From dark to light: light-coloured lignin for cultural heritage conservation

Lignin is a natural macromolecule with remarkable properties, such as UV-shielding and antioxidant capacity; however, its application is often limited by its intense, dark colour. In this paper, oxidation methods using hydrogen peroxide and peroxy-citric acid were employed to produce light-coloured lignins with tailored functional properties. The transition from the macroscale to the nanoscale enhanced both the UV-protective and antioxidant performance of bulk lignin, while further attenuating the visible coloration of the nanoparticle aqueous dispersions. Oxidized and unmodified lignin nanoparticles were incorporated into nanocellulosic films to develop protective coatings intended for the preservation of cellulosic cultural heritage artifacts, while safeguarding their aesthetic integrity. Nanoparticles derived from oxidized lignins imparted UV protection and antioxidant capacity to the films without significantly affecting their colorimetric properties. Therefore, the oxidized lignins presented herein offer a novel and environmentally friendly approach to lignin valorisation in colour-sensitive applications, including sophisticated uses such as the conservation of cultural heritage.