CHAPTER 1

I .I Polymer blends

T he progress in the area of polymer blends during the past decades has been

tremendous and is motivated by the realisation that new molecules are not

always requ~red to meet needs for new materials. Blending can usually be

tmplemented more rapidly and economically than canying out research in the

chemistry of new polymers. Polymer blends are physical mixtures of two or more

polymers without any chemical bonding between them. The objective of polymer

blending is a pract~cal one of achieving commercially viable products having either

unique properties or lower cost than some other means might provide. Property

profiles of polymer blends are superior to those of component homopolymers.

Blending technology also provides attractive opportunities for reuse and recycling

of polymer wastes. The various economic and property advantages accomplished

by blending are:

unproved modulus and hardness easy processability lower die swell improved impact and environmental stress cracking resistance lower cost light weight i decrease in density improved dimensional stability and weathering extended service range improved low temperature properties enhanced ozone resistance increased toughening ~ncreased heat distortion temperature and flame retardance.

In short, unique materials are generated through blending as far as its

processability and or performance are concerned.

Blending of polymers can be done by either mechanical or chemical

methods. Mechanical mixing of polymers includes such methods as roll milling,

melt mixing, solution blending and latex blending. In roll milling, the mixing of

polymers can be accomplished by squeezing the stock between rolls. In melt

m~xing, the polymers are mixed in the molten state. Both the aforementioned

processes introduce no impurities and require no removal of solvent. The kinetics

of mixing large polymer molecules predict that mixing will be slow and incomplete

and the degree of mixing depends very much upon temperature, shear and time. In

solution blending the two polymers are dissolved in a common solvent followed by

solvent evaporation, freeze drying or polymer co-precipitation. In latex blending, if

the two polymers are available in the latex form are mixed followed by d y n g and

or coagulation. The solution and latex blending techniques eliminate or at least

minlmise problems of incomplete mixing and chemical changes caused by heat and

shear.

Chemical blending of polymers includes copolymerisation and synthesis of

interpenetrating networks. Some of the most important commercial polyblend

systems are the incidental by-products of attempts at graft and block

copolymerisation. Interpenetrating networks are synthesised by the polymerisation

of a monomer in the presence of a crosslinked polymer. This gives rise to a

crosslinked network of the monomer completely interwoven with the first polymer.

Such precise control of polymer and blend structures offer great promise for novel

properties and applications.

1.3 Niscibilii of blends

The question of whether two polymers are miscible is of great importance

for the manifestation of superior properties. Before proceeding, clarification of the

use of the term miscibility to describe single phase polymer-polymer blends is

necessary. Prior studies and reviews have generally used the term compatible to

describe single phase behaviour. However, compatibility has been used by many

other investigators involving various studies of polymer-polymer blend behaviour

to describe good adhesion between the constituents, average of mechanical

propert~es, behaviour of two phase block and graft copolymers and ease of

blendmg. Compatibility is often used to describe whether a desired or beneficial

result occurs when two materials are combined together. After much deliberations

and discussions by many investigators involved with polymer-polymer blend

research, the term miscibility has been chosen to describe polymer-polymer blends

with behaviour slmilar to that expected of a single phase behaviour. Most of the

polymer blends are heterogeneous systems having a multiphase structure.

Compatibilisation of polymer blends leads to homogeneous, partially miscible

systems des~gnated as polymer alloys.

Generally, the formation of miscible blends has been attributed to specific

interactions between polymer molecules such as hydrogen bonding,' dipole

interaction^,^ density of interacting groups: steric e f f e~ t s ,~ flexibility in polymer

chains or complementary dissimilarity of their structure^.^

According to elementary thermodynamics, the change in free energy of a

process can be expressed as follows.

AG = AH - TAS (1.1)

For a process to be spontaneous its free energy should be negative and

satisfy the additional requirement,

wh~ch ensures stab~l~ty against phase segregation. +i is the volume fraction

Slnce two unlike molecules will have less attraction for each other than they

do for the~r own kind, the enthalpy of mixing, AH will be positive and thus

unfavourable for m~xing. When small molecules such as solvents are mixed, the

random mlxture has much more entropy than the pure ingredients, so that -TAS

overcomes the unfavourable AH, thereby making the change in free energy

negative; which favours mixing.

In mixlng large polymer molecules, on the other hand, the atoms or groups

of atoms are restricted by being tied into the polymer molecules, so that mixing is

much less random and the entropy gain is much lower; thus -TAS is generally

lnsuficient to overcome the unfavourable AH, AG remains positive and mixing is

unfavourable, making the two polymers immiscible with each other.

Small angle neutron scattering in one component amorphous polymers has

established that the polymer chain in the bulk state is essentially randomly

YU' pointed out that the homogeneity of the polymer-polymer systems, owing to its

h~gh viscosity, will depend a great deal on the methods of preparation, the time and

the temperature to which the mixture is subjected.

1.4 - Chandwisation of polymer blends

Dlrect v~sual confirmatton of the presence of two phases has been used

more often than any other method as a prel~mlnary lnd~cat~on of the degree of

rnrsc~b~l~ty in a polymer-polymer system lo Many researchers have turned to

mtcroscopy to a d In deterrnlnlng not only the presence but the connectlv~t~es of the

phases Opt~cal and electron mlcroscoples are the most w~dely used techn~ques for

charactens~ng blend morphology Although many mlsctble polymer pars have

been ident~fied, most comblnat~ons of polymers are ~mmlsc~ble The

morpholog~cal arrangement may conslst of one phase d~spersed as simple spheres

In a marnx of the other polymer On the other hand the d~spersed phase may take

the form of fibrils or platelets with varying aspect ratios. Another distinct

morphology is that in which both phases simultaneously have a continuous

character or an Interpenetrating network of phases. A schematic representation of

the vanous morphologies is shown in Figure 1.1. The typical dimensions of the

phases are Important in all these morphologies and the blend properties are greatly

~ntluenced by the morphology of a system."^" Electron microscopy has also been

successful In following the falure mechanism of polymer 14. I S

Figure 1.1. Different types of dispersion of a polymer in the matrix of an immiscible polymer The spherical droplets (a) are progressively extended into platelets (b) or fibrils (c) by deformation.

(a) Optical ~ r o s c o p y

An opt~cal microscope provides a magnified image of an object, giving

structural information with a resolution of the order of lpm, molecular information

from the btrefr~nyence observed when an optically anisotropic sample is viewed

between crossed polars and even some limited chemical information, for example,

through the observation of the colour changes that occur during degradation.16 in

add~t~on to these factors, the optical microscope is also attractive on grounds of cost

and the relative ease with which suitable samples may be produced. Taking all

these elements together, optlcal microscopy is a powerful technique, particularly for

the study of polymeric materials which transmit a reasonable proportion of the light

that is incident upon them. The available techniques in considering the optical

microscopy of polymers are transmitted light microscopy and reflected light

microscopy. In the transmission mode, when a beam of light travels through a

sample, it is modified as a result of the optical properties of the material and their

spatial vanation within the specimen. In samples where the absorption coefficient

varies from place to place this naturally leads to contrast in the final image. The

exammation of specimens in transmission necessarily requires that they be thin.

