Composite bead foam with segregated structure for high EMI absorption characteristic by one-step foaming and sinter molding

Abstract

One-step foaming and sinter molding combined with supercritical CO₂ is a green process to sustainably prepare polymeric bead foam, and presents advantages of energy savings and zero wastewater discharge. Thermoplastic polyurethane (TPU) bead foam with excellent electromagnetic interference (EMI) shielding and superhydrophobicity was prepared by this process in the CO₂/water system. A suitable co-blowing agent content (1 wt% water) and foaming temperature (130 °C) could balance the sintering effect of inter-beads and mechanical properties of the foamed product. The ball milling combined with the foaming process facilitated forming natural segregated structure and conductive network in TPU bead foam. When MWCNT content increased from 0 vol% to 0.49 vol%, the conductivity increased from 10⁻⁸ S/cm to 0.024 S/cm, and total electromagnetic shielding power (SE_T) increased from 1.0 dB to 22.8 dB. The distribution of MWCNT in reinforced phase combined with segregated structure further improved the EMI shielding and conductivity. When MWCNT content further increased to 2.96 vol%, SE_T and conductivity enhanced to 41.8 dB and 0.2 S/cm, respectively.