RepMinandUniDep

T

Su

of

2

public of nistry of d Scientifiversity opartment

ChTher

ubmitte

f Unive

of Re

010

f Iraq Higher E

fic Reseaof Techno

of Appli

Dearactmose

ed to th

ersity o

equirem

Philos

Prof

Educationarch ology ied Scien

eveloterizettin

A

he Dep

of Techn

ment fo

sophy in

Ban A

Sup

f. Dr. B

n

nces

opmeation

ng Po

A Thesi

artmen

nology

r the D

n Mate

By

yyoub

pervised

Balkees

ent an of Tolym

is

nt of Ap

y in Par

Degree

erials S

Yousif

d by

s M. Dh

and Tern

mer B

pplied

rtial Fu

of Doc

Science

f

hyaa

nary Blend

Scienc

ulfillme

ctor of

143

ds

es

ent

31

 

الرَِّحيمِ الرَّْحَمنِ اللَِّه بِْسمِ

كُلِّ َوفَْوَق َنَشاُء َمْن َدَرَجاٍت َنْرفَُع

﴾٧٦﴿َعِليٌم ِعلْمٍ ِذي

صدق هللا العظمي

 ٧٦يوسف

 

Dedication

To

Memory of my Mother

My Father

My Husband

Brothers

Sister

Brother‘s Wife

My Kids Asmaa, Mohammed Noor

With all the love and appreciation.

UtÇ   

Acknowledgment

Praise is to Almighty Allah for helping me to finish this work.

I would like to acknowledge and express my gratitude for all the

people who helped me during my course of study. I would like to express

my deepest appreciation to my advisor, Prof. Dr. Balkees Mohammed Al-

Dabbagh, for her invaluable supervision, mentorship, and support, which

were instrumental in completing this research.

I would like to express my gratitude and thanks to the staff of the

Library of College of Applied Science, and to the staff of the Central

Library at the University of Technology for their help and patience.

I would also like to extend my special thanks to my husband, and to

my family (my father, sister, brothers and my brother’s wife) for their help

to overcome the distresses and difficulties I passed through.

Sincere thanks and gratitude to my dearest friend Sanaa for her

support and help.

 

 

Abstract This work has been done with use of Epoxy and Novolac resins mixed

with either polyurthane (PUR) or polysulphide (PSR) rubbers to compose ternary polymer blends.

These polymeric blends are the matrix, which is reinforced with (TiO2) powder type with volume fraction of (10%).

Ten polymeric blends were prepared from (Epoxy + Novolac) resins and either polyurthane or polysulphide with ratios:

1. (90% EP/5% Novolac/ 5% (PUR or PSR)). 2. (80% EP/10% Novolac/ 10% (PUR or PSR)). 3. (70% EP/15% Novolac/ 15% (PUR or PSR)). 4. (60% EP/20% Novolac/ 20% (PUR or PSR)). 5. (50% EP/25% Novolac/ 25% (PUR or PSR)). The optimum mixing ratios (OMR) of those blends have been selected

depending on achieving acceptable macro miscibility, best adhesion between three phases, and highest impact (I.S) of the best resulting blends.

Four blends with (OMR) were prepared: 1. (70% EP/15% Novolac/ 15% PUR). 2. (60% EP/20% Novolac/ 20% PUR). 3. (60% EP/20% Novolac/ 20% PSR). 4. (50% EP/25% Novolac/ 25% PSR). These blends were tested by wear instrument, then the blends that

gave the lowest wear rate were chosen [(70% EP/15% Novolac/ 15% PUR) and (60% EP/20% Novolac/ 20% PSR)].

Several mechanical and physical tests are carried out on these samples, and these are: impact, compression, tensile, hardness, wear and diffusion. We are focus in this study on wear test.

These tests are carried out on samples under the influence of normal conditions (room temperature) and after immersion of blends samples in the chemical solutions (H2O, H2SO4 and KOH) for 15, 30 and 45 days. The normality for these chemical solutions is (0.2).

-I-  

Abstract  

-II-  

Results show that samples of blends reinforced with (TiO2) powder possess better mechanical properties of impact strength, tensile strength, compression strength, hardness and wear resistance.

After immersion, the blend samples in chemical solution, the compression strength, hardness and wear resistance decrease. The properties of blend that contain polyurthane rubber were affected more. The tests results are affected by all the chemical solutions, but the alkaline solution KOH is the most effective solution.

For wear test, results show that wear rate increases with increasing applied load, and increases or decreases with sliding velocity (depending on if it is high or low respectively). The wear rate also increases with increasing the time of immersion in chemical solutions, especially in acidic solution H2SO4.

The results of diffusion coefficient show that blend (60% EP/20% Novolac/ 20% PSR) has lower value than blend [(70% EP/15% Novolac/ 15% PUR), in all chemical solutions.

List of Abbreviations

Abbreviation Meaning EP Epoxy resin PUR Polyurethane Rubber PSR Polysulphide Rubber HMTA Hexamthylene Tetramine MPDA Metaphenylene Diamine NG Nucleation and Growth SD Spinodal Decomposition OMR Optimum Mixing Ratio X Flory – Huggin Factor N Normality HDT Heat Distortion Temperature IPN Interpenetrating Polymer Network UCST Upper Critical Solution Temperature LCST Lower Critical Solution Temperature T Glass Transition Temperature DSC Differential Scanning Caloimetry SEM Scanning Electron Microscopy I.S Impact Strength UTS Ultimate Tensile Strength UCS Ultimate Compressive Strength ASTM American Society for Testing Materials

-III-

List of Symbols

Symbol Meaning

A Area a Interfacial Thickness ΔGm Gibbs Free Energy for Blend ΔHm enthalpy ΔSm Entropy T Temperature Φf Filler Volume Fraction ψf Filler Weight Fraction ρ Density R Gas Constant W Total Load τ Shear Stress σ Tensile Strength ΔL Elongation ε Failure Strain D Diffusion Coefficient r Radius F Force d Thickness WR Wear Rate Uc Fracture energy M∞ Maximum Weight Gain% t Time KL Linear Wear Rate KV Volumetric Wear Rate KE Energetic Wear Rate Ar Total Real Area of Contact P Permeability S Solubility SD Sliding Distance V Sliding Velocity

-IV-

   

Introduction and Literature Review

 

Chapter One

Introduction and Literature Review

1.1 Introduction:

The subject of polymer blends has been one of the primary areas in polymer science and technology over the past several decades.

As new areas of interest develop in polymer science, polymer blends technology often becomes an important segment(1).

Polymer blends offer versatile industrial applications through property enhancement and economic benefits. The blending of two or more polymers of similar or dissimilar natures has been practiced for many years(2).

Polymer blends are defined as any combination of two or more polymers resulting from common processing step(3). These blends are used to improve some thermal, physical and mainly mechanical properties of polymer(4). The use of polymer blends and alloys has grown so fast compared with other polymeric materials system mainly because of their low cost and their acceptable performance(5).

Polymer blends and alloys have received a great interest due to their essential specifications which are demanded in many applications. These specifications are formulated by contribution of the properties of each component that forms the blend(6). In general, blends are made by mixing of homo polymers or copolymers which have different chemical structures. The blends may be named as binary, ternary, quaternary depending on the number of polymeric components, which comprise them(7).

There are many reasons why polymer blending is one of the most important areas in polymer research and development. Among these reasons, the most important is, perhaps, that polymer blends offer a fast and cheap way to obtain new polymeric materials. These materials generally exhibit a range of properties which varies between the properties of their components. Moreover, their properties may be complementary and

-1-  

 

Chapter One Introduction and Literature Review

difficult to be found together in the cast of a single component. Blends can be classified according to their homogeneity state as follows(7), (8):

1. Miscible Polymer Blend (Homogeneous Polymer Blend): A polymer blend may exhibit miscibility which means the capability

of its mixture to form a single phase over certain ranges of temperature, pressure and composition. A miscible system can be thermodynamically stable or metastable. Mixtures exhibiting metastable miscibility may remain unchanged or they may undergo phase separation, usually by nucleation or spinodal decomposition. Wherthere the single phase exists or not, depends on the chemical structure, molar mass distribution, and molecular architecture of the components present(7).

2. Homologous Polymer Blends: A mixture of two or more fractions of the same polymer each of

which has a different molar-mass distribution (usually narrow molecular weight distribution fractions of the same polymer)(8).

3. Isomorphic Polymer Blend: A polymer of two or more different semi-crystalline polymers that are

immiscible in the crystalline state as well as in the molten state. Such a blend exhibits a single, composition-dependent glass-transition temperature, (Tg), and a single, composition-dependent melting point, Tm(7).

4. Immiscible Polymer Blend (Heterogeneous Polymer Blend): A polymer blend may exhibit immiscibility, which means the inability

of its mixture to form a single phase. Immiscibility of a polymer blend may be limited to certain ranges of temperature, pressure and composition. It normally depends on the chemical structures, molar mass distributions and molecular architectures of the components(7), (8).

