Elastic properties of cast films from propylene elastomers

摘要

Propylene-rich ethylene-propylene copolymers (P-E elastomers) made using metallocene catalysts exhibit excellent elastic properties, including high elongation to break and low tension set, particularly when blended with polyethylene or polypropylene and then compression molded. During film casting, the orientation imposed on a P-E elastomer lowers the extensibility and elastic recovery of films prepared from either neat P-E or P-E blends. A reduction in elongation to break of P-E films, with or without blending, was found to correlate with an increase in planar birefringence. The presence of dispersed phases of PP or high density polyethylene in P-E blends, which are drawn into elongated ellipsoids aligned in the machine direction, further reduces the recovery of these P-E blends. This reduction in elastic recovery for films made from P-E blends with aligned ellipsoidal dispersions was attributed to strain amplification around the dispersed particles in accordance with finite element simulation results, and was directly related to the dispersion tip radius. Films from P-E elastomer blended with high density polyethylene (high interfacial tension) were demonstrated to have lower planar orientation in addition to reduced dispersion deformation, and, therefore, better elastic properties, versus films in which the P-E elastomer was blended with PP (low interfacial tension). (C) 2007 Wiley Periodicals, Inc.