A simple and efficient method for preparing high-expansion, low-shrinkage poly(ether-block-amide) foam

Abstract

Poly(ether-block-amide) (PEBA) is limited by its insufficient matrix strength and low melt viscoelasticity, which adversely affect its foaming performance and present significant challenges for preparing high performance PEBA foams. To overcome these limitations, this work introduces an epoxy chain extender KL-E4370B to modify PEBA via chain extension. The results demonstrate that the modified PEBA achieves a markedly higher branching degree, accompanied by a three order of magnitude increase in complex viscosity and storage modulus. These improvements elevate the expansion ratio from 22.05 to 26.82 and extend the foaming temperature window by 70 °C. However, the modification also leads to a decline in crystallinity performance, characterized by a 5.28 % reduction in crystallization temperature, a 13.07 % decrease in crystallinity, and a 34.62 % slowdown in crystallization rate. These changes lead to significant foam shrinkage, with a shrinkage rate of up to 83.59 % and a recovery rate as low as 21.66 %, which compromises dimensional stability. To address these issues, a secondary N₂ foaming assisted gas exchange method was implemented. This approach not only restores the expansion ratio of the shrunken foam but also surpasses the initial expansion ratio achieved by primary CO₂ foaming. Furthermore, increasing the saturation time or pressure enhances the solubility of N₂ in PEBA, thereby further improving the expansion ratio of foam. Ultimately, this study successfully fabricates a PEBA foam material with an expansion ratio of up to 44.17 and a shrinkage rate as low as 40 %. This work provides a simple and effective strategy for producing high-expansion, low-shrinkage thermoplastic elastomer foams.