Eastern Illinois University The Keep
Masters Theses Student Theses & Publications
1995
Thermoplastic Composites of Recycled High Density Polyethylene and Recycled Tire Particles
James N. McKirahan Jr.
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Recommended Citation McKirahan, James N. Jr., "Thermoplastic Composites of Recycled High Density Polyethylene and Recycled Tire Particles" (1995). Masters Theses. 4773. https://thekeep.eiu.edu/theses/4773
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Author Date Thermoplastic Composites of Recycled High Density Polyethylene
and Recycled Tire Particles
(TITLE)
BY
James N. McKiraban, Jr.
THESIS
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
Master of Science in Technology
IN THE GRADUATE SCHOOL, EASTERN ILLINOIS UNIVERSITY CHARLESTON, ILLINOIS
1995
YEAR
I HEREBY RECOMMEND THIS THESIS BE ACCEPTED FULFILLING AS THIS PART OF THE GRADUATE DEGREE CITED ABOVE
DATE
/:l, t:J� DATE/1� ir Abstract:
This study identified the mechanical properties and processibility of composite materials of recycled high density polyethylene (HDPE), recycled rubber tire particles, and/or ethyl co-vinyl acetate and poly (e-caprolactone). The composites were processed using a single screw extrusion system.
Three groups of experiments were conducted, on the composites in their extruded form to investigate the mechanical properties of ultimate tensile strength, percent elongation, and hardness. The firstexperiment investigated the effect of recycled rubber particle concentration in the composites up to 25 percent. The second experiment investigated the effect of recycled rubber particle size on the composites of recycled
HDPE and 5 percent recycled rubber. The third experiment studied the effect of ethyl co vinyl acetate and/or poly (e -caprolactone) as compatibilizers on composites of recycled
HDPE with 5 percent recycled rubber. Ethyl co-vinyl acetate (EVA) was introduced to the recycled HDPE, individually with the recycled rubber, or together with the recycled rubber as a "pre-blend" material. The pre-blend consisted of 75 percent EVA and 25 percent recycled rubber and was extruded prior to the extrusion with the recycled HDPE.
Poly ( e -caprolactone) was extruded with the recycled HDPE/ recycled rubber and the pre blend.
The first experiment showed that the strength of composites of recycled HDPE and rubber particlesdecreased with increased rubbercontent. The ductility of recycled
HDPE/recycled rubber composites decreased drastically at rubber concentration of 5 percent, then remained fairly constant as rubber content increased. The hardness of 11 recycled HOPE/recycled rubber composites decreased with increased rubber particle content.
The second experiment, involving composites of recycled HOPE and 5 percent recycled rubber, showed that recycled rubber size in the studied range did not have any . significant effect on tensile strength, while finer particles proved to increase percent elongation and decrease hardness.
The third experiment demonstrated that the addition of compatibilizers ethyl co vinyl acetate and poly ( e-caprolactone) affected the mechanical properties of the composites, but EVA improved the processibility of the recycled HOPE/recycled rubber.
Tensile strength and hardness decreased with the addition of EVA and/or poly
(e-caprolactone) to the composites, while percent elongation decreased significantlyonly in the composites not containing "pre-blend" material. Further study is recommended in the processing of the composites.
Polarized contrast and differential interference contrast (DIC) were utilized to view the distribution of the recycled rubber particles and interfacial bonding within the recycled HOPE matrix. Significant interfacial bonding and uniform distribution between recycled rubber particles were found throughout the recycled HOPE matrix. 111
Acknowledgment
I would like to take this occasion to express my sincerest appreciation and gratitude to Dr. Ping Liu for the opportunity to conduct this research and for his guidance and wisdom throughout the thesis writing process. I would like to thank Dr. Tom
Waskom and Dr.Gene Strandberg for their advisement and encouragement throughout the
research and thesis writing process. I would also like to thank the members of my
research group, Ke Wang, Jinshan Song, anze Li, QirningLou, and especially Zhongyu Y
Chen for their assistance and comraderie. It was greatly appreciated.
Financial supports from the Charles Lindbergh Foundation, Illinois Department A
of Energy and Natural Resources through Solid Waste Research of University of Illinois at
Urbana-Champaign, and the Council for Faculty Research at Eastern Illinois University are
appreciated. Quantum Chemical Co. , Aztech Industries, and Union Carbide Corp. are
acknowledged fortheir supply of materials used in the research.
