Overmolded hybrid thermoset‐thermoplastic structures: Experimental study on the bonding strength of co‐curing thermoplastic film onto thermoset composite

Abstract In the present study, an innovative approach to produce hybrid thermoset‐thermoplastic structure by means of co‐curing technique together with injection overmolding technique is proposed. To make thermoset composite bondable, a thermoplastic film was firstly co‐cured on the surface of thermoset composite. Five different types of thermoplastic film were chosen to co‐cure with thermoset composite. The bonding strength between thermoplastic film and thermoset composite was evaluated with lap shear strength. The results show that plasma treatment on thermoplastic film can promote polar groups at interface, which has positive effect on increasing wettability and can increase bonding strength by up to 69.7% of co‐cured structure. Meanwhile, increasing the surface roughness of thermoplastic film can also increase bonding strength by 162.9% because of mechanical interlock. Especially, because of low melting temperature of metallocene polypropylene, some fiber bundles in the interface zone were impregnated with molten metallocene polypropylene, resulting in strong bonding strength increased by 266.2% of the resultant co‐cured structure. Based on these results, polyamide 6 film was selected as the best thermoplastic boundary for co‐cured structure. Finally, hybrid thermoset‐thermoplastic was fabricated by injection overmolding of molten polyamide 6 on co‐cured structure, which has high average lap shear strength of around 14.9 MPa.