physical and chemical properties of polymers, mechanical properties toughness, strength, elasticity,

1. PROPERTIES OF POLYMERS
BY
CH. SAI SRI RAMA CHANDRA
MURTHY

2. Properties of polymers:
Polymers possess both physical and mechanical properties.
Physical properties of polymers are:
1. Solubility
2. Effect of heat on polymer
3. Diffusion and permeability
Mechanical properties of polymers are:
1. Toughness
2. Strength
3. Elasticity

3. Physical properties:
1. Solubility:
When a polymer is dissolved in a suitable solvent, the polymer
absorbs water and swells in size. Slowly polymer goes into solution a
viscous polymer solution which is heterogeneous. Where as a non-
polymer like NaCl when added to water, ionizes and form homogeneous
solution. Like this polymer behave differently towards the solvents.

4. 2. Effect on heat on polymer:
At room temperature all polymers are solids existing in rubber or visco
elastic state. As the temperature increases the polymer melts and this is
called the melting point of the polymer (Tf) where the material exist in visco
fluid state. As the temperature further increases to boiling (Tb) the polymer
decomposes to monomers which are in vapour phase, they exist in solid and
liquid phase depending on the temperature. When the temperature is lowered
below zero degree and below zero degree a temperature comes where the
polymer becomes hard, brittle and glassy and the polymer behaves like glass.
This temperature is called glass transition temperature (Tg).

5. The polymer remains soft flexible and rubbery above Tg an below Tg the
polymer becomes hard brittle and glassy.
For Eg: Tg of Rubber = -73ºC
Glass state
(brittle)
Rubber
Visco elastic state
Degradation of
polymer to monomer
Viscofluid
state
Tg TbTfRoom
temperature
Temperature

6. 3. Diffusion and permeability:
Crystalline polymer resist diffusion of molecules through voids or
other gaps and tends to resist diffusion because of much greater degree of
molecule packing. The diffusion rates are higher in rubber.

7. Mechanical properties:
Polymers behave differently towards the following mechanical
properties.
1. Toughness:
The impact strength is measured as toughness. Below glass
transition temperature (Tg) the polymer break with a brittle
fracture and they become tougher when the temperature proceeds
from room temperature to Tg. The size of the crystalline structure
also determines the toughness. The small spherical crystalline
masses increases toughness.

8. 2. Strength:
The strength of polymer depends on the length of polymer chain,
branching or cross-liking which are controlled by elastomeric properties,
crystallinity and branching of chain. The strength of a polymer increases with
increase in molecular weight. The inter molecular forces of attraction,
presence of polar groups and chain length increases the strength of the
polymer.
Four types of stress-strain curves ( The line ends where the sample breaks)

9. • The strength of a polymer is determined by stress-strain test.
• Typical stress-strain curves for different types of polymers are explained.
• Crystalline region cannot contribute to increase in tensile strength, where as
amorphous region contribute to increase in tensile strength.
3. Elasticity:
Elasticity is the property of recovering original shape after the removal of
deforming stress. Natural rubber possess high elasticity due to coiled helix
structure of poly-isoprene.

10. THANK YOU