Reassembleable Synthetic Adhesives Based on Epoxidized Soybean Oil and Dynamic Diels-Alder Bonds

Synthetic adhesives rely on interfacial interactions to bond various materials, and their molecular structure allows for tailored properties by adjusting components. While thermoplastic adhesives offer reassembly, they lack strength, while thermosetting adhesives provide high strength but are difficult to reassemble. This study aims to combine these advantages by introducing dynamic covalent bonds, specifically Diels-Alder bonds, into the cross-linked networks of epoxidized soybean oil (ESO). ESO was chosen as a sustainable alternative to petroleum-based materials.

The study successfully synthesized ESOF, a modified ESO containing furyl groups, enabling the formation of Diels-Alder bonds. Characterization techniques confirmed the successful synthesis and the introduction of furyl groups, which lowered the melting temperature of ESOF.

A covalent polymer network was created by cross-linking ESOF with bismaleimide (BMI), resulting in materials denoted as ESOF-Ix (where x represents the mole ratio of imide groups to furyl groups). The quantity of BMI was found to significantly influence the adhesive's properties. Higher BMI concentrations resulted in increased cross-linking density, enhancing solvent resistance and mechanical properties.

The incorporation of Diels-Alder bonds led to self-healing and recycling properties. ESO-I1.0 exhibited crack self-healing at 130ﾰC, with the crack diminishing over time due to the reversibility of Diels-Alder bonds. Furthermore, ESOF-I1.0 was subjected to three cycles of hot pressing at 130ﾰC and 10 MPa, demonstrating its ability to be recycled without significant degradation in mechanical properties.

The prepared adhesives exhibited hydrophilicity, with water contact angles less than 90ﾰ, attributed to the presence of polar groups within the networks. Vulcanization analysis revealed a rapid decrease in viscosity upon heating, facilitated by the dissociation of Diels-Alder bonds, which allowed for reassembly of the adhesive.

In conclusion, this research successfully developed a synthetic adhesive with high bonding strength, self-healing, recycling, and reassemble ability by incorporating dynamic Diels-Alder bonds into the cross-linked networks of ESO. This approach provides a promising avenue for developing sustainable and high-performance adhesives.