INFLUENCE OF MECHANICAL VITRIFICATION ON FLEXIBLE-CHAIN POLYMER DRAWING PROCESS

Factors, responsible for orientation interruption and polymer fracture under drawing are discussed in terms of molecular mobility. Mechanica l vitrification, i.e. inhibition of micro-Brownian motion of chains du ring 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 diffe rent temperatures. Stretching results in the growth of virtual glass t ransition temperature and thereby in a dramatic deterioration in draw conditions. A simple theoretical model was used to describe the molecu lar dynamic processes in polymer under load. In this model nonvitrifie d regions of polymer were considered as the Newton liquid whose weight fraction was equal to the mobile fraction measured by NMR. The equati on to describe the dynamics of the orientation process was proposed an d specifically solved for nylon-6. The obtained diagrams enable one to choose optimal conditions for drawing. Instances when the draw proces s should he carried out in two or more steps are discussed.