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LlERARY 1

Michigan State
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This is to certify that the
thesis entitled

Composite of Wood Fiber and Recycled
HDPE Bottles from Household Use

presented by

Nualrahong Thepwiwatjit

has been accepted towards fulfillment
of the requirements for

M. S 0 degree in PaCkag i 119

%M%

Major professor

Date 19/4” + //I, 157570

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

 

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

 

DATE DUE DATE DUE DATE DUE .

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32mm
MAY 16 2005 A 1 Mm
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11/00 cJCIRCanss-p.“

COMPOSITE 0F WOOD FIBER AND RECYCLED HDPE BOTTLES FROM
HOUSEHOLD USE
By

Nualrahong Thepwiwat j it

A THESIS

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

MASTER OF SCIENCE
School of Packaging

2000

 

ABSTRACT

COMPOSITE 0F WOOD FIBER AND RECYCLED HDPE BOTTLES FROM
HOUSEHOLD USE
By

Nualrahong Thepwiwatj it

The main concern in recycling is market opportunities for the reclaimed materials.
The use of recycled plastic as a composite in some structural materials could be an
attractive outlet. Lately, the use of the natural ﬁber reinforced thermoplastics has been
rising. This study investigated composites of aspen wood ﬁber reinforced high density
polyethylene from used household bottles. The effects of various ﬁber contents on the
mechanical properties of the composites, including tensile properties, impact strength,
and water absorption, were evaluated.

It was found that an increase of wood ﬁber content did not improve the tensile
properties of the composites. With an increase in the ﬁber concentration, the tensile
strength, yield strength and % elongation decreased, while the modulus and impact
strength slightly increased. The ﬁber ﬁ'action in the composites had a very large effect on
water absorption. The more the ﬁber content, the higher was the gain in weight. At the
end, most properties were worse in the recycled HDPE matrix composite than in the

virgin HDPE matrix composite.

To my family

 

ACKNOWLEDGEMENTS

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

I would like to thank Kelby Thayer for his instruction in use of Instron, and

 

Rujida Leepipattananwit for her instruction in use of several machines and a lot ofuseﬁil

information. I also would like to thank many friends for their help and support.

TABLE OF CONTENTS

List of Tables vii
List of Figures viii
Chapter 1 Introduction 1

Chapter 2 Literature Review
2.1 Background in MSW 7
2.2 Garbage Disposal Techniques
2.2.1 Landﬁlling

2.2.2 Incineration 9
2.2.3 Recycling 10
2.3 Background in Composite Materials
2.3.1 Matrix 12
2.3.2 Reinforcement 14
2.3.3 Interface 15
2.3.4 Prediction of Properties 16
2.3.5 Natural Reinforced Thermoplastics 20
2.4 Prior Research 21

Chapter 3 Experimental Design
3.1 Materials 26
3.2 Methods 27

Chapter 4 Results and Discussion

4.1 Tensile Strength 31
4.2 Yield Strength 34
4.3 Percent Elongation 36
4.4 Modulus of Elasticity 38
4.5 Izod Impact Strength 40
4.6 Water Absorption 42

Chapter 5

Appendix A
Appendix B

References

4.7 Discussion
4.7.1 Tensile properties
4.7.2 Impact Strength
4.7.3 Water Absorption

Conclusions and Recommendations
5.1 Conclusions

5.2 Recommendations

vi

46
47

48
49

50

56

69

LIST OF TABLES

Table 1. Plastic Packaging by Resin Type

Table 2. Several Methods to Manage Materials in MSW

3

7

Table 3. Energy Value Generated ﬁ'om Different Material in the WTE Facilities 10

Table 4. Sample Treatments

Table 5. Tensile Strength

Table 6. Yield Strength

Table 7. Percent Elongation

Table 8. Modulus of Elasticity

Table 9. Izod Impact Strength

Table 10. Percent Increase in Weight due to the Water Absorption

Table l 1. Comparison of Mechanical Properties of Virgin HDPE
and Recycled HDPE Resin

Table 12. Exact Composition (% by Weight) of Each Treatment
from the Experiment

Table 13. Izod Impact Strength Data

Table 14. Tensile Strength Data

Table 15. Yield Strength Data

Table 16. Modulus of Elasticity Data

Table 17. Elongation Data

Table 18. Water Absorption Data

vii

28

32

34

36

38

4o

42

45

51

52

53

53

54

54

55

Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.

Figure 6.

LIST OF FIGURES

Tensile Strength
Yield Strength
Elongation

Modulus of Elasticity
Izod Impact Strength

Water Absorption

viii

33

35

37

39

41

43

Chapter 1

INTRODUCTION

The booming of recycling has just occurred during the past ﬁfteen years when the
garbage problem was considered a crisis. At that time, several techniques were used for
waste disposal, such as landﬁlling and incineration. Typically, most of the garbage was
dumped on a landﬁll site. But with the rapidly increasing amounts of solid waste, it
seemed that the landﬁll capacity might not be enough to carry the entire load [1]. As for
incineration, which helps in volume reduction of waste materials by burning them, there
was also concern about the problems of noise and gaseous emissions [2].

In 1989, the US. Environmental Protection Agency (EPA) published a model to
manage solid wastes according to the hierarchy of waste treatments expressed in “The
Solid Waste Dilemma-An Agenda for Action” [3].

The ﬁrst step is source reduction or waste prevention, which is to avoid the
generation of unnecessary waste in the ﬁrst place before it becomes garbage. For
example, using a washable or reusable cup instead of a single-use plastic cup can
eliminate one item of trash.

Recycle comes as the second step. This technique is to recover materials from
either industrial scrap or post consumer waste and reuse them to make new products
instead of using the virgin ones. The composting of organic wastes such as food and yard
trimmings is also included in this step as a natural recycling process.

The next approach is incineration with energy recovery. The beneﬁt of

incineration is substantial volume reduction as well as energy recovery. The waste-to-

energy facility is designed to extract energy from discarded mixed refuse by burning it,
and uses the heat to generate energy, either steam or electricity.

Landﬁlling is the last step in the hierarchy. Simply, the wastes are removed ﬁ'om
the dwelling area and dumped onto a landﬁll site. EPA considered it to be the last choice
because after all other solutions are employed, there are still the rest (about 20% of
municipal Waste [4]) that has nowhere to go except to the landﬁll. F

Since then, under the inﬂuence of “green earth” and “environmentally ﬁ‘iendly”

mottoes, people turned to paying more attention and taking more action in recycling L

 

activities.

Of all the garbage, packaging is of high concern because it is widely used and has
a short lifetime [5], and thus continually ﬂows into the waste stream. Approximately 33
percent by weight of the municipal solid waste stream is packaging [6]. Among them,
paper packaging is the largest amount (percent by weight), followed by glass, plastics,
steel, wood, and aluminum respectively [7].

Generally, the share of plastics in the municipal waste stream in terms of weight
is much less than in terms of volume, due to the result of compacting and density [8]. As
the result, plastic garbage has more impact on the landﬁll capacity than other materials.

Compared to other resomces, plastic packaging is favored due to its better
characteristics of light weight with superior strength properties, easier manufacturing and
ﬁnishing, safety after damage (plastics do not injure), and low costs [8]. Consequently,
the use of plastic in packaging applications has been expanding greatly, as well as its
waste after it is used. This makes the idea about making a biodegradable product seem to

be interesting. However, this solution becomes less charming when people realize that it

also takes a long time in a landﬁll (around 10-20 years) to be thoroughly decomposed [9].
Therefore, plastics are being recycled increasingly because it not only reduces wastes, but
also saves energy used in production of new plastic items from its original resources [5].

Recycling of plastics involves several steps including materials collection,
transportation, and separation (together with sorting and cleaning), before reprocessing
into useable products [5]. Notably, the main point of reprocessing is not just to produce a
useable product but it needs to be marketable as well.

A potential market for recycling is to replace virgin resin; therefore, it needs to be
high quality and cost competitive with its counterparts. With a little help in promotion of
mechanical properties with proper additives, post-consumer resins can be made suitable
for reuse in their original applications.

In the meantime, cost competition is quite a problem. AS the price for virgin resin
ﬂuctuates, the price for recycled plastics is ﬁxed due to their stable processing costs.
Accordingly, there is a need to ﬁnd new markets for recovered post-consumer plastics,
such as by replacing other materials, i.e. wood and metals, in some applications.

Although several kinds of plastic resin are available in the market, there are six
resins that account for almost all of the plastics used in packaging (Table 1).

Table 1. Plastic packaging by resin type [10]

 

 

 

 

 

 

 

 

LDPE 33%
HDPE 31%
PS 1 1%
PP 9%
PET 7%
PVC 5%
Others 4%

 

 

 

Low density polyethylene (LDPE) is the number one in the total amount used.
This type of resin is mostly found in the forms of grocery bags, garbage bags, milk
pouches, bread wrap, plastic sandwich bags, and stretch ﬁlm [1 l]. Technically, LDPE
bags can be recycled back into plastic bags, but mostly consumers tend to throw away
them after use.

The second one is high density polyethylene (HDPE). HDPE is commonly used
for milk, juice and water containers (unpigmented HDPE bottles) as well as household
chemical containers (pigmented HDPE bottles) [10]. These rigid containers are easier to
separate and collect, thus make them become one of the top recycled materials. The rate
of recycling has increased ﬁom 252 million pounds in 1991 [12] to 734 million pounds in
1 998 [13].

Since the natural, unpigmented HDPE has a value about one third higher than
pigmented HDPE [14], it needs to ﬁnd a value-added outlet for those products. Examples
can be some structural implements. However, there is a limitation of using polyethylene
as a structural material in that it has low stiffness and high creep, which can be overcome
by making a composite material with reinforcement. Therefore, this study will use the
returned HDPE bottles from household uses such as detergent bottles, oil and beverage
bottles as the main material in the experiment.

Lately, for reinforcing thermoplastics, there has been rising interest in natural
reinforcements in the composites, due to a concern about the ultimate disposability and
environmental impact of the waste residues generated by the traditional reinforcing

materials such as glass ﬁbers, talc, and mica [15]. It was found that the properties of

wood ﬁber reinforced polypropylene composites were similar to those in glass ﬁber
reinforced polypropylene composites [16].

These natural organic ﬁllers such as wood ﬁbers and paper ﬁbers are slowly
taking the place of the dominant reinforcements in the market as a result of their low cost,
low density, acceptable speciﬁc strength properties, renewable nature, comparative ease
ofprocessability, enhanced energy recovery, and biodegradability [9, 17, 18]. However,
they have a disadvantage in that they cannot withstand high temperatures. The ﬁbers will
degrade at approximately 200°C, which limits the range of plastic materials they may be
combined with [9]. Besides, due to the different natures of the matrix and the
reinforcements in a natural reinforced material, the poor compatibility has been shown to
lead to several drawbacks such as poor interfacial adhesion, poor ﬁber dispersion, poor
water resistance, and surface defects (unaesthetic) [l 7].

