Fibrillar Geometry-Regulated Heterogeneous Bubble Nucleation in Compatibilized Long-Chain Branched Polypropylene/Thermoplastic Polyester Elastomer Foams

Polypropylene (PP) foams have attracted considerable interest for lightweight structural applications. Nevertheless, the intrinsically low melt strength of PP severely limits cellular structure regulation and, consequently, the mechanical performance of PP foams. In this study, thermoplastic polyester elastomer (TPEE) was incorporated into long-chain branched polypropylene (LCBPP) and transformed into oriented fibrils through cold drawing. Polyolefin elastomer grafted with glycidyl methacrylate (POE-g-GMA) was introduced as a compatibilizer to regulate the interfacial adhesion between LCBPP and TPEE, thereby tailoring the deformation, aspect ratio, and stability of the TPEE fibrils. Density functional theory (DFT) was further employed to elucidate CO2 enrichment and heterogeneous bubble nucleation at TPEE fibrillar interfaces. The theoretical results indicate that TPEE fibrils promote local CO2 enrichment and that elongated fibrillar morphology is more favorable for heterogeneous bubble nucleation. Foaming behavior was examined over a range of POE-g-GMA contents. The results indicate that the addition of 1 phr POE-g-GMA leads to the maximum fiber aspect ratio of 67 among the samples investigated, together with a reduced average cell size of 51.4 μm and an increase in cell density to 5.6 × 108 cells/cm3. Cyclic compression tests further reveal a marked improvement in the compressive performance, with the permanent deformation decreasing to 7.8%. This enhancement arises from compatibilizer-regulated interfacial adhesion and fibril morphology, which improve stress transfer and resistance to excessive cell growth, refine the cellular structure during foaming, and stabilize cell walls under compression, thereby enhancing recovery behavior. This study provides both experimental evidence and theoretical insight for the design of high-performance PP foams.