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This is to certify that the

thesis entitled

COMPOSITE MATERIAL OF MIXED LOW DENSITY
POLYETHYLENE/POLYPROPYLENE AND WOOD FIBER

presented by

KOBDAJ VANICHVAROD

has been accepted towards fulfillment
of the requirements for

MASTER degree in PACKAGING

 

 

514%, 51%

Major professor

 

Date %1 1; 1M2

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

 

 

 

LIBRARY

Michigan State

University

 

 

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

 

DATE DUE

DATE DUE

DATE DUE

 

APM 0% 31M

 

may ,1 6 2006‘

 

 

 

 

 

 

 

 

 

 

 

 

 

6/01 c-JCIRC/DateDue.p65—p. 1 5

COMPOSITE MATERIAL OF MIXED LOW DENSITY
POLYETHYLENE/POLYPROPYLENE AND WOOD FIBER

By

Kobdaj Vanichvarod

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
School of Packaging

2002

j/

ABSTRACT

COMPOSITE MATERIAL OF MIXED LOW DENSITY
POLYETHYLENE/POLYPROPYLENE AND WOOD FIBER

By

Kobdaj Vanichvarod

Mixing of post consumer plastics such as low density polyethylene (LDPE) and
polypropylene (PP) has been applied for reducing the amount of plastic wastes in landfill.
Poor mechanical properties may result with these mixed plastics. The addition of

reinforcing fiber seems to improve the strength of the plastics.

In this study, the mechanical properties of LDPE/PP wood composite were investigated.
Also, the effect of processing temperatures on the properties was studied. LDPE and PP
were varied in six different ratios. Each variation was compounded with 40% of aspen
wood fiber by wt. Each compound was processed at two different sets of temperatures:

above the LDPE melting point (150 °C) and above the PP melting point (180 °C).

Overall, 0:100 LDPEzPP had the highest mechanical strength for both processing
temperatures, while the best impact strength was achieved with 100:0 LDPEzPP and
0:100 LDPEzPP for the processing temperatures of 150 °C and 180 °C, respectively. In
the case of blends, mechanical strength decreased with increasing ratios of LDPE. The
best impact strength for 150 °C and for 180 °C were achieved with 80:20 and 20:80
LDPEzPP, respectively. In brief, the effect of processing temperature varied, depending

on the ratio of LDPE and PP.

To My Dearest Parents

Dacha & Sumalee Vanichvarod

iii

ACKNOWLEDGEMENTS

I would like to express my deepest impress gratitude and appreciation to my major
professor, Susan Selke, Ph.D. (School of Packaging, Michigan State University), whom I
know as a great teacher and mentor, for her valuable guidance, meaningful supervision,
continuous comments, discussion and encouragement throughout this course of study.
My special appreciation is also extended to all members of the advisory committee,
Bruce Harte, Ph.D. (School of Packaging, Michigan State University) and Indrek
Wichman, PhD. (Department of Mechanical Engineering, Michigan State University) for

their guidance and assistance.

Special thanks are given to Michael J. Rich, Ph.D. and Mr. Kelby Thayer from the
Composite Materials and Structures Center for instruction and assistance in use of
extruder. I also wish to thank Mr. Pomchai Rachtanapun and Ms. Krittika Tanprasert for
instruction in sample preparation. My appreciation also goes to Ms. Ubonrat Siritanawan
for guiding in statistical analysis and Ms. Pomnaree Cheewasakulyong for guiding in

statistical analysis and helping so many things in this research.

Finally, I greatly appreciate to my beloved parents and sister who support me with their

infinite love, attention, perception and encouragement throughout my whole life which

never be forgotten.

iv

TABLE OF CONTENTS

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

LIST OF FIGURES .................................................................................. x

CHAPTER 1

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

CHAPTER 2

LITERATURE REVIEW ............................................................................ 9
Background of Composite Materials ...................................................... 9
Matrix ........................................................................................ 10
Reinforcement .............................................................................. 12
Interfaces and Interphase .................................................................. 15
Prediction of Properties .................................................................... 17
Prior Research ............................................................................... 26

CHAPTER 3

MATERIALS ........................................................................................ 31

CHAPTER 4

METHODS .......................................................................................... 33

CHAPTER 5

RESULTS ............................................................................................ 40
Processing Above the LDPE Melting Point (150 °C) ................................. 40
Processing Above the PP Melting Point (180 0C) ....................................... 51
The Effect of Temperature ................................................................ 62

CHAPTER 6

DISCUSSION ....................................................................................... 63
Processing Above the LDPE Melting Point (150 0C) ................................. 63
Processing Above the PP Melting Point (180 °C) ...................................... 66
The Effect of Temperature ................................................................ 67

CHAPTER 7

CONCLUSIONS and RECOMMENDATIONS ................................................ 70
Conclusions ................................................................................. 70
Recommendations for Future Research ................................................. 71

APPENDIX A ....................................................................................... 72

APPENDIX B ....................................................................................... 75

APPENDIX C ....................................................................................... 77

APPENDIX D ....................................................................................... 79

APPENDIX E ....................................................................................... 86

BIBLIOGRAPHY .................................................................................. 1 02

vi

LIST OF TABLES

Table 1. Plastic resins from packaging applications in MSW during 1999 .................... 6
Table 2. Variation of LDPE and PP ............................................................... 33
Table 3. The set of temperatures over the LDPE melting point .............................. 34
Table 4. The set of temperatures over the PP melting point ................................... 34
Table 5. Average tensile strength (psi) at processing temperature of 150 °C ............... 41
Table 6. Calculated tensile strength (psi) from “rule of mixing”

at processing temperature of 150 °C ............................................................. 41
Table 7. Average yield strength (psi) at processing temperature of 150 °C ................. 43
Table 8. Calculated yield strength (psi) from “rule of mixing”

at processing temperature of 150 0C ............................................................. 43
Table 9. Average MOE (psi) at processing temperature of 150 oC ........................... 45
Table 10. Calculated MOE (psi) from “rule of mixing”

at processing temperature of 150 0C ............................................................. 45
Table 11. Average percent elongation at processing temperature of 150 °C. . . . ........47
Table 12. Calculated percent elongation from “rule of mixing”

at processing temperature of 150 °C ............................................................. 47
Table 13. Average Izod impact resistance (ft-lb/in) and type of failure

at processing temperature of 150 °C ............................................................... 49
Table 14. Calculated Izod impact resistance (ft-lb/in) from “rule of mixing”

at processing temperature of 150 °C ............................................................. 50
Table 15. Average tensile strength (psi) at processing temperature of 180 0C .............. 51
Table 16. Calculated tensile strength (psi) from “rule of mixing”

at processing temperature of 180 °C ............................................................. 52
Table 17. Average yield strength (psi) at processing temperature of 180 °C ................ 53

vii

Table 18. Calculated yield strength (psi) from “rule of mixing”

at processing temperature of 180 °C ............................................................. 54
Table 19. Average MOE (psi) at processing temperature of 180 °C ......................... 55
Table 20. Calculated MOE (psi) from “rule of mixing”

at processing temperature of 180 °C ............................................................. 56
Table 21. Average percent elongation at processing temperature of 180 °C. . . . . . . . . ........57
Table 22. Calculated percent elongation from “rule of mixing”

at processing temperature of 180 oC ............................................................. 58
Table 23. Average Izod impact resistance (ft-lb/in) and type of failure
at processing temperature of 180 °C ............................................................... 60
Table 24. Calculated Izod impact resistance (ft-lb/in) fiom “rule of mixing”

at processing temperature of 180 oC ............................................................. 60
Table 25. The effect of temperature on variations and mechanical properties .............. 67
Table 26. Properties of Dow Polyethylene 133A ............................................... 73
Table 27 Properties of Dow Inspire H704-04 ................................................... 74
Table 28. Results of tensile strength (psi) at processing temperature of 150 °C ............ 80
Table 29. Results of yield strength (psi) at processing temperature of 150 °C. . . . . . . . . ...80
Table 30. Results of MOE (psi) at processing temperature of 150 0C ........................ 81
Table 31. Results of percent elongation at processing temperature of 150 0C. . . . . . . . ...81
Table 32. Results of impact strength (fi-lb/in) and type of failure
at processing temperature of 150 °C .............................................................. 82
Table 33. Results of tensile strength (psi) at processing temperature of 180 °C ............ 83
Table 34. Results of yield strength (psi) at processing temperature of 180 °C. . . . . . . ....83
Table 35. Results of MOE (psi) at processing temperature of 180 OC ........................ 84
Table 36. Results of percent elongation at processing temperature of 180 °C. . . . . . ....84

Table 37. Results of impact strength (fi-lb/in) and type of failure
at processing temperature of 180 °C .............................................................. 85

viii

Table 38. One-way Analysis of Variance of tensile strength
at processing temperature of 150 °C .............................................................. 87

Table 39. One-way Analysis of Variance of yield strength
at processing temperature of 150 °C .............................................................. 88

Table 40. One-way Analysis of Variance of MOE
at processing temperature of 150 °C .............................................................. 89

Table 41. One-way Analysis of Variance of elongation
at processing temperature of 150 °C .............................................................. 90

Table 42. One-way Analysis of Variance of Izod impact resistance
at processing temperature of 150 °C .............................................................. 91

Table 43. One-way Analysis of Variance of tensile strength
at processing temperature of 180 °C .............................................................. 92

Table 44. One-way Analysis of Variance of yield strength
at processing temperature of 180 °C .............................................................. 93

Table 45. One-way Analysis of Variance of MOE
at processing temperature of 180 °C .............................................................. 94

Table 46. One-way Analysis of Variance of elongation
at processing temperature of 180 °C .............................................................. 95

Table 47. One-way Analysis of Variance of Izod impact resistance
at processing temperature of 180 °C .............................................................. 96

Table 48. One-way Analysis of Variance of tensile strength
at processing temperature of 150 and 180 °C ................................................... 97

Table 49. One-way Analysis of Variance of yield strength
at processing temperature of 150 and 180 °C ................................................... 98

Table 50. One-way Analysis of Variance of MOE
at processing temperature of 150 and 180 °C ................................................... 99

Table 51. One-way Analysis of Variance of elongation
at processing temperature of 150 and 180 °C .................................................. 100

Table 52. One-way Analysis of Variance of Izod impact resistance
at processing temperature of 150 and 180 °C .................................................. 101

ix

LIST OF FIGURES

Figure 1. Total waste generation before recycling in 1999 ..................................... 2
Figure 2. Waste recycling rate from 1960 to 1999 ............................................... 3
Figure 3. Recycling rates of selected materials during 1999 .................................... 4
Figure 4. Makeup of interface between fiber and matrix ....................................... 16
Figure 5. A tensile force acting on a thermoplastic composite,

with long fibers aligned in the direction of tensile stress ........................................ 17
Figure 6. Extruder diagram ........................................................................ 35
Figure 7. Four types of failures .................................................................... 38

Figure 8. Comparison between average and calculated values
of tensile strength (psi) at processing temperature of 150 °C ................................. 42

Figure 9. Comparison between average and calculated values
of yield strength (psi) at processing temperature of 150 °C .................................... 44

Figure 10. Comparison between average and calculated values
of MOE (psi) at processing temperature of 150 °C .............................................. 46

Figure 11. Comparison between average and calculated values
of percent elongation at processing temperature of 150 °C .................................... 48

Figure 12. Comparison between average and calculated values
of Izod impact resistance (ft-ib/in) at processing temperature of 150 0C .................... 50

Figure 13. Comparison between average and calculated values
of tensile strength (psi) at processing temperature of 180 °C ................................. 52

Figure 14. Comparison between average and calculated values
of yield strength (psi) at processing temperature of 180 °C .................................... 54

Figure 15. Comparison between average and calculated values
of MOE (psi) at processing temperature of 180 °C .............................................. 56

Figure 16. Comparison between average and calculated values
of percent elongation at processing temperature of 180 °C .................................... 58

Figure 17. Comparison between average and calculated values
of Izod impact resistance (fi-ib/in) at processing temperature of 180 0C .................... 61

Figure 18. “Sandwich technique” diagram ...................................................... 78

xi

CHAPTER 1

INTRODUCTION

Even if the amount of trash generated per person remains constant over the years, waste
disposal can still be a problem. Changes in living style make the waste disposal problem
become even more serious (Rodriguez, 1996). In the United States, population increased
from 180 million in 1960 to 286 million in 2000, which was more than 59% (U .8.
Census, 2000). During 1960 to 1999, municipal solid waste (MSW) generation increased

at a faster rate, with the total waste per person becoming 72% greater (U .8. EPA, 1999).

MSW is composed of product packaging, grass clippings, furniture, clothing, bottles,
food scraps, newspapers, appliances, paint, batteries and other such items. During 1999,
US. residents and businesses released 230 million tons of MSW, which is approximately

4.6 pounds of waste per person per day. Waste composition is shown in Figure 1.

 
 
    

Other 3.2%

Glass 5.5%

 

  

     
    
   
 
     

Rubber, leather
and textiles 6.6%

  

Paper 38.1%

    
 

Metals 7.8%

Yard waste 12.1%

Plastics 10.5%

  

  

Food waste 10.9%

Figure 1. Total waste generation before recycling in 1999 (U .8. EPA, 2001a).

