Interfacial Strengthening in Polypropylene/Maleic Anhydride-Grafted Polyolefin Laminate Films through Chain Interdiffusion and Partial Cocrystallization

High Resolution Image Download MS PowerPoint Slide Elucidating the comprehensive molecular-level adhesion mechanisms of polypropylene (PP), a material that is inherently difficult to bond to other polymers, is of pivotal importance for designing and fabricating advanced multilayer composites. To address this challenge, we investigated the interfacial adhesive strength of PP/maleic anhydride-grafted propylene-1-butene copolymer (POgMA) laminate films and analyzed the molecular structure at their interface. The interfacial fracture toughness and fracture surfaces of PP/POgMA laminates hot-pressed at various temperatures were evaluated by double cantilever beam testing and X-ray photoelectron spectroscopy. The interfacial fracture toughness increased with increasing hot-pressing temperature, and cohesive failure within the POgMA layer was observed in samples processed above the melting point of PP. Atomic force microscopy-based infrared spectroscopy mapping and scanning transmission electron microscopy revealed that samples hot-pressed above the PP melting point form a thicker interfacial layer with a characteristic lamellar structure, in contrast to those processed below the melting point. Wide-angle X-ray diffraction measurements and molecular mechanics simulations further suggested that POgMA chains are incorporated into the PP crystal lattice, indicating the occurrence of partial cocrystallization between PP and POgMA. These results demonstrate that the formation of an interfacial layer through chain diffusion and partial cocrystallization contributes to the interfacial adhesive strength of PP/POgMA laminates.