Cure kinetics and thermodynamics of polyurethane network formation based on castor oil based polyester polyol and 4,4’-diphenyl methane diisocyanate

In this work, isothermal curing kinetics of a non-catalysed and non-blown reaction between castor oil based polyester polyol and polymeric 4, 4'-diphenyl methane diisocyanate (MDI) has been investigated using Differential Scanning calorimeter (DSC) and viscosity build up studies. Several phenomenological models like Ozawa, Kissinger and Kissinger- Akahira-Sunose (KAS) isoconversional methods has been adopted to study polymerisation kinetics through DSC. DSC cure kinetics is studied at different heating rates (5°C/min, 10°C/min, 15°C/min and 20°C/min). Viscosity build up studies are also done for evaluating the kinetic parameters. These studies have been conducted for an isocyanate index [NCO equivalents/OH equivalents] of 1:1 and 1:2. Dynamic viscosity is measured as a function of time and rate constant and activation energy of the curing system is evaluated. Activation energy obtained for 1:1 index through Ozawa and Kissinger methods is found to be in the range of 70kJ/mol and for 1:2 index it is found to be in the range of 50kJ/mol. Thermodynamic parameters like Gibb's free energy (Activation Free Energy), activation enthalpy and activation entropy of the polymerisation kinetics is calculated using Wynne-Jones-Eyring-Evans Theory.