According to the United States Environmental Protection Agency (U .8. EPA), several
techniques for management of MSW are recommended in order to avoid waste or divert
materials fiom the waste stream. Some of these techniques are source reduction,

recycling and composting (U .8. EPA, 2001a).

Source reduction is the design, manufacture, purchase, or use of materials (such as
products and packaging) in order to decrease the amount or toxicity of trash generated. It
reduces economic costs for disposal and handling due to avoided costs of recycling,
municipal composting, landfilling, and combustion. It also preserves natural resources

and reduces pollution (U.S. EPA, 2001b).

Recycling is the method by which many materials are collected and reused as raw

materials in order to make new ones (U .8. EPA, 2001b). It diverts about 64 million tons

of materials away from landfills and incinerators during 1999. The rates of recycling have

increased since 1960, as shown in Figure 2.

70 ~— r 30
60 r ' r 25
:31“ +20
30 r i 15
20 + i 10
10 + - 5
o 0

 

 

 

 

1960 1970 1980 1990 1999

- O - Total waste recycling (million tons/year)
+ Percent recycling (%)

Figure 2. Waste recycling rate from 1960 to 1999 (U .8. EPA, 2001a).

The rates for several recycled materials in 1999 are presented in Figure 3. These
materials may be obtained from curbside programs, drop off centers, buy-back programs

and deposit systems.

100 - 93.8
90 j
80 r
70 a
60 1
50 a
40 4
30 a
20 -
10 J

54.5

45.3 41.6 40.0

26.6 26.5

 

         

drink
containers

Glass
containers
Tires

Auto batteries
Steel cans
Aluminum
packaging
Yard waste
Paper and
paperboard
Plastic sofi

Figure 3. Recycling rates of selected materials during 1999 (U.S. EPA, 2001 a).

Recycling has several benefits such as resource conservation, reduction of pollution,
energy savings, and reduction of landfill space (U .8. EPA, 2001a). There are four main

steps for recycling:

p—s

Collecting: The recyclable components are taken away from MSW.

2. Separating: The recyclable components are grouped by types of material
before or after collection.

3. Processing: Those components are changed into reusable forms.

4. Purchasing and using: The reprocessed materials are sold into the market as

new products (U.S. EPA, 2001b).

Composting is one form of recycling. It plays a key role in diverting organic wastes, such

as food scraps and yard trimmings, with microorganisms (mainly bacteria and fungi)

producing a humus-like substance. Composting can be said to be nature's way of
recycling organic wastes into new soil used in vegetable and flower gardens, landscaping,

and many other applications (U .8. EPA, 2001a).

Beside the techniques above, waste combustion and landfilling are the other ways to
manage waste. The combustion technique is the simplest method in which MSW is
burned in an incinerator (Denison & Ruston, 1990). It reduces the bulk of waste and has
the added benefit of energy recovery. However, some components may need to be
removed from the waste stream because they can cause potentially harmful emissions, be
difficult to burn, or cause problems in ash management (U .8. EPA, 2001b). A landfill is
the place where the wastes are deposited on the land; moreover, it usually has a liner as a
safeguard to ensure that components from the waste will not contaminate groundwater

(U .8. EPA, 2001a).

In MSW, the plastic wastes have grown rapidly. They can be found in the form of durable
and nondurable goods, as well as in the form of containers and packaging. Packaging is

the largest category of plastics in MSW.

Durable products are, for instance, furniture, cases, appliances and other products, while
nondurable products are trash bags, disposable diapers, cups, medical devices, household
items, etc. Many types of resin are used to produce both durable and nondurable
products. The plastics for household food containers, for example, are ofien produced

from polystyrene in the form of foam or clear items. Trash bags, another example of

nondurable products, are usually made of high density polyethylene (HDPE) or low

density polyethylene (LDPE).

For packaging, plastic resins are used to produce a variety of containers such as
polyethylene terephthalate (PET) for soft drink bottles and HDPE for milk and water
bottles. Beside these two resins, other resins such as LDPE and polypropylene (PP) can
be used to make bags, sacks, wraps, lids, etc. Table 1 shows the amounts of various resins

in packaging applications found in MSW.

Table 1. Total packaging resins in MSW during 1999 (U .8. EPA, 1999)

 

 

 

Type of resin“ Amount of resins (Thousand tons) % by weight
PET 1,850 17
HDPE 4,180 37
PVC 480 4
LDPE/LLDPE 3,230 29
PP 1,110 10
PS 250 2
Other resins 70 1
Total 11,160 100

 

 

* PET = polyethylene terephthalate, HDPE = high density polyethylene, PVC =
polyvinyl chloride, LDPE = low density polyethylene, LLDPE = linear low density

polyethylene, PP = polypropylene, PS = polystyrene

To reduce these amounts of resins above, a widespread idea is that the products should be
made biodegradable. However, this idea becomes less attractive, since some
biodegradable materials accumulating in landfills need 10 to 20 years or more to be
completely degraded. Another solution idea is that all plastic wastes should be collected
and blended together. The drawback of this technique is that blending of immiscible
plastics, such as PE and PP, will generally lead, even with virgin materials, to

heterophase systems with mediocre properties (Dumoulin et al., 1987).

With recent advancements in the science and technology of composites, the use of wood
fiber and plastic materials has gained strong momentum in process engineering and
applications, such as in construction, building and automotive components (Sain et a1,
2000). Wood and plastic composites production has grown rapidly because it combines
the benefits of two materials. Some construction industries feel most comfortable
working with wood, notwithstanding the gradual acceptance of vinyl sliding, window
profiles, decking and fencing. The addition of plastic to wood makes the composite more
resistant to rot, insects and warping. It also gives convenience for builders, and the

combination can be ideal in many applications (Lauzon, 2000).

The use of cellulosic fibers as reinforcement filler offers several benefits, including low
cost, ease of processing, low equipment abrasion, ease of surface modification, high
strength to weight ratio, renewability, non-toxicity, recyclability, and improved properties
and performance of composites. However, the problems of cellulosic fibers in

thermoplastics are incompatibility with matrix resins, thermal instability above 200 °C,

low bulk density, hygroscopicity and difficulty of dispersion in ordinary plastic mixing

equipment (Park & Balatinecz, 1997).

In this research, the mechanical properties of LDPE/PP and wood fiber composites were
studied. Also, the effect of changing processing temperature from 150 °C to 180 °C was
investigated. LDPE and PP resins, in virgin pellet form in order to control the variation,
functioned as the matrix compound while the wood fiber was used as reinforcement filler.
LDPE was selected due to it being found in large volume in MSW. PP was selected as an
impurity in solid plastic wastes (Bernhardt, 1987; Laguna et al., 1987). The wood fiber
was obtained from aspen, a hardwood. The benefits of wood fiber are the same as those
of cellulosic fibers. The proportions of wood fiber and the matrix compound were
maintained at 40% and 60%, respectively. The proportions of LDPE and PP were varied
in 6 ratios, fiom 100% to 0% of each resin. Each proportion was processed at two
different sets of temperatures: over the LDPE melting point (150 0C) and over the PP
melting point (180 °C). The properties of each variation were evaluated in terms of
mechanical strength and impact strength, and they were also compared with calculated

values from the “rule of mixing”.

CHAPTER 2

LITERATURE REVIEW

Background of Composite Materials

The term composite can be defined in several ways depending upon the aspect of study
(Schwartz, 1992). In general, composites are composed of two or more materials present
as separate phases and combined to form the desired structure. Because of the
combination of components, the composite will take advantage of certain properties from

each component (Grayson, 1983).

The classifications of composites can also be divided in many ways depending on the
concepts that need to be identified. The common identification of composites focuses on

the structure, which are basic, micro and macro composite. (Hull 1981).

First, basic composites are composed of two or more different atoms or molecules. They
may include compounds, alloys, polymers and ceramics. Second, microcomposites are
combined with two or more different molecules or phases. By this definition, many
materials considered to be homogenous could be classified as composites. Examples of
this classification are steels, brasses and bronzes. Third, macrocomposites are composed
of two or more structural forms of constituents, e. g., matrixes, and particles or fibers.

With this classification, this discussion will emphasize macrocomposites.

Since the composite is considered as a combination of components, the components can
be organic, inorganic or metallic (synthetic or natural structures), in the form of particles,
rods, fibers, plates, foams, etc. Compared with homogenous materials, these additions
provide more latitude in optimizing properties such as strength, density and cost

(Grayson, 1983).

Fiber reinforced composites, called fibrous composites, are macro composites which use
fibers to improve the mechanical strength. The fibers are characterized as having a
lengthwise direction that is longer than the cross direction. With a small diameter, they
tend to bend easily when pushed axially. Therefore, the fibers have to be supported in
order to prevent individual fiber bending and buckling (Richardson, 1987; Agarwal &

Broutman, 1990).

Matrix

The matrix is used as a structure to embed and adherently grip a reinforcing phase. The
matrix serves to transfer stress from one fiber to another and to produce a fully dense
structure (Grayson, 1983). Moreover, several functions can be performed by the matrix
such as (1) to protect the reinforcements from environmental attack, which can result in a
surface imperfections, (2) to act as a shelter to prevent cracks spreading from one fiber to
another, (3) to keep the reinforcements in the desired orientation (Callister, 1994;
Rojanarungtawee, 1998). Polymers have been used as a matrix since they successfully
perform the roles above. Two types of polymers can be used: thermosetting and

thermoplastic resins.

10

Thermosetting resins can be shaped only one time because they form irreversible
covalent bonds, called cross linking, between the chains during processing, and will not
melt and flow after that (Hernandez et a1, 2000). They are generally convenient because
they can be applied in fluid form, facilitating penetration and wetting in the
unpolymerized state. Then, they can be turned to a solid form in proper conditions that
are easily controlled by the operator. Since the condensation process is required for
polymerization in order to form the shape, exotherrnicity, shrinkage and evolution of
volatiles will be involved. Examples of these resins are epoxy, amide, and polyester

(Grayson, 1983).

On the other hand, thermoplastic resins consist of linear or branched molecular chains.
These chains are bonded together with secondary bonding forces or van der Waals forces
(Broutrnan & Krock, 1967). The resins derive their strength and stiffness from the
inherent properties of the monomer units and the very high molecular weight. This
ensures that a high concentration of molecular entanglements, acting like cross-links, will
be seen in amorphous thermoplastics, while a high degree of molecular order or

alignment will be seen in crystalline materials (Hull, 1981).

In this experiment, two thermoplastic resins were used as the matrix phase. One was
LDPE and the other was PP. LDPE is an addition polymer based on ethylene, with a
branched structure. The density of LDPE is in the range of 0.91 to 0.925 g/cm3 (Ehrig,
1992). Since the amount of crystallinity is reduced by the branching of the polymer chain,

LDPE has a low percent crystallinity, compared to other polyolefins such as HDPE. The

11

glass transition and melting temperatures are about -—102 0C and 105 to] 15 0C,

respectively (Hernandez et al., 2000).

PP is an addition polymer based on propylene. The PP molecule has one methyl group
attached to every other carbon atom, so this carbon is a chiral center. Because of the
chiral center, PP can be classified into three forms. The isotactic form has all the methyl
groups on one side of the main chain. The syndiotactic form has alternation of methyl
groups on the main chain. The atactic form has methyl groups in random position
(Rodriguez, 1996). The crystallinity of PP depends on the arrangement of the methyl
groups. The first two forms can be crystallized, but the last one cannot. The properties of
PP are also based on the formation. Isotactic PP has high stiffness, while atactic PP has a
rubbery texture. The common form of PP in packaging is isotactic because it provides
good flow properties at a wide range of flow rates (Hernandez et al., 2000). The glass
transition and melting temperatures of isotactic PP are about —20 °C and 175 °C,

respectively (Callister, 1994). The density of PP is about 0.9 g/cm3 (Brydson, 1989).

Reinforcement

A reinforcement is used to improve the strength of a matrix, so it must be stronger and
stiffer than the matrix, and must significantly modify the failure mechanism in an
advantageous way (Grayson, 1983). The composite formed with the reinforcement will
ofien be cheaper than the polymer matrix alone. The fibers alone are very brittle and their

strength and stiffness cannot be increased. Once combined with a resin, the matrix

12

provides a protection for these fibers, and transfers the load from them. For this reason,

an improvement in properties of fiber and matrix will be obtained over the matrix alone.

The strength of a composite depends on the geometry of the reinforcing filler. One or
more fillers may be used in the form of particles or fibers. In the case of particulate filler,
it has no length direction. Since the length of the filler limits the growth of cracks in a
brittle matrix, a particulate filler does not improve the fracture strength of the matrix.
However, there is an exception if a rubberlike substance is dispersed in a brittle matrix.
Under these conditions, considerable toughening occurs, and this method is standard for
improving the impact behavior of thermoplastics. High-impact polystyrene and ABS are

common examples of this case (Clegg & Collyer, 1986).

The particles will share the load with the matrix, but to a lesser extent than fibers.
Therefore, only stiffness is improved, while strength is not. The impact strength of the
brittle matrix can be reduced with the addition of hard particles, which cause localized
stress concentration within the matrix phase. Particulate filler is also used to improve
high temperature performance, reduce friction, increase wear resistance, reduce shrinkage
and improve mechanical properties. In most cases, the application of this filler is to
reduce the cost of the material. Under these conditions, the filler is known as an additive,

used to change the properties of the composite.

