Infrared spectral characteristics and surface inactivation of wood at high temperatures

Summary Spectra resulting from chemical changes in white spruce Picea glauca (Moench) Voss] microsections heated in air or nitrogen at high temperatures (100 to 240°C) were continuously recorded on an infrared spectrophotometer.A significant change occurred in the intensity of the 1730 cm^-1 band which indicates a carbonyl absorption of carboxyl and ester groups of wood. This intensity initially decreased and the increased at a greater rate. The time periods to reach the minimum inflection point, termed the times to initiate a significant oxidative carboxylation or oxidation, showed a good curvilinear relationship with heating temperatures.Quantification of this time-temperature relationship required to reach a significant level of oxidation was achieved, using wood microsections that had extractives removed to varying degrees. It was concluded that the extractives served only as catalysts for oxidation. When drying wood at temperatures over 180°C, in addition to oxidation, pyrolytic degradation occurred.Chemical evidence was further confirmed by tests of plywood panels bonded with phenolformaldehyde glue. Three separate types of veneers were investigated—non-extracted, acetone extracted, and veneer with the surface chemically stabilized by treatment with sodium borohydride. The results suggest that the time period to reach a significant level of oxidative carboxylation is also the time period to initiate a wood surface inactivated to polymer adhesion.The author wishes to thank Miss D. Bouchard and Mr. H. N. Mukai for their assistance in the experiments. Appreciation also is due to Mr. H. MacLean for a critical review of this paper.