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This is to certify that the

thesis entitled

KENAF - REINFORCED POLYPROPYLENE
COMPOSITES

presented by

Rajeev Karnani
has been accepted towards fulfillment

of the requirements for

M.S . degree in Chemical Engineering

(M w

Major professor

 

8/6/‘74

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

 

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Michigan State
University

 

 

 

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TO AVOID FINES mum on or before date duo.

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MSU loAnAfflrmuivo Action/Equal Opportunity lmtltuion
Wm:

KENAF - REINFORCED POLYPROPYLENE COMPOSITES
By

Rajeev Karnani

A THESIS

Submitted to
Michigan State University
in partial fiJlfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Chemical Engineering

1996

ABSTRACT

KENAF-REINFORCED POLYPROPYLENE COMPOSITES
By

Rajeev Karnani

Natural fibers have an outstanding potential as a reinforcement in thermoplastics. This
study deals with the preparation of kenaf reinforced polypropylene composites by reactive
extrusion processing in which good interfacial adhesion is generated by a combination of
fiber modification and matrix modification methods. PP matrix was modified by reacting
with maleic anhydride and subsequently bonded to the surface of the modifiied
lignocellulosic component. The fiber surface was modified by reacting it with a silane in a
simple and quick aqueous reaction system, similar to that employed for glass fibers. The
modified fibers are then extruded with the modified polymer matrix to form the
compatibilized composite. The various reactions between the kenaf fiber and maleated
polypropylene (MAPP) chains, is expected to improve the interfacial adhesion significantly
as opposed to simple mixing of the two components, since new covalent bonds between the
fiber surface and matrix are created in the former case. Typical mechanical tests on
strength, toughness and Izod impact energy were performed and the results are reported.
These findings are discussed in view of the improved adhesion resulting fi'om reactions

and/or enhanced polar interactions at phase boundaries.

TABLE OF CONTENTS

List of Tables
List of Figures
Chapter 1 Introduction

1.1 Objective
1.2 Structure of the Thesis

Chapter 2 Background

2.1 Polymeric Composites

2.2 Fiber Reinforced Thermoplastics

2.3 Mechanics

2.4 Fiber - Matrix Adhesion

2.5 Natural - Fiber Reinforced Thermoplastics
2.5.1 Causes of Poor Interfacial Adhesion
2.5.2 Improving Interfacial Adhesion

Chapter 3 Constituent Materials

3.1 Natural Fibers
3.1.1 Kenaf
3.2 Matrix
3.2.1 Polypropylene
3.2.2 Power-Law Model
3.3 Coupling Agents
3.3.1 Silane Coupling Agents

Chapter 4 Composites Processing

4.1 Extrusion
4.1.1 Setup
4.2 Injection Molding
4.2.1 Setup
4.3 Optimization
4.3.1 Extrusion - Process Parameters
4.3.2 Injection Molding - Process Parameters
4.4 Experimental Procedure

Page

iv

\O\1\IO\UIUI MN

H—l
NH

16

16
18
20
20
23
24
24

27

27
28
3O
31
32
33
34
36

Chapter 5 Experimental Characterization

5.1 Mechanical Characterization
5.1.1 Tensile and F lexural Tests
5.1.2 Impact Tests

5.2 Differential Scanning Calorimetry
5.2.1 Modulated DSC

5.3 Thermogravimetric Analysis

5.4 Scanning Electron Microscopy

5.5 Melt Flow Index

Chapter 6 Mechanical Properties of Kenaf Reinforced Polypropylene
Composites

6.1 Selection of Fiber Length

6.2 Experimental Approach

6.3 Results and Discussion
6.3.1 Tensile Properties
6.3.2 Halpin-Tsai Prediction of Modulus
6.3.3 Flexural Properties _
6.3.4 Impact Strengths and Toughness
6.3.5 SEM Analysis

6.4 Effect of Silane Coupling Agent

Chapter 7 Maleation of Polypropylene

7.1 Use of Maleated Polypropylene as a Compatibilizer
7.2 Experimental Approach
7.2.1 Functionalization of Polypropylene
7.2.2 Reaction Mechanism
7.2.3 Determination of MA grafted by titration
7.2.4 Determination of MA grafted by FT-IR
7.3 Study of Rheological Behavior
7.4 Melt Flow Index

Chapter 8 Conclusions & Recommendations

8.1 Conclusions
8.1.1 Development of Kenaf - PP Composites
8.1.2 Improvement in Mechanical Properties
8.1.3 Comparison with other PP Composites
8.1.4 Applications

8.2 Recommendations

Bibliography

38

38
38
4o
41
42
43
44
44

46

46
47
48
48
52
53
54
56
58

59

59
6O
6O
6O
62

66
68

69

69
69
70
71
73
74

76

Table 3.1

Table 3.2

Table 3.3

Table 3.4

Table 4.1

Table 4.2

Table 4.3

Table 4.4

Table 5.1

Table 5.2

Table 6.1

Table 6.2

Table 6.3

Table 6.4

Table 7.1

Table 8.1

LIST OF TABLES

Chemical Composition of some Natural Fibers

Mechanical Properties of some Natural Fibers

Comparison of Kenaf with other synthetic fibers

Characteristics of PROFAX 6501

Characteristics of WP-ZSK 30 Twin Screw Extruder

Operating conditions for preparation of Kenaf - PP composites
Operating conditions for injection molding

Elements of Composite Processing - Performance Relationships
Test conditions for Tensile and Flexural Tests

Test conditions for Izod Impact Tests

Tensile test results for kenaf - PP composites

Flexural test results for kenaf - PP composites

Impact strengths and Toughness for kenaf - PP composites
Mechanical properties for silylated kenaf - PP composites
Titration and IR results for maleated PP blends

Characteristics of some PP composites

Page

17
18
17
23
29
29
32
33
4o

41
49
53
55
58
63

72

Figure 2.1

Figure 3.1
Figure 3.2
Figure 3.3
Figure 4.1
Figure 4.2
Figure 4.3
Figure 4.4
Figure 4.5
Figure 4.6
Figure 4.7
Figure 4.8
Figure 6.1
Figure 6.2
Figure 6.3
Figure 6.4
Figure 6.5

Figure 6.6

LIST OF FIGURES

Fiber Modification Reactions

SEM image of kenaf bast fiber cross-section

Plot of log 17 vs log 7 to determine power law parameters
Reaction steps in the silane grafting of biofibers

Screw configuration, pressure and fill factor profile along the screw
Schematic representation of a injection molding cycle

Schematic diagram of a reciprocating injection molding machine
The effect of mixing length on fiber length

The effect of mixing length on product strength

The relationship between screw speed and fiber length

The relationship between screw speed and product strength
Typical fill pressure - fill time relationship

Tensile Stress vs Strain curves for kenaf - PP composites
Tensile Modulus for kenaf - PP composites

Tensile Strength for kenaf - PP composites

Elongation to break for kenaf - PP composites

Flexural Modulus for kenaf - PP composites

Notched Izod Impact strength for kenaf - PP composites

vi

Page

12

19
24
25
29
31
31
34
34

34

36
49
so
51
51
54

55

Figure 6.7 Toughness (area under stress-strain curve) for kenaf - PP composites 56

Figure 6.8 SEM of the fracture surface (notched Izod test) of kenaf (20%) - PP

without MAPP 57
Figure 6.9 SEM of the fracture surface (notched Izod test) of kenaf (20%) - PP

with MAPP 57
Figure 7.1 FT-IR spectra of MAPP with 0% 1%, 2%, and 3% MA in PP 65
Figure 7.2 Calibration curve for determining the incorporated MA content

from the F T-IR spectrum 66
Figure 7.3 Complex viscosity vs. frequency of neat PP and MAPP with

varying MA content 67
Figure 7.4 Modified Cole-Cole (mCC) plots of neat PP and MAPP with

varying MA content 68
Figure 8.1 Flexural Modulus for some PP composites 72

Figure 8.2 Notched Izod Impact Strength for some PP composites 73

vii

Chapter 1

Introduction

I“

In recent years there has been mounting interest in the use of renewable,
environmentally friendly materials in place of plastics based on non-renewable
petroleum resources. The combined environmental problems of overflowing landfills,
inefficient incineration of traditional fillers, excessive dependence on petrochemical
based plastics, and environmental pollution along with adverse public opinion has
further necessitated an acceleration of effort in this direction. The driving forces behind
the utilization of natural fiber reinforced composites are low cost, biomass utilization,
environmental benefits, and process benefits, all of which are achieved without
compromising performance properties. In this regard, new biobased
reinforcement/ filler materials and matrix resins offer advantages such as good
mechanical properties, biodegradability, recyclability and easy incineration. These
Lmaterials offer a value added outlet to the low cost agricultural products.
(_

The advantages of natural fibers over traditional reinforcing materials such as

glass fibers, talc, and mica are: acceptable specific strength properties, low cost, low

q. M... «no-15”"

 

density, high toughness, good thermal properties, reduced tool wear, reduced dermal

 

and respiratory irritation, ease of separation, enhanced energy recovery, and

biodegradability. It has been demonstrated that wood fiber_ reinforced polypropylene

 

 

99mp0§it98 has 3999195999192 .t9.t!§9.i.t._ippel.. glass fiber- Icinforced polypropylene

2

composites [1]. Lignocellulosic-polymer composites have been recently reviewed by
Rowell, Youngquist, and Narayan [2].
The main bottlenecks in the wide scale use of these fibers in thermoplastics have

been the poor compatibility between the fibers and the W and the inherentmhrgh

“u say-.5“. _ "cw-“Mm”

 

(moistureusgrptjgn, causin dimensional changes in the lignocellulosic based fibers. The

 

efficiency of a fiber reinforced composite depends a great deal on the fiber-matrix
interface and the ability to transfer stress from the matrix to the fiber. This stress
transfer efficiency plays a dominant role in determining the mechanical properties of the
composite and also in the material’s ability to withstand environmentally severe
conditions. Additionally, it is important to maintain a good stiffness to impact strength

balance, in order to expand the applicability of these natural fiber-reinforced

I composites.

1.1 Objective

Y”This work is a part of ongoing intensive research aimed at developing new
natural fiber reinforced thermoplastic composites. The bast Mfg PEELEE‘IEQJEEPEE
(kc naf), anannualhrbrsgufisfiber: plant, was used as the reinforcement. The goal was to
develop kenaf fiber reinforced polypropylene composites with properties tailored to suit
applications where it could be a potential low-cost substitute to the expensive glass-
reinforeed composites. It was also necessary to understand and optimize the processing
parameters, composition and interfacial adhesion in order to improve the mechanical

Igoperties of the composites.

1 .2 Structure of the Thesis

The following paragraphs give a brief outline of the contents in each chapter of
this thesis :

Chapter 2 provides a simple background on polymer composites especially
short-fiber reinforced thermoplastics, their mechanics and role of interfacial adhesion in
influencing their mechanical properties. The chapter also deals with natural fiber
reinforced thermoplastics and their advantages and disadvantages over the conventional
composites. This is followed by a discussion on the causes of poor fiber-matrix
adhesion in such systems, and the methods and approach adopted by some researchers
to overcome this problem.

Chapter 3 provides information on the constituent materials. Some natural
fibers, their composition and properties in comparison to kenaf fiber are discussed. It
also includes a description on polypropylene, its characteristics, and experimental
evaluation of its Power Law parameters. This is followed by a short introduction to
silane coupling agents, their chemistry and role in improving the fiber-matrix adhesion.

Chapter 4 describes the method of preparing the composites by extrusion and
further processing by injection molding. The setup and operating conditions of both the
equipment are discussed in detail. Since processing is a major factor influencing the
mechanical properties of the composites, an understanding of the processing variables
and their optimization is the focus of this chapter.

Chapter 5 discusses in detail the methods and instruments used in the

characterization of the composites. It deals with tensile, flexural and impact tests for

4

mechanical characterization; differential scanning calorimetry and thermogravirnetric
analysis for thermal characterization; and scanning electron rrricroscopy for morphology
study.

Chapter 6 contains data, results and discussion on the characteristics of the
various kenaf reinforced polypropylene composites. The experimental approach and the
rationale are clearly stated in this chapter. An effort has been made to explain the
differences in the mechanical properties of the coupled and uncoupled composites.

Chapter 7 covers the maleation study on polypropylene. The role of maleated
polypropylene (MAPP) in improving the mechanical properties of the composites is
explained. For better understanding of the maleation chemistry, experimental study was
conducted in which the degree of maleic anhydride (MA) grafted onto polypropylene
(PP) was varied by controlling the feed ratio of MA to the initiator. The amount of MA
incorporated was determined by both titration and FT-IR spectroscopy. An attempt is
made to correlate the rheological behavior (studied on rheometrics mechanical
spectrometer) of maleated polypropylenes with their different degree of MA grafiing.

