Bisphenol-A free bio-based gallic acid amide epoxy thermosets

Bisphenol-A (BPA)-based epoxy thermoset has been used commercially due to its many impressive properties. However, it has toxic effects on human health, and it is obtained from petrochemicals so environmentally friendly bio-based alternatives to substitute BPA for the synthesis of epoxy resins are essential. In this context, a gallic acid amide was synthesized from renewable gallic acid, and diethanol amine. The epoxy resin of the synthesized amide was obtained by the condensation reaction with epichlorohydrin in an alkaline medium. The synthesized epoxy resin was cured with a combination of two hardeners, aliphatic bio-based poly(amido amine) and aromatic 2-aminophenyldisulfide at varying weight percentages. The chemical structure of the synthesized epoxy resin was characterized by FTIR and NMR spectroscopic analyses. The synthesized epoxy thermosets showed a maximum tensile strength of 20.04 MPa along with elongation at break of 62.63%, high impact resistance (>19.3 kJ/m(2)), high scratch hardness (up to 8.5 kg), and high adhesive strength for metal-metal substrates. Moreover, the thermo-gravimetric analysis showed good thermostability with an initial degradation temperature of 224 degrees C, while the microbial broth culture test confirmed the biodegradability of the thermosets. Thus, this bio-based epoxy thermoset could find different potential applications including as a binder for eco-friendly coatings and paints.