Fiber reinforcement improves stiffness, strength and creep resistance of the thermoplastic

matrix. In general, the measurement of strength from experiments is much less than that

13

predicted from theory. This is because flaws in the form of cracks perpendicular to the
applied load are present in the bulk material. Non-polymeric fibers have higher
longitudinal strength since no flaws are present in the cross-section area (Clegg &

Collyer, 1986).

Cellulose fibers are used as reinforcements for thermoplastics due to several advantages:
(1) low cost, about 5 cents per pound, and renewable nature, (2) capable of working with
thermoplastics such as PP, HDPE and PS, which soften at low temperatures and (3)
biodegradable (Park & Balatinecz, 1997). The drawbacks of cellulose fibers are: (1) poor
adhesion and (2) decomposition of lignocellulosics at high temperature (180 ~—- 200 °C)

(Sain & Kokta, 1994).

The important physical features of cellulose fiber are as follows: (1) The natural cellulose
fiber is a long chain structure, which has a degree of polymerization of 10,000. (2) The
molecule forms into a ribbon-like structure or a sequence of flat plates, linked together by
oxygen bridges. (3) At the oxygen bridge, bending out of the plane of the ribbon and
twisting are fairly easy, so that the molecule is quite flexible although much stiffer than a
polyethylene chain.(4) Hydroxyl groups attach to other hydroxyl groups with hydrogen
bonds. (5) The molecule has properties that depend on direction (Jenkins, 1972; Gauthier

et al, 1998).

Although there are uncertainties about the exact form of the crystalline lattice, cellulose

crystallizes readily. Natural cellulose fibers, such as cotton, flax and rarnie, are highly

l4

ordered; two-thirds of the fiber is crystalline and the rest is amorphous in a two-phase

structure (Jenkins, 1972; Gauthier et a1, 1998).

The wood cell is composed of cellulose, herrricellulose and lignin. Cellulose has a
thermal softening temperature (Tg) range of 231 to 253 °C. The Tg’s of hemicellulose
and lignin are in the range of 167 to 217 °C and 134 to 235 °C, respectively. Sofiwood
fibers are 2.5 to 7.0 millimeters long and 15 to 65 micrometers in diameter, while
hardwood fibers are 1.0 to 1.5 millimeters in length and 15 micrometers in diameter (Sun

& Hawke, 1996).

Interfaces and Interphase

According to Schwartz (1992), when different constituents are intermixed or combined,
there is always a contiguous region. It may simply be an interface, the surface forming
the common boundary of the constituents. An interface is in some ways analogous to the
grain boundaries in monolithic materials. For the composite, the interface is controlled in
order to provide the desired properties from a given pair of materials. In some cases, the
interface of a composite is weak, minimizing coupling of the reinforcement to the matrix.
When the composite is deformed, cracks pass through the matrix until they reach a
whisker. Since the interface between phases is weak, the separation of the matrix causes
the whisker to pull out from the side of the advancing crack, rather than allowing the
crack to pass through the whisker. The friction resulting from this pullout dissipates an
amount of energy, which deflects the crack along the fiber. These phenomena result in

substantial toughening of the composite, in some cases doubling fracture toughness

15

relative to the unreirrforced composite. In some cases, however, the contiguous region is a
distinct added phase, called an interphase. When such an interphase is present, there are
two interfaces: between each surface on the interphase and its adjoining constituent, as

shown in Figure 4.

Interphase
(Bonding agent)

  

Interface

Fiber

 

Matrix

Figure 4. Makeup of interface between fiber and matrix.

The interphase of a composite is the region where loads are transmitted between the
reinforcement and the matrix. The interaction between the reinforcement and the matrix
varies from strong to weak, and can be controlled by using an appropriate coating on the
fiber. In general, the composite is more rigid when it has strong interfacial bonds;
although brittleness may result. On the other hand, a weak bond leads the composite to be
tougher, but it tends to decrease stiffness. If the interfacial bond is weaker than the
matrix, fracture and delarnination will occur under loading conditions. Usually, a
coupling agent is used to overcome the weak limits. The bond also affects the long term
stability of the composite such as fatigue, environmental attack and resistance to hot-wet

conditions (Schwartz, 1992).

16

Prediction of Properties

Successful prediction of mechanical properties of long fiber composites is difficult. The
properties of short fiber reinforced composites are even more complicated to predict. This
is due to the spectrum of fiber length and orientation, caused by processing to the final
part. Besides, the amount of stress taken up by fibers will be affected by the fiber length

(Clegg & Collyer, 1986).

For long fiber reinforcements, it is assumed that both the matrix and the fibers are elastic,
and the Poisson’s ratios are equal. All fibers are aligned in the direction of the tensile
stress, as shown in Figure 5. The tensile strain of the composite, the matrix and the fibers
are assumed equal throughout the material. The tensile force can be calculated by

equation 1 (Clegg & Collyer, 1986):

 

 

 

 

 

 

Figure 5. A tensile force acting on a thermoplastic composite, with long fibers aligned in

the direction of tensile stress.

Fc = Fm +Ff (1)

where F refers to tensile force.
The subscripts c, m and f refer to the composite, matrix and fibers,

respectively.

17

In terms of stress, equation 1 can be expressed as equation 2:
c'cAc = o'mAm + O'fAf (2)

where 0 refers to the tensile stress.

A is the sum of the cross-sectional areas.

As mentioned above,
8c = 8m = 8f = 8
where 8 refers to the tensile strain.

Therefore, equation 2 can be rewritten as equation 3:
EcAc = EmAm + EfAf (3)

where E refers to the tensile modulus.
Instead of area, the volume may be used. The total volumes of the composite, matrix and

fibers are expressed as follows (Clegg & Collyer, 1986):

V0 = [Ac
Vm = [Am
Vf = [Ac

where I is the length of the composite sample.

Then
Ech = Eme + Efl’f (4)

If the volume fraction is substituted in equation 4, it can be expressed as equation 5:

18

Ec = Em‘i’m + Ef‘i’f (5)

where (1) refers to the volume fraction.

Equation 5 represents the simple rule of mixtures, which gives values of the tensile
modulus of the composite for long fiber composites closer to values from theoretical
models than experimental values. If the value of the Poisson’s ratios for the matrix and
the fibers are not equal, about 1% error will be obtained from equation 5. For most

thermoplastic matrices, Poisson’s ratio is 0.4, approximately (Clegg & Collyer, 1986).

Compared to continuous fiber reinforcement, all short fibers do not work at maximum
efficiency. It is assumed that the average strain in the fiber is not equal to that in the
matrix. Due to its stiffness, the fibers limit the deformation of the surrounding matrix
under an applied load. The load is transferred from the matrix to the fiber via the

interfacial shear stress.

The shear stress will be maximum at the ends of the fiber but zero somewhere along the

fiber, while the tensile stress will be higher at the center but zero at the end. If the fiber is

long enough, the maximum tensile stress will reach the tensile stress in the matrix.(L/D)c

refers to the critical aspect ratio, which is required to achieve this condition. In this ratio,

L and D are the length and diameter of the fiber, respectively. In the case of L/D less than

(L/D)c, the tensile stress in the fiber will always be lower than that in the matrix. Thus,

the transfer of load from the matrix to the fiber is poor, so maximum utilization of the

fiber will not be achieved. In the case of L/D higher than (L/D)c, the tensile stress at the

19

interface reaches a maximum over a greater proportion of the fiber length. Although the
transfer of stress fi'om the matrix to the fiber is efficient, the average tensile stress in the
fiber is always less than that in the matrix. This results fiom the reduction of tensile stress
at the ends of the fiber. Therefore, the efficiency of stress transfer will never reach 100%

(Clegg & Collyer, 1986).

Equation 6 is used to accommodate the above change in reinforcement efficiency with

fiber length. This is the fiber length correction factor and has a value of less than unity.
Ec = Em‘bm + mm (6)
1] can be calculated from equation 7:

T] = 1- tanh(BL/2) (7)
(U2)

 

B can be calculated from equation 8:

B = (ZrtGmY’2 (8)
[EfAf rum/m"2

 

where Gm refers to the shear modulus of the matrix.

R is the mean separation of the fibers normal to their length.

r refers to the radius of the fiber.

It should be emphasized that EC depends on L/D.

20

During processing, the fibers may be broken, leading to a lower L/D ratio than planned.
Therefore, the amount of breakage of fiber is a concern. In order to model this variation

in length, the number average fiber length must be obtained.

Uniaxially aligned composites have highly anisotropic behavior, with a considerable
enhancement of tensile modulus in the direction of orientation. In this direction, the

modulus is dominated by the matrix phase and may be estimated from equation 9:

1Age = ‘PP’Ef'i' ¢m/ Em (9)

The tensile strength of the short fiber composite can be modeled using equation 5. Then,

equation 5 becomes equation 10 (Clegg & Collyer, 1986):
C5'Tc = O'Tm‘ilm + UTf‘i’f (10)
where 0T refers to the tensile strength .

In general, the ultimate tensile strain in the fiber is much less than that of the matrix. Also

the tensile strength of the fiber is much more than that of the matrix. These can be

expressed as 0Tf¢f >> 0Tm¢m. an and O'Tm are the tensile strengths of the fiber and
the matrix, respectively. There will be a stress in the matrix at which the ultimate tensile
strain is reached in the fiber. Thus, the tensile strength of the composite can be estimated

from equation 10 above.

If the fibers are not continuous, the average tensile stress in the composite will be

expressed as equation 11:

21

O’Tc = °m¢m +2It‘llf (11)

where 6'? is the average fiber stress, which is given by equation 12:

L
3f = l/L Ioflx) dx (12)
0

If the tensile stress builds up from the fiber ends in a non-linear way, the tensile strength

of fibers can be calculated by equation 13:

5f = O'foo [1—(1- B)Lc/L] forL > LC (13)

where 0 foo is the tensile stress in a continuous in the same matrix under the

same loading condition.

L and Lc represent the length and the critical length of the fibers,

respectively.
The fibers can be stressed to their tensile strengths when L > LC. If it is assumed that the

failure of the fiber occurs when 3f = O'foo, by substituting equation 13 into equation 11,

the tensile strength on the composite will be expressed as equation 14 (Clegg & Collyer,

1986).
“TC = o'foo [1 “ (1' B)Lc/L]¢f+ °m¢m (14)

Compared to equation 10, equation 14 shows that discontinuous fibers result in less
strength in the composite than continuous fibers. However, 95% of the tensile strength of

a continuous fiber reinforced composite can be reached when L/Lc is 10. In an injection

molded product, normally 80% of the fibers are reduced to a length below LC. Therefore,

22

the strength of the product is lower than the predicted strength for continuous fiber

reinforcement.

The value of LC represents the shortest fiber length that may be broken in a matrix. Below
this length, there is insufficient tensile stress to break the fibers, so failure occurs at the

fiber-matrix interface.

In general, Lc is greater than the predicted value because:
(1) debonding of the fibers occurs at the ends where the shear stresses are large.
(2) interaction between fibers constrains the motion of the matrix, leading to
embrittlement.
(3) the fracture process involves matrix fracture between bundles of fibers rather

than individual fibers.

The tensile strength of short fiber reinforced thermoplastics decreases when the angle
between the fiber axis and direction of loading increases. The tensile strength of the
composite in a transverse direction is often less than that of the matrix material owing to

the effects of the fibers (Clegg & Collyer, 1986).

Chtourou et a1 (1992) took a different approach to calculating the Young’s modulus and
the strength at yield of short fiber composites saying they can be estimated by equations

15 and 16:

Ec = keff Efo + Eme (15)

23

0c = Keff‘Tfo+ c5'mVrn (16)

where V refers to volume fraction.

E is Young’s modulus

keff and Kefi‘ are the efficiency coefficients

The efficiency coefficients depend on microstructural parameters such as dispersion,

orientation and adhesion. The effect of fiber length on Keff from equation 16 can be

expressed as equation 17:

Keff = keff(1- Lc/L) (17)

In equation 17, keff is equal to 1/6 when fibers are oriented randomly in three

dimensions. If the fibers are oriented randomly in the plane, keff is equal to 1/3. The keff

is equal to

1/2 when the orientation of fibers is random at an angle of 90° from the plane (Chtourou

& Ait-Kadi, 1992).

Mallick (1988) reported that the mechanisms of impact strength defined as the capability
for absorbing or dissipating of energy, are affected by the following conditions:
(1) Utilization of required energy in order to debond and pull out fibers from the
matrix.
(2) A weak interface between the matrix and fibers (Mallick, 1988;

Chotipatoomwan, 1998).

24

Devi et al. (1997) reported that in the case of fiber reinforced thermoplastics, the greatest

energy absorption during the pull-out process occurs when the length of the fibers is

equal to the critical length (LC). If the length of the fibers is less than Lc, the fibers tend

to pull out from the matrix rather than be broken when the composite is fractured. The
fiacture energy will be a combination of the force to debond the fibers from the matrix
and the force of fiiction between the fibers and the matrix. Equations 18 and 19 express

the fracture energy (U) from pulling out the fiber.

Ul = _le_._2 forL<Lc (18)
12d

U2 = 111:3 forL>Lc (19)
12d

where (1 refers to the fiber diameter.
1: is the interfacial friction stress.

v refers to the volume fraction of the fiber.

