chapter i - introduction

CHAPTER I

-

INTRODUCTION

Materials having

rubber

like

properties

at

room temperature

a r e called elastomers. Rubbers a r e macromolecular substances capable of passing, under the effect of vulcanisation,

from a predominantly

plastic state to a predominantly. elastic state. Rubbers have a glass transition

temperature

a r e used

and

randomly

agglomerated

introduced rubber

is

of

and

converted

into

the

long

temperature

a

When

technically

does not

Elasticity on

the

-

chemical

they

which a r e bonds

utilizable material, within a broad

dissolve

technological point 1 properties of rubber ;re important . 1.

From

which

which

are

molecules by vulcanisation, the raw

large r e v e r s i b l e deformations and

at

flexible molecules

entangled.

between neighbouring

temperature

solvents.

than

are composed

is capable of of

lower

of

but

only

view,

which range

swells

the

in

following

The a b i l i t y to undergo large, reversible deformation

application

of

relatively

small

stress.

The

flexibility

combined with elasticity is a characteristic property of rubber. 2.

Ability

to

accumulate a

considerable amount of

input

energy

during deformation, with low hysteresis. 3.

Considerable chemical resistance.

4.

Under suitable conditions. rubber has a long service life.

5.

Rubber

compounds

can

be

processed

operations to give different products. 6.

The products a r e relatively inexpensive.

by

relatively

simple

1.2

REASONS FOR BLENDING ELASTOMERS

In recent

years,

research and developmental activities in the

field of polymer science and technology have been concentrated more on the modification

of

existing polymeric materials rather than on

synthesizing new polymers. compositions

having

blending

of

on

basis

the

two

or of

the

required

properties

more

polymers.

All

their

relationship.

The

additivity of

properties.

mixed

with

most

another

The easiest method to develop polymer

-

property important

involves

materials

processing

concept

in

-

physical

attract interest cost-performance

polymer

blends

is

By t h i s we mean that when a polymer is

polymer,

the

resulting

blend

has a

property

which is the weighed average properties of the individual polymers. Modulus is one of additivity

such properties that is expected to obey some

relationship

2

.

For

blends

the

weighing functions of

composition will be sensitive to the morphology.

A very

possibility,

is

property.

although

less

frequently

observed,

the

intriguing

synergism

Here w e refer to a situation where some property,

in such

as tensile strength, for t h e blend is higher than that of the pure components. The success of a new material depends on several factors such a s combination of

properties and cost dilution.

For example.

when we blend a high thermal resistant polymer having poor processability thermal

with

another

stability,

the

polymer

having

resulting

blend

good processability and poor may

be

useful

for

certain