Polymer blends are physical mixtures of two or more structurally

M e r e n t polymers with no covalent bonds between them. The compon-

ents in polyblends adhere together through van der Wads forces, &pole

interactions or hydrogen bonding. Some level of thermodynamic

compatibility between the components is necessary to prevent phase

separation during processing and use. The other types of mixed

polymer pairs are graft copolymers, block copolymers and interpene-

trating networks. Polymer blends are the most attractive of the 'mixed

polymers' in view of the ease of designing and producing the blends

compared to other mixed polymer types',2. The relationship between

blend, IPN, block and graft copolymers can be understood from

Fig. 1.1.

For the processor and the end user, the blending technology

permits tailoring of a polymer compound to their spec& application

requirements often at a lower cost than a new material and over a

short development period.

Polymers to be combined in blends are generally selected to

complement each other in one or more of the following properties: cost,

processabdity, mechanical properties, chemical resistance, weather-

abdity, flammabhty resistance, thermal performance and a variety of

other proper tie^'.^. Blends are typically viewed as cost saving devices,

whereby an expensive polymer may be combined with a less costly

polymer to provide adequate performance at a signficantly reduced

price to the consumer. The versatihty of matching the pricelperfor-

mance requirements of spec&c application allows for a myriad of

Fig. 1.1 Schematic d i a g r a m o f s o m e s i m p l e two polymer combinations (Source Ref.5)

(a) a polymer blend; (b) a graft copolymer; (c) a block copolymer; (d) a semi - IPN; (e) an IPN (f) a cross - linked copolymer. The solid line represents polymer I, dotted line represents polymer 11, Enlarged intersections represent cross - link sites.

M e r e n t products from combination of the miscible polymers. The blend

can offer a set of properties that are not possible with either of the

polymers comprising the blend. By simply varying the concentration of

the constituents of a miscible blend, an innumerable variety of mate-

rials, each with a unique set of properties can be obtained.

Polymer alloys are the synergestic polymer combinations with

real property advantages derived from high level of thermodynamic

compatibility and greater intermolecular attractive forces between the

constituents. Alloys form practically a single phase system with unique

glass transition temperature.

1.2 COMMERCIAL IMPORTANCE OF POLYMER

BLENDS

The combination of two or more commercially available polymers

through blending represents an inexpensive route to produce new class

of materials. For example, in 1986, engineering polymer blends and

alloys represented 300 million pounds of commercial sales in the USA'.

It is estimated that by the end of 1996, US consumption of engineering

alloys and blends wdl reach approximately 700 million pounds.

Sivaram"rojected that 25% of the current world wide consumption of

high performance polymer is composed of blendslalloys which could

grow as high as 50% by the end of this decade.

1.3 BLENDING TECHNIQUES

Blenhng of polymers are carried out by a variety of means

including melt blenhng, solution blendmg, and latex or dispersion

blenhng, partial block or graft copolymerisation and synthesis of

interpenetrating net works (IPNs)~'~.

1.3.1 Melt blending

Mixing of polymer melt is the most common industrial method of

preparing polymer blends. Melt mixing avoids problems of contami-

nation, solvent or water removal etc. The disadvantages are the high

energy demands of mixing, high viscosity of the polymer melts and the

possibility of macromolecular changes like degradation, crosslinking

and chemical decomposition at high temperatures and stresses. Also,

the rheology of molten polymer systems is very complex and it is very

=cult to forecast the structure of the material from a knowledge of

the mixing conhtions.

Melt mixing of rubbers with plastics in an open-roll mill in air a t

elevated temperature induces oxidative degradation. Two techniques

which can be applied to mix a c u l t systems using a two-roll mill are

fugitive plasticisation and sequencing4. The former is useful when one

of the components has a much higher glass transition or melting

temperature than the other. The material can be softened by the

adhtion of a small amount of volatile solvent. This softened component

is then added to the fluxed second component. As mixing proceeds, the

solvent escapes. The other technique, sequencing, is similar in purpose

4

but involves heat instead of solvent. The step includes fluxing the high

Tg material first using a high roll temperature followed by addition of

second component slowly to the first with the temperature of the rolls

reduced accordingly. In addition, the roll gap must be adjusted

continuously to accommodate the increasing volume of the blend.

A widely used mixing device in the industry is the Banbury

mixer. Similar to the two-roll mill, this device has two counter rotating

rolls. In addition, the rotors are enclosed which produces more areas of

high shear and also allows the melt to be forced against the rolls by a

ram. Mixing in a Banbury is impressively rapid and efficient. But i t is

critical to have exactly the right volume of melt. Also it is possible to

blanket the Brabender with inert gas. Extruders can be used for

blending purpose. An extruder is almost a must if enough blend is to be

made for injection mouldmg.

Another useful mixing device is Wni-Max mixer. The melt is

mixed by torsional flow between two heated plates, but mixing across

flow lines can also be accomplished. This is done by periohcally chan-

ging the gap of the plates. Very small amount of polymers can be mixed

using Mini-Max mixer.

1.3.2 Latex blending

Mixing of low viscous latices is another method of obtaining

polymer blends without any organic solvent resulting to a heterogenity

of the order of micrometers. The limitation of this method is that the

components should be free from impurities and should be miscible. 5

Blenhng of latices of BR with SBR or NR is an example of latex

blending1.

1.3.3 Solution blending

Casting of a blend from a common solvent is the simplest mixing

method available and is widely practiced for coatings because i t allows

rapid and easy mixing of the components. This method causes neither

degradative colour changes nor premature crosslinking reactions. For

the preparation of solid polymer blends, the solvent is removed by

evaporation or precipitation of the polymeric components which usually

leads to phase separation and poorly controlled morphology in the

product4.

1.3.4 Mechanochemical blending

Under certain conditions, the mechanical working of a mixture of

polymers can lead to interpolymerisation leading to block copolymer

formation or graft copolymer formation. In such cases, mixing is

carried out in closed device in the absence of air. The property -

composition relationships of these blends differ from those of simple

mdl mixture. Synthesis of NR-SBR blend is an example of mechano-

chemical blenhng, where mechanical breaking of a primary bond in

the polymer chain backbone leads to the formation of free radicals4.

1.3.5 Freeze drying

With freeze drying, a solution of the two polymers is quenched

down to a very low temperature and the solvent is frozen. Freeze 6

drying has some advantages over solution casting which may be

critical for blending work. Ideally the polymers wdl have little chance

to phase segregate, but will collect randomly in regions throughout the

frozen solvent. Thus the state of Mute solution is somewhat preserved.

The freezing occurs rapidly, if the solution is single phase. Solvent is

removed by sublimation4.

1.3.6. Partial block and graft polymerisation

Partial block and graft copolymerisation is carried out in such a

way that its products are mainly homopolymers, but sufficient block or

graft copolymer is produced to ensure good adhesion between otherwise

incompatible components. Products of this process are suitable for

further mixing (in the latex or melt form) with the same or M e r e n t

homopolymers or copolymers. eg. Styrene butadiene block polymers1.

1.4 COMMERCIAL POLYMER BLENDS

1.4.1 Two phase polymer blends

Many miscible or partially miscible polymer blends have been

investigated recently because of their commercial importance. Blends of

PVC and nitnle rubber based barrier polymers are the examples where

elastomeric modification yields desired toughness by the incorporation

of an immiscible polymer phase. Other examples of commercial polymer

blends where miscibility is not achieved include bis phenol A poly-

carbonate - ABS', poly propylenetethylene propylene rubber1', chlorin-

ated polyethylene - PVC" and poly (methyl methacrylate) - PVC". The

list5of two component blends are given in Table I. 1. 7

Table 1.1

Commercial blend of immiscible components

System Property Advant,ages Applications PVC-ABS Better Processability and Mass-t,ransit interiors,

toughness than PVC, better appliance housings fire ret,ardancy than ABS

PVC-acrylic Imr~act-modified, similar Mass-transit interiors. to PVC-ABS appliance housings

PC-ABS Better toughness and heat Appliance and business distortion temperature than machine housings, ABS, t)et,t,er processability automotive components and lowcr cost t.han PC

PSF-ABS Similar to PC-ABS, composit,ion Plumbina fixtures. can be elect,roplated, lower cost food-service trays than polysulfone (FSF)

PC-PI? Bettor flow and energy Automotive applications absorpt,ion than PC

PC-PET Bett.er chemical resistance Tubing, auto bumpers, and processabilit,y and business machine housings . lower cost than PC

PC-PBT Better solvent resistance Tubing, auto bumpers, and processabilit,y t,han PC business machine housings

PET-PMMA Lower cost t,han PMMA, lower Electrical and warp and shrink than PET electronic applications

PC-SMA Impact.-modified, better Automot,ive applications, toughness and ductility than SMA, better retent,ion of properties upon ageing a t high temoerat,ure and lower cost than PC

PP-EPDM Better impact and Wire and cable insulation, toughness t,han PP auto- bumpers, hose and

gaskets PE-ethylene Bet,ter chemical resistance, Film c:opolymers impact,, st,rength and

toughness than PE Nylon-ethylene Better t,oughness Transport cont,ainers, copolymers sport,s equipments.

Source - Ref. 16

1.4.1.1 Interpenetrat ing polymer n e t work (IPN)

Interpenetrating polymer networks, (IPNs) are a class of mate-

rials formed by interlocking the net work of two or more polymers

synthesised in the presence of each other, aiming a t the enhanced

compatibility of thermodynamically incompatible net works. They are

synthesised by swelling a crosslinked polymer (I) with a second

monomer (11) together with crosslinhng and activating agents and by

polymerising monomer 01) in situ. IPN exhibits high degree of compa-

tibility. If one polymer is elastomeric and other is plastic the combina-

tion tends to behave synergestically, resulting in either reinforced

rubber or impact - resistant plastics depending upon which phase

predominates13.

Styrene butadiene rubber-polystyrene (SBR-PS) IPNs are

relatively incompatible, showing distinct phase separation14, even-

though both are non polar polymers. Density measurements of PU-PS

simultaneous 1 ~ N ' b a d e at a temperature between the glass transition

temperatures (Tgs) of the components showed a density 3% higher

than expected for intermediate IPN composition. This was attributed to

partial mixing or interpenetration of chains of the rubbery and glassy

polymer components. Examples of IPNs are listed in Table 1.2

Table : I. 2

Examples of IPN's

Source - Ref. 13,15

Component, I

Polyurethane Polyurethane Polyurethane Poly (ethyl acrylate) Poly (ethyl acrylate) Polybutadiene

1.4.1.2 Rubber - rubber polyblends

Component I1

Polyester Polyacrylat,e epoxy Poly (styrene - co - methyl methacrylate) Poly (methyl methacrylate) Polystyrene

Blends of two or more less incompatible rubbers are

commonly used in the automobile tyre industry inorder to improve

processabllity. EPDM blended with SBR has shown improvements in

ozone and chemical resistance with better compression set properties'7.

