Comparison of bio-based epoxide-diamine coatings prepared with acyclic and cyclic aliphatic diamines

As replacements for bisphenol-A, new bio-based and reactive epoxy-amine coatings have been investigated in this study. Bio-based precursor, epoxy-functionalized tung oil (ETO) was synthesized using glycidyl methacrylate (GMA) and tung oil via a Diels–Alder reaction according to our previous work. The new ETO-diamine-cured systems were prepared with the equivalent molar ratio at room temperature. ETO was cured with acyclic aliphatic (Jeffamine D400) and cyclic aliphatic (Epicure 3300) amines, at four temperatures ranging from 25 to 150°C. The coatings were then compared in terms of their thermal and mechanical properties. The cured coatings were analyzed by IR, thermogravimetric analysis (TGA), and gel content tests. TGA analysis showed that the epoxide-diamine polymers demonstrated thermal stability up to 170°C. The mechanical properties of the films were investigated by pendulum hardness, pencil hardness, cross-hatch adhesion, pull-off adhesion, impact resistance, reverse resistance, and chemical resistance testing. While all the cured systems exhibited good pencil hardness, cross-hatch adhesion, impact resistance, and reverse resistance properties, the epoxide-acyclic diamine system demonstrated greater pendulum hardness and notable pull-off adhesion at 150°C. The research demonstrates the potential for greener and more reactive tung oil-based epoxide coatings with enhanced properties.