Effects of Moisture on the Chemical Modification of Wood With Epoxides and Isocyanates
Keywords:Chemical modification, moisture content, epoxides, isocyanates, ponderosa pine
AbstractThe effects of moisture on the reaction of epoxides and isocyanates with wood were investigated. Ponderosa pine at 0%, 5%, and 10% equilibrium moisture contents was reacted separately with either propylene oxide or butylene oxide catalyzed with triethylamine, or with butyl isocyanate catalyzed with dimethylformamide. Five successive treatments were performed while recycling the treatment solutions on specimens with 5% and 10% equilibrium moisture contents. Grinding and extracting the treated wood showed significant losses of nonbonded chemical at these original moisture levels. When antishrink efficiency was determined on propylene oxide treated wood using the double water-soak method, a high resistance to dimensional changes was observed on the first water-soak cycle. Most of this dimensional stability was lost based on the second water-soak cycle, showing that nonbonded polymer had been extracted. Somewhat higher antishrink efficiency values were obtained for butylene oxide and butyl isocyanate treatments. Gas chromatographic determination of products from the propylene and butylene oxide/triethylamine treating solutions showed little water buildup. Total accountable volatile products decreased with successive treatments on specimens originally containing 5% and 10% moisture, indicating the formation of nonvolatile polyglycols in the wood cell wall. Determination of butyl isocyanate solutions following each treatment showed that one quarter or less of the active isocyanate was lost due to reaction with the water in the wood.
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