Low-Shrinkage Thermoplastic Polyamide Elastomer Foam Prepared by Microcellular Foaming With CO2 and N2 Co-Blowing Agent

Thermoplastic polyamide elastomer (TPAE) foams possess the advantages of lightweightness and high resilience, which can be widely used in footwear and sports equipment. Nevertheless, like other thermoplastic elastomers, TPAE foams prepared with supercritical CO₂ as a blowing agent exhibit serious shrinkage problems. This results in a low and unstable expansion ratio, which significantly restricts industrialized application. Therefore, this paper proposes the method of using a CO₂ and N₂ co-blowing agent for microcellular foaming, which effectively addresses the shrinkage problem of TPAE foams. Firstly, the solubility of pure gas blowing agents (CO₂ and N₂) and CO₂ and N₂ co-blowing agent in TPAE is determined and the theoretical formula of solubility is deduced. Subsequently, the effects of the blowing agents on the foaming and shrinkage behaviors of TPAE are investigated. The findings indicate that the diffusion rate of N₂ is nearly equivalent to that of air, which retards the shrinkage process of the foam. Furthermore, the introduction of N₂ reduces the growth driving force of the foam and reduces the probability of plastic deformation of the bubbles. When the N₂ content is approximately 20%–30%, TPAE foams with an expansion ratio of about 12 times and a shrinkage ratio as low as 10% can be prepared.