Biobased Divanillin As a Precursor for Formulating Biobased Epoxy Resin

Divanillin (DV), which can be facilely synthesized via vanillin dimerization, was employed as a building block to formulate epoxy resin. DV was synthesized through a novel approach in hot water in only 30 min with a yield of 87.5%. The process involved FeSO4-catalyzed Na2S2O8-based oxidative coupling of vanillin without any purification, followed by treatment with biobased epichlorohydrin. Epoxidized-divanillin (EDV) was cured with the petroleum-based, commercially available hardener isophorone diamine (IPDA) and a biobased-diamine (GX-3090). Complete curing of the mixture was confirmed by Fourier transform infrared (FTIR) spectroscopy and statistical heat resistant-indices (T-s), which indicated the formation of cross-linked networks with a thermostability similar to materials prepared with diglycidyl ether bisphenol A (DGEBA, the commercial BPA-based resin). The epoxy resin developed with this new formulation had comparable storage moduli (1.7-2.3 GPa) and similar glass transition temperatures as commercial resins. The epoxy networks exhibited good solvent resistance, while the presence of aldehyde groups in EDV yielded in more readily cleavable ester and amide bonds during the cross-linking process, yielding a resin with improved degradation under acidic conditions. Almost 40% of the segments in networks cured with EDV/IPDA were solubilized in acetone after treatment with 1 M HCl at room temperature in 24 h.