Raman spectroscopic study on the behavior of boric acid in wood

Abstract

 Raman spectra of Japanese cedar (Cryptomeria japonica D. Don) treated by vacuum impregnation with aqueous boric acid solutions (8.1 × 10⁻² to 7.29 × 10⁻¹ mol dm⁻³) were recorded using a near-infrared laser as an excitation source. Raman spectroscopic measurements were carried out on treated wood blocks of two sizes: 20(T) × 20(R) × 5(L) mm (A-type) and 15(T) × 15(R) × 50(L) mm (B-type). Our attention was focused on a prominent band (ν ₁) assigned to a symmetrical stretching vibration of the BO₃ group because no Raman band due to boron species was observed except bands of B(OH)₃. We observed a change in ν ₁ band intensity with increasing boric acid concentration in the aqueous solution used to treat the A-type wood blocks and investigated the correlation between the intensity and the peak-top wavenumber. Raman line maps in the longitudinal direction of the treated B-type wood blocks revealed that B(OH)₃ is concentrated near the cut ends. These results suggested that two groups of B(OH)₃ exist in wood in terms of the chemical species in the nearest neighbor sphere.