Evaluation of the cure kinetics of the wood/pMDI bondline

Micro-dielectric analysis (μDEA) and differential scanning calorimetry (DSC) were used to monitor cure of polymeric diphenylmethane diisocyanate (pMDI) resin with wood strands in a saturated steam environment. A first-order autocatalyzed kinetic model was employed to determine kinetic parameters. The kinetics were found to follow an Arrhenius relation. A single ramp DSC technique and μDEA produced models that predicted similar results at higher cure temperatures, but the μDEA-based model predicts a longer cure time at low temperatures. The isothermal μDEA method yields higher activation energies and Arrhenius frequency factors than models based on single DSC ramps. A modification to ASTM E698 was made to conform to the assumption of autocatalyzed kinetics. The modified ASTM E698 method predicted an earlier end of cure than the μDEA-based models and was in agreement with DSC results obtained by partial cure experiments. The activation energies and frequency factors for the different cure monitoring methods are sensitive to different stages of cure.