Investigations on performance and failure mechanisms of high temperature thermoplastic polymers as adhesives

Ability of high temperature thermoplastic polymers (TPs) to create strong bonds with metals provides an attractive solution to develop adhesives for harsh operating conditions. However, exploration of such TP based adhesives needs evaluation in desired operating temperature conditions along with understanding of failure mechanism which will serve as a platform for developing successive batches of composite adhesives or blends. In this work poly (ether sulphone) (PES), poly (ether ketone) PEK and poly (ether- ether ketone) PEEK were explored as adhesives for joining cold rolled steel lap joints. The lap joints were evaluated for bond performance at various temperatures. The adhesive-bond performance order differed at different temperatures. At ambient temperature (AT) it was as; PES>PEK>PEEK, while at higher temperatures PEK proved the best followed by PEEK. Micro-Raman spectroscopy (MRS) analysis of failed films was carried out to understand the failure mechanism as a function of thermal and mechanical stresses. Differential scanning calorimetry and scanning electron microscopy (SEM) of fractured films was carried out to understand the changes in crystallinity, thermal characteristics and failure mechanisms.