Chapter 8 presents the conclusions from the thesis and some recommendations for

future work.

Chapter 2

Background

2.1 Polymeric Composites

Composite materials can be defined as a system consisting of two or more
physically distinct and mechanically separable materials, which can be mixed in a
controlled manner to have a dispersion of one material in another to achieve optimum
properties. The properties are superior and unique in some respects to the properties of
individual components [3]. Composites in structural applications can be classified under
one of the following: ceramics, metals and alloys and polymeric composites. One or more
of these materials can be used to make various kinds of composites.

The discussion in this work will be restricted to polymeric composites only. The
polymeric composites can be subdivided into the following categories: fibrous
composites (consisting of fibers embedded in polymer matrix), laminated composites
(consisting of fibrous composites in one or more than one different planes of orientation),
particulate composites (consisting of particles of reinforcing medium in polymer matrix).

Fibrous composites are composed of fibers, which are either continuous and
aligned or short and randomly dispersed in a polymer matrix medium. The fibers
themselves can be of various types, prominent among them being carbon, glass and

polymer fibers. The polymer matrix can be either a thennoset or a thermoplastic.

6
I2.2 Fiber Reinforced Thermoplastics

The importance of fiber- reinforced thermoplastics arises largely from the fact that
such materials can have unusually high strength and stiffness for a given weight of
material. When polymer composites are compared to the unfilled polymers, the
improvements they offer are spectacular. Thermoplastic matrices offer many advantages
over thermosetting resins. They have higher temperature resistance, very good fracture
toughness, good neat resin strengths, shorter molding cycles, reduced storage and
handling problems, infinite shelf life of intermediate prepegs, capability to fusion bond,
recyclability, and repairability [4].

Difficulties in processing have hampered the use of thermoplastic composites on a
wider scale. The intractability of these matrices due to their high viscosities even at
elevated processing temperature give rise to a host of problems such as stiff and boardy
prepegs due to high resin content, poor fiber wetting, solution devolatilization during
casting leading to formation of voids and loss of mechanical strength.

Thermoplastic polymers such as isotactic polypropylene (iPP) are often reinforced
by using glass fibers in order to increase the stiffness, tensile strength and dimensional
stability at elevated temperatures. A strong interface between fibers and thermoplastic is
extremely important to develop thermoplastic composites with improved physical and

Lmechanical properties.

{—2.3 Mechanics

In reinforcing a thermoplastic or a therrnoset with fibers the aim is to exploit the
load bearing capability of the fibers to yield a composite which has higher strength [5].
There are two important rules for fiber composites: first, the modulus of the fiber should
be greater than the modulus of the matrix and second, the elongation of the fiber should
be less than the elongation of the matrix [6]. Usually, fibers have good strength and
stiffness but are very brittle. The improvement in the mechanical properties of a fiber
reinforced composite is due to its ability to withstand a higher load than the matrix it
replaces [7]. The strong and stiff fiber bear most of the load and the polymer matrix
protects the fibers and transfers the load to them [8].

It is usual to establish a critical aspect ratio (length to diameter ratio) for the
polymer-fiber composite, and for effective load transfer short fibers must exceed a certain
critical length. Generally speaking, the greater the aspect ratio of the fiber, the better the
reinforcing effect, in terms of increased tensile strength and stiffness [9]. To achieve
maximum reinforcing efficiency, the fibers must be at least 10 times longer than the

Lentical length [10].

l3.4 Fiber - Matrix Adhesion

The level of adhesion of reinforcing fibers to the polymer matrix is an important
factor in the determination of composite mechanical properties. Mechanical strength can
only be achieved by the uniform efficient transfer of stress between matrix and fibers, via

a strong interfacial bond [6]. The strength of the interfacial bond is also responsible for

promoting good environmental performance even when the composite is loaded. The role
of the matrix is to bind the fibers together and protect them from environmental
conditions. With these factors in mind, many fibers and reinforcing agents are pre-treated
before they are incorporated into the composite. A gommon pretreatment uses [a geypling

3392193:an as a brislge between the. fiber and theater: thus Greeting , e .etropger.bpnci.,.

 

between the two. Research has shown that very small additions of a coupling agent are

*,.-c— -'-r -. —- -.._-

 

sufficient to promote good bonding and improve mechanical properties.

Also, it is believed that it is essential to have good “wetting” of the fibers in order
to increase adhesion and produce a strong composite [11]. With increased dispersion, the
fibers will be “wetted out” or totally enclosed by the matrix. Absorption alone can
produce increased adhesion between the fibers and matrix. Upon examining the surface
wettability of a composite, it is seen that improved surface wettability is an important
concern in improving fiber/matrix bonding.

When producing a composite material it is very difficult to simultaneously
improve properties such as stiffness, mechanical strength, and toughness. In order to
achieve high mechanical strength one must obtain uniform stress transfer between matrix
and fibers while producing a strong bond at the interface. An entire field of research has
been devoted to understanding the mechanism involved in resolving the tensile

Lstrengtlrltoughness dilemma.

 

9
I2.5 Natural Fiber Reinforced Thermoplastics

Synthetic fibers like glass, aramid, and carbon fibers are the most widely used
reinforcements in the polymeric composites industry. These materials are designed and
engineered with respect to performance and cost, but with a limited concern about the
ultimate disposability and environmental impact of the waste residues generated [12]. The
use of natural fiber, to replace wholly or partly the conventional inorganic fibers like
glass as a reinforcement, is presently receiving increasing attention primarily because of
their low cost and environmental benefits. Several types of fibers are available depending
on the climatic conditions and potential end use such as wood fibers/pulp, kenaf, flax,

sisal, hemp, juge, rarnie, coir, recycled newspaper/wood fibers, etc. These natural fibers

 

constitute cellulose and hemrcelluloses bound to lignin and assocrated with varying

-flflu flue—M

 

amounts of other natural materials, and are commonly termed as sligngcelfllfiulosics;

Mm... w,“ Ho‘W’n—Vfl ’M “MM-a-

 

*‘w

Section 3.1 covers natural fiber chemistry and their mechanical properties in more detail.

Traditionally, the mnatural fibers have been incorporated in polymer systems

.-..‘...., ,‘“~_!

 

primarily as fillers. There use as reinforcement has been investigated over the last few

_..r-.
“a

years by many researchers. The range of commercial applications of these natural fiber

Sq.“_....-. y

composrtes has started broadening recently. Especially with thermoplastics, the range

ufi-I'I -.

includes well establrshed sheet molding compounds materials such as Woodstock

Damages-
There are number of benefits offered by natural fiber overglassfiber reinforced or

mineral filled thermoplastics. These include [13,14]:

..--.o~v -----

 

0 low cost per umt volume basis.

-Mr—n- in.

10

0 low density

-5...“- __,

0 high specific stiffness and strength
0 desirable fiber aspect ratio of the fiber
0 good thermal properties

‘I—C’If‘ '

o flexibility during processrngmwrtnh reduction In tool wear
0 value addition of ”a low eost agricultural product ..
° eerizepmental attributes:
’ 82329.???9YSWWI‘. 9.18.3.9 Weineratiee
o biedegradability
0 reduceddefiélfnfl ifSPIFaFO’Y.ilePE:
There are certain drawbacks associated with the lignocellulosic fiber composites which

we need to overcome in order to promote their wide use. The drawbacks are [14] :

0 poor interfacial adhesion

 

 

0 poor stiffness/impact balance -

[nu-”i

o inherent high moisture sorptionfl

 

0 poor fiber dispersion

° Serfaeedefectp. (anaesthetic)

0 poor water resistance.

The efficiency of a fiber reinforced composite depends a great deal on the fiber-

matrix interface and the ability to transfer stress from the matrix to the fiber. This stress

transfer efficiency plays a dominant role in determining the mechanical properties of the

ll

composite and also in the material’s ability to withstand environmentally severe
conditions.

Toughness and impact resistance of a composite are important properties in
determining whether it can be used in specific applications. High flexural modulus and
high toughness are favored structural properties but are often mutually exclusive

characteristics of real materials. Natural fiber reinforced thermoplastrcs can match gla_ss-_

 

fiber reinforced thermoplastics in elastic and flexural modulii but do not compare

LEworably in impact resistance as measured by the Izod test.

I2.5.1 Causes of Poor Interfacial Adhesion

One of the main obstacles limiting the mechanical performance of these
composites is the incompatibility of the lignocellulosic fibers and the thermoplastic. The

lignocellulosic fiber rs inherently polar and hydrophilic while many thermoplastics are

‘n—n—as- .—..-.-—---v- -‘

 

non-polar and hydrophob1c Because of the two different polar characters, poor bonding

results. The poor bonding becomes more remarkable when the different thermal

m ......__._1...-..-. — ”.h-*-M

. “-7.4 v..._.._.—-‘.—-.

shrinkage of fibers and matrix-polymer leave gaps between the two components [15]. A

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necessary condition for good fiber dispersion and good interaction and adhesion between

the two components is the compatibility of the surface energies. Another difficulty

 

encountered during the incorporation of these fibers into the therm_plast1c matrix is the

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Limitfipsrbxprpgepmedium/bid! tends .teheldjhefibers togetherj

12
I”2.5.2 Improving Interfacial Adhesion

Several studies aimed at improving dispersion of the lignocellulosic fibers in the
on-polar matrix and increasing the stress transfer efficiency of the interface have been
conducted in various laboratories. In general, it was found that enhanced interfacial
adhesion can be achieved in one of the following ways [16]:

(i) fiber modification

(ii) use of interface-active additives

(iii) matrix modification.

Fiber Modification

Fiber modification involves grafting functional groups on the lignocellulosic fibers
or coating fibers with additives that carry suitable functional groups, in order to make the
fiber surface more compatible with that of the matrix material. The various reactive species
that have been used for fiber modifications include one or more of the following - acetic
anhydride, n—alkyl isocyanates, styrene, maleic anhydride, and silanes (Figure 2.1).

0 CH3
H3C 0 CH3 Y H3C OH
+ \n/ \‘r O + T
o 0 O

OH

Natural Fiber Acetic Anhydride Acetate Acetic Acid
cu,
OH CH3 0 NH
Ouco \H/
-—-—-> o
+
NCO
NCO \

This group available

Natural Fiber 2,4-Toluene Diisocyanate for further reaction.

Figure 2.1 Fiber Modification Reactions [13].

l3
Kokta and co-workers [17,18] employed a xanthate method of grafting to graft

styrene on wood fibers that resulted in composites with improved mechanical properties as
compared to composites with non-grafted fibers. Owen et a1. [19] reacted n-alkyl
isocyanates with wood and wood components to form carbamate derivatives which
imparted hydrophobic qualities to wood. Rowell et a1. [20-22] studied acetylation of wood
and wood fibers to alter its hydrophobicity and thus enhanced the bonding characteristics
with hydrophobic polymers. Felix and Gatenholrn [23] surface coated cellulose fibers with
a solution of a commercial low molecular weight propylene-co—maleic anhydride copolymer
and studied the nature of adhesion in the composite with polypropylene. Klason et al.[24]
prehydrolyzed cellulose fibers, before incorporating them in composites, in order to permit
the fibers to finely comminute in the processing shear field. It resulted in homogeneous
dispersion of fibers and improvement in mechanical properties.
Interface-active Additives

The second method of promoting interfacial adhesion involves the use of additives
like coupling agents and compatibilizers. Sanadi and Rowell [25] used acrylic acid grafted
(AAPP) and maleic anhydride grafted (MAPP) as coupling agents in composites of
recycled newspaper fibers and polypropylene. They found the property improvements using
MAPP to be better than AAPP, because of a greater possibility of acid-baSe interactions
between the fiber surface and the carboxylic acid groups.

Karmaker et a1. [26] reduced the water absorption of short jute fiber reinforced
polypropylene by incorporating maleic anhydride polypropylene (MAPP) in the system.
The maleic anhydride of MAPP promotes chemical bonding through esterification with

hydroxyl group of cellulosic fibers. This chemical bonding eliminates the gap between

l4
lignocellulosic fibers and polypropylene caused by differential thermal shrinkage. The

absence of gaps surrounding the fiber minimizes the spaces in the composite where water
can locate.

Maldas et a1. [27-29] studied the effect of coupling agents like poly[methylene(poly
phenyl isocyanate)], maleic anhydride, and silanes on the properties of wood fiber-
reinforced thermoplastic composites. They found that fiber coating followed by an
isocyanate treatment yielded the greatest improvement in properties. Also, the isocyanate
treatment combined with grafting resulted in improved properties.

