Effect of moisture content on curing kinetics of pMDI resin and wood mixtures

The curing process of polymeric diphenylmethane diisocyanate (pMDI) with wood is affected significantly by moisture in the wood since the reaction of isocyanate is highly sensitive to water. This study determined the curing kinetics of pMDI and wood mixtures containing various moisture contents by means of differential scanning calorimetry (DSC). Model-free analysis of the kinetics suggested that the curing reactions for the oven-dried wood/pMDI mixture are different from those of the mixtures with moisture. Peak temperatures indicated that the activation energy, reaction enthalpy, and reaction rate were lower for the oven-dried wood and resin mixture because the curing process was controlled by diffusion in the absence of moisture. The activation energy increased when moisture was present, but decreased when the moisture content further increased. Both the reaction enthalpy and reaction rate increased with the increase in moisture content and remained almost unchanged or increased slightly after the moisture content reached 12%.