A review on physical foaming of thermoplastic and vulcanized elastomers

Elastomer foams have been widely used in many applications and have shown potential in some advanced fields because of their excellent flexibility. Elastomers foamed with a physical blowing agent solve the problems of traditional chemical foaming, endow elastomer foams with advantages of environmental-friendly features, uniform cell structure, adjustable material properties, and high processing efficiency. However, unlike foaming of thermoplastic materials, low matrix modulus and high gas diffusivity leads to serious foam post-foaming shrinkage and hinders the preparation of low density elastomer foams. In the past two decades, researchers have selected different elastomer systems and applied various foaming methods and strategies to prepare elastomer foams with improved performance through understanding the foaming mechanisms. This article reviews these investigations and discusses the developments made so far in physical foaming of elastomers.