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

TL;DR

This study models the curing and rheological behavior of thermosetting polyurethanes derived from epoxidized soybean oil, highlighting vitrification's role and providing a predictive master model for formulation optimization.

Contribution

It introduces a comprehensive kinetic and chemorheological model for soybean oil-based polyurethanes, emphasizing vitrification effects and establishing a predictive Kim-Macosko based formulation model.

Findings

Vitrification significantly influences cure kinetics and viscosity evolution.

Optimal catalyst and crosslinker concentrations enhance curing efficiency.

The developed model accurately predicts rheological and curing behavior.

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 the 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 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. The ESO crystallization had a melting endotherm centered at 35{\deg}C, affecting substantially the availability of reactive hydroxide groups. Dynamic Mechanical Analysis (DMA) of a post-cured sample revealed a Tg centered at 220{\deg}C, whereas quasi-static flexural mechanical tests revealed a flexural modulus of 2.14 GPa and a flexural strength of 99.4 MPa. Rheological experiments using a rheometer 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.