Effect of the temperature gradient on the interfacial strength of polyethylene/polyamide 6 during the sequential injection molding

Effect of the temperature gradient on the interfacial strength of polyethylene (PE)/polyamide 6 (PA6) during the sequential injection molding (SIM) was investigated in this article. PE grafting with maleic anhydride (PE-g-MAH) was added into PE matrix to enhance the interfacial strength through the formation of the copolymer at PE/PA6 interface. The results showed that the reaction at PE + PE-g-MAH/PA6 interface was incomplete due to the steep temperature gradient built from the melt (the second part) to the solid (the first part) during SIM. However, the interfacial reaction proceeded further during annealing through the diffusion of the reactive groups into PE + PE-g-MAH/PA6 interface so that much more copolymers were formed at PE + PE-g-MAH/PA6 interface, resulting in obvious improvement of the interfacial strength after annealing. It was also found that the relationship between interfacial strength and PE-g-MAH content was a linear relation through data fitting under gradient cooling during SIM. However, the relationship became the square relation after annealing at 220°C for 10 min. Through the rheological analysis and morphological observation, it was concluded that the interfacial temperature was a very important factor to control the interfacial strength during SIM.