Exploration of thermoplastic polyimide as high temperature adhesive and understanding the interfacial chemistry using XPS, ToF-SIMS and Raman spectroscopy

Highlights: • Polyimide showed good retention of adhesive strength at high temperatures. • Raman spectroscopy (RS) has been utilized for detecting changes in polymeric structures as a result of stresses. • XPS and ToF-SIMs helps in understanding locus of failure in relation to test temperature. Thermoplastic semi-crystalline polyimide (PI) was explored as an adhesive for elevated temperature applications for steel to steel joint. Its lap shear strength (LSS) at temperatures 25 °C, 150 °C, 225 °C and 300 °C was evaluated and analysed. The joints showed good LSS and remarkable retention up to 225 °C. The fracture mechanism was studied by scanning electron microscopy. Fractured surfaces at 25 °C and 150 °C showed shear elongated ductile type of failure features, while joint surface fractured at further elevated temperatures revealed weakened interface. The fractured surfaces were analysed using Micro-Raman spectroscopy (μRS), X ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS) to understand the failure mechanism of joint. μRS results showed changes in peak positions and intensity ratios of various functional groups as a function of test temperature.