Fundamental influences of propylene‐based elastomer on the foaming properties of high melt strength polypropylene based on extrusion foaming

High melt strength polypropylene (HMS‐PP)/propylene‐based elastomer (PBE) microcellular foams were prepared by the extrusion foam method. The fundamental mechanism of PBE improving the foaming properties of HMS‐PP was investigated. PBE 6102, with a low melt flow rate and high ethylene content, enables HMS‐PP/PBE blends to form a microphase‐separated structure and maintain good melt strength and pronounced strain hardening, which would promote cell nucleation and hold cell structure at relatively high temperatures. Furthermore, PBE 6102 postpones HMS‐PP crystallization and decreases the optimum foaming temperature, which helps balance melt elasticity and viscosity near the foaming window to avoid cell rupturing and merging. The introduction of PBE 6102 does not reduce the crystallization rate of HMS‐PP nor the crystallinity of the foamed samples, fixing the cell structure to prevent collapse during the cell solidification stage. Microcellular HMS‐PP/PBE 6102 foams with a high expansion ratio, small cell size, and large cell count were successfully fabricated.