MANUFACTURING OF POLYPROPYLENE (PP)/ GROUND TIRE RUBBER
(GTR) THERMOPLASTIC ELASTOMERS USING ULTRASONICALLY AIDED
EXTRUSION
A Thesis
Presented to
The Graduate Faculty of The University of Akron
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
Jieruo Liu
August, 2013
MANUFACTURING OF POLYPROPYLENE (PP)/ GROUND TIRE RUBBER
(GTR) THERMOPLASTIC ELASTOMERS USING ULTRASONICALLY AIDED
EXTRUSION
Jieruo Liu
Thesis
Approved: Accepted
______Advisor Department Chair Dr. Avraam I. Isayev Dr. Robert Weiss
______Committee Member Dean of the College Dr. Thein Kyu Dr. Steven Cheng
______Committee Member Dean of the Graduate School Dr. Younjin Min Dr. George Newkome
______Date
ii ABSTRACT
Compounding ground tire rubber (GTR) from whole waste tires with thermoplastic polyolefins, such as polypropylene (PP), is a possible way to manufacture thermoplastic elastomers and also to recycle waste tires to solve a major environmental problem.
The present study looks at the effect of PP/GTR mixing ratio, rubber particle size, type of extruder, maleic anhydride grafted polypropylene (PP-g-MA) compatibilizer and ultrasound on the mechanical and rheological properties of PP and
PP/GTR blends. PP and GTR were compounded at ratios of 30/70, 50/50 and 70/30.
Whole tire GTR particles of 40 and 140 mesh sizes were used. Both the single screw extruder (SSE) and twin screw extruder (TSE) without and with ultrasonic treatment were applied. PP-g-MA compatibilizer was added to PP/GTR 50/50 blends at concentration of 10 wt %. Rheological, tensile and impact properties of uncompatibilized and compatibilized PP/GTR 50/50 blends were compared. The ultlasonic treatment was carried out at a flow rate of 2 lbs/hr and amplitudes of 5, 7.5 and 10 μm. Pressure and ultrasonic power consumption were measured.
The Young’s modulus and the elongation at break of the untreated and ultrasonically treated PP is respectively found to be higher and lower in SSE than that in TSE, with the effect on the tensile strength being insignificant. Complex viscosity of the ultrasonically treated PP changes with amplitude in a complex way depending on the type of extruder. An increase or decrease of viscosity with amplitude is observed. Rubber particles of PP/GTR 50/50 blends of both meshes are reduced in
iii sizes, with their roughness increasing more in TSE than in SSE. This leads to a higher viscosity of 50/50 blends in TSE. Complex viscosity of blends from both SSE and
TSE increases with an addition of GTR particles. The viscosity of PP/GTR blends of various ratios containing 140 mesh is lower than that of 40 mesh blends. This is due to a lower gel fraction of 140 mesh GTR. Blends with the smaller rubber particle size show much higher elongation at break, indicating a better interaction between the PP and GTR. The addition of the compatibilizer improves mechanical properties of blends. In particular, the tensile strength reaches 19 MPa, and the elongation at break increases to 50%. The highest effect of ultrasound is observed for PP/GTR 70/30 blends. Specifically for PP/GTR 70/30 containing 140 mesh rubber from TSE, the viscosity drops significantly at an amplitude of 10 μm, and the Young’s modulus and elongation at break get improved. This indicates that the breakup of molecular chains leads to creation of macroradicals of components, which recombine, causing an increase in tensile properties.
iv ACKNOWLEDGEMENTS
The author hopes to express gratitude to her advisor, Dr. Avraam I. Isayev, for his patient and kind instructions on research and courses. The author also would like to thank to Dr. Jaesun Choi, Mr. Todd M. Lewis, Mr. Tian Liang and Mr. Keyuan
Huang for their great help.
v
TABLE OF CONTENTS
Page
LIST OF FIGURES…………………………………………………………………ix
CHAPTER
I. INTRODUCTION...... …………..1
II. LITERATURE SURVEY...... 4
2.1. Brief Introdcution of Rubber Recycling...... 4
2.2. Plastic/Rubber based Thermoplastic Elastomers...... 4
2.3. Polyolefin-based thermoplastic elastomers （TPO）...... 5
2.4. Thermoplastic vulcanizates (TPVs) ...... 6
2.5 Compatibility between plastic and rubber...... 6
2.5.1. Modification of rubber...... 7
2.5.1.1. Physical methods………………………………………………7
2.5.1.2. Chemical methods……………………………………..………8
2.5.2. Compatibilizer……………………………………………………..….11
vi 2.6 Ultrasound…………………………………………………………………..12
2.6.1. Effect of ultrasound on polymers………………………………….…..14
2.6.1.1. Degradation of polymer by ultrasound……………………….14
2.6.1.2. Devulcaniation of rubber by ultrasound………………...…….15
2.6.1.3. Compatibilization of blends by ultrasound……………………17
2.6.1.4 Application of ultrasound in filled polymer system….……….19
III EXPERIMENTAL...... 21
3.1. Materials ...... 21
3.2 Extruders with ultrasound treatment...... 22
3.2.1. Preparation of blends in single screw extruder……………….….……24
3.2.2. Preparation of blends in twin screw extruder…………………….…….25
3.3. Molding...... 26
3.3.1. Injection molding ...... 26
3.3.2. Compression molding ...... 26
3.4 Characterization...... 26
3.4.1. Rheological measurements……………………….……………………26
3.4.2. Tensile tests...... 27
vii 3.4.3. Impact tests...... 27
3.4.4. Morphological measurements...... 28
IV RESULTS AND DISCUSSION...... 29
4.1. Die pressure...... 29
4.2. Power consumption of ultrasound……...... 31
4.3. Rheology...... 34
4.4. Tensile properties...... 44
4.5 Impact test……………………………………………………………………57
4.6 Morphological test…………...... 59
V SUMMARY...... 62
REFERENCES...... 64
viii
LIST OF FIGURES
Figure Page
2.1 Ultrasound cavitation bubble growth and collapse …...... ……………………………...14
2.2 Schematic of the overstressed network fragment around the collapsing bubble…………………………...16
3.1 Schematic drawing of single screw extruder…………………………………..22
3.2 Design of 33:1 screw with two mixing sections before the ultrasonic treatment section and a conveying screw flights after it…...... 23
3.3 Schematic drawing of twin screw extruder……………………………………24
4.1 Die pressure of 40 mesh blends from SSE (a) and 140 mesh blends from SSE (b)………………………..………………..…30
4.2 Power consumption of 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c) and TSE (d)…………………………………….33
4.3 Complex viscosity of 40 mesh blends from SSE………………………………35
4.4 Complex viscosity of 140 mesh blends from SSE……………………………..38
4.5 Complex viscosity of 40 mesh blends from TSE……………………………….39
4.6 Complex viscosity of 140 mesh blends from TSE………………………………41
4.7 Complex viscosity for PP/GTR/PP-g-MA 50/50/10 and 50/50/0, 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c) and TSE (d) ………….42
4.8 Cole-Cole plot for PP/GTR/PP-g-MA 50/50/10 and 50/50/0, 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c) and TSE (d) …………..43
4.9 Young’s modulus (a), tensile strength (b) and elongation at break (c) for pure PP from both SSE and TSE as a function of ultrasonic amplitude…………………45
4.10 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from SSE against ultrasonic amplitude ……………………………….46
ix 4.11 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from SSE against PP weight percentage………………..……………47
4.12 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from SSE against ultrasonic amplitude………………………….49
4.13 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from SSE against PP weight percentage……………..….………50
4.14 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from TSE against ultrasonic amplitude……………………...…..53
4.15 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from TSE against PP weight percentage……………………..….54
4.16 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from TSE against ultrasonic amplitude……………………….…55
4.17 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from TSE against PP weight percentage………………………...56
4.18 Izod impact strength of PP/GTR 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c) and TSE(d)……....…58
4.19 SEM microimage of untreated 50/50 PP/GTR 40 mesh blends mesh from SSE (a), TSE (b) and 140 mesh blends from SSE (a), TSE (b)..………….60
4.20 SEM microimage of PP/GTR/PP-g-MA 50/50/10 140 mesh blends from SSE untreated (a), treated at 5 μm (b), 7.5 μm (c) and 10 μm (d)………...61
x CHAPTER I
INTRODUCTION
Thermoplastic elastomers are gaining more and more attention both in polymer
industry and rubber technology fields since they bridge the gap between the rubber
and plastic industries1. Thermoplastic elastomers (TPEs) are a class of copolymers or
blends of plastic and rubber which consist of materials with both thermoplastic and
elastomeric properties. They possess a number of advantages over conventional
rubbers2: (1) They can be manufactured using thermoplastic processing method which is unsuitable for conventional rubber, (2) Properties of product can be manipulated by changing the ratio of the components. TPEs are used for a wide range of applications, including automotive, electrical3 and medical4 industries. Current global demand for
TPEs reported in 2010 is 4,100,000 metric tons, with styrenic block copolymers
(SBCs) the largest volume, followed by thermoplastic polyolefins (TPOs). Worldwide
demand for TPEs is forecast to rise 6.3 percent per year to 5.6 million metric tons in
20155.
