Thermal transitions and foaming of a rubbery polymer, poly(ethylene-co-vinyl acetate-co-carbon monoxide), in carbon dioxide: Temperature scaling as a new approach for rational selection of foaming conditions

Abstract

The foaming of a thermoplastic elastomer, poly(ethylene-co-vinyl acetate-co-carbon monoxide) with varying copolymer compositions was explored using CO2. Copolymers with 0, 10, and 20 wt% vinyl acetate and 10 wt% carbon monoxide, with the remainder being ethylene, designated as EVACO-0010, EVACO-1010, and EVACO-2010 were evaluated. Melting and crystallization temperatures and their depression in CO2 were determined using high-pressure torsional braid analysis. Sorption and swelling assessments were carried out using a modified magnetic suspension balance. Foaming experiments were conducted at 200 bar near the depressed melting and crystallization temperatures. Foams with low (< 0.2 g/cm3) bulk densities of EVACO-1010 and EVACO-2010 were generated near their crystallization temperatures in CO2. A new concept of scaling the foaming temperature with respect to the melting or the crystallization temperature of the polymer in carbon dioxide was developed which provides an insightful new approach for the rational selection of polymer foaming conditions.