Effect of NCO/OH ratio on the physico-mechanical properties of polyurethane-polyurea hybrid spray coatings

Polyurethane- polyurea hybrid spray coating was prepared by two steps polymerization. In the first step, polyurethane prepolymers (PUs) were prepared by polyaddition reaction based on 4,4-methylene diphebyl dissocyanate (4,4 MDI), poly(oxytetramethylene) glycol (PTMG), polyoxypropylene glycol (PPG), and triol (trade name FA-703) with different NCO/OH molar ratios. IR spectroscopy and acid-base titration were used to check the NCO content of the prepolymers. In the second step, polyurethane-polyurea hybrid resin was prepared by mixing the polyurethane prepolymer (PU) with polyoxypropylenediamine (POPA) at constant molar ratio (1: 1). The effect of NCO/OH ratios on physico-mechanical properties of the polyurethane-polyurea hybrid coating films was studied including viscosity, tensile strength, elongation at break, tear strength, contact angle and adhesion. The results obtained showed that tensile strength, contact angle and hardness increased, while viscosity, elongation, adhesion and tear strength decreased with increasing NCO/OH molar ratio.