Due to the non-degradable nature of rubber and its large consumption in
modern society, the recycling of waste tires is becoming more and more critical6. The recycled rubber can meet different applications in energy and construction industries7.
In recent years, with the development of TPEs, more and more attention has been
focused on the compounding of polyolefins and finely ground tire rubber (GTR).
Polyolefin-based TPEs can be divided into two classes. One is blend of polyolefin
with rubber, thermoplastic polyolefin (TPO). The other is thermoplastic vulcanizate
1 (TPV), consisting of a relatively high amount of crosslinked rubber finely dispersed in
the thermoplastic matrix8. Compounding of GTR with thermoplastic polyolefins, such
as polypropylene, is a possible way to manufacture TPEs and also to recycle waste
tires, thus solving a major environmental problem. The mechanical properties of such
compounds depend on the concentration and nature of GTR, the polymer matrix and
the adhesion between them9. To improve the adhesion between GTR and polymer
matrix, several methods have been used, including 1) the modification of GTR through chemical, mechanical, thermo-mechanical and microwave techniques for devulcanization, 2) in-situ vulcanization of rubbers in thermoplastic matrices, i.e.
TPVs may improve the performance of final products, 3) adding compatibilizer to the thermoplastic/GTR blends is also an effective way to improve the adhesion between the two phases. In addition, ultrasonic energy has been proved to be very effective in increasing the interfacial adhesion between two incompatible and immiscible blends10.
The technique requires high power ultrasound to break the C-C bonds and then form
long chain radicals of each component of the blends. The radicals will further
combine with each other, forming a new copolymer.
Polypropylene (PP) has been used in a wide range of applications because of its
excellent properties such as high melting temperature, low density, high chemical
resistance, easy molding processability and good mechanical properties. The main
drawback of PP is the low impact strength. It was reported that the addition of some
elastomers could enhance the toughness of PP while maintaining stiffness, strength
and processability11.
The main objective of the study is to investigate the effect of PP/GTR mixing ratio, rubber particle size, type of extruder, compatibilizer PP-g-MA and ultrasound
on the rheological, mechanical and morphological properties of PP/GTR blends. In
1 the present study, an ultrasonic single screw extruder and an ultrasonic twin screw extruder were used to prepare PP/GTR blends. Different rubber particle sizes were used during compounding. Process characteristics, rheological, mechanical and morphological properties of PP and PP/GTR blends were characterized.
It is expected that new kinds of thermoplastic elastomers with better mechanical properties can be prepared using various processing techniques, such as single and twin screw extruders. These TPEs will be injection and compression molded. In addition, the effect of ultrasound and mesh size of rubber particle will be employed to establish a structure-property relationship.
2 CHAPTER II
LITERATURE SURVEY
2.1 Rubber Recycling
The world consumption of rubber (natural and synthetic) in 2010 was 24.845 kt, most of which will become waste12. Thus recycling of waste rubber is a big issue in
modern society. Tyres have a four phase life-cycle: new, part-worn, retreadable and
recyclable. Rubber recycling is strongly favored due to several reasons including
legislative actions, energy balance, etc13, 14. There are five prevalent ways to recycle
waste tire, including retreading, pyrolysis, shredding, grinding and devulcanization.
2.2 Plastic/Rubber based Thermoplastic Elastomers
Thermoplastic elastomers (TPEs) can be defined as materials with
thermoreversible crosslinks and can be processed as thermoplastics exhibiting elastic
behavior14. The emergence of TPEs is one of the most important developments in
polymer and rubber technology fields in recent years. One of the most exciting
developments is the rubber/plastic based TPEs because they possess outstanding
properties and low cost. Typically, these materials exhibit characteristics of
elastomers at room temperature with the ease of processing of thermoplastics at the
same time. They have a number of practical advantages over conventional rubbers:
3 1) No vulcanization of rubber is required in case of copolymers.
2) Easy processing methods which are unsuitable for conventional rubbers can be
conducted, such as blow molding, thermoforming, heat welding, etc.
3) Rubber can be recycled.
4) Properties of the TPEs can easily be manipulated by changing the ratio of
components of the blends.
5) Short mixing and processing cycle as well as low energy consumption are needed.
The disadvantages of thermoplastic elastomers are that with increasing temperature,
TPEs will be softened and will show a creep behavior on extended use.
Manufacturing of these materials, however, build up relationship between rubber and plastic industry.
2.2.1 Classification of Plastic/Rubber based Thermoplastic Elastomers
The component of plastic/rubber based TPEs is designed according to the expected use of the final products. Five main classes of TPEs are commercially important, including:
1) Polystyrene-elastomer block copolymers.
2) Polyurethane-elastomer block copolymers.
3) Polyether-elastomer block copolymers
4) Polyamide-elastomer block copolymers.
5) Hard thermoplastic elastomer blends, including thermoplastic polyolefins elastomer (TPOs) and thermoplastic vulcanizates (TPVs).
2.3 Polyolefin-based thermoplastic elastomers （TPOs）
4 Polyolefin based thermoplastic elastomers can be defined as materials consisted
of semi-crystalline thermoplastic polyolefin and amorphous elastomer. They show
elastomeric properties at room temperature, and can be processed by common
thermoplastic processing methods at elevated temperatures. There are several types of
polyolefin-based thermoplastic elastomers:
1) thermoplastic polyolefin/ rubber blends
2) dynamically vulcanized blends
3) block copolymer
4) graft copolymer
2.4 Thermoplastic vulcanizates (TPVs)
Dynamic vulcanization is a process during which elastomer particles are
vulcanized and dispersed in the thermoplastic matrix. The thermoplastic elastomers
prepared by dynamic vulcanization (TPVs) have properties equal to or sometimes
even better than those prepared by block copolymerization. The
polypropylene/ethylene propylene diene rubber (EPDM) blends are thermoplastic
elastomers commercialized in 1972, for application such as gaskets, hoses, etc16.
2.5 Compatibility between plastic and rubber
Compounding GTR with thermoplastic polymers is a cost effective and
efficient way to prepare TPEs. The main issue is how to improve the compatibility
between the dispersed vulcanized rubber particles and plastic matrix to obtain type of co-continuous morphology that will provide ideal mechanical properties.
5 The physical role of the compatibilization is: 17
1) Reducing the interfacial energy to improve adhesion between phases.
2) Obtaining better dispersion during mixing. For GTR-thermoplastic polymer
system, smaller particle size of GTR and de-agglomeration are the most important
factors in manufacturing ideal materials.
3) Stabilizing dispersion against agglomeration during processing.
4) Providing co-continuous type morphology to get good mechanical properties.
In general, compatibilization of polymer blends can be achieved by mechanical and chemical methods. Mechanical compatibilization refers to adjusting the ratios of viscosity to volume fraction (η/φ) of each component close to each other18. The
addition of small amount of dispersion agent helps reducing the interfacial tension to
stabilize dispersion against re-agglomeration. This cannot be applied to
GTR-thermoplastic system since GTR particles have crosslink structure that will not
melt as thermoplastics at high temperature. Compatibilization of GTR-thermoplastic
blends can be achieved by reducing particle size to increase specific surface or by
chemical methods, i.e. modification of rubber particle surface.
2.5.1 Modification of rubber particle
The oldest technique to recycle ground tire rubber (GTR) is to rebond the GTR
particles in polymer binders such as liquid thermosetting resins, thermoplastic
polymers or fresh (virgin) rubbers. However, due to the poor adhesion between the
GTR particles and corresponding matrix, mechanical properties of such compound is
not ideal. To solve the adhesion problem, i.e. to establish a smooth stress transfer
between the GTR and matrix, the surface of GTR should be modified. Modification,
6 termed as compatibilization, improves the adhesion through making interfaces of the
plastic and rubber phases similar to each other or providing specific interaction sites between the phases19.
Modifications of polymeric materials are of great importance since they can
produce new materials with unexpected properties. In other way, they can also introduce specific reactivity on the polymer chains for future reactions through yielding reactive intermediates. Methods of modification of rubber can be divided into two types: physical methods, including UV radiation, plasma, microwave, etc.; chemical methods, mainly refers to grafting monomer onto rubber particle surface.
2.5.1.1 Physical methods
High energy treatments including plasma, UV radiation, etc. induce physical and chemical reactions such as etching to produce crosslinked layer or polar group on the surface of rubber particle, which will improve the hydrophilicity and adhesion.
High energy treatment of rubber particle has advantages including simple operation without exerting pollution to environment and that it only acts on the rubber particle surface without affecting the properties of matrix20.
Zhang et al.21 carried out surface modification of ground tire rubber (GTR)
powder by plasma treatment to improve its adhesion to nitrile rubber (NBR). The
surface modification of GTR powder was carried out using a parallel plate dielectric
barrier discharge reactor. According to their observations from ATR-FTIR, -OH
groups were introduced onto GTR surface. Results from XPS confirmed the presence
of oxygen containing polar functional groups on the surface of the GTR powder. In
addition, water contact angle of the surface of GTR powder dropped from 116 to
7 0°after being treated, indicating the conversion from hydrophobic to hydrophilic
surface of the modified GTR powder. Furthermore, better adhesion between GTR and
NBR was achieved as indicated by the improved mechanical properties of plasma
treated rubber.