I would like to acknowledge my sincerest appreciation to my wife Kathy
McKirahan and my son Samuel McKirahan. Their encouragement, patience, and strength
were essential to the success of this research. lV
Table of Contents
Page
1. IN"TRODUCTION...... 1
1. 1 Statement of Research...... 2
1. 2 Significance of Research...... 2
1.3 Definitions...... 3
1.4 Assumptions...... 5
1. 5 Limitations...... 5
1.6 Delimitations...... 6
1.7 Hypothesis...... 7
2. REVIEW OF RELATED RESEARCH...... 8
3. METHODOLOGY...... 11
3. 1 Description of Materials and Processes...... 11
3.2 Application of Materials, Equipment, and Processes...... 13
4. PRESENTATION AND IN"TERPRETATION OF DATA...... 16
4.1 Effects of Recycled Rubber Percentage on Mechanical Properties... 16
4.2 Effects of Recycled Rubber Particle Size on Mechanical Properties.. 21
4.3 Effectsof Ethyl Co-Vinyl Acetate and Poly (e - caprolactone) on Mechanical Properties...... 25
4. 4 Morphological Analysis of the Composites...... 29
5. CONCLUSION...... 35
REFERENC.ES...... 36 v
List of Tables
Table Page
1 Distribution of recycled rubber particles...... 11
2 Processing parameters for composites of recycled HDPE and recycled rubber particles...... 13
3 ANOVA Table...... 16 Vl
List of Figures
Figure Page
1 Variation of tensile strength with rubber content for composites of recycled HOPE and recycled rubber...... 17
2 Variation of percent elongation with rubber content for composites of recycled HOPE and recycled rubber...... 19
3 Variation ofDurometer hardness with rubber content for composites of recycled HOPE and recycled rubber...... 20
4 Variation of tensile strength with rubber particle size range for composites of recycled HOPE and 5 percent recycled rubber...... 22
5 Variation of percent elongation with rubber particle size range for composites of recycled HOPE and 5 percent recycled rubber...... 23
6 Variation ofDurometer hardness with rubber particle size composites of recycled HOPE and 5 percent recycled rubber...... 24
7 Tensile strength ofrecycled HOPE/recycled rubber composites containing poly (E - caprolactone) and/or ethyl co-vinyl acetate...... 26
8 Percent elongation of recycled HOPE/recycled rubber composites containing poly (E - caprolactone) and/or ethyl co-vinyl acetate...... 27
9 Durometer hardness of recycled HOPE/recycled rubber composites containing poly (e - caprolactone) and/or ethyl co-vinyl acetate...... 28
10 Recycled rubber particlesdistributed within the recycled HOPE matrix in the recycled HOPE/5 percent recycled rubber composite (35 X)...... 30
11 Recycled rubber particle within the recycled HOPE matrix (700 X)...... 31 Vll
12 Recycled rubber particle within the recycled HDPE matrix
(1400 X) ...... 31
13 Recycled rubber particles at 15 percent concentration distributed
within the recycled HDPE matrix (35 X) ...... 32
14 Recycled rubberparticles at 25 percent concentration distributed
within the recycled HDPE matrix (35 X) ...... 32 1
CHAPTER I
INTRODUCTION
The solid waste disposal crisis has emerged as a major concern of environmental protection and natural resource conservation due to the decreasing number and space of landfills. In 1985, there were 6,000 landfillsand by 2005 that number is estimated to drop to 1, 500. It is estimated, by the year 2009, 80 percent of all of the landfills existing in the
United States in 1988 will be filled to capacity (Hammond, 1992). A study, conducted in
1990 for the United States Environmental Protection Agency, estimated that four pounds of trash were generated daily by every man, woman and child in the nation and that 21 percent oflandfillspace was occupied by plastics (U. S. Environmental Protection Agency,
1990).
The unregulated disposal of automotive tires across the country has caused health, safety, and environmental concerns that have focused new attention on scrap tire disposal.
The United States generates 250 million scrap tires a year ("High end markets for recycled rubber," 1994). In 1992, less than 7 percent of all discarded tires were recycled, 11 percent were incinerated for fuel, and 5 percent were exported. The remaining 78 percent is either landfilled, stockpiled or illegally dumped (Riggle, 1992). In several states, large scrap tire storage sites have caught fire, resulting in the production of enormous volumes of dense and noxious smoke. Moreover, scrap tire storage sites provide ideal breeding ground for disease-carrying insects, particularly the mosquito. This research was conducted to determine the feasibilityof compounding recycled high density polyethylene
(HDPE) with recycled automobile tire particles using an extrusion process, in hopes of 2 developing new composite materials from these two major solid waste components. The mechanical properties and the microstructures of the composites were investigated. It is hoped that applications for these recycled materials could make it possible to expand markets for these two waste constituents and thus possibly alleviate the solid waste problem.
1. 1 Statement of Research
The purpose of this research was to study the feasibility of extruding new composite materials from recycled HDPE and recycled tire particles. This was accomplished by studying the relationship between the process variables and the material properties of the composite materials. Process variables include the percentages of recycled rubber, processing methodology, and rubber particle size. The mechanical property characteristics include tensile strength, hardness, and ductility (percent elongation) of these materials. The microstructure of these composite materials was investigated in order to control the material properties of the composites. Microstructure variables include the recycled rubber particle distribution, the distribution within the composite, and interfacial bonding between the rubber particles and HDPE matrix. The effects of ethyl co-vinyl acetate and poly (E -caprolactone) were investigated in hopes of further improving the properties and structures of the composites.
1.2 Significance of Research
This research reveals the feasibility of processing two solid waste components into 3 a usable composite material. Fully understanding the processes and properties of the composites will allow their applications as usefulindustrial materials. The markets for these recyclable materials will expand and ultimately help reduce the amount of solid waste placed in landfills. This will also result in increased finanicalsupport for recycling efforts by citizens and communities. In this way, community recycling programs can be technologically and economically promoted.
1.3 Definitions
The following terms and definitionsare essential to the understanding of the research conducted.
1. Compatibilizer - A compatibilizer produces a degree of" compatibility", or desirable blend properties, even though blend constituents are not miscible thermodynamically (Koleske, 1978).
2. Ethyl co-vinyl acetate (EV A) - Ethylene co-vinyl acetate is a copolymer of ethylene. It has a melt point between 148.9 and 176. 7°C, and a density of 0.89 to 0.965 g/cm3. The addition of EVA has been found to reduce crystallinity in polyethylene. It provides low temperature flexibility, and improves impact strength and crack resistance.
