Large-scale fabrication of lightweight, tough polypropylene/carbon black composite foams as broadband microwave absorbers

Abstract

Polypropylene (PP)/carbon black (CB) composite beads were expanded using subcritical CO2 as a blowing agent via a bath-foaming process, and high expansion ratios of 11–25 were achieved by the beads even when the content of CB reached to 30 wt%. The resultant foaming beads were further processed by steam-chest molding, resulting in the PPCB foam sheets with low density, excellent compressive strength and tensile toughness. More importantly, the PP composite foams with 20 and 25 wt% CB exhibited ultralow reflection loss (RL) values of −39.3 and −60 dB over the frequency range of 1.72–18 GHz, as well as two effective bandwidths (RL < −10 dB) of 11 and 15 GHz, respectively. These results make our tough PPCB foams very promising in the large-scale fabrication of lightweight and broadband microwave absorbers for practical applications like MA pyramid or antenna.