The effect of annealing on the elastoplastic response of isotactic polypropylene

TL;DR

This study investigates how annealing at different temperatures affects the elastoplastic response of isotactic polypropylene through tensile tests and a developed constitutive model.

Contribution

It introduces a constitutive model for semicrystalline polymers that incorporates the effects of annealing on material constants.

Findings

Annealing alters the elastoplastic behavior of isotactic polypropylene.

The developed model accurately fits experimental stress-strain data.

Material constants vary systematically with annealing temperature.

Abstract

Four series of tensile loading-unloading tests are performed on isotactic polypropylene in the sub-yield domain of deformations at room temperature. In the first series, injection-molded specimens are used as produced, whereas in the other series the samples are annealed for 24 h at 120, 140 and 160 C, which covers the low-temperature region and an initial part of the high-temperature region of annealing temperatures. A constitutive model is developed for the elastoplastic behavior of a semicrystalline polymer. The stress-strain relations are determined by five adjustable parameters that are found by fitting the experimental data. The effect of annealing is analyzed on the material constants.