 Other stresses may be as a result of moulding pressures, extrusion orientation, thermal gradients during solidification and externally imparted stresses.Semi-crystalline polymers are more complex than amorphous polymers, since the crystalline regions are interspersed with amorphous regions.Amorphous regions in close association to the crystals or contain common molecules as tie molecules have less degrees of freedom than the bulk amorphous phase.