ISOCYANATE WOOD ADHESIVE BOND

We have used infrared spectroscopy to study the reaction between pheny l isocyanate and glucose, cellulose, lignin, and wood. In the latter i nstance we have investigated oven-dried wood, wood at its fiber satura tion point, and wood at 19% and 7% moisture levels. Our results show t hat the isocyanate reacts with all these entities, but that its reacti on with water is quicker than with any of the other hydroxyl-containin g compounds, and when water is present the water-isocyanate reaction d ominates all others. Lignin was found to react more readily than any o f the sugar derivatives. In oven-dried wood, the presence of strong ne w absorptions at 1712 and 1694 cm(-1) (indicative of a carbamate group ) is evidence of a direct chemical bond between the isocyanate and the wood polymer structure. We have also studied the reaction between 4,4 '-diphenylmethane diisocyanate (MDI)-a commercially used adhesive-with wood flour at various levels of moisture content (MC), and the infrar ed spectra again support the presence of a wood-isocyanate bond for ov en-dried wood and for wood at 7% moisture content. For wood at higher moisture content levels, our infrared results suggest that the isocyan ate reacts with the water in preference to the wood polymers.