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thesis entitled

COMPOSITE OF WOOD FIBER AND MIXED
RECYCLED THERMOPLASTICS

presented by

SUNETRA ROJANARUNGTAWEE

has been accepted towards fulﬁllment
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MASTER degree in W

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COMPOSITE OF WOOD FIBER AND MIXED RECYCLED THERMOPLASTICS

By

Sunetra Rojanarungtawee

A THESIS

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

MASTER OF SCIENCE

School of Packaging

1998

ABSTRACT

COMPOSITE OF WOOD FIBER AND MIXED RECYCLED THERMOPLASTICS

By

Sunetra Roj anarungtawee

The effect of mixed resins in different proportions on the mechanical properties of a
plastic/wood ﬁber composite was investigated. Polypropylene (PP) and high density
polyethylene (HDPE) represented the mixed matrices. Aspen hardwood ﬁber served as
the reinforcement. In the continuous phase, the composition of PP and HDPE was varied
from 0% to 100% by weight. The mixed resins and wood ﬁber were compounded in a
constant ratio of 60% matrix and 40% reinforcement by a twin screw extruder operating
at the PP and HDPE melting points, 180°C and 150°C respectively. At 180°C, the
maximum ultimate tensile strength was achieved at 30% PP/70% HDPE. 10% PP/90%
HDPE had the highest modulus of elasticity. At 150°C, only two variations of 0%
PP/100% HDPE and 30% PP/70% HDPE were processible. The comparison between
two ratios revealed higher tensile strength with a 100% HDPE matrix. The modulus did

not differ signiﬁcantly at the two compositions investigated.

To my parents, Phong Roj anarungtawee and France Euaritrakul.

iii

ACKNOWLEDGEMENTS

I would like to express my gratitude to my major professor, Dr. Susan Selke, Ph.D.
(School of Packaging, Michigan State University), and my committee members, Dr. Jack
Giacin, Ph.D. (School of Packaging, Michigan State University) and Dr. Indrek Wichman
(Department of Mechanical Engineering, Michigan State University) for their guidance

and academic support.

I also wish to thank Dr. Mike Rich and Mr. Brian Rook from the Composite Materials
and Structures Center for their instructions and frequent help in the use of the UTS and
extruder and I would like to thank Adedejo B. Oladipo for taking the time to train me on
extruder and compression molding operations. Special thanks to Ms. Ubonrat
Siripatrawan and Ms. Kunlakarn Lekskul for their assistance in statistical analysis and

statistics soﬂwares. My appreciation also goes to Ms. Sudawan Supachokouychai.

I would especially like to thank my family for their incredible patience and support.

iv

TABLE OF CONTENTS

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

LIST OF FIGURES ................................................................................. xi

INTRODUCTION .................................................................................... 1

CHAPTER 1

LITERATURE REVIEW ........................................................................... 6
Prediction Of Properties ................................................................... 16
Previous Research .......................................................................... 23

CHAPTER 2

MATERIALS ........................................................................................ 30

CHAPTER 3

METHODS .......................................................................................... 34

CHAPTER 4

RESULTS ............................................................................................ 38
180°C Compounding temperature ....................................................... 38
150°C Compounding temperature ....................................................... 39
Temperature effect ......................................................................... 40

CHAPTER 5

DISCUSSION ....................................................................................... 48
180°C Compounding temperature ....................................................... 48
150°C Compounding temperature ....................................................... 50
Temperature effect ......................................................................... 51

CHAPTER 6

CONCLUSIONS .................................................................................... 52
RECOMMENDATIONS ........................................................................... 53
APPENDICES ....................................................................................... 54
BIBLIOGRAPHY ................................................................................... 71

vi

LIST OF TABLES

Table 1- The effect of ﬁber orientation and stress

direction on the reinforcement efficiency .............................................. 12
Table 2- The relationship between ﬁber orientation and so .................................... 20
Table 3- % Dry weight of organic components in woods ...................................... 32
Table 4- Matrix composition ........................................................................ 34
Table 5- Set temperature in the extruder under PP melting point ............................ 35
Table 6- Set temperature in the extruder under HDPE melting point ........................ 35
Table 7- Tensile strength in the lengthwise direction at 180°C .............................. 41
Table 8- Tensile strength in the crosswise direction at 180°C ................................ 41
Table 9- Tangent modulus in the lengthwise direction at 180°C ............................. 42
Table 10- Tangent modulus in the crosswise direction at 180°C ............................. 42
Table 11- Tensile strength in the lengthwise direction at 150°C ............................. 43
Table 12- Tensile strength in the crosswise direction at 150°C .............................. 43

vii

Table 13- Tangent modulus in the lengthwise direction at 150°C ........................... 43

Table 14- Tangent modulus in the crosswise direction at 150°C ............................. 43
Table 15- Properties of PAXON® AD60-007 .................................................. 54
Table 16- Properties of PRO-FAX 7823 ......................................................... 55
Table 17- Tensile strength (lb/in2) data in the lengthwise direction under 180°C. . . . . ....58
Table 18- Tensile strength (lb/in2) data in the crosswise direction under 180°C .......... 59
Table 19-Tangent modulus (Mpsi) data in the lengthwise direction under 180°C ......... 60
Table 20- Tangent modulus (Mpsi) data in the crosswise direction under 180°C ......... 61
Table 21- Tensile strength (lb/inz) data in the lengthwise direction under 150°C ......... 62
Table 22- Tensile strength (lb/inz) data in the crosswise direction under 150°C ........... 62
Table 23- Tangent modulus (Mpsi) data in the lengthwise direction under 150°C. . . . . ....63
Table 24- Tangent modulus (Mpsi) data in the crosswise direction under 150°C ......... 63

Table 25- One-way Analysis of Variance of tensile strength in
the lengthwise direction over 7 treatments under 180°C ........................... 64

Table 26-- One-way Analysis of Variance of tensile strength in
the crosswise direction over 7 treatments under 180°C ........................... 65

Table 27- One-way Analysis of Variance of tangent modulus in
the lengthwise direction over 7 treatments under 180°C ........................... 65

viii

Table 28- One-way Analysis of Variance of tangent modulus in
the crosswise direction over 7 treatments under 180°C ............................ 66

Table 29- T-test of tensile strength in the lengthwise
direction over two treatments under 150°C .......................................... 67

Table 30- T—test of tensile strength in the crosswise
direction over two treatments under 150°C .......................................... 67

Table 31- T-test of tangent modulus in the lengthwise
direction over two treatments under 150°C .......................................... 67

Table 32- T-test of tangent modulus in the crosswise
direction over two treatments under 150°C .......................................... 68

Table 33- T-test of tensile strength of 0% PP/100% HDPE in the
lengthwise direction over two diﬁ'erent temperatures .............................. 68

Table 34- T-test of tensile strength of 0% PP/100% HDPE in the
crosswise direction over two different temperatures ............................... 68

Table 35- T-test of tangent modulus of 0% PP/100% HDPE in the
lengthwise direction over two different temperatures .............................. 69

Table 36- T-test of tangent modulus of 0% PP/100% HDPE in the
crosswise direction over two diﬂerent temperatures ............................... 69

Table 37- T-test of tensile strength of 30% PP/70% HDPE in the
lengthwise direction over two different temperatures .............................. 69

Table 38- T-test of tensile strength of 30% PP/70% HDPE in the
crosswise direction over two different temperatures ............................... 70

Table 39- T-test of tangent modulus of 30% PP/70% HDPE in the
lengthwise direction over two different temperatures .............................. 70

ix

Table 40- T-test of tangent modulus of 30% PP/70% HDPE in the
crosswise direction over two different temperatures ............................... 70

LIST OF FIGURES

Figure 1- Tensile strength in the lengthwise direction at 180°C .............................. 44
Figure 2- Tensile strength in the crosswise direction at 180°C ................................ 44
Figure 3- Tangent modulus in the lengthwise direction at 180°C ............................. 45
Figure 4- Tangent modulus in the crosswise direction at 180°C .............................. 45
Figure 5- Tensile strength in the lengthwise direction at 150°C .............................. 46
Figure 6- Tensile strength in the crosswise direction at 150°C ................................ 46
Figure 7- Tangent modulus in the lengthwise direction at 150°C ............................. 47
Figure 8- Tangent modulus in the crosswise direction at 150°C .............................. 47

xi

INTRODUCTION

Disposal handling, landﬁlls, has faced the problem of overwhelming garbage. The
generation of municipal solid waste (MSW) has increased whereas the availability and
the number of landﬁlls have declined over the years. In 1996 there were only 3,091
landﬁlls, a decrease from approximately 8,000 in 1988 ( Goldstein, 1997). The decrease
results from limited landﬁll capacity, strict Environmental Protection Agency (EPA)
requirements and the diﬁiculty of locating new sites due to the long approval process

and public resistance (Feamcombe ,1995).

In order to solve the disposal crisis, EPA recommended four alternatives: source
reduction, recovery, incineration and landﬁlling. Source reduction or waste prevention is
the top priority to diminish the quantity or toxicity of any material in the ﬁrst place before
it becomes solid waste (EPA, 1997). Recovery is basically to reprocess the material,
which is either industrial scrap or post consumer waste. This method not only saves
natural supplies and energy but also increases landﬁll space (F eamcombe, 1995).
Incineration or waste combustion is simply to burn MSW in incinerators. This technique
provides the beneﬁts of substantial volume reduction and energy recovery. However, it
requires well equipped facilities and expensive investment. In addition, air pollutants and

toxic ash such as chlorinated dibenzodioxins and dibenzofurans released

1

after the burning process become health concerns (Denison & Ruston, 1990).
Landﬁlling, the oldest and the most common method, is expected to take care of any
material that is not qualiﬁed for the previous options (F earncombe, 1995). The
disadvantages of this solution are the limited capacities and public conﬂict about siting.
In addition, the leakage of liquid from the waste into ground water leads to water
contamination (Selke, 1994). On the whole, recycling, so far, seems to get the most
public support, compared to other solutions for post consumer solid wastes. However,

success depends on community participation, which is one part of the recovery procedure.

Recycling begins with collection, consisting of curbside collection, drop-off centers, buy-
back centers, deposit systems and commercial collection. Each selection requires some
simple separation from the participants, such as separation of paper from plastic. The
more speciﬁc material sorting and recovery processes are done at Materials Recovery
Facilities (MRFs) (EPA, 1997). Recycling can be classiﬁed into three groups: primary,
secondary and tertiary. Primary recycling is to utilize recovered material to make the
same product as the virgin material does. For instance, aluminum cans are reprocessed to
make aluminum cans. Secondary recycling is to use recycled material to make lower
quality products such as plastic lumber. Tertiary recycling is basically pyrolysis. The
substrate’s structure is broken into simple forms by the combination of heat and an air

deﬁcient condition. As a result, the small molecules in the form of liquid and gas become

useful fuel (Selke, 1994).

