Model-free kinetic analysis of thermal behavior of urea-formaldehyde microcapsules

Abstract

In this study, experimental and analytical investigations were conducted concerning kinetics of thermal reactions of urea-formaldehyde microcapsules (UFM). Microencapsulated phase change materials were synthesized via in-situ polymerization using UF resin as shell and drying oil as core, and were characterized by scanning electron microscope (SEM), particle size analysis (PSA) and Fourier transform infrared analysis (FTIR). Accordingly, model-free kinetics (MFK) was used to determine the kinetics of the thermal behavior of UFM. Therefore, Thermogravimetry analysis was conducted at different heating rates of 3, 5, 7, and 10 °C/min. The apparent activation energy was obtained by MFK, which led to identify the reaction mechanisms. The results revealed that there are two stages for degradation of the synthesized microcapsules. Addition of the oil core in the UF microcapsules has hindered one stage of the suggested three stages of the pyrolysis process of UF based resins and the two stages were unified as a single extended stage. Additionally, the measured activation energy showed a low value of 20 kJ/mol due to the presence of oil in the UF microcapsules.