Influence of the Polymer Interphase Structure on the Interaction between Metal and Semicrystalline Thermoplastics

It is demonstrated that a lamellar crystalline structure may form near the metal–polymer interface during the comolding of metal–thermoplastic joints. The influence of the crystalline morphology near the interface on the rupture behavior of the joint is studied experimentally. High‐resolution scanning electron microscopy (HR–SEM), atomic force microscopy (AFM), and optical microscopy are used to characterize the microstructure of the metal–thermoplastic interface. The results show that a lamellar crystalline structure at the interface promotes cohesive failure, i.e., the crack runs in the polymer. Additional experiments show that a transcrystalline polymer structure at the interface results in failure at the interface. Herein, two methodologies have been developed to characterize the formation of the transcrystalline polymer interphase structure based on X‐ray diffraction and polarized light hot stage microscopy. The results show the importance of the polymer interphase structure for metal–thermoplastic interactions. Understanding of the formation of the polymer interphase and its influence on the interfacial bonding strength are vital for thermoplastic applications such as fiber‐reinforced thermoplastic composites, tool surface design for processing of thermoplastics, and their composites as well as for metal–polymer hybrid joints. The formation of the polymer interphase structure and its role on the bonding strength of a metal–thermoplastic interface are studied. A lamellar crystalline interphase is found to form at the metal–thermoplastic interface and it influences the rupture behavior of the interface. The bonding strength can be significantly reduced by tuning the polymer interphase to a transcrystalline structure.