Kinetics of thermal curing for aerospace sealant

Abstract

This project investigates the thermal kinetics of curing for DAPCO 18-4F silicone system by obtaining the best fitted kinetic model for each curing method, kinetic parameters of the reaction (activation energy and pre-exponential factor) and finally determining the optimum formulation of the system. Investigation was carried out using the differential scanning calorimetry (DSC). Two experimental methods were used, non-isothermal and isothermal method of curing, for three different formulations: 100/3, 100/7, 100/15 weight % of resin and curing agent respectively. Sample of resin and curing agent was pre-mixed in a weighing boat, crimped into a DSC hermetic pan and placed into the DSC machine for heating, Raw data obtained from the experiments are heat flow, temperature and time elapsed, from which secondary data such as degree of conversion and enthalpy of curing could be calculated. These secondary data were then used in the kinetic analysis to determine the best fitting kinetic model and obtain the kinetic parameters (activation energy and pre-exponential factor) for the reaction. It was found that both non-isothermal and isothermal method of curing follows the autocatalytic model where reaction rate hits maximum at intermediate conversion due to reaction intermediates acting as catalyst and Trommsdorff effect. Both methods also shown that formulation 2: 100/3 is the optimum formulation as it had the lowest activation energy was calculated among all the 3 formulations. Simulation for non-isothermal fitted well but that for isothermal did not, which is probably due to incorrect simulation equation and/or certain temperature induced rate retardation mechanism.