Effect of calcium silicate on foaming and anti-shrinkage behavior of thermoplastic polyamide elastomers: Revelation of the open-cell mechanism

Abstract

Thermoplastic polyamide elastomer (TPAE)/calcium silicate (CaSiO₃) open-cell foam with low shrinkage and high expansion ratio was prepared by using supercritical CO₂ as a blowing agent. Adding CaSiO₃ led to increased melt viscoelasticity and reduced crystallinity of TPAE. The primary mechanism of CaSiO₃ promoting TPAE foam to form the open-cell structure was discussed. The interaction between CaSiO₃ and TPAE is fragile, making CaSiO₃ easy to fall off the cell wall and form the open-cell structure during foaming process. The increasing CaSiO₃ content leads to increased cell density and thinned cell walls, thus increasing the tensile stress on cell wall. On the other hand, the agglomeration of CaSiO₃ increases particle size, making it easier to fall off from the adhesion of TPAE matrix. The two aspects work together to improve the open-cell content of TPAE foam up to 93.28%. The open-cell structure is conducive to increasing the gas exchange rate and significantly decreasing foam shrinkage ratio. Finally, TPAE foam with a shrinkage ratio of only 2.68% and an expansion ratio of 18.77 times was obtained. In addition, open-cell structure improves the adsorption performance of TPAE/CaSiO₃ foam by 500%.