In this study, the matrix material in the composite was the granulated HDPE
bottles from household uses and Aspen wood ﬁbers were used as the reinforcement. The
fact that wood ﬁbers are polar and hydrophilic, while HDPE is nonpolar and
hydrophobic, may cause such problems as those mentioned above. Most prior research
concentrated on improving the adhesion between the ﬁbers and matrix. Since these
bottles from household uses mostly contained chemical agents, they typically are
copolymer HDPE to prevent the stress-cracking phenomenon. They may therefore
combine better with the wood ﬁbers than the 100% HDPE bottles. Therefore, this study
will look into the characteristics of the Aspen wood ﬁber/ recycled HDPE bottle

composites without any inﬂuence from additives.

The primary objective of this study is to investigate the recycling potential of the
returned HDPE bottles from household uses as a composite material with Aspen wood
ﬁbers. Then the effect of varying amounts of wood ﬁbers on mechanical performance
such as tensile strength and impact strength, as well as the effect of water absorption, will
be examined.

There is an interesting point of this experiment in that these recycled bottles will
be cleaned and then ground to be used as the matrix material without removal of the
labels. It is anticipated that the glue and paper from the labels may slightly inﬂuence the
mechanical perforrmnce of the samples. However, it is assumed that the results of these
studies would provide a fundamental understanding of recycling of HDPE bottles from
household uses. As well as, it may save time and cost of the label removing process

before recycling.

Chapter 2
LITERATURE REVIEW
2.1 Background in MSW

MSW or municipal solid waste can be deﬁned as the waste generated by homes
and businesses, as opposed to industrial and agricultural waste [19]. It became a crisis
over the past ten years when single-use or throwaway items were booming for a
convenient life-style. The idea of “use it once and throw it away” became popular among
Americans and thus promoted the increase of garbage [10].

The problems in management of the generation and disposal of MSW had
oppressed many parts of the industrial world. In 1989, the European Community
generated about 110 million tons of MSW. The total of Japan’s industrial and municipal
waste was approximately 330 million tons. The United States was the worst, where the
public generated about 180 million tons of MSW in 1989 [1].

As stated before, there are several means to handle the municipal solid waste
problem. Table 2 shows that each material in MSW can generally be managed in at least
two ways.

Table 2. Several methods to manage materials in MSW [20]

 

 

 

 

 

 

 

 

 

 

Energy Prepared
Material Recycling Composting Recovery Fuel Landﬁll

Paper and

paperboard X X X X X
Plastics X X X X
Glass X X
Metals X X
Textiles X X X X
Rubber X X X X
Wood X X X X X
Yard trimmings X X X
and food wastes

 

 

 

 

 

 

 

2.2 Garbage Disposal Techniques
2.2.1 Landﬁlling

Typically, the easiest and oldest way to get rid of this garbage was to dump it on a
landﬁll site. But with the trend of higher and higher amounts of solid waste, it seemed
that the landﬁll capacity might not be enough. The problem became a crisis when many
landﬁlls in operation at that time were forced to close because their standards could not
meet the rigid regulations by government on ground-water contamination [21]. At the
same time, some landﬁlls were ﬁlled up and only a few replacement sites could be
opened since new site selection needed time for selection and processing to meet those
stricter standards. Moreover, the decision was difﬁcult because everybody gave away
garbage but no one wanted to live near it [10, 21]. This problem was one factor leading to
the development of other choices for garbage disposal, such as composting and recycling.

At this moment, the lack of landﬁll space is not a problem anymore. Although the
number of landﬁll sites is less than before, the total capacity is higher because the size of
the new landﬁlls is bigger. Moreover, the rate of waste generation has decreased Since
1994, thanks to the growth in recycling and composting programs. The MSW going to
landﬁll has declined from 83 percent of all MSW in 1986 to 55.4 percent in 1996 [22].

Nowadays, landﬁlls have evolved into special types, for example, composting
sites that more suitable for degradable materials, hazardous waste sites where toxic
chemicals can be isolated and kept securely, and sanitary landﬁlls which are speciﬁcally

designed to avoid leachate problems [4].

2.2.2 Incineration

Incineration (also waste combustion and energy recovery facility) was another
way to solve this problem. The main purpose of garbage combustion is to reduce its
volume. It can reduce up to 65 -— 70 percent of the original waste volume, while the rest
still goes to the landﬁll [21]. This not only saves more space in the landﬁll, which
increases its useful life, but also decreases the problems of odor and sanitation in the
landﬁll [7]. As a by-product, the heat ﬁ'om the burning process can be used to generate
steam or electrical energy. This modern waste-to-energy (WTE) facility needs special
combustion chambers and can reduce the volume of MSW before going to landﬁll by as
much as 90 percent [23]. The beneﬁt ﬁom selling this energy may be able to cover the
high investments in the incineration units (from costs of processing and emission control
systems, which are expensive) that sometimes exceed the costs of landﬁll operation. With
this WTE facility, incineration becomes more attractive. However, its disadvantages that
may make it lose some favor are the problems of noise and gaseous emissions [2].
Although it can be controlled by existing technologies, the disposal of the solid residues
from the combustion is still an issue (incinerator ash containing a high concentration of
hazardous heavy metals and the ﬁneness of the materials can pollute the surrounding
areas) [21].

Plastics in incineration may provide a better beneﬁt. Since plastics are obtained
from petroleum, they give more energy than other materials in MSW when they burn.
Compared to common fuels, plastics packaging generates about double the energy of

Wyoming coal and almost the same energy as ﬁre] oil (Table 3).

Table 3. Energy value generated from different material in the WTE facilities [23]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Material BTU/Pound

Plastics

Polyethylene 1 9,900

Polypropylene 19,850

Polystyrene 17,800
Rubber 10,900
Newspaper 8,000
Leather 7,200
Corrugated Boxes (paper) 7,000
Textiles 6,900
Wood 6,700
Average for MSW 4,500 — 4,800
Yard waste 3,000
Food waste 2,600
Heat content of common ﬁrels

Fuel oil 20,900

Wyoming coal 9,600

 

 

Unfortunately, the feed for the incinerator comes in the form of mixed materials.
The energy from MSW therefore is lowered to only about one-third of that from the
plastics alone. However, with their high stored energy, they can help the burning process

occur more completely and leave less ash [23].

2.2.3 Recycling
As seen in Table 2, except for landﬁlling, recycling is the only way that can deal
with almost every type of material in MSW. Since there is usually a beneﬁt in energy
reduction for production of new items, recycling seems to be a favored alternative.
Recycling, as deﬁned by Layzon and Wood is “ the recovery of materials and
products that have completed their useful service life, and their conversion into material

for further use, or a new end product” [24].

10

Recycling can be classiﬁed into four categories of techniques: primary,

secondary, tertiary and quaternary [l ].

1.

Primary recycling is the transformation of recovered material into the same or
similar items to those of virgin material with equivalent performance
characteristics. For example, glass bottles can be recycled into new glass
bottles, and aluminum cans can be reprocessed into new aluminum cans.
Secondary recycling is to utilize recycled material to produce new products
that demand less stringent speciﬁcations than the original, such as plastic toys
or trash cans from recycled plastic packaging.

Tertiary recycling is the process of producing chemicals and fuel from scrap
or waste materials. For example, pyrolysis, which is basically a thermal
decomposition, will break down large complex molecules into smaller forms
of liquid or gas that can subsequently be used as fuel.

Quaternary recycling is the recovery of energy from waste materials by

incineration.

In practice, there are three main requirements for recycling systems. The ﬁrst one

is consistent and reliable sources of recyclable materials. Collection and separation are

also included in this step. Second, some methods are needed for processing the recovered

materials into usable products. The last one is market opportunities for the reprocessed

materials [7].

11

2.3 Background in Composite Materials

Composites are one kind of structural materials. They are generally used because
of their better desired properties which could not be obtained by either of the constituent
materials acting alone. A composite is formed when two or more materials are combined
as a macroscopic structural unit. A common example of a composite is the straw-
reinforced clay bricks that had been used since ancient times. However, the ﬁrst reason
for that was presumed to be based on the need to prevent cracking of the clay during
drying, rather than on structmal reinforcement. Later, several structural composites such
as steel-reinforced concrete, polymer reinforced with glass ﬁbers and many other
materials were developed [25].

Three basic components in a ﬁber-reinforced composite are polymer matrices,
reinforcements and interfaces. Composite structural elements are now used in a variety of
components for automotive, aerospace, marine, and architectural structures, in addition to

consumer products such as skis, golf clubs, and tennis rackets [26].

2.3.1 Matrix

The matrix is the material that holds the reinforcement together. Usually, it has
lower strength than the reinforcement. The main functions of the matrix are (i) to provide
the ﬁber protection from exposure to the environment as well as protect against ﬁber
abrasion, (ii) to transfer and distribute stress load onto the ﬁber, and (iii) to separate and
keep ﬁbers in the desired location and orientation. In many cases, the matrix contributes
some desired properties such as ductility, toughness, or electrical insulation. Additionally,

it causes the ﬁbers to act as an aggregation in resisting deformation or failure under load,

12

along with limiting the maximum temperature to which the composite can be exposed.
Several materials can be used as the matrix layer in composites, such as polymers,
metals, and ceramics, depending on the speciﬁc requirements [25, 27].

In general, polymeric matrices or plastic materials are in the highest commercial
use, primarily because of the ease of processing with these materials. Plastics can be
simply divided into two groups: thermoplastics and thermosets.

In a thermoplastic polymer, the molecules are held together with secondary bonds
(intermolecular forces) such as van der Waals and hydrogen bonds. At elevated
temperatures and pressure, these bonds can be temporarily broken, and allow the
molecules to move or ﬂow into new positions. After cooling down, the bonds are restored
and result in a new solid shape. Therefore, a thermoplastic polymer can be beat softened,
ruched, and reshaped as many times as desired.

Thermoplastic polymers in composites have high impact strength and higher
resistance to failure, which provide a better withstanding of matrix microcracking in
composite laminates. However, compared to thermoset matrices, thermoplastic polymers
have developed slowly due to their high melt or solution viscosity, causing diﬂiculty in
incorporation of continuous ﬁbers into the matrix [26].

In a thermoset polymer, the molecules are chemically joined together by cross-
Ilinks, forming a rigid, three-dimensional network structure. Once these cross-links are
formed during the polymerization reaction, subsequent heating (if high enough) will not
melt these plastics but damage them. So they cannot be reformed by softening and

remolding under the application of heat and pressure.

13

Thermoset polymers in composites generally provide thermal stability, chemical
resistance, good adhesion, and relative ease of fabrication. They also Show less creep and
stress relaxation than thermoplastic polymers. However, they have some disadvantages,
for example, limited storage life (before the ﬁnal shape is molded) at room temperature,
long fabrication time in the mold, and low strains to failure causing low impact strength

[26].