5. Compatible Polymer Blend: A compatible polymer blend is an immiscible polymer mixture, but it exhibits macroscopically uniform physical properties. The compatibilization process is the process of modifying the interfacial properties in an immiscible polymer blend which results in the formation of the interphases and stabilization of the morphology that leads to the creation of a polymer alloy. This process is normally done by adding a polymer (or copolymer), which is called compatiblizer. When this

-2-  

Chapter One Introduction and Literature Review

compatibilizer is mixed with an immiscible polymer blend, it modifies the blend interfacial character and usually stabilizes its morphology. Compatibility is often established by the observation of mechanical integrity under the intended applied conditions(7), (8).

Polymer blends can also be classified according to their crosslinking structure.

1. Interpenetrating Polymer Networks (IPNs): This polymer comprises two (or more) polymer networks, which are

at least partially interlaced on a molecular scale, but not covalently bonded to each other and cannot be separated unless chemical bonds are broken.

2. Semi-Interpenetrating Polymer Networks (SIPNs): This polymer comprises one (or more) polymer network and one or

more linear or branched polymer(s) characterized by the penetration on a molecular scale of at least one of the networks by at least some of the linear or branched chains.

There is some other well-known polymer mixture, called polymer alloy. This mixture is a macroscopically homogeneous polymeric material that is comprised of a compatible polymer blend, a miscible polymer blend or a multiphase copolymer(8).

The largest application of polymer blends in term of volume without doubt is in the vehicle sector, electrical industry, building industry, sport, leisure sector, aircraft and air space(9). 1.2 Literature Review:

Multicomponent polymer systems such as polymer blends or polymer alloys have recently attracted considerable interest as a new and important challenge for researchers. The ultimate goal of using multi component polymer systems is to achieve commercially viable products through either unique properties or low cost(10).

Polymer blends and alloys are gaining importance in that they provide many useful properties, which are the result of a combination of properties of the individual components. Blends can have higher performance characteristics at reasonable prices and blends provide the means for the reuse of plastic scrap(11).

-3-  

Chapter One Introduction and Literature Review

The history of polymer blends in polymers and rubber industry is long. There are many instances at the present time in the rubber industry where two or three or more types of polymers are blended together instead of the use of a single polymer(12).

Kwei et al.(13) reported in (1977) the first systematic study of ternary blends. In their study, polyvinylidenefluoride was added to the immiscible pair polymethylmethacrylate (PMMA) / polyethylmethacrylate (PEMA) and was found to be miscible.

Wang et al.(14) have reported in (1981) ternary blend system of poly (vinylidene chloride-co-vinyl chloride) (PVDC/VC), poly (acrylonitrile-co-butadiene) (NBR), and poly (vinyl chloride) (PVC), where (PVC) acts as a common solvent for an incompatible blend of (PVCDC/VC) and (NBR).

Sunity et al.(15) studied in (1982) the curing of carboxylated nitrile rubber (XIVBR) with epoxy resin in presence of different fillers. It was observed that (7.5) phr of resin gives a compromise combination of properties. Further studies at different loading of carbon black, reinforcing silica and clay were done at (7.5) phr of resin. Silica and carbon black give a similar type of reinforcement but clay shows non reinforcing characteristics.

Feldman(16) studied in (1983) poly blend made of polyurethane (PU) and acrylic terpolymer (AT). DSC data indicate good miscibility of (PU) with (AT).This poly blend shows a higher strain than that of (PU) and a lower tensile strength. At a (2:1) (PU to AT), the resistance of this poly blend to thermal cycling exposure is better than that of (PU).

Kostanski et al.(17) investigated in (1985) the mechanism of the effect of the elastomer additives on the properties of the thermosetting resins and composites. They showed that the improvement in fracture toughness of the thermosetting resins depends on three factors:

a. The miscibility of the rubber with the modified resin in the liquid phase.

b. The particle size of the rubber. c. The selectivity and reactivity of the functional groups in the

rubber.

-4-  

Chapter One Introduction and Literature Review

The fracture mechanism of a composite depends on the size of dispersed rubber particles (factor b) which in turn depends on factors (a) and (c).

Georgius et al.(18) studied the synthesis of new IPN`s derived from novolac and epoxy, by variation of novlac percentages from (5-30)%. The curing reactions which takes place during IPN`s formation were investigated by DSC techniques, several curing parameters were determined, such as curing energy rate of curing, curing temperature; the obtained results showed that the optimum curing temperature decreases with increasing novolac constituents of the IPN`s.

Dickens et al.(19) studied in (1986) the influence of speed on the friction and wear of polyphenyleneoxide (PPO), polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE) in two sliding configurations under both dry and lubricated conditions. They found that lubricated wear for (PPO) and (PEEK) decreases monotonically with increasing speed whilst unlubricated wear remains almost constant until around (1m/s) when it begins to increase. The dry friction and wear behavior of (PTFE) is rather different. The wear rate increases only at relatively low speeds and then becomes almost constant.

Eiss et al.(20) modified in (1986) an epoxy material by chemically incorporating siloxane to improve fracture toughness. They studied the friction and wear properties, and they compared them in two test configurations, a steel ball sliding on a cast epoxy surface and an epoxy pin sliding on a glass or a steel disk. They found that the effect of the siloxane modifier is more pronounced in the steel-ball-on-epoxy-disk configuration in which the wear rate is very sensitive to the size and spacing of the elastomeric domains which segregate during curing. The wear on the steel disk was initially very high and gradually reduced to a steady state value. Both the initial and the steady state wear rates for the modified epoxies varied inversely with the fracture toughness and elastic modulus.

Lhyman et al.(21) studied in (1987) the specific wear rate for a polyethyleneterephthalate (PET) matrix reinforced with short glass fibers. They showed that there are two regions in the wear vs. sliding velocity data: the low velocity region and the high velocity region. They noticed that wear debris of the PET-glass fiber composite under a

-5-  

Chapter One Introduction and Literature Review

low sliding velocity is of round shape but under a high sliding velocity the debris has a long cylindrical shape. The microstructure of the PET-composite was examined by scanning electron microscopy (SEM).

Chiang et al.(22) studied in (1988) the mechanical and physical properties of the blends of copolymer-type polyactals (POM) with polyurethane (PU). This investigation was established by studying the morphology and compatibility of these blends. They found that less than 50% of (PU) in the continuous phase of (POM) will be distributed homogenously and acts as an energy absorber to improve impact strength of the blend.

Zheng et al.(23) prepared in (1989) binary and ternary blends (NBR/PVC,BR/PVC and BR/PVC/NBR). They were able to obtain a new type of material by adding (BR) as the principal component with (PVC) and (NBR). The ternary blend elastomer was found to have excellent mechanical strength, aging resistance, low temperature flexibility and flame resistance.

Henry et al.(10) developed in (1990) a new method of using Rayleigh-Brillouin laser light scattering experiments for constructing phase diagrams consisting of the binodal and spinodal curves. They used the Brillouin spectra to study cure kinetics of thermosetting materials. They studied by this new method the miscibility of an epoxy/carboxyl-terminated butadiene acrylonitrile copolymer (CTBN) rubber system. They found that this system has an upper consolute temperature. An increase in the acrylonitrile content of the CTBN rubber improves the miscibility and depresses the consolute temperature of this polymer system. Also they found that particle size of the rubber reinforcement in epoxies is affected by the mechanisms of phase separation.

Won et al.(24) investigated in (1991) the phase behavior of ternary polymer blends of poly (styrene-co-acrylic acid) (SAA), poly (ethylene oxide) (PEO), and poly (methyl methacrylate) (PMMA) as a function of the acrylic acid content in (SAA). The immiscible region was decreased as the acrylic acid content in (SAA) increased. They evaluated the thermodynamic interaction energy densities of all pairs between segmental units in the ternary blends by combining melting point depression and more extended binary interaction model.

-6-  

Chapter One Introduction and Literature Review

Hosseini et al.(25) presented in (1992) an investigation into the wear process of five polymers (PP, PTFE, HDPE, Nylon6.6, PEEK) tested under different contact conditions. Polymer pin on metal plate (EN24 steel) and metal pin on polymer plate configurations were used. The metal pin on polymer plate configurations gave significantly lower wear rates compared to those observed for the polymer pin on metal plate configuration. Wear tests were combined with the microscope examination of the wear debris. A scanning electron microscope was used.

Tzong et al.(26) used in (1993) dispersed acrylate rubbers to improve the toughness of cresol-formaldehyde novolac epoxy resin cured with phenolic novolac resin for electronic encapsulation application. They investigated the effect of the alkyl group of the acrylate monomer on the phase separation of resultant elastomers from epoxy resin. The dispersed acrylate rubbers effectively improved the toughness of cured epoxy resins by reducing the coefficient of thermal expansion and flexural modulus, while the glass transition temperature (Tg) was hardly depressed.

