Effect of the chain extender and selective catalyst on thermooxidative stability of aqueous polyurethane dispersions

Abstract

Polyurethane aqueous dispersion based on poly(propylene glycol) (PPG), dimethylol propionic acid (DMPA), and isophorone diisocyanate (IPDI) with catalysts of different selectivity were prepared by the conventional prepolymer isocyanate process. Two types of chain extenders were used, ethylene glycol (EG) and propylene glycol (PG). The polyurethane dispersions were characterized using thermogravimetric dynamic method. In the dynamic method, heating rates of 0.5, 1, 2 and 10 °C/min were used in the range of 30–500 °C, and degradations of 0.025, 0.05, and 0.10 were considered. From the Arrhenius plots, activation energies were evaluated ranging between 23 and 117 kJ/mol at α ≥ 0.05 for polyurethane aqueous dispersion depending on the temperature interval, selectivity of catalyst, type of chain extender and degree of degradation. The polyurethane aqueous dispersion based on ethylene glycol as the chain extender, with the more selective catalyst shows higher thermal stability. The dynamic method offered evidence for the presence of different degradation processes and was suitable for the evaluation of kinetics parameters at higher degrees of degradation.