Stress–strain behavior of cold-drawn isotactic polypropylene subjected to various drawn histories

Abstract

Uniaxial tensile properties of cold-drawn isotactic polypropylenes (iPP) subjected to various drawn histories were investigated to elucidate the molecular origin of strain-hardening in the uniaxial stress–strain behavior of semicrystalline polymers. Two series of Ziegler–Natta catalyzed iPP with a wide range of crystallinities and metallocene catalyzed iPP with a wide range of molecular weights were used in this study. We propose a tie molecular model which assumes that tie-chains anchored in adjacent crystalline lamellae are expanded into tautness, and the taut tie-chains are pulled out from the crystalline lamellae within the lamellar units. On the basis of this model, we derive a universal constitutive equation for various cold-drawn iPPs subjected to various drawn histories.