Kukureka et al.(27) investigated in (1995) the wear mechanisms of acetal (polyoxymethylene or POM) gears by testing acetal against acetal in non-conformal, unlubricated, rolling-sliding contact over a range of slip ratios. They performed tests both on discs and on gears and they compared the results. They designed a wear and friction testing machine that allows acceptable contact stresses for polymers and composites to be combined with wide range of slip ratios under well-controlled conditions. They established wear modes based on both the order of magnitude of the wear rate and on SEM observation.

Ying et al.(28) prepared in (1996) the epoxy / polyurethane semi-IPN and the glass transition behavior of semi-IPN was discussed with DSC method. The results show that the two glass transition temperatures (Tg) related to epoxy resin and polyurethane respectively get closer. Between the two (Tg) there exist another (Tg) related to interface between two polymers.

Bicakci et al.(29) investigated in (1998) the phase behavior of binary and ternary blends of polyethylene naphthalate (PEN), polyetherimide (PEI), and polyetheretherketone (PEEK) with differential scanning

-7-  

Chapter One Introduction and Literature Review

calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) techniques. The PEN/PEI and PEI/PEEK binary blends exhibited single glass-transition temperatures (Tg`s) over the full composition range, and PEN and PEEK were immiscible, particularly at the middle concentrations. When PEI was added to the immiscible PEN/PEEK system, the blend formed two separated PEN-rich and PEEK-rich phases below a PEI concentration of about 40%; above this concentration, the three homopolymers formed a miscible phase in the amorphous state exhibiting a single (Tg).

Blanchet et al.(30) developed in (1998) a simulation to model the transient wear of particle- filled polymer composites as a function of sliding distance. All inputs are parameters of physical significance, including filler bulk volume fraction, specific wear rate (relative to that of the matrix), and contact pressure. Run-in wear behavior is simulated by consideration of the accumulation of wear-resistant filler particles and the formation of a volume fraction profile near the composite sliding surface. Simulation outputs included time-dependent volume fraction profile, composite wear rate and wear volume.

Denac et al.(31) showed in (1999) that modification of polymer matrix with filled and elastomers significantly affects composite`s mechanical properties. Isotactic polypropylene (PP) modified with either untreated or treated talc and either poly (styrene-b-ethylene-co-butylene-b-styrene) (SEBS) or poly (styrene-b-ethylene-co-butylene-b-styrene) grafted maleic anhydrid (SEB-gMA) were used. They characteriesed the composites by measuring mechanical properties (Young`s modulus, yield stress, notch impact strength) and by defining morphology. They investigated binary systems (PP/talc) and (PP/elastmer), as well as ternary (PP/talc/elastomer) composites. They found out, that the use of treated modifiers (talc or elastomers) improves adhesion with matrix, which reflects on mechanical properties as better stress transfer.

Hashmi et al.(32) studied in (2001) a wear resistant polymer, ultra high weight polyethylene (UHMWPE) which was melt blended with isotactic polypropylene (PP) in different proportions. Sliding wear tests were conducted by using Cameron Plint pin-on-disc apparatus. Polymer samples in the form of pin were tested against (EN-24) steel disc at different pressures and sliding speeds. The wear volume of (PP)

-8-  

Chapter One Introduction and Literature Review

reduces significantly on the addition of (UHMWPE). Wear loss of 15%wt (UHMWPE) filled (PP) blend was significantly low as compared to PP. Reduction in wear loss of (UHMWPE) filled (PP) blend has been attributed to the reduction in temperature of contact surface.

Najlaa(33) prepared in (2002) two binary blends, polysulphide rubber (PSR) and epoxy resin (ER), polysulphide rubber and unsaturated polyester resin (UPS), for the weight ratios (0-100)%. DSC and microscope testing were done to evaluate mechanical properties (tension, impact, bending, flexural strength, hardness, creep and thermal conductivity). It was found that all binary blends have one value of (Tg). Also samples of composite material were prepared by using one value of volume fraction from fiber glass reinforcement material, and it was found that the mechanical properties of composites whose matrix is blended are larger than the properties of the composites whose matrix is single polymer.

Abdul Kader et al.(34) derived in (2002) novel thermoplastic elastomers from binary and ternary blends of polyfunctionalacrylates, acrylic rubber (ACM) and fluorocarbon rubber (FKM) which were analyzed by using Transmission Electron Microscopy (TEM), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA) and mechanical tests. They found that acrylic rubber (ACM) containing epoxy cure site monomer is miscible with FKM at all blend ratios leading to a synergistic effect in mechanical properties of the gum and filled blends.

Abdul Kader et al.(2) studied in (2003) the effect of fillers on the mechanical, dynamic mechanical, and aging properties of rubber-plastic binary and ternary blends derived from acrylic rubber, fluorocarbon rubber, and multifunctional acrylates. The addition of fillers, such as carbon black and silica, changed the nature of the stress-deformation behavior with a higher stress level for given strain. The tensile and tear strengths increased with the addition of fillers and with loading, but the elongation at break decreased, and the tension set remained unaffected. The aging properties of carbon black-filled blends were better. The swelling resistance of the binary and the ternary blends in methyl ethyl ketone increased with incorporation of fillers.

-9-  

Chapter One Introduction and Literature Review

Abdel Bary et al.(35) designed in (2004) a new reciprocating testing machine, constructed to perform wear tests under constant and fluctuating loading conditions at constant sliding speed for most of its stroke. The wear tests can be conducted under dry or wet conditions. They investigated the influence of loading mode on the wear behavior of (Nylon 66) sliding against stainless steel in dry conditions, and tested the polymer under constant and fluctuating loading conditions at two different loads and at three frequencies. Under cyclic loading condition, the polymer shows a significant increase in wear factor than those found under constant loads.

Haddadi et al.(36) studied in (2005) the wear properties of low modulus polymer-based friction materials. The wear equation was used to correlate the wear of polymer-based friction material sliding against cast iron with the wear coefficient (K), load (P), speed (V), and time (t). The results of wear experiments showed that the polymer composite friction materials exhibit higher wear resistance compared with the cast iron friction materials.

Hsu(37) prepared in (2005) a ternary blend consisting of atactic polymethylmethacrylate (aPMMA), polyvinylpyrrlidone (PVP) and polystyrene-co-vinylphenol (MPS) with a certain concentration of vinylphenol groups which are known to be miscible with both (aPMMA) and (PVP), and this blend was measured calorimetrically. According to experimental results, increasing the vinylphenol contents of (MPS) has an adverse effect on the miscibility of the ternary blends.

Awham(38) studied in (2006) the hybridization of the resin matrix with different elastomers to prepare binary polymer blends. These blends have been synthesized by mixing either of (NBR, SBR, BR) with (EP or UP). Then reinforcement of polymer blends with 30% of two types of fibers (E-glass) alone and utilizing a hybrid of (E-glass fibers) with (Kevlar fibers). She studied the behavior of these blends and their composites under different stresses, some mechanical and physical tests carried out. The impact strength of these blends has increased several times compared with that of (EP and UP). The hybrid composites have showed higher (impact, tensile, young`s modulus, flexural) strengths but lower hardness and compressive strengths.

-10-  

Chapter One Introduction and Literature Review

Nida(39) prepared in (2006) binary and ternary polymer blends from (Epoxy, unsaturated polyester resins and polysulphide rubber) with (0-100)% ratios. Mechanical and phsical properties of these blends were studied. A microscopic test was used to study the fracture surface and to find out the change between the resins and blends and their homogeneity. Samples of composite materials, unified weight fraction of 40% of short carbon fibers with different matrix materials (binary and ternary blends) have been prepared. The composite materials, based on polymeric blends matrices, have improvements in the impact strength as well as in the thermal conductivity.

Suresha et al.(40) investigated in (2006) the influence of two inorganic fillers, silicon carbide particles (SiC) and graphite, on the wear of the glass fabric reinforced epoxy composites under dry sliding conditions. For increased load and sliding velocity situations, higher wear loss was recorded, some of these observations are supplemented by scanning electron microscopy (SEM) investigations. It was observed that the Graphite filled (G-E) composite shows lower coefficient of friction than the other two composites irrespective of variation in the load / sliding velocities. (SiC) filled (G-E) composite exhibited the maximum wear resistance.

Zhaobin et al.(41) prepared in (2006) the (PA66/PPS) blend reinforced with different content of glass fiber (GF). They studied the mechanical properties of (PA66/PPS/GF) composites, and they tested the tribological behaviors on block-on-ring sliding wear tester. The result showed that (20-30)% volume (GF) greatly increases the mechanical properties of (PA66/PPS) blend. The wear volume of the GF-reinforced (PA66/PPS) blend composite decreases with the increase of (GF) content. They examined the worn surface and the transfer film on the counter face by scanning electron microscopy (SEM).