3. Extruder/Extrusion- This is a compounding device used to mechanically mix the recycled HDPE and recycled rubber and/or ethyl co-vinyl acetate and poly (e - caprolactone) to formcomposite materials. The extrusionprocess forces the constituents together by the action of the screw at operating temperatures. A viscous composite material forms as it exits the extruder die. 4
4. Hardness - Hardness is a quantitative assessment on the resistance of a material to penetration by indentation. Composites tested during this research were measured according to Durometer hardness type "D" (ASTM D2240) (Charrier, 1991).
5. High Density Polyethylene (HDPE) - This is a thermoplastic polymer produced by reacting incompressible ethylene under reaction conditions. HDPE has a melt temperature range of 110 to 135°C and a density range of0.941 to 0.965 g/cm3
(Charrier). HDPE is a partially amorphous and partially crystalline polymer. HDPE can be up to 90% crystalline in structure (Ulrich, 1993).
6. Poly (e - caprolactone) - This is a partially crystalline, tough, extensible polymer derived from ethylene with a molecular weight of 80, 000 and a density of 0. 689 g/cm3. It has a melt temperature of 60 to 62 ° c.
7. Percent Elongation - The percent elongation measures the ductility of a material
and indicates the amount, in percentage, that a specimen elongates during a tensile test as
in Equation (1) (ASTM D638M).
L - Lo e% = (1) Lo
where
e% = Percent elongation,
L = Final length,
Lo = Original length.
8. Rubber - The rubber used in this research is recycled vulcanized rubber from
ground tires. Rubber is vulcanized by the curing action of certain chemicals, mainly sulfur, 5 to produce cross-linked carbon to carbon or double bonded carbon molecular chains.
Vulcanization temperatures are a function of the chemical reactions occurring during the vulcanization process, typically at 150°C (Charrier).
9. Ultimate Tensile Strength - This measures the uniaxial resistance of a material to fracture when being pulled apart during loading (ASTM D638 M) (Charrier). It is calculated by equation (2).
,., '. a=- p (2) Ao
where
a = Ultimate tensile strength (MPa), P = Load (N), Ao = Original cross-sectional area (mm2).
1.4 Assumptions
This study assumes that the recycled HDPE, recycled rubber, ethyl co-vinyl acetate and/or poly (e - caprolactone) will mix uniformly within the extrusion process. It also assumes that these composite materials will possess certain properties that will be superior to the individual raw materials used.
1.5 Limitations
The findings of this study will be limited by the following parameters.
1. The quality of the recycled HDPE, recycled rubber, ethyl co-vinyl acetate, and 6 poly (E - caprolactone) is controlled by suppliers. 2. Human error and the accuracy of the testing equipment may affect the accuracy of the test results.
3. Material characteristics may affect the processibility of the constituents being extruded.
4. Miscibility, bonding, and the mechanical properties of the extruded constituents were dependent upon the capabilities of the extrusion system utilized in the research.
1.6 Delimitations
The study will be delimited by the following parameters.
1. The percentage of recycled rubber used in experiments one and two will be 5,
10, 15, 20, and 25 percent.
2. A concentration of 5 percent recycled rubber was used as a standard in the third
set of experiments.
3. Optimal processing parameters will be employed in the three sets of
experiments including extruder barrel zone temperatures, screw speed (rpm), and
extrusion (barrel) pressure.
4. The recycled HOPE used in this study was supplied by Quantum Chemical
Company, Heath, Ohio. The recycled rubber used was supplied by Aztech Systems;
Springfield, Illinois. The ethyl co-vinyl acetate (DQDA-6479 Natural 7) and the
poly (E - caprolactone) (Tone Polymer P-787) were supplied by UnionCarbide Corp., Danbury, CT. 7
5. The composites manufactured for this research were produced using a Killion
- 125 extrusioncompounding system with a Maddock mixer screw. The extruder has KL an LID ratio of 3 0: 1, and a die with a diameter of approximately 3. 00 mm.
6. The diameter of the sample rods used fortesting tensile strength and percent
elongation varied from between 2.27 mm to 3.98 mm .
1.7 Hypothesis
Recycled HOPE and recycled rubber can be extruded together. The composite
developed though the addition of recycled rubber to the recycled HOPE by extrusion, will
exhibit mechanical properties different from those of recycled HOPE. The addition of
ethyl co-vinyl acetate and poly (e -caprolactone) as compatibilizers to the recycled HOPE
and recycled rubber will improve the processibility of the recycled HOPE and recycled
rubber composites. 8
CHAPTER II
REVIEW OF RELATED RESEARCH
No previous studies have been conducted pertaining to the mechanical properties and the processibility of composites of recycled HOPE, recycled rubber, and ethyl co-vinyl acetate and poly (E - caprolactone). The followingis a summary on similar studies conducted:
Akhtar et al. (1989) studied blends of polyethylene with 30, 50, and 70 percent natural rubber (polyisoprene). The properties of these blends can be changed over a wide range and were comparable to those of thermoplastic elastomers. These blends could thereforebe used as automobile filler panels, gaskets, seals, truckflo or beds, cable insulation, la over wheels, and so on (Ulrich, 1993). Improved compatibility between wnm two polymers can enhance the mechanical properties of polymer blends (Paul, 1978).
