Bonding kinetics of thermosetting adhesive systems used in wood-based composites: the combined effect of temperature and moisture content

—The processes operative within wood-based composites during hot pressing are briefly reviewed, and the role of adhesion in the system is considered. A new method is described for investigating how temperature and moisture content together affect the kinetics of thermosetting adhesive bond strength development. For this purpose, powdered phenol formaldehyde to wood bonds were formed under highly controlled, nearly steady-state conditions of temperature (between 90 and 120°C) and moisture content (between 4 and 16%); after a range of curing times, the bonds were immediately destructively tested in tension. Plotting accumulated strength versus forming time enables construction of strength-development curves, which reveal an initial delay before the onset of strength development, a period of nearly constant strength development, a small discontinuity in which the bonding rate is reduced, and, finally, a period of well-defined bonding at an ever decreasing rate. All the stages of these curves were found to be...