Durability of isocyanate resin adhesives for wood. II. Effect of the addition of several polyols on the thermal properties

The thermal properties of isocyanate: (IC) resins prepared with a small amo unt of polyether polyols and water were investigated using dynamic mechanic al analysis (DMA). The bond strengths of 3-ply plywoods glued with these po lyol-containing IC resins were also measured. The thermal stability was dra matically improved by addition of dipropylene glycol-type polyols with mole cular weights of 400 and 1000. In addition, the bond strengths in a dry con dition and after aging at 250 degrees C for 10 min exhibited high values co mpared with that of an IC resin cured with water alone. However, addition o f the same polyol type with a molecular weight of 3000 resulted in low heat stability and low bond strength. In the case of glycerin-type polyol with a molecular weight of 400, good thermal stability and slightly higher bond strength were obtained. When bisphenol A and pentaerythritol-type polyols w ere used, not much improvement in thermal stability was achieved. The bond strengths were similar or inferior to that of an IC resin cured with water only. (C) 1999 John Wiley & Sons, Inc.