Plasticization effects of dihydroxyl soybean oil improve flexibilities of epoxy-based films for coating applications

Novel bio-based coating materials were developed through cationic ring-opening photopolymerization of dihydroxyl soybean oil (DSO) with commercial epoxy monomers [i.e., epoxidized soybean oil (ESO) and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ECHM). The ether cross-linking and post-polymerization of the polymeric network were observed using Fourier transform infrared spectroscopy. Thermal properties of the bio-based coating materials and their copolymerization behaviors were examined using differential scanning calorimetry and a thermogravimetric analyzer. Cross-link density and molecular weight between cross-link were obtained from dynamic mechanical analysis. ECHM/DSO (1 : 1.43 weight ratio) films showed the highest elongation at break (49.2%) with a tensile strength of 13.7 MPa. After 2 months of storage, the elongation at break and tensile strength of films were 32% and 15.1 MPa, respectively. ESO/DSO films (w/w ratios of 1 : 0.1, 1 : 0.15, and 1 : 0.2) exhibited stable flexibility of 11-13% of elongation at break without significant reductions in tensile strength (2.5-4.4 MPa) during a 2-month shelf life. Optical transparencies of the films were comparable to commercial glass and polymers, and water uptake properties (0.72% and 2.83%) were significantly low. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41773.