Ahmad et a!. (1994) investigated the mechanical properties of high density polyethylene/natural rubber blended with a cam mixer using liquid natural rubber at varying percentages a compatibilizer. The liquid natural rubber actingas a as compatibilizer increased cross-linking with the natural rubber. Both hardness and tensile strength increased, at certain percentages, in these blends.
Roy et al. (1992) analyzed the effects of natural rubber upon HOPE when blended with carbon fiber. Composites consisting of30 percent HOPE and 70 percent natural rubber, with varying amounts of carbon fibers, were made into "dog-bone" specimens and then tested for tensile strength longitudinally and transversely to the axis of the specimen.
The study reported, in regard to tensile fa ilure, that longitudinal fiberorientation produced 9 fiber breakage and fiber pull-out in the matrix, and matrix failure dominated when fibers were transversal. Rajalingam and Baker (1992) studied the role of various functional polymers in the composites of ground tire rubber, linear low density polyethylene
(LLDPE), and high density polyethylene (HDPE) using an injection molding process.
Typical tire particulate composition, as discussed in this study, includes 40-50 percent rubber (isoprene, butadiene, styrene-butadiene), 25-40 percent carbon black and 10-15 percent additives. They reported that ethylene-co-vinyl-acetate ( product IB'7B') improved the impact energy of a blend of HDPE and ground tire rubber by 74 percent.
Qin et al. (1989) investigated the compatibilization of natural rubber/polyethylene blends by polyethylene-b-polyisoprene diblock copolymers. Tensile strength was improved up to 57 percent for the composite. The diblock coploymer, however, is not
readily available. Koleske (1978) showed that poly (e-caprolactone) (PCL 700) could be
blended with both polyethylene and natural or synthetic rubber. The poly ( e-caprolactone)
served as a compatibilizer for a blend ofHDPE and tire rubber. Grijpma et al. (1994)
used poly ( e-caprolactone) to toughen amorphous, noncrystallizable, and brittle L - and
D - lactide copolymers by consolidating a discrete rubber phase into the poly lactide
matrix. This modification produced higher elongation to breakage, improved impact
strength, and lowered yield strength. Chen and Lai (1994) found that the compatibilizer,
ethylene vinyl acetate copolymer added to polyethylene terephthalate/HDPE blends caused
changes in the rheological properties of these blends. EVA minimally effected the thermal
stability of the blends, but the degree of crystallinity associated with high EVA contents
was low. In these studies, ethyl co-vinyl acetate was used as a compatibilizer. Major 10 applications for EVA have been for flexible packaging, shrink wrap, shipping racks, produce bags, bumper pads, toys, tubing and wire cable (Ulrich).
Dontula et al. (19 93) studied variables such as barrel zone temperatures, screw speed, barrel residence time, and feed rate on viscosity to determine the amount of
degradation of co-rotating, intermeshing twin screw extruded virgin HOPE. The study
concluded that increases in screw speed, feed rate, and other operating parameters could
decrease residence time (in barrel) and therefore offset degradation of extruded material.
The structural effects on repeatedly extruded high density polyethylene was examined by
Pardon et al. (1993). They observed that the melt viscosity of repeatedly extrudedHOPE
at design temperatures steadily rose. There was minimal chemical modification to the
HOPE as a result of heating and extrusion, and cross-linking and branching took place due
to the shearing and heating in extrusion. Garcia-Rejon Alvarez (1987) studied the &
mechanical properties of extruded blends of virgin HOPE and virgin low density
polyethylene (LDPE). Viscosity and die swell (expansion of the extrudates diameter as it
exits the die) decreased as the screw speed increased. An addition of 10 percent HOPE to
the LDPE increased the LDPE's modulus by 50 percent. A twin screw extruder was used
by Kim et al. (1994) to develop biaxially oriented films of polystyrene and HOPE to
identify the effects of polypropylene homopolymers and coploymers on the blends. Using
a universal testing machine, scanning electron microscopy, and polarized microscopy, the
research found that increased tensile strength in certain blends was attributed to spherulite
morphological structures within the blends. 11
CHAPTER ID
METHODOLOGY
3. 1 Description of Materials and Processes
For this research, the recycled high density polyethylene (HOPE) was supplied by
Quantum Chemical Co. in the pellet form. The recycled rubber particles were from
Aztech Industries, Springfield, The particle size of the recyced rubber was from 40 IL. mesh to dust. The particle size distribution of the rubber used is listed in Table 1.
Table 1. Distribution of recycled rubber particle
Mesh Size Percentage (%)
30 -40 0.595 mm - 0.420 mm 1.68
40 - 50 0.420 mm - 0.297 mm 49.90
50 - 70 0.297 mm-0.210 mm 27.38
70 - 100 0.210 mm-0.149 mm 12. 78
100 > <0.149 mm 8. 12
Three studies were conducted on the composites of recycled HOPE and recycled rubber. The first set of experiments was performed to study the effect of recycled rubber percentage on the mechanical properties of the recycled HOPE. The percentages of recycled rubber introduced into the recycled HOPE were5, 10, 15, 20, and 25 percent by
weight.
The second set of experiments was performed to establish the effect of recycled
rubber particle size on the mechanical properties of these composites. A concentration of
5 percent recycled rubber was used as a standard in this experiment. Five composites of
recycled HOPE and recycled rubber were produced corresponding to particle size ranges 12 listed in Table 1.
