Renewable Furfural-Based Sulfur-Bridged Epoxy Resins with Excellent Adhesive Properties

The increasing interest in reducing the dependence on fossil-based resources by searching and replacing them with renewable biobased sources has intensified in both industrial and academic sectors. Especially, lignocellulose-based biomass can be utilized in the production of many aromatic platform chemicals suitable as substitutes for known fossil-based chemicals. For example, cellulose-derived 5-(hydroxymethyl)furfural has been utilized successfully for the aforementioned purposes. On the other hand, hemicellulose-derived furfural has received rather minor attention, even though recent studies show various excellent results in applications especially utilizing furfural. In this work, two novel furfural-derived epoxy resins were synthesized. Comparative studies were conducted with commercially available and widely used fossil-based epoxy resin, diglycidyl ether of bisphenol A. Resins were cured with methylhexahydrophthalic anhydride with optimized amounts of the 2-ethyl-4-methylimidazole initiator. Curing behaviors were studied with differential scanning calorimetry while thermomechanical properties were evaluated using dynamic mechanical analysis and thermal stabilities with thermogravimetric analysis. Adhesion strengths were tested with single-lap joint steel plate samples using a tensile tester. Tensile testing was also carried out for dog-bone-shaped resin specimens. Lastly, the water absorptions were evaluated through immersion in water. Results showed that the synthesized bioresins have great potential to replace diglycidyl ether of bisphenol A in various applications.