Thus, the techniques of transmission light microscopy are inappropriate for the

examination of bulk specimens. Nevertheless, examination of such samples in

reflection may provide useful structural information through the observation of

topographical features.

(b) Scanning eltxtron microscopy

Scanning electron microscopy (SEM) offers the simplest procedure to reveal

the surface features of a specimen. The optical design of SEM endows it with a

particularly useful combination of virtues. Not only is it capable of generating high

magnificat~on images, with a resolution better than 5 nm, but also, at the other

extreme of the magnification range, excellent low magnification images may be

produced even from rough samples, as a result of the instrument's inherently large

depth of field.16 In addition to their conventional back scattered and secondary

electron imaging capabilities, most modem SEM systems are also configured such

that Images may be formed from alternative signal sources. When one or more X-

ray detectors are available, the signal characteristic of a particular element can be

displayed on the imaging screen in synchronisation with the scanning electron

beam. In this way element maps may be obtained similarly, the current generated

in the sample (electron beam induced current, EBIC) or the voltage induced by the

beam (electron beam ~nduced voltage, EBIV) may be displayed so as to form an

image that is related to spatial variations in the electrical properties of the

specimen. While such techniques find many uses in the study of metals, ceramics

and semiconductors, the elemental composition and electrical properties of most

polymers mean that such approaches are only of use in connection with particular

problems (e.g. composite systems and conducting polymers).

In SEM, a fine beam of electrons is scanned across the specimen surface

and an appropriate detector collects the electrons emitted from each point. The

amplified current from the detector is then displayed on a cathode-ray tube, which

is scanned synchronously with the electron probe, producing the image. For stable

images to be formed it is essential that the charge deposited on the sample surface

by the electron beam is able to leak away to earth. Thus, for insulating materials

such as polymers, it is usually desirable to coat the specimen with a conducting film

prior to examin&on. Generally, low accelerating voltages and low beam currents

are required to avoid radiation damage. Since SEM only reveals surface features,

the internal structure of polymer blends is investigated by viewing fracture surfaces

created at ambient or cryogenic temperatures. Photomicrographs often give

information about the arrangement of one phase within the other and also the

extent of adhesion between the phases.

(c) Tra~mission electron nricroscopy

Transmission electron microscope (TEM) constitutes a very powerful

tnstrument for the structural study of suitable samples. The potential it offers is not

limited only to the formation of high resolution images, but the ability to form very

small diameter probes means that spatial variations in chemical composition or

clystal structure may also be investigated, by spectroscopic and diffraction

techniques, respectively.16 The sample should be thin enough to transmit the beam

of electrons through it. For optimum imaging, inelastic scattering and multiple

scattering should be minimised and, for this, the sample needs to be very thin

~ndeed. While the requirement for a thin sample is shared by all transmission

electron microscopists irrespective of their discipline, TEM of polymers does

present some particular problems.

Even when the sample naturally occurs in a form that is thin enough for

direct exam~nation in the TEM, problems are encountered as a direct consequence

of the way In which the samples and the electron beam interact. In comparison

with inorganic materials, polymers are highly beam sensitive. Electron irradiation

results in chem~cal changes destruction of crystallinity and mass transport. Also,

most polymeric samples, and particularly those of technological or commercial

Importance, do not naturally tend to occur in the form of a 50 nm thick film.

lyoring diffraction and dynamical scattering effects, bright-field contrast in the

TEM arises from two sources, namely variation in sample thickness from place to

place (thickness contrast) and spatial variations in atomic number, that is, electron

density (Z contrast). Most polymers, being made up predominantly of light

elements glve rise to relatively little scattering and, of more importance vary little in

electron density from place to place. Indeed the problems of sample geometry,

beam sensitivity and intrinsically low contrast described above are such that they

are often best overcome by the indirect examination of the samples.

Staining techniques are derived from similar biological sample preparation

procedures and involve two distinct steps. Generally, some suitable staining

reagent is first allowed to diffise into the sample. After an appropriate period, the

sample 1s removed from the stain and a thin section (typically 10-100 nm thick) is

cut and examined in the TEM. The image that results contzllns mass contrast that is

der~ved from the d~stribution of staining material within the sample. Thus regions

of specimen that react readily with the stain or through which the staining reagent

diffuse easily appear dark, whilst other regions appear light.

Of all the available stzllning reagents, osmium tetroxide ( 0 ~ 0 4 ) is of

particular importance, being one of the most widely used chemical for staining

polymers 'The OsOa reacts with carbon-carbon double bonds and is therefore

w~dely used as a means of enhancing contrast in unsaturated ~ ~ s t e m s . ' ~ . ' ~

Ruthenlum tetrox~de, phosphotungstic acid and chlorosulphonic acid are some

other stiunlng reagents.

(d) Atomic force mic.roscopy

The atomic force microscope (AFM) was developed by Binnig and

coworkers19." and has the potential for atomic resolution on certain samples. The

4FM can be used to Image both conductive and insulating surfaces at ambient

conditions and IS. therefore, suitable for the analysis of polymers. In addition, there

are many new types of scanning heads which can accommodate varying i m q n g

mechanisms The samples are prepared by cryosectioning without any staining and

the cut surface of the specimen block is analysed. Lateral force microscopy (LFM)

is based on the fictional resistance of the probe as it scans across the sample. The

technique of force modulation creates images that are based on variations in elastic

modulus at the surface. The potential advantages of AFM over other microscopical

methods include higher resolution, simplicity of specimen preparation and greater

versatility in varying the mechanisms for achieving image contrast.

1.4.2 Glass transition temperahrre

The most commonly used method for establishing miscibility in polymer

blends is through determination of the glass transition (T& in the blend versus

those of the unblended constituents. A miscible polymer blend will exhibit a single

glass transit~on between the T,s of the components with a sharpness of the

transit~on similar to that of the components. Borderline miscibility results in

broadening of the transition. In the case of limited miscibility, two separate

transitions between those of the constituents may result, indicating two phases rich

~n each of the components. In cases where strong specific interactions occur, the T,

.'., , . .<

may go through a maximum as a fu"&p~f composition. The limitation of glass ...,

transition determ~nations in ascertaining $;dl$ne~-~bly&er miscibility becomes

apparent wlth blends composed of components which have equal or similar glass

transitions (< 20°C difference) whereby resolution of the two glass transitions is

not possible.

The equations commonly used to express T,-composition relationships for

polymer blends are

where T, and T& represent the glass transitions of the undiluted polymer

components, W, and Wb are the weight fractions of the blend.

(ii) Gordon-Taylor equation

TB = [W.Tw + k(l-W.)T&] 1 pa + k(l-W.)] (1.4)

where k IS the ratio of the thermal expansion coefficients between the rubbery and

glassy states of the component polymers, i.e., (a~b-) I (uI .~,) .

(111) Kelley-Bueche equation

The Kelley-Bueche equation is similar to the Gordon-Taylor equation

except that the volume fraction $i is used instead of the weight fraction.

