High-Temperature Tensile and Creep Behavior of Polypropylene/Poly(butylene terephthalate) Blends: Matrix Fibrillation and Interfacial Debonding

We investigated the deformation and tensile behavior of crystallized polypropylene (PP)/poly(butylene terephthalate) (PBT) blends across a wide range of PBT compositions. Low-PBT-content blends (100/1 and 100/3 PP/PBT) exhibited enhanced yield stresses at room temperature, as well as superior or comparable tensile ductility and creep resistance at 100 °C compared to neat PP. These improvements were driven by robust interfacial adhesion established via crystallization-induced mechanical interlocking derived from surface-induced nucleation of PP from small PBT domains. This robust interfacial adhesion, suggested by a high-temperature shift in the αc-relaxation reflecting enhanced interfacial constraint in dynamic mechanical analysis, promoted a specific deformation sequence wherein matrix fibrillation preceded interfacial debonding, thereby suppressing transverse craze propagation and enabling stable large-strain drawing. Conversely, the high-PBT-content blend (100/20 PP/PBT) exhibited brittle fracture behavior governed by a weakest-link-dominated failure mechanism, in which premature interfacial debonding at coarse domain boundaries under intense triaxial stress concentration triggered extensive transverse crazing prior to matrix fibrillation. These findings provide valuable fundamental insights for designing tough, heat-resistant polymer blends without conventional chemical compatibilizers, which can serve as a conceptual framework for upcycling mixed polymer waste streams.