The use of EPDM in polybutahene or natural rubber resists the

formation of crack by ozone attack1'. Blends of natural rubber and

polybutadiene have shown various advantages, including heat stability,

improved elasticity and abrasion resistancelg.

Recently, blends of natural rubber (NR) and ethylene vinyl

acetate copolymer (EVA) have gained importancez0. These materials

combine the excellent ageing and flex crack resistance of EVA and the

good mechanical properties of NR. DSC and DMTA results showed

that the blend components are incompatible in the crosslinked and

uncrosslinked states. The adhtion of NR to EVA decreases the

10

crystallinity of the samples as supported by DSC and X-ray anal-

ysis30-23. Table 1.3 gives the examples of rubber - rubber blends.

Table : 1.3

Example for rubber - rubber blend

I Natural rubber (NR) 1 Polybut,adiene (PB) I Component I

Nalural rubber (NR)

Nitrile rubber (NBR)

Natural rubber (NR)

Component I1

Poly (ethylene-co-vinyl acetate) (EVA)

Poly (ethylene -co-vinyl acetate) (EVA)

Ethylene propylene diene monomer (EPDM)

Natural rubber (NR) Styrene but,adiene rubber (SBR) I

1.4.1.3 Rubber - plastic polyblends ,/' l2 $ \ ', 6; :',".&, ' .r

Among polymer blends, the rubber lends which

are commonly known as thermoplastic elastomers are the most familiar

ones. The improvement of impact strength of polystyrene by the

incorporation of a low modulus rubber phase is dramatic. Similarly,

the brittle PVC after blending with elastomer has improved toughness.

For example PVC - MBS blends have good impact strength and optical

clarity. The incorporation of a random copolymer of butahene and

acrylonitrile to PVC enhances the toughness2~ppreciably. In ABS -

PVC blends, ABS offers improved heat distortion temperature and

processability, whereas PVC offers flame-retardant properties. The

Chloroprene (CR)

Butyl rubber (IIR)

Styrene butadiene copoly

Nat,ural rubber (NR) .-.'

Source - Ref. 5,17,19,20. I /' i

{

blend can have higher notched impact strength than either of the

components. Applications include power tool handles, sanitary ware,

communication relays, electrical terminal blocks and electronic

housingsz5. Sen et a12' developed a novel series of cable sheathing

compounds by blending PVC and functionahsed EPDM. EPDM has

been functionahsed by grafting dtbutyl maleate @BM) using dicumyl

peroxide as initiator. Fire retardant low smoke (FRLS) compounds

made from PVC-functionahsed polyolefin blends possess the special

characteristics of low smoke, low acid generation, increased fire-

retardance and improved volume resistivity which are requirements to

the cable industry. Examples of rubber - plastic polyblends are given in

Table 1.4.

Table : 1.4

Examples of rubbecplas t ic polyblends

Source - Ref. 3,25,26

Component I

Acrylonitrile butadiene st,yrene copolymer (ABS)

Nit,rilc rubber (NBR)

Poly (ct,hylme - co - vinyl acetate) (EVA)

Natural rubber (NR)

1.4.1.4 Plastic -plas t ic poly blends

Component I1

Poly (vinyl chloride) (PVC)

Poly (vinyl chloride) (PVC)

Poly (vinyl chloride) (PVC)

Poly (vinyl chloride) (PVC)

Blends of thermoplastics also play an increasingly impor-

tant role in industry. Polyethylene/polystyrene (PEPS) blend has been

the most thoroughly investigated of all polymer blend systems27.

12

Huarng et al." reported on the immiscible behaviour of PVC-

SAN blends. They reported that most of the compositions of PVC-SAN

blends have two distinct glass transition temperatures. Blends of high

molecular weight PS and PMMA exhibit two phase morphology and

20,30 have been shown to be incompatible by m e r e n t techniques .

Commercially important plastic - plastic blends are listed in Table 1.5.

Table : 1.5

Examples for plastic-plastic blends

Source - Ref. 3,5,27,30.

Component I

Polyethylene (PE)

Poly (vinyl chloride) (PVC)

Poly (vinyl chloride) (PVC)

Poly (methyl methacrylate) (PMMA)

Poly (met,hyl methacrylat,e) (PMMA)

Polystyrene (PS)

Poly (vinylidene fluoride) (PVFz)

1.4.1.5 Block copolymers

Component I1

Polystyrene (PS)

Poly (met,hyl methacrylate) (PMIMA)

Poly (styrene - co - acrylonitrile) (SAW

Poly (styrene - co - acrylonitrile) (SAN)

Poly (ethyl methacrylate) (PEMA)

Polp (methyl methacrylat,e) (PMMA)

Poly (methyl methacrylate) (PMMA)

In block copolymers two phase behaviour is the key factor

resulting to elastomeric properties at normal use temperatures and

thermoplastic characteristics at temperatures suitable for conventional

thermoplastic fabrication. To achieve this, the continuous phase must

be amorphous with a Tg below the normal use temperature whereas

13

the dispersed phase must have a Tg or Tm above the normal use

temperature range. The dispersed phase physically restricts the soft-

block chain ends to a specific boundary and therefore present a situa-

tion similar to cross-linlung. The dispersed phase is also a reinforcing

material. " Examples of block copolymers include styrene - isoprene-

styrene (SIS), styrene-butadiene-styrene (SBS) etc.

1.4.2 One phase polymer blends

Compatibility is the fundamental property deciding the

practical u th ty of a polymer blend. In polymer blends, the property

(P) depends on average properties of the constituents and can be

described by the following equation,

where P is the property of the blend, PI and Pa the properties of the

isolated components and C1 and C2 the respective concentrations of the

constituents. I is an interaction parameter which can be positive, zero

or negative as shown in Fig. 1.2. When I is positive the property is

synergestic, when I is zero the property is additive (one phase blend)

and when I is negative the property is non synergestic (two phase

blend).

Miscible blends have only one phase and are rnorpholog-uxxlly the

simplest case. Commercially important examples of this subclass

include PPO-PS and PVC-nitrile rubber. The glass transition temper-

ature (Tg) is the primary thermal transition for these blends, and it

14

COMPOSITION

Fig 1.2. Variation of property with composition for a binary polymer blend (Source Ref.5)

varies monotonically with composition following FOX^' equation and

Gordon Taylor equation 33, which were originally written to describe

the composition dependence of Tg of copolymers. On the property

composition diagram (Fig. 1.2) the Tg usually falls below the tie-line

connecting the Tg's of the pure components in accordance with these

equations, although values above the tie line have been reported in

some noncommercial systems involving very strong intercomponent

hydrogen bonds34.

The glass transition temperature dependence on composition in

this subclass has considerable commercial significance because it

largely determines the heat distortion temperature (HDT) or the

maximum use temperature of the blend.

Exposure to high energy rahation causes various damage to

certain polymers and limits their use in applications where radiation

stenlisation is required. Incorporation of phenyl units into the stru-

cture, for example by copolymerisation provides protection of the

rahation- sensitive units. This mechanism apparently acts over a short

range and is not operative in phase-separated materials such as graft

35,36 copolymers or immiscible blends . There is growing evidence that

such protection can occur in miscible blends where mixing is at the

segmental level. For example, PMMA undergoes chain scission and

therefore loss of mechanical properties upon exposure to y -radiation.

The studles of Nguyen and ~ a u s c i ? ~ show that the extent of chain

scission of PMMA is greatly reduced in miscible blends with SAN

copolymer.

As observed in Tables 1.1 and 1.6, i t is possible to obtain a

particular improvement in properties by forming either a miscible or

immiscible blend. For example, the heat distortion temperature (HDT)

of ABS can be enhanced by mixing ABS with a miscible styrene maleic

anhydride component".

The material properties required for engineering applications

are high heat distortion temperature (HDT), toughness, solvent resist-

ance, low shrinkage upon moulding, low cost, and ease of moulding

which usually means a highly shear-dependent melt viscosity a t

moderate temperature combined with good melt thermal stability. No

material, blend or homopolymer, meets all these criteria. High melting

polyesters and polyamides meet most of the requirements. But these

materials are often =cult to mould because of low melt viscosities.

Amorphous materials with toughness and high Tg such as poly-

sulphone,polycarbonate and poly (para phenylene oxide) (PPO) possess

low mould shrinkage. But these materials are difficult to mould

because their melt viscosities are high and shear independent. This is

especially true in the case of PPO, which can be used commercially

only in blended form with PS as a flow aid. Glassy polymers, both

blends and homopolymers, are prone to crack upon exposure to

solvents and also more expensive than high volume polyesters and

polyamides. Miscible and immiscible blends of these two classes of

materials are a logical way to meet the growing needs for high perfor-

mance materials and the polycarbonate blends with poly (ethylene

terephtalate) (PET) and poly (butylene terephthalate) (PBT) are

commercial examples of this approach.

17

Table 1.6

Commercial blends of miscible components

System Advantages Applications

PVC-nitrilc Permanent plasticisation of Wire and cable insula- rubber PVC,~mprovcd processability t,ion, food- contact service

PVC-chlorinat,ed PE Permanent plasticiser Wire and cable insula- tion, food contact service, pond liners, automobile interiors,

PPO-HIPS Better processabihty and Appliance components, toughness than PPO, business- machine better HDT than PS housings

ABS-SMA Increased HDT Automotive applications

PMMA-PVFZ Better chemical and Outdoor film uv resistance than PMMA better clarity t,han PVFZ

PEMA-PVF2 Good weatherability, Decorative stripes clarity, and chemical on automobiles resistance

PBT-PET Lower cost, better gloss Electrical and and flexibility than PET electronic applications,

brake and fuel lines film

PBT-Phenoxy Improved filler Electrical and acceptance, cross electronic linking applications

Source - Ref.16

1.5 CHARACTERISATION OF POLYMER BLENDS

There are a large number of methods for studying the miscibility

538-42 of polymer blends , These include optical appearance, glass

transition temperature, microscopy, fluorescence spectroscopy, small

angle X-ray scattering, chemical and solution methods 5. 38- 42

18

1.5.1 Optical clarity

The study of optical properties of blends is important because

the knowledge of the factors leading to turbidity of a blend leads to an

understanding of factors which cause scattering. By knowing these

factors one can design blends of superior appearance.If the blend is

homogeneous it will have a refractive index in between those of the

individual polymers. If the system is heterogeneous with one polymer

present as a dispersed phase embedded in a second polymer it scatters

light according to the size of the hspersed particle5.