2.5.1.2 Chemical methods
Acid treatment
Acid pretreatment of rubber is referred to the etching of the reused tire surface
to eliminate moieties and additives to obtain a micro-porous surface more suitable for
mechanical adhesion22. Acid treatments seem a financially worthwhile way to achieve a suitable material, given that their application does not require very specific equipment or complex technical processes.
Colom et al.23 improved the compatibility between recycled HDPE and ground
tire powder using pretreatments by H2SO4, HNO3, or a 50% mix of H2SO4 and HNO3
over the rubber before composite preparation. Three types of GTR were used, with
particle sizes of < 200μm, 200–500μm, and >500μm. The reused tire was mixed with
the recycled HDPE in a CollinW100T two-roll mixer at 153 °C. Acidic pretreatment
was found to increase the tensile strength in most cases when particle size is below
500μm. The tensile strength and Young’s modulus were both increased with acid
treatment. SEM images also proved that for sizes less than 200 μm rubber particle,
good performance of the interfacial contact between rHDPE and GTR after H2SO4
treatment of rubber particle was achieved.
8 Grafting
The purpose of grafting functional groups onto rubber surface is to introduce
new reactive groups to enhance miscibility of rubber particle with plastic phase.
With different selections of suitable monomers, functionalized GTR powder with various reactive groups can be obtained. For example, graft polymerization of methyl methacrylate (MMA), or allylamine monomer, onto the surface of rubber particle will improve hydrophilicity, thus enhancing the wettability by polymers of
GTR.
Lee et al.24 grafted rubber powder with allylamine monomer through immersion in the allylamine solution, followed by UV radiation treatment for 30 min.
Unmodified and modified waste ground tire rubber (WGRT) were blended with
isotactic PP and PP-MA using a twin screw extruder in the presence of SEBS-MA as
a compatibilizer. FTIR and EDAX analysis confirmed the existence of allylamine in
the modified structure. SEM images showed a decrease in the size of agglomerates
after modification of rubber. Through water contact test and using Washburn equation,
it was observed that dispersive component of the rubber powders decreases while the
polar component increases. In addition, the total surface energy of the modified
rubber powders was higher than the unmodified rubber powders indicating its surface
activity increase. From tensile tests, it was shown that treated WGRT/PP/SEBS-g-MA
reached the elongation at break of 165%, twice of the untreated WGTR blends.
In addition, Shanmugharaj et al.25 carried out successful grafting of allylamine
monomer onto ground tire rubber particle was also obtained under peroxide treatment.
Rubber powders were soaked in the allylamine solutions, and then mixed with benzoyl peroxide. PP and MA–PP were melted, and waste rubber powders were then
9 fed to a Brabender plasticorder. FTIR spectra confirmed the successful grafting of
allylamine onto rubber through the increase in the peak intensity at 1630 cm-1 due to
the in-plane deformation of the –NH2 group. The modified rubber powder showed a significant improvement of the elongation at break compared with the unmodified rubber/PP composites. At each mixing ratios of PP/rubber, the elongation at break for
modified rubber composites all increased twice or more, from 50% to about over
100%. It was explained that the interaction between the amine of the allylamine on
the surface of modified rubber and the maleic anhydride of MA-PP led to the
compatibilization and dispersion of the waste-rubber powder in the PP matrix.
Fang and Canhui26 performed grafting of poly (methyl methacrylate) (PMMA)
onto GTR powder aided by ozonization. GTR was first ozonized and then immersed in
the MMA solution. The presence of the PMMA layer covering the GTR particles
surface was confirmed by FTIR study indicating the presence of new absorption peak at
1730 cm-1, by XPS through increased O/C ratio and also by EDXS X-ray microanalysis
through increased O signal. In addition, the decrease of water contact angle after
modification of rubber meant the increase of hydrophicility.
2.5.2 Compatibilizer
Compatibilization carried out by adding a third component during the blending process was widely used. The third component, termed as a compatibilizer, usually possesses a graft copolymer structure and can react with both phases of the blends.
For GTR-thermoplastic systems, the compatibilizer usually contains polar groups grafted onto the thermoplastic polymers. The polar groups of compatibilizer interact with the –OH group on the surface of GTR particle, and the thermoplastic polymers
10 of compatibilizer are the same with the polymer matrix of the blends. In this way, the compatibilization between plastic and GTR can be improved. Several compatibilizers have been used in GTR-thermoplastic systems, such as maleic anhydride grafted PP
(PP-g-MA), maleic anhydride grafted styrene-ethylene-butylene-styrene
(SEBS-g-MA) and so on.
Lee et al.27 studied the effect of different compatibilizers including PP-g-MA,
SEBS-g-MA and SEBS on the GTR/isotactic PP (i-PP) or GTR/PP-g-MA.
GTR/PP-g-MA showed much higher tensile properties than GTR/i-PP, with an increase of elongation at break from less than 50% to 200%. With the addition of SEBS or
SEBS-g-MA, tensile properties improved even further. The latter was due to the presence of reactive functional group of maleic anhydride of SEBS undergoing dynamic reaction with PP during melt processing.
2.6 Ultrasound
Ultrasound is an oscillating sound pressure wave with a frequency above the upper limit of the human hearing range, i.e. > 16 KHz. Ultrasound has been applied in many fields, including biology, engineering, dentistry, geology and polymers.
The application of ultrasound falls into two areas according to frequency28: 1)
Ultrasound at high frequency (1-10 MHz) with low power, in milliwatt range. It is mainly used in used in non-destructive testing of materials and flaw detection. In addition, cure rates of resins and their composition can be measured with high frequency ultrasound. 2) Ultrasound at low frequency (20-500 kHz) with high power up to several hundred watts. The welding of thermoplastics is efficiently achieved
11 using power ultrasound, and high power ultrasound can also induce polymer degradation.
Ultrasound waves, like all sound waves, have cycles of compression and expansion. Compression exerts positive pressure on the liquid molecules by pushing them together. Expansion cycles exert negative pressure on the liquid molecules by pulling them apart. During negative half of the cycle, sound wave of sufficient intensity can generate cavities. It is known that the tensile strength of liquid is determined by attractive forces that held liquid molecules together. Thus when the pressure during the expansion cycle is large enough to overcome the strength, a cavity will form at the weak points of the structure.
The cavitation mechanism consists of mainly three steps: formation, growth and collapse of bubbles as schematically represented in Figure 2.1.
Figure 2.1 Ultrasound cavitation bubble growth and collapse29
During cavitation, bubble collapse produces intense local heating, high pressures at very short lifetimes; these transient, localized hot spots drive high-energy chemical reactions. These hot spots have temperatures of 5000 °C, pressures of about 1000 atm, and heating and cooling rates above 1010 K/s30. Furthermore, the region around cavitation bubbles has high temperature, pressure and possibly electric field gradients.
12 Liquid motion nearby also generates very large shear and strain gradients which are caused by the fast streaming of solvent molecules around the cavitation bubble and the intense shock waves released on collapse.
2.6.1 Effect of ultrasound on polymer
Ultrasound can influence polymer both physically and chemically. Acoustic streaming from liquid irradiated by ultrasound mainly causes only physical changes such as rapid mixing and heating. Though cavitation is not required for these changes, they always accompany cavitation. The welding of thermoplastics is efficiently achieved using high power ultrasound; high-intensity ultrasound dramatically increases the rates of intercalation of compounds into layered inorganic solids; the effect of ultrasound on polymer degradation and dispersion of filler in polymer matrix are also studied.
2.6.1.1 Degradation of polymer by ultrasound
In earlier studies, the ultrasound induced polymer degradation was investigated mostly in solution. Price and Smith31-33 have done a series of experiments about the effect of various ultrasonic irradiation conditions on the molecular weight change of polystyrene in solution. It should be pointed out that the degradation here only means a decrease of the molecular weight. In these studies, it was clearly shown that polymer with the higher molecular weight degrades more and reaches a limit molecule weight
Mlim, below which no further degradation occurs. In addition, for an initially narrow polydispersity sample, the distribution widens a little before reducing, while a broad
13 sample with the same initial number average molecular weight falls a lot during the sonication process. Furthermore, with an increase of ultrasound intensity, molecule weight decreases, while the dependence of degradation rate on intensity is not simple increase, but it increases to maximum and then drops. This is because the maximum radius of the bubble, R, is weight percentageal to the square root of the intensity. Hence, an increase in the intensity leads to larger bubbles per unit volume of solution and therefore higher shear forces on collapse, lower molecular weight and higher degradation rate is reached. Above a critical intensity, however, with an increase of the number of bubbles, the ultrasound field is unable to pass through the solution efficiently, leading to less cavitation, thus the degradation rate falls at very high intensity.
2.6.2.2 Devulcanization of rubber by ultrasound
In the last paragraph, “cavitation” which resulted in the degradation of polymeric chains in solution was discussed. Ultrasonic devulcanization is considered to be induced by the same phenomena “cavitation” which leads to degradation of polymeric chains in solution. During devulcanization process, the existence of cavitational bubbles in solid polymer has been verified34, 35.
Figure 2.2 Schematic of the overstressed network fragment around the collapsing
bubble34
14 When ultrasound is applied to rubber particle in the melt state, due to the
pulsating force, cavitation bubbles expand and contract, Near a solid surface, bubble
collapse becomes nonspherical, high-speed jets of liquid were driven into the surface
and creating shockwave damage to the surface, thus a large amount of energy was
released, which leads to the rupture of intermolecular bonds.