2.3.2 Reinforcement

Reinforcing ﬁbers in the composite materials are the main load-carrying
members. They provide high strength and modulus as well as resistance to bending and
breaking under the applied stress. There are three types of ﬁbrous reinforced composites,
namely particulate, continuous and discontinuous ﬁbers [28].

Particulate composites are made of different sizes and shapes of particles
randomly dispersed in the matrix. Due to the random distribution of particles, these
composites can be considered as quasi-homogeneous on a scale larger than the particle
size. Particulate composites may contain either nonmetallic or metallic particles in a
nonmetallic or metallic matrix. Examples of this type are concrete and glass reinforced
with mica ﬂakes.

Continuous ﬁber composites are reinforced by long continuous ﬁbers and are the
most efﬁcient for stiffness and strength They also have greater strength and modulus in
the ﬁber axis direction and generally lack physical strength in the transverse direction.
The continuous ﬁbers can be all parallel, can be oriented at right angles to each other, or

can be oriented along several directions.

14

Discontinuous composites consist of Short ﬁbers or whiskers in the reinforcing
phase. These short ﬁbers can be either all oriented along one direction or randomly
oriented. In a discontinuous ﬁber composite, the stress along the ﬁber is not uniform. The

length (I) to diameter (d) ratio of the ﬁber, commonly called the aspect ratio (Z/d),

determines the level of strength that the composite will reach. If the ﬁber is Shorter than
the critical length, the composite will fail at a low strength level [27, 28]. The principal

ﬁbers in commercial use are various types of glass and carbon [26].

2.3.3 Interface

An interface between the ﬁber and matrix is a bonding at the interface due to
adhesion between the matrix and the ﬁber. It is a key to determining the potential
properties of the composite, since the stresses loading on the composites are transferred
from the matrix into the ﬁber across the interface.

As a result, a strong interfacial bond between the ﬁber and matrix is needed. So
the matrix must be capable of developing a mechanical or chemical bond with the ﬁber.
Normally, ﬁbers are coated with a coupling agent that will form a bond between the ﬁber
and the matrix and provide improvement in the interface conditions [27]. Moreover, the
ﬁber and matrix materials should also be chemically compatible, so that undesirable
reactions do not take place at the interfaces [25].

Other components that may also be found in a composite material are coupling
agents, coatings, and ﬁllers. Coupling agents and coatings, as mentioned before, are

applied on the ﬁbers to improve their wetting with the matrix, thus promoting bonding

15

across the ﬁber/matrix interface. Fillers are added in some polymeric matrices mainly to

lessen cost and improve the composite’s dimensional stability [26].

2.3.4 Prediction of Properties

There are many factors that inﬂuence the properties of composites, such as ﬁber
type, length of ﬁber, aspect ratio (length to diameter ratio), ﬁber alignment, ﬁber volume,
interface, component matrix, processing procedures and environmental effects.

Several methods have been developed for the prediction of properties such as
tensile strength and tensile modulus for ﬁber reinforced thermoplastics. However, the
strength and toughness are more difﬁcult to predict. For long ﬁber reinforced composites,
the calculation is much more simple, owing to an assumption that all ﬁbers are working
at the highest eﬂiciency and the load acting on the continuous reinforced material is
shared between the matrix and all ﬁbers, with the maximum tensile strain being reached
in the ﬁbers. It is also assumed that the bond between the ﬁber and the matrix is very
good. Thus, tensile modulus and tensile strength can be predicted as shown in equations 1

and 2 respectively [29].

Ec Bar + Emzm (1)

O"; 0'th + 0'QO (2)

Where: E = tensile modulus

o tensile strength

Q volume ﬁaction

16

and subscripts c = composite
f = ﬁber
m = matrix

However, these predicted values are likely to be higher than actual values because
of the present of additional stresses, which are not considered in the assumption
mentioned above.

As compared to long ﬁber reinforcement, the properties of short ﬁber reinforced
thermoplastics are more difﬁcult to predict, since the short ﬁber reinforcements generally
distribute in a three-dimensional orientation in the matrix, and there is diversity in the
length of the ﬁbers. Tensile forces are transferred from the matrix to the ﬁbers through
the ﬁber ends and through the cylindrical surfaces of the ﬁber near the ends. For
continuous ﬁbers, the ﬁber length is greater than the length over which the stress transfer
occurs; thus the effect of the ﬁber ends can be discarded. This cannot be done for short
ﬁber reinforced composites.

When predicting the tensile modulus for short ﬁber reinforced composites, the
length correction factor must be considered. Therefore, the tensile modulus of the

composite can be calculated through equation 3.
Ec = nfEﬁf + 13QO (3)

Where: (4)

__ l—tanh(,6€/2)
’— (H2)

8 = ﬁber length

17

 

ﬂ =[ 2720,, I”
E f A f ln(R / r)
(5)
Where: G = shear modulus of the matrix
r = radius of the ﬁber
R = mean separation of the ﬁbers normal to their length
Ar = the cross-sectional area of all the ﬁbers in the
composite
Moreover, the tensile modulus also depends on the ﬁber aspect ratio (K/d). A
number-average ﬁber length should be taken into account.
For tensile strength prediction for short ﬁber reinforcement, equation 6 can be
utilized with an additional factor of average tensile stress on the composite.
a, = ome + (3'er (6)

Where: Cf = average ﬁber stress

=%[a,(x)dx

If tensile stress is built up from the ﬁber ends in a non-linear way, then the tensile

strength of the ﬁber can be calculated by:

6
of = aﬁ[l-(l—ﬂ)7c]
for f = (c (7)
Where: Cf = tensile stress in a continuous ﬁber in same matrix

under the same loading conditions

18

of... = average stress in the discontinuous ﬁber within a
distance 3/2 of either end.
[c = critical ﬁber length
When the ﬁber length is greater than the critical ﬁber length, it is assumed that the

ﬁber failure occurs when Of: of... Substituting equation 7 in equation 6 gives equation 8

as

0', = af[1-(l—ﬂ)%—]+am'¢m
(8)

Comparing equation 2 to equation 8, it can be seen that discontinuous ﬁbers result
in less stress than continuous ﬁbers. If the length of ﬁbers in the matrix is shorter than the
critical ﬁber length, the ﬁbers will not be efficient in supporting the load, thus the failure
will take place at the interface.

It is very diﬁicult to predict the impact strength resistance of Short ﬁber
reinforced composites. If brittle ﬁbers are added to a ductile matrix, the impact strength
of the composite will decrease as the ﬁber content increases. This is because the matrix is
bound by the ﬁbers and cannot deform to absorb the impact load. The failure depends on
the ability of a material to transfer stress through its structure. However, the improvement
in adhesion enhances impact strength by allowing stress to be transferred to the ﬁbers so
that the impact is spread over a larger area [30]. In addition, the stiffness of short ﬁber
reinforced thermoplastics depends on ﬁber length and/or dispersion, volume ﬁ'action of

ﬁbers, the stress transfer eﬁ'rciency of the interface and ﬁber orientation [31].

19

2.3.5 Natural Reinforced Thermoplastics

Recently, wood ﬁber reinforced polymer composites have received substantial
attention both in the literature and in industry. This is because wood ﬁbers are strong,
light-weight, non abrasive, non hazardous, cheap and plentiful as well as renewable. As
reinforcing agents, wood ﬁbers can alleviate the increase in cost and potential shortage of
plastics and provide desired properties to satisfy the high demand for inexpensive high-
performance building materials [17]. Since wood ﬁbers are a kind of short ﬁbers, they are
classiﬁed as discontinuous ﬁbers. Addition of short ﬁber reinforcement to thermoplastic
materials can be used to enhance physical properties and performance characteristics.

Wood ﬁber composites can be made by extrusion, compression, or injection
molding to form a variety of products that can be used in packaging, paper products,
building materials, automobile parts, etc. [32].

The different in polarities of the ﬁber and the matrix result in poor bonding
between these two phases. The poor bonding becomes more of a problem when the
polymer matrix shrinks due to changes in temperature and thus leaves gaps between the
two components. Another problem in the incorporation of ﬁbers into the thermoplastic
matrix is the interﬁber hydrogen bonding of the ﬁbers which tends to hold them together,
leading to poor dispersion of the reinforcements in the composites [17]. Technically, the
enhancement of interfacial adhesion can be achieved by one of the following methods:

ﬁber modiﬁcation, interface-active additives, and matrix modiﬁcation [16].

20

2.4 Prior Research

Several researchers have studied the properties of composites of polymer matrices
with reinforcements ﬁom natural resources like cellulose ﬁbers, wood ﬁbers, and paper
ﬁbers. Some of those works are summarized as follows. AS mentioned before, the
different nature of the polymer matrix and the ﬁber reinforcement causes a disadvantage
in the properties of the composite. Thus, research was also conducted to investigate the
eﬁect of additives as well as the effect of ﬁber treatments on improving the adhesion
between the ﬁbers and matrix.

Mitchell, Vaughan and Willis studied the mechanical properties of paper and high
density polyethylene compared to those of glass-ﬁlled high density polyethylene. It was
concluded that the cellulose-ﬁlled laminate compared well with the glass-ﬁlled laminate
in mechanical properties. However, it would be better if the cellulose ﬁbers were
distributed uniformly in the matrix, and if bonding were enhanced. Further, acetylation or
crosslinking of the ﬁbers with formaldehyde could enhance the water resistance of the
cellulose-reinforced polyethylene [33].

A study of HDPE and cellulose-based ﬁller composites by Klason, Kubat and
Stromvall found that the cellulose ﬁbers did not show any signiﬁcant support in the
composite. The reasons might be ﬁber damage during compounding, poor ﬁber
dispersion and poor adhesion between the two phases [34]. Then, to solve the above
problem, Dalvag, Klason and Stronvall conducted research with adding additives to the
composite. They found that several additives helped in promoting the dispersion of ﬁbers
but only maleic anhydride modiﬁed polypropylene (MAPP) promoted the adhesion of the

composite [35].

21

Kokta, Deneault and Beshay studied the mechanical properties of aspen wood
ﬁbers in the form of chemithermomechanical pulp (CTMP) reinforced polyethylene.
Compared to mica and glass reinforcements, the aspen ﬁbers showed better mechanical
properties, including polyethylene’s overall properties [36].

Zadorecki and Flodin found that the cellulose ﬁbers increased the tensile strength
and modulus of unsaturated polyesters reinforced with cellulose ﬁbers. But properties
were lowered when exposed to water because the adhesion between the phases was not
strong during wet conditions [37].

Yam et al investigated the mechanical properties of composites of Aspen ﬁber (a
hardwood), and spruce ﬁber (a softwood) with recycled HDPE fi-om post-consumer milk
bottles. It was found that the tensile strength and elastic modulus of composites made
ﬁ'om recycled HDPE were about the same as those of composites made from virgin
HDPE. No signiﬁcant difference in mechanical properties between the hardwood
composites and the softwood composites was fOund [38].