T, = [&Tw + ki 14a)Tpbl 1 + k( l+.)l (1.5)

As a l a , has been proposed to be constant for all polymers,2' k = I and the

Gordon-Taylor and Kelley-Bueche equations reduce to the Itnear form

T, = W,T,. + WbT& ( 1 6 )

T, 4aTp + bT, (1 7)

(a) @namic mechanical analysis

The elastic and viscoelastic properties of polymer derived by subjecting

polymers to small-amplitude cyclic deformation can yield important information

concerning trans~tions occurring on the molecular ~ c a l e . ' ~ Data obtained over a

broad temperature range can be used to ascertain the molecular response of a

polymer in blends with other polymers. In a highly phase separated polymer blend,

the transitional behaviour of the individual components will be unchanged.

Likewise, in a miscible blend, a single and unique transition corresponding to the

glass transition will appear. Dynamic mechanical testing can be accomplished

using vanous experimental arrangements. Free vibration dynamic mechanical

testing dev~ces include the torsion pendulum, freely vibrating reed and the torsion

braid analyser. Forced vibration techniques employ the viscoelastometer or a

forced vibrating reed.

The dynamic properties are specified by means of two basic quantities. One

of these quantities, the dynamic storage modulus (E'), provides a measure of the

effective stiffness of the material and is proportional to the peak energy stored and

received during each cycle of deformation. The other quantity known as the loss

factor or damping factor (tan a), is proportional to the ratio of net energy dissipated

per cycle as heat ( E ) to the peak energy stored (E').

1.e. tan 6 = E"E'

Generalised properties (tan 6, E') of polymer-polymer blend as a function of

temperature are illustrated in Figure 1.2 for behaviour expected of two phase

blends. In Figure 1.3, the general id behaviour expected of miscible one-phase

blends are depicted.

log tan

Figurn 12. Cknerdis.4 behaulour of the dynamic mshuucd propenies of a two- phase blend: - pure components, ---- mixture

Figurn 1-30 Gener.lis.4 behaviour of the d m c mechuucal prope*ies of a miscible blend -- pure components, ---- mixture

(b) Dielectric methodc

The elect"d propenles of polymers are analogous to mechanical

pmpen~es. The d ~ e l s h i c loss factor (E") and the dissipaion fwtor 6 ( E ~ / E ' ) , are of phmnry interest as they are commonly used to a s c e h n polymeric transitions

iuch as the glass transttion. The experimental advantage of obtaining transition

data from electrical measurements over dynamic mechanical testing is in the ease

of changlng frequency. The major disadvantage is the difftculty in determining the

transltrons of non-polar polymers. Generally non-polar polymers will require slight

mod~ficatron, such as oxidation, to provide sufficient polarity to resolve adequately

secondary loss transrtrons as well as glass transitions in blends.

The dielectric constant increases as molecular motion in a polymer

Increases. thus, large secondaq relaxations and the glass transition will yield

Increasing values An experimental example of the dielectric method for

establishing the miscibility of polymer blends is for poly(2,6-dimethyl-l,4-

phenylene oxide)/polystyrene (PPOPS) blends.12

A technique in whtch the change of dielectric loss is measured under a

definlte temperature program, termed the thermodielectric loss measurement has

been used for estimating polymer-polymer rniscibi~ity.~~ As the dielectric loss of a

sample is diss~pated in the form of heat, a differential thermal analyser has been

utilised to measure s" in this approach. This technique is claimed to be more

sensitive for measuring the degree of miscibility than other methods.

Fujrmoto and ~ o s h ~ m r ~ a ' ~ have employed drelectrrc loss along wrth

DMTA, to measure the homogenerty of NRIBR and SBR/BR blends The results

of the two methods were in good agreement and showed the greater homogenelty

of SBR/BR blends over NRBR blends They reported that nearly homogeneous

blends of SBRiBR could be obtaned In a few minutes of mtll rnlxrng while

extended mrlhng had little or no effect on lmprovlng the homogenelty of NRBR

(c) Dilatometric methods

Polymer glass transltrons have many characterist~cs similar to a second order

thermodynamrc transrtlon Wrth respect to volume change, a dlscont~nurty IS

observed in the rate of volume change with temperature in the region of the glass

transltlon. Dilatometric methods to determine polymeric glass transitions were one

of the most common techniques before mechanical methods became popular. In a

blend of two distinctly different polymers, iwo phase behaviour can be determined

by two d~scontrnuities in the derivative curve dv/dT corresponding to the T,s of the

respective phases. Dilatometric techniques are less sensitive than dynamic

rnechanlcal methods.

(d) Calorimcbic methods

In calonmetnc methods, the specific heat of polymers exhibits a change

when passing through the glass transition, generating a maximum in the value of

dCddT The most common instrument is the differential scanning calorimeter

(DSC). The DSC measures the amount of heat required to increase the sample

temperature by a value of AT over that required to heat a reference material by the

same AT Through sophisticated instrumentation, controlled rates of heating and

cooling are possible with high accuracy of heat input or output to small specimens.

This technique has successfully demonstrated polymer-polymer miscibility

for the systems ~ ~ ~ l ~ o l ~ s t y r e n e , ~ ~ nitrile rubber^^^,^^ poly(viny1 methyl

e t h e r ) ~ ~ o l ~ s t y r e n e ~ ~ and poly(viny1idene fluoride)/poly(methyl methacry~ate).~'

Uslng DSC zabrzewskiZ6 observed miscibility with PVC in all compositions at

levels of 23 to 45% acrylonitrile in the nitrile rubber, in excellent agreement with

dynamic mechanical data. He noted that the DSC results could be more clearly

illustrated by plotting the secant slope of the specific heat versus temperature, as

shown in Figure 1.4

Figure 1.4. Effect of poly(vinyl chloride) on the single glass transition of nitrile rubber (34% acrylonitrile). Data obtained on a differential scanning calorimeter [Zabrzewski, Polymer. 14, 347 (1973)J

(e) Thermo-optical ona&sis

Thermo-optical analysis (TOA) has been employed by Shultz ei to

~nvestigate the miscibility of polymer blends. This technique involves scribing

scratches onto a polymer or blend surface with a steel stylus. A polarising

nurroscope equ~pped with a hot stage capable of temperature programming is

employed. Light transmitted through the film placed between crossed polanser and

analyser is converted into volwe and plotted against temperature. The scratched

surface is birefringent and thus light is only transmitted through the scratches. As

the polymer (or constituents of the blend) passes through the glass trans~tion

temperature, the orlentation produced by scratching the film disappears and the

reduct~on ~n blrefrlngence leads to a decrease in transmitted light. Single transition

temperatures monoton~cally increasing with the content of the higher T, component

are character~stic of the rnlsclble blend whereas two transitions correspond~ng to

the blend constituents are observed for the immiscible blend. The results obtained

by t h ~ s techn~que were In good agreement with the more common techniques.

ha%hmincscence specboscopy

This unique method has been successfully utilised by Zlatkevich and

~ i k o l s k i ~ . ~ ~ Irradiation (electron or y ray) of the polymer or blend in the glassy

state results in trapped secondary electrons which are rapidly released, yielding

lum~nescence, once the sample temperature reaches the glass transition. Maximum

luminescence 1s observed at a temperature quite close to T, values. For two phase

blends, two distinct peaks can be observed in luminescence versus temperature

plots, corresponding to the respective T,s. The resolution of the T, of the minor

phase (as low as several volumes percent) is quite good, thus proving equal or

superior sensitivity to mechanical or calorimetric methods.

