Formation of reworkable nanocomposite adhesives by dielectric heating of epoxy resin embedded Fe3O4 hollow spheres

Abstract

Epoxy resin (ER) thermosetting adhesives provide highly cross-linked 3-dimensional structures leading to highly stable and strong mechanical/physical performance in a wide range of bonding applications. However, such excellent physical attributes pose a significant challenge with respect to disassembly of the bonded adherends and previous disassembly methods have resulted in damage to the adherends. Hence, this paper presents a specifically engineered re-workable nanocomposite adhesive, created by embedding dielectric sensitive Fe₃O₄ hollow nanospheres (HNSs) in epoxy resin. This nanocomposite adhesive can be completely degraded by dielectric heating, resulting in facile disassembly of bonded adherends. FESEM and 3D Micro-CT characterisation demonstrates good dispersibility of the HNSs in cured ER, while the dielectric degradation performance and hardness/modulus were investigated by FESEM and nanoindentation. Results show that the Fe₃O₄ HNSs can effectively convert the microwave energy into thermal energy to significantly degrade the mechanical properties of the adhesive modulus and hardness by 83.4% and 90%, respectively. FESEM and HRTEM imaging attributes the reduction in nanocomposite adhesive properties to the formation of spatial voids nucleating from the embedded nanomaterials. Prior to dielectric heating, tensile loaded single lap-shear bonded joint tests indicated that the nanocomposite adhesive was 19.3% stronger than its neat ER adhesive counterpart due a nano-reinforcement toughening mechanism. However, after 3 minutes of dielectric heating exposure, the nanocomposite adhesive joint strength was reduced by 96.3% compared to just 18.7% for the neat ER adhesive, demonstrating the excellent re-workable performance of our new nanocomposite adhesive.