Gogoi investigated the effects of ﬁber pre-treatment, screw conﬁguration of a
twin-screw extruder, and compounding temperature on the mechanical properties of
composites. Granulated HDPE milk bottles were used as the polymer matrix, while aspen
wood ﬁber was used as the ﬁller. The results showed that tensile strength decreased with
an increase in ﬁber content. The effect of ﬁber pre-treatment in term of tensile and
ﬂexural yield strength showed that acetylated and untreated aspen ﬁbers were better than
heat treated. The mechanical properties of the composite are sensitive to screw

conﬁguration and temperature [32].

22

Kalyankar tested the effect of ethylene vinyl acetate copolymer incorporated in a
composite of Spruce ﬁbers and regrind post consumer milk bottles. The results showed
improvement in impact strength but not in tensile strength [39].

Nieman studied the mechanical properties of recycled HDPE and wood ﬁber
composites. Five additives were used, low density polyethylene (LDPE), stearic acid,
chlorinated polyethylene, maleic anhydride modiﬁed polypropylene (MAPP) and
ionomer modiﬁed polyethylene. From tensile strength and modulus, only maleic
anhydride modiﬁed polypropylene showed potential for improving adhesion between the
polymer matrix and wood ﬁbers. Ionomer modiﬁed polyethylene also displayed some
positive results, while the others were determined ineffective for enhancing properties
[31].

Later, Maria D. Keal conducted research on the effect of dual additive systems on
the mechanical properties of composites of wood ﬁbers and recycled HDPE milk
containers. The additive systems were two of the stearic acid, maleic anhydride modiﬁed
polypropylene and ionomer modiﬁed polyethylene; thus three combinations were used.
The use of additives did improve tensile properties and creep but decreased impact
strength. Only the stearic acid/ionomer additive system did not reduce impact strength.
Compared to the effect of single additive, none of the dual additive systems provided
signiﬁcantly better improvement [40].

JoAnna Childress studied composites of 40% Aspen ﬁbers in a recycled HDPE
matrix with the inclusion of additives. Four additives were investigated in this study
(ionomer modiﬁed polyethylene (Surlyn), maleic anhydride modiﬁed polypropylene

(MAPP) and two low molecular weight polypropylenes (Proﬂow 1000 and Proﬂow

23

3000). The inclusion of MAPP in the composite improved its mechanical properties
overall. Surlyn offered some positive effects but not at statistically signiﬁcant levels,
whereas both Proﬂows decreased the mechanical properties of the composites [41].

Chtourou et al studied composites of recycled mixed polyolefms (95% PE and 5%
PP) and a mixture of45% spruce, 45% ﬁr and 10% poplar produced by chemico-
thermomechanical pulp (CTMP). The composites were made by injection molding and
compression molding. The results showed that the greater amount of ﬁbers, the higher the
Young’s modulus and the strength at yield. At 30% by weight of ﬁbers, Young’s
modulus increased 150%. By ﬁber surface modiﬁcation with acetic anhydride and phenol
formaldehyde, 10% treated ﬁber composites displayed an improvement in tensile strength
as well as lower water sorption than 10 % non-treated ﬁber composites [9].

Raj et a1 studied mechanical properties of organic ﬁbers from blending peanut
bulls and pecan shells in reinforced polyethylene composites. Variations in compression
molding temperature and ﬁber concentration, and the effect of polyisocyanate as a
coupling agent were studied. They investigated several meclnnical properties including
tensile strength, elongation, ﬁ'acture energy, modulus, and impact strength. It was found
that the tensile strength decreased as the ﬁber content increased in the untreated ﬁber
composites because of the poor bonding between ﬁber and polymer. Polyisocyanate was
found to improve tensile strength, but it had no effect on the modulus of the composites.
Both untreated and treated composites had low impact strength. They summarized that
composite matrix modiﬁcation would be necessary to maintain or improve impact

strength [42].

24

A comparison between two mixing methods, melt-mixing and solution-mixing, of
short pineapple leaf ﬁber (PALF) reinforced low density polyethylene was made by
George et al. It was found that solution-mixed composites provided better tensile
properties than melt-mixed composites. The effect of ﬁber content was also evaluated.
As the ﬁber content increased, the mechanical properties increased while the elongation
at break decreased. Longitudinally oriented composites expressed better properties than
randomly and transversely oriented composites. Compared to other cellulose-ﬁber
reinforced low density polyethylene, it was indicated tlmt PALF showed superior
performance [1 8].

PALF reinforced polyester composites were investigate by Devi, Bhagawam, and
Thomas. Again, the effect of ﬁber content was evaluated, as well as ﬁber length and ﬁber
surface modiﬁcation. As ﬁber content increased, tensile strength, Young’s modulus,
elongation at break and impact strength also increased. The optimum ﬁber length in this
study was at 30 mm [43].

Oksman and Clemons (1998) evaluated the mechanical properties of wood ﬁber-
polypropylene composites. Since polypropylene has poor impact strength especially at
low temperatures, three impact modiﬁers (two different ethylene/propylene/diene
terpolymers (EPPM) and maleated styrene-ethylene/butylene-styrene triblock copolymers
(SEBS-MA)) were investigated. All three agents were found to improve impact strength
of the composites. Addition of maleic anhydride modiﬁed polypropylene (MAPP) as a
compatibilizer was also studied. MAPP alone did not effect the impact strength of the

composite but it showed a positive effect when used together with those three elastomers

[44].

25

Chapter 3

EXPERIMENTAL DESIGN

3.1 Materials

The matrix material used in this study was high density polyethylene (HDPE)
from post-consumer containers of several kinds of household supplies such as detergent
bottles, oil, and beverage bottles which were provided by Granger Recycling Center. All
non-food bottles were labeled with “made of 25% or more post-consumer resin”. All caps
were removed and, without removal of the labels, the bottles were cleaned with warm
water and cut into small pieces (about a quarter to one-eighth of the bottle) and then air-
dried. Next, they were ground into granulates by using the granulator machine (B.T.P.
Granulator Double Angle Cut, Polymer Machinery, Granulator Div., Berlin,
Connecticut). The resins were conditioned at 23 :l: 2 °C and 50 :I: 5 %RH for about 40
hours before being used as the matrix material in the combining process.

High density polyethylene polymer has a melting point around 130 - 135°C and a
glass transition temperature of—120 °C. The density of HDPE is around 0.94-0.96 g/cc. It
is a highly crystalline structure (between 65-90% crystallinity) which promotes high
tensile strength, better stiffness, and good moisture barrier properties. It is a hydrophobic
and nonpolar thermoplastic.

Aspen hardwood ﬁbers were employed as the reinforcing ﬁller in this study.
Aspen is in the genus Populus and divided into Bigtooth aspen, Populus grandidentata,
and Quaking aspen, PopquS tremuloides. Hardwoods are different from softwoods in

that hardwoods have a vessel element while softwoods do not [45]. Generally, most

26

hardwoods are composed of four types of cells, namely: ﬁbers, vessel segments, axial
parenchyma, and transverse parenchyma. Fibers are polar and hydrophillic. The cell walls
contain approximately 40-60% cellulose and 20—30% lignin.

Aspen hardwood ﬁbers in this experiment were in the form of thermomechanical
pulp (TMP). In this mechanical pulping process, wood chips were fed into reﬁner at
about 120 °C, which ground and deﬁbrillated the chips into ﬁbers. There is only a
minimum amount of damage to the lignin or hemicellulose during this pulping process,
so the wood ﬁbers retain nearly all of their lignin and natural waxes, which can help in
better dispersion of wood ﬁber into the nonpolar hydrocarbon polymer matrix [46].

The ﬁbers were also conditioned for at least 40 hours at 23 i 2 °C and 50 :I: 5

%RH prior to the testing.

3.2 Methods
1. Test specimen preparation

The composite materials were made by combining the resins and wood ﬁbers
using a Baker Perkins Model ZSK-30, 30mm, 26:1 co-rotating twin—screw extruder
(Werner & Pﬂeiderer Corporation, Ramsey, New Jersey).

The extruder consists of three parts, feed zone, compression zone and metering
zone. The feed zone, which is attached below the feed hopper, ﬁmctions as a channel for
the resins to get into the barrel. The resins start melting in the compression zone and then
ﬂow to exit through the die at the metering zone. The compounding speed of the extruder
was set at 120 rpm and the temperature of all 6 processing zones was set at 150°C. Water

was used as a coolant to keep a consistent temperature throughout the process.

27

Six treatments, as shown in Table 4, were performed.

Table 4. Sample treatments

 

 

 

 

 

 

 

 

Ground bottle Fiber
Treatments (% by weight) (% by weight)
1 100 O
2 90 10
3 80 20
4 70 3O
5 6O 40
6 60% virgin HDPE resin 40

 

 

 

* Exact compositions (% by weight) from the experiments are shown in Appendix A

HDPE resins were fed into the extruder at zone 1 and allowed to run through the
extruder at least 15 minutes before combining the ﬁbers to minimize contamination with
the cleaning resin which may be retained in the machine. Then the wood ﬁbers were fed
into the last zone to prevent ﬁber damage ﬁom high temperatures in the process. The
extrudate exited from the die and was cut into approximately 4-inch long pieces.

The extruded materials were compressed into sheets using a compression molding
machine (Carver Laboratory Press, Model M, Fred S. Carver Inc., Menomonee Falls,
Wisconsin). About three pieces of the extrudate were put between a ﬂame, which was
topped and bottomed with Mylar sheets and two chrome plates. (Mylar sheets made ﬁ'om
polyethylene terephthalate (PET) help in preventing the melted material ﬁom sticking to
the plates.) There were two sizes of ﬁ’ames, 15x15x0.25 cm for the tensile property test
samples, and 12.7x12.7x0.3175 cm for the impact test and water absorption test samples.

The “sandwich” conﬁguration was heated up to 150 ° and held under a pressure of
30,000 psi for approximately 10 minutes. Then, the sample was cooled down with

cooling water to room temperature. The molded sheet was kept at 23 i 2 °C and 50 i 5

28

 

%RH for at least 40 hours to obtain a uniform distribution of internal stress before
cutting. The sheets were cut into the desired shape for each test, such as a dumbbell shape
for tensile testing and a rectangular shape (0.5x2.5x0. 125 in) for Izod impact testing, and

water absorption testing.

2. Tensile testing

ASTM D638-91, Tensile Standard Test Method for Tensile Properties of Plastics,
was followed. The specimens were cut into a dumbbell shape (type I) using a Tensilkut,
Model 10-13 (T ensilkut Engineering Division, Sieburg Industries, Inc., Danbury,
Connecticut).