1.5.2 Glass transition temperature (Tg)

Determination of Tg is the most commonly used method for

studying the miscibility of polyblends. The Tg of the blend is usually

compared to that of inhvidual constituents. For polymer blends

exhibiting miscibility over the entire composition range, three genera-

Lised curves (Fig. 1.3) are possible: a linear relationship and the

minimum and maximum deviations from linearity. Examples of a linear

variation of Tg versus composition include blends of nitrocellulose and

poly (methyl r n e t h a ~ r ~ l a t e ) ~ ~ .

Examples of minimum variation from linearity are quite

common. One example is (poly hydroxy ether) of bisphenol Alpoly (E

capr~lactone)~~. Many of these systems obey the Fox equation3',

(eqn.I.2) and the Gordon Taylor equationJ3 (eqn 1.3)

Fig. I. 3. Variation of Tg with composition (Source Ref.41)

Tgblend = [Wa Tga + k (I-Wa) Tgbll [Wa + k (1-Wa)] 0.3)

In these equations Tga and Tgb represent the glass transitions of the

undiluted polymer components a and b, Wa and Wb are the weight

fractions of a and b, and k is the ratio of the thermal expansion

coefficient between the rubber and the glass states of the component

polymers, which is given by

The Kelley - Bueche equation45 is similar to the Gordon - Taylor

equation except that the volume fraction $i is used instead of the

weight fraction.

As ( a , - a,) has been proposed to be constant for all polymers46,

k = 1.0 and the Gordon - Taylor and Kelley - Bueche equations reduce

to the linear form

Tgblend = Wa Tga + Wb Tgb

%blend = $ a Tga + $ b Tgb

The above equations are useful for miscible polymer blends.

Tg of any polymer is affected by its previous history, the

experimental time scale and other factors that affect its intra and

intermolecular forces. Owing to the sensitivity of Tg to the disruption

of the local structure that results from mixing two M e r e n t polymers,

the existence of the single and sharp or single and broad, or double 21

and shifted or double and non shifted Tg of a polyblend reveals the

particular macroscopic characteristics of the blend. Broadening of the

transition occurs in the case of blends showing borderline miscibility.

Two separate transitions appear in case of total immiscibility. This

method is valuable only when a quasi-binary polyblend contains

polymers whose Tg values differ by more than 20°C.

A very large variety of physical measurements have been

proposed for the determination of glass transition temperatures. The

most commonly used techniques are

1. Calorimetric determination of heat capacities as a function of temperature Qifferential scanning calorimetry-DSC)

2. Dynamic mechanical (low strain) measurements of complex modulus as a function of temperature

3. Dielectric relaxation spectroscopy

4. Thermo optical technique.

DSC technique has successfully demonstrated polymer - polymer

47 miscibility for many systems'"". Schneier used DSC to study the

effects of mixing conditions on the compatibihty of PMMA and poly

(vinyl acetate) (PVA).ln DSC, the glass transition is distinguished by a

discontinuity in the specific heat (CP) Vstemperature curve.

Mechanical methods are the more frequently cited techniques for

the determination of the transition behaviour of polymer blends. The

elastic and viscoelastic properties of polymers derived by subjecting

polymers to small amplitude cyclic deformation can also yield important

information concerning transitions occurring on the molecular scale. 22

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. The glass transition temperature is obtained

from the plot of log. of loss modulus (GI) or mechanical loss (tans) vs.

temperature.

The electrical properties of polymers are analogous to mechanical

properties. The &electric loss factor @")and the dissipation factor

(tan6) are commonly used to ascertain polymeric transitions. The

experimental advantage of obtaining transition data from electrical

measurements over dynamic mechanical testing is in the ease of

changing frequency. The major disadvantage is the difficulty in

determining the transitions of non polar polymers. Generally non polar

polymers require slight mod&cation. Both mechanical and dielectric

methods are successfully used for establishing the miscibility of various

' 41 polymer systems.

1.5.3 Spectroscopy

Among the spectroscopic methods, NMR, IR and FTIR are the

most commonly used techniques for the determination of miscibihty,

nature of interaction and phase separation and influence of tacticity on

miscibility of polymer blends 48,49,50 . Kwei and CO-workersso used NMR

to study the influence of tacticity of PMMA on its miscibility with poly

(styrene-co-vinyl phenol). 23

Nuclear magnetic resonance experiments are possible on solid

polymers and polymer melts. Elmqvist and vans son^^ 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 resonance of proton in the

soft phase is relatively sharp compared with the resonance band of the

matrix protons. The intensity of the band due to the soft segment is

accordingly very high.

Infrared spectroscopy has most often been used in the analysis

of polymer mixtures. Specific interactions in the systems poly (acrylic

acid)-poly (ethylene imine) and poly (methacrylic acid)-poly (ethylene

imine) were demonstrated by infrared spectroscopy by Zezin et a15'.

The system PMMA - poly (vinylidene fluoride) exhibits speclfic

interaction involving the carbonyl group, accordmg to infrared spectro-

scopy performed by Coleman and Co- workersG2. FTIR technique gives

evidence of the existence of speclfic interactions and elucidate the

nature of such interactions. Frequency s w t s and band broadening for

blends have been ascribed to intermolecular chemical interactions and

to changes in polymer chain conformations. Coleman and CO-workers4"

used FTIR technique to determine the lower critical solution behaviour

of PVCIEVA and EVAJchlorinated polyethylene.

Infrared and ultraviolet spectroscopy s tuhes on PSlPPO blend by

Wellinghoft and CO-workers" provided evidence for the conclusion

that, PPO is loosely packed in the glassy state and the addition of PS

reduces the free volumes. They further reported that the chains of the

two components interpenetrate significantly. The high extent of

miscibility is associated with the strong interaction between the phenyl

group of the PS and the phenylene group of PPO.

Ultraviolet emission spectroscopy has been suggested as a tool

for quantifying the degree of miscibility of polymeric components54. To

employ this technique the components of the blend must contain

chromophoric structures active in the uv region.

1.5.4 Scattering techniques

The commonly used scattering methods include X-ray scattering,

neutron scattering, light scattering, pulse induced critical scattering

and the cloud point method. Electron scattering and Rayleigh-Brillowin

scattering are also used in the characterisation of chain conformation, 55.56 local order and the morphology . All scattering experiments are

based on the existence of variation in the homogenity of the scattering

medium.

1.5.5 Inverse gas chromatography

Inverse gas chromatography (IGC) has been applied successfully

to the description of polymer blend miscibility in the liquid state. It

has also been used in studying the concentration dependence of the

glass transition temperature of polymer blend57. Glass transition

temperature, crystallinity, adsorption isotherms, heats of adsorption,

surface area and interfacial energy can be obtained from IGC~'. su5'

applied IGC to the study of thermodynamic interactions in poly (vinyl

chloride) (PVC) plasticised by di-n-octyl phthalate @ OP).

1.5.6 Fluorescence spectroscopy

Two fluorescence methods have been used for the study of

polymer blends. They are excimer fluorescence and non radiative

energy transfer techniques.

1.5.6.1 Excimer fluorescence

Excimer fluorescence is an effective and sensitive morphological

tool for the study of miscibility of an aromatic vinyl polymer with a non

fluorescent host polymer. A convenient analysis of the degree of mixing

at the molecular level is by the measurement of photostationary

excimer to monomer fluorescence intensity ratio Ie/Im. Tao, and

rank'" used excimer fluroscence technique to study miscible blends of

poly (2-vinyl naphthalene) (PZVN) and poly (cyclohexyl methacrylate).

Using fluorescence technique, Monnerie and Co-workersG0 have

determined the boundaries (binodal and spinodal curves) of the phase

hagram of anthracene-labeled polystyrene/poly (vinyl methyl ether)

blends.

1.5.6.2 Non radiative energy transfer fluorescence spectroscopy

Non rahative energy transfer (NRET) can be used to probe

polymer miscibihty and phase separation. In NRET technique, the

amount of energy transferred from a donor to an acceptor group is

assessed. Because the transfer is non radiative, the donor and acceptor

must be very close. A large amount of energy transfer imply miscibility.

Teyssie and CO-workers" used NRET technique successfully to deter-

mine the miscibility and phase separation in PVCPMMA blends. The

ratio of the fluorescence emission intensities of the donor and acceptor

(INIIA) (naphthalene and anthracene were used to label PVC and

PMMA respectively) is related to the efficiency of energy transfer. This

ratio is a measure of the degree of miscibility of two polymers. The

advantage of these methods is that the proximity of groups a t the

several Angstrom level can be unambiguously assessed.

1.5.7 Microscopy

Microscopy is used to find out both the presence and conne-

ctivities of the phases of a polyblend. Scanning electron microscope,

phase contrast microscope and transmission electron microscope are

extensively used for studying the morphology of polymer blends. For

the d e t d e d characterisation of the phase morphology in blends,

microscopy is unmatched by any other techniques. Scanning electron

microscopy (SEM) offers the simplest procedurefi? Photomicrographs of

fracture surfaces often give information about the extent of adhesion

between phases. Several polymer- polymer systems which are reported

to be miscible by less sensitive techniques have been shown to contain

domains by using the electron microscope. Matsuo et al.'"ound micro

level heterogenity (400AO) in the system of PVC-NBR containing 40%

acrylonitrile, by microscopy although only one glass transition was

observed in this blend.

Transmission electron microscopy64 ('!?EM) has been attempted

for the purpose of defining the scale of mixing. One example of an early

application of TEM to blends was the investigation of structures

produced by the spinodal decomposition of a PMMAISAN blend65.