Zhaobin et al.(42) studied in (2007) the mechanical and tribological properties of carbon fiber (CF) reinforced polyamide 66 (PA66)/polyphenylenesulfide (PPS) blend composite. They found that (CF) reinforcement greatly increases the mechanical properties of (PA66/PPS) blend. The friction coefficient of the sample decreases with the increase of (CF) content. When (CF) content is lower (below 30%) the wear resistance is deteriorated by the addition of (CF). The

-11-  

Chapter One Introduction and Literature Review

Chand et al.(43) prepared in (2007) a blend (polypropylene and polyethylene terphthalate) (PP/PET), with and without maleic anhydride (MAH), by using a melt and mixing method. They determined the abrasive wear loss in (PP/PET) blends having (5, 10, 20 and 50)% weight of (PET), with and without (MAH). They found that the addition of (MAH) reduced the density and impact strength and increased the tensile strength of blends. Wear rate of (PP/PET) blend decreased at loads (3, 5, 7) N when adding (MAH) compared to pure (PP/PET) blend.

Huda(44) prepared in (2008) binary and ternary polymer blends using thermo setting resins (Epoxy, Unsaturated polyester and Novolac). She studied wear resistance including change (load, sliding velocity, disc`s test) and she studied mechanical behavior of these blends (Compression strength and hardness) before and after immersing in (NaOH, HCl) solutions with (0.5N). Diffusion coefficient was calculated for these blends in (NaOH, HCl, NaCl, H2O). The wear resistance was increased in binary blends compared with the ternary, and also increased with load applied and immersion time.

Mofidi et al.(45) studied in (2008) the influence of aging the nitrile rubber, in various base fluids on sliding friction and abrasive wear. The lubricants used are synthetic esters, natural esters, different types of mineral base oils, poly-α-olefins and very high viscosity index oils. Friction has been studied for two directions of motion with respect to lay on the elastomer sample. The abrasive wear studies were carried out by using a two-body abrasive wear tester against dry and lubricated elastomer. They noted that two-body abrasive wear of elastomeric material was higher during rubbing in presence of the fluids as compared to that in dry condition. Further, aging of elastomer in these base fluids especially in ester base fluids, results in more abrasive wear.

Ravi et al.(46) studied in (2009) an experiment on two-body abrasive wear behavior of nano-clay filled (LDPE/EVA) composites with and without compatibilizer. Two-body abrasive wear studies were carried out using a Pin-on-Disc machine under multi-pass condition against the waterproof silicon carbide (SiC) abrasive papers in dry conditions. The

-12-  

Chapter One Introduction and Literature Review

-13-  

effect of grit size, load and different abrading distance on the abrasive wear behavior was reported. The results indicate that the nano-clay filled (LDPE/EVA) with compatibilizer composite exhibits superior abrasion resistance. The worn surfaces of the sample were examined by scanning electron microscopy.

Suresha et al.(47) studied in (2009) particulate filled epoxy composites for the three-body abrasive wear behavior using the rubber wheel abrasion test (RWAT) apparatus. The epoxy composites were fabricated with (0-20)% weight of the boron carbide. Angular silica sand particles of size in range (200-250 µm) were used as dry and loose abrasives. The wear volume and wear rate were determined as function of abrading distance. It was observed that inclusion of boron carbide filler in particulate form into epoxy matrix showed improved abrasion resistance. Scanning electron microscopy was used to study the worn surface features.

1.3 The Aim of Study

The aim of this research is to modify the properties of thermoset resin materials (Epoxy, Novolac) to reduce their brittleness by mixing them with elastomers (polysulphide, polyurethane) different ratios (to create ternary polymer blend), and to study their behavior (Mechanical and Physical), focusing on toughness property (especially measured the wear property), then reinforcing the best ratio with TiO2 powder to achieve the best mechanical properties.

   

Theoretical Part

 

Chapter Two Theoretical Part

2.1 Introduction:

Polymer blending is a fascinating method for polymer modification because it has simple processing and unfolds unlimited possibilities of producing materials with variable properties(41).

Polymer can be blended with other polymers or with some other materials. The physical properties of the resulting blends would depend directly on several factors, namely the properties and the percentages of the original components, degree of compatibility and dispersion, the nature of the interaction between the mixed materials and on the industrial processes that are utilized to produce those polymers. The polymer matrix could be thermoplastic or thermoset or elastomer which might be mixed with gases or liquids or solid substances. But if the matrices are mixed with some other polymers, a wide range of new structures would be produced(48).

In recent years, polymer is extensively utilized in sliding component such as gears and cams because of their self-lubrication properties, lower friction coefficient, and higher wear resistance(42).

This chapter is pertained to review the most important technical terms related to polymer science and summarizes the basic concepts of blends and polymer networks.

2.2 Polymers: Polymers, in general are very high molecular mass substances. A

polymer is formed through the combinations of numerous smaller units (monomer) by appropriate chemical reactions. Polymers, have different structures. The term (linear) is used for polymers in which the carbon atoms are joined together as a continuous sequence in a chain. The polymer structures with groups are generally known as (branched). Polymers also have cross-linked or space network structures. They are three dimensional systems(49). Simulated linear, branched and network polymer structures are shown below Fig. (2.1).

-14-  

Chapter Two Theoretical Part  

Fig. (2.1) Polymer Chains: (A) Linear, (B) Branched, (C) Cross-Linked,

Structures(50).

All polymers can be divided into two major groups based on their thermal processing behavior. Those polymers that can be heat-softened in order to process into a desired form are called (thermoplastics). Waste thermoplastics can be recovered and refabricated by application of heat or pressure(51). Thermoplastics have linear chains or branched chains for their structure(52). In comparison, (thermosets) are polymers whose individual chains are chemically linked by covalent bonds during polymerization or by subsequent chemical or thermal treatment during fabrication. Once formed, these cross linked networks resist heat softening, creep, and solvent attack, but cannot be thermally processed. Such properties make thermosets suitable materials for composites, coating, and adhesive applications(51). There is a separate application group, elastomers, are either thermoplastic or thermosetting, depending on their chemical nature(50). Elastomers are polymers that can show very large, reversible strains when

-15-  

Chapter Two Theoretical Part  

subject to stress, they have structure consisting of tangled polymer chains which are held together by occasional cross-linked bonds(52).

The term (homo polymer) is used to describe those polymers that are made up of just one monomer, other types of polymers, (copolymers), can be produced by combining two or more monomers in a single polymer chain. Fig. (2.2) shows four possible types of structure of copolymers based on two monomers(52).

Fig. (2.2) Structures of Copolymers Made Up of Two Monomers(52).

Depending upon the mode of formation, polymers are classified as: i. (Condensation polymer) which are formed by the elimination of

small molecules such as water in the reaction of poly functional, monomeric molecules or units(49).

ii. (Addition polymer) which are formed through the polymerization which requires the presence of an initiating molecule that can be used to attach a monomer molecule at the start of polymerization. The initiating species may be a radical, anion, or cation, depending on the nature of the catalyst used(49), (51).

The structure of polymers may vary between the amorphous and the crystalline order(53). If amorphous polymers are heated, there is a temperature at which they change from being a stiff, brittle, glass-like material to a rubbery material, this temperature is called the (glass transition temperature Tg)(52).

2.3 Blending and Alloying Blending and alloying of polymers represent an increasingly important

segment of the plastics industry(54). Polymer blending is one of the most common techniques employed for developing new polymeric materials.

-16-  

Chap

 

The alloychancom

becaplasblenapprpolymateinterpoly

Polyall hpolythe c

attrain schai

pter Two

propertieying two ngeably,

mpatible, anThese co

ause it is mtics than b

nds and alroach is tymer netwerials. Morwoven mymers(55).

The geneymer alloyhigh perf

ymer alloycompound

Fig. (

The abilaction betwsome polyin(56).

es of manor more

but technnd alloys ombinationmuch easiby creatinlloys is hto introdu

works by ost compatmatrix of

eral relatioy constituformance ys are depd structure

(2.3) Inter

lity of poween the pymers by

ny plasticse polymenically, bare mixturns are takier to deve

ng new onchow to mauce a comprovidingtibilizers af physica

on betweeutes a spec

engineeriendent on

e and the p

rrelations i

olymer topolymer m

reactions

-17- 

s can be ers. Theseblends arres that ar

king over aelop desirce(55). Oneake the co

mpatibilizeg a physicare block

ally insep

en blends cific sub-cing blendn the propephase sepa

in Polyme

o form allmoleculess that add

greatly me terms are mixturre fully coan increasable propee of the promponenter which cal link bcopolyme

parable bu

and alloysclass of p

ds are alloerties of earation stru

er Blend N

loys is in. This attrd reactive

modified bare often es that ampatible(5

sing share erties by mroblems ats adhere creates inetween seers and thut chemi

s is shownpolymer bloys. The each of theucture etc

Nomenclat

ncreased iraction cane sites to

Theoretical

by blendinused int

are not 55). of the ma

mixing knssociated together.

nterpenetraemicompaey producically dis

n in Fig. (lend; virtupropertie

e compon(8).

ture(8).

if there in be enha

o the poly

l Part

ng or ter -fully

arket nown with One

ating atible ce an stinct

(2.3). ually es of nents,

is an nced ymer

 

Chapter Two Theoretical Part  

Blending provides a fast and inexpensive way to develop and produce new polymeric materials as compared with development of new formulation, it usually needs a premixing before molding by any of the different molding methods available today(57).