According to equation 18, it can be assumed that U;L2 for L < Lc.
For L = LC, the maximum energy can be estimated using equation 20:

Umax = ”—142 (20)
12d

From equation 18, the impact energy decreases as U;L. This decrease in the impact

strength for the composites will occur when L < Lc. However, the impact strength of the
composite is found to increase linearly with the weight fraction of the fiber (Devi et al,

1997; Chotipatoomwan, 1998).

25

Prior Research

Several studies have focused on the improvement of mechanical properties for fiber
reinforced thermoplastic composites. Several types of resins have been used as the
matrix, mixed with several types of fibers. Also, cherrrical treatments have been

investigated in order to improve poor adhesion between the reinforcement fiber and the

matrix.

Tormala et al. (1985) investigated the properties of composites of LDPE and plywood
grindings. The composites were prepared by both injection and extrusion molding. The
concentration of ground plywood was maintained at 30% by weight. The tensile modulus
of the injection molded samples increased in the presence of the grindings (from 105
MPa to 230 MPa), while the tensile strength decreased about 20-30% due to poor
adhesion between the resin and ground plywood. Also, the elongation of extruded

samples was decreased in the presence of the ground plywood.

Chtourou et al. (1992) studied the reinforcement of recycled polyolefins with wood fiber.
The recycled resins were composed of 95% polyethylene and 5% PP. The reinforcement
was a chemitherrnomechanical pulp (CTMP), a mixture of 45% spruce, 45% fir and 10%
poplar. Three different types of fiber/polymer mixtures were prepared by injection and
compression molding under the same conditions. The tensile properties were presented as
a function of the fiber concentration, fiber surface treatment with acetic anhydride and
phenol-formaldehyde, and sample storage time in water. Non-treated fiber had better

strength and toughness than treated fiber. Young’s modulus increased by 150% when

26

30% of fibers by weight was added into the resins. In comparison of tensile properties,
the highest values were obtained with 10% treated fiber. For water absorption, the treated

fiber gave higher values than non-treated fiber.

Sain et al. (1994) investigated the improvement of mechanical and thermal properties of
PP-wood fiber composites by modifying the composition with various interphase
modifiers. The reinforcing fibers were chemithermomechanical pulp (CTMP), explosion
pulp (EP) and sawdust (SD). The modifiers consisted of malated PP (MPP), itaconic
anhydride-modified PP (ITPP), bismaleirrride modified-PP (BPP) and bismaleirnide
modified-CTMP (BCTMP). The results showed that the mechanical and thermal
properties were improved with the addition of modifiers, which developed interactions
between the PP and wood fiber. The best properties were obtained with 40% wood fiber

by weight in the composite in the presence of about 10% modifier by weight.

Chotipatoomwan (1998) studied the mechanical and physical properties of paper fiber
and HDPE composites. There were two kinds of fiber fillers in this experiment: mixed
and deinked paper fiber. The properties of the composites were studied by varying the
fiber content at 0%, 10% 20%, 30% and 40% and using the same processing conditions
for producing all composites. The addition of paper fiber into HDPE caused a reduction
in tensile and impact strength, but an increase in tensile modulus. Water absorption
increased with increasing paper fiber. In comparing the properties, mixed paper fiber

composites gave better results than deinked paper fiber composites.

27

Rojanarungtawee (1998) investigated the effect of mixed resins in different proportions
on the mechanical properties of plastic/wood fiber composites. The matrix phases were
formed by HDPE and PP resins, which were varied from 0% to 100% by weight. The
reinforcement was aspen wood fiber. The mixed resins and wood fibers were
compounded at two different sets of processing temperatures, 180 °C and 150 0C. At a
processing temperature of 180 °C, the greatest ultimate tensile strength and modulus of
elasticity were obtained with 30:70 and 10:90 PP:HDPE, respectively. At a processing
temperature of 150 °C, only 100% HDPE and 30:70 PP:HDPE were processable.
Studying of effect of temperatures from 150 °C tol 80 °C, 0:100 PP:HDPE statistically

showed no significant difference at both temperature.

Ricciardi (1999) investigated the impact of additives on the physical and mechanical
properties of HDPE and paper fiber composites. Three additives were used in this
experiment: maleic anhydride modified HDPE (MAHDPE), low molecular weight PP
(Proflow 1000) and LDPE with a high melt flow index. The study investigated the effects
of MAHDPE at 3%, 6% and 10%. For the effects of Proflow 1000 and LDPE at 5% and
10%, the MAHDPE was maintained at 6%. The results showed that the additives had no
significant effect on modulus of elasticity, elongation and Izod impact strength.
MAHDPE tended to improve yield strength at 10% and tensile strength at 3%. MAHDPE

also seemed to decrease debonding in water at every percentage.

Thepwiwatjit (2000) studied the mechanical properties of recycled HDPE bottles from

household use and wood fiber composites. The reinforcement was aspen fiber. Five

28

different ratios were investigated: 100% HDPE/0% fiber, 90% HDPE/10% fiber, 80%
HDPE/20% fiber, 70% HDPE/30% fiber and 60% HDPE/40% fiber. 60% virgin HDPE
with 40% fiber was produced as a control. The processing conditions were 120 RPM
screw speed and 150 0C. The addition of fiber did not improve the tensile properties of
the composites, but decreased tensile strength, yield strength and elongation. The
modulus and impact strength slightly increased. The water absorption test showed that

the composites gained more weight as fiber content increased.

Wu et al. (2000) studied the effects of fiber surface pretreatment on the interfacial
strength and mechanical properties of wood fiber/polypropylene (WF/PP) composite.
Sawdust, used as a reinforcement, was treated with two modifiers: a vinyl-trimethoxy
silane coupling agent and maleic anhydride (MA) grafted styrene-ethylene-butylene-
styrene (SEBS) triblock copolymer. The highest tensile properties were obtained with the
WF/PP composite containing fibers pretreated with an acid-silane solution. The Charpy
impact strength of WF/PP pretreated with MA grafted SESB was higher than that of the

untreated WF/PP composite.

Recently, Uerkanarak (2001) investigated the effects of processing parameters on the
mechanical properties of HDPE/wood fiber composites. The filler was aspen wood fiber.
The HDPE and fibers were maintained at 60% and 40%, respectively. The processing
parameters varied were feed port location (ports 1 to 3) and screw speed (80, 100 and 120
rpm). Feed port location 3 did not result in successful formation of the composite. The

highest tensile strength, yield strength, modulus of elasticity and elongation were

29

obtained when the fibers were loaded into port 2, while the highest impact strength and
water absorption were obtained at port 1. In the case of screw speed, the highest tensile
properties were obtained at 100 rpm, while the best impact strength and highest water

absorption were obtained at 80 and 120 rpm, respectively.

30

viii?!”

CHAPTER 3

MATERIALS

Polymer Matrix

The pellet form of medium anti-block resin low density polyethylene (LDPE) was
provided by Dow Plastics Company under the trade name Dow Polyethylene 133A. The
density and melt flow rate of this LDPE are 0.923 g/cc (ASTM D 792) and 0.22g/10 min
(ASTM D 123 8) respectively. This resin was selected because it could be used as a
substitute for recycled material from grocery or merchandise bags in MSW. Virgin resin
can be expected to provide about the same properties as recycled resin in this application

(Yam et. al., 1988). The properties of Dow Polyethylene 133A are shown in Appendix A.

The pellet form of extrusion and injection-molding-grade polypropylene homopolymer
(PP) was provided by Dow Plastics Company under the trade name INSPIRE H704-04.
The density and melt flow rate of this PP are 0.9 g/cc (ASTM D 792) and 4g/ 10 min
(ASTM D 123 8) respectively. The PP was used in this experiment as representative of a
common impurity in recycled polyolefins. This is because the polyolefins, which make
up 60 to 80% of solid plastic wastes, can be separated from more dense polymers through
techniques based on density differences, but LDPE cannot readily be separated from PP
this way (Bernhardt, 1987; Laguna et al., 1987). The properties of Dow INSPIRE H704-

04 are shown in Appendix A.

31

Reinforcement or filler

Aspen wood fibers were provided by Abitibi Corporation, Alpena, Michigan. They are
hardwood fibers, which have average length of fiber of 1.22 millimeters. The fibers were
produced by the thermal mechanical pulping (TMP) process. Wood chips are thermally
sofiened under high vapor pressure steam, at approximately 120°C. Then, they are ground
and defibrillated into fibers and fiber bundles. The fibers from TMP provide better
dispersion in nonpolar hydrocarbon polymers because they still contain lignin and natural

waxes (Sun & Hawke, 1996; Woodhams et al., 1984).

32

CHAPTER 4

METHODS

In the preparation of the matrix compound, the LDPE and PP pellets were fed into a
stirring machine, which made the pellets well-mixed. The proportions of LDPE and PP

were varied as shown in Table 2.

Table 2. Variation of LDPE and PP

 

Next, the well-mixed pellets were compounded with aspen wood fiber using a Baker
Perkins Model ZSK 30, 30 mm, 26:1 co-rotating twin screw extruder (Werner &
Pfleiderer Corporation, Ramsey, New Jersey). The proportion of wood fiber and matrix
compound was maintained at 40% fiber and 60% polymer by weight. The calculation of

this proportion is shown in Appendix B.

The extruder consists of three zones, which have different functions. These are the

feeding section, compression zone and metering zone. First, the feed zone is located

below the feed hopper and acts as a conveyor for feeding the polymers to the rest of the

33

"‘7'

barrel. Second, the compression zone makes the polymers into a melt. After the polymers
are melted completely, they go through the metering zone and the exit die (Birley et al.,
1992). In this experiment, the temperatures along the three components were divided into
six zones. The temperatures of these zones were set in two different configurations as

shown in Tables 3 and 4.

Table 3. The set of temperatures over the LDPE melting point

 

Zone 1 2 3 4 5 6

 

 

Temperature (°C) 150 150 150 150 150 150

 

 

 

 

 

 

 

 

 

Table 4. The set of temperatures over the PP melting point

 

Zone 1 2 3 4 5 6

 

 

Temperature (°C) 180 180 150 150 150 150

 

 

 

 

 

 

 

 

The temperatures of zones four to six were set to 150 °C because they ensure that while
the polymer is completely melted, the wood fibers are not burned (Oladipo et al., 1999).
The polymers were fed into the hopper, which was set at a speed of approximately 100
rpm and then passed through zone 1. The screw speed was also set at approximately 100
rpm. There are three feed ports on the extruder, shown in Figure 6. Port 2 was selected as
the fiber feed location because it provides the best mechanical properties (Uerkanarak,
2001). There, the fiber was mixed with the melted polymers, to form the composite.
Next, the composite stream exited through the die and was cut into pieces approximately

6 inches long.

34

tr “-1

 

gamma. Sunbeam . e 25mg

8:05 3.2 3:05 cos 8:2: 2: 3w

    
       

 

Saw—ramm—

aoaw .8.“ .8332 winged

318%

v.53. .5.“ 553e— ”5234

35

The composite was molded into sheets using a Carver Laboratory Press, Model M (Fred
S. Carver, Inc., Menomonee Falls, Wisconsin). The extrudate for each composite was put
into a frame, which was laid between two chrome plates. There were two different
frames, measuring 15 x 15 x 0.25 cm and 12.7 x 12.7 x 0.3175 cm, used in the molding
step. The first one was used for preparing samples for tensile property testing, while the
latter was used for samples for Izod impact testing. Sheets of polyethylene terephthalate
(PET) (Mylar®, Dupont Teijin Films, Hopewell, Virginia), were inserted between the
chrome plates and the frame on both sides in order to prevent stickiness. This method was
called a “sandwich” technique and is shown in Appendix C. Once the plate-frame
structure was assembled completely, it was heated at 150 °C under a pressure of 30,000
psi for 5 minutes. When the extrudates were completely melted into a sheet, the press was
cooled to a temperature of 30°C using tap water. Finally, the molded sheet was

disassembled from the frame.

Tensile property testing conformed to ASTM D 63 8-99 (2000), Standard Test Method for
Tensile Properties of Plastics. The composite test specimens were cut along the
lengthwise (extrusion) direction into a dumbbell shape, type I, using Tensilkut, Model
10-13 (Tensilkut Engineering Division, Sieburg Industries, Inc., Danbury, Connecticut).
Afier the specimens were cut, they were preconditioned at 23 :i: 2 °C and 50 i 5% relative
humidity at least 40 hours before testing. During the test, the conditions of the test were
controlled as much possible to match the preconditions. The tensile property testing was
done by a United Testing System (U TS) model SFM-20 Mechanical Test System. This

machine worked with laser extensometer no. EXT 62LOE and laser power source model

36

no. EXT-62-LI-IMO (United Calibration Corp. 5802 Engineer Dr. Huntington Beach,
Ca), to detect the distance of extension of the specimen. Before testing, the thickness and
the width of specimens were measured along their narrow sections, using a digital vernier
caliper Digimatic (Mitutoyo Corporation, Japan). The UTS machine was set, according to

the ASTM 63 8-99 type I condition, as follows:

Load cell = 1000 lb
Speed of testing = 0.2 in./min
Extension gage length = 2 i 0.01 inches

Distance between grips 4.5 i 0.2 inches

The data for tensile strength and modulus of elasticity were recorded and calculated
automatically. The force (lb)/extension (in) curves were plotted on a Graphtec XY

Plotter, type MP 3200 (Japan).