Packaging and containers are the largest part of MSW in landﬁlls. In 1995, they were

72.9 million tons or 35.0% of the 208 million tons of total wastes. It was estimated that
they will continue to grow to 36% by 2000 and 38% by 2010. Among the variety of
packaging and containers in landﬁlls, plastic containers and packaging have shown a fast
increase. In 1960, there was only 120,000 tons or, 0.1% of total generation and in 1995,
it went up to 7.7 million tons or 3.7% of total waste generation. The constituents are
polyethylene terephthalate (PET), high density polyethylene (HDPE), low density
polyethylene (LDPE), linear low density polyethylene (LLDPE), polyvinyl chloride
(PVC), polystyrene (PS), polypropylene (PP) and other resins. The sources mainly are
from soft drink bottles, milk bottles, base cups, ﬁlm goods such as bags and sacks, and
other plastic packaging such as coatings and caps. In 1995, discarded plastics were

10.6% of total packaging and containers (EPA, 1997).

These post-consumer plastic wastes have worried the responsible organizations. Firstly,
they last forever in the landﬁlls because of their persistent property. Secondly, the light
weight but large volume of plastics increases transportation costs of recovery processes.
The loose plastic bottles occupy 100 cubic yards/ton whereas paper takes up only 4 cubic
yards/ton (Steuteville, 1995). Obviously, shredding or crushing processes are needed to
decrease the volume (Curlee & Das, 1991). Thirdly, the single use products for
convenience increase the deposit of packaging materials into landﬁlls. In order to relieve
the problems, new technologies are developed to make the plastics susceptible to certain
environments such as biodegradability and photodegradability. However, there are some

arguments over whether or not it really ﬁmctions (Wolf & Feldman, 1991).

The use of reclaimed resins is another eﬁ‘ective effort. A number of reclamation
techniques have been developed to obtain well-sorted resins that can substitute for or
blend with the virgin resins in many applications (Bisio & Xanthos, 1994). However,
chances are that the separated resin is contaminated by other resins. The adulteration
usually causes adverse results in product performance, mainly due to the incompatibility

of the resins.

There have been investigations of utilizing the reclaimed resins with a reinforcement in
the form of composite materials. The addition up to 40% by weight of ﬁber
reinforcement is common (Birley et al., 1992). It was found that the products are less
sensitive to the impurities. As a result, the contamination does not signiﬁcantly affect the
product quality. On the other hand, it is interesting to see how much of the contaminant
can appear in the dominant resin stream without lowering the product strength and there
is also the possibility of synergistic eﬁ‘ects at certain levels. Therefore, the purpose of
this study was to investigate the performance of composite made of mixed plastics and
wood ﬁber, and to compare the mechanical properties of mixed plastics-based composite

with the single polymer-based composite.

For this project, polypropylene (PP) and high density polyethylene (HDPE), representing
the impure resins, functioned as the matrix, and wood ﬁber from aspen hardwood was
used as the reinforcement. HDPE was selected because of its high recycling rate. PP was
chosen because it is often a contaminant in the recycled HDPE. Six to seven percent of

PP in the HDPE stream does not make any signiﬁcant change in HDPE properties (Rader

et al., 1995). The mixed ratios vary from 0 to 100% of each resin. The variation shows
how one resin type affects the other as the contaminant and if the contaminant level
aﬁ‘ects the product performance. Wood ﬁber was a choice because it is plentiful, light
weight, non-toxic and has great strength (Marcin, 1991). It is also low cost, about 40%
the cost of glass ﬁber (Babyak, 1993). The combination of resins and wood ﬁber was
maintained at 60% of mixed resins and 40% of wood. To control the variation of the
quality of recycled resins, the virgin resins were used. Product performance was

evaluated by the mechanical properties of tensile strength and modulus of elasticity.

Chapter 1

LITERATURE REVIEW

A composite can be deﬁned in different ways depending on which principles and
standpoints are used to identify it. It can be as broad as anything consisting of two or
more dissimilar components on microscopic view (Hull, 1981). On the other hand, it can
be narrowed down to the point that it is a composite only if, ﬁrst, it illustrates a distinct
property that is superior to the original materials; second, the volume fraction of one
constituent is greater than 10%; third, the property of one part is about 5 times greater
than the other (Agarwal & Broutman, 1990). It also can be described as a man-made
multiphase material that consists of chemically distinct constituents having an obvious
interface (Callister, 1994). Despite differences in deﬁnitions, the ultimate goal is to
create a composite that unites the advantageous attributes from the constituents and

illustrates superior properties to the individual substrates, regardless of any point of view

(Hull, 1981).

The properties of composites greatly depend on the properties of the substrates, the

7
distribution of components and the interaction between them. Consequently, the

geometry of the reinforcement, one of the components, needs to be speciﬁed in terms of
shape, size, and size distribution. The shape of the discontinuous materials can be
referred to as spheres, cylinders, and platelets. Size and size distribution determine the
composite structure and, when volume fraction is included, they also determine the

interfacial area between matrix and reinforcement (Agarwal & Broutrnan, 1990).

In addition, the properties also depend on the concentration, the concentration distribution
and orientation of reinforcing materials. The concentration of the reinforcement is easily
adjusted from the weight or volume ﬁaction of the components, and it is considered the
individual most powerful factor controlling the composite properties. The concentration
distribution indicates the uniformity of the composite texture, which results in
homogeneous physical and mechanical properties. A nonuniform characteristic lowers
the material strength because the failure will take place at the weakest area. Therefore,
the result does not represent the total strength of the material. The orientation of the
reinforcement determines how the properties of the composite are in diﬂ‘erent directions
in the system. If the properties of the material are the same regardless of the direction,
such a material is an isotropic material. On the other hand, an anisotropic material

illustrates different properties in different directions (Agarwal & Broutrnan, 1990).

The composite components can be classiﬁed into two types. The continuous phase is
called the matrix and a discontinuous phase dispersed into the matrix, which can be one

material or more, is named reinforcement or reinforcing material (Agarwal & Broutrnan,

8
1990). In this experiment, the polymers, HDPE and PP, are the matrices and wood ﬁber

serves as reinforcement.

The matrix has several roles. First, it keeps the reinforcements together and protects them
from surface imperfection as a result of environmental attack. A surface ﬂaw leads to
crack propagation and eventually to failure at a small extent of applied stress. Second, it
takes an external load and evenly transfers most of the burden to the reinforcers. The
geometry of reinforcement determines how much load the reinforcement can take. In the
case of ﬁber reinforcement, the matrix not only shelters the ﬁbers but also keeps ﬁbers
from damaging one another. The softness and plasticity of the matrix prevent crack
spreading out from one ﬁber to another (Callister, 1994). Third, the continuous phase
secures the reinforcer arrangement if there is any (Birley et al., 1992). They are
commonly classiﬁed into polymer, metal and ceramic. The polymers are the focus of
interest in this experiment. There are two types of polymers. One is thermosetting and
the other is thermoplastic polymer. Therrnosets develop cross linkages when they are
heated in the so-called curing process. Once heated, they will not remelt but decompose.
Examples of thermosets are epoxides, polyesters, phenolics, ureas and melamine. The
polymer chains in thermoplastics are developed in linear or branched form. They remelt
and can be reprocessed by heat and pressure. Examples of thermoplastics are PE, PP, PS,

and Polyether-ether ketone (PEEK) (Agarwal & Broutrnan, 1990).

Thermosetting and thermoplastic matrices require diﬂ‘erent processing parameters. The

operation for thermosets can be manually done at room temperature due to their low

9
viscous liquid state. Therefore, the composites made of thermosetting polymers are

suitable for small production scales. The drawbacks of these matrices are part ﬁ'agility,
solvent sensitivity and need of chemical reaction leading to many problems. In addition,
the reactive unprocessed thermosets have a relatively short shelf life, prolong the
processing time and generate hard-to-recover material. Thermoplastic-based composites
beneﬁt economically from large production scales due to the need for a high temperature
and pressure process which demands fully-automated manufacturing. The advantages of
thermoplastic polymers are the promotion of composite toughness and long shelf life

(Bigg et al., 1988).

The reinforcement, in particular its geometry, plays a signiﬁcant role in composite
strength. Particle and ﬁber reinforcements are two main categories which are also used as
the composite classiﬁcation. A particle reinforcement can be anything that has
approximately equiaxial dimensions such as spheres, cubes, tetragons and platelets
(Agarwal & Broutrnan, 1990). It can be divided into large and small particles which are
referred to as large-particle composites and dispersion-strengthened composites,
respectively. Large particles, or so-called ﬁllers, are usually more rigid and solid than the
matrix. These particles limit the movement of the matrix surrounding them. The
amelioration of mechanical properties depends on the matrix-reinforcement adhesion. In
this case, the applied load is taken by both matrix and reinforcement. Particles in
dispersion-strengthened composite are quite small sizes. The diameter ranges from 0.01
to 0.1 pm or 10 to 100 nm. The strengthening mechanism microscopically takes place in

the way that the matrix takes the major applied load and the reinforcement blocks the

10
dislocation movement in the matrix. As a result, plastic deformation is limited, which

leads to the improvement of mechanical properties in terms of tensile strength, yield
strength and hardness (Callister, 1994). On the whole, the particles work by promoting
the stiffness of the particulate composites but they are not as effective in taking the load
from the matrix as ﬁber reinforcements. Especially, when hard particles are included in a
brittle matrix, they create stress concentration in the composite. Consequently, the

system strength is reduced (Agarwal & Broutrnan, 1990).

Fiber, by nature, has two different dimensions. One, length, is relatively much longer
than the other, cross sectional diameter (Agarwal & Broutrnan, 1990). The characteristic
of a great length-to-diarneter ratio makes the small ﬁbers become stronger than the bulk
material (Callister, 1994). Fiber reinforcers produce the ﬁber reinforced composites, or
ﬁbrous composites. Based on the standpoint of properties, there are two kinds of ﬁbrous
composites: single-layer and multi-layer. The idea of single layer is that the composite is
composed of many separated layers whose orientation and properties are identical. Short
ﬁber reinforced composites made from compression molding process are included in the
single-layered category even though they do not show an obvious separation between
each layer and have preferential ﬁber orientation. The multi-layer composites consist of
single-layered composites having diﬁerent orientations or even diﬁ‘erent components. To
focus on one individual layer, the reinforcement can be continuous ﬁbers, which are
simply long ﬁbers, or discontinuous ﬁbers, as the name implied, short ﬁbers. Long ﬁbers
generate continuous ﬁber reinforced composites and short ﬁbers make up discontinuous

ﬁber reinforced composites (Agarwal & Broutrnan, 1990).

1 1
Fiber length is the key factor to judge whether or not such ﬁbers are either short or long

ﬁbers. Usually, the ﬁber length of continuous ﬁber is 15 times or more the critical length,
and anything less falls into discontinuous ﬁber. The critical length can be calculated

according to Equation 1.