Dalvag and co-workers [30] reported the use of a titanate compound and a low
molecular weight propylene-co-maleic anhydride copolymer as a coupling agent. Coupling
agents based on trichloro-s-triazine were synthesized and used to improve adhesion between
cellulose fibers and an unsaturated polyester [31]. The authors suggest the formation of
covalent bonds between the fiber and the matrix as opposed to just wetting of the fibers by
the matrix material. As a result, these composites exhibited decreased water absorption as
compared to the materials formulated without the coupling agents.

Myers and co-workers [32] studied the effect of a commercial additive, Epolene E-
43, (low molecular weight propylene-co-maleic anhydride copolymer) on the mechanical
properties of wood flour-polypropylene composites. The effect of Epolene E-43, wood flour
concentration, residence time, and wood flour particle size on the mechanical properties
were evaluated. Epolene E-43 exhibited a coupling behavior with improved properties. It
was suggested that the high cost of Epolene E-43 could be offset by increasing the wood

flour concentration in the composite.

 

 

15
Sapieha and co-workers [33] showed that the addition of dicurnyl peroxide resulted

in the direct grafting of polyethylene on cellulose fibers and improved mechanical
properties of the composite. They proposed the existence of a critical peroxide
concentration greater than which the grafting reaction was terminated, since the fiber
surfaces were covered with grafted polyethylene.

Matrix Modification

Takase and Shiraishi [34] have modified a thermoplastic matrix by incorporating a
maleic anhydride functionality and fabricated composites with wood pulp that exhibited
good mechanical properties.

Krishnan and Narayan [16] performed reactive extrusion processing to modify
polypropylene matrix with maleic anhydride and then subsequently generated in-situ grafts
between the modified matrix and low-density hardwood residue by use of a suitable
catalyst. They reported significant property improvements over the composites made

Lwithout the compatibilizer.

 

Chapter 3
Constituent Materials

{.23.] Natural Fibers

Plant fibers are conveniently classified according to the part of the plant where

they occur and from which they are extracted, viz. leaf, bast, or seed. Kenaf, jute, flax

Am—DH-fl 4"

and ramie fall under the group of bast fibers since they are obtained from the bast tissue

Wen—w. -r .....n

or bark of the plant stem. These long, mutlicelled fibers can be readily split into finer

#‘mmem

 

 

deg—“Mr" ._ I... I...

 

 

cells which are manufactured into textile and coarse yarns. Sisal and cotton are

- _.. ,. -9--..~v-

 

 

examples of leaf and seed fibers respectively.

vamm "WV-"'- am. vim-m

 

 

 

The strength of natural Wfrhers is provided by cellulose, a rigid linear chain

 

polymer composed of B-D-glucose units. Another major component is lignin, a highly

cross linked polymer of substrtuted phenyl propene units, which plays the role of the

Ilflflmh W.,m.r.-o ye... .‘hfiyv-nn-

matrix. Also present are the hemicelluloses, which are branched polymers of galactose

I!" m F "" "
Mthwn-u- (W' .v..--- "

 

glucose, manngse, _and xylose. Table 3.1 compiles the chemical composrtlon data of some

MM "Jar-"~— "'

natural fibers. The increased use of lignocellulosic fiber reinforced composites has led to

,Wm .—

 

much research on new fillers, fibers, coupling agents, and compoundmg techmques

“Mm” ‘

 

Generally, among the various reinforcing fibers, the hgnocellulosrcs have the

,-..._....-.-
.-_._~ r..- _- -.-u-—

 

___,..—--—-e-

highest elastic modulus and tensile strength approached only by a few cf highly oriented

"~_,_
vww

fibers [35]. Specific tensile modulus and strength of the cellulosic fibers, which provide

.5“...

 

an indication of the characteristics of a void free fiber on a basis of equal mass, are

16

l7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NS ad 9 a: 5d ed 9 a: dd ecu—38%.?—
ddm dd_~ Rd - mad fin - vmd ms 32m
95 ddfl 2: ad on; 3 .333.
32 Si 3 3 8.. 22.50
mdm v.9 and On vmd mam—0.."—
m.mm_ odd 3.3 Q: Ed .233—
am: 358: £0 .m: 35 5325 £0 62 M53» 3
3..an
050on 3.262 uzmsm ”.50on 59.2% 0.35... £80m
.Wn— E3: 9:05: m .35: :33 3:3— ..o Ezra—:50 n6 0......PV
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ad 3 d._ _ ad 3: fin» 325:3 9.an .35
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$58?

£33 .332 2:8 3 £52.58 33.55 3 2.3.5

 

18
equally high. Table 3.2 compiles mechanical properties data of some natural fibers. Their

specific properties are close to those of glass fibers. Like glass fibers, the elongation at
break of these fibers is low (2 to 5 %) but this is not a serious disadvantage in a

reinforcing fiber. The length/diameter (l/d) of reinforcing fibers must be above a certain

v... ”a.-.“ _._._. ,M“ "H. H“ M'thm-s. -3... Hr... -, ”h;-

level which depends on tbe efficiency of fiber-matrix adhesion before the fiber strength 1s

Mflfifilmmv—r-v-D r In V'Vu W8‘VN j "M

completely util1zed. Lignocellulosic fibers are relat1vely short and coarse in comparison to

“av-«u “A“ ”-4
W our. waMm’V—é ""“"' --—- "“"u‘ A“

most reinforcing fibers. Thus, bonding of matrix to fiber is likely to be important in

WW” ““

 

determining whether the full strength of the fiber can be utilized in a composite. Tbe

_ ...-..- .«flfl~
a“- w— "w

 

 

 

 

 

relatively shogfifixtsralso place this Wfi.malgrialti,,at.-a-disadvantag¢ if {(292119988... is

[required in the composite.

 

 

< Table 3.2 Mechanical Properties of some Natural Fibers [36,13].

 

 

 

 

 

 

 

 

 

Fiber Average Dimensions Ultimate Strain Tensile Tensile
Length Diameter at break Strength Modulus
L, mm D, mm % GPa GPa
Cotton 25 0.019 4 - 9 3.54 5.0
Flax 32 0.019 2 - 3 20.0 85.1
Jute 2.5 0.018 1 - 5 5.38 8.0
Kenaf 3.3 0.023 2 - 4 11.91 60.0
Ramie 120 0.040 2 - 7 13.25 76.0
Sisal 3 0.021 2 - 3 6.14 12.7

 

 

 

 

 

 

Fill Kenaf

Kenaf (ke naf‘), an annual hibiscus plant related to cotton, has been an important

M—Mm-‘O—C‘. _—

 

source of food, clothing, rope, sacking and rugs in central flfricaand partsoffrsia for
several thousand years [37]. One of the major uses for kenaf is an alternative fiber for the

pulp and paper industries. Kenaf fiber has great potential as a short-fiber reinforced

m---m. .M~-—-—

 

19
thermoplastics because of its superior specific tensile strength compared to other fibers.

See Table 3.3 for comparison of mechanical properties of Kenaf and other synthetic
fibers. Successful development of useful and novel composites that contain a high
percentage of kenaf will result in the increased utilization of kenaf fiber, thereby
enhancing markets for US. farmers.

Kenaf has a bast fiber, which contains approximately 75% cellulose and 15%

“Mu-w.~w._i.- _. m

lignin, and offers the advantage of being biodegradable and environmentally safe. _Tbe

bast fiber is actually a bundle of fibers bound by lignins and pectins. Chemical

K~.- M

modification of the fiber has been studied by Rowell et a1. [38] to make it more

Lbydrophobic so as to improve its compatibility with non-polar thermoplastics.

 

< Figure 3.1 SEM image of kenaf bast fiber cross-section.

 

20

X“The kenaf fibers used in this work were obtained from Department of Agriculture,

Mississippi State University, and were chopped into lengths of approximately 1.59 mm
(1/16 in). The kenaf fiber cross-section (Figure 3.1) is unsymmetrical therefore the single

}_fiber tests cannot be performed on it.

G2 Matrix

Fibers, since they cannot transmit loads from one to another, have limited use in
engineering applications. When they are embedded in a matrix material, to form a
composite, the matrix serves to bind the fibers together, transfer load to the fibers, and
protect them against environmental attack and damage due to handling. The matrix has
a strong influence on several mechanical properties of the composite such as transverse
modulus and strength, shear properties, and properties in compression. Physical and
chemical characteristics of the matrix such as melting or curing temperature, viscosity,
and reactivity with the fibers influence the choice of fabrication process. The matrix

Lrnaterial for a composite system is selected, keeping in view all these factors.

[32.1 Polypropylene

Polypropylene, the second largest volume thermoplastic - next only to
polyethylene, continues to experience significant technological developments which
promise to extend its applications dramatically. Total world capacity of polypropylene
was 43.7 billion lbs/year in 1994 and is projected to grow to 51 billion lbs/year by 1998.
Production gains will be fueled by increasing capacity and better prospects for end use

markets such as fibers, packaging, and automotive parts [39].

21

The high production figures and diversity of applications reflect the many
advantages of polypropylene. These include easy processability, lowest specific gravity of
any thermoplastics, and resistance to most organic solvents, with the exception of very
strong oxidizing agents such as fuming nitric acid or sulfuric acid. Polypropylene offers a
wide variety of melt flow rates (from 0.3 to 800 g/ 10 min). Other advantages of the
polymer includes its high melting temperature and its ease of recycling, an important

consideration in many of the packaging and automotive application its use in.

Polymerization of propylene monomer under controlled conditions of heat and
pressure in the presence of Ziegler Natta catalysts, which have multiple active sites, is the
conventional method of producing polypropylene. The polypropylene produced by this
method has a broad molecular-weight-disn'ibution (MWD) and hence poor control over

the resin properties.

Montell Polyolefins (formerly Himont Inc.) emphasized development of process
and catalyst technology to broaden its polypropylene application base. It developed the
Spheripol process that uses high activity, high selectivity catalysts to improve the
impact/ stiffness balance of traditional polypropylene products. An additional development
of a rheological nature enhances strain-hardening behavior, thus providing high melt
strength not normally present in linear polyolefins and expanding polypropylene’s
markets in thermoforming, high speed extrusion coating, foamed sheet, and large-part

blow molding [40].

22
The recently introduced metallocene single-site catalyst (SSC) technology [41],

heralded as a revolution in the olefin polymerization, offers narrow MWD polymers,
which have numerous advantages over the broad MWD polymers: e. g. higher toughness,
better optics, lower heat-seal-initiation temperatures, and higher crosslinking efficiency.
The disadvantage of narrow MWD, however, is poor processability due to low shear
sensitivity and low melt strength. But this problem has been offset by Insite technology,
developed by Dow Plastics, which involves use of constrained-geometry (CG)
homogeneous catalysts that produce highly processable polyolefms with a unique

combination of narrow MWD and long-chain branches.

There are three basic types of polypropylene: isotactic, atactic, and syndiotactic.
Each variety has a well-defined niche in the industrial sector. Isotactic polypropylene,
which contains ordered monomer units inserted in the same configuration, is the most
commercial polypropylene. Its molecular structure allows it to assume a helical and
crystalline configuration, which makes the material stiff enough for use in a wide range of

commercial applications.

In this work PROFAX 6501, an isotactic polypropylene homopolymer
manufactured by Montell Polyolefins, was used. The properties of PROFAX 6501 are

)Ncompiled in Table 3.4.

\Table 3.4 Characteristics of PROFAX 6501.

 

 

 

 

 

 

 

Composition Isotactic Polypropylene
Manufacturer Montell Polyolefins
Melt Flow Rate (230°C, 2.16 kg) 5.8 g/ 10min

Density 0.91 g/cc

M, x 10‘3 365

M, x 10'3 39.5

M, x 104 386

 

Complex Viscosity, n' (Pa-s, T = 180°C)

Storage Modulus, 0' (Pa, T = 180°C)

 

" 0.1 rad/s 25,990

" 0.1 rad/s 1,034

 

 

“ 100 rad/s 895.3

 

 

" 100 rad/s 78,860

 

 

{—32.2 Power-Law Model

 

 

Power law constitutive equation for non-newtonian polymer melts is:

r = -M7""i=-m\/%(izi)""i (3.1)

where 1: is the shear stress, 7 is the shear rate; m (N .s“/m2) and dimensionless n are
parameters called the consistency and power law index, respectively. According to the
model, the shear viscosity is linearly related to shear rate in the region 10< 7 <103 3", and
is given by :

77 = "17"" (32)

108(7)) = l0g(m) + ("-1)10g(}") (3.3)

24

A plot of logn vs log)" (Figure 3.2) was generated for polypropylene (PROFAX

6501) by performing a shear rate sweep in steady mode on rheometric mechanical

spectrometer (RMS-800) at 180°C. The parameter m

temperature. It was experimentally determined that for PP (at 180°C): no (zero shear

Lyiscosity)= 26000 Pa-s, m = 1490 N.s"/m2, n = 0.18.