To develop polymer alloys and blends with desirable properties, an in-depth understanding of the following topics is needed(8), (58). • Miscibility – thermodynamics and phase behavior. • Morphology–control via interfacial properties and processing

conditions. • Homogenization – interchange reactions. • Blend compatibilization – use of compatibilizers. • Rubber toughening.

Polymer blends can be made by one of several techniques, including melt mixing, solvent casting, precipitation from a solvent, or freeze-drying of a solution(59).

2.3.1 Behavior of Polymer Blends and Alloys: Polymer blends and alloys are often used synonymously; however,

thermodynamically speaking, there is a distinction between these two terms.

Polymer alloys are conditionally miscible thermodynamically. This means that the components of the alloy are homogeneous (single phase) under at least one specific set of thermodynamic conditions. Alloys as such provide the opportunity to change morphology and properties through variation in history(10).

Polymer blends, however, do not form single-phase systems under any thermodynamic condition. Their properties are largely dependent on mechanical dispersion and are usually tied to the arithmetic average of the values, at most, of the components. Polymer alloys can be synergistic polymer systems. As such, their properties can exceed a simple arithmetic averaging value (additive rule) of multi component systems(10).

In the simplest cases, the properties of polymer blends reflect a composition weighted average of the properties possessed by the components. In general, however, the property dependence on composition varies in a complex way with the particular property, the nature of the

-18-  

Chapter Two Theoretical Part  

components (glassy, rubbery, or semi-crystalline), the thermodynamic state of the blend (miscible or immiscible), and its mechanical state (whether its molecules and phases are oriented by the shaping of the material for testing). The amorphous portions of the blend components for a miscible pair form a single phase. The property dependence on composition for such systems is different from that for immiscible mixtures, where each component in the blend is present as a separate phase(60).

Polymer blend phase behavior is determined by the nature of the molecular interactions, it may also be influenced by many other factors, including molecular weight, copolymer composition, blend ratio, temperature, and pressure(59).

2.3.2 Miscible Blends Polymer blends are generally considered to be mixtures of chemically

different homopolymers or copolymers. These are mainly classified as (1) homogeneous blends, in which the components are miscible, and (2) heterogeneous blends, in which the components are immiscible(61). Miscible polymer blends recently have reached an attractive position in polymer science and technology(22).

Miscible binary blends of amorphous polymers have only one phase, morphologically the simplest case, and their properties are easily related to those of the blend components. The glass-transition temperature Tg is the primary thermal transition for these blends, and it varies monotonically with composition(58).

Properties of miscible polymer blends may be intermediate between those of the individual components (i.e., additive behavior), as is typically the case for Tg. In other cases, blend properties may exhibit either positive or negative deviation from additivity, as illustrated by Fig. (2.4). For example, both modulus and tensile strength of miscible polymer blends exhibit a small maximum at some intermediate blend composition, while impact strength and permeability will normally go through abroad minimum(51).

The mechanical properties of miscible blends that contain a crystallizable component depend, in part on the state of crystallization of this component and, hence, on the thermal history of the material(58).

-19-  

Chapter Two Theoretical Part  

Fig. (2.4) Typical Property vs. Composition Relations for Miscible Blends

of Polymers A and B(51).

Miscible blends show a single, composition- dependent glass transition, reflecting the mixed environment of the blend(8), (58).

2.3.3 Immiscible Blends An immiscible mixture of polymers shows multiple amorphous phases as determined, for example, by the presence of multiple glass-transition temperatures(58). Polymers are generally immiscible with each other unless there are specific interactions between them. However, in the absence of specific interaction, a homopolymer may be miscible with a copolymer over a certain copolymer composition range, exhibiting a “miscibility window” (7), (8). The intramolecular interaction between two different types of segments in the copolymer plays an important role in determining the miscibility behavior of a homopolymer/copolymer blend(62).

In polymer mixtures, at least one component substance of which is copolymer, the miscibility window is the range of copolymer composition that gives miscibility over a range of temperatures and pressures. • Outside the miscibility window, immiscible mixtures are formed. • The miscibility window is affected by the molecular weights of the

component substances.

-20-  

Chap

 

• TfupT

comexamthe comFig.

Fig.

Ptran

Sare forcinterusua

pter Two

The existeforce betwunits assopolymers(

The presemposition mple, in a

heat-distmponent la

(2.5)(58).

. (2.5) Pro

Poor elongsfer betweSince lowresponsibes betweerfacial adhal crack-op

ence of mween the mociating p(7). ence of mu

diagrams amorphoustortion teargely dete

operty vs. C

gation andeen the ph

w moleculle for imm

en phases hesion caupening me

miscibility wmonomer

preferentia

ultiple amdifferent

s immiscibemperaturermine th

Composit(--

d impact-shases of thar attractimiscible-pare to be

uses premechanisms

-21- 

windows units of t

ally with t

morphous t from thble binaryre (HDT)he properti

ion Profile-) Blends(5

strength prhe immisciive forcesphase beh

expectedmature failus(58).

has been the copolythe mono

phases cahose for

y mixtures) properties of the

es of Imm58).

roperties aible blends betweenhavior, low, and it isure under

attributedymer that omer units

an result inmiscible

s, the stiffnties of blend, as

miscible (-)

are related.

n the blenw attractivs believed

stress as

Theoretical

d to an aveleads to t

s of the o

n propertysystem.

fness, strenthe princ

s illustrate

) and Misc

d to poor s

d componve or adhe

that this a result o

l Part

erage those other

y vs. For

ngth, ciple ed in

cible

stress

nents esive poor f the

 

Chapter Two Theoretical Part  

2.3.4 Interpenetrating Polymer Network The term “IPN” covers a broad range of polymeric systems, varying in chemical composition and structure. The IPNs form a particular class of multi component polymeric systems, consisting of two or more separate cross linked polymers with no covalent bonds between networks(63). At least one of the polymers is synthesized and/or cross linked in the presence of the others. As such, IPNs share some of the advantages of both polymer blends and network polymers. If the two polymers in an IPN are thermodynamically immiscible, phase separation will occur as the monomer or monomers polymerize, however, the size of the dispersed phase will be smaller (10 to 100nm) than would be the case for a physically mixed blend or for a block copolymer or graft of the two components. A wide range of morphologies is possible, depending upon the volume fraction of components, the viscosity of the phases, and the relative rates of cross linking and phase separation(51). Fig. (2.6) illustrates IPN. IPNs can be formed by sequential or simultaneous cross linking of the component networks, in the latter case, the resulting IPNs are designated as SIN IPNs(54).

Fig. (2.6) The Idealized Structure of The IPN’s(64).

2.3.5 Glass Transition Temperature for Polymer Blends The glass transition behavior of solid polymer blends has long been used as a measure of component miscibility, as each glass transition observed in the blend reflects a distinct segmental relaxation environment (i.e. phase) over the size scale inherent to the segmental motions. The appearance of a single, reasonably sharp glass transition at a temperature

-22-  

Chapter Two Theoretical Part  

intermediate to the Tg`s of the pure components is indicative of molecular homogeneity, while the appearance of multiple Tg`s reflects macro phase separation or partial miscibility of the blend`s components(59).

An approximate relationship between Tg of a miscible mixture and composition is given by the simple “rule of mixtures”, which for a binary mixture is given as(51):

∑

(2.1)

Where Wi is the volume fraction and Tgi is the glass transition temperature of the ith component. For a multicomponent mixture, can write:

(2.2)

If the Tg’s of the polymers are not too different, “inverse rule of mixtures” can be used:

(2.3)

Another commonly used empirical relation is the “logarithmic rule of mixtures” given as:

(2.4)

Thermal, mechanical, electrical, and volumetric methods are available to perform glass transition measurements(59).

2.3.6 Equilibrium-Phase Behavior Whether particular polymer blends will be homogeneous or phase separated will depend upon many factors, such as the kinetics of the mixing processing temperature, and the presence of solvent or other additives; however, the primary consideration for determining miscibility of two polymers is a thermodynamic issue that is governed by the (Gibbs) free energy. The relationship between the change in Gibbs free energy due to mixing (ΔGm) and the enthalpy (∆Hm) and entropy (∆Sm) of mixing for a reversible system is given as(51)

(2.5) ∆ ∆ ∆

-23-  

Chap

 

 

volu(2.7curvrangposscurvnecerespzero

FBinanMTh

minisepathat of ea

pter Two

Three diume fracti). If ΔGm

ve I, the poge and wisibilities aves II and essary: ΔGpect to theo over the

∆,

ig.(2.7) Dnary Mixtu

nd Temperiscibility. he Free En

If ΔGmima in tharate at eqeach phas

ach polym

ifferent don of polyis positiveolymers aill coexistare those III, respec

Gm must be volume entire com

0

Dependencure on Vorature. I. T

and nergy Cur

Occur

0, but Eqhe free-enquilibriumse (i.e. the

mer.

ependenciymer) at ce over the

are totally t at equili

of partiactively. Fobe negativfraction o

mposition

ce of the Golume FracTotal Imm

Corresprve. Spinor at The P

q. (2.6) is nergy curvm into twoe disperse

-24- 

ies of ΔGconstant t

e entire coimmisciblibrium as al and totor compleve and theof componrange(51).