Over the last two decades, extensive work on ultrasonic devulcanization has
been done by Isayev and co-workers. It is demonstrated that ultrasonic
devulcanization is rapid, clean and effective technique for recycling the waste tires
rubber. The three-dimensional network of crosslinked rubber breaks down in seconds
under ultrasound treatment. In addition, the devulcanized rubber can be revulcanized
to obtain the same or sometimes even better mechanical properties than the virgin
rubber.
The effect of different operating parameters on the devulcanization of GTR was
studied by Tukachinsky et al.36 The variables included ultrasonic amplitude, gap and
flow rate. The degradation or devulcanization of GTR is characterized by crosslink
density and gel fraction. It was shown that the effect of ultrasound on the degree of
devulcanization is more significant when ultrasonic amplitude is high or when
residence time is longer. Devulcanized GTR was divided into “undertreated” and
“overtreated” at an intermediate value of 0.1 kmole/m3 of crosslink density. It was found that the overtreatment of GTR induces significant degradation of macromolecular backbone, and the undertreatment indicated insufficient ultrasound
treatment. At the intermediate value of crosslink density, highest strength and
elongation were obtained36.
2.6.2.3 Compatibilization of blends by ultrasound
15
Ultrasound has been proved to be useful in improving the interfacial adhesion between two different incompatible phases. The sustained application of ultrasound on the polymer blends induces the stresses due to cavitation phenomena, resulting in homolytic cleavage of polymeric chains. Ultrasonic energy induces the breakage of
C-C bonds, creating long chain radicals, which will further combine with long chain radicals from another component of blends to form copolymer.
In an interesting series of experiments, Isayev and his coworkers studied the effect of ultrasound on different blend systems. Oh et als37 carried out research about polypropylene (PP) /natural rubber (NR) blends. PP/NR was first mixed using a co-rotating twin screw extruder at a ratio of 25/75, 50/50 and 25/75. Then the extrudates were fed to the extruder without and with ultrasound treatment of 5, 7.5 and 10 μm. Mechanical properties of PP/NR of 75/25 are more influenced by ultrasound. For untreated sample and sample treated at 10 μm , the tensile strength increased from 11.9 to 16.8 MPa, and the elongation also improved from 12 to 26%,
Young’s modulus increased from 300 to nearly 500 MPa, the toughness from 1.3 to
4.2 MPa. The improvement of mechanical properties was correlated with the results of morphological properties: The AFM analysis of section of 75/25 PP/NR blends indicated sharp steps at the height of 100 nm at the interface between PP and NR in the untreated sample, while the untreated sample exhibited small step at the height of
15nm, indicating a good adhesion and formation of copolymer.
In situ compatibilization of PP/EPDM blends using ultrasound aided extrusion was studied by Feng and Isayev38. Ultrasound resulted in an increase in the elongation at break from 1100 to 1370 %, the tensile strength from 20 to 26 MPa and the toughness from 126 to 180 MPa for 50/50 PP/EPDM. SEM microimages showed that domain size
16 decreased for ultrasonically treated PP/EPDM than that of the untreated sample, after annealing treatment. The morphology of treated blends is more stable than that of the untreated blends since the in situ compatibilization at the interface delays the phase growth.
Luo and Isayev8 studied the recycling of GTR through compounding with polypropylene. In their research, GTR was devulcanized by ultrasound. Then devulcanized ground tire rubber (DGTR), GTR and revulcanized ground tire rubber
(RGTR) were compounded with PP in a twin screw extruder and a Brabendar internal mixer. It was found that phenolic resin cure system improved the Young’s modulus and tensile strength, while it induced an increase in Izod impact strength compared with
PP/GTR. In addition, from SEM micrographs, it was observed that rubber particles were smaller and more uniform from the twin screw extruder than blends prepared by the internal mixer. Furthermore, the addition of PP-g-MA improved the Young’s modulus and tensile strength.
Oh and Isayev39 compounded polypropylene (PP) with GTR at a fixed ratio of
40/60, using a co-rotating twin screw extruder. Then the prepared compound passed through plastic single screw extruder without and with ultrasonic treatment at 5, 7.5 and 10 μm. Dynamic revulcanization was carried out in an internal mixer. Die pressure turned out to drop tremendously with ultrasonic treatment. In addition, rubber particle size of revulcanized blends decreased becoming more uniform compared to the untreated sample.
2.6.2.4 Application of ultrasound in filled polymer system
17 Fillers are materials that are added to a polymer blends formulation to improve
properties of final products or to lower cost. Through the proper selection of filler type
and amount, processing and mechanical behavior can be greatly improved. Various
kinds of fillers have been added to the polymer matrix to improve its processing and
mechanical properties and to make compounds applicable to the desired usages.
Ultrasound was found to be useful in the filled polymer system, since it helps
breaking the agglomeration of fillers. Thus better dispersion of filler throughout the
polymer matrix can be obtained.
Isayev et al.40 studied the effect of ultrasound on the dispersion of silica in rubber. The polarity of silica induces strong agglomeration. In their research,
EPDM/silica mixture was first compounded by Brabender Plasticorder, followed by
further milling in a two-roll mixer. Then the mixture was fed into a single screw
extruder with ultrasonic treatment. The ultrasonic amplitude applied was 10 μm. From
SEM micrographs, it was found that ultrasound treatment lowered number of
aggregates of silica. Smaller particles were well dispersed, compared with untreated
sample.
The effect of ultrasound on PP/clay nanocomposites were studied by Lapshin
and Isayev by applying continuous ultrasound assisted extrusion process41. It was
found that with the aid of ultrasound, rapid intercalation of clay into the polymer
matrix was obtained, without usage of any chemical modification of the polymer
matrix. Furthermore, nanocomposites samples treated by ultrasound showed an
improved elongation at break and toughness, compared to the untreated ones.
18 CHAPTER III
EXPERIMENTAL
3.1 Materials
Metallocene based polypropylene PP3825 used in the experiment was supplied by Exxon Chemical Company. Its melting point is 148.7 °C, melt flow rate is
32 g/10min, and molecular weight is 144, 80042.
The GTR used in the experiment was 40-mesh and 140-mesh ground whole
tire rubber powder produced by Lehigh Technologies. It is a free flowing, black
rubber powder produced from end-of-life tires that easily disperses into a multitude of systems and applications (e.g., roof coatings, adhesives, asphalt, plastic resins, sealants, etc.) 43. The composition of the material is as follows: 7.2% extractables,
57.7% polymer rubber hydrocarbon, 29.9% carbon black and 5.2% ash. 40-mesh
ground tire rubber (GTR) has a particle size distribution of 10% of rubber particle
with diameters larger than 400 μm, and 90% less than 400 μm. 140 mesh GTR has a particle size distribution of 10% of rubber particle diameters larger than 105 μm, and
60% of rubber particles with diameters between 75~105 μm, and 30% less than 75 μm.
Surface area of 40 mesh GTR and 140 mesh GTR are 0.066 and 0.58 m2/g,
respectively.
Polybond 3002 is a polymer modifier from Chemtura Company. The
composition is maleic anhydride modified homopolymer polypropylene (PP-g-MA).
19 It has a melting temperature of 157 °C, density of 0.91 g/cc (23 °C), melt flow rate of
7.0g/10min. The maleic anhydride level is 0.2 weight %.
3.2 Extruders with ultrasound treatment
Single screw extruder (SSE) with ultrasonic treatment is used.
Figure 3.1 Schematic drawing of single screw extruder
Its schematic drawing is shown in Figure 3.1. Materials were fed into the extruder through hopper. The screw had two mixing sections before ultrasonic treatment zone, consisting of Union Carbide Mixer (UCM) and a Melt Star mixer
(Figure 3.1.2). Total length of the screw is 838 mm. The screw diameter is 25.4 mm for the first 624.5 mm. Before entering the ultrasonic treatment zone, the screw diameter is enlarged to 38.1 mm. There is no screw flight near the horns. The purpose is to provide 2.54 mm gap for ultrasonic treatment. After the ultrasound treatment zone, the screw diameter is reduced to 25.4 mm. The L/D ratio of screw is 33:1. The
20 ultrasonic extruder was built based on a Killion extruder with L/D ratio of 24. The screw design is shown in Figure 3.2.
Figure 3.2 Design of 33:1 screw with two mixing sections before the ultrasonic treatment section and a conveying screw flights after it.
For ultrasonic treatment, two 6 kW ultrasonic power supplies (2000bdc,
Branson, Danbury, CT) were connected to two ultrasonic converters (Branson H.P.
101-135-124) to generate ultrasonic waves at a frequency of 20 KHz. Each converter was connected to a 1:1 titanium booster (Branson 101-149-096) and a water-cooled titanium horn. The horn was inserted into the barrel. The clearance between the two horns and the barrel was kept at 2.54 mm. The amplitude of ultrasound was varied from 5 to 15 μm. The ultrasonic amplitude applied in our research is 5, 7.5 and 10 μm.
A pressure transducer of maximum pressure 34.5 MPa (PT435A, Dynisco, Franklin,
MA) was attached to the barrel before the ultrasonic treatment zone. Three nozzle thermocouples are used to monitor the melt temperature. They were located on ultrasonic treatment zone, between ultrasound treatment zone and die area, and in the die zone, respectively.