The third set of experiments was performed to establish whether ethylene co-vinyl acetate (EVA) and/or poly (e - caprolactone), could be extruded with recycled HOPE and recycled rubber, and to determine the mechanical propertiesthese composites. A "pre blend" of 75 percent EVA and 25 percent recycled rubber by weight was produced and then re-extruded with recycled HOPE. A second blend containing recycled HOPE, 20 percent pre-blend, and 15 percent poly (e - caprolactone) was also produced. Finally a blend of recycled HOPE, 5 percent recycled rubber with an additional 5 percent EVA, was produced. These three experiments are denoted 3a, 3b 3c, respectively, in Table 2 & along with their respective processing parameters. The processing parameters in experiment three were established as optimal extrusion processing conditions for the components and corresponding room temperatures. 13
Table 2. Processing parameters for composites of recycled HOPE, recycled rubber particles, and compatibilizers
Experiment 1 Experiment 2 Pre-Blend Experiment 3 Experiment 3a& 3b
Operation Recycled Recycled 75%EVA, (3a) (3b) (3c) Variables HDPEw/ HDPEw/ 25% Recycled Recycled Recycled 5%, 10%, 5% - recycled HDPEw/ HDPEw/ HDPE, 15%, .20%or 30-40, 40-50, rubber 20% 15% 5% 25% 50-70, pre- P- 787 recycled recycled 70-100 blend & rubber
rubber or >lOOmesh 20% pre- + recycled blend 5%EVA rubber
Barrel Heating Temperatures: Zone 1 221.1 °C 221.1 °C 107.2 °C 107.2 °C 107.2 °C 176.7 °C Zone 2 204.4 °C 204.4 °C 121.1 °C 121.1 °C 126.7 °C 190.6 °C Zone 3 171.1 °C 171.1 °C 135.0 °C 148.9. °C 160.0 °C 204.4 °C Zone 4 171.1 °C 171.1 °C 148.9 °C 162.8 °C 176.7 °C 204.4 °C Clamp Ring 168.3 °C 168.3 °C 135.0 °C 148.9 °C 160.0 °C 190.6 °C Die 132.2 °C 132.2 °C 135.0 °C 135.0 °C 143.3 °C 179.4 °C
Melt Temp. 171.1- 172.8- 151.7 °C 163.3 °C 177.2 °C 204.4 °C 174.4 °C 174.4 °C
Room Temp. 21.7 °F 23.3-25.6 °C 24.4 °C 27.8 °C 23.3 °C 25.6 °C
Barrel 2.76-5.52 2.76-5.52 4.18 MPa 4.18 MPa 2.76MPa 2.76MPa Pressure MP a MP a
Tachometer 6.8 rpm 6.8 rpm 4.8 rpm 4.8 rpm 3.0 rpm 3.0 rpm (Screw Speed)
Cooling Water Ambient Ambient Ambient Ambient Ambient Ambient Temp. (17 -22 °C) (21.5 - 25 °C) (24 °C) (24 °C) (20 °C) (22 °C)
3.2 Application of Materials, Equipment and Processes
The recycled rubber, recycled HOPE, and/or compatibilizers ethyl co-vinyl acetate
and poly ( e - caprolactone) were weighed separately, thoroughly mixed, and then placed into the hopper of the extruder. The material was gravity fed into the extrusion barrel and
allowed to pre-heat for approximately 15 minutes before extrusionin experiments 1 and 2. 14
In experiment 3, components were immediately extruded. Once barrel heating temperatures were reached as in Table 2, the extruder screw drive was then turned on to the optimal screw speed for each experiment. This speed setting was used to uniformly mix the materials and to provide an appropriate cooling once the extrudate exited the die.
Material exited the die when sufficient barrel pressure, varying approximately from 1.38 to
5.52 MPa, was obtained. The extrudatewas cooled by ambient air before being cooled into a water bath approximately 86 cm underneaththe die.
Tensile strength and percent elongation were tested on the extruded material in its original extruded form according to ASTM D638-89. Five randomly chosen lengths of extrudates were tested for longitudinal tensile strength and percent elongation on a
universal testing machine, SATEC model UTC 60 . Durometer hardness specimens HVL
were prepared by pelletizing sample strands and compressing them at 150°C on a
metallurgical specimen mounting press. The specimens of 25.4 mm in diameter and 13
mm in thickness were tested on an automated type "D" Durometer controlled by an IBM
466DX2/D computer. The Durometer hardness was taken after one (1) second of
penetration onto the composites.
Polarized contrast and differential interference contrast (DIC) were utilized to
investigate recycled rubber distribution in composites of 5, 15, and 25 percent recycled
rubber and the interfacial bonding of rubber particles within the HDPE matrix, with the
Buehler Versamet 3 optical microscope. The cross-section of originally extruded rod was
viewed on a color video display monitor. The image was taken by a color video camera
(Sony, DXC-151A) interfaced with an image analysis system, Image Pro-Plus, through an 15
IBM 466DX2/T computer. 16
CHAPTER IV
PRESENTATION AND INTERPRETATION OF DATA
In this chapter, graphs are used as an aid to understand the effectsof processing variables on the material properties of the composites. Analysis of variance (ANOVA) was performed on results of tensile strength, percent elongation, and hardness for composites in experiments 1 and 2. General linear model (GLM) procedure was used with the statistical analysis system (SAS) to determine data significance. The results of the
ANOVA are dispalyed in Table 3.