1.4.3 Sceitaing methods

By definition, a stable homogeneous mixture is transparent, whereas an

unstable non-homogeneous mixture is turbid unless the components of the mixture

have identical refractive indices. Given a stable homogeneous mixture, the

transition from the transparent to the turbid state can be brought about by variations

of temperature, pressure or composition of the mixture. The cloud point

corresponds to this point-the point of incipient phase separation. For polymer

mixtures, the cloud point curves are usually measured using a thin film made from

a thoroughly mixed blend. The film is observed through a microscope illuminator

for low-angle back or forward scattering relative to the incident light. The

specimen is heated at a very low rate such that the temperature increases at an

~nfinitesimally slow rate. When the first fmnt cloudiness appears, denoting the

cloud point, the temperature is recorded. A few degrees above this cloud point the

cycle is reversed; the sample is gradually cooled. This is repeated for a series of

compositions and a temperature-composition plot known as cloud point curve

(CPC) is generated. Systems studied using CPC measurements include

polystyrene/poly(vinyl methyl ether):3 mixtures of polfivinylidene fluoride) with

poly(methy1 methacrylate), polfiethyl a c r y ~ a t e ) ~ ~ and low molecular weight

mixtures of polyisobutylene and poly(dimethy1 si~oxane).~'

The classical techniques of X-ray and light scattering have been used in the

study of polymer blends. X-ray scattering is sensitive to density fluctuation. In the

light scattering technique for multicomponent systems and polydisperse polymers,

the scattenng 1s made up of two contributions due to density and concentration

fluctuations. For poly(2,6-dimethyl-1,4-phenylene oxide) in caprolactarn,

~ m o l d e r s ~ determined the spinodal locus by light scattering method. While X-ray

scattering is sensitive to density fluctuations and light scattering to density and

concentration fluctuations, neutron scattering measures the differential neutron

scattering cross section of small concentrations of protonated polymer (tagged

molecules) dispersed in a matrix of deuterated polymer. This allows a rather

precise determination of the conformation of the tagged polymer, even in bulk.

Low angle neutron scattering studies of poly(deutero a-methyl styrene)/polydeutero

styrene and or polystyrene3' and mixtures of a normal protonated poly(dimethy1

siloxane) and a series of deuterated poly(dimethy1 siloxanes) of varying chain

lengthJ%e reported.

1.44 speclroscopic techniques

Proton NMR experiments on polymers are generally confined to studying

the spin-spin and spin-lattice relaxation processes as a function of temperature and

composition. By convention, the latter is characterised by a relaxation time TI

while the sp~n-spin relaxation time is called T2. AS with mechanical measurements,

simpler results are expected with one phase than with two phase mixtures. But

NMR has an advantage over mechanical measurements in that the signal should be

independent of the shape and intercomectivity of the phases in a two phase

mixture. This allows one to decompose a multi-time relaxation process and analyse

the phases thereby. The magnitudes of TI and Tz are influenced by molecular

motions and the changes with temperature can be analysed in terms of the onset of

such motions. The resulting TI versus temperature curve looks much like inverted

mechanical loss response, while the Tz versus temperature curve is quite

reminiscent of an inverted modulus response.

Nuclear magnetic resonance, has a particular advantage in two phase

systems. Here two times are often resolvable, one for each phase. This technique

has been applied successfully to crystalline systems where Tz for the protons in the

amorphous phase is much greater than that for the protons in the crystalline phase.

The phase separation in polystyrene/poly(vinyl methyl ether)39 and the

compositional variations of poly(viny1 c h l o r i d e ) / ~ ~ t ~ e l ~ ~ have been studied using

NMR Elmqvist el showed that broad line NMR is a sensitive tool for the

detection of small amounts of a soft phase embedded in a hard matrix. The reason

1s that the resonance of protons in the soft phase is relatively sharp compared with

the resonance band of matrix protons. figh resolution NMR is possible in

polymer-polymer systems after slight swelling with a low viscosity solvent.

Deuterated solvents avoid unnecessary complication of the spectrum.

Fourier transform infrared (FTIR) spectroscopy has been used to investigate

the mechanism of specific interactions involved in blend miscibility. Much

attention has been devoted to systems that involve hydrogen-bond formation.

Simple observation of bond shifts is often used to identify the interacting chemical

groups. Many miscible blends involve polymers containing ester moieties in the

chain or part of the pendant group and significant shift in the carbonyl band are

observed in such cases. Infrared and ultraviolet spectroscopy on the well known

blend polystyrene/poly(2,6dimethyl-1,Cphenylene oxide) (PSPPO) by

Wellinghoff el provided evidence for the following conclusions: PPO is

loosely packed In the glassy state and the addition of PS reduces the free volumes,

the chains of the two components interpenetrate significantly and the reason for the

hlgh miscibility is a strong interaction between the phenyl group of the PS and the

phenylene group of the PPO.

Fluorescence spectroscopy has been proved to be useful for studying the

m~scibil~ty of polymer b~ends . '~ The essential advantage that distinguishes it from

other techniques is the high sensitivity of detecting phase s e w o n and the ability

of analys~ng phase behaviour in blends containing a component of very small

concentrations, with a relative easiness. Recently, an increased attention has been

w d to the use of fluorescence spectroscopic techniques such as non-radiative

energy transfer and excimer fluorescence.

Ultraviolet emission intensity, based on non-radiative energy transfer, has

been successful in quantifying the degree of miscibility of two polymeric

components. To employ this technique the components of the blend must contain

chromophoric structures active in the ultraviolet, or they must be modified with

appropriate groups (e.g. naphthyl, anthryl). This is a possible disadvantage because

any modification of structure can change phase relationships in the region of

modification. Two different chromophores are incorporated, one on each

polymeric component at a level of about 1%. These groups are selected so that a

radiationless transfer can occur between the two. This transfer is assumed to be

more efficient as the miscibility increases because close proximity (e.g. 4 A) of the

groups is critical to the transfer process. The measured emission reflects this

efficiency. In a study using this method, naphthyl and anthryl-tagged PMMA and

Poly(methy1 methacrylate-co-butyI methacrylate) were found to show steadily

decreasing miscibility as the butyl content of the copolymer was increased from

0 to 4 0 % . ~ ~

Excimer fluorescence is generally employed for blends in which one of the

polymers contains aromatic rings and exhibits intrinsic fluorescence. Excimer is a

complex formed by an excited molecule and a ground sate molecule of the same

species through a partial charge transfer. Fluorescence emission from excimer

complex is a broad structureless band and appears at longer wavelengths compared

to monomer fluorescence emission which results from an isolated molecule. As the

excimer formation needs specific geometrical configuration of the rings, the

concentration of the excimers is sensitively controlled by intra and intermolecular

lnteractrons of fluorescent polymer chains in the blend. The polymer miscibility is

reflected by the relatlve excimer fluorescence intensity with respect to the monomer

emlsslon. The compatib~lity of blends from poly(2-vinyl naphthalene) in a series of

poly(alky1 methacrylates) was understood by Frank er U I . ' ~ using excimer

fluorescence method

1.4.5 Wscomebic technique

An lnsrght to lnteractlons in polymers and hence to mlsc~bll~ty can be

obtained by s~mple vlscomemc techn~que Basically, the dllute solut~on wscometry

depends on the class~cal Huggln's equat~on45 that expresses the spec~fic vrscos~ty

