Confined batch foaming of semi-crystalline rubbery elastomers with carbon dioxide using a mold

Confined foaming of poly(ethylene-co-vinyl acetate-co-carbon monoxide) using carbon dioxide as a physical blowing agent in a mold with either permeable or impermeable boundaries has been explored as a strategy to control final foam dimensions and morphology. The results are discussed in terms of comparisons to free-foaming experiments conducted at the same pressure and temperature conditions following the same pressurization and depressurization paths. Foaming experiments were carried out at 30 and 40°C and 100, 200, and 300 bar followed by rapid depressurization of the foaming cell. Confined foaming led to smaller pores with more uniform distributions across the polymer cross-section. However, bulk foam densities of the foams generated under confinement were higher than those generated under the free-foaming mode. Surface characteristics and skin layer formation were altered by expansion against both the permeable and impermeable boundaries. Confined foaming promotes uniform pore distribution and overall dimensional uniformity and may impart surface texture but the trade-off is in the degree to which the bulk foam density can be lowered.