Synthesis, characterization, and properties of isocyanate-free urethane coatings from renewable resources

Abstract

Isocyanate-free urethane coatings were prepared from renewable resources through the aminolysis reaction of five-membered cyclic carbonate from linseed oil and phenalkamine from cashew nut shell liquid. The five-membered cyclic carbonate functional reactants were synthesized from epoxidized linseed oil through carbon dioxide insertion. The porous-free urethane coatings were prepared on aluminum substrates using synthesized carbonated linseed oil and phenalkamine at three different mixing ratios (1:0.5, 1:0.75, and 1:1.25) and at three different cure temperatures (60, 80, and 100°C). The formation of urethane linkages and the rate of cyclic carbonate conversion during the aminolysis reaction were characterized using FTIR spectroscopy. The thermal behavior of the cured urethane films was characterized using thermogravimetry. The effects of amine concentration and cure temperature on the optical, mechanical, and end-use properties of the coatings were evaluated by measuring specular gloss, solvent resistance, crosshatch, solvent swelling, and impact strength. The increase in cure temperature was directly proportional to the rate of aminolyis reaction and also to the coating performances.