Morphology of blends is the organisation of components i n

supermolecular scale. It indicates the form, size and orientation of

blend's crystallites, structure of groups of molecules of the components

and other boundaries, degree of crystallinity and the spatial arran-

gement of blend component phases. The major factors that govern

morphology of the blend system are 1) viscosity of the components 2)

ratio of the components 3) processing conditions such as shear rate

and temperature and (4) presence of additives. Additionally the

niorphology is also dependent on the thermodynamic properties of the

components and the mixing process.

Makarewiez and ~ i l k e s " carried out extensive stuhes on

morphology associated with the liquid-induced crystallisation of poly

(ethylene terephthalate) (PET) blend with poly (tetramethylene

terephthalate) (PTMT), atactic polystyrene (APS) and poly carbonate of

bis phenol A. SEM was used to study the morphology. They observed

that melt mixed blends of PET and PC showed no large scale phase

separation prior to liquid-induced crystahsation. This was accounted

for by copolymer formation due to interchange reaction occurring

during sample fabrication. The morphology of both pure PET and

PETIPC blends after liquid-induced crystallisation appears identical.

Danesi and porterfi7 have reported that composition, processing

history and difference in melt viscosity influence the morphology.

Similar melt viscosity values lead to uniform chstribution of minor

component in the major one with a very fine morphology. If the minor

component has lower viscosity than the major, the minor phase will be

finely and uniformly chspersed as domains oriented in the extrusion

direction. The minor component gets coarsely dispersed in essentially

spherical domains if its viscosity is higher than that of the major

component. SEM and phase contrast microscopy have been successfully

used in these studies by Danesi and

Morphology of different polymers has been studied by many 68.68 groups using a number of techniques .

1.5.8 Melting point depression

In polymer - polymer blends in which one component is

crystalhne, melting point depression can be used to determine the

miscibility of the system. Examples include isotactic po lys tyrene-~~070

and poly (vinylidene fluoride) - poly (methyl methacrylatejl,. Nishi and

wang7' calculated interaction parameter from melting point depression.

1.5.9 Viscosity studies

The basis for using dilute solution viscosity as a parameter for

compatibility determination of polymer blends lies in the fact that

while in solution the repulsive interaction may cause shrinkage of the

polymer coils resulting in a viscosity of the polymer mixture that is

lower than the value calculated from viscosities of the pure components

on the assumption of the adhtivity law. On the other hand attractive

interation increases the viscosity of the system.

Kulshreshtha et alT2 applied the viscosity method to the

PVCIABS polyblend system to study the compatibility. They found

that the plot of absolute viscosity versus composition deviates from

linearity accordmg to the degree of compatibility. chee7' also proved

viscometry as a simple and reliable tool for identifying the compati-

bllity of PVCJPMMA, PMMAfPiBMA and PVCffiBMA blends.

1.5.10 Mechanical properties

Utlimate mechanical properties such as tensile strength, tough-

ness, abrasion resistance, elongation, fatigue resistance and environ-

mental stress crack are of considerable interest for end application of

blends74. Usually compatible polymer blends show synergism in

mechanical properties while in the case of miscible blends an adhtive

value is obtained between the component polymers5.

Modulus of rigidity is roughly intermediate between the two

components and it depends fairly linearly on the ratios of the two3'.

When the two polymers exist in separate phases the relationship

between the composition and modulus is not nearly as simple. When

one of the components is present in larger amount it should form the

continuous matrix phase and should play the primary role in deter-

mining the modulus. A steep transition between the two components is

expected in the region where both components are present in equal

30

amounts. On the other hand, the dispersed phase may be considered as

a filler and effect of such content on the modulus of the filled matrix

can be calculated.

Strong exothermic interactions between components of miscible

blends leads to denser packing and loss of free volume. In such cases

mechanical properties are expected to be higher than prehcted by

simple additivity rule. Experimental results in some systems generally

conform to this expectationT5. Poor interfacial adhesion results in

inferior ultimate properties compared to the expected average property

of the constituents in totally incompatible blends. In a polyblend where

a moderate concentration of tiny rubber particles are hs-n a ,*.::, 4 L!li>

glassy plastic matrix, tremendous improvement i y d m P H 3 t r e &

// .< .

.1 results.

1.5.11 Rheological properties

The two or more polymers used for malung

difference in molecular structure. This may result in a different

rheological behaviour for the blendsT6.

Usachev et al.I6 proposed that the flow of polymer blends must

be regarded as the combined flow of M e r i n g viscosity. Parasiewicz et

al.I7 found that polymers of similar chemical structure exhibit

rheological behaviour deducible from adhtivity considerations and

blends with polymers having different chemical structure generally

have lower viscosity than the individual component of the blend.

Polymer blends with a second component, which is rubbery with high

31

molecular weight, can provide improvements in melt strengthm. This

improves processability for blowing and thermoforming.

The use of solution or melt rheology to judge interactions in

blends is largely empirical in nature. The expectation in rheology is

that, polymers with strong favourable or unfavourable interactions will

show viscosity Vs. concentration response that are largely n ~ n - l i n e a r ~ ~ .

A typical expression 64 to indcate the blend viscosity is

This is capable of fitting quite complex blend viscosity behaviour. In

this equation q, is the blend viscosity, q, and q, are the viscosities of

the components, and B1 and B2 are interaction terms. W, and W, are

the weight fractions of components.

1.5.12 Empirical approach at predicting compatibility:

solubility parameter approach

According to the solubility parameter approach at predicting

compatibihty, two polymers mix well if the difference in the pure

component solubihty parameter is s m d , typically 1.7-2.0'~. For

polymer molecules, the solubility parameter is best calculated using

tables of molar attraction coefficients, E, by using the equation

where E is summed over the structural units of the polymer, M the

'mer' molecular weight and e is the density7" Tables of calculated

values of 6 have been publisheds0.

Although the solub~lity parameter approach is not rigorous, it

allows a useful first approximation to polymer solubility. The difFerent

temperature coefficient for the pure component solubility parameter

has even been suggested as the reason for high temperature phase

separations1.

sanchezsz compared the predictions of polymer-polymer compati-

bility from the equation of state theories and the solubility parameter

method.

1.5.13 Interaction parameter and critical interaction

parameter

The miscibhty of a polymer blend system can be predicted by

calculating the interaction parameter and critical interaction para- 5 meter . The interaction parameter XAB, can be written in terms of

solubility parameter as

where Vr is the reference volume, R the gas constant, 6 the solubility

parameter and T the temperature in the absolute scale.

The critical interaction parameter can be calculated using the

equation

33

where XI and X2 are the degrees of polymerisation of polymer 1 and 2

respectively. Miscibility can occur over the entire cayosition range only 83

if (X ~B)er >XAB.

1.5.14 Enthalpy of mixing of polymer-polymer blends

The heat of mixing is an approximate measure of free energy of

84.85 mixing and thus may indicate the degree of compatibility. schneirsG

suggested that the following equation may be deduced for the heat of

mixing for two component polymer blends.

where XI, p and M are the weight fraction of polymer, polymer density

and the monomer unit molecular weight respectively and 6 is the

solubihty parameter of a polymer. Singh et a1.8"redicted the compati-

bility of poly (methyl methacrylate) / poly (vinyl acwtate) (PMMAIPVA)

and poly (methyl methacrylate/polystyrene (PMMAIPS) blend systems

using the above equation.

1.6 THERMODYNAMICS AND PHASE SEPARATION

OF POLYMER BLENDS

The structure and stability of polymer blends depend primarily

on the miscibility of polymers used in making the blend. The stability

of any binary system requires that the Gibb's free energy of mixing

AGm be negative. AGm is given by

A Gm - - AHm - TA Sm

In this equation A Gm = change in free energy of mixing

AHm = change in enthalpy of mixing

A s m = change in entropy of mixing

T - - absolute temperature

A negative AGm is necessary, although not a sufficient condition for

the stability of the mixture. Thermodynamic stability for a one phase

system exists when

where is the compositional variable. Graphically, the above

conditions are shown in Figure 1.4. The restriction of eq.0.14) requires

that the free energy-composition diagram be concave downward. For a

system that is miscible over the entire composition range a t one

temperahre, a curve similar to Fig. 1.4a would be followed. A partially

miscible system would include some compositions that are incompa-

tible. Several interesting features of the phase diagram can be derived

from Figure 1.4 b. Between the composition C and the pure component

1 and composition D to pure component 2, the behaviour of AGm with

composition obeys eq. 0.14). However, phase separation of two phases

denoted by A and B would lower the free energy from G' to G? The

binary compositions between A and C, D and B exist in a metastable

35

COMPOSITION

Fig. 1.4 Free energy versus blend composition for (a) miscible, and (b) partly miscible polymer blends (Source Ref.78)

state; stable to small perturbations in the system but unstable to large

disturbances. The boundary between the stable region and the

metastable region (point A and B) is termed the binodal. Compositions

between C and D do not satisfy the restriction of eq. 0.14) and are

unstable. The boundary between the unstable and metastable state

(points C and D) is called the spinodal.

The locus of the spinodal is in principle easy to calculate. The

spinodal boundary is simply the inflection points of the free energy-

composition hagram given as

The binodal is much more difficult to calculate since the

boundary does not necessarily coincide with any critical points on the

free energy - composition diagram. The locus of the binodal is found by

setting the chemical potentials of both homopolymers equal in the two

co-existing phases. Graphically this means that the binodal is found by

drawing a common tangent between the two concave section of the free

energy hagram (dashed line in Figure 1.4 b)78.

As the temperature is changed, so does the free energy plot.

Upon an increase in temperature, the binary system can phase

separate. The temperature a t which phase separation first appears is

called the lower critical solution temperature (LCST). Analogously,

phase separation upon a decrease in temperature is inhcative of the

existence of an upper critical solution temperature (UCST). The

position of the critical solution temepratures can be calculated by 78

37

Figure 1.5 illustrates the phase diagram for binary polymer-

polymer blends. The solid line is the binodal and the dashed line

indicates the spinodal. Figure 1.5 (a) shows UCST behaviour. This is

very common in polymer solution thermodynamics, where the critical

point at infinite molar mass represents the well-known Flory, 9 ,

condltions8? The existence of a polymer-polymer UCST has been

predicted but convincing evidence has not been found. Based on the

appearance of two mechanical loss peaks below O°C, Koningsveld et

al.87 reported that blends of SBR and natural rubber exhibit UCST

behaviour.

