Thermal degradation kinetics of two acrylic-based copolymers

Acrylic copolymers and acrylates are of high interest in a wide variety of applications including coatings. This interest is increasing due to the possibility of being obtained by environmentally friendly procedures. In this research, the thermal stability in non-oxidizing atmosphere of two copolymers, a styrene/butyl acrylate and a diacetone acrylamide/butyl acrylate, is investigated by thermogravimetry (TG). A model consisting of a mixture of generalized logistic functions, which was used to fit calorimetric curves, was adapted to isothermal and non-isothermal contexts. The model was already applied to different materials and processes, being this time the first one that it is applied to TG degradation studies. In the current form, making use of multiple linear heating rates and isothermal experiments at several temperatures, the model allows for obtaining the true energy barrier and other kinetic parameters. The degradations of these copolymers were successfully fitted by the proposed model, and the main overlapping process was separately studied. The kinetic parameter values obtained from both compounds are compared to each other and to those reported from other cases where the model was applied. An important parameter is the critical temperature, which represents the minimum temperature for a given degradation processes to occur. Values of 495 and 525 K were obtained, respectively, for S/BA and BA/DAAM. True energy barrier values obtained for the degradation of these two polymers are approximately a half of those obtained in polymer crystallizations from the melt, and five times of those obtained in the case of an epoxy curing. The accelerating effect of applying a heating ramp is similar to that observed for polymer crystallization and smaller than that observed in thermoset curing.