Thermal cure kinetics of highly branched polyurea resins at different molar ratios

Highly branched polyurea (HBPU) resins have been developed as wood adhesives even though their cure kinetics was not well understood. Here, we report thermal cure kinetics of HBPU resins at three molar ratios (2.0, 2.5, and 3.0), using differential scanning calorimetry. A main endothermic peak at 200–240 °C of HBPU resins was used to calculate their thermal cure kinetics with several model-free kinetics methods such as Friedman (FR), Flynn–Wall–Ozawa (FWO), and Kissinger–Akahira–Sunose (KAS) method. Furthermore, Málek method was also used to predict an optimal reaction model. Thermal curing of HBPU resins changed from chemical-controlled reaction at low molar ratio to diffusion controlled one at high molar ratio, as the molar ratio of HBPU resins increased. FWO method was suitable for calculating the activation energy of 2.0 HBPU resins, while FR method was suitable for 2.5 and 3.0 HBPU resins. Furthermore, Málek method revealed that all of HBPU resins apparently followed autocatalytic reaction model, regardless of molar ratios. In addition, FWO and KAS method was appropriate to predict the reaction model of 2.0 and 3.0 HBPU resins with Málek method.