to deform plastically. Crystalline regions of the polymer are linked by the amorphous regions. Tie molecules prevent the amorphous and crystalline phases from separating under an applied load. When a tensile stress is applied the semi-crystalline polymer first deforms elastically. While the crystalline regions remain unaffected by the applied stress, the molecular chains of the amorphous phase stretch. Then yielding, which signifies the onset of plastic deformation of the crystalline regions, occurs.

The molecular mechanism for semi-crystalline