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 amount of polyether polyols and water were investigated using dynamic mechanical analysis (DMA). The bond strengths of 3-ply plywoods glued with these polyol-containing IC resins were also measured. The thermal stability was dramatically improved by addition of dipropylene glycol-type polyols with molecular weights of 400 and 1000. In addition, the bond strengths in a dry condition and after aging at 250°C for 10 min exhibited high values compared with that of an IC resin cured with water alone. However, addition of 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 were 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.