Thermal decomposition of polymeric resin [(C29H24N205)n]: Kinetic parameters and mechanisms

The casting sand generated in the foundry industry is classified as hazardous waste. Two types of sand are generated by the foundry industry: core sand (CS) and green sand (GS). The surface of CS is coated with a polymeric resin. The polymeric resin used in this work is formed by the reaction of formaldehyde with phenol-methylene diphenyl isocyanate catalyzed by dimethyl propylamine. Pyrolysis is an alternative method for the removal of the polymeric resin that is attached to the surface of CS. The kinetic parameters were determined for the removal of polymeric resin incorporated into the sand. The kinetics were monitored by thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) under isothermal and non-isothermal conditions. The triplet kinetics were evaluated by model-fitting methods (Coats-Redfern/MacCallum-Tanner/van Krevelen). The thermogravimetric analysis indicates that the degradation of the polymeric resin occurs in three distinct steps. In the main weight loss step (553-773 K), the activation energy ranged from 73.09 to 115.35 kJ/mol, and the pre-exponential factor ranged from 9.27 × 105 to 1.70 × 109 min−1 under non-isothermal conditions. Under isothermal conditions, the activation energy was 61.98 kJ/mol, and the pre-exponential factor was 3.13.102 s−1. Experiments performed under isothermal conditions indicate that the pyrolysis kinetics of the polymeric resin are controlled by a chemical reaction (Fn) at conversions lower than approximately 0.8, whereas at conversions above 0.8, a change in the rate-limiting step (chemical reaction to diffusion) was observed.