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Open‐cell, porous microcellular foams with nanofibrillated structures were prepared from high tacticity isotactic polypropylene (i‐PP) with a crystal nucleating and gelling agent. The 1,3:2,4 bis‐O‐(4‐methylbenzylidene)‐d‐sorbitol gelling agent (Gel‐all MD) was used as the crystal nucleating and gelling agent, which enhanced the crystallization and gelation of i‐PP with a three‐dimensional network of highly connected nanofibrils. The core‐back foam injection molding technique was employed to foam the i‐PP with nitrogen (N2) at a high expansion ratio, where the crystal nucleating agent induced bubble nucleation and bubble growth in the inter‐lamella region and opened the cell walls with a nanoscale‐fibrillated structure. The effects of the nucleating agent on the open cell content (OCC), density and crystallinity were thoroughly investigated. We prepared open‐cell micro/nanocellular foams with an average cell size of microscale voids of < 5 μm. Nanometer‐scale fibrillated structures were formed on the cell wall of the microscale void, the expansion ratio was five‐fold and the open cell content was over 90%. POLYM. ENG. SCI., 54:2075–2085, 2014. © 2013 Society of Plastics Engineers

A new thermally expandable microcapsule was developed for use with foaming polypropylene (PP) by injection molding and extrusion processes at operating temperatures above 2008C. The microcapsule consists of a blowing agent as the core and a shell polymer. The rheological properties of the shell polymer were controlled by a crosslinking agent to design the expandability and shrinkage. The effects of rheological properties on the expandability and the surface appearance of foam products were thoroughly investigated. It was found that storage modulus G 0 and tan d significantly affected the expandability and shrinkage and were controllable through crosslinking polymerization. Visual observation of batch foaming, rheological measurement, and experiments of foam injection molding and extrusion elucidated the existence of the optimal degree of crosslinking that could realize more than 30% density reduction while maintaining a smooth surface at PP foam injection molding and extrusion. POLYM. ENG. SCI., 50:835-842,

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