 

 

is a sensitive function of

\.
\~

y = -0.8207x + 3.1732

 

‘1
?
3.5+ \
l \
3 R
I
10g(77),.5L \
i
21
i
1.5! . . _- .
-1 -o.5 o 0.5
loam

 

 

< Figure 3.2 Plot of log 77 vs log 7 to determine power law parameters.

[3.3 Coupling Agents

The coupling agents used in this work are: (i) Maleated polypropylene (MAPP)

and (ii) Silane coupling agent. A detailed discussion on MAPP is presented in Chapter 7.

3.3.1 Silane Coupling Agents

Silane coupling agents are widely used to improve interfacial adhesion at the glass

fiber or particulate filler-matrix interface. The coupling agent can be represented by the

 

25
formula RnSiX3, where X is a hydrolyzable alkoxy group and R is a nonhydolyzable

organic radical that possesses a functionality which enables the coupling agent to bond
with the organic resins and polymers. Most of the widely used organosilanes have one

organic substituent.

Hydrolysis
RSi(OR')3 + 3 H20 ——> RSi(OH)3 + 3 R'OH
(Silanol)
Condensation
R R R
3RSi(OH)3 -—> HO —Si—O—Sl1—O—ii—OH + 2H20
OH OH (EH
(Siloxane)
Hydrogen Bonding
R it R
Biofiber— OH + HO—Sli—O—Si—O—Si—OH
OH OH OH
R R R
HO —Si —O—Si—O-—Si—OH
.OOO. ‘0’. .00.
H H H H H H
.‘O'. .0" .00.
_Biofiber — Biofiber — Biofiber—
Surface Grafting
R R R R R R
HO—ii—O—Li—O—ILi—OH HO _S|i_0_ii_0_ii_.0
OOAQ. .A’. '30.. —-O A O A
H H H H H H L I I
‘Oo' ’Oo' ’(ix _Bio iber _ Biofiber _Brofiber.
—Biofiber — Biofiber —— Brofiber- + 3 H20

< Figure 3.3 Reactions steps in the silane grafting of biofibers

 

 

26
Reaction of these silanes involves four steps (Figure 3.3). The natural fiber

contains bound moisture which could hydrolyze the three labile X groups attached to
silicon atom. Condensation to oligomer follows. The oligmers then hydrogen bond with
OH groups on the natural fiber surface. Finally reaction of the functional organic group
on R along with the polymer completes the bridge like structure between the fiber and the

polymer [42].

The choice of chemical structure and the concentration of coupling agents play an
important role in achieving the optimum mechanical properties of the composite. The

most commonly used coupling agents are silanes and titanates. The dispersion of fiber 1n

W‘H- ,._

the matrix is one of the important factor to achieve a lower degree of variation in the

-"~--«-- -....«. .1.

 

 

“33"" «4‘. Ian—- 'W“ hw- v“:-

ultimate properties of “392199.539;

Kenaf fibers were surface-grafted with srloxane chams usrng a 2 wt % silane

".-
--«— ‘Wwvfid—thmh .5, . WWW”..- HnWM”

solution in water: Amino-ethyl armno-propyl trrmethoxy silane (Dow Corning Z6032)

Mgu¢u ”M‘vpnmw‘hn hm, WW

was used as the fiber surface mod1fymg agent. The amount of silane necessary to obtain a

”H“

minimum uniform Pvltirear_-°°va38.¢ can. be obtained by knowing the values. of mag

M““"

surface 0‘ silane KWWQE surfassprea (lithiftllfir.

amt. of filler x surface area of filler
wetting surface (ws)

 

( amt. of silane = (3.4)

Relative surface area of Kenaf was assumed to be 0. 2m / g Wetting surface (ws) of

1-..”, ~-.—_... ._..,_.._._.‘-

)Amino-ethyl amino-propyl trimethoxy silane = 353 m / g

--‘n.-..M~_ _H.. -‘m _._... “-3,-

‘,_.«~.-——a.—-.. .J'

 

Chapter 4

Composites Processing

[#111

e processing of kenaf reinforced polypropylene composites involves two major steps:

L(i) extrusion and (ii) injection molding.

‘—-h

4.1 Extrusion

In extrusion the raw material passes from a hopper into a cylinder in whichmitjs

 

 

 

melted and dragged forward by movement of a screw. The screw compresses, melts, and

..., ‘— -m..‘ 4r- “”“’"“‘

 

_ -.-.‘r4 mnMwM-t my .va-um-u-v-v- ;- ., . 11¢...“ w” h-W r—‘ m.

homogenizes. When the melt reaches the end of the barrel, it is forced through the die that

wwmn—wv—H—n o- IL...» L‘- “‘-

 

 

gives the desired shape with no break 111 continuity The aim of the extrusion process in

. -..‘__--.. r-r- . ..t
M- ”1“.“ ”v.51 f. .v, -»..q~. n..-. M, . uw- a ‘1 am»

 

this work 15 to mix the matr1x and the fiber so that samples taken from any portion of the

“1"“L‘WOTM- ‘-» '

 

extrudate show Wuniform propert1es

WWW-M’-

k;

 

w

 

Fibrous reinforcement of a polymer matrix demands a sophisticated mixing

—““-‘.- WMflmfim_ _
*r a... -

equipment which must provide extens1ve in take and conveymg capabilities Lpolymer

M— “-4 “H.2—
I... "- .

wetting, and dispersion of the reinforcement. The process should provide for controlled

._.-fi._—.___ ”n~_

 

ry—NAII

shear, temperature and residence time. This is to minimize material exposure to heat,

‘m‘W—rrwr— «mm-r-~—~-—‘M -~...~.-u.-,.-.. _

 

\.

prevent degradation, and to meet product requirements.

Wr-num--p4 _ ‘_

 

The extrusion process is a proven economical method for fiber reinforcement of

mv>M- ...... -—-' ‘wu’dmfimh-I-um*—g. U.- a”... .. ._ . -M-- ”' "‘ "'- h’ "‘ - -,.

polymers and co-rotating 1ntermesh1ng twin screw extruders are part1cularly suited for

Mun—- .-—-’

these tasks [43]. Positive conveying, self wiping, and shear sensitive mixing,

‘ ,1...“- o. “-7,,”

characteristics provided by the screw mechanism satisfy requirements of reinforcement

~s
‘Fm~_ Mxfln'fi 27

 

28

 

mpounding- Thiiwhgnfimcglts i9..i,rtte.rtup.t.i9a2£§u.e§mline .fl9%.lhj9.h is needed

- h-“ _. _,

 

t0 diSPerse bgthflhighjnd. low .aSPect ratio. reinforcing. 38mm. into .3 511191219 mlxmer
19¢an

Tflnjmw extrusion)?» ”a comma. P!99¢S$,..inyolving. all. .fqrms--o.f, ...transmr.t

. rm-Mm‘nh—fl‘fi '1’

phenomena (momentum, heat and mass transfer). Modeling the flow of viscoelasticflujuds

,.~e.fi.--M‘Mu

 

in extrudgsmhasb‘een an active area of study since long. “11191451 hagdiscussed the

Lsubject ingreatfldetaiflland has presented fiXPfihflWfil I¢.S.11,.l_t.s..9f,WEEXEQIQPOSitQfiYSECWEr

4.1.1 Extrusion Setup

A co-rotating, intermeshing twin screw extruder (Werner & Pfleidererer ZSK30)
was used in this study (Table 4.1). The screw profile is designed so that the tip of the
screw wipes the flank and root of the other screw, resulting in a self-cleaning action. This
type of twin-screw mechanism provides efficient conveying, pressure build-up with close
control over residence time distribution, shear input and temperature generation.
Modularity of screw design

Different screw elements or kneading blocks of varying profiles can be placed
along the shaft to generate a controlled shear or mixing effect. The screw consist of
continuous shafts on which screw-flighted components and special kneading elements are
installed in any required order. The screw elements are available in various lengths,
pitches, and pitch directions, and can be combined with kneading elements in many
different ways. The kneading elements are made up of kneading discs which are
staggered in relation to each other. The effect of the kneading elements can be altered by

varying the width of the discs and/or the angle at which they are staggered.

Table 4.2 Operating conditions for preparation of kenaf-PP composites.

29

Table 4.1 Characteristics of WP-ZSK 30 twin screw extruder.

 

 

 

 

 

 

 

 

 

Designation Values

Screw outside diameter 30.7 mm
Screw root diameter 21.3 mm
Flight depth 4.7 mm
Center distance of screws 26.2 mm
Length of processing section 960 mm (30 D)
# of screw elements 27

# of kneading blocks 13

 

 

 

 

Barrel Zone Temperatures (°C)

165,170,175,l80,180,180

 

 

 

 

 

 

 

Screw Speed 150 rpm

Feed Rate 5 kg/h

Residence Time ~ 120 sec

Pressure Profile (P) As shown in Figure 4.1
F ill Factor (i) As shown in Figure 4.1

 

 

 

 

 

 

d_

 

 

 

 

3.09 12.18

18.28 24.38

Axial Position (D)

 

Figure 4.1 Screw configuration, pressure and fill factor profile along the screw.

30
[4.2 Injection Molding

The aim of this process is to heat and masticate the extrudate into a melt, which is
injected into a mold of desired shape. An injection molding cycle comprises plastication,
injection, packing, cooling and ejection of a polymer (Figure 4.2).

A reciprocating-screw injection molding machine with a mold network is shown
in Figure 4.3. A typical machine consists of a screw housed in a barrel which is provided
with heater bands. Each machine has a hydraulic system which provides the power to
close the mold. During injection, the polymer is transferred through a nozzle which is
coupled to the mold block with a sprue bushing. The mold is made of runners which
convey the hot polymer melt into cavities. Gates which act as restriction to the flow of the
polymer connects runners to cavities.

A few studies on the flow and molding behavior of fiber reinforced polymers have
been published by Folgar and Tucker [45], Chan et al.[46] and Xavier et al [47]. Utracki
[48] presents an excellent description of the issues to be resolved in the processing of
fiber reinforced polymers in the light of their peculiar rheology.

Fiber Orientation

Goettler [49] found that the converging flow orients fibers in the flow

._‘ ’-m..,w- .v_v-w -‘. “*~.WFM~ n..-,__ _’ ,
‘W—‘u dN—fl—fivn

 

(longitudinal) direction, while the diverging flow orients them perpendicular to the

an' "‘"Ore

 

’ "a’w Mr.

streamlines of flow (transverse). The overall structure of the specimen is a transversely

”swan—H"

 

M """*‘W—..

oriented core surroundedflby a longitudinally oriented skin. This type of skin/core pattern

- r-n- n-‘.rW

is formed only at very low fill times and causes non-uniformity of properties.
«Co-”W —-».......—-~'~'""“""“ _-,.,.........._.«v —-—--r~ " ’ H " ’ *v v . , .~

 

PACKING

COOLING

PRESSURE

 

FILLING

 

 

TIME
Z Figure 4.2 Schematic representation of a injection molding cycle.

CAVITY RUNNER FEED HOPPER

    
  

HEATING BANDS

HYDRAULIC SYSTEM
SCREW GEAR SYSTEM

 

 

(Figure 4.3 Schematic diagram of a reciprocating injection molding machine.

4.2.1 Injection Molding Setup

The extrudate were injection molded on 350 kN Arburg Allrounder injection
molding machine (Model 221-75-350). The machine contains a 33 mm single screw and a
barrel which is provided with four heating zones inclusive of the one in the nozzle
adapter section. Throughout the molding trials the processing conditions (Table 4.3) were

held such that mold filling occurred in roughly 5 seconds and the average cycle time was

32
about 35 seconds. The mold used produced a ASTM D-638 Type I tensile bar and a

ASTM D-256 impact bar per cycle.

Table 4.3 Operating conditions for injection molding

 

 

 

 

 

 

 

 

 

 

Hopper to nozzle temperature 175,180, 200,200

profile (°C)

Injection Injection Holding Cooling Die Opening
Delay Time Time Time Time
2.0 s 4.5 s 3.0 s 20 s 1.5 8

Screw back pressure 0.69 MPa

Pack/Hold pressure 2.0 - 6.2 MPa

Screw Speed 75 - 100 rpm

 

 

 

V2.3 Optimization

The processing of short-fiber reinforced thermoplastics requires the following
considerations [50]:

1. control of rheological properties.

2. an efficient method of mixing.

3. control of mechanical/physical properties resulting from mixing.

4. control of the microstructure in the solid state.
A better understanding of the rheological behavior of the filled polymers would help in ‘
the choice of optimal processing conditions. Table 4.4 lists the elements of a composite

Lst’ructure and properties that depend on processing techniques.

33
<Table 4.4 Elements of Composite Processing-Performance Relationships [49].