I, = 0761/22; (1)
1c is critical length.

oyis ultimate or tensile strength of ﬁber.

d is ﬁber diameter.

Tc is shear yield strength of the matrix or the ﬁber-matrix bond strength.

When the ﬁber length equals the critical ﬁber length, the middle of the ﬁber takes on the
maximum applied stress. As the ﬁber is longer, the stress taking area is also broader.

Consequently, the strengthening mechanism becomes more effective (Callister, 1994).

Fibers in continuous ﬁber reinforced composites primarily function as load carriers in the
burden direction. The strength of the composites is determined by the ﬁbers. The matrix
is only the binder and protector. Continuous ﬁbers are able to be oriented into either
unidirection or bidirection. High strengthzweight ratios and anisotropic adjustability are
two beneﬁcial attributes of oriented ﬁber-reinforced composites (Agarwal & Broutrnan,
1990). Strength:weight ratios are speciﬁc modulus and speciﬁc strength which are the
ratio of modulus to density and the ratio of tensile strength to density, respectively

(Nielsen & Landel, 1994). Fibrous composites show superior strength to metals on a

12
weight basis perspective. The anisotropic adj ustability lets the composites take advantage

of preferable properties in a certain direction. In addition, the ﬂexibility of processing
and manipulated structure of ﬁbrous composites create new materials having certain
properties that are impossible to achieve in conventional materials (Agarwal & Broutrnan,
1990). The relationship between ﬁber orientation, stress direction and reinforcement

efﬁciency is shown in Table 1.

Table 1. The effect of ﬁber orientation and stress direction on the reinforcement

 

 

efficiency.
Fiber orientation Stress direction Reinforcement
emciency
Unidirection Parallel to ﬁbers 1
90° to ﬁbers 0

 

random orientation and even distribution Any direction in the plane 3/ 8
on a certain plane

 

 

random orientation and even distribution Any direction 1/ 5
in three dimensions in space

 

 

 

Source: H. Krenchel, Fibre Reinforcement, Copenhagen: Akademisk F orlag, 1964
(Callister, 1994).

Short or chopped ﬁbers are similar to the particulate reinforcements. The properties of
the short ﬁber composites are considerably sensitive to the ﬁber length and the matrix
ﬁmction is more important than just a binder. In general, random orientation is expected
in short ﬁber reinforced composites (Agarwal & Broutrnan, 1990). The tensile strength is
determined by the bond between matrix and ﬁbers. In the case of wood ﬂour and
polymer composites, the ﬁber orientation is a more critical factor to the modulus than to
tensile strength, whereas the polymer-ﬁber bonding plays a more important role in tensile

strength than in modulus (Maldas & Kokta, 1994).

 

13
There are several advantages of short ﬁber reinforcement. At the same weight fraction,

the short ﬁber possesses more speciﬁc surface area than do the long ﬁbers. The ﬁber
dispersion is quite even. It establishes the dimensional stability and ﬁber damage
resistance during processing. Unlike long ﬁbers, short ﬁbers have no entanglement
problem and the other typical properties of the ﬁber are still the same (Maldas & Kokta,

1994)

Wood ﬁbers are one of the potential reinforcements. They are naturally plentiﬁrl organic
ﬁbers. In MSW, there was about 39 percent by volume of wood, paper and paperboard
(Pieper, 1993). Wood ﬁbers also offer strength that is close to that of the traditional
reinforcing materials. The strength and modulus of wood pulp ﬁbers are comparable with
those of glass ﬁbers in the same unit weight. The wood ﬁber composites show the same
or higher stiﬂ‘ness per weight than the steel, aluminum, glass ﬁber composites and talc-
contained polyoleﬁns (Woodharns et al., 1984). As a result, cost effectiveness is an
outstanding advantage. The other beneﬁts are low abrasions to machinery, non-hazardous
substance generation, low density and the possibility of surface modiﬁcation (Beshay et
al., 1985). However, there are some limitations. The low processing temperature, about
200°C, of wood ﬁbers makes them unavailable for some polymers that require high
melting temperature. The water sorption of wood ﬁbers causes a weak interface between
the matrix and wood ﬁbers (Chtourou et al., 1992), and leads to biodegradation after

repeated exposure (Babyak, 1993).

Composites of thermoplastic polymers and wood ﬁber yield poor mechanical properties

14
due to the incompatibility between them. The thermoplastics, especially polyoleﬁns, are

hydrophobic whereas wood ﬁbers are hydrophilic. The difference causes poor ﬁber
distribution into the matrix and poor interfacial bonds between ﬁber and matrix. As a
result, the ﬁber strength cannot contribute to the composite strength as much as it is
supposed to be. This phenomenon leads to easy failure of composites in mechanical

testing (Chtourou et al., 1992).

According to Chtourou et a1. (1992), the interfacial bond between matrix and ﬁber plays
an important role in the improvement of mechanical properties. It can be contributed by
ﬁve mechanisms: adsorption and wetting, interdiffusion, electrostatic attraction, chemical
links, and mechanical adhesion. In the case of composites consisting of hydrocarbon
polymer matrices and wood ﬁbers, wetting and mechanical adhesion may be the main

inﬂuences.

The equipment is another factor affecting the composite properties. The preferential
orientation degree usually occurs from the ﬂowing of molten streams in the injection
molding machine. The outer layers face higher shear stress than do the inner layers. As a
result, ﬁbers on the surface of the molded piece are arranged along the ﬂow direction
whereas those inside are 90° to the ﬂow. In a compression molding machine, a random

orientation in three dimensional space should be observed (Chtourou et al., 1992).

It is apparently that mechanical properties are the important criteria for material

evaluation and selection. Tensile testing, one type of mechanical testing, is the indicator

15
of the ability of a material to resist the tension force that elongates the object at a constant

rate (Nielsen & Landel, 1994) until the breakage occurs (Shah, 1984). In tensile testing, a
stress-strain diagram is established, and the following values can be obtained: stress (Y -
axis), strain (X-axis), elongation, yield point, yield strength, proportional limit, elastic

modulus, ultimate strength and secant modulus (Shah, 1984).

In this work, the point of interest is the tensile strength and modulus of elasticity of a
composite of mixed PP/HDPE and wood ﬁber. The tensile strength or ultimate strength
is the measurement of the maximum load taken by the specimen. In other words, it is the
highest nominal stress (engineering stress), which is the ratio of maximum force to the
cross-sectional area before the load is applied (Felbeck & Atkins, 1984). The modulus of
elasticity or Young’s modulus is simply the slope of the initial straight portion of the
stress-strain curve. It determines the stiffness of the material (Shah, 1984). In the case of
a non-linear curve, the tangent or secant modulus is applied. The secant modulus is the
straight secant line drawn from the origin to a certain point of the non-linear curve. The
tangent modulus is the linear line drawn barely to touch the curve at any segment to get
the slope value (Callister, 1994). In this experiment, the tangent modulus equals the

modulus of elasticity because it is taken at the very beginning of the stress-strain diagram.

The tensile results are inﬂuenced by molecular orientation, specimen making process,
strain rate and temperature. A force application that is parallel to the molecular alignment
is higher than a force application that is perpendicular to the orientation and vice versa for

the elongation. The injection-molded samples result in higher tensile strength values than

16
the compression-molded samples. The tensile strength and modulus are proportional to

the rate of strain: the higher the strain rate, the higher the tensile values. On the contrary,

the increase in temperature reduces the tensile strength and modulus (Shah, 1984).

There are some drawbacks in the stress-strain tests, however. A difficulty in result
interpretation can be the case if the stress keeps changing from place to place due to
variation in the specimen. Also, chances are that the result may reﬂect interference by
other possible reactions instead of predicted phenomena. For instance, the recorded stress
may result ﬁ'om the spherulitic failure in crystalline polymer instead of amorphous

portion rearrangement as usual (Nielsen & Landel, 1994).

Prediction of properties

There are several equations for property prediction of composite materials. The most

popular equation is the rule of mixtures.

According to Callister (1994), in particulate composites, the upper and lower limits of
elastic modulus can be estimated by applying the rule of mixtures as shown in Equation 2
and 3 respectively. The parameters aﬂ‘ected the composite properties are the particle size,
the particle distribution and the volume fraction of the components.

E, = Em V,,, + Ep Vp (2)

E, = (Em Ep)/ (V,,.Ep + Vp Em) (3)

E and V are elastic modulus and volume fraction respectively.

17
Subscripts c, m and p denotes composite, matrix and particle, respectively.

In ﬁbrous composites, the properties are aﬁected by the ﬁber orientation and ﬁber type.
Continuous and oriented ﬁbers result in an anisotropic system. The load applied in
parallel to the ﬁber alignment is called longitudinal loading. The load applied
perpendicular to the ﬁber alignment is called transverse loading. Again, the rule of
mixtures is applied to predict the mechanical properties. In longitudinal loading, it is
assumed that the continuous ﬁbers are identical in properties and size, and oriented

unidirectionally all over the matrix. The composite stress is predicted by Equation 4.

oc= ome+ ofo (4)
V; and V", are volume fractions of ﬁber and matrix respectively.
Vf =A/A. (5)

V,,, = Am/Ac (6)

Equation 4 is derived from Equation 7 by assuming that composite, matrix and
ﬁber phases have the same length.

ooAc = UfA 1+ omAm (7)

o, ,Uf and on. are stresses of composite, ﬁber and matrix respectively.

A f, Ac and A", are cross-sectional area of ﬁber, composite and matrix respectively.

18
If the interfacial bonding between matrix and ﬁbers is perfect in such a way that both

phases take an equal strain. The strain of composite is equivalent to that of matrix and

ﬁber.

ac = em = 8f (8)

cc, 3",, and afare the strain of composite, matrix and ﬁber respectively.

If the system is characterized by elastic deformation, dividing the stress of each phase by

the strain of each phase gives the modulus of elasticity of the composite.

EC = Eme + £7fo (9)

EC, 5,. and Efare elastic moduli of composite, ﬁber and matrix respectively.

In the transverse direction, the external load is applied perpendicular to the ﬁber

direction. The elastic modulus is estimated by Equation 12.

Cc=0m=6f=0 (10)
ec=eme+eij (11)
E.=(E..Ef>/[(1-V;)Ef+ 1012.1 (12)

In the case of short and oriented ﬁber composites, the system is assumed to have an even
ﬁber dispersion and the ﬁber is longer than the critical length. The longitudinal strength

of the composite is predicted in Equation 13.

19
(TS)c =(TS)fV/(1-(1J20)+(TS)’m(1-V/) (13)

(TS), is the longitudinal strength of the composite.
(TS)fis the fracture strength of the ﬁber.

(TS) 3,, is the stress in the continuous phase at failure.

I and 1c is ﬁber length and critical length respectively.

Vfis volume fraction of ﬁber phase.

If the ﬁber length is shorter than the critical length, the longitudinal strength is calculated

by Equation 14.

