Creating orientated cellular structure in thermoplastic polyurethane through strong interfacial shear interaction and supercritical carbon dioxide foaming for largely improving the foam compression performance

Abstract

This work presented a novel strategy for enhancing foam compressive properties through structuring orientated cells introduced by combining barrier film and supercritical CO2 foaming. The low permeability and the strong interface bonding of barrier films were employed to hinder the CO2 escaping from thermoplastic polyurethane (TPU) surface and induce the bubble orientation growth, respectively. The compressive modulus and strength of TPU foamed with films constraints increased by as much as 355% and 121%, respectively, relative to the freely foamed counterparts. The polyimide (PI) films, which possessed higher bonding strength with TPU due to the molecular diffusion at the interface, could boost more cell nucleation, improve the cell uniformity and increase the orientation degree and compressive performance, compared to the poly(ethylene terephthalate) (PET) films. A modified constitutive model for assessing the compressive modulus of closed-cell foams was developed to uncover the positive effect of cell orientation on compressive behavior.