the polymer matrix improve the strength and stiffness of the
material. The weakness of bast fibers is their lack of impact strength. Leaf fibers
on the other hand perform very differently when incorporated into a polymer
matrix. Leaf fibers offer very good improvement in impact strength but do not

offer the improvement in strength and modulus that bast fibers provide.

 

 

 

Biofibers- types and sources

 

 

 

 

 

I I l 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Straw Non-wood Cellulose Wood
Biofibers Biofibers Nam-whiskers Biofibers
Bast Leaf Fruit
I 1 Soft or Hard
W (1
Kenaf, Flax, Cotton, Coir 00
Jute, Hemp
Corn Wheat Sisal, Henequen, Modification of
Rice Straws Pineapple Leaf natural fibers to
Fiber (PALF obtam nano-
cellulose fibers

 

 

 

 

 

 

Figure 1.3 Classification of natural fibers.

Of course the standard for performance of the natural fibers is whether
they improve the performance of the material as much as their synthetic counter-
part would. Glass fiber offers a very good improvement in strength and
modulus and impact strength when added to polymers and is reasonable in cost

as well. Hybridization of the natural fibers offers the potential for achieving

similar levels of performance as glass fiber. Glass fibers do have disadvantages
over that of the natural fiber, namely it’s density. The density of glass fiber is
roughly twice that of natural fiber. The weight savings is an important issue for
industries such as automotive where biocomposites could be used to produce
structural car parts of lower weight for improved fuel efficiency. Glass fiber
although recyclable, is less energy efficient than natural fiber to produce. It has a
higher density and is more expensive. Natural fiber when incorporated in a
weight percentage shows comparable reinforcing properties as glass. Natural
fibers can be surface treated or sized just as glass.

The focus of this study is for a soy plastic based matrix material to be
reinforced by hemp fibers. Hemp fiber has the best reinforcing properties of the

other natural fibers and therefore the best upside for the material performance

2.5 20 7O
1 .4 25 30-50

1 .48 1 3-30 55
1 .46 25-200 1 0-30
1 .33 50-200

Table 1.2 Properties of various fibers.

 

1O

Chapter 2
Literature Review
2.1) Soy plastics

There has been a substantial amount of research done on soybeans.
Research examining the nutritional benefits of soy meal has gained knowledge of
the thermal and chemical behavior of soy proteins. Of late work has focused on
the ability to polymerize soy proteins in an effort to develop plastic.

Soybeans consist of proteins, fat, ash and carbohydrate fractions in a
distribution as shown in Figure 1.1. The protein constituent consists of three
different fractions, 78, 118 and 158. The 78 fraction comprises about 35% cf
the soluble protein. The 118 fraction also referred to as glycinin comprises from
31 to 52 percent of the soluble soy protein. The final fraction of extractable soy
protein is the 158 fraction, which accounts for about 5% of the extractable
protein.

The 78 globulin, conglycinin makes up about 85% of the 7S fraction and
consists of 4 to 6 different components. The molecular weights of the various 78
fractions range from 140,000 to 170,000 Daltons. At low ionic strengths, the 7S
globulins form dimers with molecular weight of 280,000 to 350,000 Daltons.

The 118 globulin, glycinin has a molecular weight of 320,000 to 360,000
Daltons. Glycinin is separated by cryoprecipation. When the 11S globulin is
completely dissociated, fractions having molecular weights of 34,800 and 19,600
Daltons are recovered. The larger species have isoelectric points of 4.75 to 5.4

and are called the acidic subunits. The three acidic subunits have isoelectric

11

points of 4.75, 5.15 and 5.40. The basic subunits were also separated into three
groups having isoelectric points of 8.0, 8.25 and 8.5. The isoelectric point is the
pH value where the protonation and deprotonation rates are equal to one
another. Essentially the system is stabilized. The acidic subunits have been
shown to contain three proteins with differing N-terminal amino acids, eg.,
Leucine, lsoleucine and Phenylalanine. The basic subunits all contain a terminal
glycine.

Intact 11S globulins are dodecimer compounds of six basic and six acidic
subunits. Under proper conditions, 118 can be fractionated into units of 78.
These 78 units appear to be composed of three acidic and three basic subunits.
The 118 protein can also be broken to yield 38 subunits which appear to be
dimers consisting of one acidic and one basic subunit each. The bond between
the acidic and basic subunits might be a disulfide linkage. Reduction of this bond
yields individual subunits of about 28 which are individual acidic and basic
subunns.

The soy proteins of glycinin and conglycinin are very inter-related
structures. Both proteins are quaternary structures with four base subunits on
each protein. The 118 protein is the largest and most prevalent of the three and
can be broken down into sub-components that are equivalent of the small
proteins

When isolated 11S proteins are heated to 80°C, a portion of the protein
precipitates. The precipitate consists almost exclusively of basic subunits. The

acidic subunits remain soluble after this heat treatment. When the whole soybean

12

protein is given a similar heat treatment, no precipitation occurs. Recent work
has shown that the addition of isolated 78 globulin to the 11S fraction will prevent
the precipitation of the basic subunits.

The final fraction of extractable soy protein is the 158 fraction. This
material comprises about 5% of the total extractable protein. It is poorly
characterized, and little is know about the thermal and chemical stability of the
158 protein“.

The basis of polymerizing proteins is reacting functional groups on the
protein. Proteins are large oligimers composed of amino acids. There are
twenty amino acids as shown in Figure 2.1. The crosslinking process of the soy
protein occurs primarily between carboxyl and hydroxyl groups. When the soy
protein unfolds more functional groups are exposed. This increases interaction
of functional groups.

The study and development of new materials has many facets, (J.U.
Otaigbe, H. Goel, T. Babccck, J Jane)12 investigated the processing effects on
soy protein-starch plastics. There have been many problems associated with
protein-based polymers; one of the primary issues is the effect of moisture. The
authors suggest that this problem could possibly be addressed by compounding

the soy polymer with the addition of polyphosphate fillers.

13

II I
HzN-Cfig—C—OH HzN—cH—ii—orr HzN-CH—é—OH HzN-rlm—ii—on

.1.- °H= a; e
m” m0 CHI
((31,, G) alanin- H cpl-[CH
(Ala, A) .m- . 3 3
(Val, v) laucine
(Ion. L)
(II (II II II
HgN—(I'IH—C—OH HzN-(IIH—C—OH HgN—(fH—C—OH HzN-(I‘JH—C-OH
(EH2 (EH: (EH2 ch—(FH
SH (EH; OH OH
cysteine s scrim tin-Ionian
(Cys, C) (EH (sari 8) (Th!) T)
3
methionine
(Met. M)

l
(EH: (EH2 CH: (EH:
CH2 CH2 |——‘|— écx .
I I + O 0
(EH: (EH: HNVNH
+ ”pm
N33 Pl”: histidine (ASP. D)
lysine $=NH2 (mm
(L’s) K) NH:
alumina
(Ara. R)

O O
HgN-CHg—g—OH HzN—C'L'H—g—OH lizN—CH—yl—OH HgN—CH—yfi—OH

cm ’03
W639 H C CH
(any, G) duh. 3 3 c/Clj
(Ah' A) v-lino Ho Cilia
(VOL v) lauds.
(Eon. 1)
‘3 ii
HzN— —Cl{—(':— —0H HzN— (EH—4: —OH HzN— —-CH—E—-OH HgN—Flfliz—E—OH
mC—C‘H
(:JH2
CH)
lsoleucine
all. I) phenylalanin-
(no.1) W
(Ty, Y) (Tm. W)

Figure 2.1 The twenty amino acids.

14

The focus of this study is processing between extrusion and injection
molding. Soy isolate mixed with cornstarch, glycerol, water, sodium sulfite, and
soybean oil was extruded between 100°C and 125°C, the material was then
conditioned to 10wt% moisture and injection molded. The moisture acts as a
plasticizer and aids processing of the material. When injection molded the
temperatures did not exceed 120°C. The authors cite thermal degradation of the
material if the temperatures during compounding and molding are higher than the
afore mentioned values. However materials that were processed at higher
temperatures manifested changes in properties that could be attributed to higher
crosslinking density. The paper does not comment on possible reasons for this
change.

Samples were tensile tested and the fracture surfaces were investigated
through SEM. DMA testing was run after the samples had been conditioned to
3.5wt% moisture. TGA and DSC studies were run to investigate thermal
degradation temperatures of the soy protein — cornstarch plastic and the material
seemed stable up to 200°C. More extensive Pressure Volume Temperature
(PVT) studies were run on the material to further the investigation into the
thermal properties. Through PVT measurements and the use of the Tait
equations a glass transition temperature was found at 80°C. The Tait equation
allow the T9 to be found through a change in specific volume as a function of

change in temperature. The DSC showed a T9 at 60°C, the difference is

15

attributed to moisture content and the effect of heat treatment on crystallinity of
the soy isolate.

