Development of thermoplastic foams with heterogeneous cellular structures for acoustic applications

Abstract

Manufacture of heterogeneous thermoplastic foams is of great interest to damp low frequency noise in transportation and building industries. Most of the fabrication methods reported either use cumbersome batch processes or produce foams that are not appropriate for sound absorption. In this context, this work aimed at manufacturing of thermoplastic acoustic foams with double porosity and graded porosity by processes that can potentially be scaled up for mass production Foams containing a combination of small cells and large cells were developed by foaming of a low melt strength polymer in presence of sodium bicarbonate and wollastonite. The same results were obtained by foaming a blend of a base polymer and a low melt strength polymer. Thermoplastic foams with graded porosity were fabricated by molding the samples under a temperature gradient before expanding them in a heating oven. For all these foams, sound absorption coefficient increased by about three times.