 

 

 

Process Composnte Composite
Parameters Structure Properties
Forming Fiber concentration Modulus
geometry Fiber aspect ratio Strength
Rate Fiber dispersion Impact resistance
Temperature Fiber wet-out Shrinkage
Pressure Fiber orientation

 

 

4.3.1 Extrusion - Process Parameters

It is important to understand the influence of extrusion process parameters on

fiber length, fiber dispersion and fiber orientation in short-fiber reinforced thermoplastics.

The optimum composite would comprise aligned long fibers that are well dispersed in the

matrix.

Wall [51] has studied the effects of different mixing lengths and screw speed on

the fiber/matrix bond and the degree of fiber length degradation :

i)

ii)

as the mixing length is increased, there is a linear decrease in fiber length (Figure
4.4). The tensile strength of the extrudate increases initially with increasing mixing
length until it reaches a maximum, beyond which there is no improvement (Figure
4.5).

for a particular screw configuration, the screw speed has only a small effect on fiber
length in the extrudate (Figure 4.6). As the screw speed was further increased to
higher rates, there was a slight drop in fiber length. Increasing the screw speed
increases the tensile strength until it reaches a maximum and decreases thereafter
(Figure 4.7). With a proper temperature profile, there is a linear relationship between

the throughput rate and screw speed.

 

 

E 170 T
E 500 v g 165 ;
3 .: 160 +
.: 45°] ‘6, 155
‘6: 40° ’ E, 150
C s.
s a :2:
- 300. 2
3 m 3 135 .
if. 250 «rr—tfla g 130 %'
o 1 2 3 l- o 1 2 3
Mixing Length I Screw Diameter Mixing Length/Screw Diameter

Figure 4.4 The efiect of mixing length on fiber length. Figure 4.5 The effect of mixing length on product
strength.

UIQ
UIO
00

(db
UIO
0°

 

a

250 350 450 550

Fiber Length (pm)
A 0|
8 8
m.
Tensnle Strength (MPa)
55‘

_a
(II
0

250 350 450 550

_A
0|
0

Screw Speed (rpm) Screw Speed (rpm)

Figure 4.6 The relationship between screw speed Figure 4.7 The relationship between screw speed
and fiber length and product strength.

4.3.2 Injection Molding - Process Parameters

There are four basic parameters in the injection-molding process: fill time, melt
temperature, mold temperature, and peak cavity pressure. In turn, these parameters are
dependent upon the machine variables, mold variables, and the polymer employed.
Literature has many examples detailing the effect of these variables to the properties and
morphology of the molded parts.

The effect of fill time on mechanical properties, surface appearance and

dimensions of the injection molded specimens has been studied by Cox and Mentzer [52].

35

They attribute variations in mechanical properties and shrinkage on variations in
molecular orientations. Melt temperature was found to be the most important parameter
when related to residual stress. The importance of melt temperature was evinced by the
fact that it affects melt flow time, melt pressure at the nozzle and the cavity and the
cooling time. Mold temperature is manipulated during filling and cooling stage to reduce
molecular orientation and residual (thermal) stresses. In order to minimize cycle time and
to maintain correct gate freeze-off it is essential to monitor cavity pressure.

A typical fill pressure-fill time relationship for a hot polymer melt flowing into a
cold mold has a minimum as shown in Figure 4.8 [52]. At very short fill times (fast flow
rates), the fill pressure is very high and the flow is controlled by the viscous forces which
resist the flow. In this region, the flow is completed very quickly, shear stresses are high,
molecular orientation is high, and viscous heating occurs. As the fill time increases
(slower flow rates), the viscous resistance decreases, resulting in a lower filling pressure.
At some point, the fill pressure passes through a minimum and starts increasing with
increasing fill time. This region is heat transfer controlled as the hot melt is filling the
cold mold slowly with substantial heat transfer occurring. This lowers the temperature of
the melt which in turn increases the viscosity and thus the pressure. From a processing
viewpoint it is desirable to operate at the minimum in fill pressure because it is most

stable portion of the curve.

 

‘6
I ’ u

Viscous Flowl Heat Transfer
ll Controlled I Controlled

Fill
Pressure

 

__
‘7

Fill Time
Figure 4.8 Typical fill pressure-fill time relationship.

[14 Experimental Procedure

The raw materials - PROFAX 6501 (polypropylene) and kenaf bast fibers were
fed into the extruder. Where necessary, they had to be mixed with compatibilizer
(MAPP) or the fiber treated before being fed to the extruder. The extrudate was

pelletized, dried and further processed by injection molding.

Before processing, kenaf fibers were dried in a convective oven at 100°C for 48

' ’ ~‘UF-e-q... ’w—o Pan‘s-hu-

 

 

hogs. Polypropylene and dried kenaf fibers were fed through a common feed port.
Polypropylene was fed using a gravimetric feeder (Acrison Inc.. Model 406). The product
discharge is precisely regulated by the MD-II 2000 Controller (Acrison Inc.) on a weight
loss basis. The feeder was operated in the internal gravimetric control mode (continuous)
after calibration. This maintains the output rate constant according to the set feed rate.
Dried kenaf fibers were fed by a volumetric feeder (K-Tron) after its calibration. The feed
rates were set such that composites of various fiber weight fractions could be prepared.
The extruder was operated under the conditions specified in Table 4.2. Once the

extrudate was free of purge material, strands of the extrudate were pulled out of the die

 

37

into a water bath and were fed into a pelletizer. Since the pelletizer was not able to pinch
or cut soft material, the strands were cooled in a quench tank filled with water. An
arrangement was made to blow off water from the strands by using pressurized air, just
before they entered the pelletizer. Pelletization of the material was stopped, when the load
(torque) of the extruder, which was kept constant during extrusion, started decreasing.

The composite pellets were dried in an oven at 100°C for 30 hours, before they

u-t—uw-p‘ W 11w - .

 

.,...~ “pd“ .w. , .mr'ov- Megg_fi---w;mw

were injection molded. The injection molding machine was operated under conditions

specified in Table 4.3, with a mold suitable for ASTM D638 specimens. Mold

 

temperature, screw speed and injection speed were varied so as to produce samples with
good surface appearance.

Since this study involves inter-comparison of different natural fiber composites,
best efforts were made to maintain same conditions while carrying out processing of
different blends. Purging of the extruder and injection molding machine was always
conducted before and afier a run. The purge resin was chosen (usually PS or HDPE) such
that it is more viscous than the raw material under the operating conditions. The material

Lhfiandling equipment were maintained clean.

Chapter 5

Experimental Characterization

The injection molded specimens of kenaf reinforced polypropylene composites were
characterized by mechanical tests (Tensile, Flexural and Impact) and thermal analysis
tests (TGA and DSC). The melt flow properties were measured with a melt flow indexer.
The morphology was studied by scanning electron microscopy. The data obtained from
these tests are appropriately reduced to evaluate various material properties that can later

be used for analysis and design of practical structures.

5.1 Mechanical Characterization

The specimens for these tests were conditioned for at least 48 hours at room
temperature and 50% humidity prior to testing. At least five specimens were tested for

each composite blend and property.

5.1.1 Tensile and Flexural Tests

These are static tests which are greatly dependent on the fiber orientation in the
composites with respect to loading axis. Typical stress-strain curves obtained are as
shown in Fig 6.1 (Chap. 6). In stress-strain tests the buildup of force (or stress) is
measured as the specimen is being deformed at a constant rate. In these tests the stress

can become non-homogeneous as it varies from region to region in the specimen as in
38

39

cold-drawing or necking and in crazing. Also, since a polymer’s properties are time
dependent, the shape of the observed curve will depend on the strain rate and
temperature.

In tensile test the specimen is exerted to tension in the longitudinal direction. A
flexural test subjects the interface to a complex mixture of tension, compression and shear
such that results are difficult to interpret in terms of mechanics, but the test is simple to
run and relates well to composite performance. Both these tests were performed on a UTS
of United Calibration Corporation (Model SFM 20) with the parameters as listed in Table
5.1, under ambient conditions.

The properties measured from these tests are: tensile and flexural strengths,
elongation at yield and break, toughness, initial tensile and flexural modulus. All

properties except the following can be directly obtained from the stress-strain plots.

Initial Tensile Modulus:

 

d5 1,,

(10' F
(E) = T) = —(,,_f, ] (5.1)
£—>0 L411,

where F/A is the force per unit cross-sectional area,
L is the specimen length when a tensile force F is applied, and
L0 is the unstretched length of the specimen.

Initial Flexural Modulus:

 

(EFlex)

3 3
PS ] _ Sm (5.2)
640

= 4bt36 " 412:3

40
where P = load, S = span, 8 = deflection, b = width , t = thickness, and

m = slope of the tangent to the initial straight line portion of the deflection.
Toughness is measured as the area under the stress-strain curve till the break point.

Therefore, it is an indication of the energy that a material can absorb before breaking.

Table 5.1 Test Conditions for Tensile and Flexural Tests

 

Tensile Test 3-point Flexural Test

 

 

 

 

 

ASTM D638 D790
Temperature 30°C 30°C

Strain recorder Laser Extensometer Strain Gage
Loadcell Capacity, lb. 1000 1000

Test Speed 0.25 in/min 0.1 in/min

 

Sample Dimensions Gage length - 2 in Span - 2 in
Width - 0.5 in Width - 0.5 in
Thickness - 1/8 in Thickness - 1/8 in

 

 

 

 

 

5.1.2 Impact Tests

Impact tests measure resistance to breakage under specified conditions when the
test specimen is struck at very high velocity. These properties are difficult to define and
analyze in scientific terms, and hence it has been difficult to employ the results directly in
designs.

Impact strengths quoted are critically dependent on specimen dimension and the

geometry of notches. The notch in the Izod specimen serves to concentrate the stress,

41
minimize plastic deformation, and direct the fracture to the part of the specimen behind

the notch, scatter in energy-to-break is thus reduced.

Impact is the commonest way of measuring toughness of plastics and composites
in industry. The toughness (area under stress-strain curve) and impact should be related in
some manner. But the difference is due to the very high testing speed of impact tests
compared to tensile tests.

The notch of depth 0.1in was made in the specimen on a TMI Notching Machine
(Model 22-05). Then the test was conducted on a TMI Impact Machine (Model 43-02-00)
with the parameters as listed in Table 5.2. The machine is programmed to give digital
readout for the average impact strength and the standard deviation. Printed results were

obtained from an on-line printer.

Table 5.2 Test Conditions for Izod Impact Test

 

 

 

 

 

 

ASTM D256
Temperature 30°C
Izod Pendulum 5 lb.
Sample Dimensions 2.5 in X 0.5 in X 0.125 in

 

 

5.2 Differential Scanning Calorimetry (DSC)

DSC is an analytical technique in which the difference in heat flow between a
sample and an inert reference is measured as function of time and temperature as both are
subjected to a controlled environment of time, temperature, atmosphere and pressure.

DSC is used to measure temperatures and heat of transition, specific heat, rate and degree

42

of crystallinity, purity, rate of reaction, etc. Since the heating is controlled by a computer,

it is possible to follow a complex heating algorithm.

5.2.1 Modulated DSC (MDSC)

A new technique, invented by Dr. Mike Reading, which provides the same
information as conventional DSC plus additional benefits which significantly increase
our understanding of the material properties. In MDSC heat flow is measured as a
fimction of both a linear change and a sinusoidal change in temperature. The sinusoidal
change permits the measurement of both the components of heat flow: reversing heat

flow (heat capacity component) and non-reversing heat flow (kinetic component).

Temperature change in DSC is given by :
T(t) = 7; + ,6: (5.3)
where T(t) = program temperature , T0 = starting temperature , t = time (min)

and [3 = linear heating rate (°C/min).

Temperature change in MDSC is given by :
T (t) = 7:, + ,6: + A]. sin(a)t) (5.4)
where AT = amplitude of temperature modulation (:t°C),
a) = 21t/P, the modulation frequency (360"), and

P = period (see).

 

43
DSC-Modulated DSC and Thermal Analyst 2200 System (TA Instruments) was used for

determination of initial crystallinity of polypropylene with different level of maleation.
Since the MDSC can separate the kinetic component from the total heat flow, it can
measure the crystallization that occurs as the material is heated. When the enthalpy of
crystallization (non-reversing) is compared to the enthalpy of melting (reversing), the
excess melting enthalpy is due to the excess crystallinity. Another benefit of using MDSC

is - increased resolution without loss of sensitivity.

5.3 Thermogravimetric Analysis (TGA)

TGA is performed by continuously measuring the mass of a material as a function
of temperature or time in an instrument called thermobalance. The analytical result, or
TGA curve, is a plot (as shown in Fig. 6.10) of the mass or the percentage of original
mass remaining at the temperature or time depending on the objective of the experiment.
The heated sample can be bathed in an inert environment using gases such as nitrogen or
argon. TGA serves as a simple technique to obtain useful information about moisture,
fiber or plasticizer content, degradation temperature, etc.