SEM micrographs of the failure surface reveal a slow crack growth
followed by increase in crack growth where the material fails catastrophically.
The failure surface is dual phase with a ductile rough surface and a smooth
glassy brittle surface. The rough surface results from tearing of the material
where the crack growth is slow. The smooth surface is the result of the crack
speed increasing to a point where the material behaves as if it were at low
temperatures.

The paper reported a modulus of 0.104GPa and strength of 3.45MPa,
both properties decreased drastically when moisture or heat were applied during
testing.

(Sue HJ, Wang S, Jane JL)“ focus on soy isolate films, in three
conditions; dry, moist and plasticized with glycerol. The materials were molded
at 150°C and 19.6 MPa for six minutes. Plaques of both 0.25 and 0.125 inches
thick were molded. Samples were machined into specimens for tensile testing
and four point bending testing

The soy isolate film becomes thermally unstable at 165°C. Fracture
energy of the soy plastic drastically drops off once plasticizers or moisture is
introduced into the material.

Dry soy polymer has a reported modulus of 4.4 GPa and a T9 of 150°C.
With the incorporation of glycerol as a plasticizer the modulus drops to 0.52 GPa

and the Tg drops to -50°C. The virgin soy polymer has a modulus and T9 that

16

would compete with fossil fuel based materials very well. Polycarbonate has a
modulus of 2.10 GPa and a T9 of 150°C.

The authors concluded that the potential for the application of soy plastics
is high, however the obstacle of moisture absorption, and the correct amount of
plasticizer needs to be identified for the material to be an effective engineering
polymer.

(Qiagxian Wu and Lina Zhang)14 also found that the soy polymer has low
resistance to water. The soy protein plastics absorb moisture, which causes the
material to lose structural integrity through swelling of the polymer. Although the
moisture is only physically absorbed into the material the damage that occurs
through swelling of the polymer is permanent. The authors have decided to
focus their energy on structure, morphology, mechanical properties and water
resistance of the soy plastics.

Soy protein isolate was mixed with ethylene glycol and specimens were
compression molded at 150°C. Thin sheets were made for FTIR and X-ray
diffraction study while large specimens were molded for mechanical testing.

The soy isolate plastic showed a very sensitive relationship to the amount
of plasicizer incorporated in the sample. The Modulus drastically decreased with
addition of ethylene glycol and the break elongation greatly increased, as shown

below in figure 2.2.

17

 

 

 

-o— % elongation

250 +Modulus ‘
fl —~ 500
\ / \f .- 400 E
' é
\ / -. 300 '3
S

 

 

 

 

 

N
8

 

 

B

 

percentage elongation to fallure
8

 

8

 

 

O
O

 

1 5 25 35 45 55 65 75
Percent of ethylene glycol

 

 

 

Figure 2.2 Effect of plasticizer on modulus and elongation to failure of the soy
polymer“.

The ethylene glycol content decreased tensile strength and modulus.
Percentage of elongation is greatly increased with incorporation of large amounts
of plasticizer.

The authors surmised that materials with good material properties could
be made from soy protein isolate and ethylene glycol. Soy isolate with 50%
ethylene glycol had a tensile strength of 4.23 MPa and a break elongation of
220%.

Other work has been done with soy protein isolate, however most work
has been with the use of glycerin as the plasticizer. C. H. Schilling etal.16
discusses the use of soy protein isolate and glycerin to develop soy plastics. The
major focus of their study was to examine the mechanical properties and water

resistance of the material. The material was compression molded at 140°C for

18

six minutes loaded with eight to ten tons of force. The samples were then tensile
tested to determine mechanical properties.

Soy protein plastic without glycerin showed linear elastic deformation.
The modulus of the pure protein plastic was measured to be 4.6 GPa. With
incorporation of glycerin the modulus drops off and the deformation becomes
less and less linear as the content of plasticizer increases. Schilling et al.
reported values of 3.5 GPa and 1.8 GPa at 10 and 20% glycerin content.

One unique facet of Shilling et al. was their investigation of particle size.
The raw materials were sieved before processing. This processing step was
found to have a significant effect on the properties of the soy plastic because the
soy plastic material is a brittle material and corresponds well with Griffith’s brittle
crack propagation model. The critical variable in this model is the initial size of
the initial imperfection in the material, therefore sieving out the larger particles in
the soy powder allows there to be more uniform sized particles. The underlying
goal is to improve load-bearing ability of the material by removing large particles
that would be stress concentrations and sites to initiate croid development.

The authors also concluded that adding glycerin in the polymer increased
strain to failure. Glycerin content also decreased modulus and strength.
Hardness of the materials decreased rapidly when immersed in water.

One topic not discussed thoroughly is the concept of blending the soy
polymer with synthetic polymers to improve processing and material

performance. This is counter-intuitive to the development of a fully agro-based

19

material system, but it could improve material properties and eliminate the need
for the use of plasticizers

(Bhattacharya and John)17 found that blending of plant-based material with
synthetic materials could drastically improve properties and applications of the
biobased polymer. However the materials usually do not mix well unless the
synthetic polymer has a reactive group that would interact with the natural
polymer. The authors reference Otaigbe etal21 in their findings of using
anhydride groups in the backbone of the synthetic polymer to aid in blending with
the plant-based polymer.

In this study, anhydride groups were attached to the polyester chain to
improve interaction with the soy protein polymer. The polyester used was
polycaprolactone, which is a synthetic biodegradable polyester. The main goal of
the research is to investigate the potential of making biodegradable polymeric
articles from soy protein.

Polycaprolactone, Eastar polyester and Bionelle were blended with soy
protein on a twin-screw extruder. These polymers are all biodegradable
synthetic polymers. Easter is Eastman Aliphatic -Aromatic Copolyester. Bionelle
is the tread name from Showa Highpolymer, Japan. Chemically it is
poly(butylene succinate-co-butylene adipate) or in short PBSA. The extrudate
was pelletized, injection molded and tested to obtain mechanical data from the
material. DSC, DMA, X-ray diffraction as well as optical microscopy were used

to evaluate the materials.

20

The soy component was not dried before processing, allowing the
reported 5 to 7 percent moisture to act as a processing aid (or plasticizer) in the
extrusion and injection molding steps. The study found that it was harder to
injection mold samples that were extruded at higher temperature. The authors
comment that this could be due to protein degradation.

Increasing protein content increased strength and modulus with a
decrease in percent elongation to failure of the sample. Samples were
compounded with varying degrees of protein with the maximum amount being
65% soy isolate, materials with more than 65% soy isolate were difficult to
process. X-Ray diffraction was also used to examine crystallinity of the material.
It found that the crystalline nature of the polyester as well as the soy protein did
not change through processing, and that the final material was partially
crystalline.

Bhattacharya and John conclude that anhydride groups were found to be
effective in blending the two non-miscible materials, the protein and polyester.
The anhydride was found to decrease the size of aggregates of the individual
phases allowing for better phase interaction and ultimately increased material
properties.

Mungara et al.18

blend soy protein polymers with synthetic polyesters in an
effort to overcome the issue of water absorption of the plant-derived polymer.
The authors hypothesized that the hydrophilic polyester would help in repelling

moisture from the soy protein.

21

Soy protein isolate, soy concentrate and soy flour were used and mixed
with Biomax as well as glycerol and some compatiblizing reagent salts. A twin-
screw extruder was used to compound the materials, and the compounded
materials were injection molded to make materials for testing. Polyvinylactams
were used as a compatiblizer to improve interaction of the protein and the
Biomax. Glycerol was added to the Biomax to decrease the processing
conditions so that it could be blended with the soy protein.

The authors found material properties to have tensile strengths between
16 and 22 MPa and a modulus between 1.1 and 1.8 GPa. Water absorption was
found to decrease with the incorporation of higher content of synthetic polymer.

Thermal stability and characterization of the soy proteins themselves can
also give some insight into the potential for a fully protein based material.

Ogale et al.‘9

conducted a large amount of research into the thermal
stability of soy isolate proteins. Samples were freeze-dried before processing for
24 hours to reduce moisture content to 5-7%. Through the use of TGA Ogale et
al. were able to find some trends in the soy protein and the plasticized protein
plastics. Weight loss is small below 150°C, intermediate between 150°C and
180°C, and significant above 180°C for soy protein isolate with glycerol. For pure
soy protein isolate, the ranges move to 180°, 200°, and above 200°. The
optimum process temperature is stipulated at 150°C due to the vapor point of
glycerol; this is verified from previous studies.

Microstructural analysis of the samples that were compounded for the

study suggests that there is a critical amount of plasticizer needed for the protein

22

matrix to develop. Samples were prepared with 0, 20, 30 and 40 percent
plasticizer based on weight. The critical value of plasticizer appeared to be
around 30% as the material failure surface changed from brittle to ductile at this
value. Cross-section SEM micrographs of the films containing 30 and 40 percent
glycerol show existence of ductile rupture in the samples as evidenced by the
rough appearance of the fracture surface topography in the material.