Figure 1.5 (b), showing LCST behaviour, is the normal phase

hagram for high molar mass homoploymer blends where specific

interactions are present. Many systems showing LCST behaviour have

been reported in literature". Examples are PSIpoly (vinyl methyl

ether)", poly (methyl methacry1ate)lpoly (styrene-co a ~ r ~ l o n i t i r i l e ) ~ ~

and poly (capro1actone)l poly (styrene-co a~r~lonitrile)"'. Figure 1.5 (c)

shows a phase diagram which exhibits a UCST and a LCST above it.

This behaviour is common in polymer solutions where the LCST is

usually above the boding point of solvent. It has been suggested that

polystyrenelpoly (2-chlorostyrene) blends might be in this categoryg2.

There are experimental =culties in determining such phase hagrams

since the UCST may be below the glass transition temperature (Tg)

and the LCST may lie above the decomposition temperature. It is also

38

Fig. 1.5. Schematic phase diagrams for polymer polymer blends:- (Source Ref.88)

--spinodd lines - binodal lines (a) a phase diagram of the UCST type : (b) a phase hagram of the LCST type :

(c) a phase diagram in which both an UCST and LCST occur, (d) an 'hourglass' phase hagram; and

(e) a phase diagram in which the UCST occurs above the LCST

possible for the UCST to merge with the LCST, producing an 'hour

glass' type of phase hagram as shown in Bg.I.5(d) or the UCST can lie

above the LCST, producing a 'closed loop' phase diagram as shown in

Figure 1.5(e). The 'hour glass' phase diagram (FigureI.5(d)) has no

temperature region for which a single phase exists over the entire

compdtion range. This represents the phase behaviour of compatible

blends. For homopolymers, the equation of state theory would predict

that UCST should always occur at or below an LCST. But such

restrictions may not apply to copolymer blends.

1.6.1 Kinetics of phase separation

The phase separation in miscible polymer systems are generally

brought about by variation in temperature, pressure andlor compo-

sition of the mixture. In polymer blends, the mixture can subsist inside

the spinodal below Tg and remain in a one phase system.

The lunetics of phase separation are different inside the spinodal

as opposed to the metastable region. Between the spinodal and binodal,

the system is stable to small compositional fluctuations whereas inside

the spinodal, any change in composition results in a change in free

energy, favouring phase separation. Two different mechanisms of phase

separation have been porposed to explain the lunetics in the two

regions.

Inside the spinodal, there is no thermodynamic barrier to phase

separation and the process should be spontaneous until separation is

complete. The phase separation requires diffusion against the concen-

40

tration grahent ie, a negative diffusion coefficient or so called "uphill"

hffusion. (Fig.1.6) Phase separation by this process is called spinodal

93,94 decompo&ion and has been treated theoretically by Cahn . Since

the spinodal decomposition mechanism is spontaneous and continuous,

the morphology is characterised by interconnected phases.

In the metastable region, the Wusion coefficient becomes

positive and phase separation is by nucleation and growth. A nucleus

is formed from a large fluctuation in composition and once established,

grows by normal Musion processes. The work required to form a

nuclueusdepends on the metastability of the system, vanishing to zero

a t the spinoda19? In the nucleation and growth mechanism, composition

of the growing phases remains constant. Schematic representation of

the two mechanisms are given in Egure 1.6. A good review on the

kinetics of phase separation is given by Kwei and wangY5.

1.6.2 Polymer mixture theories

The various theories of polymer mixture are arranged chronolo-

gically in this section. Many reviews on polymer solution thermodyna- 96-90 mics have been published . The first attempt to describe polymer

solution thermodynamics was made by Flory R5,99.100 and Huggins 101.102

(F-H theory). The expression derived by Flory and Huggins contained

a combinatorid entropy of mixing term due to the length and volume

of the polymer in solution. A van Laar type enthalpy of mixing was

also added to obtain the free energy of mixing. Although the F-H

theory was useful as a first approximation, it was unable to predict the

details of polymer solution behaviour.

41

Nucleation and growth

Nucleation Growth \ Equilibrium

\

M

$ 2 ~ --

Spinodal phase separation / Fluctuation Growth of Saturation and continued

fluctuation separation (Phase hardening)

$M = Composition of mixture

41 13 = Equilibrium composition of phase

Fig. 1.6. Modes of phase separation in miscible blends (Source Ref. 88)

Extension of F-H theory to polymer-polymer system was done by

scottIo3 and omp pa'^! The expression for the free energy of mixing

two polymers derived by Scott was103

RTV A G ~ = ----(v, /X,)lnV,+V,/X,lnV, +x,,V,V, (1.17) V1t

where V is total mixture volume,VR the reference volume which equals

the molar 'mer' volume,V, and V2 are the volume fractions, X, and X,

are the polymer chain length and x,, is the polymer- polymer intera-

ction parameter. The terms containing X, are entropic and as X,

increases, these terms go to zero. In other words, the entropy of mixing

of polymers goes to zero at high molecular weights. Given the above

situation, AG, can only be negative if the enthalpic term is negative,

ie. negative x,, Thus the interaction parameter reflects the strength of

interpolymeric contacts.

Calculations based on Flory-Huggins theory can account for the

existence of an UCST, but not for the LCST. The extension of F-H

theory to include free volume was done by Prigogine'06 and lor^''^,

~ c ~ a s t e r " applied the Prigogine-Flory theory to polymer-polymer

systems. Although the equations derived by McMaster were very

complex, several important conclusions were reached. The existence of

a polymer-polymer LCST was predicted. Moreover, it was found that

the thermal expansion coefficient was the most important parameter

for polymer blend systems. Small merences in the thermal expansion

coefficient of the pure components was the cause for LCST behaviour.

Patterson and ~ o b a r d ' ~ offered a simpler form of the Prigogine-

Flory Theory as applied to polymer-polymer systems. In their treat-

ment, they concluded that the primary cause of LCST behaviour was

not unfavourable free volume effects, as McMaster" implied, but

instead on the favourable polymer-polymer interaction at low tempera-

tures which decreases with temperature. However, the predictions of

McMaster and Patterson are similar.

1.6.3 Lattice fluid theory

Sanchez 82,108-110 formulated a new theory which has been charac-

terised as a lattice fluid theory and M e r s from the corresponhng state

theories of Prigogine and Flory.

Several conclusions of the phase behaviour of blends could be

reached using lattice fluid theory. In all cases, LCST behaviour was

prehcted. An increase in molecular weight of one of the components

serves to decrease the LCST and increase the UCST. The pressure

dependence of the CST's predicts a larger change in the LCST than the

UCST. Finally, very few polymer pairs would be expected to be

miscible. The approach used by Sanchez is a useful tool for under-

standmg the mechanism of polymer-polymer phase behaviour.

1.6.4 Phase behaviour of ternary polymer blends

Su and ~ r i e d " ' applied the Flory-Huggins theory to polymer

blends of three monodisperse homopolymers. The free energy of mixing

AGm of three monohpserse homopolymers may be expressed in terms

of volume fractions (c$~) as

G = ( A G ~ 1 k ~ ) (VU 1 V) 0.18)

= (4, +(& /m2)ln42+(43 /m3)ln$3

+X12 $1 $2 +X23 4 2 43 +x3143 41 (1.19)

where Vu is the volume per lattice site, V is the mixture volume, mi is

chain length and xij is the Flory interaction parameter between

segments of polymers i and j. The equation of the spinodal may be

obtained from the relation

2 Jsp = G,, G,, -(GZ3) = 0

where Gij = (6 G 1 6$i 6$j) ,p

From equations 1 and 2, the equation of the spiondal for a

ternary solution becomesLL',

ml$l +m,$, +m,43

-2[m,m2 ( X I + ~ a ) $ l 4 2 f m 2 m 3 ( ~ 2 + ~ 3 ) 4 2 4 3 +m3m1 (XS + ~ 1 ) 4 1 4 3 ]

+4m,m,m3 (xIxz + X ~ X , +~3~1)41$243 = 0 0.22)

where X, = (xij + xik - xjk) 12 0.23)

The critical points must satisfy the additional condition112

G,, SJSP I 64, -G,, s JSP 164, = o 0.24)

If desirable, blends of one or more random copolymers may be

included in the development by adopting an appropriate expression for

45

113-116 Xi, . For example x,, between two copolymers where copolymer 1

has segzment fractions fA and f, of comonomers A and B respectively,

and copolymer 2 has corresponding segment fractions fc and fD may be

given as

where xkl is the segmental interaction parameter between comonomers

k andl .

1.6.5 Experimental determination of phase separation

in polymer blends

Wideline and pulsed NMR", FTIR 117-119 , light scattering120

uv-visible absorption spectroscopy and fluorescence spectroscopy61 have

been successfully used to the study of phase separation in polymer

blends. In wide Line NMR, the temperature variation of the line width

and in pulsed NMR, the relaxation time can be used for characterising

the composition of the phases. The relative signal contributions give

information concerning the amounts of the phases. In FTIR, phase

separation is studied by monitoring the frequency of vibration of the

interacting groups as a function of temperature. A non linear relation-

ship is observed in this case. The temperature at which the relative

strength of the interactions appears very weak is the LCST. The light

scattering invariant can be quantitatively used to describe the early

stages of phase separation.

In uv-visible absorption spectroscopy'" appearance of an

adhtional peak at higher wave length region inhcates the onset of

phase separation. In excimer fluorescence spectroscopy, the LCST is

indicated by the point where the plot of Ie/Im Vs temperature shows a

change in slope.

1.7 PVC BASED BINARY BLENDS

Poly (vinyl chloride) represents one of the most rigorously

investigated components of polymer blends. PVC has been found to be

miscible with a number of structurally M e r e n t polymers and

copolymers. The capability of weak specific interaction is possible with

PVC. The a-hydrogen of PVC is capable of hydrogen bonding,

particulady with polymers which have electron donor groups (amides,

c a r b ~ n ~ l ) ' ~ ~ .

For the miscible blend of PVC and poly (E-caprolactone) charge-

transfer interactions between the pendant chloride and ester oxygen

has been proposed1".

1.7.1 PVCINBR blends

Blends of PVC and butadiene/acrylonitnle copolymers WBR)

historically represent the initial observation that miscibility with

polymer mixtures is possible124. In the technical literature, this blend

has been described as miscible, partially miscible and even hetero-

geneous based on m e r e n t experimental techniques.Generally dynamic

mechanical results inhcate miscibility with some broadening of glass

47

transition temperature. 'Using microscopic techniques separate phase

resolution was possible69. ~mbler '" observed that under certain poly-

merisation conditions, compositional variation in butadiene acrylo-

nitrile copolymers would result in nonhomogeneous materials. The

range of acrylonitrile content sufficient to yield miscibility in PVC

appears to be quite large and equal to 23-45%'"".