TGA was used for the determination of fiber content in kenaf polypropylene
composites. Hi-Res TGA 2950 Thermogravimetric Analyzer (TA Instruments) with

Thermal Analyst 2200 System was used for TGA experiments.

44
5.4 Scanning Electron Microscopy (SEM)

The SEM (JEOL 6400) is employed to observe the surface morphology of a
sample. The normal SEM image is formed when secondary electrons from the atoms of
the sample are given out as a result of inelastic scattering by the electron beam. These
secondary electrons are then detected by an Everhart-Thornley detector. The production
of secondary electrons is very sensitive to the changes in topography of the sample. The
projecting areas of the samples giving out a large number of these electrons and thus
appear brighter. The electrons cannot escape from low lying areas like crevices and thus
these appear dark in the final image. A resolution of 4 to 6 nm is possible with this
technique.

Sample Preparation

The samples for SEM are typically 2 to 4 mm in diameter. The samples are
mounted on Aluminum stubs and coated with gold in sputter coater. When a
backseattered electron image is desired, the sample has to be coated with Carbon. A
coating of about 20 nm thickness and the use of graphite paint was found to be sufficient

to prevent charging of the sample with a 15 kV accelerating voltage.

5.5 Melt Flow Index

Melt flow indexer can be considered as a simple form of low shear capillary
rheometer. It consists of a vertical cylinder bore with heating arrangement, a die at the
bottom of the bore and a piston which fits on to the bore from the top. When the cylinder

reaches the set temperature, it is charged with a weighed amount of sample and the piston

45
is loaded with the specified weight. Melt flow index (MFI) is measured as the amount of

material discharged through the die in 10 min.

Melt flow indexer is run under a constant stress but the shear rate is dependent on
the melt viscosity. Actual shear rate of measurement is around 2.5 - 3 times the MFI.
Melt flow index provides relative comparison of melt viscosities between different
polymeric systems, though it does not provide any elastic information. The tests were
conducted on a Ray-Ran Melt Flow Indexer with a melt temperature of 225°C and load of

2.16 kg (ASTM D1238-85).

Chapter 6

Mechanical Properties of Kenaf Reinforced
Polypropylene Composites

The mechanical properties of composite materials are determined by the properties of the
components, the morphology of the system, and the nature of the interface between the
phases. Therefore a great variety of properties can be obtained by varying the structure of
the system or interface properties. An important property of the interface is the degree of
adhesion bonding between phases. Other parameters which influence the mechanical

properties were discussed in section 4.3.

6.1 Selection of Fiber Length

The minimum fiber aspect ratio required for reinforcements is usually 20 times
the critical fiber aspect ratio (le). Single-fiber tests are usually conducted to determine

the critical fiber length (1,) and interfacial shear strength (1:) using the equation :

i _ 91
(d) _ 21 (6.1)

where of“ is the fiber ultimate tensile strength.
There are certain limitations to the use of single fiber tests with kenaf fibers for
determination of 1,. The non-uniform cross-section of kenaf fibers violate the basic

assumption of the model equation (6.1), The average diameter of kenaf fiber is about 50

46

47

um and it can be assumed that a minimum reinforcement length of 0.5 mm would be
required. Therefore the kenaf fibers were chopped to a length of 1/16 in (1.58 mm) to
start with. Further processing in an extruder and injection molder shortens the fiber thus
decreasing its reinforcing efficiency. The burnt residue obtained from thermogravimetric
analysis (TGA) of the sample were investigated under a microscope. It was found that

more than 50 - 60 % of the fibers had a minimum length of 0.75 mm (aspect ratio of 15).

6.2 Experimental Approach

The objective of these experiments was to study the influence of the following
factors on mechanical properties: (1) fiber fraction, (2) amount of compatibilizer -
maleated polypropylene (MAPP), and (3) fiber modification by silane coupling agent.
Based on the results an optimal composition for the composite can be determined.

The following kenaf based composites were prepared and investigated in this
work. All percentages are in wt %.

1) Neat PP
2) Uncompatibilized composites (without MAPP)
20% Kenaf - 80% PP, 40% Kenaf - 60% PP, and 60% Kenaf - 40% PP.
3) Compatilbilzed composites (with MAPP)
With 2 % MAPP: 20% Kenaf - 78% PP, 40% Kenaf - 58% PP, and 60% Kenaf -
38% PP.
With 5 % MAPP: 20% Kenaf - 75% PP, 40 % Kenaf - 55%PP, and 60% Kenaf -

35% PP.

 

48
4) Silylated Composites - 20% Kenaf (treated with silane), 70% PP, 2% MAPP

The maleation of PP was performed by extruding a mixture of PP, maleic
anhydride at 2 phr (parts per hundred resin) and 0.1 phr of an initiator, 2,5-dimethyl-2,5-
di(t-butyl peroxy) hexane (Lupersol 101, Atochem). A detailed study on maleation of PP

is presented in Chapter 7.

6.3 Results and Discussion

The composites were characterized by the tests mentioned in Chapter 5. At least
five specimens were tested for each composite blend and property.The results presented
are within a 5% confidence interval of the mean.

6.3.1 Tensile Properties

The stress-strain curves of the uncompatibilized and compatibilized composites
are shown in Figure 6.1. The non-linearity in the curves is mainly due to the plastic
matrix deformation. However, the distribution of fiber lengths present in the composite
can also cause the slope of the stress-strain curve to decrease with increasing strain [3].
This is because the load taken up by the fibers and the efficiency of the fibers decreases
as the strain increases.

Table 6.1 compiles the tensile test results for various kenaf reinforced
polypropylene composite systems. It can be seen that the tensile modulus (stiffness) is
strongly dependent on the fiber fraction (Figure 6.2) because the fiber stiffnesss
contribution is dominant in the composite. There is a slight increase in stiffness with

addition of MAPP to the composites.

 

 

Tensile sum m)
a 3

 

 

 

  
 

PP-Kenat (20%). w 'Ihout MAPP

 

 

 

8 10
Strain (9‘)

12 14

16 18

thAPP

 

Figure 6.1 Tensile Stress vs Strain curves of kenaf - PP composites.

Table 6.1 Tensile test results for kenaf-PP composites.

 

 

 

 

 

 

 

 

 

 

 

Composite Kenaf Fiber Tensile Initial Elongation Elongation
Material Strength Tensile to yield to break
Modulus
(wt '7.) (vol %) (MPa) (GPa) (7.) (°/.)
Neat PP o o 28.4 1.2 9.5 800
PP Without -29..-. _§§ _____ Z§9______.2;7._____-.5;2_ ______ 1.1-1--
MAPP _5_9__£_§9 _____ 261343096
60 77 25.8 3.9 2.6 8.0
PP with -29.-.___0 ______ ‘11-9_______2;9_______§.-_§__s "171-2---
2% MAPP __59_-.__§§ _____ §%9--,_-_§J.-__ ___4.8___f__15_-9___
60 77 37.5 41 f 3.3 ' 13.4
PP With “.29 ...... 0 ______ ‘1 ‘i-Q______.§;Q_-____§_-.1_ ______ 1%--..
5% MAPP -59.-.__§§ _____ {1.5_-I______9;9__-____§.-_Q ______ 1].-9---
" 60 77 44.8 4.0 4.2 14.8

 

 

 

 

The result of tensile strength is shown in Figure 6.3, indicating that the tensile

strength of the composite increases with the addition of MAPP. However, a tremendous

increase for its tensile strength was noted up to 2% addition, on the whole composite.

50
Surprisingly, such a small addition of MAPP could improve tensile strength by about

50% compared without MAPP. An addition of MAPP in a quantity up to 5% resulted in
a slight improvement of the strength. From literature [34], it is known that further
addition of MAPP would decrease the strength of the matrix portion of the composites.
The increase in fiber fraction causes a slight decrease in tensile strength in both
compatibilized and uncompatibilized composites. The higher tensile strength of the
MAPP-composite system over the uncompatibilized system is due to improved interphase
properties. This is due to a combination of some formation of covalent linkages (due to
reconversion to the anhydride form) and enhanced acid-base interactions between the
fibers and MAPP (see Chapter 7). The elongation to break (Figure 6.4) increases on

addition of MAPP but decreases with increase in fiber fraction.

 

 

 

I . l
6 , 1’ _PP wrthout ‘ ‘
” MAPP
’
5 /
f E PP With 2%

MAPP

- PP WOith 5%

 

MAPP
Halgin-Teai Model
_._.with E(kenaf) = .

 

 

 

 

 

 

5 GPa. Ild =15 >
_ _.. _with E(kenat) = 1 1
10 GPa, 178 =15! -i
Neat 20% 40% 60% ' ' 3
PP Kenaf Kenaf Kenaf 1

 

Figure 6.2 Tensile Modulus for kenaf-PP composites.

51

 

 

 

 

 

 

 
 
 

l . PP without MAPP
DPP with 2% MAPP
. PP with 5% MAPP

 

 

 

 

Neat PP 20% Kenaf 40% Kenaf 60% Kenaf

 

Figure 6.3 Tensile Strength for kenaf-PP composites.

 

 

 

 

 

. PP without
MAPP

a PP with 2%
MAPP

.PP with 5%
MAPP

 

 

 

Neat 20% 40% 60%
PP Kenaf Kenaf Kenaf

 

Figure 6.4 Elongation to break for kenaf-PP composites

 

 

 

 

 

52

6.3.2 Halpin-Tsai Prediction of Modulus
The Halpin-Tsai equations can be used to predict the elastic modulus of an
anisotropic specimen of short fiber reinforced thermoplastics [53]. The following

empirical relations are used:

 

 

 

E....... = 3E. + it". (6.2)
1+ 21d V
i ___ ( / )771. f (6.3)
E... l—nLV,
. 1+2 V

_EL _-. ___nl—f (6.4)

E," 1‘17er

where 77L = (El/Em) — l (6.5)
(El/Em) + 2W")
E E — l

and 27L=( ’/ .) (6.6)
(Ef/Em) + 2

In the above equations Emdom = overall elastic modulus, EL: longitudinal
modulus, 13T = transverse modulus, Ef = fiber modulus, 13m = matrix modulus, Vf = fiber
volume fraction, and (l/d) = aspect ratio.

The comparison of Halpin-Tsai predictions with experimental results is shown in
Figure 6.3. The fiber volume fraction (V f) were calculated from the corresponding weight
percentages using the specific gravity of kenaf fibers as 0.45 (experimental average). The
results indicate that elastic modulus of kenaf fiber is between 5-10 GPa. Although the
Halpin-Tsai model gives a good estimate of modulus it does not incorporate the effect of

coupling agent on interfacial adhesion.

53
6.3.3 Flexural Properties

Table 6.2 compiles the 3-point flexural test results for various kenaf reinforced
polypropylene composite systems. Since a flexural test subjects a specimen to a complex
mixture of tension, compression and shear, the flexural properties are greatly dependent
on the processing mode, fiber length and fiber orientation. The behavior of flexural
strength and modulus is similar to tensile strength and tensile modulus respectively.
Unlike tensile modulus, flexural modulus (Figure 6.5) improves tremendously by
addition of MAPP. This indicates that the flexural properties give a better reflection of

the improvement in interfacial adhesion between kenaf fibers and PP.

Table 6.2 Flexural test results for kenaf-PP composites.

 

 

 

 

 

 

 

Composite Kenaf Fiber Flexural Initial Flexural
Material Strength Modulus
(wt %) (MPa) (GPa)
Neat PP 0 34.8 1.3
PP without ____gg ________ 4 321 _________ g._3 _____
MAPP “"59. _______ 4i 9 _________ Z-Z _____
60 f 47.2 3.2
PP with +---29 ________ ‘1 6._-§__-.___--§-_0 _____
2% MAPP “-319 ________ 5:4 _~§__..._____§-.9 _____
60 63.2 4.4
PP with ____29 ________ 5. 2.1---.__-___3.-_8 _____
5% MAPP ““29. ________ :5. 88 _________ 5.1 _____
60 67.3 4 6

 

 

 

 

 

54

 

 

  

 

f .PP without
MAPP

DPP with 2%
MAPP

.PP with 5%
MAPP 1
“-4

 

 

 

. .i, ._
Neat PP 20% Kenaf 40% Kenaf 60% Kenaf

 

 

 

Figure 6.5 Flexural Modulus for kenaf-PP composites.

6.3.4 Impact Strengths and Toughness

Table 6.3 compiles the impact test results for various kenaf reinforced
polypropylene composite systems. The notched Izod impact strength (Figure 6.6)
decreases with increasing fiber content due to incorporation of more brittle fibers. In this
case, the impact strength is only a measure of crack propagation energy since the
initiation has already occurred because of the notch.