(”A = (Ira/d)V/+ (TS/nu (1-Vf) (14)

d is the ﬁber diameter.

For discontinuous and randomly aligned ﬁber composites, the elastic modulus is given in

Equation 15.

K is a ﬁber eﬂ'rciency factor determined by Vf and E/Em ratio. It is between 0.1

and 0.6.

According to Bigg et al. (1988), tensile strength of ﬁber reinforced thermoplastic-based

composites can be predicted by applying the rule of mixtures shown in Expression l6.

20
0c = 0p¢p + 0106180 (16)

o; is composite tensile strength.

0;, is polymer tensile strength.

oyis ﬁber tensile strength.

(4,, and ¢f are volume fraction of polymer and ﬁber in the composite respectively.

a] is an efﬁciency factor related to the effectiveness of load transfer between the
matrix and reinforcement.

80 is an emciency factor related to the orientation of the ﬁbers in the composite.

Table 2. The relationship between ﬁber orientation and so.

 

 

 

 

 

Fiber orientation 80
Unidirection 1 .0
Random orientation in a plane 0.33

 

For continuous ﬁbers, 81 is 1.0.
For discontinuous ﬁbers, 81 is affected by the critical aspect ratio, which is the ratio of

length to diameter of a ﬁber (Lee, 1989), of each matrix-ﬁber set.

(L/D)c = (If/2 2'1 (17)
(L/D), is the critical aspect ratio.
07 is tensile strength of the ﬁber.

27 is ﬁber-matrix interfacial strength.

21
81 value depends on each pair of matrix and ﬁber, and is strongly inﬂuenced by the

efﬁcacy of coupling agents which enhance matrix-ﬁber adhesion.

It was found that the random oriented ﬁber works most effectively when

Lf= 10(L/D), (18)

Lf is average ﬁber length.

The critical aspect ratios of several sets of polymer-ﬁber composite are in a range of 20:1
to 50:1. In order to achieve the maximum load transfer capability, the aspect ratio of

ﬁbers should be at least 500: 1.

For the elastic modulus, the rule of mixtures is also applied and exhibited in Equation 19.

Ec=Ep¢p+E/¢ﬂ (19)
e is an efﬁciency factor.
EC, Ep and E f are the elastic moduli of the composite, polymer and ﬁber,

respectively.

However, the factors that are taken into consideration are different between tensile
strength and modulus. The ﬁbers in woven form that do not reinforce the strength of the
composite in the warp direction do enhance the modulus. The interbonding between
ﬁbers and matrix in the case of short ﬁbers does not matter to the modulus as much as it

does to the tensile strength. The fact that the addition of non-strengthening ﬁllers results

22
in increase of modulus only and does nothing with polymer strength is the proof. Based

on these different affected factors, there is no numerical relationship between the

efficiency factors for modulus and tensile strength.

According to Chtourou (1992), there are two equations, based on rule of mixtures, used to

estimate the elastic moduli and the strength at yield of short ﬁber reinforced composites.

Ec=keﬁr*F¢*Vf+E,,,*V,,, (20)
O'czKeﬂ*07*I/f+ a... V... (21)
EC and a“, are Young’s moduli and the strength at yield of the composite.
Efand a; are Young’s moduli and the strength at yield of the ﬁber.
5,, and 0'," are Young’s moduli and the strength at yield of the matrix.
Vfis the volume fraction.
Keﬂ' and keﬂ‘ are the efﬁciency coefﬁcients, depending upon the composite
microstructures such as distribution, orientation and adhesion.
keﬁ‘ is 1/6 when the ﬁber orientation is random in three dimensional space.
keﬂ‘ is 1/3 when the ﬁber orientation is random in the plane.
kc); is 1/2when the ﬁber orientation is random in the angle of 90° in the

plane.

The relationship between Keﬂ' and ﬁber length shown in Equation 22.

23

Iowan-Lem) (22)
L is the ﬁber length.

L, is the critical length.

L, = r * a/Y (23)
r is the ﬁber radius.

Y is the interfacial shear strength.

Previous research

Yam et a1. (1988) investigated the mechanical properties of wood ﬁber/recycled HDPE
composites in comparison to wood ﬁber/virgin HDPE. Aspen ﬁber, a hardwood, and
spruce ﬁber, a softwood, were used. Recycled HDPE was made from chopped post-
consumer milk bottles. The ﬁber and polymer were extruded through a corotating
intermeshing twin extruder at 150°C. The extrudates were compression molded at 150°C
and 4.22 MPa for 10 minutes and cooled under pressure for 15 minutes. The tensile
strength and the elastic modulus of composites made ﬁom recycled HDPE and wood
ﬁber were about the same as those of composites made ﬁom virgin HDPE. There was
also no signiﬁcant difference in mechanical properties between the hardwood composites

and the softwood composites.

Chtourou et al. (1992) studied the composites of recycled polyoleﬁns and wood ﬁbers.
The polyolefms were 95% PE and 5% PP. A mixture of 45% spruce, 45% ﬁr and 10%

poplar produced by chemico-thermomechanical pulp (CTMP) was used as a

24
reinforcement. The composites were made by injection molding and compression

molding. The impact of ﬁber concentration, the effect of ﬁber surface modiﬁcation by
acetic anhydride and phenol formaldehyde, and the effect of moisture exposure on the
composites were evaluated by tensile properties. The result was that the greater the non-
treated ﬁber percentage, the higher the Young’s modulus and the strength at yield. More
than 30% of ﬁber could be incorporated into the composites and at 30% ﬁber content by
weight, Young’s modulus increased 150%. Improvement in tensile strength was
observed in the composites with 10% treated ﬁber. 10% treated ﬁber composites also
displayed lower water sorption and higher mechanical properties than 10% non-treated

ﬁber composites.

Maldas and Kokta (1994) studied the mechanical properties of the composites of recycled
thermoplastics and wood ﬂour. Three types of polymers were used: recycled LDPE,
recycled PP and mixed plastics consisting of 50%LDPE, 15%HDPE, 15%PVC, 5%PS,
5% recycled PET and 10% maleated PP by weight. The reinforcement was maple wood
ﬂour precoated by maleated thermoplastics in different sizes. The degradation of the
molten mixture during processing was reduced by the addition of ﬂame retardant/heat
resistant/antioxidant materials. There were four treatments of 0%, 20%, 30% and 40%
per composite weight of treated and untreated wood ﬂour mixed with each polymer.
Mixing temperatures were 170°C to 175°C for PE, and 180°C to 185°C for PP and
commingled plastics. Compression molding was done at 160°C for PE, 170°C for
commingled plastics and 180°C for recycled PP, under 2.2 MPa pressure and 10 minute

cooling time by cooling water under pressure. The treated ﬁber composite showed

25
substantial improvement in tensile strength, compared with the untreated ﬁber

composites. The composites of PP/non treated ﬁber and PE/non treated ﬁber exhibited
lower tensile strength than did the non-ﬁber contained polymers because of poor bonding
between matrices and untreated ﬁber. On the other hand, the composites of commingled
plastics and ﬁbers, both with and without surface treatment, displayed improvement of
tensile strength in comparison with the non-ﬁber contained polymer due to the maleated
PP in the commingled plastics. Biﬁmctional acids and anhydrides in maleated PP served
as the coupling agent between the hydrophilicity of ﬁber and hydrophobicity of polymer.
Particularly in the pretreated ﬁbers, the hydrophobic coating developed a soft ﬁlm
surrounding the hydrophilic ﬁbers. The ﬁber dispersion in the matrix was also improved
due to weakening of the intermolecular hydrogen bonds between ﬁbers. The composites
of polymers and ﬁbers both with treatment and without treatment showed an
improvement in modulus, compared to unﬁlled polymers. The elongation and tensile
toughness (ﬁacture energy/volume) of non-ﬁber contained polymers > treated wood
ﬂour/polymer composites > untreated wood ﬂour/polymer composites was a
consequence. The effect of thermoplastic types on the composite properties was that the
increase of tensile strength in PE/treated ﬁber composites was observed up to 30% weight
of ﬁber whereas the opposite result was found in PP based composites. In commingled
based composites, the increase of tensile strength was associated with the increase of
ﬁber content. The effect of the ﬁber concentration on the mechanical properties of
composites was that the increase of % ﬁber content heightened the modulus but reduced
elongation and tensile toughness. The ﬁber length was also an important factor to the

composite properties, with the shorter the ﬁbers, the better the properties. In other words,

26
the smaller size of wood ﬂour particles increased the compatibility between polymer and

ﬁber.

Youngquist et a1. (1995) investigated the development of new techniques- air-laying and
melt-blending- for producing composites from recycled plastics and wood ﬁber in
comparison to the virgin materials. PET and HDPE, representing matrices, were
compounded with different types of wood ﬁber by the air-laying method. The plastics
and ﬁbers were tested in both recycled and virgin forms. The results ﬁ'om PET-based
composites made by this method revealed that there was no signiﬁcant diﬁerence in
mechanical properties, water resistance, and dimensional stability between virgin and
recycled materials. The composites, consisting both of virgin and recycled wood ﬁbers,
had a higher modulus in the recycled PET matrix than in the virgin PET. The HDPE-
based composites showed no difference in mechanical and physical properties between
the products fabricated from virgin and recycled materials. There was no signiﬁcant

effect of wood ﬁber type and formulation on the impact strength.

The melt-blending procedure was to mix the ﬁber into the molten plastic stream by using
an extruder or injection molding. The composites produced by this technique were able
to include up to 50% wood ﬁber. Recycled matrices were PP from battery cases, PP from
ketchup bottles and HDPE ﬁom milk bottles in comparison to virgin PP. Waste ﬁbers
were old newspaper and old magazines against pure cellulose ﬁber and wood ﬂour. It
was found that old newspaper composites had better properties than wood ﬂour

composites. Old magazines were also possible to use as a reinforcer but the clay and

. 27
impurities caused a difficulty in achieving uniform dispersion into the matrix. With the

same reinforcer, the properties of recycled HDPE composites were inferior to virgin PP in
terms of strength, stiffness, and unnotched impact energy. The composites of PP battery
cases and HDPE milk bottles with old newspaper had a better impact performance than
those of virgin PP with old newspaper. The effect of recyclability on the mechanical
properties was tested by the comparison of the reground HDPE and non-reﬁberized
HDPE panel from the air-laying technique. It turned out that the second cycle composites
gave the same or even superior mechanical properties, water resistance and dimensional

stability to the ﬁrst cycle composites.

