A nonequilibrium constitutive equation for tensile behavior of polyolefinic thermoplastic vulcanizates.

Polyolefinic thermoplastic vulcanizates (TPVs) composed of iPP (isotactic polypropylene) and crosslinked EPDM (ethylene-propylene-diene rubber) prepared by dynamic vulcanization process exhibit rubber domains dispersed in the iPP matrix, even though the EPDM component is the major component. Here we proposed a kinetic nonequilibrium constitutive equation that considers the transition of the mechanical nature from plasto-rigid deformation to rubbery deformation during uniaxial extension to explore the origin of the thermoplastic elastomer behavior of TPV (thermoplastic vulcanizate) materials. Fitting of the constitutive equation to the experimental stress‒strain curves quantitatively revealed the critical transition point of the mechanical properties. The transition shifted to higher strains with decreasing EPDM content. In situ wide-angle X-ray diffraction profiles monitored during the uniaxial extension confirmed the mechanical transition process. [Display omitted] • A nonequilibrium constitutive equation is analyzed for tensile behavior of TPV. • Mechanical transition is determined by in situ wide-angle X-ray diffraction. • Morphological feature under tension was identified by Takayanagi model. [ABSTRACT FROM AUTHOR]