THE EFFECTS OF TEMPERATURE AND HUMIDITY ON PHENOL-FORMALDEHYDE RESIN BONDING

The effects of temperature and relative humidity on phenol-formaldehyd e resin bonding were evaluated. Two flakes in a lap-shear configuratio n were bonded under an environment of controlled temperature (110 degr ees C, 120 degrees C, 130 degrees C, 140 degrees C) and relative humid ity (41%, 75%, 90%) for a series of time periods (0.25 to 16 min). The lap-shear specimens were then shear-tested on a mechanical testing ma chine and the results were used to establish a family of bond strength development curves at each temperature and level of relative humidity . At 110 degrees C, the higher relative humidity appeared to retard re sin bonding. The effects of relative humidity diminished as temperatur e increased to 140 degrees C. Bond strength development was chemical r ate-controlled. The rate of bond strength development at each relative humidity follows a first order reaction mechanism. The activation ene rgy of resin-wood bonding, determined by bonding kinetics, was higher than that of resin alone, determined by differential scanning calorime try. This comparison indicates that to form a strong resin-wood bond, a higher energy level might be required.