1.7.2 PVCIEVA blends

Blends of PVC with ethylene-vinyl acetate copolymers (EVA)

have been widely studied 48, 121-133 . Miscibility appears optimum a t

vinyl acetate contents of 62-70%''~. Marcincin et d."* studied EVA

(45%VA)/PVC and chlorinated EVAPVC blends. Definite phase

separation was observed with the EVAPVC blends. But chlorinated

EVAIPVC blends has single Tg.

Feldman and R U S U ' ~ ~ reported that PVCIEVA-45 blends are

miscible based on the studies of mechanical and &electric loss data.

The composition dependence of the tensile strength and ultimate

elongation for these blends exhibited the characteristics of mechanical

compatibility. EVA with vinyl acetate content 45% has been experi-

mentally observed to have limited miscibility1".

hbscibihty has also been inferred from diffusion data of gas

molecules, which can be used as probes to assess the level of molecular

131.13" mixing . Permeabhty results show that phase inversion occurs in

the case of PVCIEVA-45 blends at higher compositions of EVA. The two

polymers are assumed to be largely incompatible. PVC and EVA form

48

separate phases and may be molecularly dissolved only to a very small

extent. Small amounts of EVA polymer (addition of 5 5%) could be

dissolved in the PVC enclosed in voids or adsorbed on certain surfaces

of the PVC grains. Monteiro and ~haumaturgo'" used viscometry

studies to chatacterise the miscibihty behaviour of PVClEVA blends

with various vinyl acetate content and reported that PVClEVA

mixtures from EVAs with 45 to 70% vinyl acetate content may be

considered miscible.

Nuclear magnetic resonance (NMR)~' data on blends based on a

copolymer of 45% vinyl acetate content indicated partial miscibility

and the extent of miscibility was very much dependent on sample

preparation conditions.

Terpolymers of ethylene vinyl acetatelsulphur dioxide have been

shown to exhibit miscibihty with PVC over the entire composition

range by Hickman and Ikeda '". Sulphur dioxide incorporation allowed

the utihzation of much higher concentrations of ethylene in the

terpolymer than in EVA copolymer while still maintaining miscibility

with PVC. Similar results were noted by Robeson and McGrath13%th

terpolymers of ethylene vinyl acetatelcarbon monoxide and ethylene

ethyl acrylatetcarbon monoxide. With ethylene ethyl acrylate copoly-

mers, it was noted that no copolymer composition exhibited miscibility

with PVC. However, as low as 5 wt% carbon monoxide in the

terpolymer yielded miscible blends with PVC. As with the ethylene

vinyl acetate/S02 terpolymers, a broad range of terpolymer compo-

sitions was observed to be miscible with PVC. These results were

believed to be due to the specific interaction of the carbonyl group of

the terpolymer with the a-hydrogen of poly (vinyl chloride). The

interaction was classified as a weak 'acid-base' type where PVC

represented the proton donor and the terpolymer carbonyl represents

the proton acceptor. This interaction, although weak, allowed a large

variation in the composition of the terpolymer with retention of

miscibility with PVC.

1.7.3 PVCIPCL blends

Poly (E-caprolactone) (PCL) was reported by Koleske and

~ u n d b e r ~ ' " to be miscible with PVC over the entire composition range.

In fact, the Tg-composition data were used to determine the Tg of

amorphous PCL by extrapolation of the amorphous blend data to 100%

PCL. Crystallization kinetics of PCL in PCL-PVC blends were reported 123 . by ~obeson'". Olabisi investigated the PCL-PVC blends using

solvent probes by inverse gas chromatography technique. The

experimental data allowed for estimation of the interaction parameter

for PCL and PVC which prehcted miscibihty based on its negative

value. Khambatta et al . I3 ' studied the morphology of these blends

using small angle X-ray and light scattering.

1.7.4 PVCIPMMA blends

The effect of tacticity of poly (methyl methacrylate) (PMMA) on

its miscibility with PVC was studied by Schurer et al.'"". From their

s tuhes, it was concluded that the isotactic (i-) PhiIMA and PVC formed

an immiscible system with phase separation between two phases, and

50

two different Tgs were found over the entire composition range. One

phase was rich in PVC and the other in i-PMMA. On the contrary, the

Tg of syndiotactic (s) PMMA and PVC blends increased regularly with

composition upto 60 wt% s-PMMA. At higher s-PMMA contents, this

Tg did not change any more but was accompanied by a second Tg above

120°C indicating the value of pure s-PMMA. These results indicated

that a miscible system was formed up to 60wt% s-PMMA. Beyond

this concentration, a higher PMMA blend showed a separate phase

representing the excess pure s-PMMA.

The e ~ p l a n a t i o n ' ~ ~ of the variation comes from structural

Merences. Isotactic PMMA has a helical conformation while synho-

tactic PMMA possesses a planar structure. The helical structure makes

the ester groups less accessible to intermolecular interactions. Since the

microstructure of commercial atactic PMMA is much more syndiotactic

than isotactic, it is understandable that blends of an a-PMMA with

PVC give nearby the same DSC and dynamic mechanical results as

blends of S-PMMA do, and the blend should be considered a miscible

one.

1.7.5 PVCIPU blends

Blends of polyurethane and poly (vinyl chloride) (PUIPVC) have

been studiedI4'. PUPVC polymer blends offer increased flexibility,

abrasion resistance, tensile strength, impact strength, fire retardance14'

and acoustic damping1":'. They can be used as foams, elastomers,

coatings, adhesives and plastics. It was reported that PCL based

polyurethanes were miscible with PVC at all compositions over a broad, 51

temperature range144. The miscibility is most likely due to the hydrogen

bonding between the ester group in PCL and the a- H (H-C-C1) in PVC.

On a broader basis, there is evidence to suggest that polyether based

urethanes are more miscible with PVC than similar polyester based

polyurethanes143. This suggestion is based on thermal analysis which

yielded a single Tg.

1.7.6 PVCICPE blends

Chlorinated polyethylene (CPE) is structurally similar to PVC

with the only difference in chlorine content. The compatibility is

dependent upon the chlorine content and the distribution of the

chlorine atoms on the polyethylene back bone. Polymers containing

less than 25% C1 are incompatible with PVC. Those with 24-40% C1 are

the best impact modifiers having practical miscibility'45. CPE having

42 wt% C1 was found to be miscible with PVC with a lower critical

solution temperature b e h a v i ~ u r ' ~ ~ .

Xu et ~111~' stuhed binary blends of PVC, CPE, high density

polyethylene (HDPE) and low density poly ethylene (LDPE). They

concluded that CPE increased the impact strength of PVC.

1.7.7. PVC/ a - methyl styrene based polymer blends

Several high Tg polymers based on a-methyl styrene exhibit

miscibdity with P V C . ~ ~ Shur and ~ a n b ~ ' ~ ' reported on blends of PVC

with ABS. Using a series of experimental methods for characterisation

of these blends, they concluded that the styrene-acrylonitrile matrix of

ABS was miscible with PVC. However, other investigators have

reported two phase behaviour of styrene acrylonitile and PvCI4'.

Studies of Huarng et al." have shown that PVClSAN blends are

partially miscible depenhng on composition.

1.8 COMPATIBILISATION OF IMMISCIBLE BINARY

POLYMER BLENDS

Most pairs of high molecular weight polymers are incompa- tible150.152 . They have high interfacial tension and poor adhesion

between the phases. As a consequence of this they often exhibit poor

mechanical properties. This problem can be alleviated by the addition

or the in situ formation of a compatiblliser.

The use of block or graft copolymers as compatibilisers in binary

polymer blends has been well studied 5.153-157 . The choice of a block or

graft copolymer as compatibiliser is based on the miscibility or

reactivity of its segments with atleast one of the blend components. A

properly chosen block or graft copolymer preferentially locates at the

interface between the two immiscible phases. As pointed out by ~ a u l ' ,

this type of surface activity should reduce the interfacial energy

between the phases, permit a finer dispersion during mixing, provide a

measure of stability against gross segregation and result in improved

interfacial adhesion.

1.8.1 Addition of block copolymers for compatibilisation

Several s tuhes have been reported on the compatibilising action

of block copolymers in heterogeneous polymer systems. Molau and Co-

worker 155-157 demonstrated the ability of block copolymers to emulsify

polymer dispersions in solutions.

Inoue et a1.15%eported on the mechanism of domain formation

on a ternary system consisting of PS/poly(styrene- b- isoprene)/

polyisoprene. The domain structure was investigated by light and

electron microscopies using an osmium tetroxide fixation technique.

They concluded that when the molecular weight of the homopolymer is

much higher than that of the corresponding arm of the copolymer, the

block copolymer can no longer act as an emulsifier. Riess and Co-

workers 159,160 found that block copolymers are more effective than graft

copolymers i n increasing the compatibility of polystyrenelpoly (methyl

methacrylate) (PSIPMMA) and PSI polyisoprene blends. In these

studies the compatibility was monitored by the degree of optical trans-

parency of thin f lms cast from various solutions. These authors also

reported that the best compatibihsing action is obtained with a block

copolymer whose composition is 50:50 and whose molecular weight is

higher than those of the homopolymers. They found that &blocks were

more efficient than triblocks.

Gailard et al.'" have examined the surface activity of copoly-

mers by studying the interfacial tension reduction in demixed polymer

solutions. Addition of poly (styrene-b-butahene) to PS/polybutahene/

styrene ternary system showed first a characteristic decrease in inter-

54

facial tension followed by a levelling off. Several additional studies in

the area of compatibilisation of binary blends by the addition of

162-164 copolymers have also been reported . For example, the studies of

Coumans et al.'" and Paul and CO-workersIG3 deal with the emulsi-

fication of heterogeneous polyethylene (PE)/PS blends by the addition of

block copolymers.

Teyssie and CO-workers'" observed a significant reduction in

the dispersed phase size and an increase in interfacial adhesion as a

result of melt 'blending PE and PS with as little as 2 wt.% of poly

(butadiene-b-styrene). The copolymer also stabllised the system against

coalescence. Moreover Teyssie and CO- worker^"^ clearly demonstrated

that the copolymer is uniformly adsorbed a t the interface between the

two polymers.

