Light-induced color change of acetylated wood meal of kiri (Paulownia tomentosa Steud)

For improving surface color of kiri wood (Paulownia tomentosa Steud.), the wood meal and the extracted wood meal were acetylated in acetic anhydride-acetic acid-perchloric acid mixtures after pretreating in acetic anhydride-acetic acid mixtures, and subsequently irradiated by the light emitted by a 400 W mercury lamp. Large color changes were observed in the acetylated wood meal (acetyl content: 24.4%) that were produced in medium containing 0.06 mol% of perchloric acid as a catalyst and subsequently irradiated for 168 h. CIE (Commission Internationale de l'Eclairage) whiteness (L*) and yellowness (b*) increased by 15 points from 69 to 84 and by 1.5 points from 17.1 to 18.6, respectively, and redness (a*) decreased by 3.2 points from 2.9 to -0.3, compared with those of the unirradiated, acetylated wood meal. After 168 h of irradiation, the significant photostability was shown. The extracted wood meal treated as above had color changes comparable with that of the wood meal treated as above, but the effect of extraction on color changes was not significant.