Using an Instron testing machine, Model SFM-20 (United Calibration Corp.,
Huntington Beach, California) with a load cell capacity of 1000 lbs, the results of tensile
strength, % elongation, modulus of elasticity and yield strength were calculated using the
incorporated computer program. The results were then analyzed using the SPSS program
for One Way AN OVA and Least Signiﬁcant Diﬁ‘erence (LSD). The comparisons

between compositions were analyzed by the LSD method at the 95% conﬁdence level.

3. Izod impact strength testing

By following ASTM D256-92, Standard Test Methods for Impact Resistance of
Plastics and Electrical Insulating Materials, Izod impact strength was determined. The
specimens were cut in the dimensions of 0.5x2.5x0.125 in and notched by a TMI
notching cutter. (The angle of the notch was 22.5° i 0.5° and the depth of the notch was

0.1 inch)

29

At least ten specimens were tested using a TMI 43-1 IZOD impact tester with a 5-
lb pendulum. They were held as a vertical cantilever beam and broken with a single
swing of the pendulum. When the sample failed, the type of failure was classiﬁed
following the ASTM standard.

The statistical analysis and the comparison between compositions were analyzed

by the same method as described above.

4. Water absorption testing

ASTM D570-81 was followed with some adaptation. Composite material samples
were cut into 0.5x2.5x0.125 in dimension, and the edges were smoothened with sand
paper to prevent absorption ﬁom the uneven surface. The specimens were conditioned at
23 i 2 °C and 50 :I: 5 %RH no less than 48 hours prior to the testing. The samples were
immersed in water at room temperature and allowed to reach equilibrium in about 2
months. The change in weight was monitored and used to calculate the % water
absorption. Before weighing, the samples were wiped of surface water with ﬁlter paper.

Percent water absorbed was calculated when equilibrium was reached by the
formula:

% water absorption = gain in weight (g) x 100
original wt. (g)

30

Chapter 4

RESULTS AND DISCUSSION

The mechanical properties of the composite samples were evaluated by the test
methods described in the previous chapter. At least ﬁve specimens of each treatment
were tested for tensile properties and water absorption. Twelve specimens of each

composition were tested for Izod impact strength.

4.1 Tensile Strength

Table 5 presents the tensile strength results for various ﬁber amounts in the Aspen
wood ﬁber reinforced recycled HDPE composites. It was found that the tensile strength
of the composites had a tendency to decrease as the ﬁber content increased (Figure 1).
The one-way analysis of variance method (AN OVA - see Appendix B for Statistical
Analysis results) conﬁrmed that there was a signiﬁcant difference in the tensile strength
between the treatments. However, the result by the least signiﬁcant difference method
(LSD) at the 95% conﬁdence level showed no signiﬁcant difference between 10%, 20%
and 30% ﬁber content, and no signiﬁcant difference between 30% and 40% ﬁber content.
This might be affected by the wide range of the tensile strength values of the 20%, 30%
and 40% samples (see exact data in Table 12 in the Appendix A).

In comparing matrices of recycled HDPE and of virgin resin at 40% wood ﬁber, it
was found that the tensile strength of the composite of virgin HDPE was higher than that

of the recycled one.

31

 

Table 5. Tensile Strength (lbs/in2)

 

 

 

 

 

 

 

 

 

 

Conditions Average SD
0% ﬁber (100% ground 3528.5714 49.7187
recycled bottle)
10% ﬁber + 90% ground 2926.1429 77.9090
recycled bottle
20% ﬁber + 80% ground 2872.8333 238.6901
recycled bottle
30% ﬁber + 70% ground 2673.6667 251.9727
recycled bottle
40% ﬁber + 60% ground 2377.166? 343.6780
recycled bottle
40% ﬁber + 60% virgin 3332.8333 460.3540
HDPE resin

 

32

 

 

Figure 1. Tensile Strength

 

 

Average Tensile Strength (lbs/inz)

 

 

N

O

O

O
l

p—n

8

O
1

H
8
O
4

500-

 

 

 

0% 10% 20% 30% 40% 40%“
Fiber Content (%)

 

40%* = 40% wood ﬁber + 60% virgin HDPE resin

33

 

4.2 Yield Strength

The yield strength results of the test samples are shown in Table 6 and Figure 2.

Similar to the results for tensile strength, the yield strength of the composites tended to

decrease as the ﬁber content increased.

The AN OVA result, again, showed there was a signiﬁcant difference in the yield
strength between treatments. The LSD results indicated no Signiﬁcant difference between
10% and 20% ﬁber content, and between 30% and 40 % ﬁber content. However, the

group of 10% and 20% had a signiﬁcant difference in yield strength ﬁ'om the group of

30% and 40%.

Table 6. Yield Strength (lbs/inz)

 

 

 

 

 

 

 

 

 

 

Conditions Average SD

0% ﬁber (100% ground 3174.6986 203.2025
recycled bottle)

10% ﬁber + 90% ground 2605.5971 301.5207
recycled bottle

20% ﬁber + 80% ground 2385.7667 579.8986
recycled bottle

30% ﬁber + 70% ground 1842.5500 510.9522
recycled bottle

40% ﬁber + 60% ground 1770.0757 309.7499
recycled bottle

40% ﬁber + 60% virgin 2391.0650 315.0880

HDPE resin

 

Furthermore, the difference in yield strength was signiﬁcant for the different
polymer matrices. The 40% wood ﬁber composite with the recycled HDPE matrix had

much lower yield strength than the 40% wood ﬁber composite with the virgin HDPE

matrix.

The exact data for yield strength testing and the statistical analysis results can be

seen in Appendices A and B respectively.

 

Figure 2. Yield Strength

 

 

Average Yield Strength (lbs/inz)

 

 

 

 

 

 

 

0% 10% 20% 30% 40% 40%"‘
Fiber Content (%)

 

40%"‘ = 40% wood ﬁber + 60% virgin HDPE resin

35

 

4.3 Percent Elongation

The test results for percent elongation of wood ﬁber reinforced recycled HDPE
composite systems are presented in Table 7 and Figure 3.

By ASTM standards based on the shape of the stress-strain curve, the %
elongation of 100% recycled HDPE was deﬁned as the % elongation at yield while that
of the rest was deﬁned as the % elongation at break. It was obviously that the elongation
was strongly dependent on the ﬁber content. It decreased tremendously with addition of

reinforcement even at only the 10% level.

Table 7. Percent Elongation

 

 

 

 

 

 

 

 

 

 

 

 

Conditions Average SD
0% ﬁber (100% ground 43.04001 17.9953
recycled bottle)
10% ﬁber + 90% ground 4.88002 1.3025
recycled bottle
20% ﬁber + 80% ground 5.00432 1.6680
recycled bottle .
30% ﬁber + 70% ground 2.27862 0.9684
recycled bottle
40% ﬁber + 60% ground 1.90432 0.7266
recycled bottle
40% ﬁber + 60% virgin 1.34332 0.4852
HDPE resin
= % elongation at yield

2 = % elongation at break
According to the LSD statistical testing, there was no signiﬁcant difference
between the conditions for the various ﬁber contents in the recycled matrix. However,
Figure 3 shows a slight trend of declination as the ﬁber amount increased. In addition, no

signiﬁcant difference was found between the recycled and virgin HDPE matrix.

36

Figure 3. Elongation

 

 

 

 

 

 

 

U)
C
1

 

 

 

N
O

 

 

Average Elongation (%)
N
U!

H
M
1

10-

 

 

 

 

 

 

0% 10% 20% 30% 40% 40%*
Fiber Content (%)

 

40%" = 40% wood ﬁber + 60% virgin HDPE resin

37

 

4.4 Modulus of Elasticity

Table 8 and Figure 4 demonstrate the results for modulus of elasticity for the

wood ﬁber reinforced HDPE composite systems.

Unlike tensile strength, yield strength and % elongation, the modulus of elasticity
in the test specimens tended to increase with an increase in the ﬁber ﬁ‘action. Statistical

analysis at the 95% conﬁdence level by the LSD method conﬁrmed that the modulus was

affected by the incorporation of wood ﬁber.

On the other hand, the different polymer matrices had no effect on the modulus of

the composite (no signiﬁcant difference was found by the LSD method).

Table 8. Modulus of Elasticity (KPsi)

 

 

 

 

 

 

 

 

 

 

Conditions Average SD
0% ﬁber (100% ground 91.5714 37.5449
recycled bottle)
10% ﬁber + 90% ground 211.5714 28.3482
recycled bottle
20% ﬁber + 80% ground 183.1667 61.4242
recycled bottle
30% ﬁber + 70% ground 281.2857 91.2080
recycled bottle
40% ﬁber + 60% ground 290.4286 79.8850
recycled bottle
40% ﬁber + 60% virgin 393.1667 98.4630
HDPE resin

 

38

 

Figure 4. Modulus of Elasticity

 

 

 

450

 

A
O
O

 

09
U1
O

300

 

250

 

200

 

 

150

 

§

 

Average Modulus of Elasticity (KPsi)

 

 

 

0% 10% 20% 30% 40% 40%*
Fiber Content (%)

 

40%* = 40% wood ﬁber + 60% virgin HDPE resin

39

 

4.5 Izod Impact Strength

The results of Izod impact strength testing are tabulated in Table 9. Figure 5
shows a trend of slight increase in impact strength with an increase in amount of
incorporated ﬁber. However, no signiﬁcant difference was found at the 95% conﬁdence
level by the LSD method except for the pair of 10% and 30%. Moreover, the impact
strength was reduced at 40% ﬁber content.

At 40% wood ﬁber, the impact strength of the virgin matrix system was much

lower than that of the recycled matrix system.

Table 9. Izod impact strength

 

 

 

 

 

 

 

 

 

 

 

 

Izod impact strength
Conditions Type of failure (ft-lb/in)
Average SD
0% ﬁber (100% ground Partial 0.8888 0.0698
recycled bottle)
10% ﬁber + 90% ground Partial 1.1149 0.1051
recycled bottle
20% ﬁber + 80% ground Partial 1.2318 0.0715
recycled bottle
30% ﬁber + 70% ground Partial and Complete 1.2786 0.2052
recycled bottle
40% ﬁber + 60% ground Partial, Hinge, and 1.2225 0.2347
recycled bottle Complete
40% ﬁber + 60% virgin Hinge and complete 0.8991 0.1414
HDPE resin

 

 

40

Figure 5. Izod impact strength

 

 

Average Izod Impact Strength (ft-lb/ln)

 

 

 

 

 

0% 10% 20% 30% 40% 40%“
Fiber Content (%)

 

40%" = 40% wood ﬁber + 60% virgin HDPE resin

41

 

4.6 Water Absorption

Table 10 shows the percent water absorption in term of % increase in weight for
each condition. The effect of ﬁber content in the conrposite materials is illustrated in
Figure 6.