LeiblerIG6 and Noolandi and Hong 167, 168 have proposed statistical

thermodynamic theories concerning the emulsifying effect of copoly-

mers. The theory of Leibler holds for nearly compatible systems,

whereas the theories of Noolandi and Hong 167.168 apply to the case of

highly incompatible systems, for concentrations below the critical

micelle concentration (CMC). Leiblerlti6 developed a mean field

formahsm to study the interfacial properties of mixtures of two

polymers, A and B, with an AB copolymer. ~ o o l a n d i ' ~ ~ reported that

both copolymer concentration and molecular weight are equally

important in reducing the interfacial tension. The locahsation of the

copolymer at the interface and the separation of the blocks into

corresponding homopolymer phases lead to various phenomena such as

the lowering of the interaction energy between the two immiscible

homopolymers, the broadening of the interface between the

homopolymers, the reduction in entropy of the system, a decrease in the

energy of interaction of the two blocks with each other, and a large

decrease in the interaction energy of the oriented blocks with

homopolymers. The sum of all these contributions should be considered

to determine the effect of copolymers on the surface tension between

the two phases'".

169 . Thomas and Prud' homme investigated quantitatively the

effect of molecular weight, composition and concentration of &block

copolymer of PS and PMlMA on the morphology of PSPMMA binary

blends. A sharp decrease in dispersed phase dimension was observed

with the addition of a few percent of block copolymer having equal

segment mass (50150 PSIPMMA), followed by a levelling off as the

copolymer content was increased above the critical micelle concen-

tration. For concentrations below the critical value, the particle size

reduction is linear with copolymer volume fraction. The experimental

results were in agreement with the prehctions of Noolanh and

on^'".

Chen et a1.I7O examined the compatibilising effect of block copoly-

mers on various binary systems like PEIPS, PEI Nylon-6, PS/Nylon-6

and polystyrenelpoly (ethylene terephthalate).

1.8.2 Addition of graft copolymers for compatibilisation

Adhtion of graft copolymer was reported as a means of impro-

ving the properties of high impact polystyrene (PS), poly (acrylonitrile-

171,172 co- butahene-co-styrene) (ABS) and PSPE blends . The decrease of

particle size of the hspersed phase upon the addition of graft copolymer

was substantiated by optical and electron microscopies. Chen et al.'73

studied the effect of added graft copolymers, on compatibilisation of

nylons with polyethylenes and polystyrene. They found that the

tendency of the melts to coalesce is decreased by the addition of maleic

anhydride graft polypropylene. (MA-g-PP)

Heino and ~ e ~ ~ a l a ' ~ ~ stuhed the compatibilising effect of maleic

anhydride grafted polypropylene, (PP-g-MA) and a reactive ethylene

based terpolymer on blends of polypropylene and an aromatic polyester-

type thermotropic main-chain liquid crystalline polymer. It was found

that the PP-g-MA compatibfiser h d not improve the impact strength

of PPLCP polymer blends. But clear enhancement in tensile strength

and elastic modulus was found.

1.8.3 Reactive compatibilisation

1.8.3.1 In situ formed copolymers

Recently the in situ formed compatibihsation in polyblends has

attracted great attention as an alternative to replace the conventional

block or graft copolymers. Ide and ~ a s e g a w a ' ~ ~ studied the use of

maleic anhydride modified isotactic polypropylene (ipp) in iPP-nylon 6

blends. During the melt mixing process, the anhydride groups react

57

with the amino end groups of nylon to yield a graft copolymer. HIPS

and ABS'"%~~ the classical examples of systems compatibilised by

block or graft copolymers formed through free radical reactions in situ.

Saleem and ~ a k e r ' " compared the compatibilising action of

in sit;u formed copolymer of polystyrene having oxazoline reactive

groups (OPS), polyethylene with carboxylic acid groups (CPE) and a

preblended graft copolymer of OPS-g-CPE in PSPE blends. The

preblended graft copolymer OPS-g-CPE imparts compatibility to PS-PE

blend but not effectively. They suggested that the addition of OPS and

CPE during melt mixing of PS and PE forms OPS-g-CPE polymer at

the interface and that these ingradients act as in situ reactive

compatibilisers and thus improve physical properties.

The in situ compatibilised polymer blends involving the reactive

glycidyl methacrylate (GMA) monomer have become important because

of the versatile application in many blenhng systems1"*.

Maa and changl"' used styrene-glycidyl methacrylate (SG) as in

situ compatibhser for the blends of poly (ethylene terephthalate) (PET)

and polystyrene (PS). The copolymer contains reactive epoxy functional

groups that are able to react with PET end groups (-OH and - COOH)

under melt conditions to form SG graft PET copolymer. The presence of

small amount of phosphonium catalyst (200PPM) accelerates the graft

reaction and results in a better compatiblised blend. The compatibllised

PETPS blend has a smaller phase domain and higher viscosity than

that of the correspondmg noncompatibllised blend. Mechanical

properties of the com&ibilised blends are superior to the correspon&ng

non compatibilised blend.

Nando and co- worker^.'^' studied the effect of the ethylene -

methacrylate copolymer as a chemical compatiblliser in the 50:50 blend

of low density polyethylene (LDPE) and poly (&methyl siloxane)

(PDMS). Ethylene - methacrylate (EMA) reacted with PDMS rubber

during melt mixing at 180°C to form EMA -grafted PDMS rubber (EMA

-g- PDMS) in situ which acted as a compatibihser in the LDPE -

PDMS rubber blend. The optimum amount of the compatibiliser ( E m )

was found t o be 6 wt% based on the results of dynamic mechanical

analysis, adhesion studles and phase morphology. Dynamic mechanical

analysis showed a single glass transition (Tg). X-ray diffraction

stu&es exhibited a remarkable increase in the degree of crystallinity.

The phase morphology showed a drastic reduction in the size of the

hspersed phase at the optimum concentration of E m .

1.8.3.2. Added reactive copolymer

Reactive copolymers of the type A-C may also compatibilise the

immiscible polymer pair A and B provided that C is capable of forming

a chemical reaction with B'". Although the non-reactive segment of

the copolymer has often a f e r e n t chemical and structural identity from

component A, i t may be capable of having miscibdity by specfic

interactions. ~ x a m ~ l e s ' ~ ' of added reactive copolymers as compati-

biliser include poly (styrene-co-acrylonitrile) (SAN)/maleic anhydride

for the system ABSIpolyamide 6 @A6) and poly ethylene-co-propylene

elastomer (EPM)/maleic anhydnde for the system PPIpoly amide 6.

(PA61

1.8.4 Homopolymers as compatibilisers

From the practical view point the ternary systems offer the possi-

bility of extending the list of miscible or mechanically compatible

blends as practised in utilising scrap or recycled plastic material.

Kwei and CO-workers182 conducted the first systematic study of

a miscible blend involving poly(methy1 methacrylate) (PMMA)lpoly

(ethyl methacrylate) (PEMA) compatibilised with poly (vinylidene

fluoride) (F'VDF2).

Paul and CO-workersJs3 reported on the compatibilisation of

polaarbonate (PC)/SAN using aliphatic polyesters. Ternary blends

comprising polycarbonate, styrene acrylonitrile copolymer and a

polyester of either poly (1,4-butylene adipate) (PBA), poly(l,4 cyclo-

hexane &methyl succinate) (PCDS) or poly (E - caprolactone) (PCL),

were found to be miscible based on the presence of a single glass

transition temperature at many compositions. For all systems, the

addition of 1% by weight of polyester resulted in a miscible blend for

SANlPC ratios of 111 and 311 and a region of immiscibility was

generally observed for PC rich composition with low polyester content.

A thermodynamic analysis was attempted in which the melting point

depression of the PCL in the miscible region of the ternary and in the

miscible binary solutions with PC and SAN, respectively was used to

evaluate the binary interaction parameters associated with the heat of

60

mixing and to predict the locus of ternary compositions which mark the

boundary between miscible and multiphase behaviour.

Paul and CO-workersla4 further made an attempt to predict the

boundary between miscible and immiscible compositions using the

binary interaction parameter obtained from PCL melting point

depression in ternary blends comprising of bisphenol - A polycarbonate

(PC), the polyhydroxy ether of bisphenol - A phenoxy and poly

(E-caprolactone) CPCL). In this case the interaction parameters were

used to calculate the locus of composition for which the heat of mixing

is zero. The locus was found to agree well with the observed boundary

between miscible and multiphase behaviour in the ternary. It is

concluded that the phase behaviour of ternary blend is largely

determined by the same enthalpic considerations known to govern the

phase behaviour of binary blends.

The phase equilibrium behaviour of a more complex system, poly

(vinyl chloride)(PVC)/styrene acrylonitrile copolymer (SAN)/ poly

(methyl methacrylate) (PMhL4) has been studied by Huarng, Min and

~ h i t e " ~ . They made a ternary phase diagram for the PVCISANIPMMA

system by both turbidimetry and DSC measurements. Miscibility was

investigated using a combination of turbidity, scanning electron micro-

scopy [SEMI and Merential scanning calorimetry experiments. PMMA

was found to be a good choice to add to PVCISAN blends to induce

miscibility.

White and Co-workers 28 have reported the miscibility behaviour

of binary and ternary blends of poly (vinyl chloride) (PVC), polycapro- 61

lactone (PCL) and styrene acrylonitrile copolymer using differential

scanning calorimetry (DSC) and turbidity techniques. PCLlPVC and

PCLISAN are largely miscible systems while PVCISAN is immiscible.

The ternary system shows considerable miscibihty. The blends are

characterised by polarised light microscopy and wide angle X-ray

diffraction. The former measurements characterise the structure of the

spherulites. Adchtion of PVC, SAN or PVCISAN causes the spherulites

observed in PCL to grow in size and become coarse. Melting point

depression measurements were used to calculate the Flory interaction

parameters x for PCLIPVC and PCLISAN blends.

The phase behaviour and morphology of a ternary blend

consisting of polystyrene (PS), bisphenol A polycarbonate PC) and

tetramethyl bisphenol A polycarbonate (TMPC) were investigated by

thermal and mechanical analysis and transmission electron micro-

s ~ o p ~ ' ~ ~ . It is shown that the TMPC, which is miscible with each of the

other components of the blend, does not solubllise the two immiscible

polymers, PS and PC. Two glass transition temperatures are observed

for most of the blend compositions. Based on the predictions of

~ o m ~ a " ~ , Zeman and ~atterson'" and Su and ~r ied" ' , Landry et al!"

developed a simple schematic hagram (Fig. 1.7) to represent the

various morphologies.

