Correlation of mechanical and chemical cure development for phenol–formaldehyde resin bonded wood joints

In this study a relationship between the chemical and mechanical degree of cure (i.e. α and β, respectively) is investigated for a standard phenol–formaldehyde resin (PF). Dynamic mechanical analysis (DMA) is conducted on PF-bonded wood joints under various isothermal and linear heating regimes. Model free kinetics (MFK), viz Friedman, Vyazovkin and Kissinger–Akhira–Sunnose algorithms, are assessed for predicting the mechanical cure kinetics of PF. All MFK algorithms are found to provide a good description of PF mechanical cure. In parallel, chemical cure of the same PF samples is assessed with differential scanning calorimetry (DSC) under the same heating regimes. The relationship between chemical and mechanical degree of cure is thus obtained and observed to follow a sigmoid curve, which is best modeled with a two-parameter Weibull cumulative distribution function. The sensitivity of mechanical cure with respect to chemical cure dβ/dα is also evaluated. A maximum in sensitivity is systematically observed at the vitrification point. The models developed in this study should be useful for incorporating information on the chemical and mechanical cure kinetics of adhesives in hot-pressing models and other processing models.