(qq) of the polymer as a funct~on of concentratlon C, when one of the components

alone IS In solut~on

where [q] IS the lntr~nstc vrscoslty Alternat~vely k[~# = b can be used, where b 1s

the lnteract~on term

qJC = [q] + bC (1 10)

The theoretical cons~deratlon starts from the derlvat~on by Kr~gbaum and

Wall The specific vlscostty, qVm, of a m~xed polymer solut~on can be expressed

as follows

qrpn, [q1]C1 4 [q2]C2 + ~ I I C I ' + ~ Z Z C I ' + 2bl~C1C2 ( 1 1 1 )

where [ql] IS the lntnnslc v~scos~ty of the component 1 alone in solut~on and [qz]

I S the ~ntrrns~c \~scos~ty of the component 2 In solut~on CI and C2 are the

concentration of component I and 2, respectively In rn~xed polymer solut~on and b12

is the interaction coefticlent for the mixture of components 1 and 2. For

mathemat~cal wnventence Kngbaum and defined the interspecific

lnteracfion coefficient b12 as

The values of bii and b22 are obtained from comparison of equations (1.9) and

(1.10).

But the definition of b12 according to equation (1.12) is not valid for systems that

have negat~ve values for bll or b22. Therefore, the modification by Williamson and

wrightJ7 1s used to evaluate biz which can be expressed as

The value of bl2 can be theoretically calculated from equation (1.15) and can also

be obtained from equation ( I . 11).

According to Krigbaum and information on the interaction between

polymer 1 and 2 can be obtained by comparison of experimental biz and theoretical

b*12 values. Here the compatibility is characterised by a parameter, Ab, expressed as

Ab = biz - b*12 (116)

where b12 IS the experimental value and b*12 is the theoretical value. Negative

values of Ab are found for solutions of incompatible polymer systems while

positive values refer to attractive interaction in compatible systems. We can reduce

equation (1.11) to the following form when total concentration of the mixture (C)

approaches zero

Equat~ons ( 1.16) and ( 1.17) are used to characterise the compatibility

~ o r a w e t z ~ ~ has shown that interacting polymer system may exhibit very high

values of b compared with the average for each polymer. Miscibility of

PVCIEVA" and PVCImodified liquid natural rubber blendsSo was characterised by

vlscometry

The determination of polymer-polymer miscibility by rheological

measurements on binary systems is rare and indeed may be difficult to justify. But

because the morphology of a two phase system can change with shearing rate,

whereas the structure of a soluble system cannot, it is expected that the shear

viscosity function of soluble systems will change monotonically with composition.

Dewat~on from monotony can be taken as positive evidence of two phases.

Kongarov and ~artenev" found a monotonous change of the viscosity function

with composition for the system cis-l,4-polyisoprenelnatural rubber but completely

unpredictable behaviour for natural rubberlnitrile rubber.

Another rheologlcal techn~que for the detect~on of two phases in polymer

m~xtures has been suggested by Hubbell and Cooper 52 T h ~ s method persumes that

the segmental onentation of the components in a mlsc~ble system will be the same

whereas the segmental orlentation of the components in a two phase mixture wlll

differ sign~ficantly

1.5 Studies on elastomer Mends

The use of blends remains at a high level throughout the rubber industry

Most elastomer blending continues to be based on mechanical mixing procedures.

Usually, blends of elastomers are immiscible because mixing is endothermic and

the entroprc contrrbution rs small because of the hlgh molecular welghts

Fortunately. mrscibrl~ty IS not a requirement for most rubber appllcatlons Even

though homogeneity at a farly fine level is necessary for optlmum performance,

some degree of m~croheterogenerty is desirable to r e a n the ~ n d ~ v ~ d u a l properties of

the respectwe polymer components McDonel et al.I3 have revrewed the usage of

elastomer blends in tire appl~cat~ons

Callan et ~ 1 . ~ ' employed automated image analysis measurements to classify

the compatibility of different elastomer blends using phase contrast images. The

results of these studres are rllustrated in Table 1.1.

Table 1.1. Average Areas (p2) of Disperse Phase in 75/25 Pure Gum Blends

Listed in the table are the measured areas of the disperse phase tn more than

50 combinations of Banbury mixed 75/25 binary blends containing eight different

elastomers. Excluded are blends of IIRICIIR (no contrast) and SBRiBR which was

loo low in contrast for the image analysis measurements. Only 75/25 blend

EPDM

I IR

CIIR -

3 5

3 0

2.2

75

15

25

2.8

3.0

2.3

2.6

4.2

2.5

225

7 5

85

-

1.0

1.2

2.0

-

-

I 5

-

proportions were measured to assure that there would be a disperse phase rather

than a co-continuous mixture. The smaller the average disperse phase area, the

more compatible the polymers. This generalisation is largely related to the

sirnilanties in solubility parameter, viscosity and polarity. It can be seen that NBR

produced the greatest heterogeneity in all blends except those with CR. Many of

the CR blends were also quite heterogeneous, with BR, SBR and NBR, indicating

the smallest domains in the order of their diminishing size. ICresge5' has applied a

solvent extraction procedure for preparing specimens of blends for SEM analysis.

W ~ t h uncured blends of SBRIEPM, the SBR phase was crosslinked with sulphur

rnonochlonde and the uncrosslinked EPM phase was then extracted with

n-heptane Thrs method has been applied quite extensively to thermoplastic

elastomer systems. In the case of TEM analysis, if the polymers differ significantly

in unsaturaon, osmium tetroxide ( 0 ~ 0 4 ) is the best method for developing

contrast. .AndrewsS6 employed osmium tetroxide to study NRIEPDM blend

morphology. Ruthenium oxide (Ru0.i) has also been employed as a staining agent.

Ban and ~ a r n ~ o ~ ' employed both Os04 and RuOd to stain dynamically vulcanised

alloys of BIIR EPDM and PP. The OsO4 provided information on the overall

EPDM phase morphology and filler location, while Ru04 attached selectively to the

BIlR and enabled differentiation of this polymer from the EPDM.

Achieving contrast for TEM analysis of blends of high unsaturation rubbers

is a much greater problem. Smith and .4ndriess8 have developed a staining method

that is applicable to SBRBR blends which is based on the sulphur hardening

(ebonite) method. Small rubber specimens are immersed in a molten mixture of a

90:5:5 weight ratto of sulphur, a sulphenamide type accelerator and zinc stearate

tor about 8 h This treatment also hardens the sample for ultramicrotomy Contrast

is achieved by selective absorption of the zinc salts in the SBR phase which renders

it darker than the BR in a TEM. Lewis el have used an autoradiographic TEM

method to identify the polymer phases in elastomer blends with SBR and NR. This

is a rather lengthy procedure (3-5 months) based on changes in a silver emulsion in

contact with sectlons of the blends which contiuned either SBR or NR.

Based on phase contrast optical microscopy and electron microscopy,

almost all bulk mtxes of elastomer blends are microheterogeneous to varying

degrees Whtle true miscibility may not be required for good rubber properties,

adhesion between the polymer phases is necessary and the respective interfacial

energies are important in this respect. shershnev6' has summarised the importance

of and requtrements for cowlcanisation of the components of elastomer blends.

