Durability of isocyanate resin adhesives for wood III: degradation under constant dry heating

The durability of isocyanate resins consisting of emulsion-type polymeric diphenylmethane diisocyanate (EMDI) was investigated under constant dry heating. Two kinds of resin, water only-added resin and polyol/wateradded resin, were used in this study. The kinetic studies based on the weight losses of the resins were carried out by isothermal thermogravimetry (TG) at temperatures ranging from 260° to 320°C. The apparent activation energies of the resins were calculated for weight losses of 5%, 10%, and 15%. The values of apparent activation energy of the resins increased with increasing weight loss. The bond-strength reductions of the specimens bonded with the resins were observed at various temperatures from 120° to 180°C. The best-fitting regression function for the behavior of bond-strength reduction was determined statistically. The apparent activation energy of each resin was calculated from the regression function for the half-life period. According to the calculated values, the adhesion durability of polyol/wateradded resin was superior to that of water only-added resin. To speculate on the changes in weight loss and the chemical structure of the resins in the glue lines under dry heating, changes in the cured resins were also observed.Part of this paper was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, 1999