An issue of interest with the soy polymer is how the plasticizers work
within the crosslinking process. (Sun and Mo) discuss how the plasticizers work
in the polymer. There are three mechanisms plasticizers use to facilitate
polymerization. 1) They can lubricate or facilitate the movement of
macromolecules over one another. 2) They can gel or disrupt the polymer-
polymer interactions of hydrogen bonds and van der Waals or ionic forces. 3)
They can decrease the polymer free volume. Soybean proteins are large
oligomers that are mostly stabilized by hydrogen bonds, electrostatic forces and
hydrophobic interactions and therefore would be affected by the addition of the
proper plasticizer .

This paper focuses on four plasticizers; glycerol, propylene glycol, 1,2-
butanedicl and 1,3butanediol. Glycerol was the most effective plasticizer as it
improved the strain to break more than the other plasticizers.

A larger decrease in T9 of the material would indicate a more favorable or
effective interaction of the plasticizer with the soy protein, which occurs with the
glycerol. One of the primary jobs of a plasticizer is to improve strain to failure as

well as toughness; this is accomplished with a decrease of modulus.

23

The study also discusses how the protein is structured having amino acid
groups arranged with hydrophobic groups folded onto the inside and hydrophilic
groups on the outside. Heating of the soybean protein converts the protein from
its normal state to a denatured state with unfolding and disruption of the
intramolecular bonding. The denaturization process aids in the polymerization of
the proteins. This is verified with DSC curves in the study, which shows two
endothermic peaks that are present from the soy protein. The peaks correspond
with the two different proteins, the glycinin and conglycinin.

Summarizing the above information, soy proteins are complex molecules
which makes it hard to predict individual reactions when the proteins are
polymerized. The proteins are structured marco-molecules with defined
structures that can be manipulated through chemical and thermal treatments.
The manipulation of the protein allows the proteins to be polymerized.
Pclymerizing the virgin soy protein results in a very stiff, brittle material with low
strength. The addition of plasticizers to the process reduces the modulus but
results in a stronger material.

Moisture has a negative influence on the material properties of the soy
polymer. Moisture in the soy protein can act as a plasticizer during processing,
however absorption of moisture after process leads to material degradation.
Processing conditions from study to study vary, and so do explanation of thermal
stability. This leads to some non-conformity from study to study.

2.2) Natural Fibers

24

The state of natural fiber production, availability, awareness of their
potential application, and cost are all issues that effect their current use in
industry. Another concern that has been voiced is the potential for the fibers of
have varying properties from year to year due to climatic changes. These
concerns are all substantial issues that govern the future of biofiber applications.
A brief overview of some articles will be given here to allow the reader some
explanations as to how biofibers will overcome these obstacles.

Mohanty et al.3 investigated biofibers and their make-up. Biofibers are
lignocellulosic materials. Lignocellulose is composed of cellulose, hemicellulose
and lignin. The amount of each constituent varies from plant to plant as well as
with age. The base constituents are the same from plant to plant but the degree
of polymerization in the cellulosic materials varies from one to another. The
degree of polymerization is important as it is directly related to the properties of
the fiber.

A negative issue of working with bio-fibers is that of dealing with their low
degradation temperature. The biofibers begin to degrade at 180°C to 200°C.
Incorporation of natural fiber into polymer matrices is governed by this

temperature limitation. Another concern with bio-fibers is their affinity to water.

25

Io
__
Io

Ioaxo

 

_ .V

 

$3-58 Bones—2

 

 

 

 

 

 

 

 

Figure 2.3 Structure of lignin and cellulose, base materials of natural fibers.

26

There are a lot of different biofibers available in different parts of the world.
The cost versus performance relationship of a fiber is fairly dependent on what
geographic locale and the availability of the said fiber. Each geographic location
tends to produce a dominant biofiber in the region. In temperate areas hemp or
flax fiber are the most readily available materials. In tropical regions, jute,
pineapple leaf fiber or coconut fruit fiber are abundant and have a cost
advantage.

One constant in the synthetic fiber industry is the use of sizing to improve
the interaction of the reinforcing fiber and the polymer matrix. This is one
technique that will have a lot of effect on natural fibers as well. Sizing natural
fibers can be a different endeavor than the sizing of synthetic fibers. When sizing
synthetic fibers there is the addition of functional groups. The sizing of biofiber
can have a lot to do with the removal of naturally existing compounds that
interfere with the bonding of the fiber and matrix

Ray et al.1 investigated the effects of surface treatment on the
performance of natural fiber. Using a 5% NaOH solution to soak the fibers for
four and eight hours respectively for different treatments, the researchers
attempted to modify the surface of the jute fibers. The fibers were then
incorporated into a vinylester thermoset matrix.

The cured samples were tested and the data was analyzed to evaluate the
effectiveness of the modification of the fiber. Three-point bending was done on

the samples to evaluate flex strength and flexural modulus. Mechanical

27

properties improved with larger percentages of fiber in the material, as expected.
Composites with untreated fibers exhibited debonding and some fiber pull-out on
the fracture surface. A four hour alkali surface treatment produced fibers with
better fiber wet-out and better mechanical bonding between fiber and matrix.

Hodzic et aF investigated the potential of flax fiber composites with
polypropylene. Investigation of the use of silane coupling agents on the biofibers
as well as the use of other compatibilizers was explored. The goal of this
exploration was to size the fiber for better adhesion to the polymer matrix. There
is generally a larger variance within the properties of the natural fibers than
synthetic fiber and this increases the difficulty to get standardized material
properties of natural fibers.

The authors most specifically investigated flax fiber composites and used
flax as an exemplar for other fibers. The study concluded that the flax fiber was
useful to reinforce polymers. Silane treated fibers showed the most promise of
the natural fiber with better wet-out than untreated fibers.

Natural fibers are a good reinforcement selection and can be modified to
achieve similar reinforcing properties, compared to their synthetic counter parts.
Fiber treatments are just as easily administered to natural fibers as to
conventional fibers and greatly improve the performance of the fiber. Natural
fibers are a cost effective, lightweight option for reinforcing polymers. The added

environmental benefits are a secondary reason to use them.

28

2.3) Biocomposites

Biocomposites with soy protein have been around for a while, and soy has
also been used as a source for making adhesives. The manufacturing of the
adhesives is dependent upon using sodium hydroxide and the like to denature
and unfold the protein. The adhesive is primarily used for soft fiber board
applications where a strong adhesive bond strength is not needed.

Mo, Sun and Ratto6 use soy protein and wheat straw in an effort to make
biocomposites where soy protein is used as an adhesive to create particleboard.
Protein adhesion is related to dispersion and unfolding of the protein molecule
much like the crosslinking process. The incorporation of chemical and heat
treatments to encourage the unfolding or denaturing of the protein can greatly
effect the interaction of the protein to the wheat straw.

Soy protein isolate was used as the base for the adhesive; the isolate was
modified with sodium hydroxide, urea, and dodecylbenzene sulfonic acid. The
dodecylbenzene sulfonic was used as a promoter to react the urea with the soy
protein. The chemically modified protein was stirred for two hours at room temp
before being mixed with the wheat straw to make the particleboard. The control
adhesive was soy protein isolate and water. The soy adhesives were compared
with conventional synthetic adhesive versions of urea-formaldehyde and phenol

formaldehyde (no values provided).

29

In an effort to change the surface of the wheat straw, the straw was
soaked in a dilute solution of sodium hydroxide, a dilute solution of hydrogen
peroxide and a bleach solution.

The various types of treated straw and chemically altered adhesives were
mixed one to one and then pressed at 140°C. The samples were also
investigated as a function of moisture content; samples were made with 10, 20,
30, and 40 percent moisture to quantify bonding between the adhesive and the
biofiber.

The major bonding interaction between the protein and fiber takes place
between polar groups; on the protein these include the amide, hydroxyl, and
carboxyl. The sodium hydroxide breaks the internal hydrogen bonds of the
protein molecules; thus unfolding the protein molecule and exposing the polar
groups results in an improvement in adhesion. Soy protein was also partly
unfolded by urea and dodecylbenzene sulfonic acid, however the large molecular
size of the protein could have prohibited the protein from interacting with the
straw surface. Stearic hindrance is a concern with large molecules like the
proteins and interferes with potential reactions.

Soy protein molecules are very large structures, and although there is a lot
known about how they react to heat and chemical modification, there is still a lot
of supposition as to how they interact with one another and substrates.
Specifically, why is it that the mechanical strength is better with increased
moisture content as a result of one chemical modification but lower with the same

moisture content and another chemical treatment. It would seem that the

30

moisture would interfere with the protein straw interaction and the end result
would be poor material procurement.

Mo, Sun and Ratto make several conclusions. The adhesive bonds better
with the wheat straw after bleaching; the bleaching removed wax and oils on the
surface of the fiber. The best tensile and compression strength values were
obtained with 40% moisture and soy adhesive and with 10% moisture using a
methylene diphenyl diisocyanate adhesive. Moisture and an isocyanate react to
form C02, which basically decomposes the isocyanate, making moisture an
adversary to processing. Particleboard tensile or compressive strength data
reported in this study does not exceed 3000kPa for any material.

