Mechanism analysis of interface characteristics of sequential Co-injection self-reinforced parts

Abstract The mechanism analysis of the interface characteristics of sequential co-injection self-reinforced parts starts from the following three aspects. Firstly, the formation process of the bonding interface and the factors affecting the bonding strength were investigated in theory. A theoretical model of interface bonding degree, which explains the bonding degree of the interface by the penetration depth of polymer chains through the initial solid-melt interface, was proposed, and then combines the average critical penetration depth to analyze the influence of different molding parameters on the interface bonding degree. Then, the interface bonding strength of the prepared polypropylene sequential co-injection self-reinforced parts under different molding parameters (including melt temperature, mold temperature and injection speed, etc.) was studied experimentally, and the reliability of the model was verified. Finally, the interrelationship function between effective penetration degree of molecular chain diffusion and interface bonding degree on both sides of the interface is established, which provides a new theoretical basis for interfacial mechanism analysis of sequential co-injection self-reinforced parts. The results show that the interface bonding degree between experiment and theory has a good consistency, and the deviation between them is within 10%, which proves that the theoretical model is reliable. In addition, the theoretical critical penetration depth and the theoretical maximum degree of bonding sequential co-injection polypropylene products are 1.399 nm and 0.857, respectively. The performance test results of different molding parameters show that the temperature change of reinforced melt is the key factor affecting the interfacial fusion of sequential co-injection self-reinforced parts. The high temperature melt is beneficial to the diffusion and intertwining of molecular chains on both sides of the interface and to the improvement of the degree of interfacial bonding.