Crystallization, thermal, and mechanical properties of ethylene-propylene block copolymer/random copolymer blends

The development of ethylene-propylene block copolymers (PP-b-PE) via chain-shuttling catalysis technology presents new opportunities for polyolefin modification, offering advantages over conventional ethylene-propylene random copolymers (EPC). However, the synergistic effects and property optimization in PP-b-PE/EPC blend systems remain insufficiently understood, particularly concerning crystallization behavior and phase morphology. This study systematically investigates the crystallization, phase structure, and mechanical properties of PP-b-PE/EPC blends with varying compositions using differential scanning calorimetry (DSC), synchrotron X-ray scattering (SAXS/WAXD), scanning electron microscopy (SEM), polarized optical microscopy (POM), and mechanical testing. DSC analysis reveals complex melting behavior and enhanced crystallization attributed to nucleation effects, notably in the 10:90 blend. SAXS results show PP-b-PE-rich blends maintain a dominant PE lamellar structure with a long period of approximately 18.47 nm, while intermediate compositions exhibit dual PE and PP lamellar structures. WAXD confirms the formation of both α and γ crystal forms, with the γ-phase becoming particularly prominent at the 50:50 blend ratio, corresponding to optimal impact strength (18.60 kJ/m²). These findings elucidate the interplay between composition, crystallization, and properties, providing valuable insights into structure–property relationships in polyolefin blends and advancing the development of high-performance materials through synergistic interactions and strategic composition control.