Kuo et al.5 outline some previous work done in an attempt to create
fiberboard with non-wood agricultural reinforcements and focus on the use of
corn stalk for reinforcement. It has received some attention in the past but also
has been abandoned due to the high cost of processing compared to that of
wood fiber. With the decrease in supply of wood fiber alternative reinforcements
are being sought out from agricultural residue.

This study compares various reinforcements bonded with soy adhesive
and a synthetic adhesive. Reinforcements that are investigated are switch grass,
cornstalk and wood fiber. The study also investigated the feasibility of using a
soy-based adhesive versus the use of a synthetic adhesive.

The evaluation of the reinforcement led to the finding that wood fiber
produced the best overall material, cornstalk was better than switch grass but not

as good as the wood fiber for overall material performance.

31

The adhesives that were examined were a phenol-formaldehyde, a urea-
formaldehyde and a soy protein based adhesive. The phenol and urea
formaldehydes performed better than the soy adhesive, material properties as
well as manufacturing of the fiberboards were both issues where the soy
adhesive was inferior. Another issue of the soy adhesives was that the end
product was subject to moisture absorption. However a blend of the synthetic
adhesive and the soy adhesive was able to produce a suitable binder with
intermediate properties in processing and material performance.

From the information gathered in these articles there are several points to
be commented on. Soy protein is temperature sensitive and cannot be
processed at high temperatures. 150°C is a high-end limit on process
temperatures. The proteins have and can be polymerized but the use of a
plasticizer is needed to get a material that is useable. Natural fiber is an effective
reinforcement but the use of surface treatment improves the interaction between
the fiber and the polymer matrix.

Moisture is the Achilles heal of the soy plastic. Exposure to moisture
leads to material property degradation. Biocomposites suffer the same fate as
the moisture destroys the fiber matrix interface and the material properties

decrease drastically.

32

Chapter 3
Experimental procedure
3.1) Extrusion of soy concentrate plastics

Materials used to compound the original soy polymer were obtained from
different sources. The soy concentrate was obtained from Archer Daniels
Midland (ADM), Decatur Illinois. Midwest grain products, Atchison, Kansas,
supplied the wheat starch, Midsole 50. Glycerol supplied by J.T. Baker
Phillipsburg, New Jersey. Sigma-aldrich chemicals of St. Louis, Missouri
supplied maleic anhydride, the compatiblizer and Bis(tert-butyl peroxy)-2,5-
dimethyl hexane, the peroxide initiator. Lastly Bayer Corp supplied the polyester-
amide synthetic biodegradable polymer, Bak4TM.

Soy concentrate, wheat starch and the polyester-amide were dried at
80°C under vacuum for 24 hours before processing. After drying of the materials
the soy concentrate, wheat starch, and glycerol along with maleic anhydride and
initiator were mixed in a kinetic mixer. Dry powder components were added and
mixed for 5 minutes, as the dry powders mixed the liquid components were

added, the glycerol and peroxide initiator. The total batch was then mixed for 30

 

 

 

 

 

 

minutes.
5% maleic anhydride 75 grams
1% luprosal (initiator) 15 grams
47% soy concentrate 705 grams
18.8% wheat starch 282 grams
28.2%jycerol 423 grams
Total 1500 flms

 

 

 

 

Table 3.1 Breakdown of soy polymer components.

33

After mixing, the batch of 1500 grams was hand fed into the extruder, a
ZSK-30 Werner and Pflieder twin-screw extruder. The original soy based
polymer, SCP5 was then pelletized and re-extruded with polyester-amide. After
blending with polyester amide the polymer was deemed SCP6. SCP is an
acronym for Soy Concentrate Plastic. The six indicates which level of revision in

order of experimentation the material was.

Feeder

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

9
9
0
9
© P-2 P-3 P-4
l 7 l W
Extruder Zonel Zone2 Zone3 Zone4 ZoneS ZoneG :|
Drive Motor
A

 

 

 

 

 

 

 

Figure 3.1 Schematic of W&P ZSK twin-screw extruder.
Rpm was a variable in the experiments ran on the soy plastic.
Temperature profiles were held constant. Process temperature profiles are

shown below in table 3.2.

 

 

 

 

 

 

 

 

 

Zone Extrusion 1 Extrusion 2
1 110 130
2 120 130
3 130 130
4 140 130
5 150 130
6 150 130
Die 150 130

 

 

 

 

Table 3.2 Temperature profiles of extrusion runs.

34

The process to achieve a final material for injection molding took two
extrusion runs. The ZSK-30 has six different temperature zones shown in figure
3.1 that are controlled through digital program logic controllers. Zones one

through five all are water-cooled. Zone six is not equipped for cooling and the

die does not have a temperature controller.

 

Figure 3.3 MSU/CMSC extrusion screw configuration.

35

 

 

 

WORLL P998
afimqosrq

Figure 3.4 MSU/CMSC diagram of screw configuration.
The screw configuration has two kneading zones where the majority of the
mixing occurred for the extrudate. Table 3.3 explains how the screw
configuration relates to the extruder barrel and where the majority of mixing

occurred.

 

Table screw
Materials exit the extruder and were too hot to be pelletized directly.

Because of this the compounded material was allowed to air cool for three to five

36

minutes before pelletization. After the material cooled sufficiently it was then
pelletized and injection molded which is explained in section 3.4.
3.2) Extrusion of composite materials

Soy plastic was compounded as explained in section 3.1. The soy plastic
was then extrusion compounded with hemp fiber. The K-Tron K2V-T20 twin
auger feeder was calibrated to 859rams/min. 159rams/min of hemp fiber was
added by hand onto the screws, the fiber was made into 7.59ram fiber balls that

were added to the extruder over a 30 second time period.

® Addition
! Hemp flber Thermoformabl

    

Feeder

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Extruded
Composites
to bdnieciton
P011 1 112 B. P4 mold
111) —
\
Extruder Zone 1i Zone :BZone 3 Zone llZone 5 Zone 6 — 1
Drive Motor J #4

 

 

 

 

 

 

 

Figure 3.5 extruder schematic for addition of fiber to soy plastic.

Hemp fiber was added into port 2, which is a conveying zone of the screw.
Addition of fiber at this point in the extruder allow the fiber and matrix polymer to
be passed through a mixing zone of the screw which provides good mixing of the
fiber and matrix.

The composite extrudate is then pelletized and injection molded.

3.3) Fiber treatment and preparation
Hempline Corporation supplied hemp fiber. Hemp fiber used in this study

was raw and surface treated. Raw fiber was used as received; no treatment was

37

done to the fiber before it was compounded into the plastic. The second form
was alkali treated hemp fiber.

The raw fiber from hemp line was two to four inches in length and 50 to
100 microns in diameter. Before addition to the extruder the fiber was dried
under vacuum at 80°C for at least 12 hours. The natural fibers absorb moisture
and this step ensured removal of all moisture in the fibers before they were
added to the soy plastic.

Alkali treated fiber was soaked in a bath of five weight percent sodium
hydroxide and water for one hour. Sodium hydroxide was dissolved in distilled
water and the hemp fiber was added to the water, in a weight ration of 1:20, i.e.
loograms of fiber for 20009rams or 2000mL of water and sodium hydroxide
solution.

After immersion for one hour the fiber was removed and rinsed with water
several times to remove excess solution. The fiber was checked for Ph and
acetic acid was used as needed to bring the Ph to seven.

At this point the fiber was treated, and neutralized but still saturated with
water. The fiber was placed under a hood for 24hours to dry. After this step the
fiber was placed in a vacuum oven at 80°C for at least 12 hours before addition

to the melt flow in the extruder.

3.4) Injection molding

A Cincinnati Milacron Injection Molder was used to injection mold the soy

plastic and the soy plastic composites. The soy polymer and soy polymer

38

composites are new, novel materials. The parameters for injection molding these

materials were not established prior to molding these materials.

 

Figure 3.6 Schematic of Cincinnati Milacron Injection Molder.

Process development for the new materials was accomplished using
several guidelines. These guidelines were put into place to ensure good part
processing parameters and to protect the injection molder from misuse. The
parameters used to establish the part processes for the soy plastic and the soy
composite materials are outlined below.

An injection molding process has three basic steps to filling the part, fill,

pack and hold.
1) Set transfer point to 0.50 inch and ensure that the transfer from fill to
pack steps occurs due to position, not from time or pressure.

2) Set the shot cushion to 0.25 inch.

39

3) Turn off pack and hold pressures to ensure that the filling of the part
occurs during the fill process of the cycle and not the pack or hold
portions of the cycle. Set the shot size so that during the fill process
the part is filled 75 to 90 percent.
4) Begin with low shot size and fill velocity, 0.8 in and 0.3in/sec.
5) Increase shot size until part is filled 75 to 90 percent, then turn on pack
and hold pressures. Increase pack pressure to fill part remaining 10 to
25 percent.
The soy plastic and soy plastic composites were injection molded at
132°C. The dye temperature was set at 20°C.
3.5) Material property measurement

Material properties were measured through tensile and impact testing.
Fracture surfaces were analyzed with an Environmental Electron Scanning
Spectroscopy referred to as ESEM, and morphology was investigated with

optical microscopy.