Izod impact testing conformed to ASTM D 256-97 (2000), Standard Test Method for
Determining the Izod Pendulum Impact Resistance of Plastics. The composite test
specimens were out along the lengthwise (extrusion) direction into pieces 12.7 x 64 x
3.18 mm and notched with an angle of 22 1/2° :t 1/2 ° to a depth of 2.5 mm, according to
Test Method A. The notching was done by a TMI notching cutter (Testing Machine Inc.,
Amityville, New York). These specimens were preconditioned at 23 i 2 °C and 50 i 5%
relative humidity at least 40 hours before testing. When the test was performed, the test
condition was set as much as possible to match the preconditioning. The Izod impact
testing was performed using a TMI 43-I Izod impact tester (Testing Machines Inc.,

Arrrityville, New York) with a 5-lb pendulum. The specimens were positioned as a

37

I: —"_E

vertical cantilever beam and were broken by a single swing of the pendulum. Both type
of failure and impact resistance values were recorded. Four possible types of failures are

defined and shown in Figure 7 as follows:

C Complete Break - A break where the specimen separates into two or more
pieces.

H Hinge Break - An incomplete break that cannot support itself above the
horizontal when the other part is held vertically (less than 90° included
angle)

P Partial Break - An incomplete break that does not meet the definition for a
hinge break but has fractured at least 90% of the distance between the
vertex of the notch and the opposite side.

NB Non-Break - an incomplete break where the fracture extends less than

90% of the distance between the vertex of the notch and the opposite side.

E’I I

Complete Hinge Partial Non-
break break break break

     

Figure 7. Four types of failures

38

Finally, both tensile property testing and Izod impact testing data were compared to

values from the rule of mixtures, shown in Equation 21:

PC = W LDPE 1’an + WPP PPP (21)
where 1’ refers to the property value.

Wrepresents the weight fraction.

The subscripts of C, LDPE and PP refer to the composite, low

density polyethylene and polypropylene, respectively.

The data were evaluated using statistical analysis from SPSS software, using the Least

Significant Difference Method (LSD) test and Duncan’s Multiple Range Test (DMRT) at

the 99% significance level.

39

CHAPTER 5

RESULTS

Processing Above the LDPE Melting Point (150 °C)

1. Tensile Strength

The results of tensile strength measurements are presented in Table 5 and Figure 8. For
comparison, calculated values from the “rule of mixing” are shown in Table 6 and also
presented graphically in Figure 8. Tensile strength decreased as the amount of LDPE

increased.

The highest tensile strength was obtained with 100% PP, and the lowest tensile strength

with 100% LDPE. Statistical analysis at the 99% confidence level showed significant

differences between all samples except pure LDPE and 80:20 LDPEzPP.

40

«w.

 

Table 5. Average tensile strength (psi) at processing temperature of 150 °C

 

”I:

 

 

 

 

 

 

 

Rm Tensile Strength]
0:100 3,763.10:l:71.31 a2
20:80 3,017.57 i 97.72 b
40:60 2,564.38 i 65.71 c
60:40 2,011.38 3: 43.17 d
80:20 1,517.46 1 42.06 e
1000 1,350.73 1r 69.44 e

 

 

 

ITensile Strength (psi) = Mean i Standard Deviation (SD).

2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

Table 6. Calculated tensile strength (psi) from “rule of mixing” at processing temperature

of150 °C

 

 

 

 

 

 

 

 

 

Rm Calculatfiensile Strength
0:100 3,763.10
20:80 3,280.63
40:60 2,798.15
60:40 2,315.68
80:20 1,833 .20
100:0 1,350.73

 

 

41

 

4,500
4,000 _
3,500
3,000
2,500
2,000 ,
1,500
1,000
500

 

Average Tensile Strength

 

 

 

% LDPE by weight

 

-Tensile Strength +Calculated value ]

 

Figure 8. Comparison between average and calculated values of tensile strength (psi) at
processing temperature of 150 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

2. Yield Strength
The results for yield strength are presented in Table 7 and Figure 9. Yield strength also
tended to follow the “rule of mixing”. Calculated values are shown in Table 8 and also

presented graphically in Figure 9. The yield strength decreased as the amount of PP was

decreased.

Statistical analysis at the 99% confidence level again showed significant difference

between all samples except pure LDPE and 80:20 LDPE2PP.

42

Table 7. Average yield strength (psi) at processing temperature of 150 °C

 

1r-fl

 

 

 

 

 

 

 

 

m Yield StrengthI
0:100 3,756.91 i 157.42 a2
20:80 3,017.48 i 218.01 b
40:60 2,563.51 i 147.23 c
60:40 2,010.22 i 96.33 d
80:20 1,510.22 :1: 110.88 e
100:0 1,348.97 1 156.68 e

 

 

Wield Strength (psi) = Mean 1 Standard Deviation (SD).

2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

Table 8. Calculated yield strength (psi) from “rule of mixing” at processing temperature

 

 

 

 

 

 

 

 

 

 

of 150 °C
Ratio of LDPE:PP Calculated Yield Strength
0:100 3756.91
20:80 3275.32
40:60 2793.73
60:40 2312.15
80:20 1830.56
100:0 1348.97

 

 

43

 

4,500
4,000 .,
3,500 , ,
3,000
2,500 ,
2,000 ,
1,500
1,000 ,
500

 

Average Yield Strength

 

 

 

% LDPE by weight

 

-Yield Strength +Calculated value '

 

Figure 9. Comparison between average and calculated values of yield strength (psi) at
processing temperature of 150 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

3. Modulus of Elasticity (MOE)
The results of MOE are shown in Table 9 and Figure 10. These results tended to differ
from those calculated from the “rule of mixing,” which are presented in Table 10 and

graphed in Figure 10. Thus, the results of MOE did not follow the “rule of mixing”.

The highest MOE values were found at 0:100, 20:80, 40:60 and 60:40 LDPE:PP, which
were significantly higher, at the 99% confidence interval, than 80:20 and 100:0
LDPE:PP. The differences within these two groups were not statistically significant.

Table 9. Average MOE (psi) at processing temperature of 150 °C

44

lat—fl U 4

Table 9. Average MOE (psi) at processing temperature of 150 °C

 

 

 

 

 

 

 

 

fifio of LDPE:PP MOE‘
0:100 243,210 i 51,927.77 .12
20:80 274,725 i 57,243.69 a
40:60 208,232 i 21,620.67 a
60:40 206,438 i 24,888.48 a
80:20 128,924 i 18,104.69 b
100:0 109,632 :l: 11,922.92 b

 

 

IMOE (psi) = Mean i Standard Deviation (SD).

2Different letters within the colrunn show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

Table 10. Calculated MOE (psi) from “rule of mixing” at processing temperature of

150 °C

 

 

 

 

 

 

 

 

 

 

We Calculated MOE
0:100 243,210
20:80 216,494
40:60 189,779
60:40 163,063
80:20 136,348
100:0 109,632

 

 

45

 

350,000
300,000
250,000

200,000 ,,
150,000
100,000
50,000
0

 

Average MOE

 

 

 

% LDPE by weight

 

-MOE —.—Calculated Value i

 

Figure 10. Comparison between average and calculated values of MOE (psi) at
processing temperature of 150 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

4. Percent Elongation
The results for percent elongation are presented in Table 11 and Figure 11. Again, these
results tended to differ from those calculated from the “rule of mixing,”which are

presented in Table 12 and presented graphically in Figure 11.

The highest value of percent elongation was obtained with 100% PP and the lowest with
60:40 LDPE:PP. Statistical analysis at the 99% confidence level showed significant
differences between the higher value and all others. The 20:80 and 60:40 blends also
differed. However, the differences in percent elongation at 40:60, 80:20 and 100:0

LDPE:PP were not statistically significant.

46

Table 11. Average percent elongation (%) at processing temperature of 150 °C

 

 

 

 

 

 

 

 

 

WQP ficent ElongationI
0:100 5.35 i: 0.56 a2
20:80 3.33 i 0.78 b
40:60 3.02 :1: 0.49 bc
60:40 2.01 i 0.20 c
80:20 2.47 :1: 0.60 bc
100:0 2.51 :t 0.47 bc

 

 

IPercent Elongation (%) = Mean i Standard Deviation (SD).

2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

Table 12. Calculated percent elongation (%) from “rule of mixing” at processing

 

 

 

 

 

 

 

 

temperature of 150 °C
Ratio of LDPE:PP Calculated Percent Elongation
0: 100 5.35
20:80 4.78
40:60 4.21
60:40 3.65
80:20 3.08
100:0 2.51

 

 

47

 

 

 

 

 

 

 

 

 

Average Elongation

 

 

 

% LDPE by weight

 

- Elongation +Calculated value

 

 

 

Figure l 1. Comparison between average and calculated values of elongation (%) at
processing temperature of 150 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

5. Izod Impact Strength

Table 13 and Figure 12 present the results for Izod impact strength. For comparison,
calculated values from the “rule of mixing” are shown in Table 14 and Figure 12. Izod
impact strength increased as the amount of LDPE increased. Then, it tended to follow the

“rule of mixing.”

The highest Izod impact strength was obtained with 100% LDPE. Statistical analysis at
the 99% confidence interval showed significant differences between all samples except
two groups: the group of pure PP and 80:20 LDPE:PP, and the group of 60:40 and 80:20

LDPE:PP.

48

There were also differences in type of failure. All of the specimens with 100% PP, 20:80,
40:60 and 60:40 LDPE:PP were completely broken after impact by the hammer, while
those specimens with 80:20 LDPE:PP and 100% LDPE gave different results. For the
80:20 variation, the failure was a mix of hinge and complete breaks. The type of failure

from pure LDPE was a mix of hinge and partial break.

Table 13. Average Izod impact strength (fi-lb/in) and type of failure at processing

 

 

 

 

 

 

 

 

temperature of 150 °C

Ration of LDPE:PP Izod Impact Strength ‘ Type of Failure
0:100 0.630 :t 0.235 d2 Complete
20:80 0.949 t 0.576 (1 Complete
40:60 1.302 t 0.252 c Complete
60:40 1.925 1 0.190 b Complete
80:20 2.076 :1: 0.184 b Complete and Hinge
100:0 2.559 :l: 0.388 a Hinge and Partial

 

 

 

‘ Izod Impact Strength (fi-lb/in) = Mean i Standard Deviation (SD).

2Different letters within the colrunn show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

49

 

Table 14. Calculated Izod impact strength (ft-lb/in) from “rule of mixing” at processing

 

 

 

 

 

 

temperature of 150 °C
Ratio of LDPE:PP Calculated Izod Impact Strength
0:100 0.630
20:80 1.016
40:60 1.402
60:40 1.787
80:20 2773
100:0 2.559

 

 

 

 

 

 

 

 

 

 

 

Average Izod Impact Strength

 

 

 

O 20 40 60 80 100
% LDPE by weight

 

-Izod Impact Strength +Calculated valuei

 

 

Figure 12. Comparison between average and calculated values of Izod impact strength .
(ft-lb/in) at processing temperature of 150 °C, for composites with 40% wood fiber and

60% matrix of PP/LDPE

50

Processing Above the PP the Melting Point (180 0C)

1. Tensile Strength
The results of tensile strength measurements are presented in Table 15 and Figure 13. For
comparison, calculated values from the “rule of mixing” are shown in Table 16 and also

presented graphically in Figure 13. Tensile strength decreased as the amount of LDPE

increased. Then, it tended to follow the “rule of mixing”.
The highest tensile strength was obtained with 100% PP, and the lowest tensile strength
with 100% LDPE. Statistical analysis at the 99% confidence level showed significant

differences between all samples except 60:40 and 80:20 LDPE:PP.

Table 15. Average tensile strength (psi) at processing temperature of 180 °C

 

 

 

 

 

 

 

 

Ratio of LDPE:PP Tensile Strength1
0:100 3,382.12 2t 206.72 a2
20:80 3,025.78 i 246.37 b
40:60 2,673.01 :t 137.17 c
60:40 2,145.80 :t 91.02 (I
80:20 1,893.03 1 89.95 d
100:0 1,393.74 1 161.18 e

 

 

 

TTensile Strength (psi) = Mean :1: Standard Deviation (SD).

2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

51

Table 16. Calculated tensile strength (psi) from “rule of mixing” at processing

temperature of 180 °C

 

4,500
4,000
3,500
3,000
2,500
2,000 -
1,500 ,
1,000
500

 

Average Tensile Strength

 

 

 

% LDPE by weight

 

-Tensile Strength +Calculated valufl

 

Figure 13. Comparison between average and calculated values of tensile strength (psi) at

processing temperature of 180 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

52

2. Yield Strength
The results for yield strength are presented in Table 17 and Figure 14. Yield strength also
tended to follow the “rule of mixing”. Calculated values are shown in Table 18 and

presented graphically in Figure 14. The yield strength decreased as the amount of PP

decreased.

The highest yield strength was obtained with 100% PP. Statistical analysis at the 99%
confidence interval showed significant differences between all samples except two
groups: the group of pure PP and 80:20 LDPE:PP, and the group of 60:40 and 80:20

LDPE:PP.

Table 17. Average yield strength (psi) at processing temperature of 180 °C

 

 

 

 

 

 

 

 

Ratio of LDPE:PP Yield Strengthl
0:100 3,378.41 :1: 208.16 a2
20:80 3,005.62 :1: 334.74 b
40:60 2,670.74 3: 137.33 b
60:40 2,134.66 i 101.55 c
80:20 1,892.80 :1: 90.06 c
100:0 1,392.60 i 161.14 (1

 

 

IYield Strength (psi) = Mean i Standard Deviation (SD).