Cowlcanisation was defined in terms of a single network structure including

crosslinked macromolecules of both polymers. They should be wlcanised to

similar levels with crosslinking across the microdomain interfaces. The nature of

the polymer (e.g. unsatuation, polarity) determines curative reactivity, which is

also influenced by solubility. Vulcanisates with components having similar

curative reactivity generally give better properties than those whose components

have large differences in thts respect.

~ a r d i n e t ' ~ ~ used phase contrast optical analysis of heated rubber films

under pressure to study curative diffusion across the boundaries of several different

polymer combinations. The individual polymers were CIIR, IIR, EPDM, CR,

SBR, BR and NR. Curative diffusion between the domains of an elastomer blend

takes place during wlcanisation. This process may deplete curatives from one side

of the polymer-polymer interface and actually speed up cure on the other side.

Thus, there is an interfacial layer of rubber with a different state of cure than the

bulk The net result can be a weaker layer of rubber at the interface which may

reduce adheslon. ~ a r d i n e r ~ ' measured a diffusion gradient, D, which represents

the concentration change as a function of distance and time. His measurements for

the diffusion of accelerator (tellurium diethyldithiocarbarnate) and sulphur from IIR

to other elastomers are listed in Table 1.2. The highest diffusion coefficients for

the accelerator was observed with BR. Sulphur diffusion was higher with SBR in

wmpanson to NR and Increased sign~ficantly with 50 phr of N700 type carbon

black in the SBR

Table 1.2. Curative diffusion coefficients in different elastomer blend systems

Gardiner emphasised that curative migration is related to diffusion during

curing and not transfer during mixing. He was able to control diffusion through

selective mlxing of curatives into the individual polymers using specific curative

combinations. For blends of CIIR with NR he selectively mixed zinc oxide and

steanc acid into the CIIR and SICBSITMTD combination into the NR. Sulphur

type cures alone were not satisfactory for curing low unsaturation rubbers in blends

with high unsaturation or more polar polymers.

Woods et improved the covulcanisatlon of EPDM/NR blends by using

a TETD accelerator-lead oxide activator combination. The lead salts of TETD are

insoluble in both polar and nonpolar materials, which eliminates the

thermodynam~c dnvlng force for curative diffusion. With improved

covulcanisat~on, the properties of the blends were more close to the additive line

with respect to the properties of the two individual elastomers. The blends with

Curat~ve

Accelerator

(TDDC)

- Sulphur

From

IIR

IIR

To

BR - EPDM

CR

SBR

NR

SBR

SBR & 50 phr N700 CB

NR

D x 10' (cm2/s)

12 66

1 09

1 08

0 58

0 70

4 73

17 20

2 82

poor covulcantsation were well below the additive line in terms of their properties.

Rauer and improved the covulcanisation of CIIR/BR blends by adding the

curatives separately to the ~ndiv~dual polymers pnor to blending Vulcanisates of

blends prepared in this manner ~nd~cated a broad T, peak in the mechan~cal loss

spectra (tan 6 vs temperature) In contrast, the conventional mixes (curat~ves

added to the preblends) gave well defined ~nd~v~dua l T, peaks for CIIR and BR

Callan el showed the separate T, peaks for both polymers in unvulcanlsed

SRR/BR blends, wtth or w~thout carbon black However, vulcanised samples

indicated only a single ~ntermed~ate T,, or one that was closer to BR This was

atmbuted to the actton of crossltnk~ng as opposed to any change in actual blend

morphology The results of Callan el al. are given in Figure 1.5.

0*-SBR tUNCUREDl 8R-589 (CURED)

z w

V W - I S b F I U N C V R L D I B R - S B R - I S 4 F l C U R E D l

! i

-- ~ J

TEMPERlTURE .C

Figure 1.5. DTA thermograms of cured and uncured SBRlBR blends, with and without carbon black [Callar~, el a/., Rubber Chem. Technol.. 44. 814 (1971)).

ora an^ achieved better cure compatibility for EPDM/NR blends by

rnod~fying the EPDM with rnaleic anhydride. This permits the EPDM to be

crosslinked independently with the zinc oxide in the accelerated-sulphur

vulcanising system. An iontc crosslink network is produced in the EPDM phase.

Compared to conventjonal EPDM/NR blends, those with the modified EPDM

exhibited higher tensile strength and fatigue life along with reduced hysteresis and

permanent set, all of which reflect better covulcanisation. The maleic anhydride

treatment has also been applied to IIR and EPDM by Suma and coworker$' for

improved blending with NR.

~ o r i ~ * reported on an improved vulcanising agent (Zisnet DB) to improve

the interfacial bonding in blends of fluorinated rubber (FR) with NBR. The Zisnet

DB acts as a vulcanising agent for halogen rubbers in the presence of accelerators

and zinc oxide. The better interfacial bonding in FRMBR blends was determined

from swelling ratios as well as direct SEM analysis of the interfacial layers found

between adherents of FR and NBR.

Marsh and coworkers69 first reported the tendency of carbon black to

migrate from a NR masterbatch to the phase boundaries of CR when mixed with

this polymer Sircar and ~ a m o n d ' ~ studied carbon black transfer in a number of

different elastomer systems which included SBR, NR and BR. They utilised

changes in BR crystallisation, elastic modulus, and electrical conductivity, in

conjunct~on with electron microscopy to determine if transfer had occurred in

various blends. They confirmed that no carbon black transfer takes place between

SBR, NR and BR if conventional Banbury mixes are blended. Transfer did occur

from a solution mix and also from CIIR to BR. In the latter instance, the carbon

black showed a tendency to locate at the interface of the polymer domains.

Callan, Hess and scotts4 first employed pyrolysis GC to analyse the polymer

composition of the carbon gel (bound rubber) content in a number of elastomer

blends. Bound rubber represents the amount of polymer insolubilised by the

carbon black during mixing, and is measured by swelling small pieces of the

unvulcanised polymer for an extended period of time (at least overnight) in a good

solvent. All of the carbon black remains in the carbon-polymer gel, but any soluble

polymer (typically the lower molecular weight fraction) is removed. It follows then

thar the relatlve percentages of polymers in the bound rubber should reflect the

dlstribut~on of carbon black in an elastomer blend. They also used this technique in

conjunct~on w~th TGA and TEM analyses to study carbon black distribution in

blends of IIR wth NR and SBR. In these blends, significant amounts of the high

unsaturation polymer were found in the gel even when the carbon black

(N 347 type) was initially mixed into the IIR

Conon and ~ u r ~ h ~ ' ' have studied transfer in blends of SBR with NR using

pyrolysis GC analysis of the bound rubber. They reported significant transfer of an

N 339 type carbon black to solution SBR (solprene-1204) from NR masterbatches

which had been prepared in a Brabender EP2 laboratory mixer (cam type mixing

head. rotor speed of 50 rpm, oil temperature of 80°C). However, there is no full

explanation for these notably different results from other earlier studies relative to

carbon black transfer from NR to SBR emulsion.

Hess and coworker^'^ applied the differential swelling method for the

analysis of carbon black distribution in IRBR blend. The IRIBR studies were

limited to very low carbon black loadings (5-20 phr) but did indicate a carbon black

prefaence for BR relative to IR. Marsh et canied out additional studies and

reported that this differential swelling technique could be influenced by the

presence of carbon black. Therefore, the method was not suitable for commercial

compounds contiilnlng high carbon black loadings.