4O

(I)
m
o o o
3:: L1near region
CD
to select

modulus from

 

 

strain
Figure 3.7 Schematic stress strain curve.

The injection molded tensile coupons were tested to determine the tensile
strength and tensile modulus as per the ASTM 0638 standard. The testing
system used was a United Testing System SFM-20 loadframe. System control
and data analysis were performed using Datum software. Load was measured
using a 1000 lbs. load cell and the strain was measured using a model
EXT62LOE laser extensometer with a 2-inch gage length. Crosshead speeds of
0.2 and 0.05 inches per minute were used for testing the plastics and the
composites respectively. A preload of 2 lbs was used. Tensile strength was
measured form the peak load and tensile modulus was measured from the slope

of the tangent line to the initial part of the load-displacement curve.

41

For impact testing the injection molded tensile coupons are cut so that the
samples are 2.5”x0.5”x0.125”. 0.1” deep notches were cut into the sample
beams using a TMI notch cutter. Notched Izod impact testing was performed on
a Testing Machines lnc. 43-02-01 Monitor/Impact machine as per the ASTM
0256 standard. A 5 ft-lb pendulum was used to impact the samples

The ESEM used for this work was manufactured by Electroscan
Corporation (model number — 2020). It is equipped with a Lanthium Hexaboride
filament. Water vapor is used as the imaging gas. The samples to be examined
are placed on the sample holder located in the sample chamber. The imaging
pressure (chamber pressure) is set between 2 and 3 Torr. The working distance
between the detector and the sample is set between 8 and 10 mm. The
accelerating voltage is set at 20 W. The sample is focused at different points on
its area and micrograph pictures were taken.

3.6) Data evaluation

Evaluation of the experimental data and comparison to the rule of mixtures
was used to evaluate the effectiveness of the composite. The volume fraction of
fiber content within the composite had to be measured for rule of mixtures
computations. To change the weight fraction to volume fraction the density of
hemp fiber needed to be found.

The density of hemp fiber was obtained using Archimedes method.
Archimedes method uses buoyancy forces of a liquid medium to measure the
volume of an immersed solid. Due to the nature of the hemp fiber, it is hard to

measure its volume in other ways. The fiber was dried under vacuum for 24

42

hours and then small bundles of the fiber were made. The bundles of fiber were
weighed dry, and then weighed when they were immersed in ethanol.

The wet weight was then subtracted from the dry weight, which gave the
weight or mass of the ethanol displaced. This values was then divided by the
density of ethanol, 0.8159/cm3, which gave the volume of the fiber bundle. The
volume of the fiber was then divided the dry weight of the fiber and the density
was obtained.

(dry weight) — (wet weight) = weight of displace ethanol
(weight of displace ethanol) + (density of ethanol) = volume of fiber

(dry weight) + (volume of fiber) = density of fiber

Schematic of immersed fiber

. . iber bundle
Bridge suspending
ethanol above scale

 

 

Ethanol

 

 

 

 

 

 

 

 

 

Scale weigh pad

Figure 3.8 Schematic of apparatus used to weigh immersed hemp fiber.
Figure 3.8 gives a schematic of how the weight of the fiber was obtained

when immersed in ethanol.

43

Chapter 4
Results and Discussion
4.1) Soy concentrate plastics/composites

The previously published extrusion of soy protein was summarized in
chapter 2. In most instances, researchers were either doing small quantities or
examining the physical properties of the specimen. The majority of research
done on polymerizing soy polymers has utilized plasticizers in order to aid in the
processing of the soy polymer. Scientists have approached the issue in different
ways, in some instances the plasticizers are added to the raw materials; in other
instances moisture is used as the plasticizer. The presence of moisture poses a
problem for processing.

Water acts like a plasticizer, and fortunately or unfortunately there is a
certain degree of moisture in the soy protein and wheat starch when received.
Moisture levels in the raw materials are affected by the level of humidity in the
environment, which changes with weather conditions and the laboratory
environment depending on the time of year. Some published reports have
conditioned the raw materials to adjust the level of moisture in the soy protein so
it is constant, while other groups have attempted to dry or remove all the
moisture from the raw materials.

In this project, the latter approach was taken. Experiments were run to
evaluate the effect of initial moisture on material properties of the soy plastic.
Figures 4.1 and 4.2 show the effect of different moisture content on material

behavior and properties. Here there is no baseline data, as the initial moisture

44

content of the samples was not quantifiable. The moisture content increases in

the data from left to right. The important conclusion from this data is that with an

increase in moisture, which acts like a plasticizer, the material properties (both

strength and modulus) decrease, as shown.

 

Strength (MPa)

 

Changes in SCP2 due to moisture content

0.35

 

 

 

from bag to extuder exposed to moisture for 24 10wt% water

- 0.3

 

~ 0.25

2: 3:. c}.
L; L; in
U"
Modulsu (GPa)

T
.0
o
01

 

I
0

hours

 

 

Figure 4.1 Effect of initial moisture content on final material properties.

 

Stress (MPa)

 

Stress strain curves of soy plastic

 

12
10

8

6

”from the bag

4 exposed to

2 -— 10% water added

0

0 0.05 0.1 0.15 0.2

Strain

 

 

Figure 4.2 Change in stress-stain behavior as a function of moisture content.

45

The importance of and the sensitivity to moisture were not realized until
many experiments were conducted which did not produce reproducible results.
Drying of the materials before extrusion, followed by overnight equilibration in the
laboratory before being injection molded did not reduce the variability. Drying the
material before injection molding the material in a forced air desicator also was
not effective. During the course of this study, other interesting phenomena were
observed. It was found that glycerol that was added to the soy protein and
wheat starch as a plasitizer would leach out of the plastic and then condense on
the sides of the desicator during storage. An analysis of the condensate with

FTIR as shown in figure 4.2 identified the glycerol.

 

FTIR of glycerol and residue on desicator

 

2.5

 

— glycerol

2
/ \— residue on desicator
A 1.5
J & <
1

 

 

 

 

 

 

 

 

 

 

 

- - 0.5
I T T Y I I l o
3900 3400 2900 2400 1900 1400 900 400

cm-1

 

 

 

Figure 4.3 FTIR of glycerol and residue on desicator.
As a result several changes were made in the processing. The material
could not be easily and reproducibly dried, nor could it be exposed to moisture.

Water quenching of the polymer melt out of the extruder was not allowed. Drying

46

of any of the extruded materials was discontinued. The extrudate was
immediately injection molded and tested after extrusion to eliminate moisture
absorption into the soy plastic.

Moisture content had to be stabilized. Drying the material before
processing accomplished this goal. The soy concentrate and wheat starch was
dried at 80°C for 24 hours under vacuum to remove all the moisture in the raw
materials. The risk of exposing the proteins to temp of 80°C or higher is that they
begin to denature at temperatures on this order. The denaturing of the proteins
enhances the ability to polymerize the proteins by unfolding of the protein to
expose more functional groups. However, to establish a baseline of processing
and material properties exposure to heat for removal of moisture is also affecting
the structure and property of the protein. Therefore the materials were always
given a 24-hour drying cycle to establish a baseline set of process parameters. It
is important to point out that this step could not only be removing moisture, but

also denaturing the protein, which would improve physio-mechanical properties.

47

 

TGA of soy concentrate plastic

120

 

1004

 

80

 

 

60

 

4O

 

 

weight percent of sample

20

 

 

 

0 1 00 200 300 400 500 600 700
Temperature (Degrees C)

 

 

 

Figure 4.4 TGA of soy concentrate plastic

Drying of the soy concentrate and wheat starch before processing
removed the moisture and provided a stable baseline material but it also
removed some plasticizing agent in the soy polymer, the water. The removal of
the moisture increased the stiffness of the soy concentrate polymer to a point
that it could not be processed at the previous temperature profiles. A TGA
(Thermal Gravimetric Analysis) was conducted on the soy polymer to determine
the onset of degradation. The TGA measures weight as a function of
temperature, as the temperature increases, eventually the components begin to
volatilize, decreasing the original weight of the sample.

The original TGA temperature-processing profile suggested a maximum

processing temperature of 130°C but the TGA profile shown in figure 4.4

demonstrated thermal stability to approximately 180°C. This allowed the

48

extrusion temperature profile to be increased. The profile shown in table 3.1 was

necessary in order to reduce the viscosity to improve the processability.

 

SCP6 baseline data

14.00
12.00
10.00
8.00
6.00

4.00
2.00 7 Strength (MPa)

Strength (MPa)

-o— Modulus

 

0.00
1

 

 

 

Figure 4.5 baseline material properties of the soy concentrate plastic.

Once the baseline set of extrusion parameters was established, a set of
baseline injection molding parameters was also required to be set. All samples
were molded with a melt temperature of 132°C. The injection molder has three
heating zones and a nozzle temperature control. All temperature controls were
set to 132°C. The material was injected into a dogbone cavity mold held at 20°C.
The fill pack and hold pressures for the soy plastic were 1100, 1300, and 900 psi
respectively. Timers for fill, pack, hold and cooling were set for 10, 3, 3, and 55
seconds. Shot size was found to work best at 1.1inches, and the injection speed
was set at 0.3in/sec. This process worked consistently to produce a part without
flash and fully filled. Most importantly the material processed in this manner had

reproducible properties.

