Improving the lightfastness and thermal stability of black urushi (oriental lacquer) by kraft lignin oleate

Abstract

Urushi, an oriental lacquer, is sensitive to light and easily deteriorates upon light exposure, leading to the fading and loss of gloss of its coatings. In this study, we attempted to improve the lightfastness of black urushi by utilizing the UV-absorbing properties of kraft lignin. Oleic acid-esterified kraft lignin was prepared and added to the black urushi to improve the compatibility. No aggregation of oleic acid-esterified lignin occurred in the black urushi, and the physical properties of the films were maintained to a large extent. A possible chemical interaction between lignin and black urushi was suggested upon thermal analysis. It was also found that the addition of lignin improved the thermal dimensional stability of black urushi. Finally, the high gloss factor of the black urushi film was maintained by adding oleic acid-esterified lignin after 168 h of light irradiation. Oleic acid-esterified lignin therefore appears as a promising functional additive to improve photostability of urushi coatings.