Table 3 ANOVA Table
Variable Y Variable Significance Correlation X
Rubber Tensile Strength Yes, PR>F=0.0001 Linear Concentration (%) (MP a) (99.99%)
Rubber Percent Elongation Yes, PR>F=0.0001 Non-Linear Concentration (%) (%) (99.99%)
Rubber Hardness After Yes, PR>F=0.0001 Linear Concentration (%) 1.0 Second (99.99%)
Rubber Distribution Tensile Strength Yes, PR>F=0.0578 Linear (Mesh Size) (MP a) (94.22%)
Rubber Distribution Percent Elongation Yes, PR>F=0.0001 Non-Linear (Mesh Size) (%) (99.99%)
Rubber Distribution Hardness After Yes, PR>F=0.0001 Linear (Mesh Size) 1.0 Second (99.99%)
4. 1 Effects of Recycled Rubber Percentage on Mechanical Properties
Figure 1 shows the effect of rubber concentration on the tensile strength of
recycled HOPEblended with recycled rubber particles. It is noted that there is a negative
linear correlation between the tensile strength and rubber percentage. As the rubber 17
28
: l 1 26 -�------�------f------+------+------l------� 24 !ji -· : i i - -
'-" ::::::::::: ::::::::::::::: ::::r::::::::::::::::r:::::::::::::::::::::::::::::::::: :_ :::::::::::::::::::::::::: _ � 22 : Ell : : : ...c...... : : 1 bJJ $ i::: 20 i i i :
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Fig. 1 Variation of tensile strength with rubber content for composites of recycled HDPE and recycled rubber 18 concentration increased, the tensile strength decreased. The confidence level of the data represented in Fig. 1 was 99. 99 percent
Figure 2 depicts variation of percent elongation with rubber concentration for the composite of recycled HOPE and rubber particles. The percent elongation decreased drastically at 5 percent rubber concentration. It remained fairly constant with increased rubber concentration. The confidence level of the data represented in Fig. 2 was 99. 99 percent.
Figure 3 characterizes a negative linear correlation between the hardness of the material after 1. 0 second of penetration and the percentage of recycled rubber introduced into the recycled HOPE. An increase in recycled rubber led to a decrease in hardness. The confidence level of the data represented in Fig. 3 is 99. 99 percent 19
160
140 . ,� ...... ···········'··· ...... , .. -�·-········•"""""""+""""""""""""""""): ...... �. . . 1...... 1.--.... l l -- 120
�'--' ...... +r!r:...... � . . . . { ...... ; ...... r·.: . . . . .: . . . 100 = ...... , ...... 0 . ro : m :i · i :� OJJ 80 = ...... 0 60 l:.il..... ; r =
Fig. 2 Variationof percent elongation with rubber content for composites of recycled HDPE and recycled rubber 20
72
70 ··············· ····· ··········· ···············---- -·················· ·················· ·················- ················ ,.-._ ' · j 1 t t 1 m : : B00 68 . : . . . : . 00 . . . . . Q.) I i 66 p:: : I ! ; I 1� B 64 I : : : m m 8 j j � m� �'. 111' ·············· . ················ . ···············--...-·················· ··············------············ ················ 62 . . . . Q� + + ! t -�- 1 ...... 60 . . . . . -5 0 5 10 15 20 25 30 Rubber Concentration (%)
Fig. 3 Variation of Durometer hardness with rubber content for composites of recycled HDPE and recycled rubber 21
4.2 Effects of Recycled Rubber Particle Size on Mechanical Properties
Figure 4 shows the variation of tensile strength with rubber particle size range for composites of recycled HDPE and 5 percent recycled rubber particles. No significant trend can be attributed to variations in particle sizes in regard to tensile strength. The confidencelevel of the data represented by Fig. 4 is 94.22 percent.
Figure 5 shows the percent elongation as a function of rubber particle size range in mesh forcomposites of recycled HDPE and 5 percent recycled rubber particles. It is noted that there is a positive correlation between the percent elongation and the rubber particle size (mesh). Percent elongation increased as rubber particles became finer. The data represented in Fig. 5 has a confidence level of 99. 99 percent.
