Mechanical and rheological properties and CO2-foaming behavior of reactively modified TPEE with controlled chain entanglement

Abstract

Thermoplastic polyether ester elastomer (TPEE) foams can be fabricated using supercritical carbon dioxide (CO2) as an environment-friendly blowing agent. In this study, we investigated the effect of chain entanglement on the mechanical properties, viscoelasticity, and CO2-foaming behavior of TPEE. A series of branched TPEE samples with controlled chain entanglement were prepared by reactive extrusion using modifiers with epoxy groups. The gel-permeation chromatography–intrinsic viscosity (GPC-IV) methodology was employed to determine branch density. The junction point of chain entanglement was obtained; it increased at higher branch densities. The tensile behavior revealed that the branched TPEE samples became more rigid and poorer ductility, with stronger chain entanglement. Small-amplitude oscillation rheology showed enhanced shear thinning and zero-shear viscosity, reduced loss factor, and slower relaxation; these parameters indicated an improvement in linear viscoelasticity. Furthermore, nonlinear viscoelasticity was studied using elongational rheology, and the results were analyzed in combination with molecular stress function (MSF) model. The experimental results revealed that strain hardening was steeper with stronger chain entanglement, as proved by increasing value of free parameters fmax2 and β from MSF model. The reactively modified TPEE samples exhibited a larger expansion ratio than that of raw TPEE during the CO2-foaming process. Additionally, broader foaming temperature window to fabricate high-fold TPEE foams at CO2-foaming process enable the reactively modified TPEE to be used in the industrial production of TPEE foam with stable quality like bead and molded foaming.