GIBBS Frection of Poiscibility. ponding todal Pointsoints of In

not satisfve as shoo mixed-cd and con

Gm on solemperaturmpositionle over thetwo disti

tal miscibete miscibie second nent 2 (

ee Energy olymer, II. Partial

o Points os Composinflection (

fied (i.e. town in Ficompositio

ntinuous ph

lution comre are illun range, ase completinct phasebility, as ility, two derivative2) must b

of Mixing2, at Cons

l Miscibilif Commonitions ,(X)(51).

the appeaig.(2.7), ton phaseshase) will

Theoretical

mposition ustrated in s illustratete composes. Two oillustratedcondition

e of ΔGm e greater

g, ΔGm, ofstant Pressity. III. Ton Tangent

, and

arance of lthe blend s. This ml contain s

l Part

(i.e. Fig.

ed by sition other d by s are with than

2.6

f a sure otal t to

,

local will

means some

Chap

 

any a ch

behaillustemp(UCsepaphas(binmetaabov(LC(LCthe u

satiswith

pter Two

Phase eqof three ty

hange in thIn gener

avior, incstrated byperature T

CST), of parate into ses A and

nodal) at Tastable reve the UST) locateST), (e.g.upper bino

Fig. (2

The binsfies the fh respect to

quilibriumypes of ph

he temperaral, polym

cluding upy the liquT1, which phase sepa

two phased B, are T1. The begion, whi

UCST but ed at T4, t at T5), twodal(51).

2.8) The Phand Low

nodal and following o composi

m is stronglhase behavature (or pmer blendpper and uid-liquidis below

aration is les, the cogiven byinodal sepich is bou

below ththe blend wo phases

hase Diagwer Critica

spinodalequality fition(51).

-25- 

ly affectedvior, illust

pressure) ods can elower cr

d phase dw the Uppe

located atmposition

y points lyparates thunded by he Loweris miscibl

s again co

gram for Lal Solution

l conincidfor the der

d by solutitrated in F

of the systeexhibit a ritical soldiagram ger Criticat T2, the en of the twying alon

he stable (the (spin

r Critical le at all co

oexist with

Liquid Mixn Temper

de at therivative o

ion tempeFig. (2.7), em(51). wide ran

lution temgiven in l Solutionquilibrium

wo phasesng the cur(single phnodal). At

Solutionompositioh composi

xtures withrature(65).

e critical f the Gibb

Theoretical

erature. In may resu

nge of pmperatures

Fig.(2.8)n Temperam mixtures, identifierve calledhase) fromt T3, whic

n Temperaons. Aboveition give

h The Upp

point, wbs free en

l Part

fact, ult by

phase s, as . At ature will ed as d the m the ch is ature e the

en by

per

which nergy

 

Chapter Two Theoretical Part  

∆, 0 2.7

Recently, there has been interest in blends containing three-component polymers. The phase behavior of these ternary blends is difficult to determine experimentally as well as difficult to theoretically predict and to visualize. One way of representing their phase behavior is through the use of the triangular diagrams. The experimentally determined phase diagram for ternary blends of (PMMA), poly (ethyl methacrylate) (PEMA), and poly (styrene-co-acrylonitrile) (SAN) is shown in Fig. (2.9). In this example, SAN (30wt% acrylonitrile) is compatible (miscible) with PMMA and PEMA; however, PMMA and PEMA, themselves, are immiscible. As illustrated, there is a moderately wide range of compositions (represented by the open circles lying outside the phase envelope) for which the three polymers can exist as homogeneous mixtures even though one polymer pair (PMMA/PEMA) is immiscible(51).

Fig. (2.9) Triangular Phase Diagram for Ternary Blends of

(PMMA/PEMA/SAN). Filled Circles ( ) Represent Blend Composition That are Phase-Separated as Indicated by The Detection of Multiple Tg’s.

Open Circles ( ) Represent Homogeneous Compositions(51).

2.3.7 Flory-Huggins Theory The thermodynamic treatment of the phase behavior for mixtures becomes more useful when specific models for the enthalpic and entropic

-26-  

Chapter Two Theoretical Part  

terms are used. The simplest of such model, which introduced the most important elements needed for polymer blends, is that developed by Flory and Huggins originally for the treatment of polymer solutions(58).

For binary systems that contain an ingredient i=1 or 2 (traditionally, for polymer solutions the subscript 1 indicates solvent, and 2 polymer) the Flory-Huggins, F-H, relation has been expressed in several equivalent forms:

∆

∆

;

2.8

In Eq. (2.8), R, T, V, i are respectively; the gas constant, temperature, molar volume of the system and the volume fraction of component i=1, 2. The polymer-polymer interaction parameter, , contains both the enthalpic and entropic parts.

The first two logarithmic terms give the combinatorial entropy of mixing, while the third term the enthalpy. For polymer blends Vi is large, thus the combinatorial entropy is vanishingly small-the miscibility or immiscibility of the system mainly depends on the value of the last term,

. F-H theory was extended to ternary systems comprising poly

disperse polymer(65).

2.3.8 Polymer-Polymer Adhesion Many polymer systems, such as polymer blends, composites, and laminates, include polymer/polymer interfaces, whose integrity determines their commercial viability(66). Polymer-Polymer adhesion plays a significant role in determining the ductility-related properties of immiscible blends. Better adhesion between ductile and brittle components improves ductility. The extent of local or segmental diffusion across the interface between the blend components, characterized by the interface thickness (a), as shown in Fig.(2.10) critically affects the mechanical strength of the adhesive bond. Low

-27-  

Chapter Two Theoretical Part  

segmental diffusion is the result of polymer-polymer immiscibility, or insolubility, and leads to sharp interface and poor bond strength. However, statistical thermodynamic theories predict that various degrees of inter diffusion of polymer segments occur in the interfacial layer as required to minimize the interfacial energy. These theories predict that the characteristic interfacial thickness (a) is related to the Flory-Huggins interaction parameter X for a binary immiscible mixture by

AB

a c/ XAB (2.9)

Where c and m are slightly different constants, depending on assumptions in the derivations. Eq.(2.9) clearly suggests that the interfacial thickness and strength of the adhesive bond increase as the value approaches zero(8).

Fig. (2.10) Composition Profiles at a Polymer-Polymer Interface and Interface Thickness(58)

Polymer-polymer adhesion increases substantially and blend ductility properties improve when the polymer components are miscible or partially miscible, a circumstance corresponding to negative or small positive values, respectively(58).

Eq. (2.9) sugge s tst hat the properties of immiscible mixtures would be improved if the interfacial zone could be increased or strengthened by incorporating an interfacial active block or graft copolymer compatibilizer Fig. (2.11).

-28-  

Chapter Two Theoretical Part  

Fig (2.11) (a) Ideal Configuration of a Block Copolymer at The Interface

Between Polymer Phases A and B. (b) Formation of an Inter Phase Between Phases A and B Promoted by a Compatibilizer(58).

2.4 Mechanism of Phase Separation The phase separation takes place when a single-phase system sees a change of either composition, temperature or pressure that forces it to enter either: (1) the metastable or (2) the spinodal region (Fig. (2.8)). There is a drastic difference between the phase separation mechanisms that take place for case (1) and case (2). When the system enters from the single-phase region into the metastable region, the phase separation occurs by the mechanism resembling crystallization-slow nucleation followed by growth of the phase separated domains. Thus, this process is known as the nucleation and growth, or NG. By contrast, when the system is forced to jumb from a single phase into the spinodal region of immiscibility, the phases separate spontaneously. The process starts with instantaneous segmental density fluctuation. The process is known as the spinodal decomposition, or SD(65). For SD, three stages and three mechanisms of domain growth have been identified: diffusion, liquid flow and coalescence(65). An example of the morphology developing during SD is shown in Fig. (2.12).

-29-  

Chap

 

Fig

that domdropthe t

2.4.1 solupolyThe incre of a

pter Two

. (2.12) D

The mecin the (N

mains is cops changintime(8).

1 Phase SRubber

ution of anymerizatio

presenceeasing theFig.(2.13

rubber m

Developing

chanism ofNG) regioonstant, wng with tim

Separationmodified

n elastomon precipite of thee energy re3) illustratodified ep

g of Morph

f the phason, while with only tme, in SD

n in Rubbthermos

mer in a thtates a dis second equired totes the phapoxy with

-30- 

hology in

e separatiin NG th

the size aD both the

ber Modifsets are phermosettiscrete, ran

phase ino maintain ase separaa diamine

Polymer B

on in (SDhe compoand size d composit

fied Therprepared ng resin, ndomly dintroduces a given cr

ation takine(67).

