Crystal Melting-Controlled Interdiffusion and Adhesion at the Interface between Poly(ether ether ketone) and Poly(ether imide)

Adhesion technologies for super engineering plastics have attracted growing interest because of their importance in reducing structural weight in mobility applications and improving manufacturing productivity. The adhesion interface is formed through polymer chain interdiffusion, and the resulting interfacial structure governs the adhesion properties. Understanding the interfacial aggregation states is therefore essential. Here, we investigate how the adhesion temperature near the melting point of PEEK influences interdiffusion behavior and adhesion performance at the PEEK/PEI interface. Composition profiles obtained from Raman scattering spectroscopy were analyzed using a diffusion equation, revealing that complete melting of PEEK crystals markedly increased chain mobility and greatly enhanced interdiffusion. At lower temperatures, where chain mobility was restricted by PEEK crystallites, the adhesion strength increased with adhesion time. In contrast, at higher temperatures, where chain diffusion was strongly promoted, the adhesion strength reached saturation within short adhesion times. These findings provide molecular level insights that are useful for designing and controlling adhesion strength in super engineering plastic interfaces.