Crystallization, Mechanical and Barrier Properties of PA6-66 Films under Constrained Uniaxial Stretching

Abstract

The polyamide 6-66 (PA6-66) films were prepared via extrusion film casting, followed by constrained uniaxial stretching (CUS) on a biaxial stretcher. It is revealed that the increasing of stretch ratio gave rise to increased crystallinity of PA6-66, indicating the presence of the strain-induced crystallization during stretching. The tensile strength of the PA6-66 films was both increased in the MD as the increasing of stretch ratio, accompanied by the decreasing of the elongation at break. This could be attributed to the orientation of the crystalline region and amorphous phase, giving rise to the highly aligned molecular chains and lamellae that may withstand high stress whereas present low flexibility. A monotonous decreased tendency of the permeability as increasing the stretch ratio was found for both water vapor and oxygen permeability. The increased crystallinity and the orientation of the crystal lamellae could be the primary reasons for the decrement of the gas permeability.