Influence of diisocyanate, glycidol and polyol molar ratios on the mechanical and thermal properties of glycidyl-terminated biobased polyurethanes

Abstract

A series of epoxy terminated polyurethanes (EPUs) were synthesized from castor oil, 4, 4’methylene bis (cyclohexyl isocyanate) (H12MDI) and 2,3 epoxy-1-propanol (glycidol) by changing the molar ratio of H12MDI: glycidol to polyol. FTIR, 1HNMR and solid state 13C CP/MAS NMR spectroscopy analysis revealed the presence of epoxy linkages within the polyurethane (PU) backbone. Thermogravimetric analysis (TGA) shows that, EPU4 with a polyol: diisocyanate: glycidol molar ratio of 1:6:6 exhibited an initial decomposition temperature of 128 °C, which was 26 °C higher than that of EPU1 (1:3:3 molar ratio). Differential scanning calorimetry (DSC) shows an upward shift in the glass transition temperature (Tg) with increasing molar ratio. Mechanical analysis demonstrated that the tensile modulus of EPU4 was found to be 7.8 times greater than that of the EPU1. The crosslinking densities of EPUs were determined by swelling studies which revealed a gradual increment in the crosslinking density with increasing epoxy content within the PU. The surface morphology of cryo-fractured surfaces of EPUs were determined through scanning electron microscopy (SEM) to analyze the phase dispersion of epoxy and PU.