Blends Fo

D) is quite osition of distributiontion and s

mosets from a which in ispersed r

a toughrack-growng place d

Theoretical

ollowing S

different fthe separ

n of nuclesize depen

homogenthe cours

rubbery phhening efwth rate. during the

l Part

SD(8)

from rated eated nd on

neous se of hase. ffect,

cure

 

Chap

 

 

Fig w

contof ththe tentrophassepasize matrwithdesithe rwhemoldconv

pter Two

(2.13) Phwith a Diam

P=The

Initially tribution ohe systemthermosetopy of mse separaaration is pdistributiIt is kno

rix must bh the epoxred providrubber is

en a part md, phase version vs

hase Separmine ( ermoset Co

the sysof the entr

m. Howevet increasesixing. Eve

ation begipreventedon is attai

own that tbe promotxy resin); ded that tthe effect

made fromseparation

s. temperat

ration Dur ; Epoxy r

onversion

stem is ropy of mier, as cross leading entually ains to ta

d due to dined(66), (67)

the interfated throug

also, a hthe thermotively dep

m the rubbn profiles ture histor

-31- 

ing The Cresin, , Pc=Clou

heterogenixing of smss linkingto a decre

a point is ake place,iffusional ). acial adhegh a chemiigh volumoset rema

pleted fromber modifi

will be dry with po

Cure of a R ; Diamin

ud Point, P

neous dumall moletakes placease in threached (

, when trestriction

sion betwical bond

me fractionains as them the mated thermodevelopedosition in t

Rubber Mone,

Pgel=Gel P

ue to thecules to thce the mo

he absolut(Pc=cloudthe matrins and the

ween the r(i.e. end-n of dispee continuotrix. On thoset is curd due to cthe specim

Theoretical

odified Ep; Rubbe

oint(67).

he signifihe free en

olar volume value o

d point) wx gels pe final par

rubber andcapped ruersed phaous phasehe other hred in a hechanges inmen(67).

l Part

poxy er)

ficant nergy me of f the

where phase rticle

d the ubber ase is e and hand, eated n the

Chapter Two Theoretical Part  

2.4.2 Blend Morphology The morphology is usually a matrix containing spheres of the minor phase whose size is determined by the number of particles nucleated. Because of the incompatible nature of most polymer mixtures, a two-phase morphology is typically formed in binary blend. Rheological properties of such two-phase systems depend on the viscosities and elasticities of each component, composition ratio and temperature(48). Most polymer blends obtained by mixing melted components form heterogeneous systems with an emulsion type structure. The component with the lower volume fraction takes the form of particles dispersed in the medium of the second component. The dimensions of the particles of the dispersed component determine the degree of dispersion of the blend, thus determining many of the physical properties of this type of material in both the molten and solid states(68). The morphology of polymer blends depends on the arrangement of the phases, whether continuous or discontinuous, and the degree of order in the phases, namely, crystalline or amorphous(22). Although many miscible polymer pairs have been identified, most combinations of polymers are immiscible. In many instances, phase separated blends are preferred for achieving useful results. The spatial arrangement or morphology of the phases may consist of one phase dispersed as simple spheres in a matrix of the other polymer, as shown in Fig. (2.14). On the other hand, the dispersed phase may take the form of fibrils or platelets with varying aspect ratios, as shown in Fig. (2.14 c and b), respectively. Another distinct morphology consists of both phases simultaneously having a continuous character or an interpenetrating network of phases Fig. (2.15)(58).

-32-  

Chap

 

FigT

Prog

in dedepephascondor rearr

FPh

pter Two

g. (2.14) DThe Matrixgressively

The moreterminingens on thses, rheoditions, etbreak-up rangemen

Fig. (2.15)ases by Sh

Different Tx of an Im

y Extended

rphology og their endhe type oological c. and ref

caused nt driven b

) Concepthowing Th

Types of Dmmiscible Pd Into Plat

(c) by

of immiscd-use perfof mixingcharacteri

flects a dyby stres

by the tend

tual Illustrhe Two In

A

-33- 

DispersionPolymer. telets (BiaDeformat

cible polymformance. g device, istics of

ynamic balss imposedency to m

ration of annterlockingAnother(58

n of a PolyThe Spher

axial) or Fition(58).

mer blendThe deveinterfacia

f the colance betwed and

minimize s

n Interpeng Material8).

ymer (Darkrical Dropibrils (Un

ds is an imelopment oal tensionomponentsween phasphase co

surface ene

netrating Nls Separate

Theoretical

k Regionsplets (a) ariaxial) (b)

mportant faof morphon betweens, processe deformaoalescenceergy(69).

Network oed From O

l Part

s) in re ) and

actor ology n the ssing ation e or

of One

 

Chapter Two Theoretical Part  

2.5 Toughened Polymers A process of adding synthetic rubbers to rigid plastics in order to increase their fracture resistance was first used commercially in 1948. The early success of “high-impact” polystyrene (HIPS) led to the development of similar blends based on other rigid polymers, with the result that rubber-toughened grades are now available for most commercial plastics and thermosets of any significance(70). Visually, a small amount of an elastomer is incorporated as a discrete particulate second phase. The properties of such plastics are balanced; the significant improvement of the impact strength is offset by only a small reduction of modulus and tensile strength(58). The possibility of toughening epoxy resins by an elastomeric second phase was first proposed in 1968. Toughened epoxy resins are prepared in situ by quiescent bulk polymerization of epoxy in the presence of dissolved rubber. To control the rubber particle morphology and the final properties, the composition and concentration of rubber and hardener and the curing temperature must be considered. Mechanical properties of rubber-modified epoxy resins depend on the extent of rubber-phase separation and on the morphological features of the rubber phase(58). In general, the rubber-toughened epoxy often possesses outstanding fracture properties. However, the presence of the rubbery phase may somewhat decrease the modulus and thermal stability of the material, and increase the tendency for water absorption with an accompanying loss of properties at elevated temperatures(71). Rubber-modified epoxies have been widely used as high-performance engineering materials, structural adhesives, electronic packaging materials and information storage media(10).

2.5.1 Thermosetting Resins Epoxy, unsaturated polyester, vinyle ester and phenol-formaldehyde resins cover a very broad class of chemicals with a wide range of physical and mechanical properties. In thermosetting polymers, the liquid resin is converted into a hard rigid solid by chemical cross-linking, which leads to the formation of a tightly bound three-dimensional network. The mechanical properties depend on the molecular unit making up the network and on the length and density of the cross-link(72).

-34-  

Chapter Two Theoretical Part  

Curing can be achieved at room temperature, but it is usual to use a cure schedule to achieve optimum cross-linking and hence optimum properties. A relatively high-temperature final post-cure treatment is often given to minimize any further cure and change in properties during service(72). In general, thermoset resins such as phenolic resin and epoxy, etc. are inherently brittle due to their high cross-link density(73). Epoxy polymers show excellent adhesion to the most common metals, glass, ceramics, concrete, and other materials(74). Phenolic resin has an irreplaceable material for selective high technology applications offering high reliability under severe circumstances. It has been widely used in thermal insulation materials, molding compounds, foundry, wood products industry, coatings, and composite materials due to its excellent ablative property, structural integrity, thermal stability and solvent resistance. There are two types of phenolic resins, i.e. novolac and resol type of resin. Novolac resin is almost unable to cross-link without curing agent, which is allowed to modify the novolac resin by melt blending with flexible thermoplastic polymers. Recently, thermoset resins have been modified with flexible elastomers and/or thermoplastic polymers to improve their brittleness(73).

2.5.2 Elastomers

Elastomers are polymers which show very large strains when subject to stress and which will return to their original dimensions when the stress is removed. They are essentially amorphous polymers, having a glass transition temperature below their service temperature. The polymer structure is that of linear-chain molecules with some cross-linking between chains. One way of classifying elastomers is in terms of the form of the polymer chains (52):

1. Only carbon in backbone of the polymer chin. e.g. natural rubber, butadiene-styrene.

2. Polymer chain with non-carbon atoms in the backbone: (a) Oxygen, e.g. polypropylene oxide, (b) Silicon, e.g. fluorosilicone,

(c) Sulphur, e.g. polysulphide. 3. Thermoplastic elastomers, these are block copolymers with

alternating hard and soft blocks, e.g. polyurethane, styrene-butadiene-styrene.

-35-  

Chapter Two Theoretical Part  

2.6 Composite Materials Composite materials are materials which are made by artificially combining two or more components. Thus, interfaces are present in a composite material and they tend to govern the properties of a composite material, in other word a composite is any material made of more than one component(75). Polymeric composites are made from polymers, or from polymers along with other kinds of materials. The polymers are of low density. They have good short-term chemical resistance but they lack thermal stability and have only moderate resistance to environmental degradation (especially that caused by the photochemical effects of sunlight). They have poor mechanical properties, but are easily fabricated and joined(75). Polymer materials have been filled with several inorganic synthetic and/or natural compounds in order to increase several properties like heat resistance, mechanical strength and impact resistance or to decrease other properties like electrical conductivity or permeability for gases like oxygen or water vapour. The resulting materials must be seen, however, as filled polymers since there is no or little interaction between the two mixed components(76). Composites are used in a wide range of applications, wherever high strength-to-weight ratios are important. Principal uses are found in the automotive, marine, and construction industries(51). In most cases, composite matrices are thermosets, the most important class of thermosets for composite use is epoxy. Although epoxy resins are inexpensive and easy to process, they are brittle and have relatively high moisture absorption, which can affect the strength of the filler-matrix interface(51).

