A novel biomass-derived Schiff base waterborne epoxy coating for flame retardation and anti-bacteria

Flammability and pollution of solvent-based epoxy resin coatings are thorny issues that brings series of adverse factors to the daily life and industrial manufacture. Therefore, the coatings from waterborne bio-renewable alternatives are one of the most popular topics. A novel biobased waterborne epoxy resin (WPDE) with flame retardancy and antibacterial ability was synthesized from a biomass-derived Schiff base compound [4,4′-(1E,1′E-(methylenebis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene)) bis(benzene-1,2-diol), PH-DDM], followed by the reaction with epichlorohydrin and diethanolamine. The resultant WPDE was characterized by FTIR and 1 H NMR analyses. After curing reaction of WPDE with long chain fatty amine curing agent (BC919), the cured WPDE epoxy thermoset (WPDE/BC919) possessed excellent flame retardancy due to the introduction of Schiff base structure, showing a 57.3% and 25.6% decrease in peak heat release rate and total heat release value, respectively, compared with cured waterborne bisphenol A type epoxy thermoset (WE51/BC919). WPDE/BC919 also showed a superior antibacterial performance due to the formation of hydration layer and the lone pair electrons in an SP (Ahmadi et al.) hybridized nitrogen atom of Schiff base structure. Moreover, WPDE/BC919 possessed a higher glass transition temperature (Tg) of 79.6 °C and showed a 40% and 268.2% increase in storage modulus (at 20 °C) (1506.8 MPa vs. 1084.4 MPa) and Young′s modulus (306.0 MPa vs. 83.1 MPa), respectively, compared with WE51/BC919. The paper provides a novel strategy for further investigation on biobased waterborne epoxy resins as a multifunctional coating.