Structure type Miscibhty Examples

Figure 1.7. Basic phase structure types that may occur for a blend of three

high-molecular weight polymers,

In Figure 1.7, structure type I represents the simple case where

all the binary blends are immiscible ( x i j > 0). Three phases will thus

be present each consisting of the pure component. Many ternary

blends show this type of morphology. Structure type 2 and 3 occur

when two of the binary blends are either miscible ( ~ i j '0) or partially

miscible ( ~ i j ~ o ) , and the third pair is immiscible (~ij>o). Thus

depending on the relative x values and the symmetry of the system (a

symmetry system is one in which the ~ i j values of two or three of the

pairs are similar to each other in magnitude and sign.) the ternary

blend may separate iC to either two phases (type 3) or three phases

(type 2). The glass transition temperature will be shifted relative to

those of the pure components. Single phase compositions may also

occur. When AB and BC are miscible, but CA is marginally miscible or

immiscible (type 3) phase separation is predicted11' to occur in a

manner that preserves the most energetically favourable pair

interactions. Also, symmetry xAB = xBC favours miscibility. In some

cases component B may act as a compatibihser for component A and C.

Su and ~ r i e d ' " prehcted that the compatibiliser would be effective

only when the base blend is marginally immiscible (xCA>o). The

ternary blend of poly (ethyl methacrylate) (PEMA), poly (methyl

methacrylate) (PML\L4) and poly (vinylidene fluoride) (PVDF) s tuhed

by Kwei et a ~ . ' * ~ is an example of a symmetric system of type 3 where

PVDF acts as a compatibiliser for PEMA and PMMA to produce a

single-phase ternary blend over a wide range of composition. Two -

phases are observed at low PVDF concentrations.

Finally structure type 4 occurs when all thlee pairs of polymers

are miscible. If all three x i values are similar in magnitude (symme-

tric) then a single phase wdl be obtained. The ternary blend (PS/PC/

TMPC)'*"~~IS into structure type 3. In this case single phases are

obtained only at very high TMPC content. It has been found that the

relative molecular weights of the polymers have a considerable effect

on the phase diagram of the ternary blend.

Kalfoglou and CO-workers1*' tried to compatibihse the immi-

scible blends of chlorinated polyethylene (CPE) and poly (vinyl chloride)

(PVC) using epoxidised natural rubber (ENR). Based on the single glass

transition data the miscibility behaviour was studied. The ternary

blends were found to have good mechanical properties even at low

amounts of the compatibiliser.

Ternary blends were developed by melt mixing up to 30% poly

(butylene terephthalate) (PBT) with poly carbonate (PC) and phenoxy

in an attempt to improve the miscibhty of the PCIphenoxy binary

blend'". Although most of the blends with a PBT content higher than

10% appeared as transparent, two Tgs appeared at all the blend

compositions. These Tgs correspond to PC-rich and phenoxy rich

phases.

191 Young and Lee used poly (E-caprolactone) (PCL) to compati-

bilize polycarbonate (PC)/styrene acrylonitrile copolymer (SAN). The

improvement of compatibility was confirmed by mechanical properties

and morphology. Tensile strength showed maximum while impact

strength and elongation at break increased with increasing PCL 65

content in the blend. The domain size decreased with increasing PCL

content. Addition of PCL to the PCISAN blends increased the light

transmittance of the blends due to improved compatibility. At higher

concentrations of PCL light transmission decreased because of crysta-

llisation of PCL and PC in the blend.

Perrin and ~ r u d ' h o m m e ' ~ investigated the miscibility behaviour

of ternary poly(viny1 chloride)/poly(n-propyl methacrylate)/ poly

(n-amyl methacrylate) (PVCIPPMAIPAMA) and poly(viny1 chloride)/

poly (n-butyl methacry1ate)lpoly (n-amyl methacrylate) (PVCPBMAI

PAMA) blends by merent ia l scanning calorimetry. In both systems, a

binary mixture of the two polymethacrylates is totally immiscible

(PPMA with PAMA),(and PBMA with PAMA). For PVCPPMAPAMA

blends containing less than 70% PVC, the immiscible phase consists of

two coexisting binary PVCIPPMA and PVCPAMA phases. For an equal

amount of the two polymethacrylates in the ternary blend, the PVCI

PPMA phase contains 65% of the total weight of PVC and the whole

quantity of PPMA. The total amount of PAMA mixes with the remai-

ning 35% PVC to form the PVCPAMA phase. In contrast, the miscibi-

lity zone is predominant in the ternary P V C P B W A M A system,

since blends containing 30% or more of PVC exhibit a single glass

transition temperature. In the immiscible zone, the PVC is distributed

equally between PBMA and PAMA, which is in contrast to the 65-35%

distribution found in the previous system.

Another interesting work on miscible ternary blend is due to

Pomposo et a l . I g 3 They used poly (p-vinyl phenol) (PVPh) to compatibi-

lise immiscible blends of poly (methyl methacry1ate)lpoly (ethyl metha-

crylate). The assessment of miscibility was based mainly on the

presence of a single glass transition temperature. In this ternary blend,

PVPh is miscible with PMMA and PEMA. More than 60 weight

percent PVPh was required to cause miscibility between PMlMA and

PEMA. Based on the glass transition temperature data, a ternary phase

diagram was constructed. The miscibihty behaviour of the ternary

PMMAIPEWVPh blends as well as of the P W E M A I poly

(vinylidene fluoride) (PIT2) and PMMAPEMAlpoly(styrene-co- acrylo-

nitrile) (SAN) systems were rationahsed using the spinodal condition

and the Flory- .Huggins theory.

Machado and ~ee'"%sed PMMA to compatibilise four immis-

cible blend systems, styrene-maleic anhydridelstyrene-acrylonitrile

( S W SAN), styrene-maleic anhydridelacrylonitrile-butahene-styrene

(SMAI ABS), poly (vinylidene fluoride)/styrene acrylonitrile (PVF2/SAN)

and PWzl ABS. PMMA is miscible with each blend component. In

every case, the adhtion of PMMA led to the improvement of properties

such as tensile strength, tensile elongation and notched impact

strength. Further more, the addition of PMMA resulted in finer, more

uniform dispersion of the primary blend components.

Carty and whiteIg5 found that incorporation of polypropylene

into the ABSIPVC system has signficant effects on flammabihty and

smoke density. Recently Valenza and ~cierno'"' s tuhed ternary blends

of poly propylenelnylon-12lfunctionalized polypropylene. The effects of

addition of modified polypropylenes (one func t ionbed with maleic

anhydride and the other with acrylic acid) to blends of nylon 12 and

polypropylene were studied by considering morphological, thermal,

rheological and mechanical properties. The thermal property data

indicated that both the moddied polypropylenes influence the

crystallisation behaviour of the PP causing different shdts of the peaks

and lowering the crystallisation enthalpy. The differences between the

two modi£ied PPs also correspond to difference in the morphology. In

tensile measurements, yielding phenomenon was observed.

AIM AND SCOPE OF THE INVESTIGATION

The purpose of the study is to prepare novel class of miscible

ternary blends of PVC, EVA AND SAN (PVCIEVAISAN) by

compatibilising the immiscible pair EVMAN using PVC as a

compatibiliser. In this study, we selected PVC owing to its inherent

flame retardancy, chemical resistance, versatility, low cost and

capability to interact with other polymers. But without modification

processabAty, heat stability and impact strength of PVC are poor.

However conventional low molecular weight additives like plasticisers,

lubricants, stabilisers and other additives are usually used to attain

these properties. But these additives have an adverse effect on flame

retardant properties. Therefore a novel attempt has been made to

increase the processability, impact strength, thermal stability and

smoke characteristics of PVC by blending i t with EVA. Interestingly,

EVA copolymer is reported to have good smoke supprasant characte-

ristics. For applications like wire and cable insulation, the blend

formulation should have good mechnical properties. In view of this,

PVCBVA blend can be added with the SAN copolymers which possess

excellent tensile,tear and wear properties. Thus by preparing ternary

blends of PVC, EVA and SAN (PVCIEVAISAN) one can combine the

flame retardant properties of PVC, excellent low smoke characteristic of

EVA and superior tensile properties of SAN. Since PVC is miscible with

EVA and partially miscible with SAN, in these ternary blends, PVC

acts as an interfacial agent for the immiscible SANIEVA blend.

For the manlfestation of superior properties, miscibility of the

homopolymers is a requirement. Phase behaviour of the ternary blend

depends on the phase behaviour of binaries. Therefore it is important

to investigate the miscibhty characterstics and phase behaviour of both

binary and ternary blends. In view of this, various techniques have

been used to investigate the miscibility, phase separation and phase

behaviour of binary and ternary blends of PVC, EVA and SAN.

Infrared spectroscopy, DSC, TG, density, viscosity, microscopy (SEM

and optical) and flow characteristics have been used to analyse the

miscibhty. Heat of mixing and interaction parameters are also

calculated. Attempts have been made to correlate miscibility with

various other properties such as thermal stability, mechanical

properties and rheology. Study of blend morphology is important

because it relates the properties of the blend to the manner in which it

is processed. Therefore optical and scanning electron microscopic

techniques have been used t o study the morphology of the various

polymer blends. Optical microscopic studies of blends after phase

separation can clearly explain the mechanism of phase separation.

The LCST values have been used as a quantitative guide to the degree

of miscibhty in the binary and ternary blends.

Solution rheology stuhes provide a simple method to study the

flow behaviour of polymers and blends in solution which can be related

to solution processing of polymer blends. Solution rheology studies

can also give information about miscibility behaviour of polymer

blends. Therefore, the solution rheology of the blends has been

analysed.

70

Since these blends find potential applications in wire and cable

industry, various thermal and flammability characteristics such as

static thermal stability, smoke density, limiting oxygen index and

amount of volatile gas evolution have been assessed. It is expected that

by compounding this novel ternary polymer base matrix with various

additives such as acetyl tributyl citrate @lasticiser),DBTDL (stabiliser),

hydrated alumina (filler), ferrocene (pigment as well as smoke

supprasant) and stearic acid (lubricant) in controlled amount can give

rise to novel ternary blend formulations which can replace many of the

existing flame retardant polymeric compounds.

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