2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

53

 

Table 18. Calculated yield strength (psi) from “rule of mixing” at processing temperature

of 180 °C

 

4,500
4,000 - ,
3,500 ,
3,000 ,
2,500 ,
2,000
1,500 ,. ,
1,000
500 -

 

Average Yield Strength

 

 

 

% LDPE by weight

 

-Yield Strength +Calculated Value?

 

Figure 14. Comparison between average and calculated values of yield strength (psi) at

processing temperature of 180 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

54

3. Modulus of Elasticity
The results of MOE are shown in Table 19 and Figure 15. Again, these results tended to

follow the “rule of mixing.” Table 20 and Figure 15 present these calculated values. The

MOE decreased as the amount of LDPE increased.

The highest MOE values were found at 0:100, 20:80 and 40:60 LDPE:PP, which were

significantly different, at the 99% confidence interval, from 80:20 and 100:0 LDPE:PP.

Table 19. Average MOE (psi) at processing temperature of 180 °C

 

 

 

 

 

 

 

 

Ratio of LDPE:PP MOE‘
0:100 261,252 :l: 72,383.16 :12
20:80 246,143 i 42,566.01 a
40:60 231,061 1- 30,348.36 a
60:40 197,231 3: 19,133.61 ab
80:20 155,988 :l: 21,747.54 bc
100:0 101,857 2t 21,948.84 c

 

 

IMOE (psi) = Mean :1: Standard Deviation (SD).
2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

55

 

Table 20. Calculated MOE (psi) from “rule of mixing” at processing temperature of
180 °C

 

350,000
300,000 ,
250,000 ,
200,000
150,000
100,000 ,
50,000 _
0 ,

 

Average MOE

 

 

 

% LDPE by weight

 

[-MOE +Calculated value 1

 

Figure 15. Comparison between average and calculated values of MOE (psi) at

processing temperature of 180 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

56

4. Percent Elongation
The results for percent elongation are presented in Table 21 and Figure 15. These results
tended to differ from those calculated from the “rule of mixing,” which are presented in

Table 22 and presented graphically in Figure 15.
Elongation at 100% PP and 20:80 LDPE:PP was significantly higher than at 60:40 and
80:20 LDPE:PP. 80:20 had the lowest percent elongation, significantly different from all

other samples except for 60:40 LDPE:PP.

Table 21. Average of percent elongation (%) at processing temperature of 180 °C

 

 

 

 

 

 

 

 

Ratio of LDPE:PP Percent Elongatio?
0:100 3.76 i 0.38 a2
20:80 3.28 i 0.61 a
40:60 3.22 i 0.53 ab
60:40 2.36 i 0.33 bc
80:20 1.96 d: 0.36 c
100:0 2.92 :t 0.43 ab

 

 

IPercent Elongation (%) = Mean i Standard Deviation (SD).

2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

57

 

Table 22. Calculated percent elongation (%) from “rule of mixing” at processing

temperature of 180 °C

 

 

Average Elongation

 

 

 

% LDPE by weight

 

-Elongation +Calculated value }

 

Figure 16. Comparison between average and calculated values of elongation (%) at
processing temperature of 180 °C, for composites with 40% wood fiber and 60% matrix

of PP/LDPE

58

5. Izod Impact Strength
The results of Izod impact strength are shown in Table 23 and Figure 16. These results
tended to differ from those calculated from the “rule of mixing,” which are presented in

Table 24 and graphed in Figure 16.

The highest Izod impact strength was obtained with 100% PP. Statistical analysis at the
99% confidence level showed significant differences between 100% PP and all other
samples except 20:80 LDPE:PP. The group of 40:60, 60:40 and 80:20 LDPE:PP had

significantly lower impact strength than the other samples.

There were also differences in type of failure. All of the specimens with 100% PP, 20:80,
40:60 and 60:40 LDPE:PP were completely broken, while 80:20 LDPE:PP and 100%
LDPE differed. There were three types of failure, hinge, partial and complete break, for

the 80:20 variation. Only partial breaks were obtained from pure LDPE.

59

Table 23. Average of Izod impact strength (fi-lb/in) and type of failure at processing

 

 

 

 

 

 

 

 

temperature of 180 °C

Ratio of LDPE:PP Izod Impact Strength r Type of Failure
0:100 1.935 3: 0.316 a1 Complete
20:80 1.867 3: 0.316 ab Complete
40:60 1.104 t 0.443 c Complete
60:40 1.212 i 0.370 c Complete
80:20 1.108 :1: 0.165 c Complete, Partial and Hinge
100:0 1.555 i 0.368 b Hinge and Partial

 

 

 

I Izod Impact Strength (fi-lb/in) = Mean :1: Standard Deviation (SD).

2Different letters within the column show highly significant differences by Duncan’s

Multiple Range Test (DMRT) at 99% significance level.

Table 24. Calculated Izod Impact Strength (fi-lb/in) from “rule of mixing” at processing

 

 

 

 

 

 

 

 

 

 

temperature of 180 °C
Ratio of LDPE:PP Calculated Izod Impact Strength
0:100 1.935
20:80 1.859
40:60 1.783
60:40 1.707
80:20 1.631
100:0 1.555

 

60

 

3.0

 

 

 

 

 

 

Izod Impact Strength

 

 

0 20 40 60 80 100
% LDPE by weight

 

 

{-Izod Impact Strength +Calculated valu_e1

Figure 17. Comparison between average and calculated values of Izod impact strength

(fi-lb/in) at processing temperature of 180 °C, for composites with 40% wood fiber and
60% matrix of PP/LDPE

61

The Effect of Temperature

The effect of temperature was studied by a comparison of each of the mechanical
properties for the same resin ratio between those two temperatures. With statistical
analysis at the 99% confidence interval, the results for tensile strength and yield strength
for the two ratios of 100% PP and 80:20 LDPE:PP showed a significant difference
between the two temperatures while the rest did not show significant difference between

these temperatures.

For modulus of elasticity, statistical analysis at the 99% confidence interval showed the

ratios of 40:60 and 80:20 LDPE:PP had significant differences between the two

temperatures while the remaining ratios did not show significant differences.

For percent elongation, there were five ratios that showed significant difference between
the two temperatures; only the ratio of 20:80 LDPE:PP did not show a significant

difference.

For Izod impact resistance, statistical analysis at the 99% confidence interval showed that

all of the ratios had a significant difference between the temperatures.

The raw data for all mechanical properties are shown in Appendix D and the statistical

analyses are reported in Appendix E.

62

CHAPTER 6

DISCUSSION

Processing Above the LDPE Melting Point (150 0C)

The mechanical behavior of composites can be investigated by measuring tensile
properties. In this study, all test specimens were cut only in the lengthwise (extrusion)
direction, since these are less variable than those from the crosswise direction
(Rojanarungtawee, 1998). The tensile measurements used were tensile strength, yield
strength, modulus of elasticity and % elongation at yield. These results are useful for

qualitative characterization and development (Chotipatoomwan, 1998).

In general, the addition of fibrous fillers is used to improve mechanical properties of
composites; however, a lack of adhesion between the hydrophobic polymer and
hydrophilic fiber may cause poor strength properties. Sain et al. (1993) studied the effects
of the composition of composites on their mechanical properties. Their results showed
that the presence of cellulosic fiber, e.g. aspen, in the PP composites caused a reduction
of tensile strength. Herrera-Franco and Aguilar-Vega (1997) also confirmed that the
addition of fiber reduced the tensile strength because the high viscosity of the matrix

during composite fabrication may hinder proper dispersal of fiber.

The highest tensile strength was obtained with 100% PP. The tensile strength of the

composite is less than that of 100% PP without fiber. This is due to the reason above. The

63

tensile strength of the composite tended to decrease with addition of LDPE. Comparison
with strength calculated from the “rule of mixing” confirmed that tensile strength

reasonably followed the “rule of mixing.”

The addition of LDPE tends to decrease the tensile strength of the composite because it
affects the crystallinity of the composite. The crystallinity is one of the factors that affects
the tensile strength. As it is increased, the tensile strength will be increased. Basically,
LDPE has a more branched structure. Most PP in packaging is isotactic, which is highly
crystalline. The presence of branches in the backbone chain limits the formation of
crystallinity by introducing irregularities in the structure. Therefore, LDPE is less
crystalline than PP. The addition of LDPE resulted in the amorphous region of the
composite being increased while the crystalline region was decreased. Then, the tensile

strength also decreased.

The results for yield strength, MOE and elongation also changed for the same reason as
the tensile strength. The highest values for both yield strength and elongation were
obtained with 100% PP, while the highest MOE was obtained in the group of 0: 100,
20:80, 40:60 and 60:40 LDPE:PP. Statistical analysis did not show significant differences
within these groups. This is because MOE is affected by various factors such as filler
geometry, particle size dispersion, and filler concentration. In addition, fiber orientation

and spherulite size of the polymer components also affect the modulus (Bigg, 1987).

64

The last mechanical property in this experiment was Izod impact resistance. This test
method is used to determine the resistance to breakage by flexural shock of plastics and
composites, as indicated by the energy extracted from a standardized pendulum-type
hammer, mounted in a standard machine, in breaking standard specimens with one
pendulum swing. The notch on the specimen concentrates the stress in order to minimize
the deformation and direct the fracture to the part of the specimen behind the notch

(Chotipatoomwan, 1998).

In general, the inclusion of fillers in plastic matrices makes the composite more brittle.
However, the fracture behavior is mostly determined by the properties of the polymer
matrices. Most of the energy used for material fracture is required for straining and
fracturing of the matrices (Berlin et al, 1986). For brittle matrices, the introduction of a
disperse filler raises the surface energy of the material fracture, and can improve the
impact strength of the composites. The filler decreases the surface energy in case of non-
brittle matrices because of the reduction of the volume fi'action in the plastic zone. Then,

the impact strength decrease with the addition of fillers (Chotipatoomwan, 1998).

According to the Izod impact resistance data, the highest value was obtained with 100%
LDPE. This can result from the lesser amount of crystallinity. Again, crystallinity plays
an important role for irnpactresistance. Since the addition of LDPE, which is less
crystalline than PP, increases the amorphous region of the composite, the impact

resistance will be increased.

65

Processing Above the PP Melting Point (180 °C)
As previously described, the results of tensile strength, yield strength, MOE and
elongation also depend on the same factors. The highest values are obtained with 100%

PP except for MOE and elongation.

The highest MOE was found at three variations, which are 100% PP, 20:80 and 40:60
LDPE:PP, for the same reason as in processing at 150 °C. Statistical analysis at the 99%
confidence level showed no significant difference within this group. For elongation, there
were two highest values, obtained with 100% PP and 20:80 LDPzPP. The reason for the

elongation results might be inconsistent fiber distribution during processing.

Examining the “rule of mixing, ” only elongation differed, while tensile strength, yield
strength and MOE tended to follow the rule. Again, inconsistent fiber distribution might

occur during processing.

For Izod impact resistance, the highest value was obtained with 100% PP. The results
also differ from the “rule of mixing. ” In fact, the value of Izod impact resistance should
increase with the presence of amorphous regions. Poor adhesion between the matrix and
the wood fiber might occur during processing, causing dissipation of the maximum
energy resulted from mechanical friction during the pullout process and debonding of the

fiber (Lawrence, 1974).

66

The Effect of Temperature

A summary of the effect of processing temperatures on variations and mechanical

properties is presented in Table 25.

Table 25. The effect of temperature on variations and mechanical properties

 

 

 

 

 

 

 

 

Variation LDPE:PP
Mechanical properties 0:100 20:80 40:60 60:40 80:20 100:0
Tensile Strength - 0 0 0 + 0
Yield Strength - O 0 0 + 0
MOE 0 0 + O + 0
Percent elongation - 0 + + - +
Izod impact resistance + + + - - -

 

 

 

 

 

 

 

 

 

Wifferent symbols represent signifmfferences between processing temperature
of 150 °C and 180 °C by Duncan’s Multiple Range Test (DMRT) at the 99% confidence
level. Where + refers to properties at 180 °C significantly higher than at 150 °C, - refers
to properties at 150 °C significantly higher than at 180 °C and 0 refers to no significant

difference between properties at 150 °C and 180 °C.
From Table 25, the effect of processing temperature can be described in 6 cases. First, the

results from 0:100 LDPE:PP showed that increasing the temperature from 150 °C to 180

°C affected tensile strength, yield strength, percent elongation and Izod impact resistance.

67

The first three properties tended to decrease with increasing temperature, while the latter

tended to increase. On the other hand, MOE was not affected by increasing temperature.

Second, the effect of processing temperature on 20:80 LDPE:PP revealed that increasing
temperature had no effect on tensile strength, yield strength, MOE and percent

elongation, whereas Izod impact resistance improved with increasing temperature.

Third, increasing the processing temperature showed no effect on tensile strength and
yield strength obtained with 40:60 LDPE:PP, while it tended to increase MOE, percent

elongation and Izod impact resistance

In the case of 60:40 LDPE:PP, increasing the processing temperature from 150 °C to 180
°C did not affect tensile strength, yield strength, and MOE. On the other hand, percent
elongation and Izod impact resistance were affected by increasing temperature;

elongation tended to increase, but the impact resistance decreased.

