Fabrication of Lightweight Polyphenylene Oxide/High‐Impact Polystyrene Composite Bead Foam Parts via In‐Mold Foaming and Molding Technology

Bead foam is one kind of important polymeric foam product, which has the advantages of complex product shape, a wide range of parts density, and a wide variety of available materials. Steam-chest molding is usually used to prepare bead foams. However, it is challenging to prepare polymers with high melting point (T m) or glass transition temperature (T g). Herein, in-mold foaming and molding technology (IMFM) is proposed to prepare bead foams from polyphenylene oxide/high-impact polystyrene composite (PHC). PHC bead foam parts (PHCPs) with densities from 0.11 to 0.25 g cm−3 are successfully prepared by controlling the process parameters. Due to good interbead bonding, the bead foams have superior mechanical properties. The tensile and compression strength for PHCPs with a density of 0.25 g cm−3 are 2.84 and 2.93 MPa, respectively. The PHCPs also show high dimensional stability at 120 °C and good flame-retardant properties, characterized by a high limiting oxygen index (LOI) value and HBF rating. In addition, the fabrication mechanism behind IMFM is proposed. This technology provides a new way to produce polymer bead foams, especially for engineering materials.