Influence of Mechanical Vitrification on Flexible-Chain Polymer Drawing Process

Abstract

Factors, responsible for orientation interruption and polymer fracture under drawing are discussed in terms of molecular mobility. Mechanical vitrification, i.e. inhibition of micro-Brownian motion of chains during deformation and especially under tensile stress is considered to be the main physical factor limiting orientation processes. Broad-line NMR was used to study molecular motion in stretched polymers at different temperatures. Stretching results in the growth of virtual glass transition temperature and thereby in a dramatic deterioration in draw conditions. A simple theoretical model was used to describe the molecular dynamic processes in polymer under load. In this model nonvitrified regions of polymer were considered as the Newton liquid whose weight fraction was equal to the mobile fraction measured by NMR. The equation to describe the dynamics of the orientation process was proposed and specifically solved for nylon-6. The obtained diagrams enable one to choose optimal conditions for drawing. Instances when the draw process should be carried out in two or more steps are discussed.

Key Words:

• Drawing
• molecular motion
• NMR
• mechanical vitrification.