A Biobased Epoxy Resin with Sequential Thermoplastic-to-Thermoset Curing Enables Removable-to-Permanent Adhesive Bonding

Adhesives are commonly designed either as reworkable thermoplastics or permanently crosslinked thermosets. Here, sequential thermoplastic-to-thermoset curing enables a simple two-component formulation based on a bio-based epoxy resin to function first as a removable hot-melt adhesive and subsequently as a permanent structural adhesive. Reaction of diglycidyl ether of vanillyl alcohol (DGEVA) and anilinium methanesulfonate at 110 °C produces a thermoplastic intermediate that is solid at room temperature but flows upon reheating and dissolves in selected solvents. This intermediate forms load-bearing joints that can be thermally debonded and rebonded or disassembled by dissolution. Further heating induces crosslinking and converts the same adhesive layer into a permanent epoxy network, increasing the apparent lap-shear strength nearly eightfold and rendering the joint resistant to disassembly under the same solvent conditions. This curing sequence therefore assigns reworkability and high-strength permanent bonding to successive adhesive states within the same formulation.