Impact strength does not have a simple relationship with adhesion between the
fiber and polymer. It can be greatly affected by such factors as the perfection of packing
and alignment of the fibers and imperfections such as voids. The increase in impact
strength on addition of MAPP is probably due to improved adhesion.

Toughness, which was measured as the area under the stress-strain curve, also
shows a similar behavior as the impact strength (Figure 6.7). Like impact, toughness is

also a measure of the fracture energy of a composite. But it is not justifiable to compare

55

the two because the rate and conditions under which the two tests are conducted is

entirely different.

Table 6.3 Impact Strengths and Toughness for kenaf-PP composites.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Composite Kenaf Fiber Notched Izod Toughness (area under
Material Impact Strength stress-strain curve)
(wt %) (Jlm) (GPa)
Neat PP 0 42.1 Very high
PP without 20 41.3 114.8
MAPP 40 38.0 110.0
60 33.4 108.3
PP with 20 47.6 141.4
2% MAPP 40 41.4 136.8
60 38.7 127.0
PP with 20 50.1 145.8
5% MAPP 40 43.9 139.3
60 39.2 132.7
1 .0. i
I
40 l 1
so -

l
l

.I PP without MAPP ‘

N
O

E] PP with 2% MAPP

Impact Strength (Jlm)
8

.PP with 5% MAPP .
J ,

  

   

 

1
0 _. - ,_ ,m ‘t‘ , J
Neat PP 20% Kenaf 40% Kenaf 60% Kenaf

 

 

Figure 6.6 Notched Izod Impact Strength for kenaf-PP composites.

56

 

 

180 -

160 ..

140 J.
‘3 27 *7 r:
n_ 120 . .PP Without
0 ‘ MAPP
v100 ..
3 D PP with 2%
2 8° 1 MAPP
'5, so .. . PP with 5%
3 4o MAPP
.— - 7 7

20

O ,

 

 

 

 

Figure 6.7 Toughness (area under stress- strain curve) for kenaf-PP composites.

6.3.5 SEM Analysis

SEM observations of the fracture surface of notched Izod specimens indicate that
there is considerable difference in the fiber-matrix interaction between the compatiblized
and uncompatilbilized composites. Uncompatibilized composite fracture surfaces show
some fiber pull-out and fairly clean fiber surfaces (Figure 6.8). Addition of the MAPP
coupling agent appears to produce a significant improvement of the wettability of kenaf
surface by the polymer. The improved bonding is clearly seen in Figure 6.9 where the
fiber has pulled out from the matrix but a fair amount of polymer residue remains on the

fiber.

 

Figure 6.8 SEM of the fracture surface (notched Izod test) of
kenaf (20%) - PP without MAPP.

 

Figure 6.9 SEM of the fracture surface (notched Izod test) of
kenaf (20%) - PP with 2% MAPP.

6.4 Effect of Silane Coupling Agent

Silane coupling agents are widely used to improve adhesion at the glass fiber or
particulate filler-matrix interface. The silane chemistry and its role in improving the
interfacial adhesion was discussed in section 3.3.1. Kenaf fibers were surface grafted
with siloxane chains using a 2 wt% amino-ethyl amino-propyl trimethoxy silane (Dow
Corning Z6032)solution in water. Composites were made with 20% by wt. silanized fiber

loading in polypropylene. The injection molded specimens of these composites where

58

then mechanically characterized (Table 6.4).

Table 6.4 Mechanical properties for silylated kenaf (20%) - PP composites.

 

 

 

 

 

 

 

 

 

 

 

 

 

PP - Kenaf PP - Kenaf PP - silanized
Composite Material without with 2% Kenaf with 2%
MAPP MAPP MAPP
Tensile Strength, MPa 26.9 41.0 42.5
Tensile Modulus, GPa 2.7 2.9 3.3
Elongation to break, % 11.8 17.2 18.4
Elongation to yield, % 5.2 5.6 6.4
Flexural Strength, MPa 43.1 46.3 57.7
Flexural Modulus, GPa 2.3 3.0 4.0
Izod Impact Strength, J/m 41.3 47.6 54.6
Toughness, GPa 114.8 141.4 149.2

 

The results show that silane treatment of fiber improves the properties similar to
the addition of MAPP. There is a remarkable increase in Izod impact strength and failure
strain. The siloxane chains are believed to increase the ductility of fiber-matrix interface.
Thus by incorporation of silane coupling agent stiffness could be increased without

reducing the impact strength. But excess addition of silane to the fiber could cause the

interface to become brittle.

 

Chapter 7

Maleation of Polypropylene

The role of maleated polypropylene (MAPP) in improving the mechanical properties of
kenaf - PP composites was discussed in Chapter 6. Selection of MAPP with an optimal
degree of grafting of maleic anhydride (MA) onto polypropylene (PP) is very crucial. The
aim of this study was to understand the effect of MA and initiator concentration on the
degree of grafting.

Reactive extrusion processing is an efficient approach for modification of
polymers which involve grafting reactions and good control over rheology. Therefore the
maleation of PP was carried out in a twin-screw extruder under controlled shear rates and

temperature, with residence time of about 1.5 min.

7.1 Use of Maleated Polypropylene as a Compatibilzer

It was learnt from the results in section 6.3 that MAPP tremendously improves the
interfacial adhesion between kenaf and PP. It is believed that the improved properties in
the MAPP systems are due to a combination of formation of covalent linkage (by
esterification with OH groups on fiber) and enhanced acid-base interactions between the

fibers and MAPP.

59

60
7.2 Experimental Approach
The approach followed in these experiments was to prepare MAPP blends with
varying concentration of MA and initiator. The amount of grafted MA on PP was then
determined by titration and confirmed by IR spectroscopy. The rheological behavior and
melt flow index (MFI) were determined for the blends on rheometrics mechanical

spectrometer (RMS) and melt-flow indexer respectively.

7.2.1 Functionalization of Polypropylene

The MA at 2 phr (parts per hundred resin) was added, after dissolving in a small
amount of acetone, to the PP powder. The initiator, 2,5-dimethyl-2,5-di(t-butyl peroxy)
hexane (Lupersol 101, Atochem) was also added at 0.1 phr to the mixture. The mixture
was dry blended and fed into the hopper through a volumetric feeder at 5 kg/h. The
extruder was run with a flat temperature profile at 180°C and a screw speed of 200 RPM.
The modified polymer was extruded through a strand die, into a water bath, and finally to

a pelletizer.

7.2.2 Reaction Mechanism

Although numerous studies have been made on maleation reactions no definitive
mechanism is available. The following reaction mechanism has been proposed by

Gaylord [54]:

61
The radicals generated by initiator decomposition attack the PP to generate PP'

macroradicals which disproportionate in the absence of MA and add MA when the latter

is present.
1 i w i
PP—CH,C‘CH,- c‘— PP ——> PP-CHzéiCI-Iz- Ci- PP (7.1)
CH, CH, CH, CH,
1 l H
I
PP‘CHzc‘C- + CH2:(I-PP (72)
CH, CH,
1' ’1' ’i H
pp—cfizcc- + CCH; PP —> PP—CHztiCl-b + 6:04-”, (7 3)
CH. CH. CH. 12H, '
H H
PP—CszCHz-d-PP T EH3
EH3 —.. PP—CH2CCHz >13? (7 4)
DIG—ALO 04 :OAO
MA undergoes excitation as a result of the rapid decomposition of the initator.
— R 1' e + _
—-> \ + \ (7.5)
o O o 0 GAO o O/\o
The MA excimer abstracts hydrogen from PP to generate a PP' microradical.
EH3 CH,
——> PP—CHZCM
PP-c m -
”2 \ . + _ . + - (7.6)

H .
OJ :vo 04 :0 \0 0A 0A

62
The PP' radical either undergoes degradative disproportionation, as shown in eqns. (7.2)

and (7.3), adds MA as shown in eqn. (7.4), or couples with the MA excimer.

PW 9H3
' + ' ' ——> CHZC + - . (7.7)
\
0 GAO 0 0A0 0 CAD 0 GAO

Graft copolymer is formed by the coupling of the PP’ macroradical and the poly-MA’

 

 

radical.
CH3
' ' H —->
A L j J. '
0 GAO 0 GAO 0 0A0
‘1 (7.8)
CH,
1 7 1"
(3;vo O OAOJ ()2vo
I1

7.2.3 Determination of MA grafted by titration

Purification

The MAPP extrudate, which contains some unreacted MA, is dissolved by
refluxing in xylene at 110-120°C for 45 min. The hot solution is then washed with excess
acetone in order to precipitate out the polymer and extract unreacted MA in the solvent.

About 1 g of the precipitate is then used for titration.

63
M

Solutions of 0.05 N ethanolic KOH and 0.01 N ethanolic HCl were prepared. The
KOH solution was standardized against a solution of potassium hydrogen phthalate, and
HCl against KOH. A known amount (~ 1 g) of the MAPP sample is then dissolved in 50
ml xylene as mentioned earlier. To the hot solution was added 5 ml of ethanolic KOH and
34 drops of 1% thymol blue in dimethyl fonnamide as indicator. This was immediately
followed by back-titration to yellow end point by the addition of ethanolic HCl (V Ha) to
the hot solution. A blank sample (50 ml xylene + 5ml KOH) was also titrated likewise.

The difference between blank and sample is the % anhydride as follows:

1%. anhydride = (V1.66...) - VHC,(,,_,,,,,) * NBC, * 98.06 g/mol * loo/w...”Ie (7.1)

where V is volume in liters, W is weight in grams.

Table 7.1 Titration and IR results for maleated polypropylene blends.

 

 

 

 

 

 

 

MA wt % Initiator % MA Carbonyl Melt Flow Index
on PP wt% on MA incorporated Index (gl10 min)
Titration FT-IR ASTM 1238
Neat PP 0.0 0.0 0.0 5.8
___-9.1 ________ 0- §2_ _______ 9-55 ________ 1 _3_2-__-_
PP- 1% MA ___-(La ________ 0 21. _______ 1.1-29 ________ 2 _4-7___-_
0 3 0.17 0.42 *
___.0-1 ________ 1 _-17___--_-1._7§ ________ 1 sis-___-
PP-2% MA ___-0.2 ________ 1 nan-“1512 _________ *- _____
0 3 0.94 1 61 *
___-0.1- ________ 1 _-‘-19._-_.--__1-8_ _________ *_ _____
PP - 3% MA -__Q_-Z__-.__--1_-22--_-.-_-1§2 _________ * ______
' 0 3 1.08 1 5 *

 

 

 

 

 

 

" Melt flow rate is too high to be measured.

54
The results (Table 7.1) show that the % MA incorporated decreases with increase

in initiator concentration, and a fixed MA concentration to start with. This can explained
by the fact that increased free radical presence favors dirnerization of MA thus depleting
it. Maximum change in MA incorporated occurs when the initial MA concentration is
increased from 1% to 2%, further increase doesn’t increase the MA grafting onto PP

much.

7.2.4 Determination of MA grafted by IR spectroscopy

The MA content was determined by Fourier transform infrared (FTIR)
spectroscopy (Perkin Elmer System 2000 FT-IR). The purified MAPP sample films (50-
100 um thickness) were prepared using a Carver laboratory press at 180°C with 5-10 tons
force between polyimide (Kapton) films. The spectrum was recorded in the region of
4000 - 400 cm".

An empirical method of analyzing MA content in MAPP films was tried, using
the ratios of the areas of the characteristic carbonyl absorption at 1790 cm" (in anhydride)
and PP absorption bands at 900 cm", the latter being used as the internal standard (Figure
7.2). A calibration curve of these ratios were constructed against the titration values of the
same samples (Figure7.3). This preliminary result should encourage the use of this much

simpler IR method for analyzing MA in MAPP.

65

r: 5 <2 e\en can :x.N .e\o— {\oc .53 a; he «.59on main fin PS»:—

:5
cficv C cam: 0an _ cch

{It/\II. .. .1. (.6

J) z ...-.. 5, .< s
«z .31.: K g SQ >_ 1
. _,

11.11!) 1
l4 1.. . l1- 1:

Esau: é-.-<<:.<-<-. A _. ./

 

 

1111 1'11

(\II\II

.. 31:54:11

 

 

sass-eggiéi 1)

\III’II...
:/\r

{‘11 till.

 

66

 

Carbonyl Index (SiAISPP)

 

 

 

0 0.2 0.4 0.6 0.8 1 12 11.4
% MA incorporated

 

 

 

Figure 7.2 Calibration curve for determining the incorporated
MA content from the FTIR spectrum.

