Probing Into the Annealing Effects on Microstructure and Mechanical Properties of Impact Polypropylene Copolymer With Nodular Crystalline Morphology

ABSTRACT The performance of polypropylene materials in high‐temperature environments is closely linked to changes in their microstructure and properties. For impact polypropylene copolymer (IPC), the evolution of structure induced by annealing remains elusive due to the complex molecular chain structure and phase morphology. Herein, we investigate the effects of the initial crystalline morphology on the microstructure and mechanical properties of IPC after annealing. Results show that melt‐quenched IPC (IPC‐m) exhibits a nodular crystalline morphology. As the annealing temperature (T a) increases, the mesomorphic phase in IPC‐m progressively transforms into monoclinic α crystals. Simultaneously, both the size of nodular particles and their internal crystalline regions gradually increase, while the initial nodular morphology remains unchanged. Furthermore, the nodular morphology restricts the lateral growth of crystals in IPC‐m, thereby inhibiting the cavitation during stretching and resulting in higher yield strength for annealed IPC‐m. This research sheds light on the microstructure evolution mechanisms and structure–property relationships of IPC and will provide theoretical guidance for the evaluation of service life and performance optimization of polyolefins in harsh environments.