Kinetic and chemorheological modeling of thermosetting polyurethanes obtained from an epoxidized soybean oil polyol crosslinked with glycerin

Abstract

Thermosetting polyurethanes were obtained using an aromatic isocyanate and a hydrophobic polyol formulation obtained from epoxidized soybean oil (ESO) crosslinked with glycerin. A systematic DSC analysis of the effect of catalyst type, crosslinker concentration, isocyanate index and ESO crystallization on cure kinetics was conducted. The combination of a stannic catalyst at 0.2 wt% and glycerin at 20 wt% produced a cure kinetics governed by an autocatalytic heat flow where vitrification played a key role in the formation of chemical bonds. The evolution of Tg as a function of conversion, which followed Di-Benedetto's predictions, supported the hypothesis that vitrification was a preponderant phenomenon during cure. Dynamic Mechanical Analysis (DMA) of a post-cured sample revealed a Tg centered at 220°C, whereas quasi-static flexural mechanical tests shown a flexural modulus of 2.14 GPa and a flexural strength of 99.4 MPa. Rheological experiments at isothermal conditions supported the hypothesis that vitrification played a key role in the evolution of apparent viscosity. A master model using Kim-Macosko equations was obtained for the proposed formulation. The results presented in this work will serve to further extend the use of biobased polymers applied in the polymer composite industry.