Foam-Foam composites from foam wastes. A way to evaluate properties of irregular variable-shape small reinforcing pieces via a foaming assembly process

The usual recycling methods for foam wastes result in the loss of the desirable porous structure of the raw material. To solve this, the present research work evaluates Foam-Foam composite panels as an innovative strategy to give a second use to end-of-life foams as foamed small pieces. These light and porous panels were successfully fabricated using macro-foamed fillers (the “small pieces” as reinforcement) and a polyurethane foaming resin that functioned as a very soft and adhesive assembling matrix. The reinforcement foams included chips of end-of-use thong sandals and extruded foamed rods (production waste polymers), which were employed separately, obtaining different foam-foam composite panels. Extruded foamed strands comprised either rigid thermoplastic foams (polymethyl methacrylate, PMMA) or soft thermoplastic elastomer foams (Pebax). Remarkably, this foaming assembly method allowed a random-like fabrication of reproducible composites containing high-volume fractions of reinforcement foam wastes, ranging from 30 % to 50 %. Results showed that such Foam-Foam panels exhibit predominantly the properties of the dispersed phase, even if the reinforcing lumps were highly heterogeneous in shape, size and orientation. Moreover, some mechanical properties (eg, compression modulus and strength, energy absorption, and rebound coefficient) displayed outstanding reproducibility. Some of these materials exhibited a very low thermal conductivity (0.032 W/m/K), suggesting their potential as thermal isolating panels. Therefore, it can be claimed that “foaming assembly” is an efficient way to introduce new types of Foam-Foam composites and to valorize any type of foam when they are only available as disparate or small pieces, i.e., scraps, crushed waste, extrusion rods/strands, plastic rushes, etc.