Annealing‐Induced Crystalline Reconstruction and Toughening Mechanisms in β‐Nucleated Long Glass Fiber‐Reinforced Polypropylene Random Copolymer

ABSTRACT Long glass fiber‐reinforced modified polypropylene random copolymer (LPM) systems are widely applied in lightweight structural components. However, rapid injection molding induces heterogeneous crystallization, limiting mechanical performance. Moreover, the intrinsic brittleness of polypropylene matrices and the incomplete toughening effect of ‐nucleating agents restrict the simultaneous achievement of stiffness and toughness. Herein, this study aims to elucidate the role of annealing in regulating crystalline reconstruction and multiscale structure–property relationships in ‐nucleated LPM composites (LPMT). A combination of ‐nucleating modification and post‐annealing treatment was employed, and the resulting structural evolution and mechanical responses were systematically characterized. The results show that annealing significantly enhances overall crystallinity and lamellar development in both systems. For LPMT composites, the ‐phase content reaches a maximum at 130°C ( = 46.8%), followed by a pronounced to recrystallization at 140°C. The annealing treatment resulted in the thickening of crystalline and amorphous layers, indicating progressive lamellar reorganization. Meanwhile, annealing effectively improved both the storage modulus and the damping energy dissipation capacity of the materials. Concurrently, the heat distortion temperature of the materials was significantly enhanced, reaching 126.3°C for LPM and 135.7°C for LPMT. Mechanical tests reveal improved tensile strength and impact toughness (27.7% for LPM, 18.3% for LPMT) due to higher crystallinity and optimized segmental mobility. These findings indicate that annealing‐driven crystalline reconstruction, combined with controlled ‐phase stability, enables effective tuning of stiffness–toughness balance. This work may pave the way for designing high‐performance thermoplastic structural materials via annealing.