During compounding, independent process variables are flow rate and gap thickness in the ultrasonic treatment section. Flow rate determines the mean residence time in the treatment zone, shear rate (screw speed) is defined by the gap thickness and flow rate, temperature and ultrasonic amplitudes. Ultrasonic power consumption and pressure in the treatment zone are dependent process variables. All the independent and dependent process variables were recorded. The single screw
21 extruder is connected to a laptop computer, and all the data are collected by data acquisition system (DI-715-U, Data instruments, Akron, OH) based on National
Instrument software.
Twin screw extruder with ultrasonic treatment
Figure 3.3 Schematic drawing of twin screw extruder
Compounding PP with GTR was also carried out using a co-rotating twin-screw extruder (TSE, Prism USALAB 16, Thermo Electron Co., UK), modified with an ultrasonic horn attached onto the barrel. This modification was designed by
Mr. Todd Lewis. Schematic of this ultrasonic twin-screw extruder is shown in Figure
3.3. Two screws with a diameter of 16 mm were used to convey and mix PP with
GTR. A pressure transducer (PT460E-5M-6, Dynisco Instruments, Sharon, MA) was mounted at the die. The barrel temperature was monitored by thermocouples mounted in the barrel. For ultrasonic treatment zone, power supply generates ultrasonic waves at a frequency of 40 kHz imposing to the materials through a horn. The horn was a 28 mm × 28 mm square cross section. It was mounted in the barrel, and connected to a booster. The gap between the horn tip and screws was 2.5 mm, and the volume of ultrasonic treatment zone was 1.9 cm3. The die of the extruder has a diameter of 4 mm
22 and a length of 11 mm. The ultrasonic horn was cooled by water at 50 °C coming from a thermostat (GP-100, NESLAB Instruments Inc., Newington, NH) set.
3.2.1. Preparation of blends in single screw extruder
PP/GTR/PP-g-MA blends of 30/70/0, 50/50/0, 70/30/0 and 50/50/10 composition were physically mixed and then fed to the SSE at a flow rate of 2 lbs/hr without imposing ultrasound. Screw speed is set at 100 rpm in SSE. Zone temperatures in the extruder were 130/180/190/190/190/190/190 °C. The extrudates were then cooled, dried, and then crushed into particles using a grinder (WEIMA) with a screen of 5 mm. The pellets were then fed into the extruder at a flow rate of 2 lbs/hr. Amplitudes of 0, 5, 7.5 and 10 μm were applied. Due to the fact that the flow during the first extrusion was not stable, indicating a bad mixing of PP and GTR, a second extrusion without and with the ultrasonic treatment was applied. The gap between the horns and screw shaft was 2.54 mm.
3.2.2 Preparation of blends in twin screw extruder
PP/GTR/PP-g-MA blends of 30/70/0, 50/50/0, 70/30/0 and 50/50/10 composition were physically mixed and then fed to the TSE at a flow rate of 2 lbs/hr without and with ultrasonic treatment under amplitude of 5, 7.5 and 10 μm. The screw speed is set at 200 rpm. Zone temperatures in the extruder were
130/180/190/190/190/190/190 °C. The extrudates from both extruders were then
23 cooled, dried, then crushed into particles using a grinder (Weima) with a screen of 5
mm.
3.3. Molding
3.3.1. Injection molding
For characterization, tensile and impact samples were prepared by injection
molding for both PP and PP/GTR blends with a mini-jet injection molding machine
(DSM Research B.V). A cylinder temperature of 200 °C and a mold temperature of
60 °C at pressure of 6 MPa were used.
3.3.2. Compression molding
For pure PP, rheological specimens were molded at 180 °C under pressure of
25 MPa for 20 minutes using a compression molding press (Carver, Inc). As injection molding was used to prepare tensile and impact sample, rheological specimens of
PP/GTR belnds were molded at 180 °C under a pressure of 25 MPa for 10 minutes using the same compression molding press. The samples had a diameter of 25 mm and width of 2 mm.
3.4. Characterization
3.4.1 Rheological measurements
24
The rheological behavior of pure PP was tested using Advanced Rheometrics
Expansion System (ARES) at a temperature of 180 °C, a strain amplitude of 5%. A 25 mm diameter parallel plate was used. Thickness of the sample is 2.2 mm. The complex viscosity, storage modulus, loss modulus as a function of frequency was measured.
The rheological behavior of the blends were investigated using an Advanced
Polymer Analyzer (APA2000, Alpha Technologies), at a temperature of 180 °C, at a
strain amplitude of 7.1%.
3.4.2. Tensile tests
The tensile properties of both pure PP and PP/GTR were investigated by an
Instron-5567 at room temperature at a crosshead speed of 50 mm/min. For both PP
and PP/GTR, at least 6 samples were tested. The samples were made according to
ASTM D638 standard.
3.4.3 Impact tests
Notched Izod impact strength was measured according to ASTM D-256
standard. Impact test was carried out by an Impact Tester (Testing Machines, Inc.
Model 43-1). All impact tests were conducted at room temperature. Sample bars were
made from injection molding, and the 0.1mm notch was made by a notch cutter
(Testing Machines, Inc.). The average impact resistance is calculated in joules per
25 meter of specimen width. The unit of impact tester is ft*lb (1ft*lb = 1.356J), and the
read of the tester will be divided by sample width, 1.2 cm.
3.4.4 Morphological measurements
The phase morphology of PP/GTR blends was observed using scanning electron microscopy (SEM, Hitachi S-1250). Due to the low contrast between PP and
GTR phases, etching technique was applied to extract PP phase. The tensile sample from injection molding was fractured in liquid nitrogen, and then immersed in xylene at 90 °C for 30 minutes. After etching, the samples were dried in a vacuum oven at
70 °C for 12 hours, and then were coated with silver using sputter coating.
26 CHAPTER IV
RESULTS AND DISCUSSION
4.1 Die pressure
The pressure measured before ultrasonic treatment zone of 40 mesh and 140 mesh blends from single screw extruder (SSE) as a function of ultrasonic amplitude is presented in Figure 4.1 (a) and (b). It should be pointed out at first that the overall level of the pressure during the extrusion is very low, i.e. below 1.1 MPa. Firstly, it can be observed that the die pressure reduced substantially with an increase of ultrasonic amplitude, resulting in better processability of the melts. The decrease of die pressure can be explained as a result of the acoustic cavitation leading to both permanent and thixotropic changes in the melt under ultrasonic treatment. The permanent changes here mainly refer to the degradation of polymer, which may lead to permanent reduction of matrix viscosity due to the polymer chain scission. In addition, changes may be caused by the effect of ultrasound mixing. The effect of degradation is observed from the rheological behavior of the material, causing a decrease in complex viscosity, as shown below.
27 1.2 (a) 1.0 30/70 50/50 50/50 0.8 with compatibilizer
0.6 70/30 0.4 100/0 Die Die pressure (MPa) 0.2
0.0 0 2 4 6 8 10 12
Amplitude (m) 1.2 (b) 1.0
0.8 30/70 50/50 0.6 70/30
0.4 Die pressure (MPa) 0.2 50/50, with compatibilizer 100/0 0.0 0 2 4 6 8 10 12
Amplitude (m) Figure 4.1 Die pressure of 40 mesh SSE (a) and 140 mesh blends (b) from SSE as a function of ultrasonic amplitude at various PP/GTR ratios.
28 In addition, ultrasonic waves may also induce thixotropic effect — enhancing shear thinning behavior of the melt, resulting in a transient decrease of melt viscosity which will recover after ultrasonic treatment. Thus, the decrease of pressure with the ultrasonic amplitude for PP and blends, in addition to degradation, can be explained as a combined effect of the shear thinning behavior 44 and a possibility of the reduction of the friction of material along the horn surface due to ultrasonic waves.
Secondly, the pressure of 40 mesh blends is higher than that of 140 mesh blends. The pure PP exhibits a lower pressure than all blends. This behavior is also in accordance with the rheological behavior of these materials, as discussed later. Thirdly, the die pressure increases with an increase in GTR weight percentage in PP/GTR blends.
This is due to the higher viscosity of GTR than PP. Because of the presence of the network structure of rubber from vulcanization process, the flowability of GTR during processing is worse than that of the plastic melt, resulting in a higher viscosity of blends. Thus higher rubber weight percentage in the blend led to an increase in die pressure. Last but not least, the presence of compatibilizer in 50/50 blends caused an increase of the die pressure. This is because with the addition of compatibilizer, the viscosity of blends will increase, which may be due to the fact that the compatibilizer helps the formation of new copolymers and improves the compatibility between PP and GTR, resulting in a change of viscosity, also reflecting in the die pressure.
4.2 Power consumption of ultrasound
Ultrasonic power consumption of both SSE and TSE are plotted as a function of ultrasonic amplitude in Figure 4.2 (a), (b), (c) and (d). With increasing ultrasonic
29 amplitude, power consumption increases. Power consumption includes two parts, the
dissipated energy leading to heat, and the energy exerted to the melt to induce the
interaction between PP and rubber particle45. In TSE, it can be observed that 140 mesh blends show higher power consumption than 40 mesh blends and pure PP, indicating more energy was transmitted from the horn to the polymer melt. This may
due to smaller rubber particle size, having more surface area for reaction to take place
due to the exerted more energy. In SSE, however, 40 mesh blends show the higher
power consumption. This is due to a possibility of the formation of new copolymer in
SSE for 40 mesh blends due to the exerted more power.
