Cure kinetics of low-molar-ratio urea-formaldehyde resins reinforced with modified nanoclay using different kinetic analysis methods

This study reports on low-molar-ratio urea-formaldehyde (UF) resins modified with transition-metal-ion-modified bentonite (TMI-BNT) nanoclay assessed using different kinetic analysis methods in order to understand the effect of TMI-BNT on the cure kinetics of these modified resins. Differential scanning calorimetry was used to determine the kinetic parameters using two types of cure kinetic analysis: 1) model-fitting (MFT) methods, which include the Kissinger and nth-order approaches, and 2) model-free kinetics (MFK) methods, including the Friedman (FR), Flynn-Wall-Ozawa (FWO), and Kissinger-Akahira-Sunose (KAS) approaches. Of these kinetic methods, the Kissinger, FWO, and KAS approaches exhibited the best fit in terms of explaining the resins' curing behavior, showing that, in general, the apparent activation energy (E-a) decreased as TMI-BNT levels increased, which indicates that the curing process is accelerated by the addition of TMI-BNT. These results suggest that TMI-BNT is a potential additive for the effective acceleration of the curing of low-molar-ratio UF resins and may possibly improve their adhesion as well. In addition, according to the Malek method, it is found that UF resins curing behavior are likely to follow the autocatalytic nature of reaction.