Coran and ~ e e ~ ~ have produced dynamically vulcanised blends of a rubbery

acrylate copolymer (ACR) with NBR. In this case the acrylate derived ester groups

in the ACR were used as the sites of vulcanisation without affecting the NBR. The

A C m B R blends remain millable after dynamic wlcanisation and curatives are

subsequently added to the NBR phase. A further improvement in processing

results from the fact that no post-curing is required, as is typical of acrylate rubbers.

Evans and ~ a r t n d ~ e ~ ~ showed that a single stage preblending procedure was a

more cosr-effective method for preparing blends of NBR and CIIR and it was

found that the mbber properties were not significantly different for the two

compounding procedures.

The blending of highly incompatible elastomers can sometimes be improved

by the addition of small amounts of another polymer. Setua and applied

thls techn~que to improve the homogeneity of binary and ternary blends of CR,

small amount of chlorinated polyethylene (CM) is added to the mix. The CM can

be cons~dered as the compatlbilising agent.

Bhaumik and coworkersn have studied the influence of carbon black

distribuhon on the rheological properties of EPDMIBIIR blends. Viscosity

increased wtth more w b o n black mixed into the BIIR phase, but became lower

with increas~ng BIIR content in the blends. b e swell increased with higher BIIR

at a high shear rate ( 1 223 s").

~ a m e d ~ ~ has reported on the importance of blend morphology and

~ntertactal adheston on the tensile properties of 75/25 EPDM/BR blends. The

energy at break (Eb) increased significantly when the disperse phase (BR) changed

from large and fibrous to small and spherical. Improved interfacial adhesion raised

the Eb of the blend to a level above the cohesive strength of either of the two

polymer components. Hess and ~ h i r i c o ' ~ showed that in NRJSBR blends better

tear properties were indicated for a higher loading of carbon black in the SBR

phase. T h ~ s was attnbuted to the fact that SBR is the more continuous phase in a

50150 blend with NR. The higher fatigue life of NRBR blends relative to NWSBR

has also been reported by them. Fatigue life was lowest for a high concentration of

carbon black in the BR phase. The changes in NRBR fatigue life as a function of

carbon black type and phase distribution are illustrated in Figure 1.6.

Figure 1.6. NRBR 50/50 fatigue life as a hnction of carbon black weight % in the BR phase for various blacks [Hess and Chirico, Rubber Chern. lechnol.. SO. 301 (1977)l

: looa. W LL 2

W 3 0 loo. ,- < LL

I0

5 0 / M HR/BR s a / n ce/aL

HZ90 N!1\

0 1 5 M 75 100

% CARBON B U C K in BR

hiev and ~eath'" developed a quantltatlve method based on pyrolysis GC for

the identificatlon of elastomers employed in tire treads (IR. SBR, BR) The

py~olysis degradation products of these three polymers fall into four basic units:

I ,4-~soprene. I -4-butadiene, 1,Z-butadiene and styrene. Variations in the peak

intensity ratios were employed to assess different polymer proportions in blends.

Companson to known control compounds is important in quantifying blend

composit~ons S~rcar and ~amond*' used DSC to distinguish SBR, BR or blends

from NR or IR The DSC scans for NR/BR blends are given in Figure 1.7 The T,

values were used to distinguish between these polymers. The T, approach was able

to resolve different proportions of SBR and BR in SBR/BR blends, but not at high

percentages of BR in the compound. They also reported82.83 that the DSC and

DTG curves for samples degraded in nitrogen gave the best results in identifying

comb~nations of NR, SBR, EPDM and halobutyl rubbers. The curves in oxygen

were not as sensitive but did corroborate the results obtiuned under nitrogen.

A PEROXW CURED

MU BR A 20/6O At 40/m A, 80120

- B TIRE S E C T W S

- - NR/W - 01 WIW 01 w 4 0

8. 9, 80/20

Figure 1.7. DSC traces of W R blends [Sircar and Larnond, Rubber ('hem. lech~iol.. 48, 301 (1975))

The blends of carboxylated nitrile rubber (XNBR) with two grades of

thiokol rubbers (TM) were reported by Roy and as." The processability of the

duokol rubber was improved by blending with XNBR. IR spectral analysis

revealed that on heating interchain crosslinking occurred between TM and XNBR.

Preheating of the preblends, before the addition of curatives, improved the

properties of the blends. The degradation and weight loss were also retarded.

Tripathi and coworkersuJ employed inverse gas chromatography to study the

thermodynamic compatibility of the industrially important elastomers polybutadiene

(BR) and nitrile rubber (NBR). The Flory-Huggins interaction parameter showed

that BR and NBR are incompatible in all compositions and that incompatibility

mcreases with acrylonitrile content.

Biswas e l s~c~e~s fu l ly used thiophosphoryl disulphides as a novel

coupling agent to fonn a blend comprising polar carboxylated nitrile rubber

(XNBR) and non-polar styrene-butadiene rubber (SBR) establishing close

proximity between than through chemical bridging. The study reveals that XNBR

in the presence of thiophosphoryl disulphide greatly improves the physical

properhes of SBR and thus acts as a reinforcing filler.

Chough and changU studied the relationship between vulcanisation

r d v i t y and chemical structure using a rheometer and DSC for NR, BR, SBR and

their blends. The overall rate of the vulcanisation was SBR>BR>NR. This was

the same trend as the number of allylic hydrogens in the statistical repeat unit of the

rubber used. As the wrrespondmg rate constant for an allylic hydrogen was very

s~milar regardless of the rubbers, it was found that the vulcanisation condition for a

compounded rubber could be predicted by comparing the number of allylic

hydrogens. The activation energy of the vulcanisation for each rubber was also

calculated. Recently, a detailed study on NR/EVA blends has been reporteduu

from our laboratory. The morphology, vulcanisation kinetics, melt flow properties,

miscibility behawour, effect of fillers and degradation behaviour of these blends

have been studied. The effects of blend composition and filler on the cell structure

and propertles of microcellular soles based on NRfEVA blends were also

tnvestlgated

1.6 SMps and objectives of the work

As delineated in the previous sections, polymer blends of dissimilar

copolymers are of considerable technological importance and high research value.

Blending provldes a means for improving physical properties of the component

polymers and leads to the development of novel and commercially viable products

with des~rable propertles at a lower cost.

Acrylonitnle butadiene rubber (NBR) compounds have excellent oil

resistance, abrasion resistance and mechanical properties but poor ozone resistance.

The oil resistance of acrylonitnle butadiene rubber is due to the polarity of the

acrylonitnle group. Acrylonitrile butadiene rubber is highly resistant to non-polar

oils and solvenh. Hot oil resistant blends of NBR with polyethylene and

polypropylene have been developed by Coran and patel.@ Blends of NBREPDM

are found to exhibit better oil swelling resistancew A flame resistant conveyor

belting was developed from NBRIPVC b~ends.~ ' Several other polymers are also

blended with NBR to make high performance materials. 54.68.74-76.8486

Poly(ethylene-co-vtnyl acetate) (EVA) is a random structured copolymer which

offers excellent ozone resistance, weather resistance and mechanical properties.