Lovinger and Williams (1980) reinvestigated tensile properties and morphology of blends
of high density polyethylene (HDPE) and polypropylene (PP). Two polymers in the pellet
form were mixed by hand into the following ratios; 75/25, 50/50, 25/75, 20/80, and 10/90
by weight of PE/PP. A two-roll mill was employed to mix the polymers at 200°C for 15
minutes. The mixture was compression molded to 1.25 mm thickness. The tensile
samples were specirnened according to Type IV of ASTM D 638 and tested by an Instron
instrument. Polarized-light and scanning electron microscopes were used to study
morphology. The polymer blends in the form of thin ﬁlm were also studied by a
transmission electron microscope. It was found that the ultimate elongation of all blends
was inferior to those of an individual polymer due to a molecular incompatibility between
PP and HDPE. The gradual increase in tensile strength at yield, along with the increase in
PP percentage, implied that the elongation at yield of each ratio did not vary greatly. The

composition between 75 to 90% PE expressed the highest ultimate tensile strength. The

28
maximum modulus at 1% elongation was achieved at 80%PP. The morphological study

of the tensile samples revealed the different sizes of PP and PE spherulites. Spherulites
of PE were much smaller than those of PP due to fast growth rates and high nucleation.
From the micrograph, the average size of Spherulites of all PE/PP blends decreased due to
the PE effect. The study of the broken area at liquid nitrogen temperature showed that the
failure took place at the PE/PP interphase. Transmission electron microscopy on PE/PP
thin ﬁlms demonstrated that at a 75/25 PE/PP ratio, the distinct interphase between PE
and PP disappeared whereas a network was created throughout the space. At 50%PP, the
PE part dispersed in PP was more obvious and at higher %PP, the PE characteristic was
clearly seen. Based on the microstructural studies, it was concluded that at lower than
50%PP, the permeating network of PP and PE was formed and at 50%PP or more, PE
was distributed in a continuous PP matrix. The mechanical properties can be explained
by these morphological discoveries. The immiscible phases and incompatibility were
responsible for poor mechanical properties in terms of early yielding point and failure
occurrence at the interphase. The size reduction of Spherulites, the increase in
crystallinity, and the forming of a permeating network were synergistic effects. It was
harder for the failure, taking place at the interboundary, to occur at the small spherulite
size than it was at the big spherulite size. As a result, an increase in the stress at yield and
ultimate strength was observed. The increase in total crystallinity by adding PE to PP
yielded the improvement of modulus. The interlinking network throughout the structure
created a better load transfer at interphase and consequently improved the strength. On
the whole, the synergistic effect functioned at the low % elongation proportional to PP

concentration, and the incompatibility played a major role at the high % elongation.

29
Shan Ren and David N.-S. Hon (1993) evaluated the effects of components, processing

and additives on the mechanical properties of the composites made of newspaper ﬁber
and PP. The test specimens were made by a mixing and molding process. The increase
in the ﬁber from 0 to 10% proportionally reduced the strength. Then, the strength leveled
oﬂ‘ at 10 to 50 % ﬁber content and started decreasing again when the ﬁber content was
greater than 50 % as a result of poor matrix-reinforcement adhesion. In contrast, the
modulus of elasticity increased proportionally to % ﬁber concentration. The optimum
elastic modulus was achieved at the range of 40 to 50 % ﬁber content. The different
types of reinforcement, which were commingled newspaper ﬁber, TMP and chemical
wood pulp, were also tested and showed an improvement of elastic modulus. The eﬂ‘ect
of processing temperature revealed that the higher the temperature, the higher the
strength. The optimum temperature was between 190 and 205°C. The tensile strength
also increased proportionally to the addition of additives but there was no signiﬁcant
effect on modulus of elasticity. From the scanning electron micrographs, pulled-out
ﬁbers at the broken surface after tensile test were evident. The presence of stretched

ﬁbers conﬁrmed the poor interfacial bonding between matrix and ﬁber.

Chapter 2

MATERIALS

High density polyethylene (HDPE) in pellet form was provided by Paxon Polymer
Company under the trade name Paxon®AD 60-007. It was a virgin HDPE homopolymer
having a medium molecular weight distribution. The virgin thermoplastic was able to be
a substitute for the recycled HDPE because the properties of virgin HDPE composites
were the same as those of recycled HDPE composites, according to Yarn et al. (1988).
HDPE is the product of the polymerization of ethylene monomers under moderate
temperature and pressure. It is a highly crystallized and non-polar thermoplastic
(Toensmeier, 1994). The linear structure with a few side branches allows the molecular
chains to get close and pack to one another (Hanlon, 1992) in the high structural
regularity manner (Brydson, 1989). As a result, the % crystallinity can be up to 95% with
stifﬁress and irnpermeability (Hanlon, 1992). Glass transition and melting temperatures

of HDPE are about -90°C (-l30°F) and 137°C (279°F) respectively (Callister, 1994). The

properties of Paxon® AD 60-007 are shown in Appendix A.

Polypropylene (PP) in the pellet form was supplied by Himont USA, Inc. under the trade

30

31
name Pro-Fax 7823. This PP type was recommended for high extrudate strength.

According to the product data, it gives good melt strength and very good toughness,
which is a characteristic of low ﬂow propylene copolymers. In general, PP is a linear
addition polymer of propylene monomers if it is a homopolymer. The problem of
homopolymer PP is the occurrence of the brittleness as the temperature reaching about
0°C. The solution is to block copolyrnerise propylene with 4 to 15 % of ethylene to
decrease the brittle temperature and increase strength, and it is called propylene
copolymers. PP can be classiﬁed into three forms according to the methyl group
arrangement on the main chain. The isotactic form has all methyl groups on the same
side of carbon backbone. The syndiotactic structure has methyl groups alternately on the
hydrocarbon chain. The atactic form is the random arrangement of methyl groups on the
carbon chain. The ﬁrst and second structures are possible to crystallize whereas the last
form is completely amorphous. Isotactic PP has high stiffness, melting point and
crystallinity. Atactic PP has a rubbery texture and low value. 90 to 95% PP in
commercial resins is in the isotactic form. PP glass transition temperature and melting
point are -20°C (-4°F) and 175°C (347°F) respectively (Callister, 1994). In comparison
with HDPE, isotactic PP has a higher softening point, no problem with environmental
stress cracking (ESC), higher brittle temperature, more sensitivity to oxidation and lower
density, which is about 0.9 g/cc (Brydson, 1989). From a morphological standpoint, the
complex structure of crystalline PP is consisted of the carbon backbone chain folding
back and forth into crystallite structures surrounded by the amorphous structure. Each
polymer crystallite is connected into a ribbon-like form by amorphous-like chains. The

conglomeration of a number of wrenched ribbons around a nucleating origin forms a

32
spherulite (Nielsen & Landel, 1994). The properties of Pro-Fax 7823 are shown in

Appendix A.

Aspen hardwood ﬁber was used as the reinforcement. Hardwoods are categorized in the
subdivision angiospermae attributing to ovary wrapped seeds. Hardwood leaves are
broad and color changed in the fall season in temperate areas. Aspen is in the genus
Populus and divided into Bigtooth aspen, Populus grandidentata, and Quaking aspen,
Populus tremuloides. The main difference between hardwoods and softwoods is that
hardwoods have a vessel element whereas soﬁwoods do not. The organic components of
hardwoods are cellulose, hemicellulose and lignin. The approximate dry weight

percentage of each in hardwood and softwood are shown in Table 3.

Table 3. % Dry weight of organic components in woods.

 

 

 

 

 

 

 

Type Cellulose Hemicellulose Lignin
(% dry weight)

Hardwood 40-44 15-35 18-25

Softwood 40-44 20—32 25-35

 

(Haygreen and Bowyer, 1982)

Cellulose (Cd-110 Os)“, is made of 5,000 to 10,000 units of glucose anhydride connected
by B type linkage and characterizes the straight polymer chain. The linkage results from
glucose hydrolysis. The longest cellulose chain is approximately 5 microns or 1/2000 cm
in length and 8 Angstroms or 1/ 10,000,000 cm in diameter. Hemicelluloses are the low

molecular weight and mostly branched-chain polymers composed of 150 or less sugar

33
anhydride units. Lignin is made of phenylpropane units into the complex and high

molecular weight polymer. It has a phenolic structure even though it consists of carbon,
hydrogen and oxygen like those ﬁrst components. Lignin can be found between and
within cell walls. It is a part of the strength inside cell walls and also glues cells together.
Lignin possesses thermoplastic characteristics. It is hard at cool temperatures, and
becomes soft and ﬂexible as the temperature increases (Haygreen and Bowyer, 1982).
The reaction between the matrix and the ﬁber in the composite materials takes place at
lignin containing methoxyl groups. The level of methoxyl groups in hardwoods is higher
than in softwoods, although the lignin content in hardwoods is a little lower than in
softwoods. The higher level of methoxyl groups make hardwoods be the better choice
than softwoods (Babyak, 1993). Aspen hardwood ﬁber in this experiment was produced
by a therrnomechanical pulping (TMP) method. Wood chips were fed into the
approximately 120°C reﬁner which ground and deﬁbrillated those chips into the ﬁbers.
The TMP ﬁbers still hold a lot of lignin and natural wax which help to disperse the ﬁbers

into the hydrophobic polymers (Woodhams et al., 1984).

Chapter 3

METHODS

In order to form the continuous phase, PP and HDPE pellets were manually mixed
following the ratios illustrated in Table 4. Each treatment was compounded and
incorporated with wood ﬁber at two temperatures representing PP and HDPE melting
points. The proportion of the continuous phase and wood ﬁber in each treatment was
maintained constantly at 60% polymers and 40% wood ﬁber by weight. The calculation

was described in Appendix B.

Table 4. Matrix composition.

 

 

 

 

 

%HDPE %PP
0 100
10 90
30 70
50 50
70 30
90 10
100 0

 

34

35

A Baker Perkins Model ZSK-30, 30 mm, 26:1 co-rotating twin-screw extruder (Werner &
Pﬂeiderer Corporation, Ramsey, New Jersey) was employed to compound the polymers
and wood ﬁber. It is consisted of three parts, feed zone, compression zone and metering
zone, ﬁmctioning differently. The feed zone attached below the feed hopper works as the
pathway for the resin pellets to get into the barrel. The compression zone is where some
granules start melting. Then, all become liquid and ready to exit at the die in a constant
rate at the metering zone (Birley et al., 1992). The temperatures were set differently in

six ports along three zones of the extruder.

Table 5. Set temperature in the extruder under PP melting point.

 

Port 1 2 3 4 5 6

 

 

 

 

 

 

 

 

Tenyerature (°C) 180 180 155 155 155 155

 

Table 6. Set temperature in the extruder under HDPE melting point.

