History and background
- After the advent of atomic energy after WWII
- Found exposure of special thermoplastic formulation to high intensities of radiation led to cross linking.
- polymeric materials, which are cross linked either by irradiation, or by chemical means, such that when their temperature is raised beyond the normal base polymer crystalline melting point, they do not melt but merely become rubbery.
- if the material is then mechanically expanded and held in this position until the temperature falls below the crystalline melting point. It remains in the expanded state. Subsequent heating in an unconstraint state will then result in the material recovering or shrinking to its original extruded or moulded size and shape.