49

 

Effect of excessive drying on soy concentrate plastic

Strength (MPa)
-o- Modulus

Strength (MPa)
Modulus (GPa)

 

time dried in hours

 

 

 

Figure 4.6 effect of extended drying on soy plastic material properties.

The denaturing effect of extended time at temperature that would occur to
the soy proteins if they were held at temperature for extended times was
investigated as shown in Figure 4.6. The experiment was to investigate if there
was a need to consistently dry the materials for 24 hours or if it the material was
stable and could be exposed to temperature for indefinite times.

The conclusion from this part of the research was that the soy protein and
wheat starch are not stable at 80°C under vacuum for an extended period of
time. There is a clear change in material properties with changes in processing.
It was also found that the denaturing of the soy protein aids in the polymerization

as shown by an increase in modulus and strength of the soy plastic.

50

 

Effect of rpm/residence time on soy plastic

Strength (MPa)
Modulus (GPa)

' ‘1-153 Strength (MPa)

-I-~ Modulus (GPa)

 

100rpm 200rpm
Extruder rpm

 

 

 

Figure 4.7 effect of change in rpm

Process changes and stability of the soy protein polymer is one area of
high interest. Extrusion processing of large quantities of material can lead to
small changes from lot to lot. Stability of the soy polymer is of interest in respect
of finding a window of operating parameters where the material properties of the
soy polymer remain constant. Figure 4.7 illustrates what occurs when residence
time is reduced. The soy concentrate plastic was processed at 100 rpm and 200
rpm and each set of processing parameters allowed for the same material
properties. The observation being that the soy plastic could be processed at 100
or 200 rpm and it would not affect the properties of the final material.

After standardized material properties were established the next step was
to experiment with the addition of the natural fiber to the matrix and to determine

the resulting composite material properties.

51

 

 

Soy composite physio-mechanical properties; SCP6

 

25 2.5
22.20
20.53
20 2.0
’6 S
E 15 1.5 a
F 3
'3‘. _
g 10 1.0 '§
5 s
5 Strength 0.5
-o—- Modulus
o 0.0
soy plastic soy plastic with 15wt% soy plastic with 15wt%
raw hemp alkali treated hemp
Material

 

 

Figure 4.8 Effect addition of fiber on soy plastic.

Figure 4.8 illustrates the effect of addition of hemp fiber on the modulus
and strength of the soy plastic. With the addition of 15wt% raw fiber into the soy
plastic, modulus is more than doubled and the strength is almost doubled.

The natural fiber is an effective reinforcement for the soy plastic but alkali
treatment of the fiber improves the strength and modulus over the raw or
untreated fiber. This improvement in modulus with surface modification would
seem to imply that the raw fibers were not distributed well within the soy polymer
matrix and or they were not fully wet-out. The alkali treatment of the hemp fiber
is believed to roughen the surface, remove oils and waxes on the surface
allowing for better interaction of the matrix and reinforcement, improving strength.

The modulus values of a filled polymer system should be constant with constant

52

filler content. The positive influence of surface treatment on the effecting modulus
values would imply poor dispersion of untreated fibers within the matrix.

Addition of the hemp fiber to the soy plastic lead to an increase in the
viscosity of the melt flow which require to modifications of the injection molding
parameters. All samples were still molded with a melt temperature of 132°C. All
of the temperature controls were held at the same temperature of 132°C. The
material was then molded into a dogbone shaped with a mold held at 20°C. The
fill pack and hold pressures for the soy plastic composite were increased to 2000,
2200, and 1200 psi respectively. Timers for fill, pack, hold and cooling were set
for 10, 3, 3, and 45 seconds. The cooling time could be reduced with the
addition of the fiber. Shot size was still held at 1.1 inches, and the injection
speed was set at 0.3in/sec. The modification of the process allowed composite
parts with 15wt% fiber to be molded effectively. This process was used for both
raw and alkali fiber reinforced composites.

Notched IZOD impact testing was done on the plastic and composite
samples. Figure 4.9 displays the results of the effect of the hemp fiber on the
impact properties of the soy plastic composite There was a slight increase in
impact energy when the hemp fiber was surface treated, however, without a
surface treatment, the impact energy of the composite was the same as the soy

plastic.

53

 

 

Impact energy of soy materials

 

 

Energy (J/m)

 

 

 

 

scp6 scp6 15hp raw scp6 15hp akt

materlal

 

 

Figure 4.9 Impact energy of soy plastic and composites.

The experimental data was compared to theoretical data. One of the
methods was to compare the tensile modulus of the composite data with the
values calculated using the rule of mixtures. The rule of mixtures uses volume
fractions to calculate the amount of material interacting within the composite.
The composite manufacturing process outlined in the experimental section was
set up on a weight fraction basis. The conversion of weight fraction to volume
fraction was necessary to obtain the density of the hemp fiber. The density of
hemp was obtained using Archimedes method as described Chapter 3.

The density of hemp was found to be 1.299/cm3. This value was then
used to convert the weight fraction values into volume fraction values. The
15wt% values became twelve volume percent.

The rule of mixtures implies that the composite stiffness is a simple

weighted mean dependent on the volume fraction of the fiber and matrix. So the

54

modulus of the composite is equal to the modulus of the fiber multiplied by fiber
volume fraction plus the modulus of the matrix times the matrix volume fraction.

Ec = VrEr + VmEm
Where:

Ec is the modulus of the composite

E: is the modulus of the fiber

Em is the modulus of the matrix, and

V, is the volume fraction of the fiber, and

VIm is the volume fraction of the polymer matrix.

However, this model is designed for 100% aligned fibers. Extrusion and
injection molding does not allow the fibers to be fully aligned. Some orientation
occurs due to flow of the melt into the part. Because of this, an orientation factor
is added to the rule of mixtures as a correction factor for the alignment of the
fibers. The equation below is what was used for the prediction of the composite
properties.

Ec = cViEi + VmEm

o is the orientation factor. The data in figure 4.10 was compiled with an
orientation of 0.25. The experimental data falls short of the predicted data from
the rule of mixtures. The predicted modulus value is 2.3 GPa, the experimental
data that collected as shown in figure 4.8 shows a modulus value of 1.6 and 1.9

for the different types of hemp fiber.

55

 

Rule of mixtures

 

’6
a.
£2
en
g -e— raw fiber
g —-|- alkali treated fiber
+theoretical rule of
mixtures
0.0 0.1 0.1 0.2 0.2 0.3
Volume fractlon

 

 

 

Figure 4.10 Rule of mixtures for composite properties.
Discrepancies between data and predicted values can be explained from
microscopy images of fracture surfaces and internal morphology of the
composite samples. Lack of good adhesion or poor fiber orientation also could

change the predicted values of the composite.

eeeeeeeeeeeeeeeeeeeeeeee

 

fly“; %

 

 

 

 

i, Fracture
initiation site

 

Figure 4.11 Illustration of fracture of soy plastic tensile coupon.

56

Brittle Ductile area
cleaved area

\

 

 

 

 

Fracture
initiation site
Figure 4.12 End view, schematic of fractured tensile coupon.

 

Figure 41 SEM of dctlle fracutre Initiation srte of soy plastic; 100x.

Fracture surfaces of the plastic or composite can explain a lot about a
material. The soy plastic for instance, has a fairly unique fracture mechanism.
The soy matrix has a ductile initiation site as illustrated in figures 4.11 and 4.12.
Micrographs of this fracture area are shown in figures 4.13 and 4.15. The soy
plastic fracture initiation is a slow ductile tearing of the material, however as the

crack progress, the load bearing cross-section of the material decreases and the

57

velocity of the crack propagation increases. The increase in crack speed leads
to a change in mode of failure. The failure surface changes from a ductile failure
to a brittle cleaved fracture surface; this is illustrated schematically in figure 4.12.

The actual failure surface is shown in figures 4.14 and 4.16.

 

Figure 4.15 1000x ductile initiation fracture area of tensile failed specimen.

58

 

Figure 4.16 1000x brittle fracture area of tensile failed specimen.

With addition of fiber to the soy plastic, elongation to failure drastically
decreases. In the soy plastic matrix, elongation to failure was in the five to ten
percent range. This is limited in composite materials by the elongation of the
fiber. In general the natural fibers will not elongate more than a percent or two.
If the sample is elongated further than a percent or two the fiber begins to
debond from the matrix. When this occurs it leads to void creation and
catastrophic failure of the composite.

Composite fracture surface gives information about the adhesion between
the matrix and the fiber, as well as information about fiber dispersion within the
matrix. If there is poor wet-out of the fiber or clumping of fibers so that they are
not fully distributed within the matrix there is usually evidence of this in the
fracture surfaces of the composites. Fiber length in the fracture surface is also a

useful piece of information taken from fracture surfaces. Long fiber pull-out

59

indicates poor adhesion between the fiber and matrix and can explain poor
material performance of the material. The micrographs of the composite failure
surfaces in figures 4.17 - 4.20 focus on the fibers. From these micrographs one
can see shorter fiber pull-out in the alkali treated fibers vs. the raw fiber

composite samples.