 

Port 1 2 3 4 5 6

 

 

Temperature (°C) 150 150 155 155 155 155

 

 

 

 

 

 

 

The temperature at port three to six was adjusted to be lower than port one and two for PP
to reduce the burning of wood ﬁber. The resin pellets were fed at port one and wood
ﬁber was incorporated at port three. This technique decreases ﬁber breakage, results in
ﬁber distribution and lessens wear of equipment (Agarwal & Broutrnan, 1990). The
screw speed was set at 100 rpm. At the die exit, the continuous stream of well-mixed

composite ﬂowed consistently out and was cut into six inches in length before it

 

 

36

solidiﬁed at room temperature. The extrudates were compression molded by a Carver
Laboratory Press, Model M (Fred S. Carver Inc., Menomonee Falls, Wisconsin). Three
pieces of six-inch extrudate were needed for each molding process. They were put into a
6*6*0. 125 inch square mold which was topped and bottomed with Mylar sheets and steel
platens. This mirror-like structure was heated up to 160°C within approximately 12
minutes and held under a pressure of 25,000 psi for 15 minutes. Then, the system was
cooled down by cooling water to room temperature. The diagram was shown in
Appendix C. The molded sheet was taken out, and kept at 23i2°C and 50:l:5%RH for
about 40 hours to obtain the uniform distribution of internal stress (Ren & Hon, 1993)

before test specimens were cut.

Tensile property testing conformed to ASTM D63 8-94b (Standard Test Method for
Tensile Properties of Plastics). The test specimens were made in the shape of dumbbells.
In order to perform the test, the molded sheets were cut into 6*0.75*0.125 inch strips
using a New Hermes Safety Saw, in both crosswise and lengthwise directions, relative to
the orientation of the extrudates in the sheet. Then, dumbbell-shape specimens were
made by using Tensilkut, Model 10-13 (Tensilkut Engineering Division Sieburg
Industries, Inc., Danbury, Connecticut). The specimens were conditioned at 23:I:2°C and
50:1:5%RH for at least 40 hours before being tested for tensile strength and modulus of
elasticity. The tensile properties were performed on the United Testing Systems (U .T.S)
SFM-20 Mechanical Test System, using laser extensometer model no. EXT 62LOE, and
laser power source model no. EXT-62-LHMO (United Calibration Corp. 5802 Engineer

Dr. Huntington Beach, CA). The specimen was elongated by moving the upper gripper at

37

0.02 inch/minute by gripper mover model no. SFM—20 (United Calibration Corp. 5802
Engineer Dr. Huntington Beach, CA). The parameters of the U.T.S were set as follows:
1000 lb load cell, test speed 0.02 inch/minute, extension gage length 2 inches. All test
samples were measured by a digital vernier caliper Digimatic (Mitutoyo Corporation,
made in Japan). Tensile strength and modulus of elasticity were automatically calculated
and the curves between load (lb) and % extension were plotted by the plotter Graphtec
XY plotter, type MP 3200 (Made in Japan). X axis or % extension was set at maximum 3
% and Y axis or load was set at 250 lb maximum load. Statistical analysis of the tensile
strength and elastic modulus was performed by using One Way AN OVA ﬁ'om STATG
program and T-test from SPSS software. The comparison between each composition was

made and analyzed at the 95 % conﬁdence level.

Chapter 4

RESULTS

180°C compounding temperature

Tensile strengt_h

The results of tensile strength in both lengthwise and crosswise directions were shown in
Tables 7 and 8, as well as in Figures 1 and 2, respectively. It turned out that a ratio of
30% PP and 70% HDPE gave the highest tensile strength in both directions. Statistical
analysis showed a signiﬁcant difference between the 30% PP/70% HDPE and other
proportions. In the lengthwise direction, 30% PP/70% HDPE was signiﬁcantly diﬁerent
ﬁ'om 50% PP/50% HDPE, 70% PP/30% HDPE, 90% PP/10% HDPE and 100% PP/0%
HDPE. On the other hand, it was not signiﬁcantly different from 0% PP/100% HDPE
and 10% PP/90% HDPE. In the crosswise direction, 30% PP/70% HDPE was

signiﬁcantly different from all other proportions.

Modulus of elaiticity
The values obtained for the modulus of elasticity in both lengthwise and crosswise

directions were tabulated in Tables 9 and 10, as well as presented graphically in Figures 3

38

39
and 4, respectively. The ratio of 10% PP/90% HDPE showed the best performance in

both directions. In the lengthwise direction, a signiﬁcant difference was found between
10% PP/90% HDPE and every ratio, excluding the ratio of 50% PP/50% HDPE. In the
crosswise direction, the 10% PP/90% HDPE was signiﬁcantly different from every

proportion but 30% PP/70% HDPE.

150°C compounding temperature

Tensile strength

The results of tensile strength in both the lengthwise and crosswise directions were
summarized in Table 11 and 12 respectively. They were also presented graphically in
Figure 5 for the lengthwise direction and in Figure 6 for the crosswise direction. Both
directions revealed a good agreement that 0% PP/100% HDPE had a higher tensile
strength than 30% PP/70% HDPE. The statistical analysis also showed a signiﬁcant

difference between these two ratios in both directions.

Modulus of elasticity

The values determined for the modulus of elasticity were summarized in Tables 13 and
14, as well as in Figures 7 and 8 for the lengthwise and the crosswise directions,
respectively. In the lengthwise direction, the ratio of 0% PP/100% HDPE exhibited a
higher elastic modulus than 30%PP/70%HDPE and vice versa in the crosswise direction.

However, statistical analysis showed no signiﬁcant differences in both directions.

40
Temperature effect

The eﬂ‘ect of temperature was determined by a comparison of the mechanical properties
between 180°C and 150°C of 0% PP/100% HDPE and 30% PP/70% HDPE. For 0%
PP/100% HDPE, there were no signiﬁcant differences between two temperatures in both
tensile strength and modulus of elasticity. In the contrast, there were signiﬁcant
diﬂ'erences between two temperatures in both tensile strength and modulus of elasticity

for 30% PP/70% HDPE.

The raw data for all tensile values were shown in Appendix D and the statistical analyses

were reported in Appendix E.

Table 7. Tensile strength in the lengthwise direction at 180°C.

41

 

 

 

 

%PP %HDPE Tensile strength (psi)
average std. dev.
0 100 2723 303
10 90 2621 538
30 70 2880 336
50 50 2460 314
70 30 2327 3601
90 10 2304 426
100 0 2119 443

 

 

 

 

 

Table 8. Tensile strength in the crosswise direction at 180°C.

 

 

 

 

%PP %HDPE Tensile strength (psi)
average std. dev.

0 100 1745 96

10 90 2134 149'

30 70 2288 207

50 50 1963 144

70 30 1804 27

90 10 1253 67

100 0 1804 95

 

 

 

 

 

Table 9. Tangent modulus in the lengthwise direction at 180°C.

 

 

 

 

 

 

 

1%PP %HDPE Tangent Modulus (my) I
average std. dev. J

0 100 0.3740029 0.0683980l

10 90 0.4965418 0.0533967

30 70 0.4337601 0.0716733

50 50 0.4513923 0.0616853

70 30 0.4036430 0.0332676

90 10 0.4190089 0.0587326

100 0 0.4227439 0.0600575

 

 

Table 10. Tangent modulus in the crosswise direction at 180°C.

 

 

 

 

 

 

%PP %HDPE Tangent Modulus (Mpsi)
average std. dev.

0 100 0.3783813 0.0834753

10 90 0.4805773 0.0876116

30 70 0.4303778 0.07541 1 l

50 50 0.4004511 0.0673725
70 30 0.3702770 0.0629460!

90 10 0.326341 1 0.0609941

100 0 0.4000848 0.0269124

 

 

 

43

Table 11. Tensile strength in the lengthwise direction at 150°C.

 

 

 

 

%PP %HDPE Tensile strength (psi) 1
average std. dev. I

0 100 2441 379

30 70 2022 245

 

 

 

 

Table 12. Tensile strength in the crosswise direction at 150°C.

 

 

 

 

%PP %HDPE Tensile strength (psi)
average std. dev.
0 100 1809 86
30 70 1702 38

 

 

 

 

 

Table 13. Tangent modulus in the lengthwise direction at 150°C.

 

 

 

 

 

%PP %HDPE Tangent Modulus (Mpsi)
average std. dev.
0 100 0.360235 0.056787
30 70 0.328016 0.033399|

 

 

 

 

Table 14. Tangent modulus in the crosswise direction at 150°C.

 

 

 

 

%PP %HDPE Tan Modulus (Mpsi)
average std. dev.
0 100 0.310325 0.043495
30 70 0.355487 0.054241

 

 

 

 

 

Tensile strength (psi)

Tensile strength (psi)

 

%PP by weight

Figure l. Tensile strength in the lengthwise
direction at 180°C.

 

% PP by weight

Figure 2. Tensile strength in the crosswise
direction at 180°C.

Tangent modulus (Mpsi)

Tangent modulus (Mpsi)

0.6
0.5
0.4

0.3

 

45

 

% PP by weight

Figure 3. Tangent modulus in the lengthwise
direction at 180°C.

 

% PP by weight

Figure 4. Tangent modulus in the crosswise
direction at 180°C.

Tensile strength

.-

Tensile strength (ps

2000

.383

1820
1800
1780

§§§§§

 

0 % PP by weight 30

Figure 5. Tensile strength in the lengthwise
direction at 150°C.

 

% PP by weight

Figure 6. Tensile strength in the crosswise
direction at 150°C.

 

47

0.37

§

0.35
0.34
0.33

Tangent modulus (Mpsi)

0.32

 

031
0 °/. PP by weight 3”

Figure 7. Tangent modulus in the lengtth
direction at 150°C.

0.36
0.35
0.34
0.33
0.32
0.31

Tangent modulus (Mpsi)
9
La

0.29
0.28

 

30

° °/. PP by weight

Figure 8. Tangent modulus in the crosswise
direction at 150°C.

Chapter 5

DISCUSSION

180°C compounding temperature

Tensile strength values reported in the present study referred to an average of the ultimate
strength. The results had a good agreement with the previous work of Lovinger and
Williams (1980). They investigated tensile properties and morphology of blends of
polyethylene and polypropylene. The tensile properties were % elongation at yield and
break, tensile strength at yield and break, and tensile modulus. The morphology was
consisted of scanning electron micrographs, transmission electron micrographs and
polarizing microscope. According to their morphological study, an improvement of
tensile strength resulted from PE spherulitic effect and the development of an
interpenetrating network. The small HDPE Spherulites considerably reduced the average
spherulite size in every blend. As a result, the total crystallinity of the system was
increased and intercrystalline linkage was developed. Based on this previous study, the
development of the network without the distinct boundaries between PP and HDPE were
found at 25%PP/75%HDPE. The strong linkage between PP and HDPE created at PP

proportions lower than 50% contributed to the strength of the material through the

48

49
increase in the interphase adhesion yielding load transfer improvement between

crystalline regions, where the failure usually occurred. In this experiment, the maximum
tensile strength was found at 30% PP/70% HDPE, which was very close to that of 25%
PP/75% HDPE. Therefore, a synergistic effect might be taking place in the mixed
plastics-based composite in the same manner with the polymer blend, but the composite
had lower tensile strength than did the blends. The lower strength was mainly caused by
the poor adhesion, as a result of the incompatibility between the hydrophobic polymers
and the hydrophilic wood ﬁber. According to statistical analysis in the lengthwise
direction, the PP impurity not only could be allowed into the HDPE main stream up to
30% by weight but the contamination also brought about the synergistic effect to the
system. Therefore, the HDPE adulterated with up to 30% PP could be utilized in the
composite making process instead of using 100% HDPE. Consequently, the cost of raw
material was reduced due to less separation process. On the other hand, PE was easier to
handle than PP, because it had less stiffness than PP. The result in the crosswise
direction might be interfered with the incomplete melting of PP in the extrudates, due to
the low compression temperature (160°C). The pieces of extrudate did not bond as well

as they were supposed to. The failure often occurred at the interpiece area.