Next, all mechanical properties of 80:20 LDPE:PP were affected by increasing
temperature. Tensile strength, yield strength and MOE tended to increase, while percent

elongation and Izod impact resistance decreased.

For the last variation of 100:0 LDPE:PP, its tensile strength, yield strength and MOE

were not affected by increasing the processing temperature from 150 °C to 180 °C. In

68

contrast, percent elongation increased and Izod impact resistances decreased when the

processing temperature increased.

Increasing the temperature also affected the color of the extrudate. The color of extrudate
from the processing temperature of 180 °C tended be slightly darker than that from 150
°C. This could be due to thermal degradation of the fiber at high temperature (Sain &

Kokta, 1994).

Rojanarungtaee (1998) processed composites of mixed HDPE and PP with wood fiber.
The PP was Pro-Fax 7823, Himont, USA, which had 0.5 g/min melt flow rate and 0.897
g/cm3 density. It was found that only 70:30 HDPEzPP and 100:0 HDPEzPP was
processable. Since the melting point of PP was around 175 to 185 °C, the compounding
temperature at 150 °C was too low for PP to melt during processing. Therefore, it was
surprising that the PP in this research melted sufficiently to form a composite at 150 °C.
This might result from the effect of molecular structure on melt viscosity of the PP
(Birley et al, 1992). Polymer chains are highly coiled in the equilibrium state and there is
a high degree of both inter- and intra-chain entanglement. When resins are forced to
move by the extruder, the chains tend to become aligned and disentangled. There will
also be some slippage of the chains over each other (Birley et al, 1992). Thus, the

viscosity decreases as shear increases. However, this should be investigated further.

69

CHAPTER 7

CONCLUSIONS

In the study of mechanical properties of LDPE/PP and wood composites, the values of
tensile strength, yield strength, MOE and elongation were measured, as well as impact
resistance. The variation of 0:100 LDPE:PP for both processing temperature seemed to
provide the highest mechanical strength, while the impact strength tended to differ. The
highest Izod impact strength of 150 °C was obtained with 100:0 LDPE:PP, but the

highest value of 180 °C was gained with 0: 100 LDPE:PP.

In the cases of tensile strength and yield strength, decreasing the crystalline fraction,
which resulted from the presence of LDPE in the PP matrix, led to decrease these two
properties. However, lack of crystallinty in the PP matrix could not be used to explain the
results for MOE and elongation because they did not vary gradually. Geometry, size and
concentration of the fiber filler rrright cause changes in MOE and elongation (Bigg,
1987). The explanation of the impact strength differs for the two temperatures. For
processing at 150 °C, the increase in the impact strength might be the same reason as for
tensile strength and yield strength, but the value from 180 °C might be due to increased

mechanical friction during the pullout process and debonding of fibers (Lawrence, 1974).

The effect of the processing temperature on mechanical properties of the blends varied

with blend composition.

70

RECOMMENDATIONS FOR FUTURE RESEARCH

Interference with mechanical properties of polymer-wood composites might occur due to
poor compatibility between the polar hydrophilic wood fiber and the non-polar
hydrophobic polymer matrix, indicating weak interfacial adhesion and poor dispersion of
wood fiber in the matrix due to strong fiber-fiber interactions resulting from hydrogen

bonding.

A recommendation for future research is to investigate the addition of chemical
modification as a coupling agent, such as maleic anhydride modified HDPE (MAHDPE),
bismaleic modified-PP (BPP), etc, in order to modify compatibility between the matrix

and the fibers.
Also, the physical characteristics of the composite such as fiber orientation and
nucleation size of blends should be investigated in order to provide more explanation of

for the effects on mechanical properties.

Instead of compression molding, injection molding might be used to prepare the

specimens in order to provide more precision in experimental data.

71

APPENDIX A

72

T.____

 

Table 26. Properties of Dow Polyethylene 133A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Physical Properties Test method Value‘" English (SI)
Resin Properties
Melt Index, g/10 min ASTM D 1238 0.22
Density, g/cc ASTM D 792 0.9230
DSC Melting point, °F (°C) Dow Method 232 (111)
VICAT Softing Point, °F (°C) ASTD D 1525 203 (95)
Film Pro erties, 2.0 mi] (51 um)
Puncture Resistance, f’t-lbp’in3 (J/cms) Dow Method 44 (4)
Dart Impact (Method A), g ASTM D1709 253
Elmendorf Tear, g MD ASTMD 1922 302
CD 197
Tensile Yield, psi (MPa) MD ASTM D 882 1933 (13)
CD 1688 (12)
Ultimate Tensile, psi (MPa) MD ASTM D 882 3604 (25)
CD 3824 (26)
Ultimate Elongation, % MD ASTM D 882 328
A - CD 620
Toughness, fi'lbf/IHJTJ/ij) MD ASTM D 882 1627 (135)
CD 2249 (186)
Gloss, 45° ASTM D 2457 46
Haze, % ASTM D 1003 14

 

 

 

(”Typical value, not to be construed as specification (Dow Plastics Chemical, Midland,

MI).

73

«tn—q

 

Table 27. Properties of Dow Inspire H704-04

 

 

 

 

 

 

 

 

 

Physical Properties Test method Valuem English (SI)
Melt Index, g/ 10 min ASTM D 1238 4.0
Density, g/cc ASTM D 792 0.9
Tensile Strength at yield, psi (MPa) ASTM D 638 5000 (34.5)
Elongation at yield, % ASTM D 638 12
Flexural Modulus ASTMD 790A 250,000 (1725)
Deflection Temperature Under Load ASTM D 648 207 (97)
Unannealed, °F (°C)
Notched Izod, ft-lbp/in3 (J/cm") ASTM D 256A 0.8 (42.5)

 

 

 

(”Typical value, not to be construed as specification (Dow Plastics Chemical, Midland,

MI).

74

 

APPENDIX B

75

Calculation for the proportion of wood fiber and matrix compound

In order to attain a proportion of wood fiber and matrix compound of 40:60, w/w, it is
necessary to calculate the polymer feed rate and fiber feed rate to know how much fiber
must be fed into the extruder port (Rojanarungtawee, 1998). The calculations were as

follows:

1. Polymer feed rate
1.1 Feed the well-mixed pellets through the extruder hopper with screw speed at
100 rpm.
1.2 Once the extrudate exits the die, start cutting the extrudate every one minute
until five samples of extrudate are cut.
1.3 Wait until the extrudates cool and weigh each extrudate.

1.4 Calculate the polymer feed rate from

Polymer feed rate (g/min) = Total extrudate weigl_rt (g)
5 (min)

2. Fiber feed rate,
2.1 Calculate the fiber feed rate from
Fiber feed rate (g/min) = Polymer feed rate x (40/60)

2.2 Calculate the amount of fiber to be fed into the port per minute from

Amount of fiber (g) = Fiber feed rate (gzmin)

1 min

76

APPENDIX C

77

Compression molding process: “sandwich technique”

This process is called a sandwich because the extrudate is placed between two chrome

plates before applying pressure. The processing steps are shown as follows:

1.

2.

Chrome plate

Set temperature on top and bottom of mold plate to 150 °C.
Assemble the extrudate, frame, Mylar sheets and chrome plates as shown in

Figure 17.

. Once the temperature of mold plates reaches 150 °C, place the assembly on

the bottom mold plate.

. Turn off the hydraulic chamber valve by turning clockwise and increase the

pressure to 30,000 psi by moving the handle. Avoid wrinkles by pressing the

assembly softly

. Hold for 5 minutes. If pressure drops, apply more pressure.

. To cool down the temperature, turn the temperature setting to 30 °C and turn

on the cooling system (tap water).

. After the temperature reaches 30 0C, withdraw the assembly from the mold

and remove all components with care.

. For clean up, set the temperature to 200 °C. Place the chrome plates on the

mold plate and wait for 5 minutes. Then, remove all resins with a scraper.

Mylar sheet

  
 

Extrudate
Frame
Mylar sheet

Figure 18. “Sandwich technique” diagram

78

APPENDIX D

79

Table 28. Results of tensile strength (psi) at processing temperature of 150 °C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0:100 3,579.62 3,704.80 3,953.17 3,905.58 3,672.35 3,763.10 159.47
20:80 3,203.63 2,834.02 2,755. l 7 3,247.70 3,047.33 3,017.57 218.52
40:60 2,747.34 2,619.26 2,541.24 2,571.65 2,342.40 2,564.38 146.93
60:40 2,012.95 1,901.00 1,942.53 2,052.48 2,147.94 2,01 1.38 96.52
80:20 1,430.55 1,469.15 1,468.08 1,664.61 1,554.90 1,517.46 94.05
100:0 1,5fi.94 1,213.28 1,308.43 1,434.26 1,219.72 1,350.73 155.28

Table 29. Results of yield strength (psi) at processing temperature of 150 °C

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0:100 3,571.41 3,702.23 3,949.10 3,889.62 3,672.21 3,756.91 157 .42
20:80 3,203.63 2,835.30 2,755.17 3,246.90 3,046.42 3,017.48 218.01
40:60 2,747.17 2,618.67 2,538.46 2,571.65 2,341.60 2,563.51 147.23
60:40 2,012.27 1,898.97 1,942.53 2,051.20 2,146.14 2,010.22 96.33
80:20 1,430.39 1,589.54 1,460.31 1,663.39 1,4(fi46 1,510.22 110.88
100:0 1,577.35 1,211.35 1,307.48 1,434.26 1,214.41 1,348.97 156.68

 

 

80

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1.—

Table 30. Results of modulus of elasticity (psi) at processing temperature of 150 °C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0: 100 259,462 158,918 299,264 259,273 239,136 243,210 5 1 ,927 .77
20:80 332,961 209,561 288,135 220,157 332,810 274,725 57,243.69
40:60 229,628 217,054 175,006 199,112 220,359 208,232 21,620.67
60:40 200,780 181,660 197,835 203,646 248,271 206,438 24,888.48
80:20 100,910 139,283 120,473 140,120 143,832 128,924 18,104.69
100:0 1 10,432 104,007 104,075 129,849 99,797 109,632 11,922.92

Table 31. Results of percent elongation at processing temperature of 150 °C

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0:100 6.25 4.72 5.26 5.33 5.21 5.35 0.56
20:80 2.78 378i 2.64 4.49 2.98 3.33 0.78
40:60 3.4 2.26 3.19 3.43 2.83 3.02 0.49
60:40 2.27 2.06 1.86 2.09 1.77 2.01 0.20
80:20 2.63 1.77) 3.14 2.88 2.00 2.47 0.60
100:0 2.18 3.32 2.40 2.19 2.48 2.51 0.47

 

 

 

 

 

 

 

 

 

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Table 33. Results of tensile strength (psi) at processing temperature of 180 °C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

83

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0:100 3,218.89 3,390.15 3,715.41 3,200.11 3,386.06 3,382.12 206.72
20:80 2,964.24 3,142.92 2,726.13 2,917.90 3,377.71 3,025.78 246.37
40:60 2,506.23 2,663.90 2,740.70 2,862.99 2,591.24 2,673.01 137.17
60:40 2,131.33 2,278.19 2,087.60 2,187.47 2,044.42 2,145.80 91.02
80:20 1,861.05 1,901.40 1,783.05 1,888.24 2,031.42 1,893.03 89.95
100:0 1,348.26 1,298.79 1,678.37 1,294.97 1,348.30 1,393.74 161.18

Table 34. Results of yield strength (psi) at processing temperature of 180 °C

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0:100 3,208.87 3,389.93 3,713.89 3,199.81 3,379.56 3,378.41 208.16
20:80 ND ND 2,725.94 2,914.40 3,376.51 3,005.62 334.74
40:60 2,504.79 2,656.26 2,739.99 2,861.81 2,590.85 2,670.74 137.33
60:40 2,130.97 2,277.28 2,086.71 ND 2,043.66 2,134.66 101.55
80:20 1,860.83 1,901.08 1,782.64 1,888.08 2,031.35 1,892.80 90.06
100:0 1,347.38 1,296.59 1,677.07 1,294.38 1,347.56 1,392.60 161 . 14

Note: ND = Not Detected

lf’m‘“,

Table 35. Results of modulus of elasticity (psi) at processing temperature of 180 °C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0: 100 277,349 300,233 137,245 269,020 322,412 261 ,252 72,3 83.16
20:80 237,610 253,850 212,300 211,665 315,289 246,143 42,566.01
40:60 182,539 264,432 245,676 230,256 232,400 231,061 30,348.36
60:40 218,078 208,886 180,810 204,923 173,459 197,231 19,133.61
80:20 158,328 176,654 127,284 176,431 141,242 155,988 21,747.54
100:0 91,962 85,344 139,363 102,949 89,670 101,857 21,948.84

Table 36. Results of percent elongation at processing temperature of 180 °C

Ratio Replication

LDPE:PP 1 2 3 4 5 Mean SD
0:100 3.58 4.07 4.13 3.20 3.82 3.76 0.38
20:80 ND ND 3.48 3.77 2.59 3.28 0.61
40:60 3.70 3.34 2.89 2.47 3.68 3.22 0.53
60:40 1.93 2.36 2.43 ND 2.73 2.36 0.33
80:20 1.57 2.10 2.41 1.62 2.09 1.96 0.36
100:0 3.16 3.52 2.47 2.56 2.91 2.92 0.43

 

 

 

 

 

 

 

 

 

 

 

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85

APPENDIX E

86

Table 38. One-way Analysis of Variance of tensile strength at processing temperature of

150°C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 21461 102.8 5 429222057 187.920 .000
Within Group 548176.185 24 22840674
Total 22009279.0 29
Post Hoc Tests
Multiple Comparisons and Homogeneous Subsets
Dependent Variable: tensile strength at processing temperature of 150 °C
Man
Variation Subset for alpha = .01
LDPE:PP N e d c b a
100:0 5 13507260
80:20 5 1517.4580
60:40 5 20113800
40:60 5 25643780
20:80 5 30175700
0:100 5 3763.1040
Sig. .094 1.000 1.000 1.000 1.000

 

 

 

 

 

 

 

Means for groups in homogeneous subsets are displayed.

