Ph. D.

Control of the rate of heat generation and the resulting temperature variations during the processing of thermosets is very necessary both to achieve the desired ultimate properties of the final product and to conserve energy and time. With this motivation, theoretical and experimental studies on the kinetics and thermal characterization of the curing reaction of thermoset polyesters were accomplished, and a mathematical curing model was proposed for the casting operation of these plastics. Temperature distribution through the thickness of the polymer mass was obtained by monitoring thermocouples placed at known locations with the aid of PDP-11/40 computer. Both isothermal and dynamic techniques of differential scanning calorimetry (Du Pont DSC) were used to obtain the heats of reaction and a kinetic expression for the polymerization reaction. The proposed kinetic model can be utilized to obtain the rates of heat generation a different curing temperatures. The overall activation energy of the curing reaction was calculated as 17.0 kcal/mole and the overall reaction rate constant as 2.60X10⁹exp(-17,000/RT) min⁻¹. The thermal properties of the polyester were determined as a function of temperature, and also attempts were made to measure these properties as a function of extent of reaction. The specific heat of cured polyester samples was determined over the temperature range 60-180°C. A more or less linear increase in specific heat was observed with increasing temperature between 60° and 120°C where the values were 0.38 and 0.43 cal/g-°C, respectively. Thermal conductivity measurements were accomplished by using a Colora Thermoconductometer, but a new sample system had to be developed for use with this instrument for the measurements of uncured and partially cured samples. A linear increase in conductivity of cured polyester with increasing temperature from a value of 4.5 X 10⁻⁴ cal/cm-sec-°C at 40°C to 5.0 X 10⁻⁴ cal/cm-sec-°C at 94°C was observed. Simulation of the curing process was based upon differential equations describing one-dimensional unsteady-state conductive heat transfer through the casting and the rate of the crosslinking reaction. The numerical scheme that was presented predicts the temperature and concentration profiles during the curing process. Agreement between the simulated and experimental temperature profiles was very good. The proposed model can be readily utilized in characterizing the curing process, predicting curing performance, and establishing guidelines for better design of the casting and other reaction molding operations with most of the thermoset plastics. / Ph. D.