The modulus of elasticity or Young’s modulus was simply the slope of the initial straight
portion of the stress-strain curve. In this study, the tangent modulus was equivalent to the
Young’s modulus, because the slope was taken at the very beginning of the stress-strain
diagram. According to Bigg (1987), the parameters that affected the modulus of ﬁlled

polymers were ﬁller geometry, particle size dispersion, and ﬁller concentration. In

50
addition, the modulus also depended on ﬁber orientation, crystallinity and spherulite size

of the polymer components. According to Maldas & Kokta (1994), ﬁber orientation was
a more critical factor to the modulus than to the tensile strength, whereas the interbonding
between polymer and ﬁber contributed more to the tensile strength than to the modulus.
The addition of wood ﬂour to the polymer improved the modulus in comparison to the
pure polymer. The increase in the crystallinity also improved the modulus (Nielsen &
Landel, 1994). According to the previous research of Lovinger and Williams (1980), the
investigation of the effect of reducing the size of the PP spherulite on its tensile modulus
revealed that the modulus increased as the PP spherulite size was decreased. Besides
these molecular eﬁ‘ects, the strain, which measured how far the specimens could be pulled
apart until broken, might also affect the modulus values since the modulus was the ratio
of stress over strain. Therefore, the reduction of PP spherulite size, due to PE acting as
nucleating agent and the low elongation resulting in low strain, might be responsible for
the highest modulus achieved at 10%PP/90%I-IDPE. Based on the statistical point of
view, there was no signiﬁcant difference between 10% PP/90% HDPE and
50%PP/50%HDPE in the lengthwise direction. Thus, either 10%PP or 50%PP impurity
in HDPE stream gave the same performance in term of elastic modulus. Again, the result

in the lengthwise direction should be more precise than in the crosswise direction.

150°C compounding temperature
The lower tensile strength values in 30% PP/70% HDPE than in 100% HDPE might be a
consequence of the partial melting of PP and incompatibility between PP and HDPE.

Since PP melting temperature was about 175 to 185°C (Ren & Hon, 1993), the

51
compounding temperature at 150°C was apparently too low for PP to melt during

processing and resulted in incomplete melt PP which leaded to inconsistent ﬁber
distribution (Ren & Hon, 1993). In addition, the low temperature also caused dimculty in
taking a piece of extrudate out at the die exit. The higher the percentage of PP, the harder
it was to process at this condition due to the stiffness of PP. As a result, only up to 30%

PP was processible in this work.

In contrast, there was no signiﬁcant diﬂ‘erence between the two ratios in the case of
modulus of elasticity. At this point, up to 30% PP impurity in HDPE system did not

affect the modulus of elasticity of the composite under this condition.

Temperature effect

HDPE obviously worked well in both temperatures. The higher temperature at 180°C
was above its melting point but was not high enough to cause signiﬁcant thermal
degradation of the polymer or the ﬁber, at the residence times used. In contrast, an
introduction of 30% PP into 70% HDPE at 150°C signiﬁcantly lowered the strength at
150°C compared to 180°C, probably as a result of the partial melt of PP leading to non-
uniform ﬁber distribution and encapsulation of poorly bonded PP particles in the HDPE

matrix.

Chapter 6

CONCLUSIONS

Inclusion of PP in a HDPE/wood ﬁber composite resulted in an improvement in the
mechanical properties at certain proportions. Under the 180°C compounding
temperature, the maximum ultimate tensile strength and elastic modulus in both
directions were achieved at 30% PP/70% HDPE and 10% PP/90% HDPE respectively.
An increase in total crystallinity due to an addition of one polymer to the other and an
intercrystalline network were believed to play major roles in a synergistic effect on the
tensile strength. Under the 150°C compounding temperature, the data were available
only at 0% PP and 30% PP due to the difﬁculty in operation. 0% PP/100% HDPE
displayed a higher tensile strength than 30% PP/70% HDPE. The inferior performance in
30% PP/70% HDPE might result from an incompatibility between PP and HDPE, and the
low processing temperature leading to non-unifonn ﬁber distribution and partial melt of
the PP. 0% PP/100% HDPE statistically showed the same performance at both 180°C
and 150°C. However, the inclusion of 30% PP required compounding at 180°C to result

in acceptable properties.

52

RECOMIVIENDATION S

Since synergistic performance occurred in the mixed plastics-based composites under the
180°C processing temperature, the recommendation for fruther research is to improve the
interphase adhesion through the addition of coupling agents or surface modiﬁcation of
either the continuous phase or the reinforcement. Also the specimen preparation should
be switched from compression molding to injection molding in order to improve the

precision of experimental data.

53

APPENDICES

Table 15. Properties of PAXON® AD60-007

APPENDDK A

 

 

 

Properties AD60-007 AD60-007 Test Method
(US. system) (Metric system)

Melt index 0.7 g/ 10 min 0.7 g/ 10 min ASTM D 1238-89

Density 60.0 lbs/ft3 0.960 g/cm3 ASTM D 1505-85

Tensile strength at 4,400 psi 30 MPa ASTM D 638-89

yield

Elongation at break >600 % >600% ASTM D 63 8-89

Tensile modulus of 155,000 psi 1,070 MPa ASTM D 638-89

elasticity

Flexural stiffness, 145,000 psi 1,000 MPa ASTM D 747-86

Cantilever Beam

Tensile impact 90 ft-lbs/inz 19 J/etn2 ASTM D 1822-89

Impact brittleness <-105°F <-76°C ASTM D 746-79

temperature

Environmental stress 10 hrs 10 hrs ASTM D 1693-70

crack resistance

Hardness, Shore D 70 70 ASTM D 2240-86

Vicat softening 260°F 127°C ASTM D 1525-87

temperature

Heat deﬂection 175°F 79°C ASTM D 648-82

temperature, 66 psi

load

Coefﬁcient of linear 6"‘10'5 in/in/°F 1.1*10“‘ cm/cm/°C ASTM D 696-79

thermal expansion

Bulk density 37 lbs/R3 590 kym3 ASTM D 1895-89

 

 

 

 

(HIMONT U.S.A., Inc, 1988)

 

55

Table 16. Properties of PRO-FAX 7823

 

 

 

Properties PRO-FAX 7823 PRO-F AX 7 823 Test Method

(U .S. system) (Metric sgtem)
Melt ﬂow rate 0.5 dg/min 0.5 dg/min ASTM D 1238
Density 55.9 lbs/1t3 .897 g/etn3 ASTM D 792A-2
Tensile strength at yield 4,100 psi 28.5 MPa ASTM D 638
Elongation at yield 15% 15% ASTM D 638
Flexural modulus 185,000 psi 1,280 MPa ASTM D 790B
Notched Izod impact 10 ft—lbs/in at 73°F 530 J/m at 23°C ASTM D 256A
strength
Rockwell hardness, R 80 - ASTM D 785A
scale
Deﬂection temperature 185°F 85°C ASTM D 648
at 66 psi (455 kPa)
Drop-weight impact at - 17 ﬁ-lbs 23 J/m HIMONT method
20°F Q29°C)

 

 

 

 

(PAXON POLYMER COMPANY, 1990)

 

APPENDIX B

In order to obtain the proportion of 60% matrix and 40% wood ﬁber in the compounding
process, the feed rate of wood ﬁber and polymer were calculated as follows:
1. Fiber feed rate
-Adjust the ﬁber feeder speed to 2000rpm and ﬁll with wood ﬁber. Then, turn the
feeder on until some of the ﬁbers dropped from the delivered pipe to make sure
that the pipe was full with ﬁbers.
-Weigh the empty tray (T grams) and put under the pipe.
-Tum the feeder on and start timing simultaneously. Wait about 10 minutes or
more (t seconds) to cover all the ﬂuctuated feeding cycle.
-Weigh the wood ﬁber-ﬁlled tray (F grams).
-Calculate the amount of wood ﬁbers from
Fiber weight (grams) = F—T grams/t seconds
Fiber feed rate (lb/hr) = [(F-T)/t]*[3600/454]
2. Polymer feed rate
-Calculate the polymer feed rate ﬁ'om
Polymer feed rate (lb/hr) = Fiber feed rate*(60/40)

-Input the polymer feed rate in the polymer feeder.

56

APPENDIX C

Diaggam of compression molding process

Three pieces of the extrudate in the mirror-like structure of Mylar sheets and the metal

platens
1

Wait for 12 to 15 minutes to heat the system up to 160°C
1

Remain at 160°C for 5 minutes while pushing up the lower platens

1
Put 25,000 psi load on and hold for 15 minutes
1

Adjust the temperature to 60°C and turn on the cooling water
4

Wait for 5 to 7 minutes in order to let the system cool down to 60°C
1

Hold at 60°C for 10 minutes
1

Adjust the temperature to 30°C and hold for 20 minutes

57

APPENDIX D

Table 17. Tensile strength (lb/m2) data in the lengthwise direction under 180°C.

 

 

 

 

Replications Variation PP/HDPE
0/100 10/90 30/70 50/50 70/30 90/ 10 100/0
1 2363 2406 2570 2200 2612 3141 2122
2 3104 2654 2716 2620 2400 23 10 2631
3 3061 2169 3295 2472 2481 3229 2795
4 2265 2500 3207 2274 2384 2176 2479
5 2760 2434 2908 2518 2884 2318 2690
6 2764 2871 2759 2560 2365 2244 1609
7 3023 3938 2429 2391 2403 2154 1516
8 2620 2425 2667 1727 2423 2438 1975
9 2547 2194 3366 2656 1742 1944 1925
10 2841 2614 2014 2146
1 1 2804 1908 2059 1951
12. 1709 2140 1594
13 1789

 

 

 

 

 

 

 

 

58

 

 

59

Table 18. Tensile strength (lb/m2) data in the crosswise direction under 180°C.

 

 

 

Replications Variation PP/HDPE
0/100 10/90 30/70 50/50 70/30 90/ 10 100/0

1 1721 1971 2218 2061 1782 1172 1901
2 1683 2268 2118 2036 1797 1204 1680
3 1646 2413 2222 2067 1834 1 171 1719
4 1840 2204 2114 2035 1304 1855
5 1691 1955 2087 1732 1232 1901
6 1887 2051 2072 1751 1347 1767
7 2039 2055 1908 1288
8 2179 2498 1890 1305 -
9 2122 2556 1921

10 2448 1816

1 1 2558 2225

12 2509 1978

13 2100

 

 

 

 

 

 

 

 

 

60

Table 19. Tangent modulus (Mpsi) data in the lengthwise direction under 180°C.