30 100 100 30/70 30/70 50/50 50/50 80 80 50/50, with comaptibilizer 50/50, with compatibilizer 70/30 70/30 100/0 60 100/0 60
40 40
20 20 Power ConsumptionPower (W)
0 Power Consumption (W) (a) 0 (b) -20 -20 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Amplitude (m) Amplitude (μm)
100 100 30/70 30/70 50/50 50/50, with compatibilizer 80 80 50/50, with compatibilizer 50/50 70/30 70/30 100/0 60 60 100/0
40 40
20 20 Power Power Consumption (W) Power Power Consumption (W) 0 (d) 0 (c)
-20 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Amplitude (m) Amplitude (μm)
Figure 4.2 Ultrasonic power consumption of 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c) and TSE (d) as a function of ultrasonic amplitude at various PP/GTR ratios.
31 4.3 Rheology
Figure 4.3 shows the complex viscosity as a function of frequency for PP/GTR
(40 mesh) blends of 100/0, 70/30, 50/50 and 30/70, from SSE. First of all, with GTR
weight percentage increases, the complex viscosity increases tremendously. This is
due to the fact that the viscosity of rubber is higher than plastic due to the network
structure of rubber, resulting in worse flowability of blends. Thus, when rubber
weight percentage increases, viscosity also increases. This is in accordance with the
die pressure trend discussed earlier. Secondly, it is seen that the complex viscosity of
PP decreases at an amplitude of 5 μm, which is supportive evidence of the degradation of PP. The dependence of complex viscosity does not decrease monotonously with increase of ultrasonic amplitude. This is because the complex viscosity of blends is the result of a competition between chain scission of polymer creating macroradicals and their recombination through radical polymerization. For
PP/GTR blends with ultrasound treatment, the viscosity is affected by three factors: the devulcanization of GTR, the degradation of PP, and the formation of new copolymer. For PP/GTR 70/30, there is also an obvious viscosity drop at an ultrasonic amplitude of 5 μm. For PP/GTR 50/50, the viscosity does not change much at 5 μm.
For PP/GTR 70/30, the viscosity reaches highest value at amplitude of 5 μm. This is due to higher PP weight percentage in the blends, the effect of PP degradation is a determining factor in the viscosity. However, with a decrease of PP weight percentage, the other two factors may dominate.
32
105 30/70 0m m m 10m
50/50 104
Pa*s 70/30 103
100/0
102 100 101 102 103 Frequency (s-1)
Figure 4.3 Complex viscosity of 40 mesh blends from SSE as a function of frequency at various PP/GTR ratios and various ultrasonic amplitudes.
33 Figure 4.4 depicts the complex viscosity as a function of frequency for
PP/GTR (140 mesh) blends of 100/0, 70/30, 50/50 and 30/70, from SSE. Generally, plastic/rubber blends with smaller rubber particle size should have higher viscosity due to the large surface area which allows greater filler-matrix interaction. In our case, however, for PP/GTR 30/70 and 50/50, the viscosity of 140 mesh blends is lower than that of 40 mesh blends. This is because of the different values of gel fraction of 40 mesh GTR and 140 mesh GTR. According to swelling test results from Tian et al, the gel fraction of 40 mesh GTR is 85.2%, while gel fraction of 140 mesh GTR is
69.4%46. Higher gel fraction is the reason why higher viscosity is obtained with larger particle size. For PP/GTR 70/30, at an ultrasonic amplitude of 5 μm, there is an obvious viscosity increase. This correlates with improved tensile properties of these blends, discussed later.
Figure 4.5 shows the complex viscosity as a function of frequency for
PP/GTR (40 mesh) blends of 100/0, 70/30, 50/50 and 30/70, from TSE. Degradation of PP in both SSE and TSE can be observed from viscosity drops. It is seen that the complex viscosity of PP in TSE decreases at an amplitude of 10 μm, while the complex viscosity of PP in SSE decreases at an amplitude of 5 μm. It is observed that degradation is larger in TSE due to higher shear stress. This can be explained by the fact that at same flow rate of 2 lbs/hr, in TSE, a screw speed of 200 rpm was used, while in SSE, the value was 100 rpm, which leads to more shear occurring in TSE. In addition, the ultrasonic frequency is different for TSE and SSE. In TSE it is 40 kHz,
34 while in SSE it is 20 kHz. The effect of ultrasound is observed for PP/GTR 70/30, where viscosity drops significantly at an amplitude of 7.5 μm, which also correlates with tensile properties discussed below.
35
105 30/70 0μm 7.5μm 5μm 10μm
104 50/50 Pa*s 103 70/30
100/0
102 100 101 102 -1 Frequency (s ) Figure 4.4 Complex viscosity of 140 mesh blends from SSE as a function of frequency at various PP/GTR ratios and various ultrasonic amplitudes.
36
106 0m 30/70 m m 10m 105
104 50/50
Pa*s 70/30 103
102 100/0
101 100 101 102 103 Frequency (s-1) Figure 4.5 Complex viscosity of 40 mesh blends from TSE as a function of frequency at various PP/GTR ratios and various ultrasonic amplitudes.
37 Figure 4.6 depicts the complex viscosity as a function of frequency for
PP/GTR (140 mesh) blends of 100/0, 70/30, 50/50 and 30/70, from TSE. It can be observed that viscosity of 140 mesh blends are generally lower than that of 40 mesh blends from TSE. The same phenomenon was observed for blends from SSE. This can also be explained by the difference of gel fraction between 40 and 140 mesh GTR.
The effect of ultrasound is also evident in PP/GTR of 70/30 blends, as there is an obvious viscosity drop at 10 μm.
Figure 4.7 shows complex viscosity of uncompatibilized and compatibilized
40 mesh blends, i.e. PP/GTR/PP-g-MA 50/50/0 and 50/50/10, from SSE (a), TSE (b) , and 140 mesh blends from SSE (c), TSE (d). Figure 4.8 are Cole-Cole plots of both
40 mesh blends, from both SSE (a) and TSE (b), and 140 mesh blends from SSE (c) and TSE (d). Firstly, from the Cole-Cole plot, it is observed that the addition of compatibilizer affects the molecular structure of blends. Secondly, with the addition of compatibilizer, viscosity of all blends increased, due to the fact that compatibilizer changed the molecular structure of blends, increasing the reactivity between PP and
GTR, which is also reflected in tensile properties discussed in the next section. Also, one can see that in the presence of compatibilizer, the effect of ultrasound on viscosity becomes more significant.
38
105 30/70 0μm 7.5μm 5μm 10μm
104
50/50 Pa*s 103 70/30
100/0
102 100 101 102 Frequency (s-1) Figure 4.6 Complex viscosity of 140 mesh blends from TSE as a function of frequency at various PP/GTR ratios and various ultrasonic amplitudes.
39
4 10 105 50/50, with compatibilizer (a) 50/50, (b) with compatibilizer
104 50/50, without compatibilizer 3
Pa*s 10 Pa*s 50/50, 103 without compatibilizer
0m 7.5m 5m 10m 0m m m 10m 102 102 100 101 102 103 100 101 102 103 Frequency (s-1) Frequency (s-1)
5 104 10 50/50, with compatibilizer (c) (d)
104 50/50, with compatibilizer 50/50, without compatibilizer 3 Pa*s
Pa*s 10 103 50/50, without compatibilizer
0m 7.5m 0μm 7.5μm 5m 10m 5μm 10μm 102 102 100 101 102 103 100 101 102 103 -1 Frequency (s-1) Frequency (s ) Figure 4.7 Complex viscosity of PP/GTR/PP-g-MA 50/50/10 (filled symbols) and 50/50/0 (open symbols), 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c) and TSE (d), at various ultrasonic amplitudes.
40
6 10 106 0m m (b) m 10m (a) 0m m m 10m
5 10 105 50/50, without compatibilizer 50/50, without compatibilizer G'' (Pa) 50/50, with compatibilizer G'' (Pa) 4 10 104 50/50, with compatibilizer
103 103 102 103 104 105 106 101 102 103 104 105 106 G' (Pa) G' (Pa) 106 106 0m 7.5m 0m m (c) (d) 5m 10m m 10m
5 10 105 without compatibilizer 50/50, without compatibilizer G'' (Pa) G'' (Pa) 4 10 with compatibilizer 104 50/50, with compatibilizer
103 103 101 102 103 104 105 106 101 102 103 104 105 106 G' (Pa) G' (Pa)
Figure 4.8 Cole-Cole plot for PP/GTR/PP-g-MA 50/50/10 (filled symbols) and 50/50/0 (open symbols), 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c) and TSE (d), at various ultrasonic amplitudes.