 

Figure 4.17 15wt% AlkalI treated hemp In SCPSITTBI'ISIIG farlure surface, 400x
The shorter fiber lengths in the fracture surfaces are indicative of better
adhesion and hence the better strength values for the alkali treated fiber

composites.

60

 

 

 

4.19 15wt% raw hemp in SCP6, tensile failure surface, 1000x.

61

 

 

4.20 15wt% raw hemp in SCP6, tensile failure surface, 300x.

From the material properties of the alkali treated samples and the fracture
surfaces of the failed composites it is clear that the alkali treatment of the fiber
improves the properties of the composite. What exactly happens in the alkali
treatment process to the fiber? There are a couple things that happen to the
fiber. As illustrated in figure 4.21, the surface oils and waxes are washed away
from the surface of the fiber. The long cellulose chains within the fiber are also
broken up. These two processes allow for the fiber to have more bonding sites
available to the polymer, for chemical interaction. The washing away of the oils
and waxes also roughens up the surface, which allows for better mechanical
interlocking of the fiber and matrix. The alkali treatment enhances the chemical

and physical interactions.

62

Surface oils
Cellulose

 

Alkali flaw/vixen.»
=>
Wash (“J M

 

 

 

 

 

Li gnin

Figure 4.21 Schematic of alkali treatment of natural fiber.

    

m-
Figure 4.22 1000x raw hemp fiber.
Figure 4.22 shows a raw hemp fiber. In comparison to figure 4.23 in

which the fiber has been alkali treated. The physical changes are not overtly

63

significant, yet still effective for improvement in performances. One can see the
more exposed fibrils in the alkali treated fiber. In comparison to the alkali fiber,

the raw hemp fiber shows a smoother surface.

 

Figure 4.23 1000x alkali treated emp fiber.

One major unresolved issue of plant-based materials is their affinity to
moisture and the drastic effects moisture has on material properties of the plastic
or composite. The composite samples were compounded and were placed on a
desk in an air-conditioned office for 30 days, approximately one month, then re-
tested. Comparison between material properties of the aged samples and the
samples tested after compounding is shown in figures 4.24 through 4.27. After
exposure to an office environment for thirty days the modulus of the raw fiber
composite dropped by thirty one percent, the alkali treated fiber composite
modulus dropped by twenty two percent. These are drastic reductions in the

material properties that would effect applications of the material.

64

 

 

Effect of ging on soy plastic composites made of
15wt% akali treated hemp in SCP6
25 2.0
1.8
A 20 1.6 A
5 1.4 a
E 15 1.2 9.
E 1.0 3
g1 10 0.8 E
$ 5 . Strength (MPa) 3': :
-I-Modulus (GPa) 0:2
0 0.0
tested after molding Aged 30 days

 

 

 

Figure 4.24 Effect of moisture on soy plastic with 15% raw hemp.

 

Comparison of stress strain curves of 15wt%
alkali treated hemp fiber in soy plasltc

 

N
U!

 

N
O

 

.4
U1

   

 

 

Stress (MPa)
8

------------------- composite tested after fabrication

 

 

 

 

5 ' —composite aged 30 days
0 l T I
0 0.005 0.01 0.015 0.02
Strain

 

 

 

Figure 4.25 Change in stress-strain behavior of alkali fiber composite with aging

65

 

Effect of aging on soy plastic composites made of
15wt% raw hemp In SCP6

2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6 s
Strength (MPa) o_4

+Modulus 0.2

0.0

odulus (GPa)

Strength (MPa)

 

tested after molding Aged 30 days

 

 

 

Figure 4.26 Effect of moisture on soy plastic with 15% raw hemp.

 

Comparison of stress strain curves of 15wt% raw
fiber composite

 

25

 

N
O
1

Stess (MPa)
ES 5:

 

 

 

 

 

 

 

5 ~ — composite teste 30days after fabrication
tested directly after fabrication
O I I I
0 0.005 0.01 0.015 0.02 0.025
Strain

 

 

 

Figure 4.27 Change in stress-strain behavior of raw fiber composite with aging.

66

What occurs within the material is shown in the below micrographs of the

composite sample tensile fracture surfaces in figures 4.28 — 4.31.

 

days after composition, 300x.

 

Figure 4.29 Tensile fracture surface of 15wt% raw fiber in soy plastic, tested 30

days after composition, 1000x.

67

 
 

- .w-mmam .
Figure 4.30 Tensile fracture surface of 15wt% alkali treated fiber in soy plastic,

tested 30 days after composition, 300x.

Figure 4.31 Tesenrlfracture surface of 15wt% alkaltrt fiber in soy plastic,

tested 30 days after composition, 1000x.

68

Fiber pull-out lengths in figures 4.28 — 4.31 are much larger than pull-out
lengths in figures 4.17 - 4.20. Fiber pullout length is related to the adhesion of
the fiber to the matrix. Longer fibers in the fracture surface, relates to a poorer
bond between the fiber and matrix. With exposure to moisture of the soy plastic,
the soy plastic and fiber debond. This leads to the fiber and matrix, not working
as a one material but two separate materials. When the sample is then tested
the modulus decreases because of slippage between the fiber and matrix. This
is evident in figures 4.24 - 4.26 and the micrographs relate well with this trend in
properties.

These micrographs show how the material internal morphology relates to
its material properties, the fracture surfaces of the composites tested after
fabrication indicate that there is good wet-out of the fiber, within the polymer
matrix.

The predicted material properties from the rule of mixtures does not
compare well with the actual data collected from the samples. This has to come
down to fiber orientation within the matrix.

Figure 4.32 is a schematic of how the composite melt flow fills the mold
during the injection molding of the dog-bone samples. The melt flow advances
and fills the cavity; as this happens the layer near the surface begins solidify.
This forms a skin layer of the sample where the fiber is highly ordered in the flow
direction, and in the case of the dog-bone, in the direction of applied load.
However further into the bulk of the material the fiber is less aligned and more

random, this is illustrated in figures 4.33 and 4.34.

69

 

Solidified material

F' er orientation

 

 

Mold Melt flow Advancing flow
front

Figure 4.32 Schematic of melt flow filling part cavity?0

 

Figure 4.33 n example of a glass filled polypropylene injection-molded part,

longitudinal cross-section”.

70

, V. A .
“ONO. u

s A .
ouwufis»
s. f... “131.»
v

.. 1., x.
$3.

m ,o'
rMszW'

,4

u...
m
we

3. ~

.u‘. o
,3 . m?
.. «6..

 

molded part,

ion

t

jec

in

lled polypropylene

Figure 4.34 An example of a glassf

20

IO"

sect

transverse CI'OSS-

 

4.35 Surface of bone sample scp6 with 15wt°/ ravvhepm fibre 100x, some

black.

In

fibers highlighted

71

Figures 4.32 - 4.34 show how the fiber is orientated during the injection
molding process, this is evident in the soy composites as well, shown in figure
4.35 the fiber aligned in the direction of the flow. This occurs on the surface; in

the bulk the fibers become less orientated as shown in figure 4.36.

  
  

‘ s":

Figure 4.36 optical microgrph f fibers in bulk of a injection molded dog bone

 

15wt% raw hemp fiber 100x, some fibers highlighted in black, longitudinal cross-
section.

Figures 4.35 and 4.36 illustrate what is shown schematically in 4.32.
Fibers within the bulk of the sample are not orientated with the direction of flow
and hence not the direction of loading when the sample tested under tensile
loading. This is primary reason that the material properties do not come close to
the predicted rule of mixture values. Rule of mixture values were computed with

an orientation factor of 0.25, implying that 25% of the fibers are aligned in the

direction of load.

72

 

 

 

 

 

 

 

 

 

 

 

 

 

Break down of soy plastic and soy plastic composites, on
weight basis (grams)
scp6 scp6 with 15% fiber

[maleic anhydride 50 42.5
[luprosal (initiator) 10 8.5

Isoy concentrate 470 399.5
Iwheat starch 188 1 59.8
[glycerol 282 239.7
BAk4 500 425
IFiber 225
ITotal weight per batch 1500 1500
[Percentage ag-based 43.8% afiased 52.2% ag-based

 

 

 

Table 4.1 Breakdown of plastic and composite components.

The final comment on the soy plastic hemp fiber composite is to outline
the percentage of the plant-based products that are in the final products. In the
samples compounded and tested the bio-based components were; soy
concentrate, wheat starch and hemp fiber. The break down of the materials that
compose the soy plastic and the composite is outlined in Table 4.1. The plastic

itself is 43.8wt°/o bio-based and the composite is 52.2wt°/o bio-based.

73

Chapter 5
Conclusions
5.1 ) Conclusions

From the data presented there are several points and conclusions that can
be made:

o Moisture acts like a plasticizer in the raw materials and softens the

material.

