(230j) Mechanism and Kinetic of Moisture-Curing Process of Reactive Polyurethane Hot Melt Adhesive

The sample of reactive polyurethane hot melt adhesive (HMPUR) was prepared by polycondensation of polyesters, Pentaerythritol diacrylate (PEDA) and 4,4'-Methylene diphenyl diisocyanate (MDI). The moisture curing behavior of PUR hot melt adhesive is studied to provide theoretical guidance for industrial operations. The moisture-curing kinetic experiments for the film of HMPUR with 2.0 mm thickness are carried out at different temperatures (283, 293, 303 and 313K) and 85% relative humidity by monitoring the mass changes of the film to investigate the moisture curing process of HMPUR. A diffusion-reaction assumption is proposed to describe the mechanism of moisture-curing process and three kinetic models are established to correlate the above moisture-curing kinetic data: (i) rapid reaction; (ii) zero-order reaction; (iii) first-order reaction. On this basis, three non-steady-state moisture curing kinetic models are established and the above experimental data are correlated. The results show that the first-order reaction kinetic model has the smallest average relative deviation and can be used to describe the reaction mechanism and kinetic of the moisture curing behavior. Based on this model, the water concentration distribution in the HMPUR film at different time is predicted and the depth of water diffusion(x*) at θ is defined. The depth of water diffusion corresponding to five specific moisture cure time(10²s, 10³s, 10⁴s, 10⁵s, and 10⁶s) is calculated. The results show that when the moisture curing time is greater than 10⁵s, the x^* value is almost constant (1.082~1.606 mm), which indicates that the hypothesis about the non-steady-state kinetic model is reasonable. According to the Arrhenius equation, the activation energy (E_k) and diffusion activation energy (E_D) are 9.52 kJ/mol and 28.45 kJ/mol, respectively, indicating that the influence of temperature on the diffusion process is greater than that of the reaction process.