41 4.4 Tensile properties
Figure 4.9 depicts Young’s modulus (a), tensile strength (b) and elongation at
break (c) of pure PP from both SSE and TSE. The Young’s modulus of PP from TSE
decrease significantly compared with that of PP from SSE due to higher shear stress
in TSE. At same flow rate of 2 lbs/hr, a screw speed of 200 rpm in TSE is applied,
leading to higher shear rates compared with a screw speed of 100 rpm in SSE. The
Young’s modulus, tensile strength and elongation at break of 40 mesh blends from
SSE are respectively plotted as a function of the ultrasonic amplitude at various
PP/GTR ratios in Figure 4.10 (a), (b) and (c). In addition, to better show the effect of
ultrasound on tensile properties, these values plotted against PP weight percentage of
the blends in Figure 4.11 (a), (b) and (c), at ultrasonic amplitudes of 5 and 10 μm.
From Figure 4.10, through comparing PP/GTR/PP-g-MA 50/50/0 and 50/50/10, one can see the addition of compatibilizer to the blends increases the Young’s modulus by
15%, tensile strength by 5% or more and elongation by 25%. In addition, the tensile properties dependence on the various PP/GTR ratios can be observed. With an increase of PP weight percentage, the Young’s modulus and tensile strength generally increase. However, the PP/GTR 70/30 blends treated by ultrasound at 10 μm, the modulus decreases by 30% in comparison with the untreated blends and the tensile strength decreases by 20%, while the elongation at break increases slightly. This effect can be correlated with the viscosity drop at an amplitude of 10 μm, indicating that the breakage of macromolecular chains leads to decrease in the modulus and strength. At the same time, the break-up of macromolecular chains creating macroradicals of PP and rubber may form copolymer that provides higher elongation at break.
42
1600
1400
1200
Young's modulus (MPa) SSE TSE (a)
1000 0 2 4 6 8 10 12 Amplitude (m) 46
44
42
40
38
Tensile strength (MPa) SSE TSE 36 (b)
0 2 4 6 8 10 12 Amplitude (m)
5.5
5.0
4.5
Elongation at break 4.0 SSE TSE (c)
3.5 0 2 4 6 8 10 12 Amplitude (m) Figure 4.9 Young’s modulus (a), tensile strength (b) and elongation at break (c) for pure PP from both SSE and TSE as a function of ultrasonic amplitude. Symbols are slightly shifted along the abscissa for clarity.
43 800 50/50 50/50, with compatibilizer
700
70/30 600 30/70 500
400 Young's modulus (MPa) 300 (a)
200 0 2 4 6 8 10 12 Amplitude (m)
22 50/50 50/50, with compatibilizer 20
18
16
14 70/30 12 30/70 Tensile strength (MPa) 10 (b)
8 0 2 4 6 8 10 12 Amplitude (m) 0.5
0.4
0.3
0.2
Elongation at break 50/50 0.1 50/50, with compatibilizer 70/30 (c) 30/70 0.0 0 2 4 6 8 10 12 Amplitude (m)
Figure 4.10 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from SSE as a function of ultrasonic amplitude at various PP/GTR ratios. Symbols are slightly shifted along the abscissa for clarity.
44 800
5m, without compatibilizer 700 10m, without compatibilizer 5m, with compatibilizer 600
500
400
Young's modulus (MPa) 300 (a)
200 20 30 40 50 60 70 80 PP weight percentage (%) 22 5m, without compatibilizer 20 10m, without compatibilizer 5m, with compatibilizer 18
16
14
12
10 Tensile strength (MPa) 8 (b)
6 20 30 40 50 60 70 80 PP weight percentage (%) 0.50
0.45
0.40
0.35
0.30
0.25
Elongation at break 0.20 5m, without compatibilizer 10m, without compatibilizer 0.15 5m, with compatibilizer (c) 0.10 20 30 40 50 60 70 80 PP weight percentage (%) Figure 4.11 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from SSE as a function of PP weight percentage. Symbols are slightly shifted along the abscissa for clarity.
45 Young’s modulus, tensile strength and elongation at break of 140 mesh blends from SSE are respectively plotted as a function of the ultrasonic amplitude in
Figure 4.12 (a), (b) and (c). In addition, to better show the effect of ultrasound on tensile properties, these values are plotted against PP weight percentage of the blends in Figure 4.13 (a), (b) and (c), at ultrasonic amplitudes of 5 and 7.5 μm. From Figure
4.12, it can be observed that with an increase of PP weight percentage in PP/GTR blends, the Young’s modulus and tensile strength increase, while the elongation at break does not change much. In addition, the compatibilized blends
PP/GTR/PP-g-MA 50/50/10 showed an increase of the elongation at break at 5 μm and the tensile strength increases with ultrasonic amplitude.
In Figure 4.13, one can see an obvious dependence of the tensile strength and
Young’s modulus on PP weight percentage, while the elongation at break does not show such a behavior. Generally with an increase of content of rubber, the elongation of plastic/rubber blends will increase. However, result from the present study does not indicate such an effect. This may be due to the fact that the waste GTR acted as defects in the structure of blends. Furthermore, the addition of PP-g-MA helps to increase the elongation at break by 50%, and the tensile strength increase by 25%, evidently due to an improvement of adhesion between PP and GTR blend.
46 800
700 70/30 50/50, with compatibilizer 500
400
300 50/50
Young's modulus (MPa) 30/70 200 (a)
100 0 2 4 6 8 10 12 Amplitude (m) 22
20
18 50/50, compatibilizer 70/30 16
14 50/50 30/70 Tensile strength (MPa) 12 (b)
10 0 2 4 6 8 10 12
Amplitude (m) 0.6 50/50, with compatibilizer
0.5
0.4 Elongation at break Elongation 50/50 0.3 30/70 (c) 70/30
0 2 4 6 8 10 12 Amplitude (m)
Figure 4.12 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from SSE as a function of ultrasonic amplitude at various PP/GTR ratios. Symbols are slightly shifted along the abscissa for clarity.
47 800 5m, without compatibilizer 7.5m, without compatibilizer 7.5m, with compatibilizer
600
400 Young's modulus (MPa) modulus Young's 200 (a)
20 30 40 50 60 70 80 PP weight percentage (%)
24 5m, without compatibilizer 7.5m, without compatibilizer 22 5m, with compatibilizer
20
18
16
14 Tensile strength (MPa) 12 (b)
10 20 30 40 50 60 70 80
PP weight percentage (%)
0.6
0.5
0.4
Elongation at break Elongation 0.3 5m, without compatibilizer 7.5m, without compatibilizer 5m, with compatibilizer (c) 0.2 20 30 40 50 60 70 80 PP weight percentage (%)
Figure 4.13 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from SSE as a function of PP weight percentage. Symbols are slightly shifted along the abscissa for clarity.
48 Tensile properties including the Young’s modulus, tensile strength and elongation at break of 40 mesh blends from TSE are respectively plotted as a function of the ultrasonic amplitude in Figure 4.14 (a), (b) and (c). In addition, to better show the effect of ultrasound on tensile properties, these values are plotted against PP weight percentage of the blends in Figure 4.15 (a), (b) and (c), at ultrasonic amplitudes of 5 and 7.5 μm. From Figure 4.15, the Young’s modulus and tensile strength increase with an increase of PP weight percentage, while the elongation at break decreases with PP weight percentage increase. One can also observe the effect of ultrasound on PP/GTR 70/30 at 7.5 μm. The decrease of complex viscosity curve at
7.5 μm, from Figure 4.5, indicating that the breakage of macromolecular chains formed macroradicals, and the recombination of them improved Young’s modulus.
Furthermore, the addition of compatibilizer gives rise in the elongation by 30%.
Figure 4.16 shows tensile properties including the Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from TSE as a function of ultrasonic amplitude. In addition, to better show the effect of ultrasound on tensile properties, these values are plotted against PP weight percentage of the blends in Figure 4.17 (a), (b) and (c), without and with ultrasonic treatment at an amplitude of 10 μm. In Figure 4.17, it is seen that the Young’s modulus and tensile strength increase obviously with an increase of PP weight percentage, and the elongation at break decreases with an increase of PP weight percentage. The effect of compatibilizer reflected in increasing of the tensile strength by 10% and the modulus by 100%. However, the elongation at break does not improve with the addition of compatibilizer. The effect of ultrasound is seen in Figure 4.17, for PP/GTR 70/30.
One can observe an increase in the Young’s modulus and also in the elongation at break at an ultrasonic amplitude of 10 μm. As was shown in Figure 4.6, the complex
49 viscosity of PP/GTR 70/30 with 140 mesh GTR from TSE drops at an ultrasonic amplitude of 10 μm. This indicates that the breakage of the macromolecular chains occur, leading to a forming of macroradicals, and then the radicals recombine with each other to form new copolymer, providing increase in the Young’s modulus and elongation.
50 1400 70/30 1200 50/50, with compatibilizer 50/50 1000 30/70
800
600
400 Young's modulus (MPa) 200 (a)
0 0 2 4 6 8 10 12
Amplitude (m) 26
24
22
20
18
16 14 70/30 12 50/50, with compatibilizer 50/50
Tensile strength (MPa) 10 30/70 8 (b)
6 0 2 4 6 8 10 12
Amplitude (m) 0.6 70/30 50/50, with compatibilizer 0.5 50/50 30/70 0.4
0.3
0.2 Elongation atbreak Elongation
0.1 (c)
0.0 0 2 4 6 8 10 12 Amplitude (m)
Figure 4.14 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from TSE as a function of ultrasonic amplitude at various PP/GTR ratios. Symbols are slightly shifted along the abscissa for clarity.