Figure 6 depicts variation ofDurometer hardness with rubber particle size ranges for composites of recycled HDPE with 5 percent rubber particles. It indicates that there is
a linear correlation between hardness and rubber particle size. Composites containing
larger particles of recycled rubber exhibitedhigher hardness than composites containing
finer recycled rubber particles. 22
26
25 ------1------<------r------ei ,....._ ------:------r-- (d -...------... �- . ------. ------.. �-. ------. 24 - -.. -----... -... �-.. . --. . 0.. ------.. -... ---�--...... -- - -. �------. . . '-' ------;------� 23 ______! $ ...c: i 1 r .....bIJ ___! ] i::: 22 � ------'------a) Ell. :. Ell. Ell. �:. b ------�-- L L i IZl ···------···· ! ·······------····---- ! -·····------·--··· ! --········--·--···--·Ejl--· ------· ------··----· -a) 21 1 --; ; ; ...... "' i i::: , : Ej3 a) 20 ai E-< 19 T t l T I 18 30-40 40-50 50-70 70-100 > 100 Particle Size (Mesh)
Fig. 4 Variation of tensile strength with particle size range for composites of recycled HDPE and 5% recycled rubber 23
140
120 ·················· ····················· � ····················· ···········-········· ····················· i ·················· r. r . r . r . r . ' ' ' . .: :' . .' :. . .. . ,.--.. 100 ...... L ...... L ...... L ...... L ...... lfl: ...... �'-' . . . . ' ...... i::: : : : !il
0 ·················· ······················ ······················ '······················ ······················ ··················· ...... 80 -:� -: -: -: -:[ . ('j . . . . . b£) .' . . . . i::: ...... 0 60 ...... 'l.. . . � . . . l ...... � ...... :. .. . . Jl..l . . ...' ...... ' ...... i:::Q) ················· ·················-- ---·················· ····················- ·· ...... 40 -r -�: r i 1 i , i ...... �Q) p... 20 . . ·················· ····················- ...... ! ...... ! ...... ! 1 L . ' ' ' 0 ' . . . 30-40 40-50 50-70 70-100 >100 Particle Size (Mesh)
Fig. 5 Variation of percent elongation with particle size range for composites of recycled HDPE and 5% recycled rubber particles 24
70
' ' ,..--._ 68
B"-' I "-' tU $ t I i . ----;---·················- ---················ .. ················ 66 ...... i...... m ...... ill ijj : � r ljl : ::I:: : : ] � """""""""' """"""'"""'"'"""""'"'"""" """""""""" """""""""' i:ii ...... � 64 1 ]" 1": �
a EB i i 8:::l 0 62 111 l r 60 30-40 40-50 50-70 70-100 100 > Particle Size (Mesh)
Fig. 6 Variation of Durometer hardness with rubber particle size range for composites of recycled HDPE and 5% recycled rubber particles 25
4.3 Effects of Ethyl Co-Vinyl Acetate and Poly - caprolactone) on Mechanical ( E Properties
Figure 7 indicates the ultimate tensile strength of the composites of recycled
HOPE with 5 percent recycled rubber and similar composites containing EVA and/or poly
(e-caprolactone). The blend containing 20 percent pre-blend (3a) and that containing 5
percent recycled rubber and 5 percent EVA(3c), exhibited similar tensile strength.
However, both showed lower strength than the blend of recycled HOPE and 5 percent
recycled rubber. The blend containing 20 percent pre-blend and 15 percent poly ( e
caprolactone)(3b) exhibited the lowest tensile strength.
Figure 8 demonstrates the percent elongation of the recycled HOPE with 5 percent
recycled rubber and the composites containing EVA and/or poly (e-caprolactone). The
recycled HOPE/5percent recycled rubber and the recycled HOPE/20 percent pre-blend
blends (3a) displayed similar percent elongation. The composite ofrecycled HOPE/20
percent pre-blend/15 percent poly (e-caprolactone) blend (3b) and the material of recycled
HOPE/5% recycled rubber/5 percent EVA blend(3c) displayed lower percent elongation.
Figure 9 displays the Durometer hardness of the recycled HOPE/5 percent
recycled rubber composite and those of similar composites containing EVA and/or poly
( e-caprolactone). The hardness of the blend containing 20 percent pre-blend was similar
to that of 5 percent recycled rubber/5 percent EV A blend while the 20 percent
pre-blend/15 percent poly (e-caprolactone) blend exhibited the lowest hardness. 26
26 �ote:· Pr�blend cqnsisted qf 75% e,hyl co-v�nyl· ······� ·· ace � and�5% recy led 24 $ jat ? ru����- EE ··· Eir 22 .. . ..E!i .. $ ffi & EE ...... •...... •.. ·· ·· ffi··· �'-"' 20 ...... Eli i '5 $ ...... on ·· EE .. s::(!) .... 18 ...... •...... + ...... T ...... J.····· ·· ····· ··· . . r/J :::::::::::: : 16 j- �"" ...... s::(!) . 14 ...... ,...... $ ...... E-< 12 $ 10 95% Recyled (3a) (3b) (3c) HDPE 80% Recycled 65% Recycled 95% Recycled HDPE 5% Recyled HDPE HDPE 5%+ Recycled rubber rubber 20% pre-blend 20% pre-blend 5% EVA 15%- poly ( E caprolactone)
Fig. Tensile strength of recycled HD PE/recycled rubber composites 7 containing poly (E - caprolactone) and/or ethyl co-vinyl acetate 27
25 Note: fre-blen consist:tid of 75% ethyl c9-vinyl· 4cetateatjd 25% r�ycled rubber.
------; - - ,...... ____ _ , ______, ______20 $ ------;--- - :- �'-' s::::: $
0 ------· ------'' ·a ro 15 if 01) s::::: $ �-$ 0 $ ------m...... 10 � s:::::
0 95% Recycled (3a) (3b) (3c) HDPE 80% Recycled 65 % Recycled 95% Recycled HDPE 5% Recycled HDPE HDPE 5%+ Recycled rubber· rubber 20% pre-blend 20% pre-blend 5% EVA 15% poly ( E - caprolactone) Fig. Percent elongation of recycled HDPE/recycled rubber composites 8 containing poly (e - caprolactone) and/or ethyl co-vinyl acetate 28
70
! Note: Pre-blenq consisttid of 75% ethyl c¢>-vinyl· �cetate� d 25% r�ycled �bber. $ ------E!l-·----·---··-- -····- : : -- -- : --.. ·--- . --- : : ·--- ·---·-- ·--·------+-! . ,...... _ 68 r ...... t ...... --r-----...... : . .. r .. -r .. 0 '-"00 00 . . ------·---- ····--- --···- - __ Q) ,. !: mIll :r ! : :! :! ! t:: .66 ...... �-. ------r . r .. .. --...... r ...... i ...... T ]::r:1-t j j 64 : : �: � Q) e e::s 62 0 ! � I 1 l 1 T 60 (3b) 95% Recycled (3a) (3c) 65% Recycled HDPE 80% Recycled 95% Recycled HDPE HDPE 5% Recycled HDPE 5% Recycled rubber 20% pre-blend + rubber 20% pre-blend 5% EVA 15% poly (E - caprolactone) Fig. Durometer hardness of recycled HDPE/recycled rubber composites 9 containing poly (E - caprolactone) and/or ethyl co-vinyl acetate 29
Processing parameters may have contributed to the diminished mechanical properties of experiment 3a, 3b, and 3c materials. Dontula et al. (16) mentioned that varaibles such as screw speed, feed rate, residence time, and so on, affected extruded
H;DPE. Processing variables may have caused detrimental effects on the poly -caprolactone) (Tone Polymer P-787) which has a melt temperature of 63 °C. The (e recycled HDPEand poly (e -caprolactone) were very difficult to extrude together. Lowered barrel heating temperatures were used to accommodate the low melt temperature of poly (e -caprolactone). The recycled HDPE/20 percent pre-blend/15 percent poly (e -caprolactone) exhibited lower mechanical properties than any of the other composites. It exhibited a brittle nature that may have contributed to its lessened tensile strength.
