Linear thermo-viscoelasticity of polypropylene

Observations are reported on isotactic polypropylene in tensile relaxation tests in a wide interval of temperatures (from 20 to 120 C) that Involves alpha- and beta-relaxation points Constitutive equations are derived for the linear viscoelastic response of sernicrystalline polymers A polymer is modeled as an equivalent transient network of chains whose rearrangement is governed by the Eyring equation with a fictive temperature The stress-strain relations involve four adjustable parameters that are found by fitting the experimental data It is demonstrated that (i) the dimensionless fictive temperature reaches its maximum at the alpha-relaxation point and (ii) the rate of rearrangement increases with temperature following the Arrhenius law outside the beta-relaxation region (C) 2010 Elsevier Ltd All rights reserved