 

Replications

Variation PP/I-IDPE

 

0/100

10/90

30/70

50/50

70/30

90/ 10

100/0

 

 

~

10

11

12

13

 

0.3486166

0.4560768

0.4573495

0.3538164

0.2394241

0.4296247

0.3501414

0.3458416

0.3851348

 

0.4644395

0.5602943

0.4987969

0.4588165

0.4559348

0.4199073

0.5877076

0.5096734

0.5133056

 

0.4344537

0.3200044

0.3969684

0.5128456

0.4554398

0.4227754

0.4410043

0.3639745

0.5563747

 

0.3767412

0.4646209

0.3247268

0.4657305

0.4900326

0.4565800

0.4988192

0.3873344

0.4866557

0.5263295

0.4877445

 

0.4531586

0.3804117

0.4223617

0.4219338

0.4578639

0.3635188

0.3806679

0.3806616

0.3541729

0.4168977

0.3946897

0.4173779

 

0.4655113

0.3093931

0.3489718

0.3167362

0.4337922

0.5015044

0.4542786

0.4631735

0.4485103

0.4413261

0.4325031

0.4102132

0.4212017

 

0.4312822

0.4074772

0.4483089

0.3449261

0.4173105

0.3673371

0.4817018

0.4960938

0.4741886

0.3177987

0.4989465

0.3875557

 

 

61

Table 20. Tangent modulus (Mpsi) data in the crosswise direction under 180°C.

 

 

 

 

Replications Variation PP/I-IDPE
0/100 10/90 30/70 50/50 70/30 90/10 100/0

10.4749848 0.5807528 0.4711415 0.3392065 0.4422742 0.2239746 0.3718728
20.3720138 0.4940500 0.4173815 0.3848750 0.3256472 0.3379837 0.4392896
30.4615679 0.5009187 0.3651493 0.4534989 0.3429095 0.2461646 0.3970512
40.3956999 0.3837360 0.3346263 0.3747366 0.3832713 0.4257525
50.2776831 0.3645246 0.3431248 0.4830866 0.3346625 0.3885158
60.2883382 0.6105639 0.4160498 0.3440493 0.3947271 0.3780266
7 0.5194026 0.4117317 0.3052333 0.3575835

8 0.4879864 0.5428627 0.4018511 0.3323618

9 . 0.3832604 0.5903392 0.5189132

10 0.4068566 0.3265231

11 0.4455095 0.3731373

12 0.4197614 0.4870637

13 0.4136896

 

 

 

 

 

 

 

 

 

Table 21. Tensile strength (lb/inz) data in the lengthwise direction under 150°C.

 

 

 

 

Replications Variation PP/HDPE
0/100
1 2397 1958
2 17 14 1736
3 2610 1843
4 1822 1820
5 2589 2246
6 2502 2378
7 2786 2128
8 2996 2387
9 2363 2130
10 2638 1722
1 1 2436 1893

 

 

 

 

Table 22. Tensile strength (lb/inz) data in the crosswise direction under 150°C.

 

 

 

 

Replications Variation PP/HDPE
0/ 1 00
1 1823 1628
2 1682 1707
3 1812 1722
4 1767 1713
5 1802 1735
6 1971 1704

 

 

 

 

62

63
Table 23. Tangent modulus (Mpsi) data in the lengthwise direction under 150°C.

 

 

 

 

Replications Variation PP/HDPE
0/100 30/70
1 0.2994451 0.3284089
2 0.3141345 0.3288897
3 0.3815890 0.3001226
4 0.3153619 0.3814775
5 0.4000295 0.3494355
6 0.2652121 0.3294654
7 0.3597577 0.2921225
8 0.3813177 0.2803313
9 0.3649814 0.3488516
10 0.4443442 0.2959661
11 0.4364102 0.3731069

 

 

 

 

Table 24. Tangent modulus (Mpsi) data in the crosswise direction under 150°C.

 

Variation PP/HDPE
0/ 100 30/70

Replications

 

 

 

@thw

 

0.3915240
0.2781950
0.2913819
0.3190162
0.3265355
0.2552978

 

0.3409836
0.3360364
0.3027846
0.3998013
0.4417873
0.31 15257

 

 

APPENDIX E

Table 25. One-way Analysis of Variance of tensile strength in the lengthwise direction
over 7 treatments under 180°C.

Analysis of variance

 

 

 

 

 

 

Source of Variation Sum of Squares d.f. Mean Square F-ratio Sig-level
Between groups 4360468 6 726744.69 4.616 0.0005
Within groups 10706592 68 157449.89

Total (corrected) 1 5067060 74

Multiple range analysis

Method: 95 percent LSD

Level (%PP) Count Average Homogeneous groups

100 12 2119.4167 x

90 13 2304.3077 xx

70 12 2327.0833 xx

50 1 1 2460.2727 xx

10 9 2621.2222 xxx

0 9 2723.0000 xx

30 9 2879.6667 x

 

64

65

Table 26. One-way Analysis of Variance of tensile strength in the crosswise direction
over 7 treatments under 180°C.

Analysis of variance

 

 

 

 

 

 

Source of Variation Sum of Squares d.f. Mean Square F-ratio Sig-level
Between groups 59198899 6 986648.32 48.192 0.0000
within groups 10236738 50 20473.48

Total (corrected) 6943563.7 56

Multiple range analysis

Method: 95 percent LSD

Level (%PP) Count Average Homogeneous groups

90 8 1252.8750 x

0 6 1744.6667 x

100 6 1803.8333 x

70 3 1804.3333 xx

50 13 1963.0769 x

10 9 2133.5556 x

30 12 2287.9167 x

 

Table 27. One-way Analysis of Variance of tangent modulus in the lengthwise direction
over 7 treatments under 180°C.

Analysis of variance

 

 

Source of Variation Sum of Squares d.f. Mean Square F-ratio Sig-level
Between groups .0833286 6 .0138881 4.060 0.0015
Within groups .2326275 68 .0034210

 

Total (corrected) .3 159560 74

 

66

Table 27 (cont’d)
Multiple range analysis
Method: 95 percent LSD

 

 

Level (%PP) Count Average Homogeneous groups
0 9 .3740029 x

70 12 .4036430 xx

90 13 .4190089 xx

100 12 .4227439 xx

30 9 .4337601 x

50 1 1 .45 13923 xx

10 9 .4965418 x

 

Table 28. One-way Analysis of Variance of tangent modulus in the crosswise direction
over 7 treatments under 180°C.

Analysis of variance

 

 

 

 

 

 

Source of Variation Sum of Squares d.f. Mean Square F-ratio Sig-level
Between groups .1169157 6 .0194859 3.884 0.0029
Within groups .2508585 50 .0050172

Total (corrected) .3677742 56

Multiple range analysis

Method: 95 percent LSD

Level (%PP) Count Average Homogeneous groups

90 8 .3263411 x

70 3 .3702770 xx

0 6 .3783813 xx

100 6 .4000848 xx

50 13 .4004511 x

30 12 .4303779 xx

10 9 .4805773 x

 

67

Table 29. T-test of tensile strength in the lengthwise direction over two treatments under

 

 

150°C.
%PP N Mean Standard deviation t
0 1 1 2441.1818 379.4443 3.080*
30 1 1 2021.909] 244.6252

 

*denotes a statistically signiﬁcant difference.

Table 30. T-test of tensile strength in the crosswise direction over two treatments under

 

 

1 50°C.
%PP N Mean Standard deviation t
0 6 1809.5 94.2226 2.607 *
30 6 1701.5 37.7187

 

*denotes a statistically signiﬁcant difference.

Table 31. T-test of tangent modulus in the lengthwise direction over two treatments under

 

 

150°C.
%PP N Mean Standard deviation t
0 1 1 0.36023484 0.05678685 1.622
30 11 0.32801618 0.03339860

 

*denotes a statistically signiﬁcant difference.

68

Table 32. T-test of tangent modulus in the crosswise direction over two treatments under

 

 

150°C.
%PP N Mean Standard deviation t
0 6 0.31032506 0.04764612 -1.532
30 6 0.35548648 0.05424078

 

*denotes a statistically signiﬁcant difference.

Table 33. T-test of tensile strength of 0% PP/100% HDPE in the lengthwise direction
over two different temperatures.

 

 

Temperature (°C) N Mean Standard deviation t
150 11 2441.1818 379.4443 -1.805
180 9 2723 302.7796

 

* denotes a statistically signiﬁcant diﬁerence.

Table 34. T-test of tensile strength of 0% PP/100% HDPE in the crosswise direction over

 

 

two different temperatures.
Temperature (°C) N Mean Standard deviation t
150 6 1809.5 94.2226 1.179
180 6 1744.7 96.2552

 

* denotes a statistically signiﬁcant difference.

69

Table 35. T-test of tangent modulus of 0% PP/100% HDPE in the lengthwise direction
over two different temperatures.

 

 

Temperature (°C) N Mean Standard deviation t
150 1 1 0.36023484 0.05678685 -.492
180 9 0.37400287 0.06839803

 

* denotes a statistically signiﬁcant difference.

Table 36. T-test of tangent modulus of 0% PP/100% HDPE in the crosswise direction
over two different temperatures.

 

 

Temperature (°C) N Mean Standard deviation t
150 6 0.31032506 0.04764612 -1.734
180 6 0.37838128 0.08347528

 

* denotes a statistically signiﬁcant difference.

Table 37. T-test of tensile strength of 30% PP/70% HDPE in the lengthwise direction
over two diﬂerent temperatures.

 

 

Temperature (°C) N Mean Standard deviation t
150 11 2021.9091 244.6252 -6.609*
180 9 2879.6667 335.8832

 

* denotes a statistically signiﬁcant difference.

70

Table 38. T-test of tensile strength of 30% PP/70% HDPE in the crosswise direction over

 

 

two different temperatures.
Temperature (°C) N Mean Standard deviation t
150 6 1701.5 37.7187 -9.487*
180 12 2287.9167 207.3738

 

* denotes a statistically signiﬁcant difference.

Table 39. T-test of tangent modulus of 30% PP/70% HDPE in the lengthwise direction
over two different temperatures.

 

 

Temperature (°C) N Mean Standard deviation t
150 11 0.32801618 0.03339860 -4.367*
180 9 0.43376008 0.07167331

 

* denotes a statistically signiﬁcant diﬁ‘erence.

Table 40. T-test of tangent modulus of 30% PP/70% HDPE in the crosswise direction
over two diﬂ'erent temperatures.

 

 

Temperature (°C) N Mean Standard deviation t
150 6 0.35548648 0.05424078 -2. 155*
180 12 0.43037785 0.07541109

 

* denotes a statistically signiﬁcant difference.

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