EVA may improve the processibilty of extruded recycled HDPE with minimally decreased mechanical properties. The ethyl co-vinyl acetate was observed to have decreased the viscosity of constituents at low extrusion temperatures. The lowered tachometer settings in Experiment 3 seen in Table 3, were adopted to suit this change.
Bonding appears to have been promoted between EVA and recycled rubber, as the pre blend of 75 percent EVA/25 percent recycled rubber composite showed a relatively good
ductility.
4.4 Morphological Analysis of the Composites
Figures 10 is a micrograph showing recycled rubber particle distribution in the
composite of recycled HDPE and 5 percent recycled rubber particles. The recycled rubber 30
Fig. 10 Recycled rubber particles .distributed within the recycled HOPE matrix in the recycled HDPE/5% recycled rubber composite (35 X) 31
contained in the samples had a size range of 40 mesh to finer than100 mesh. Figure 10
shows that recycled rubber particles are evenly distributed throughout the cross section of
the sample.
Figure '11 displays the interfacial bonding of a recycled rubber particle within the
recycled HDPE matrix. This random rubber particle shows a close contact between the
, recycled rubber particles and the recycled HDPE matrix. The fringe rings on the recycled
rubber particle were shown due to the application of differentialinterf erence contrast
(DIC) technique. This phenomena shows the surface of the recycled HDPEbeing raised
minutely higher than the recycled rubber particle. The enlarged outer ring of this recycled
rubber particle, as shown in Figure 12 at a magnificationof 1400, noticeably indicates that
there is significant interfacial bonding between the recycled rubber particle and the
recycled HDPE.
Figure 13 reveals the impregnation of recycled rubber particles at a 15 percent
concentration within the recycled HDPE matrix. Notice that the recycled rubber particles
are uniformily distributed but are at a closer proximity than the 5 percent recycled rubber
concentration sample shown in Fig.10.
Figure 14 presents the impregnation of recycled rubber particles at a concentration
of 25 percent within the recycled HDPE matrix. The absense of definition between
recycled rubber particles indicates that the recycled rubber particles are distributed at a
very close proximity due to the higher rubber content. 32
Fig. 11 Recycled rubber particle within the recycled HDPE (700 X)
Fig. 12 Recycled rubber particle within the recycled HDPEmatrix (1400 X) 33
Fig. 13 Recycled rubber particles at 15 percent concentration distributed within the recycled HDPE matrix (35 X)
Fig. 14 Recycled rubber particles at 25 percent concentration distributed with the recycled HDPE matrix (3 5 X) 34
The uniform distribution and close interfacial bonding of the recycled rubber particles suggests that the recycled rubber is readily assumed into the recycled HDPE matrix through extrusion at 5 percent recycled rubber concentration. This can be confirmed through the use of Figs. 1, 2 and 3. These graphs show that mechanical properties are only minimally effected by the addition of recycled rubber to the recycled
HDPE at 5 percent recycled rubber content. The recycled rubber is assimilated into the recycled HDPE matrix through extrusion at 15 percent and 25 percent recycled rubber concentration, but mechanical properties became greatly diminished due to the increased proximity of the recycled rubber particles within the matrix. 35
CHAPTER V
CONCLUSION
The following conclusions were made according to the study of extruded composites of recycled HOPE, recycled rubber, and compatibilizers ethyl co-vinyl acetate and poly(e - caprolactone).
1. The strength of composites of recycled HOPE and rubber particles decreased
with increased rubber content.
2. The ductility of recycled HOPE/rubber composites decreased drastically at
rubber concentration of 5 percent, then remained fairlyconstant as rubber content
increased.
3. The hardness of recycled HOPE/rubber composites decreased with increased
rubber particle content.
4. There is no significant effect of rubber particle size on the strength of the
composites. Finer particle size seemed to improve the ductility, but decreased the hardness
of the composites of recycled HOPE and 5 percent recycled rubber particles.
5. The addition of compatibilizers such as ethyl co-vinyl acetate (EVA) and poly
( e-caprolactone) did not show beneficialeffect on the mechanical properties of the
composites. However, EVA improved processibility of the recycled HOPE/recycled
rubber composites. Further study is needed in processing of the composites.
6. Significant interfacial bonding and uniform distributionbetween recycled rubber
particles throughout the recycled HOPE matrix were identifiedin the investigated
materials. 36
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