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

336-342In 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

Microstructural analysis of natural rubber/millable polyurethane blends using positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) was used to investigate the relationship between the free volume properties and miscibility of natural rubber (NR)/millable polyurethane (MPU) blends. The free volume parameters (Vf and I3) have been found to be increased regularly with an increase in NR concentration in the blend. The morphological analysis of the samples has been performed by scanning electron microscopy. The results obtained from PALS technique have been correlated with the observations from X-ray diffraction analysis and differential scanning calorimetry. Thermogravimetric examination highlighted the enhancement in thermal stability upon blending MPU with NR