One of the major issues in establishing baseline material parameters of
the plastic was removal of moisture. Due to the varying degree of moisture in the
environment there was a varying degree of moisture in the raw materials and
hence a varying amount of plasticizer in the final product. This lead to material
property values that were inconsistent.

. Drying the material under vacuum and heat removes moisture but also

denatures the protein, which increases the modulus.

The soy protein is not thermally stable at 80°C. To ensure removal of all
moisture within the raw materials the soy concentrate has to be held at
temperature for an extended period, which leads to the proteins denaturing. The
final material properties are enhanced due to the protein unfolding that takes
place as a result of the denatuization process. Resulting in exposing more
reaction sites on the protein and therefore improved cross-link density.

. Removal of moisture increases difficulty of processing.

74

 

Removal of excess moisture has the same effect of adding less plasticizer
and increases the viscosity of the melt flow. This leads to a need for higher
processing temperatures.

. Addition of biofiber improves strength and modulus

The hemp fiber has a modulus of SSGPa. The incorporation of this into a low
modulus matrix leads to an overall improvement in modulus. The hemp fiber
also has a higher tensile strength than the soy plastic, which leads to an
improvement in tensile strength as well.

. Surface treatment of the natural fiber improves fiber matrix bonding and

overall strength of the composite, tensile and impact.

The alkali treatment of the hemp fiber improves fiber surface roughness as
well as removes oils and waxes that interfere with bonding of the matrix and
reinforcement. The rougher surface and better bonding sites allows the polymer
and fiber to have a stronger bond and improved material properties.

. The soy plastic failure in tensile loading is a dual mechanism; a ductile

initiation site and brittle crack propagation.

The soy plastic elongates slowly and eventually a site of crack initiation is
formed. When this occurs the crack slowly begins to grow until it reaches a
critical size. When this occurs the material fails catastrophically and the crack
growth velocity increases and the material changes failure modes to a brittle or
cleavage failure.

. The alkali treated fiber performs better than the raw fiber.

75

 

From the data it is observed that the alkali treatment not only improves the
strength and modulus but also has shorter fiber pullout lengths, which would
imply better adhesion. The alkali fiber composite materials also perform better
after aging and exposure to moisture. The samples retain more of their strength
and stiffness.

. Fiber orientation in the injection-molded samples is not homogenous
through the thickness of the coupon and not aligned with the axis of
loading.

The injection molding process allows fibers to randomly orientate themselves
with in the bulk of the material. As shown in the micrographs the fiber with in the
bulk is not orientated to the axis of loading.

. The bio-based composites achieve the properties of polyethylene.

Table 4.1 shows the breakdown of the martial components that make up the
soy plastic and composites and shown the overall composite is more than 50%
ag-based. The strength and modulus of PE was achieved. PE has modulus
values in the range of 0.7 — 1.4 GPa, and strength values of 18 - 35 MPa.

. Material properties of the biocomposites are comparable to glass

reinforced petroleum based polymers.

76

Chapter 6
Research Recommendations
6.1) Recommendations

As a result of this study, it has been shown that soy protein based plastics
reinforced with biofibers can possess significant structural properties, i.e.
modulus, strength and strain, to be considered for structural applications and as
an alternative to petroleum based materials. However there are significant
challenges that remain to be addressed before these biocomposites can be used
in a real-world application.

The largest challenge is to improve the hydrothermal stability of the soy
plastic. Moisture absorption in unmodified soy plastic is large and has a serious
effect on mechanical properties. Long-term applications will depend on the
ability to produce a material that is not easily affected by exposure to moisture
and temperature extremes.

Another challenge is to improve the properties of the soy matrix to
produce a polymer with a higher degree of cross-linking and hence higher
stiffness. Reacting more functional groups on the protein could do this,
specifically hydroxyl groups. Reaction of these groups could also lessen the
effect of moisture absorption. This might be accomplished with additional
denaturing of the protein over what was done in the current process before or
during extrusion with the addition of sodium hydroxide or urea, either as an

additive to the extruder or used as a chemical treatment before processing.

77

Alternatively, this could be accomplished with a more aggressive heat treatment
while drying the material.

The blending of the soy protein polymer with the polyester-amide has
been shown to improve the processing and mechanical properties of the end
material. Another avenue of interest would be to blend the soy protein and
starch directly with the polyester-amide and maleic anhydride. This could
eliminate the usage of glycerol, and eliminate the problem of the leaching of the
glycerol. This change in processing could also increase the percentage of
biobased components in the end product. As a result, the final product could
have improved material properties, reduced moisture absorption, and a larger
fraction of biobased materials. This could improve material performance to have
an extended life expectancy and open the door to applications that require a
more durable material that is environmentally stable such as structural materials

for housing or transportation applications.

78

BIBLIOGRAPHY

1) Dipa Ray, B.K. Sarkar, S. Das, A.K. Rana (2002). Dypamic mechanical and

thermal analysis of vinylester-resin-matrix composites reinforced with untreated
and alkali-treated jute fibers. Composites science and technology: 62, 911- 917

2) A. Hodzic, R. A. Shanks and M. Leorke (2002). Polypropylene and aliphatic

polyester flax fibre composites. Polymers & Polymer composites: 10(4), 281 —
290 (2002)

3) AK. Mohanty, M. Misra, G. Hinrichsen (2000). BiofibresI biodegradable

polymers and biocomposties: An overview Macromolecular Materials &
Engineering 276/277, 1-24

4) http://class.fst.ohio-state.edu/FST822/lectures/Soy.htm (2001)

5) Monlin Kuo, Daniel Adams, Deland Myers, Daniel Curry, Howard Heemstra,

John L. Smith, Yilin Bian (1998), Progrties of wood/agricultural fiberboard
bonded with somean-based adhesive Forest products journal: 48(2), 71 - 75

6) Xiaoqun Mo, Jie Hu, X Susan Sun, Jo A. Ratto (2001) Compression and

tensile strength of low-density straw-protein particleboard, Kansas State
University, Industrial Crops and Products: 14(1), 1-9

7) HO. Huang, E.G. Hammond, C.A. Reitmeier, and DJ. Meyers (1995)

Properties of fibers produced from soy protein isolate by extrusion and wet-
spinning Journal of American oil and chemists society: 72(12), 1452 - 1460

8) Delia A. Sorgentini, Jorge R. Wagner, And Maria Cristina Anon (1995)

Effects of thermal treatment of soy protein isolate on the characteristics and

structure - function relationship of soluble and insoluble fractions Journal of
Agricultural food chemicals

9) P. Cunningham, A.A. Ogale, P.L. Dawson, and JD. Acton (2000)

Tensile Progrties of Soy Protein Isolate Films produced by a thermal
compaction technigue. Journal of Food Science: 65 (4)

10) Q. Lei and W.L. Boatright (2001 ), Compounds Contributing to the odor of

agueous slurries of soy protein concentrate. Journal of Food Science: 66(9),
1306 - 1310

79

11) C. M. Vax, j.F. Mano, M. Fossen, R. F. van Tull, L. A. de Graaf, R. L. Reis,

and A. M. Cunha (2002) Mechanical, dynamic-mechanical, and thermal

properties of soy protein-based thermoplastics with potential biomedical
applications Journal of macromolecular science: 41(1), 33-46

12) J.U. Otaigbe, H. Goel, T. Babcock, J Jane (1999) Processability and

properties of biodegradable plastics made from agricultural biopolymers Journal
of Elastomers and Plastics. 31, 56-71

13) Sue HJ, Wang S, Jane JL (1997) Morphology and mechanical behavior of
engineering soy plastics. Polymer: 38(20), 5035 — 5040

14) Qiagxian Wu and Lina Zhang (2000) Properties and structure of soy protein

isolate — ethylene glycol sheets obtained by compression molding. lndustrual
engineering chemical res.: 40, 1879 —1883

15) Xiaoqun Mo, Xiuzhi Sun (2002) Plasticization of soy protein polymer by
polyol-based plasticizers. Journal of the American Oil Chemists' Society: 79(2)

16) CH Schiling, T. Babcock, S. Wang, and J. Jane, (1995) Mechanical

properties of biodegradable soy-protein plastics. Journal of Material Research:
10(9), 2197 — 2202

17) Jacob John and Mrinal Bhattacharya (1999) Properties of reactively blended
soy protein and modified polyesters. Polymer International: 48, 1165-1172

18) Perminus M. Mungara, Tao Chang, Jie Zhu and Jay-lin Jane (2000)
Processing and physical properties of soy protein/biodegradable synthetic
polymer blends Polymeric Materials: Science& Engineering: 86,364-365

19) AA. Ogale, P. Cunningham, P.L. Dawson and J.C. Acton (2000)
ViscoelasticI thermal, and microstructural characterization of Soy Protein Isolate
Films. Journal of food science: 65(4), 2000

20) D. Hull and T. W. Clyne second edition; An introduction to composite
materials, pages 279-280

21) Otaigbe JU and JaneJ, (1997) Environmental Polymer Degradation: 5(75)

80

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

lllll'lllllllllllljjljllllljllllllljlll‘l