As the percent ﬁbers increased, the gain in weight due to the water absorption
increased. Results from AN OVA (see Appendix B) showed that there was a signiﬁcant
difference in these ﬁve conditions, which means the amount of ﬁber incorporated has an
effect on water absorption. The LSD method at the 95% conﬁdence level conﬁrmed that
there were signiﬁcant differences between the 10%, 20% and 30% ﬁber content, but no
difference between 30% and 40%. (Details of the data for water absorption testing and
the statistical analysis are Shown in Appendices A and B.) There was also a signiﬁcant
difference in % water uptake between recycled and virgin polymer matrices.

Table 10. Percent increase in weight due to the water absorption.

 

 

 

 

 

 

 

 

Conditions Average SD
0% ﬁber (100% ground 0.0891 0.0082
recycled bottle)
10% ﬁber + 90% ground 1.5705 0.2598
recycled bottle
20% ﬁber + 80% ground 3.4039 0.7856
recycled bottle
30% ﬁber + 70% ground 9.3568 2.7460
recycled bottle
40% ﬁber + 60% ground 9.5649 1.6313
recycled bottle
40% ﬁber + 60% virgin 7.2532 1.5822
HDPE resin

 

 

 

 

42

Figure 6. Water Absorption

 

 

% Change in Weight
0 I-' N w «h Ur O\ \l 00 \O

 

~
~

 

u—s
O

 

 

 

 

 

 

 

 

 

 

 

 

 

0% 10% 20% 30% 40% 40%“
Fiber Content (%)

 

40%* = 40% wood ﬁber + 60% virgin HDPE resin

43

 

4.7 Discussion
There are many factors that inﬂuence the properties of composites, such as ﬁber
type, length of ﬁber, aspect ratio (length to diameter ratio), ﬁber alignment, interface,

matrix resin morphology, processing procedures and environmental effects.

4.7.1 Tensile properties

Basically, the purpose of using ﬁber reinforcement is to improve the strength of
the polymer matrix [30]. However, weak adhesion between the polymer and ﬁller can
cause difficulty in development of a composite property.

Since the wood ﬁber and the polymer matrix of the composite samples had a
diﬁ‘erence in polarity, the interface of the composite was poor. Therefore, the tensile
strength and yield strength in this experiment were decreased with increasing ﬁber
content.

The wide range of tensile properties in the composition, which can be seen in the
high standard deviations, may result ﬁom poor ﬁber dispersion. The high viscosity of the
matrix during the composite fabrication and the polarity of the ﬁber, which tend to hold
the ﬁbers together, may cause poor distribution of ﬁbers. Instead of spreading out evenly
in the polymer, the ﬁbers were more likely to crowd randomly in the matrix, leading to
lack of uniformity of the composite systems. Thus, the more the ﬁber ﬁ'action, the higher
was the variation.

In most cases, no signiﬁcant difference was found between the 10% and 20%
wood ﬁber samples, as well as between the 30% and 40% wood ﬁber samples. It could be

that somewhere between 20% and 30% is a critical point that affects the difference in the

properties, or it could be simply that the large standard deviations obscure the smaller

differences.

In comparing the recycled HDPE to the virgin resin at the same ﬁber content,

except for the % elongation, most tensile properties of the composite with virgin HDPE

matrix were superior to those of the composite with recycled HDPE. This was probably

because the virgin HDPE itself had higher tensile properties than the recycled HDPE

ﬁ'om household used bottles (Table 11).

It was also found that percent decrease of tensile strength, yield strength, and %

elongation in recycled HDPE matrix is higher than those in virgin HDPE matrix. This

might show that the recycled HDPE matrix in the composite provided worse properties

than the virgin HDPE matrix in the composite. However, it is very difﬁcult to make an

exact comparison since the collected bottles, by their nature, are a complex mixture of

blow molding grades of HDPE.

Table 11. Comparison of mechanical properties of virgin HDPE and recycled

 

 

 

 

 

 

 

 

 

 

HDPE resins.
Mechanical Virgin HDPE Recycled HDPE
properties 0% 40% % 0% ﬁber 40% %
ﬁber“ ﬁber change ﬁber clung:
Tensile Strength 3882 3332.83 -l4.15 3258.57 2377.17 -27.05
G’si)
Yield Strength 3850.11 2391.07 -37.90 3174.7 1770.08 -44.24
(Psi)
Modulus (KPsi) 110 393.17 257.43 91.57 290.43 217.17
% Elongation 26.96 1.3433 -95.02 43.04 1.9043 -95.58
Impact Strength 1.73 0.8991 -48.03 0.8888 1.2225 37.55
(ft-lb/in)

 

 

 

 

 

* Source from previous experiment by Chotipatoomwan (1998) [47].

45

 

4.7.2 Impact strength

The trend towards increasing impact strength with a higher ﬁber content was not
the result which was expected from a ductile matrix such as HDPE. The addition of wood
ﬁber is generally found to reduce the impact strength of such composites [29].

However, the ﬁacture behavior of the composites can be mainly determined by
the properties of the polymer matrix, because most of the energy required to break the
materials is used for straining and fracturing of the polymer matrix [48].

For brittle matrices, an incorporation of the dispersed ﬁllers increases the surface
energy of material fracture, which means tlmt the ﬁller can improve the impact strength
of the composites. In contrast, the ﬁller reduces the surface energy in the non-brittle
matrices because of the decrease of the volume portion of matrix in the plastic zone. As a
result, the impact strength decreases with the addition of ﬁller [47].

The rmtrix of the composite samples in this experiment is of the non-brittle type.
Therefore, how the addition of ﬁber can increase the impact strength of the composite
was not clear. A possible reason could be that the ﬁller might absorb the extra energy
required to pull ﬁbers out of the matrix during crack propagation. During the impact
strength testing, the type of failure of most test samples was evaluated as partial and
hinge break, rather than the complete break type. The upper and lower parts of the notch
of the samples were observed to be held together by groups of ﬁber in the composite
materials. This may contribute to an increase in impact strength of the samples.

Another possible reason may be related to the fact that there is a correlation

between the work of fracture and the impact strength for ductile polymer. It was assumed

46

that a decrease of adhesion between matrix and ﬁller might cause an increase in the

relative elongation at rupture and thus increase certain impact strength.

4.6.3 Water absorption

Owing to their hydrophillic characteristics, wood ﬁbers tend to absorb water.
However, the polymer matrix that covers these ﬁbers should play some role in preventing
direct contact between the water and the ﬁbers, so the absorption should happen only
with the water that permeates through the plastic layer.

In this study, the samples were cut and edges were smoothed with sandpaper
before immersion into water. However, this did not protect the ﬁbers at the cut edges
ﬁ'om exposure to the water. Therefore most of the water uptake was assumed to be from
absorption by the ﬁbers at the edge.

It can be seen that the effect of water absorption in the composite is strongly
dependent on the ﬁber fraction. A tremendous increase in % water absorption occurred at
30% ﬁber.

Many polymeric matrix composites are able to absorb moisture ﬁom the
surrounding environment. Not only would the weight of the composite be increased,
dimensional changes and some properties might be affected as well. If this will result in a
defect in an application, the composite surface must be defended ﬁom water diffusion by

proper paints or coatings.

47

Chapter 5

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

An increase of wood ﬁber content did not improve the tensile properties of the
composite made of Aspen wood ﬁber and recycled HDPE used household bottles. One
reason for that might be the poor bonding between the two main components in the
materials. Overall, the amount of wood ﬁbers incorporated in the composite systems had
an effect on their properties.

The tensile strength, yield strength and % elongation decreased with an increase
in the ﬁber concentration. On the other hand, the modulus and impact strength tended to
improve with increase in the ﬁber content.

The % water uptake also increases with an increase in % ﬁber content. Finally,
most properties were worse in the recycled HDPE matrix composite than in the virgin
HDPE matrix composite, but this may be due to differences in the HDPE resins

themselves, rather than to the effect of recycling.

48

 

5.2 Recommendations for future research

In this experiment, an improvement in tensile properties of the composite failed to
result, due to the poor bonding between the matrix and the reinforcement. Therefore, the
effect of coupling agents to improve the adhesion between the wood ﬁber reinforcement
and the recycled HDPE used household bottles should be investigated.

Another issue is ﬁber treatment to develop a better distribution of ﬁber in the [
matrix. This method may be a factor for improving the mechanical properties of this

composite system.

 

49

APPENDIX A

50

Table 12. Exact composition (% by weight) of each treatment from the

 

 

 

 

 

 

 

 

experiment.
Treatment HDPE rate Fiber rate % HDPE % wood ﬁber
(g/min) (g/min)
1 29.82 - 100 0
2 26.08 3.12 89.32 10.68
3 24.97 5.98 80.68 19.32
4 14.50 6.46 69.18 30.82
5 10.67 6.68 61.50 38.50
6 9.92 6.51 60.38 39.62

 

(virgin resin)

 

 

(virgin resin)

 

 

51

 

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52

Table 14. Tensile Strength Data (lbs/m2)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0% ﬁber 10% ﬁber + 20% ﬁber + 30% ﬁber + 40% ﬁber + 40% ﬁber +
S arnpl e (100% ground 90% ground 80% ground 70% ground 60% ground 60% virgin
recycled bottle reqcled bottle recycled bottle recycled bottle recycled bottle HDPE resrn
1 3346 2861 3045 2949 2834 3629
2 3184 3018 3179 2495 n/a 2849
3 3261 3018 2909 2434 2464 3498
4 3242 2812 n/a 2415 2118 2765
5 3251 2963 2485 2826 2714 n/a
6 3238 2900 2780 2923 2048 3301
7 3288 291 1 2839 n/a 2085 3955
Average 3258.5714 2926.1429 2872.8333 2673.6667 2377.1667 3332.8333
SD 49.7187 77.9090 238.6901 251.9727 343.6780 460.3 540
Maximum 3346 3018 3179 2949 2834 3629
Minimum 3184 2812 2485 241 5 2048 2765
Table 15. Yield Strength Data (lbs/m2)
0% ﬁber 10% ﬁber + 20% fiber + 30% ﬁber + 40% ﬁber + 40% ﬁber +
Sample (100% ground 90% ground 80% ground 70% ground 60% ground 60% virgin
recycled bottle) recycled bottle recycled bottle recycled bottle recycled bottle HDPE resin
1 3344.34 2835.57 2891.28 2182.92 2062.02 2312.35
2 3182.78 2372.75 2381.44 n/a 1666.83 2130.96
3 3247.37 2961.82 2847.77 1731.92 1762.56 2490.4
4 3236.49 2746.05 n/a 1565.21 1544.55 1981.01
5 3248.22 2352.12 1622.09 2712.82 1832.87 n/a
6 3236.81 2800.58 1734.06 1383.31 2221.69 2605.88
7 2726.88 2170.29 2837.96 1479.12 1300.01 2825.79
Average 3174.6986 2605.5971 2385.7667 1842.5500 1770.0757 2391.0650
SD 203.2025 301.5207 579.8986 510.9522 309.7499 312.0880
Maximum 3344.34 2961.82 2891.28 2712.82 2221.69 2825.79
Minimum 2726.88 2170.29 1622.09 1383.31 1300.01 1981.01

