Study on co-injection molding of poly(styrene-ethylene-butylene-styrene) and polypropylene: Simulation and experiment

In this paper, poly(styrene-ethylene-butylene-styrene) (SEBS) triblock copolymer blends were used as the soft skin material and polypropylene (PP) was used as the hard core for co-injection molding. The effect of different SEBS thermoplastic elastomer skin materials on the filling state of the core layer of the co-injection sample was analyzed, and the co-injection molding was evaluated by the filling factor and shape distribution factor. When the core material flows at the matched skin interface, the core layer gradually changes from an uneven finger-like flow front to a smooth flow, and the shape distribution factor increases greatly. Both simulation and experimental results show that the shape distribution factor can correctly evaluate the filling effect of co-injection, and the corresponding samples have uniform skin-core interface, good compatibility and maximum skin thickness. According to the change of shearing rate, a dynamic viscosity ratio method was established to evaluate the coinjection process. When the dynamic viscosity ratio of the core/skin material is greater than and close to 1, the movement of the molecular chains on the interface matches, the flow front is smooth and the shape distribution factor is high. By changing the injection temperature of the material to adjust the dynamic viscosity ratio, the optimization of co-injection can also be achieved. The dynamic viscosity ratio method can be used to guide the flow forming and interface interaction analysis of heterogeneous materials.