7 .3 Study of Rheological Behavior

The rheological behavior of the samples was determined in terms of viscoelastic
properties by employing a Rheometrics Mechanical Spectrometer (RMS-800) with 25
mm diameter parallel plate at 180°C. The oscillatory shear experiments were done within
the linear viscoelastic range of strain at frequencies from 0.1 to 100 rad/s. The dynamic
mechanical properties like the storage modulus (G’) and loss modulus (G“) were also
measured.

The plot of complex viscosity (11*) vs frequency (0)) shows a dramatic decrease
in viscosity for maleated blends at low 00 though the shear thinning rate decreases relative
to neat polypropylene (Figure 7.4). The plot of G“ vs G‘ known as the modified Cole-

Cole plot (mCC) provides information on MWD, branching and morphology, etc.[55]. In

67

general, data positioned to the right and below the equimodulii line, G‘ = G‘ ‘(Figure 7.5),

indicate that elastic mechanisms dominate the sample behavior, whereas data located to

the left and above the equimodulii line show that the sample behavior is dominated by the

viscous component, also, the broadening of MWD shifts the mCC plot to lower G‘ values

and increases its slope.

The shear rates in an extrusion process are usually 500 sec'1 or more. Such high

shear rates are not achievable on a RMS therefore a time-temperature superposition is

used. An alternative technique would be to use a capillary rheometer.

 

11* (Pa-S)

 

 

 

 

 

 

 

 

 

 

1.005104
_\
i—____NeatPP
i----PP-1%MA
1.00803 . _______ "34%”
\ |_._._PP-3%MA
.............. 1........,.._: ‘_~ -‘ ‘
"h ______ '_-- ........ \..
-__ ~~\\‘...J
1.005102 . .
1.00501 1.005100 1.00501 1.005102
(0 (rad/s)

 

 

Figure 7.3 Complex viscosity vs. frequency of neat PP and
MAPP with varying MA content.

68

 

8.00803 ..

6.005403 1.

G" (Pa)

4.00803 1

2.00803 -1

 

0.00800
0.00800

 

 

1 .00803

2.00803

3.00803

6‘ (Pa)

4.00803

__-l

u

 

___NeatPP

!_ - _PP-3%MA
(- -.-_..PP-2%MA
:_ _ _PP-1%MA

 

 

Figure 7.4 Modified Cole-Cole (mCC) plots of neat PP and
MAPP with varying MA content.

7.4 Melt Flow Index

The melt flow index of the blends were determined in a Ray-Ran melt indexer at
230°C under a load of 2.16 kg (ASTM D1238). The increase in melt flow index (Table
7.1) of the maleated blends is due to increased chain scission. For some of the blends the
increase in melt index was so high that it was not possible to accurately measure the melt
index. Many studies [54,56-57] have being conducted with different additives that could

inhibit chain scission without affecting the cross-linking capability of the maleated

blends.

 

Chapter 8 ._ -_-_-_____h

Conclusions & Recommendations

8.1 Conclusions

l”N

atural fibers possess a variety of appealing properties to be used in thermoplastic
composites of moderate strength. Though most of the natural fiber thermoplastics are still
in development stage, the interest in using them has been growing in recent times. we
end, the biodegradability and "low-cost of natural fibers combined with the

-W ~15“ “a ._ ,- f H” Fem-v4 muse-n waca». “m. ”Mu ”a— a Mm

reprocessability 01?. 99.988110811181188. . alight-Play.11.19.1192. role behind MST-121.081.195.92- i!)

 

1:113 11919...-

r811 Development of Kenaf Reinforced Polypropylene Composites

Composites of kenaf and polypropylene were prepared by mixing in a twin screw
extruder followed by injection molding. A systematic study of the different processing
variables was done with a view to develop optimum processing conditions. The
composite properties were improved by incorporation of maleated polypropylene

WW”. nee- ~ -51

(MAPP) as a coupling agent or by treatment of kenaf with a silane coupling agent. Since
each of these variables affects the composite properties in its own way and also the
variables are interdependent to a certain extent, the system presents a multivariable

problem. Therefore, composites with different composition of fiber, resin and interfacial

Lagents were prepared and characterized.

69

70
51.2 Improvement in Mechanical Properties

The inclusion of MAPP resulted in composites with good mechanical properties
as compared to the uncoupled composites. Tensile and flexural strength and failure strain
increased with the addition of MAPP at all levels, with the most significant increase
occurring with the addition of 2% MAPP. Further addition of MAPP resulted in only
slight improvement of the properties. The impact strength increases but the modulii are
relatively unaffected.

The ability of MAPP to enhance mechanical properties supports the theory of it
having the potential, to improve adhesion between the matrix and fibers. This was
attributed to the anhydride functionality in the modified polymer which served to form
bonds between the polar lignocellulosics and the non-polar thermoplastic component. A
strong interfacial bond between the fiber and matrix allows the matrix to efficiently
transfer stress to the fibers. Also a strong interfacial bond can prevent the propagation of
microcracks along the fiber length.

The tensile modulus increagedwrm the fiber 90111991,...‘59119- the 11919.--.9119. (breaking

mum _mn—a- .--

 

Stiff-5.15212811199-ISIQPYCIY. unaffected. The y failure __strain and “the. impact strength fell

sharply when the fiber content W3§i§91933991 The treatment of kenaf with a silane

MM'W WMH‘I’P

coupling agent increased _ the. impact strength. toughness” and the failure strain, other

properties were relatively unaffected. Combination of: silane treatment and addition of

. _... .4 - 1
4*Mg—v-1-—A-wvm~,....—.mnw -

MAPP-could _be used to improve thehstiffness of the composite without decreasing” the

.9111??? strength,

71

The process conditions and the composition can be suitably modified to fabricate
either composites that exhibit elastic modulii approaching glass-fiber reinforced materials
or composites that duplicate the elongation characteristics of the neat PP, while showing

Lat—rproved tensile strengths.

1?.

1.3 Comparison with other Polypropylene Composites

Table 8.1 compares the tensile, flexural and impact properties of the neat PP and
its composite systems containing 20% by wt. of sisal, kenaf, glass and tale. The
comparison is meant as a general guideline and not as an exact comparison, which would
be possible only if all the specimens were prepared and tested under identical conditions.

Addition of glass, sisal or kenaf fibers to neat PP with proper interfacial agents
can improve the overall mechanical properties but to a different degree for each fiber
system. Both the natural fiber composites, sisal and kenaf reinforced, have poorer flexural
modulus and impact strengths (Figures 8.1 & 8.2) compared to the glass reinforced PP.
But the difference is not so significant if one considers the specific strengths (per unit
weight basis). It implies that for a given weight of composite the natural fiber reinforced
would have almost an equal mechanical strength as the glass reinforced.

Talc just acts as filler when added to PP, it increases the modulii and flexural
strength but decreases the impact strength and tensile strength. It produces a low cost
composite with a good surface finish but poor mechanical properties.

Figures 8.1 and 8.2 show that kenaf reinforced PP has a higher flexural modulus
compared to sisal reinforced but much poorer impact strength. The higher modulus is due

to the higher stiffness of kenaf compared to sisal fibers. The poorer impact property of

72

kenaf is possibly due to the irregular shape of kenaf fibers resulting in local stress

Leoncentrations in the matrix.

( Table 8.1 Characteristics of some PP composites.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Property Neat PP PP - Sisal PP - Kenaf PP - Glass PP- Talc
Fiber/Filler (wt %) 0 20 20 20 20
Density, gmlcm3 0.9 1.0 0.95 1.15 1.05
Tensile Strength, MPa 28.4 35.6 41.0 55.0 24.1
Tensile Modulus, GPa 1.2 4.8 2.9 8.3 2.2
Elongation to break, % 300 9.2 5.6 3.5 4.0
Flexural Strength, MPa 34.8 56.4 46.3 75.8 44.1
Flexural Modulus, GPa 1.3 2.3 3.0 4.2 2.1
Izod Impact Strength, Jlm 42.1 89.7 47.6 107.0 21.4
Specific Tensile Strength 31.6 35.6 43.2 47.8 22.9
Specific Tensile Modulus 1.3 4.8 3.0 7.2 2.1
Specific Flexural Strength 38.7 56.4 48.7 65.9 42.0
Specific Flexural Modulus 1.4 2.3 3.2 3.6 2.0
4.5 ,
1
4 ..
E 3.5 -
9,
a 3 ..
3
5 2.5 .
.5
5 .
E 15 .. 12m:- 1' it at; l
3 . , (
fi 1 “ 1116's; 11:21 so A ‘
0 51-1. TI" 11 12"" 1 v? + "fr-*1:- H '
Neat PP PP - Sisal PP - Kenaf PP - Glass PP - Talc l

 

< Figure 8.1 Flexural Modulus for some PP composites.

 

73

 

‘ 120 --

 

8

 

4
*1
_,.._ ___-__fl—a—M

 

 

 

Notched Izod Impact Strength (Jlm
8

 

 

 

 

 

 

 

 

 

 

 

O

 

L I
7 T

Neat PP PP - Sisal PP - Kenaf PP - Glass PP — Talc

1
fl

 

 

 

(Figure 8.2 Notched Izod Impact Strength for some PP composites.

Y”8.1.4 Applications

Kenaf - PP composites have distinct advantage of a substantially low density, an
important factor in applications where light weight is imperative. Material cost savings
resulting from the reduced use of PP can be significant. Judicious use of these fibers will
make it possible for natural fibers to define their own niche in the plastics industry, and in
manufacture of low-cost, high-volume composites for wide variety of applications.

As mentioned in Section 8.1.3, the strength per unit weight (specific strength) of the
natural fiber reinforced composites is usually higher or close to that of synthetic fiber
reinforced composites. This performance is afforded at low costs with an added advantage
of biodegradability. Thus these composites can potentially substitute glass-fiber composites
in applications where the strength can be traded off for less weight, lower cost, ease of

recyclability or energy recovery.

74

Potential areas of application for such composites include traditional injection
molded articles, consumer disposables, replacement for PVC laminates and profiles,
automotive interior parts, etc. Commercial production of such composites would open a
new avenue for the utilization of kenaf fiber and represent value addition to the

1 agricultural crop.

8.2 Recommendations

Inspite of its high stiffness and strength potentlal kenaf fiber did not producem as

IW 50" 4m

 

 

high a degree of reinforcement as would be expected for any synthetic fiber. It is believed

_Ild'r‘sra. _a. j” “wad-.1 \-

that this could be due to several factors such as:

_m‘.."' rmm’WW-F Hm I‘ve‘ mm“ J-n-DM

 

i) length reduction brought about by the intense shear forces in extruder and in) eetion

“Asa-Gun.MLMMWMV‘thwHWa1HW-'-Nt ‘M‘nl-‘w.n..-.Hm -W- a, Walt-mfi'vs 1L

molder.

“ac-M”

ii) poor interfacral adhesion between kenaf fiber and PP matrix

iii) imprpper_di§persigg [of the fibers in the matrix.

y-W W..." Wbluiwaw

To overcome these problems a thorough understanding of the variables which

influence this behavior rs required. Optimum compounding and processing conditions!

'5“ MW- M‘HUNW--'“fl~M\W*Mww1rq~uy:-W 'H" pm “ H11 ‘J-v—

 

need to be determined which would reduce the attrition of fibers. In addition, there is a

 

scope for Wm agents which could function better than the ones used

 

currently. Some technique or dispersion aids need to be developed to ensure proper

dispersion of fibers to maintain homogeneity of the composite product.

75

Other major problems which hinder the commerc1ahzatlon of kenaf fiber

"A

 

4A.. ..._
~ 0‘ “M an -v-‘u “WI -.—. we .-. fio-l 1.1.. An.“

composites is their poor stiffness - impact balance and poor water resistance. Research

”I ~m -M . I..- I ’ —'I.MI l~h\mW

 

 

studies [15, 20-23, 25-26] are being conducted to understand and solve these problems.

Use of a biodegradable polymer sueh as e thermoplastlc polylactlde (eorn based

.“ \pm

plastic) with natural fibers is recommended t9. make 9. composite which is fully

.W—aw. adv v“: W—u‘r‘th

 

"W .rf.” __ H." 1,". “Ad-o Irv-11"! ‘0'! .. In;

 

biggegmregables This would be a completely new area requiring study of the
compatibilization between polylactide and kenaf. Products developed from these
composites could replace existing non-agricultural based plastics used in disposables and
other consumer products.

Use of natural fibers in woven or non-woven met form is recommended because it

P" vym ..x .r “Mu. ‘ -,

1..-, n'L—v’

is believed thet such contmuous fiber composnes would have better mechanical

AW-qr-n a». -‘_-,,‘rg ~r~v

{Emperties than this shortrfibqrrsinfqrced~

3"

10.

11.

12.

13.

14.

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”lllllllllllllll“