Microwave-Assisted Physical Foaming of Polymers: A Review

Over the past two decades, the use of microwaves for physical foaming of polymers has undergone significant advancements. Typically, the preparation of polymer foams during physical foaming relies on heat transfer heating, which results in temperature gradients and consumes significant time and energy. In contrast, microwave-assisted physical foaming offers a simple, convenient, fast, and cost-effective approach for obtaining polymer foams. These features render microwaves an alternative clean energy source that can replace or complement the conventional heating in various foaming processes. This review provides an overview of recent research on the application of microwaves to five different methods for preparing polymeric foams, namely batch foaming, bead foaming, steam foaming, salt immersion foaming, and 3D-printing. The study also highlights key challenges and opportunities for the development of microwave foaming processes and identifies potential areas for future research.