The mechanical properties of composites are strongly influenced by the size, type, concentration, and dispersion of filler, as well as the extent of interfacial adhesion between the filler and matrix (i.e. continuous phase) and the properties of the matrix(51).

Although most calculations on composite materials are based on the volume fractions of the constituents, it is sometimes important, particularly when calculating the density of the composite, to use weight fractions. The appropriate conversion equations are(72):

-36-  

Chapter Two Theoretical Part  

2.10

2.11

Where , are the volume fractions, , are the weight fractions

tes is

erties

and the , are the densities of the filler and matrix respectively. Use of inorganic filler dispersed in polymeric composi

increasing. Filler not only reduces the cost of the composites, but also meet performance requirements, which could not have been achieved by using reinforcement and resin ingredients alone(40).

Particle filled polymer composite have become attractive because of their wide applications and low cost. Incorporating inorganic mineral fillers into plastic resin improves various physical properties of the materials such as mechanical strength, modulus of elasticity and thermal stability. In general, the mechanical properties of particulate filled polymer composites depend strongly on size, shape and distribution of filler particles in the matrix polymer and a good adhesion at the interface surface(77). For most composites, the particulate phase is harder and stiffer than the matrix. In essence, the matrix transfers some of the applied stress to the particles, which bear a fraction of the load. The degree of reinforcement or improvement of mechanical behavior depends on strong bonding at the matrix-particle interface(78).

2.7 Mechanical Prop ed to forces (loads) when they are used. Often materials are subject

Therefore, they deform (elongate, compress) or break as a function of applied load, time, temperature, and other conditions. More about these mechanical properties must be known by testing the materials. Results from the tests depend on the size and shape of material to be tested (specimen), how it is held, and the way of performing the test(79).

2.7.1 Stress-Strain Behavior Force divided by area is ctests, the relevant area (A ) is th

alled stress δ. In tension and compression o at perpendicular to the force (F)(80):

-37-  

Chap

 

For

shea

resuspecto th

Polytempthtem

is p

incre1). Dand curv

Fig.FailuFailuRub(Cur

depe

pter Two

tensile or

ar stress

The unit There is

ult of tencimens of he length L

∆

ymers exhperature a

range operatures, easing straDuctile po3). Rubb

ve (4)(51).

(2.16) Tyure (Curvure with

bbery Behrve 4)(51).

The exaends upon

compress

is a change

nsile or different L. This is

hibit a wiand rate of behavio

brittle pain (i.e. hiolymers exbery polym

ypical Strve 1). Duc

Cold Drahavior w

act nature n the chem

sive stress

10 /e in dimencompressilengths, thcalled stra

ide range f deformaor are illpolymers igh modulxhibit stremers follo

ress-Straintile Failur

awing andwith Evid

of the tmical struc

-38- 

. nsions, orive stresshe elongaain, ε(80):

of mechation. Typlustrated exhibit a

lus) up to ess-strain bw stress-s

n Curves re with Ned Orientatdence of

tensile rescture of th

r deformats. To enation is als

anical behpical stressin Fig. (

a rapid inthe point behavior rstrain beh

for Sameck Formational Har

Strain-In

sponse ofhe polyme

tion elongnable comso normali

havior des-strain cu(2.16). Ancrease iof samplerepresente

havior sim

mples Exh

ation (Currdening (Cnduced C

f a polymer, conditi

Theoretical

(2.12)

(2.13)

gation, ∆ mparison ized, this

2

epending uurves cove

At normal n stress

e failure (ced by curv

milar to tha

ibiting Brve 2), DuCurve 3), Crystalliza

meric matons of sam

l Part

)

)

as a with time

.14

upon ering

use with

curve ve (2 at of

rittle uctile

and ation

terial mple

 

Chapter Two Theoretical Part  

preparation, molecular-weight, molecular-weight distribution, crystallinity, and the extent of any cross linking or branching(51).

2.7.2 Impact Strength It is the degree of resistance of polymeric material to sudden fracture in the presence of a sharp stress concentration polymers may exhibit ductile or brittle fracture under impact loading condition, depending on the

e, strain rate and mode of loading(39). temperature, specimen siz Impact tests measure the energy expended up to failure under conditions of rapid loading. There are a number of different types of impact tests. These include the widely used Izod and Charpy tests in which a hammer like weight strikes a specimen and the energy-to-break is determined from the loss in the kinetic energy of the hamme (51)r . The impact strength is calculated from the following relation(81): . . (2.15)

Where I.S. is impact strength, U is energy of fracture, A is area of cross section.

Impact strength decreases with decreasing temperature and with increasing rate of deformation. Brittle polymers can be made to be moreim ct resistant by dispersing small (

Chapter Two Theoretical Part  

• Methods where the measurement is carried out after removal of the load (Brinell, Rock well R, S, V, L, M and P, Vickers). Here, hardnes d as the as is define pplied force divided by the area of the indent.

2.7.4 Wear Wear is a process in which material is removed from the surfaces of com (83)

sliding or rolling contact between surfaces or from the movement of fluids

articles over surface(52). It is the result of a combination of

te

ponents, or by which these surfaces are seriously disturbed . Also wear is a progressive loss of material from surface as a result of

containing pphysic-chemical processes that take place on polymer friction surface and boundary layers(84). Wear debris can be measured either as a weight loss or as a change in volume or size of one or both of the rubbing members. Research results indicate the use of both of these measures of wear, and the following three distinct wear criteria have been proposed(85):

1. Linear wear ra

(2.16)

2. Volumetric wear rate

∆

(2.17)

3. Energetic wear rate

∆ (2.18)

The linear and volumetric wear rates are leidentical, since ∆ . The energetic and linear wear rates are related

/ ( Where F is the force of friction, Kindex

n imen recorded beforee w (83)

ss dimension and also

by the Eq.(2.19): 2.19)

E is also referred to as the energy of abrasion. The mass change of the specimen is measured as the difference i

mass of the spec and after the test. For mass loss measurements, th ear rate is calculated from the relationship :

-40-  

Chapter Two Theoretical Part  

∆

2.20

where ∆W is the mass loss (gm) and SD is the sliding distance (cm). Because wear is a surface effect, surface treatments and coatings play

an important role in improving wear resistance. Lubrication can be considered to be a way of keeping surfaces apart and so reducing wear(52). Different kinds of polymer blends have been studied by some

blend

rtant factor in friction and wear

aring of the material. The degree of deformation

th mild and severe behavior,

researchers, and it is found that the friction and wear behaviors of polymer s vary continuously with compositions, the friction coefficient and

wear resistance of blends are superior to those of component polymers and reach optimum at certain compositions(42). The wear process involves a number of complex interactions, but it can be considered to be caused by the energy created by the frictional work and released during sliding within the contact zone. The mode in which the frictional energy is dissipated depend on the contact configuration, which therefore, should be considered as an impobehavior of polymers(25). Wear of polymer materials occurs as a result of the fatigue mechanism of failure. This mechanism is primarily defined by the character of the friction contact: multiple deformation of the polymer occurs during the external friction process at separate points of real contact, and leads to fracture and subsequent tedepends upon the surface geometry and properties, and also upon the sliding velocity, pressure, and temperature(84). Wear behavior is frequently characterized as being mild or severe. Mild wear is generally used to describe wear situations in which the wear rate is relatively small and the features of the wear scar are fine. Severe wear, on the other hand, is associated with higher wear rates and scars with coarser features. Most materials can exhibit bodepending on the specific of the wear system in which they are used(86). Fig.(2.17) shows mild and severe wear.

-41-  

Chap

 

 

by wwearedu2.7.4

(2.1

pter Two

In order which it oar and eauction(83). 4.1 Types

The seve8), and are

Fig. (2.

o reduct eoccurs in each one

s of Wear en main te describe

17) Mild a

e wear, it each case.requires

types of wed in more

Fig.(2.18

-42- 

and Sever

is importa. There ara differe

wear are e detail in

) Types of

re Wear Cu

ant to undre a numbent practi

shown dithe follow

f Wear(83).

urve (44).

derstand thber of diffcal appro

iagrammatwing parag

.

Theoretical

he mechanferent typeoach to w

tically in graphs(83):

l Part

nism es of wear

Fig.

Chapter Two Theoretical Part  

1. Abrasive Wear Wear is used when material is removed from a surface by contact

with hard particles, sliding resulting in the “ploughing out” of the softer ma