 

 

 

 

 

 

 

53

 

 

Table 16. Modulus of Elasticity Data (KPSi)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0% ﬁber 10% ﬁber + 20% ﬁber + 30% ﬁber + 40% ﬁber + 40% ﬁber +
S ample (100% gound 90% ground 80% gound 70% gound 60% goqu 60% virgin
recycled bottle) recycled bottle recycled bottle recycled bottle recycled bottle HDPE resrn
l 82 202 226 290 454 578
2 68 193 1 l l 243 209 356
3 103 241 239 454 324 301
4 50 225 n/a 267 259 399
5 156 230 202 159 248 n/a
6 121 230 221 237 277 327
7 61 160 100 319 262 398
Average 91.57 211.57 183.17 281.29 290.43 393.17
SD 37.5449 28.3482 61.4212 91.2080 79.8850 98.4630
Maximum 156 241 239 454 454 578
Minimum 50 160 100 159 209 301
Table 17. Elongation Data (%)
0% ﬁber 10% ﬁber + 20% ﬁber + 30% ﬁber + 40% ﬁber + 40% ﬁber +
S anrple (100% ground 90% gound 80% gound 70% gound 60% gound 60% virgin
recycled bottle) recycled bottle recycled bottle meled bottle recycled bottle HDPE resrn
l 40.15 5.12 7.97 2.28 1.89 0.96
2 21.09 3.74 4.03 1.60 0.77 0.86
3 28.16 5.83 4.93 1.07 1.50 1.47
4 63.95 6.98 5.86 2.44 2.00 1.10
5 32.60 3.78 2.58 4.19 2.99 Na
6 69.01 5.29 4.46 2.12 2.57 2.18
7 46.32 3.42 5.20 2.25 1.61 1.49
Average 43.0400 4.8800 5.0043 2.2786 1.9043 1.3433
SD 17.9953 1.3025 1.6680 0.9684 0.7266 0.4852
Maximum 69.01 6.98 7.97 4.19 2.99 2.18
ﬁrimum 21.09 3.42 2.58 1.07 0.77 0.86

 

 

 

 

 

 

 

 

 

 

Table 18. Water Absorption Data (%)

 

 

 

 

0% ﬁber 10% ﬁber + 20% ﬁber + 30% ﬁber + 40% ﬁber + 40% ﬁber +
Sample (100% gound 90% ground 80% ground 70% gound 60% gound 60% virgin
recycled bottle) recycled bottle recycled bottle recycled bottle recycled bottle HDPE resrn
1 0.0879 1.2577 3.2945 5.4515 10.6477 8.4229
2 0.1046 1.4987 3.4151 6.5410 8.5238 9.6172
3 0.0852 1.9548 3.1166 9.9285 8.6182 8.5555
4 0.0958 1.2676 3.9327 10.1722 7.3558 5.7433
5 0.0822 1.5427 4.7845 13.8606 10.6187 5.6356
6 0.0827 1.7955 2.2805 10.2418 9.0621 6.3248
7 0.0854 1.6764 3.0036 9.3020 12.1282 6.4729
Average 0.0891 1.5705 3.4039 9.3568 9.5649 7.2532
SD 0.0082 0.2598 0.7856 2.7460 1.6313 1.5822

 

 

 

 

 

 

 

55

 

APPENDIX B

56

One-Way Analysis of Variance (ANOVA)

 

 

TENSILE STRENGTH

Sum of df Mean F Sig.
Squares Square

Between 397027244 5 794054.49 1 1.0296 0.0000

Groups

Within 230376840 32 71992.76

Groups

Total 627404084 37

 

 

 

 

 

 

 

57

 

Post Hoc Tests

 

 

 

 

 

 

 

 

 

Multiple Comparisons

Dependent Variable: TENSILE STRENGTH

L32

(1) (J) Fiber Mean 95% Conﬁdence Interval
Fiber Content Difference Std Error Sig. Lower Upper

Content (I-J) Bound Bound

0% 10% 332.4286" 143.4202 0.0270 40.291 1 624.5660
20% 385.7381 * 149.2765 0.0145 81.6718 689.8044
30% 584.9048“ 149.2765 0.0004 280.8385 888.9710
40% 881 .4048“ 149.2765 0.0000 577.3385 1 185.4710
40%* -74.2619 149.2765 0.6223 -378.3282 229.8044

10% 0% -332.4286* 143.4202 0.0270 -624.5660 -40.291 1
20% 53.3095 149.2765 0.7233 -250.7568 357.3758
30% 252.4762 149.2765 0.1005 -51.5901 556.5425
40% 548.9762“ 149.2765 0.0009 244.9099 853.0425
40%" 4066905" 149.2765 0.0104 -710.7568 -102.6242

20% 0% -3 85.7381 * 149.2765 0.0145 -689.8044 -81.6718
10% -53.3095 149.2765 0.7233 -357.3758 250.7568
30% 199.1667 154.9115 0.2078 -1 16.3778 514.71 12
40% 4956667“ 154.91 15 0.0031 180.1222 811.2112
40%" -460.0000* 154.91 15 0.0056 -775.5445 -144.4555

30% 0% 684.9048“ 149.2765 0.0004 -888.9710 -280.83 85
10% -252.4762 149.2765 0.1005 -556.5425 51.5901
20% -l99.l667 154.9115 0.2078 -514.7112 116.3778
40% 296.5000 154.9115 0.0646 -19.0445 612.0445
40%* -659. 1667* 154.91 15 0.0002 -974.71 12 -343.6222

40% 0% -881.4048* 149.2765 0.0000 -1 185.4710 -577.3385
10% -548.9762* 149.2765 0.0009 -853.0425 -244.9099
20% 495.6667“ 154.91 15 0.0031 -811.21 12 -180.1222
30% -296.5000 154.91 15 0.0646 -612.0445 19.0445
40%" -955.6667* 154.91 15 0.0000 -1271.21 12 -640.1222

40%* 0% 74.2619 149.2765 0.6223 -229.8044 378.3282
10% 406.6905“ 149.2765 0.0104 102.6242 710.7568
20% 460.0000* 154.9] 15 0.0056 144.4555 775.5445
30% 6591667“ 154.91 15 0.0002 343.6222 974.71 12
40% 9556667“ 154.91 15 0.0000 640.1222 1271.21 12

 

 

 

 

 

 

1"

The mean difference is signiﬁcant at the 0.05 level

58

 

One-Way Analysis of Variance (ANOVA)

 

 

YIELD STRENGTH

Sum of df Mean F Sig.
Squares Square

Between 91 13564.99 5 182271300 12.4207 0.0000

Groups

Within 484267302 33 146747.67

Groups

Total 1395623801 38

 

 

 

 

 

 

 

59

 

Post Hoe Tests

 

 

 

 

 

 

 

 

 

Multiple Comparisons

Dependent Variable: YIELD STRENGTH

L_S_D

(I) (I) Mean 95% Conﬁdence Interval
Fiber Fiber Difference Std Error Sig. Lower Upper

Content Content (I-J) Bound Bound

0% 10% 569.1014* 204.7630 0.0089 152.5079 985.6950
20% 788.9319" 213.1241 0.0008 355.3276 1222.5362
30% 1332. 1486* 213.1241 0.0000 898.5443 1765.7529
40% 1404.6229* 204.7630 0.0000 988.0293 1821.2164
40%* 783.6336* 213.1241 0.0008 350.0293 121 7.23 79

10% 0% -569. 1014* 204.7630 0.0089 -985.6950 -152.5079
20% 219.8305 213.1241 0.3098 -213.7738 653.4348
30% 763.0471 * 213.1241 0.001 1 329.4428 1 196.6515
40% 835.5214" 204.7630 0.0003 418.9279 1252.1 150
40%* 214.5321 213.1241 0.3214 -219.0722 648.1365

20% 0% -788.9319* 213.1241 0.0008 -1222.5362 -355.3276
10% -219.8305 213.1241 0.3098 -653.4348 213.7738
30% 543.2167* 221.1694 0.0195 93.2442 993.1891
40% 615.6910* 213.1241 0.0068 182.0866 1049.2953
40%* -5.2983 221 . 1694 0.9810 455.2708 444.6741

30% 0% -1332.1486* 213.1241 0.0000 -1765.7529 -898.5443
10% -763.0471 * 213.1241 0.001 1 -1 196.6515 -329.4428
20% -543.2167* 221.1694 0.0195 -993.1891 -93.2442
40% 72.4743 213.1241 0.7360 -361 . 1300 506.0786
40%* -548.5150* 221.1694 0.0184 -998.4875 -98.5425

40% 0% -1404.6229* 204.7630 0.0000 -1821.2164 -988.0293
10% -835.5214* 204.7630 0.0003 -1252.1 150 418.9279
20% -615.6910* 213.1241 0.0068 -1049.2953 -182.0866
30% -72.4743 213.1241 0.7360 -506.0786 361.1300
40%* -620.9893* 213.1241 0.0064 -1054.5936 -187.3850

40%* 0% -783.6336* 213.1241 0.0008 -1217.2379 -3 50.0293
10% -214.5321 213.1241 0.3214 -648.1365 219.0722
20% 5.2983 221.1694 0.9810 444.6741 455.2708
30% 548.5150“ 221.1694 0.0184 98.5425 998.4875
40% 6209893“ 213.1241 0.0064 187.3850 1054.5936

 

 

 

 

 

 

* The mean difference is signiﬁcant at the 0.05 level

60

 

One-Way Analysis of Variance (ANOVA)

 

 

PERCENT ELONGATION

Sum of df Mean F Sig.
Squares Square

Between 9325.33 5 1865.07 32.971 1 0.0000

Groups

Within 1979.84 35 56.57

Groups

Total 1 1 305. 1 7 40

 

 

 

 

 

 

 

61

 

Post Hoe Tests

 

 

 

 

 

 

 

 

 

Multiple Comparisons

Dependent Variable: PERCENT ELONGATION

L_S_D

(I) (.1) Fiber Mean 95% Conﬁdence Interval
Fiber Content Difference Std Error Sig. Lower Upper

Content (I-J) Bound Bound

0% 10% 38.1600* 4.0202 0.0000 29.9986 46.3214
20% 38.0357* 4.0202 0.0000 29.8743 46.1971
30% 40.7614* 4.0202 0.0000 32.6000 48.9228
40% 41 . 1357* 4.0202 0.0000 32.9743 49.2971
40%* 41 .6967* 4.1843 0.0000 33.2020 50.1913

10% 0% -38. 1600* 4.0202 0.0000 46.3214 -29.9986
20% -0. 1243 4.0202 0.9755 -8.2857 8.0371
30% 2.6014 4.0202 0.5218 -5.5600 10.7628
40% 2.9757 4.0202 0.4641 -5.1857 1 1.1371
40%* 3.5367 4.1843 0.4037 4.9580 12.0313

