A Study on the Use of Graphene-PEEK Composites As High Temperature Adhesives: Mechanical Properties and Microwave Activation

Polyetheretherketone is a widely used engineering polymer that is especially suitable for high-temperature applications. Graphene is a two-dimensional form of carbon nanomaterial that has been studied extensively for its mechanical, electrical and thermal properties and its use as a filler in polymer matrices. Compounding graphene into polymers has the potential to improve various properties, even at very low concentrations. In this work, we have examined the incorporation of graphene nanoplatelets (GNP) into PEEK. We have fabricated composites using melt-mixing techniques, as well as by graphene functionalization and in-situ polymerization of the PEEK. In this way, we can compare the performance of the composites by two different processing methods. The GNP-PEEK composites were characterized by DSC, TGA, and SEM. Lap-shear joints using the GNP-PEEK as the adhesive were made and mechanically tested. Results show that the weight fraction of GNP has a major effect on the strength of the joint. In this work, we aim to produce a material that functions as a reusable high-temperature, thermoplastic adhesive, which can be activated by conventional heating methods, or by microwave heating. The GNPs act as microwave absorbers and heat the surrounding PEEK matrix to the point of melting, in contrast to the neat PEEK, which does not melt upon exposure to the microwaves under the same parameters. Additionally, we explore 3D printing methods to fabricate a lap shear joint, where the adherends are pure polymer and the adhesive region is a polylactic acid/carbon nanofiber (PLA/CNF) composite that can be activated by microwaves. We show that solid adherends can be bonded together when a solid PLA/CNF piece is placed between the adherends and melted by microwave exposure. The microwave absorption properties and adhesive properties will be discussed.