51 1400 0 m, without compatibilizer 1200 7.5 m, without compatibilizer 7.5 m, compatibilizer 1000
800
600
400
Young's modulus (MPa) (a) 200
0 20 30 40 50 60 70 80 PP weight percentage (%) 26 24 0 m, without compatibilizer 22 7.5 m, without compatibilizer 7.5 m, with compatibilizer 20
18
16
14
12
Tensile strength (MPa) 10 (b) 8
6 20 30 40 50 60 70 80 PP weight percentage (%) 0.6
0.5
0.4
0.3
0.2
Elongation at break 0 m, without compatibilizer 0.1 7.5 m, without compatibilizer 7.5 m, with compatibilizer (c) 0.0 20 30 40 50 60 70 80 PP weight percentage (%)
Figure 4.15 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 40 mesh blends from TSE as a function of PP weight percentage. Symbols are slightly shifted along the abscissa for clarity.
52 900
800
700 30/70 600 50/50, with compatibilizer 50/50 500 70/30
400
Young's modulus (MPa) 300 (a)
200 0 2 4 6 8 10 12 Amplitude (m) 22
20
18
16 30/70 50/50, with compatibilizer 14 50/50 70/30 12 Tensile strength (MPa) 10 (b)
8 0 2 4 6 8 10 12 Amplitude (m) 0.50 30/70 50/50, with compatibilizer 0.45 50/50 70/30 0.40
0.35
0.30 Elongation at break 0.25 (c)
0.20 0 2 4 6 8 10 12
Amplitude (m)
Figure 4.16 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from TSE as a function of ultrasonic amplitude at various PP/GTR ratios. Symbols are slightly shifted along the abscissa for clarity.
53
900
800 10m, without compatibilizer 700 0m, without compatibilizer 10m, with compatibilizer 600
500
400 Young's modulus (MPa) 300 (a)
200 20 30 40 50 60 70 80 PP weight percentage (%) 22
20
18
16
14
12 10m, without compatibilizer
Tensile strength (MPa) 0m, without compatibilizer 10 10m, with compatibilizer (b) 8 20 30 40 50 60 70 80 PP weight percentage (%) 0.50 10m, without compatibilizer 0.45 0m, without compatibilizer 10m, with compatibilizer
0.40
0.35
0.30 Elongation at break 0.25 (c)
0.20 20 30 40 50 60 70 80 PP weight percentage (%)
Figure 4.17 Young’s modulus (a), tensile strength (b) and elongation at break (c) of 140 mesh blends from TSE as a function of PP weight percentage. Symbols are slightly shifted along the abscissa for clarity.
54 4.5 Impact test
Izod impact strength of PP/GTR 40 mesh blends as a function of ultrasonic
amplitude at various mixing ratios from SSE (a) and TSE (b), PP/GTR 140 mesh
blends from SSE (c), TSE (d) are plotted in Figure 4.18. First of all, all PP/GTR
blends showed much lower impact strength, compared with pure PP. This is because of the large particle size of GTR make them to act as defects in the structure of PP continuous phase. Secondly, compatibilizer provides an increase in the impact strength. Thirdly, the impact strength does not increase with increasing GTR weight percentage. However, it is observed that in most cases, 50/50 PP/GTR brings about the highest impact strength among all mixing ratios, thus is in accordance with an
47 earlier observation . Last but not least, the impact strength of blends containing finer rubber particles is higher than those with larger rubber particles. This confirms that
GTR particles introduce defects into the structure, which are so large that they can initiate unstable crazes, reducing their fracture resistance.
55
160 160 100/0/0 100/0/0 140 140
120 120
100 100 50/50/0 80 50/50/10 50/50/0 80 50/50/10 30/70 70/30/0 70/30/0 30/70 60 60
40 40 Impact strength (J/m) Impact strength (J/m) 20 20
0 (a) 0 (b)
0 2 4 6 8 10 12 0 2 4 6 8 10 12 Amplitude (m) Amplitude (m) 160
140 100/0/0 140 100/0/0
120 120
100 50/50/10 70/30/0 100 50/50/0 50/50/10 30/70/0 50/50/0 70/30/0 30/70/0 80 80
60 60 Impact strength (J/m) Impact strength (J/m) 40 40 (c) (d)
20 20 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Amplitude (μm) Amplitude (m)
Figure 4.18 Izod impact strength of PP/GTR 40 mesh blends from SSE (a), TSE (b), 140 mesh blends from SSE (c), TSE (d) as a function of ultrasonic amplitude at various PP/GTR ratios. Symbols are slightly shifted along the abscissa for clarity.
56 4.6 Morphological test
Figure 4.19 shows the SEM micrographs of untreated 50/50 PP/GTR 40 mesh blends from SSE (a), TSE (b) and 140 mesh blends from SSE (c), TSE (d). First of all, it can be observed from Figure 4.19(b) that particles in blends of 40 mesh obtained by
TSE are smaller than particles in blends of 40 mesh obtained by SSE (Figure 4.19 (a)).
Similar effect is seen for blends of 140 mesh by comparing Figure 4.19 (d) and Figure
4.19 (c). This is because of the fact that rubber undergoes more devulcanization in TSE than in SSE, due to higher shear stress in TSE. At same flow rate of 2 lbs/hr and a screw speed of 200 rpm in TSE, shear rates are higher than in SSE operating at a speed of 100 rpm, leading to more shear occurring in TSE. In addition, the ultrasonic frequency is different for TSE and SSE. In TSE it is 40 kHz, while in SSE it is 20 kHz.
Secondly, a rougher surface of rubber particles in blends is obtained by TSE, than by
SSE. This can explain why viscosity of 40 mesh blends from TSE is higher than that of SSE. The higher surface roughness of particles provides higher resistance to flow.
Thus, the viscosity rises.
The SEM micrographs of PP/GTR/PP-g-MA 50/50/10 of 140 mesh GTR without (a) and with ultrasonic treatment at amplitudes of 5 μm (b), 7.5 μm (c) and 10
μm (d), are presented in Figure 4.20. One can observe in Figure 4.20 (b) that rubber particles of blends under an ultrasonic amplitude of 5 μm are better attached to the matrix, which is in accordance with the fact that the elongation at break of the blend gets improved at 5 μm, as seen in Figure 4.16 (c).
57
(a) (b)
(b) (d)
Figure 4.19 SEM microimages of untreated 50/50 PP/GTR, 40 mesh blends from SSE (a), TSE (b), and 140 mesh blends from SSE (c), TSE (d)
58
(a) (b)
(c) (d)
Figure 4.20 SEM microimages of PP/GTR/PP-g-MA 50/50/10 140 mesh blends from SSE untreated (a), treated at 5 μm (b), 7.5 μm (c) and 10 μm (d).
59 CHAPTER V
SUMMARY
Compounding PP with GTR using ultrasonically aided extrusion is carried out.
The effect of 1) PP/GTR mixing ratio, 2) rubber particle size, 3) type of extruder, 4)
PP-g-MA compatibilizer and 5) ultrasonic amplitude are considered. GTR of 40 and
140 mesh were used. PP/GTR/PP-g-MA of 30/70/0, 50/50/0, 50/50/10 and 70/30/0 were compounded. Both single and twin screw extruders without and with ultrasonic treatment at amplitudes of 5, 7.5 and 10 μm were used.
With an increase of concentration of rubber particles, die pressure increases
in comparison with pure PP due to low viscosity of plastic melt and rubber particles
acting as filler. The Young’s modulus and tensile strength decrease upon an addition of
GTR. GTR has lower modulus and acts as defects in the blends. Generally, blends
containing higher amount of GTR particles show higher elongation.
With finer particles of GTR, lower complex viscosity of PP/GTR blends is
obtained, due to the lower gel fraction of 140 mesh than 40 mesh GTR. A higher
elongation at break value is obtained for 140 mesh blends than 40 mesh blends since
finer particles allow better adhesion with plastic matrix.
The Young’s modulus and of the untreated and ultrasonically treated PP is
higher in SSE than that in TSE. Besides, from SEM micrographs, rubber particles of
PP/GTR 50/50 blends are smaller in TSE than in SSE, and have a rougher surface,
resulting in higher viscosity.
60 The compatibilizer is seen to affect various aspects of blends. Firstly, from
Cole-Cole plot, it is observed that PP-g-MA affected the molecular structure of blends.
An addition of the compatibilizer increases the complex viscosity of PP/GTR blends. In addition, PP-g-MA helps to increase all tensile properties of PP/GTR blends. For 40 mesh blends from TSE, the elongation at break up to 50% is observed with an addition of compatibilizer, an increase of 100% in comparison with the uncompatibilized blends.
For PP/GTR 140 mesh blends, PP-g-MA increases the tensile strength by 30%, reaching 19 MPa.
Complex viscosity of the ultrasonically treated PP changes with amplitude in a complex way depending on the type of extruder. An increase or decrease of viscosity with amplitude is observed. Besides, ultrasonic treatment induced chemical reactions between PP and GTR with highest effect being cases of PP/GTR 70/30 blends.
Generally, the increase of viscosity is related to increase of the Young’s modulus, tensile strength and elongation at break.
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65