When vinyl acetate content is in the range of 10-20°!, partly crystalline polymers

with various levels of rubberiness reminiscent of plasticised PVC (referred to as

thermoplast~c EVA rubbers) are obtained.gz Thermoplastic elastomers bridge the

gap between conventional elastomers and thermoplastics by combining the

excellent processing characteristics of thermoplastics at higher temperatures and

the wlde range of propertles of elastomers at service temperature. One of the main

advantages of thermoplastic elastomers is their reprocessability. The blends of

EVAisilicone rubber have unique heat shrinkable characteristics, good mechanical

properties and lower cost " Cable ~nsulant was developed from E\..A/I-DPE

blends "" Se~eral other blends based on EVA are also reported 95-100 Howeber, no

attempt has been made so far to develop blends of NBR and EVA

The work embodied in this thesis focuses on the preparation and

charactensat~on of polymer blends based on NBR and EVA. Blending of NBR and

EVA leads to a new class of materials with good oil resistance, ozone resistance

and mechanical properties, if we can combine the positive aspects of the

component polymers. The investigation carried out on NBREVA blends are

addressed to aspects such as preparation of the blends, wlcanisation and

incorporat~on of fillers. The main objectives are to study the effect of blend

composition and cure systems on the morphology, mechanical, rheological,

dynamic mechanical. transport, thermal and ageing characteristics. The influence

of nature of crosslinked network, filler type and filler concentration on the

properties has also been studied.

Acrylon~trlle butadiene rubber/poly(ethylene-co-vinyl acetate) (NBRIEVA)

blends with different blend ratios were prepared by using a two roll mixing mill.

The morphology of the blends is studied using optical and electron microscope

techniques. Since polymeric materials are subjected to different loads or

deformation levels during the course of their application, the stress-strain behaviour

of NBRlEVA blends IS of practical relevance. The influence of blend composition

on the mechanical properties such as tensile strength, elongation at break, stress-

stran behav~our. tear strength and hardness has been investigated. The changes in

properties have been correlated with the morphology of the system. During service

these mater~als may undergo tearing and hence an understanding of the fracture

mechanism is important to predict the service life of the products. The tear failure

surfaces of the blends are examined using a scanning electron microscope.

Crossl~nk~ng 1s a method for forclng rnlsc~bllity by the introduct~on of

cokalent links between the components NBWEVA blends w~th vary~ng

proportions of the components are crosslinked using merent crosslinking systems,

viz., sulphur (S), dicumyl peroxide (DCP) and mixed system (S + DCP). The cure

characteristics of the blends are analysed in tams of optimum cure time, scorch

safety, etc. The morphology of the crosslinked systems is proposed based on the

morphology of the uncrosslinked systems. The effect of blend composition and

crosslinking systems on the mechanical properties such as stress-strain behaviour,

tensile strength, elonwon at break, Young's modulus, tensile set, tear strength

and hardness is studied. The tensile and tear failure surfaces are analysed using

scanning electron microscope in order to understand.the failure mechanism. Fillers

are used to improve the processing characteristics, mechanical properties and also

to reduce cost. The effect of high abrasion furnace black (HAF), semi reinforcing

finace black (SRF), silica and clay on the mechanical properties and failure

mechanism of 50150 blend of NBRtEVA has also been studied. Kraus equation

has been applied to analyse the extent of polymer-filler interaction. Applicability of

various theoretical models has been investigated to predict the properties of the

blend systems.

A study of the flow behaviour of materials in the melt state is essential to

owmise the processing conditions and also to improve the efficiency and quality of

product manufacture. The melt rhealogical behaviour of NBWEVA blends has

been studied with special reference to the effect of blend composition, crosslinking

system and shear rate using a capillary rheameter. Various theoretical models are

used to predict the melt viscosity of the blends. Parameters such as die swell,

principal normal stress difference, recoverable shear strain and elastic shear

modulus are calculated to characterise the melt elasticity of these blends. The

extrudate deformation at different shear rates is also studied. The morphology of

the blends at different shear rates has been examined by scanning electron

microscope.

Dynamic mechanical analysis can provide insight into various aspects of

material structure besides being a convenient measure of polymer transition

temperatures. Since polymers are viswelastic in nature, the study of viscoelastic

behaviour of NBRIEVA blends provides valuable information regarding the

damping characteristics. The dynamic m e c k c a l analysis of NBREVA blends

has been carried out as a function of blend composition, crosslinking systems,

temperature and frequency. The variations in tan 6, storage modulus and loss

modulus of the blends with temperature and frequency have been investigated. The

effect of b l ed composition, crosslinking density and frequency on the glass

transition temperature has been analysed. The activation energy for the transition is

calculated. Cole-Cole analysls has been carried out to assess the blend

heterogeneity. A master curve for the modulus of the blends is generated by

applying the time temperature superposition principle. Applicability of various

theoretical models has been attempted to predict the modulus of the blends.

The design of economically viable barrier materiais and membranes

necessitates studies on the transport properties.of various penetrants in polymers.

Knowledge of mechanism involved in sorption, diffusion and permeation of

penetrants through polymers is important in various applications. The diffusion

and bansport of organic solvents through crosslinked and filled NBREVA blends

have been canied out. The influence of blend wmposition, crosslinking systems,

fillers, filler loading and temperature on the diffusion of cyclohexanone through

these blends is studied. The variations in the transport coefficients (D*, S and P)

have been analysed. Various theoretical models have been used to predict the

permeability of the system. The sorption data have been used to estimate the

activation energies for permeation and diffusion. Van't Hoff relationship is used to

determine the thermodynamic parameters. The S n e and phantom models for

chemical crosslinks are used to predict the nature of crosslinks. The influence of

penetrants 1s studied using dichloromethane, chloroform and carbon tetrachloride.

The thermal behaviour of NBREVA blends is studied by thermogravimetric

analysis and differential scanning calorimetry. A knowledge of how polymers

break-down on heating is important when these materials are processed and

fabricated for use. Therrnogravimetric analysis has proved itself as a successful tool

in determining the thermal stability of polymers and polymer blends. The effects of

blend composition, crosslinking systems, fillers and filler loading on the thermal

propemes are evaluated. The weight loss at different temperatures is studied. The

activation energy for the degradation process is also calculated. A quantitative

information about melting and phase transitions of the blends are obtained from the

DSC thmograrns. The thermal ageing of these blends is carried out at 50 and

100°C for 72 h and retention of mechanical properties is studied. The resistance of

NBRlEVA blends to a few aggressive environments is also studied.

J. E. Hanis, S. H. Goh D. R Paul and J. W. Barlow, J. Appl. Polym. Sci., 27, 839 (1982).

D. Nard and R. E. P~d'Homme, J. Appl. Po@. Sci., 27,559 (1982)

1.3 . Ziska, J. W. Barlow and D. R.Paul, Polper , 22,918 (1981).

C. A. Cruz, 1. W. Barlow and D. R Paul, Macromolecules, 12, 726 (1979).

M. Mikura R S. Porter and G. Salee, J. P o l p . &I., P o l p . Phys. FA, 21, 367 (1983).

W. A. Knrse, R. G. Kriste, J. Haas, B. J. Schmitt and D. J. Stein, Makromol. Chem.. 177, 1145 (1976).

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