Twinning as a Fundamental Process in Polymer Crystal Orientation

Abstract

During a deformation experiment the chain molecules are orientated. The mechanisms of chains orientating producing the crystal orientation differ from orientating of chains within the amorphous phase. Some of them may be active. Twinning processes changing the c-axis direction within the crystallites are possible. They rotate the crystal lattice and change the shape of crystals. This explains easily numerous observed properties previously described in literature. Twinning modes of the orthorhombic and the monoclinic crystal modification of polyethylene, which are believed to be involved, are discussed. Twinning processes observed macroscopically by deforming single crystals of poly(diacetylene), will be of universal importance during the deformation of semicrystalline polymers.

Key Words:

• Twinning
• Deformation
• chain orientation
• yield stress
• polyethylene.