87

 

 

Table 39. One-way Analysis of Variance of yield strength at processing temperature of

150°C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square (11' Mean Square F Sig.
Between Groups 214567642 5 429135285 183.769 .000
Within Group 560444.945 24 23351.873
Total 220172092 29
Post Hoc Tests
Multiple Comparisons and Homogeneous Subsets
Dependent Variable: yield strength at processing temperature of 150 °C
M
Variation Subset for alpha = .01
LDPE:PP N e d c b a
100:0 5 1348.9700
80:20 5 1510.2180
60:40 5 2010.2220
40:60 5 2563.5100
20:80 5 3017.4840
0:100 5 3756.9140
Sig. .108 1.000 1.000 1.000 1.000

 

 

 

 

 

 

 

 

Means for groups in homogeneous subsets are displayed.

88

"f
B

"if—m -,

 

Table 40. One-way Analysis of Variance of MOE at processing temperature of 150 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 7.805E+10 5 1.561E+10 17.964 .000
Within Group 2.086E+10 24 869017305
Total 9.891E+10 29
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: MOE at processing temperature of 150 0C

 

 

 

 

2mm
Variation LDPE:PP Subset for alpha = .01
N b a
100:0 5 109632.00
80:20 5 128923.60
60:40 5 206438.40
40:60 5 208231.80
20:80 5 234724.80
0:100 5 243210.60
Sig. .311 .082

 

 

 

 

 

Means for groups in homogeneous subsets are displayed.

89

‘1? a‘ y - .

Table 41. One-way Analysis of Variance of percent elongation at processing temperature

of 150 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 34.274 5 6.855 21.668 .000
Within Group 7.592 24 .316
Total 41.867 29
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: percent elongation at processing temperature of 150 0C

 

 

 

 

 

 

 

 

 

 

.Ilunqan.
Variation Subset for alpha = .01
LDPE:PP b a
60:40 2.1 100
80:20 2.4700 2.4700
100:0 2.5140 2.5140
40:60 3.0220 3.0220
20:80 3.3340
0: 100 5.3540
Sig. .026 .034 1.000
Means for groups in homogeneous subsets are displayed.

90

‘ "a! I a '- .I

Table 42. One-way Analysis of Variance of Izod impact resistance at processing

 

 

 

 

 

 

 

 

 

 

 

 

temperature of 150 °C
Analysis of variance
Sum of square (11' Mean Square F Sig.
Between Groups 39.899 5 7.980 69.804 .000
Within Group 9.603 84 .114
Total 49.502 89
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: Izod impact resistance at processing temperature of 150 °C

 

 

 

 

29m

Variation Subset for alpha = .01

LDPE:PP N d c b a
60:40 15 .62980
80:20 15 .94862
100:0 15 1.30180
40:60 15 1.85853
20:80 15 2.07633
0:100 15 2.55927

Sig. .012 1.000 .081 1.000

 

 

 

 

 

 

 

Means for groups in homogeneous subsets are displayed.

91

‘1‘

Table 43. One-way Analysis of Variance of tensile strength at processing temperature of

180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 138137676 5 276275351 100.707 - .000
Within Group 658404.641 24 27433527
Total 144721722 29
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: tensile strength at processing temperature of 180 °C

 

 

 

 

m

Variation Subset for alpha = .01

LDPE:PP N e d c b a
100:0 5 1393.7380
80:20 5 1893.0320
60:40 5 2145.8020
40:60 5 2673.0120
20:80 5 3025.7800
0:100 5 3382.1240

Sig. 1.000 .024 1.000 1.000 1.000

 

 

 

 

 

 

 

Means for groups in homogeneous subsets are displayed.

92

 

 

Table 44. One-way Analysis of Variance of at yield strength processing temperature of

180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square (11’ Mean Square F Sig.
Between Groups 128833909 5 257667818 84.534 .000
Within Group 640099.152 21 30480.912
Total 135234900 26
Post Hoc Tests
Multiple Comparisons and Homogeneous Subsets
Dependent Variable: yield strength at processing temperature of 180 °C
Bunsen.
Variation Subset for alpha = .01
LDPE:PP d c b a
100:0 13925960
80:20 1892.7940
60:40 2134.6550
40:60 2670.7400
20:80 30056167
0:100 3378.4120
Sig. 1.000 .054 .010 1.000

 

 

 

 

 

 

Means for groups in homogeneous subsets are displayed.

93

 

 

 

Table 45. One-way Analysis of Variance of MOE at processing temperature of 180 0C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F . Sig.
Between Groups 9.208E+10 5 1.842E+10 11.890 .000
Within Group 3.717E+10 24 1.549E+9
Total 1.292E+1 l 29
Post Hoc Tests
Multiple Comparisons and Homogeneous Subsets
Dependent Variable: MOE at processing temperature of 180 0C
22mm
Variation Subset for alpha = .01
LDPE:PP c b a
100:0 101858.80
80:20 155987.80 155987.80
60:40 197231.20 197231.20
40:60 231060.60
20:80 246142.80
0:100 261251.80
Sig. .040 .l 1 l .025

 

 

 

 

 

 

Means for groups in homogeneous subsets are displayed.

94

‘15

Table 46. One-way Analysis of Variance of percent elongation at processing temperature

of 180 °C

Analysis of variance

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 10.223 5 2.045 10.603 .000
Within Group 4.050 21 .193
Total 14.272 26

 

 

 

 

 

 

Post Hoc Tests
Multiple Comparisons and Homogeneous Subsets

Dependent Variable: percent elongation at processing temperature of 180 °C

 

 

 

 

 

 

 

 

 

 

m
Variation Subset for alpha = .01
LDPE:PP N c b a
80:20 5 1.9580
60:40 4 2.3625 2.3625
100:0 5 2.9240 2.9240
40:60 5 3.2160 3.2160
20:80 3 3.2800
0:100 5 3.7600
Sig. .189 .012 .016
Means for groups in homogeneous subsets are displayed.

95

 

Table 47. One-way Analysis of Variance of Izod impact resistance at processing

temperature of 180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

96

Sum of square df Mean Square F Sig.
Between Groups 10.689 5 2.138 18.446 .000
Within Group 9.736 84 .116
Total 20.425 89
Post Hoc Tests
Multiple Comparisons and Homogeneous Subsets
Dependent Variable: Izod impact resistance at processing temperature of 180 oC
D_u_n_can_
Variation Subset for alpha = .01
LDPE:PP N c b a
40:60 15 1.10367
80:20 15 1.10787
60:40 15 1.21160
100:0 15 1.55507
20:80 15 1.86680 1.86680
0:100 15 1.93487
Sig. .418 .014 .585
Means for groups in homogeneous subsets are displayed.

 

 

Table 48. One-way Analysis of Variance of tensile strength at processing temperature of

150 and 180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 353096400 11 320996727 127.698 .000
Within Group 120658083 48 25137.101
Total 365 16220.8 59
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: tensile strength at processing temperature of 150 and 180 °C

Duncan

 

Variation

LDPE:PP

Subset for alpha = .01

 

2

f

d

c

 

 

100:0 @ 150°C
100:0 @ 180°C
80:20 @ 150°C
80:20 @ 180°C
60:40 @ 150°C
60:40 @ 180°C
40:60 @ 150°C
40:60 @ 180°C
20:80 @ 150°C
20:80 @ 180°C
0:100 @ 180°C
0:100 @ 150°C
Sig.

 

1350.72
1393.73
1517.45

MMMMMMMMMMMU‘

.122

 

 

1893.03
2011.38
2145.80

.020

2564.38
2673.01

.284

 

 

3017.57
3025.78

.935

 

3382.12

1 .000

 

3763.10
1.000

 

 

Means for groups 111 homogeneous subsets are displayed.

97

 

Table 49. One-way Analysis of Variance of yield strength at processing temperature of

150 and 180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 34341854.4 11 312198676 117.021 .000
Within Group 120054410 45 26678.758
Total 355423985 56
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: yield strength at processing temperature of 150 and 180 oC

Duncan

 

Variation

LDPE:PP

Subset for alpha = .01

 

2

f

d

C

 

 

100:0 @ 150°C
100:0 @ 180°C
80:20 @ 150°C
80:20 @ 180°C
60:40 @ 150°C
60:40 @ 180°C
40:60 @ 150°C
40:60 @ 180°C
20:80 @ 180°C
20:80 @ 150°C
0:100 @ 180°C
0:100 @ 150°C
Sig.

 

1348.97
1392.60
1510.22

MMUIMMM-bMMMML/I

.162

 

 

1892.79
2010.22
2134.66

.037

2563.51
2670.74

.322

 

 

3005.62
3017.48

.912

 

3378.41

1 .000

 

3756.91
1.000

 

 

Means for groups 1n homogeneous subsets are displayed.

98

'lfl'm

Table 50. One-way Analysis of Variance of MOE at processing temperature of

150 and 180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

99

Sum of square df Mean Square F Sig.
Between Groups 1.717E+11 11 1.561 E+10 12.915 .000
Within Group 5.803 E+10 48 1.209 E+09
Total 2.298 E+11 59
Post Hoc Tests
Multiple Comparisons and Homogeneous Subsets
Dependent Variable: MOE at processing temperature of 150 and 180 °C
Duncan
Variation Subset for alpha = .01
LDPE:PP N c u, a
‘
100:0 @ 180 C 5 101858.80
100:0 @ 150°C 5 109632.00
80:20 @ 150°C 5 128923.60
80:20 @ 180°C 5 155987.80 155987.80
60:40 @ 180°C 5 197231.20 197231.20
60:40 @ 150°C 5 206438.40 206438.40
40:60 @ 150°C 5 208231.80 208231.80
40:60 @ 180°C 5 231060.60
20:80 @ 150°C 5 234724.80
0:100 @ 150°C 5 243210.60
20:80 @ 180°C 5 246141.80
0:100 @180°C 5 261251.80
Sig. .027 .033 .014
Means for groups in homogeneous subsets are cisplayed.

 

Table 51. One-way Analysis of Variance of percent elongation at processing temperature

of150 and 180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 45.208 1 1 4.1 10 15.886 .000
Within Group 11.642 45 .259
Total 56.850 56
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: percent elongation at processing temperature of 150 and 180 °C

 

 

 

 

 

 

 

 

 

 

Duncan
Variation Subset for alpha = .01
LDPE:PP N e d c b a
80:20 @ 1805C 5 1.9580
60:40 @ 150°C 5 2.1100 2.1100
60:40 @ 180°C 4 2.3625 2.3625 2.3625
80:20 @ 150°C 5 2.4700 2.4700 2.4700
100:0 @ 150°C 5 2.5140 2.5140 2.5140
100:0 @ 180°C 5 2.9240 2.9240 2.9240 2.9240
40:60 @ 150°C 5 3.0220 3.0220 3.0220
40:60 @ 180°C 5 3.2160 3.2160
20:80 @ 180°C 5 3.2800 3.2800
20:80 @ 150°C 5 3.3340 3.3340
0:100 @ 180°C 5 3.7600
0:100 @ 150°C 5 5.3540
Sig. .012 .018 .014 .031 1.000

 

Means for groups in homogeneous subsets are displayed.

100

 

 

Table 52. One-way Analysis of Variance of Izod impact resistance at processing

temperature of 150 and 180 °C

Analysis of variance

 

 

 

 

 

 

 

 

 

 

 

Sum of square df Mean Square F Sig.
Between Groups 51.030 11 4.639 40.302 .000
Within Group 19.338 168 .115
Total 70.369 179
Post Hoc Tests

Multiple Comparisons and Homogeneous Subsets

Dependent Variable: Izod impact resistance at processing temperature of 150 and 180 °C

 

 

 

 

 

Duncan
Variation Subset for alpha = .01
LDPE:PP N g f e d c b a
0:100 @ 1503C 15 0.6298
20:80 @ 150°C 15 0.9486 0.9486
40:60 @ 180°C 15 1.1037 1.1037
80:20 @ 180°C 15 1.1079 1.1079
60:40@180°C 15 1.2116 1.2116
40:60 @ 150°C 15 1.3018 1.3018
100:0 @ 180°C 15 1.5551 1.5551
60:40 @ 150°C 15 1.8585 1.8585
20:80 @ 180°C 15 1.8668 1.8668
0:100 @ 180°C 15 1.9349
80:20 @ 150°C 15 2.0763
100:0 @ 150°C 15 2.5593
Sig. .010 .051 .147 .041 .016 .109 1.000

 

 

 

 

 

 

 

 

Means for groups 1n homogeneous subsets are displayed.

101

 

 

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102

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