20% 0% -38.0357* 4.0202 0.0000 46.1971 -29.8743
10% 0.1243 4.0202 0.9755 -8.0371 8.2857
30% 2.7257 4.0202 0.5022 -5.4357 10.8871
40% 3.1000 4.0202 0.4458 -5.0614 1 1.2614
40%* 3.6610 4.1843 0.3876 4.8337 12.1556

30% 0% 407614" 4.0202 0.0000 48.9228 -32.6000
10% -2.6014 4.0202 0.5218 -10.7628 5.5600
20% -2.7257 4.0202 0.5022 -10.8871 5.4357
40% 0.3743 4.0202 0.9264 -7.7871 8.5357
40%* 0.9352 4.1843 0.8244 -7.5594 9.4299

40% 0% 41 .1357* 4.0202 0.0000 49.2971 -32.9743
10% -2.9757 4.0202 0.4641 -1 1 . 1371 5.1857
20% -3.1000 4.0202 0.4458 -1 1.2614 5.0614
30% -0.3743 4.0202 0.9264 -8.5357 7.7871
40%* 0.5610 4.1843 0.8941 -7.9337 9.0556

40%* 0% 41 .6967“ 4.1843 0.0000 -50. 1913 -33.2020
10% -3.5367 4.1843 0.4037 -12.03 1 3 4.9580
20% -3.6610 4.1843 0.3876 -12. 1556 4.8337
30% -0.9352 4.1843 0.8244 -9.4299 7.5594
40% -0.5610 4.1843 0.8941 -9.0556 7.9337

 

 

 

 

 

 

The mean difference is signiﬁcant at the 0.05 level

62

 

One-Way Analysis of Variance (AN OVA)

 

 

MODULUS

Sum of df Mean F Sig.
Squares Square

Between 349739.66 5 69947.93 14.0873 0.0000

Groups

Within 168820.24 34 4965.30

Groups

Total 518559.90 39

 

 

 

 

 

 

 

63

 

Post Hoc Tests

 

 

 

 

 

 

 

 

 

Multiple Comparisons

Dependent Variable: MODULUS

TAD.

(I) (.1) Fiber Mean 95% Conﬁdence Interval
Fiber Content Difference Std. Error Sig. Lower Upper

Content (I-J) Bound Bound

0% 10% -120.0000* 37.6651 0.0031 - 1 96.5446 43.4554
20% -91.5952* 39.2030 0.0255 -171.2654 -1 1.9251
30% -189.7143* 37.6651 0.0000 -266.2589 -113.1697
40% -198.8571* 37.6651 0.0000 -275.4018 -122.3125
40%* -301.5952* 39.2030 0.0000 -381.2654 -221.9251

10% 0% 120.0000* 37.6651 0.0031 43 .4554 196.5446
20% 28.4048 39.2030 0.4737 -51.2654 108.0749
30% -69.7143 37.6651 0.0729 -146.2589 6.8303
40% -78.8571* 37.6651 0.0438 -155.4018 -2.3125
40%* -181 .5952* 39.2030 0.0001 -26l .2654 -101.9251

20% 0% 91.5952* 39.2030 0.0255 1 1.9251 171.2654
10% -28.4048 39.2030 0.4737 -108.0749 51.2654
30% -98.1 190* 39.2030 0.0173 -1 77.7892 -1 8.4489
40% -107.2619* 39.2030 0.0098 -186.9321 -27.5917
40%* -210.0000* 40.6829 0.0000 -292.6777 -127.3223

30% 0% 189.7143* 37.6651 0.0000 1 13.1697 266.2589
10% 69.7143 37.6651 0.0729 -6.8303 146.2589
20% 98.1 190* 39.2030 0.0173 18.4489 177.7892
40% -9.1429 37 .6651 0.8097 -85.6875 67.4018
40%* -1 1 1 .8810* 39.2030 0.0073 -191.5511 -32.2108

40% 0% 198.8571 * 37.6651 0.0000 122.3125 275.4018
10% 78.8571* 37.6651 0.0438 2.3125 155.4018
20% 107.2619* 39.2030 0.0098 27.5917 186.9321
30% 9.1429 37.6651 0.8097 -67.4018 85.6875
40%* ~102.7381* 39.2030 0.0130 -182.4083 -23.0679

40%* 0% 301.5952“ 39.2030 0.0000 221.9251 381.2654
10% 181 .5952* 39.2030 0.0001 101.9251 261.2654
20% 210.0000* 40.6829 0.0000 127.3223 292.6777
30% 111.8810* 39.2030 0.0073 32.2108 191.5511
40% 102.7381 * 39.2030 0.0130 23.0679 182.4083

 

 

 

 

 

 

it

The mean difference is signiﬁcant at the 0.05 level

 

One-Way Analysis of Variance (AN OVA)

 

 

IMPACT STRENGTH

Sum of df Mean F Sig.
Squares Square

Between 1.7297 5 0.3459 16.2409 0.0000

Groups

Within 1.3419 63 0.0213

Groups

Total 3.0716 68

 

 

 

 

 

 

 

65

 

 

Post Hoc Tests

 

 

 

 

 

 

 

 

 

Multiple Comparisons

Dependent Variable: IMPACT STRENGTH

@

(I) (J) Fiber Mean 95% Conﬁdence Interval
Fiber Content Difference Std. Error Sig. Lower Upper

Content (I-J) Bound Bound

0% 10% -0.2262* 0.0596 0.0003 -0.3452 -0. 1071
20% -0.3431* 0.0609 0.0000 -0.4648 -0.2213
30% -0.3899* 0.0609 0.0000 -0.51 16 -0.2681
40% -0.3337* 0.0609 0.0000 -0.4554 -0.2120
40%* -0.0103 0.0596 0.8629 -0. 1294 0.1087

10% 0% 0.2262* 0.0596 0.0003 0.1071 0.3452
20% -0.1 169 0.0609 0.0595 -0.2386 0.0048
30% -0.1637* 0.0609 0.0092 -0.2855 -0.0420
40% -0. 1075 0.0609 0.0824 -0.2293 0.0142
40%* 0.2158* 0.0596 0.0006 0.0968 0.3349

20% 0% 0.3431 * 0.0609 0.0000 0.2213 0.4648
10% 0.1169 0.0609 0.0595 -0.0048 0.2386
30% -0.0468 0.0622 0.4547 -0.1712 0.0775
40% 0.0094 0.0622 0.8809 -0.1 150 0.1337
40%* 0.3327* 0.0609 0.0000 0.21 10 0.4545

30% 0% 0.3899* 0.0609 0.0000 0.2681 0.51 16
10% 0.1637* 0.0609 0.0092 0.0420 0.2855
20% 0.0468 0.0622 0.4547 -0.0775 0.1712
40% 0.0562 0.0622 0.3701 -0.0682 0.1805
40%* 0.3796* 0.0609 0.0000 0.2578 0.5013

40% 0% 0.3337* 0.0609 0.0000 0.2120 0.4554
10% 0.1075 0.0609 0.0824 -0.0142 0.2293
20% -0.0094 0.0622 0.8809 -0.1337 0.1150
30% -0.0562 0.0622 0.3701 -0.1805 0.0682
40%* 0.3234* 0.0609 0.0000 0.2016 0.4451

40%* 0% 0.0103 0.0596 0.8629 -0.1087 0.1294
10% -0.2158* 0.0596 0.0006 -0.3349 -0.0968
20% -0.3327* 0.0609 0.0000 -0.4545 -0.21 10
30% -0.3796* 0.0609 0.0000 -0.5013 -0.2578
40% -0.3234* 0.0609 0.0000 -0.4451 -0.2016

 

 

 

 

 

 

* The mean difference is signiﬁcant at the 0.05 level

66

 

One-Way Analysis of Variance (ANOVA)

 

 

% CHANGE IN WEIGHT

Sum of df Mean F Sig.
Squares Square

Between 581.4926 5 1 16.2985 52.1 147 0.0000

Groups

Within 80.3372 36 2.2316

Groups

Total 661 .8297 41

 

 

 

 

 

 

 

67

 

Post Hoc Tests
Multiple Comparisons

Dependent Variable: % CHANGE IN WEIGHT
LSD

 

 

 

 

 

 

 

 

 

(I) (J) Fiber Mean 95% Conﬁdence Interval
Fiber Content Difference Std. Error Sig. Lower Upper
Content (I-J) Bound Bound

0% 10% -1.4809 0.7985 0.0718 -3.1004 0.1385

20% -3.3148* 0.7985 0.0002 4.9342 -1 .6954

30% -9.2677* 0.7985 0.0000 -10.8871 -7.6483

40% -9.4758* 0.7985 0.0000 -1 1.0952 -7.8564

40%* -7.1641* 0.7985 0.0000 -8.7835 -5.5446

10% 0% 1.4809 0.7985 0.0718 -0. 1385 3.1004

20% -1.8339* 0.7985 0.0276 -3.4533 -0.2144

30% -7.7867* 0.7985 0.0000 -9.4062 -6.1673

40% -7.9949* 0.7985 0.0000 -9.6143 -6.3754

40%* -5.6831* 0.7985 0.0000 -7.3025 4.0637

20% 0% 3.3148* 0.7985 0.0002 1.6954 4.9342

10% 1.8339* 0.7985 0.0276 0.2144 3.4533

30% -5.9529* 0.7985 0.0000 —7.5723 4.3334

40% -6. 1610* 0.7985 0.0000 -7.7804 4.5416

40%* -3.8492* 0.7985 0.0000 -5.4687 -2.2298

30% 0% 9.2677* 0.7985 0.0000 7.6483 10.8871

10% 7.7867* 0.7985 0.0000 6.1673 9.4062

20% 5.9529* 0.7985 0.0000 4.3334 7.5723

40% -0.2081 0.7985 0.7958 -1.8276 1.41 13

40%* 2.1036* 0.7985 0.0123 0.4842 3.7231

40% 0% 9.4758* 0.7985 0.0000 7.8564 1 1.0952

10% 7.9949* 0.7985 0.0000 6.3754 9.6143

20% 6.1610* 0.7985 0.0000 4.5416 7.7804

30% 0.2081 0.7985 0.7958 -1.41 13 1.8276

40%* 2.31 18* 0.7985 0.0064 0.6923 3.9312

40%* 0% 7.1641 * 0.7985 0.0000 5.5446 8.7835

10% 5.6831* 0.7985 0.0000 4.0637 7.3025

20% 3.8492* 0.7985 0.0000 2.2298 5.4687

30% -2. 1036* 0.7985 0.0123 -3.7231 -0.4842

40% -2.31 18* 0.7985 0.0064 -3.9312 -0.6923

 

 

 

 

 

 

1"

68

The mean difference is signiﬁcant at the 0.05 level

 

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