Aimed at the problem of weld line during injection molding process, the initial interface model of vertical orientation was established when polymer flow fronts meet. Based on the molecular dynamic simulation method, molecular morphology evolution mechanism of poor and strong bond was researched by comparing migration and diffusion of molecular chain, chain orientation, radius of gyration and bonding energy at CIM and RHCM weld line interface. The results indicate that the molecular orientation of the surface and intermediate layer of CIM weld line is rapidly frozen with low temperature and fast cooling rate. Molecular chain motion is blocked and the diffusion rate is low. The weld line interface is ob-vious and interface bonding energy is low. The molecular morphology changes little, so the interface forming poor bond. However, RHCM weld line and the core layer of CIM weld line have a long time to maintain high temperature and the cooling rate is slow at packing stage, which is beneficial to the migration and diffusion of molecular chain and promotes the relaxation of molecular chain. Chain disorientation is obvious and the ra-dius of gyration reduces. The polymer molecular chains show winding and curling state and intertwine together at the interface. So the interface bonding energy increases and the interface forms strong bond. Therefore, the essence of molecular morphology evolution at weld line interface is the process of the relaxation and interdiffusion of oriented molecular chain. RHCM process greatly promotes the course of molecular morphology evolution and dramatically improves poor bond of weld line. © 2019, Materials Review Magazine. All right reserved.
