Study On UV-curing Chinese Lacquer And Its Composites

Chinese lacquer with a high gloss and superhigh durability is dried by enzyme-catalyzed process at room temperature, which is a natural, energy-saving coating, as well as an environmentally friendly product and, most importantly, a people-friendly material, and it has been used to coat objects for more than 7000 years in China. However, Chinese lacquer films are formed by a laccase-catalyzed oxidation polymerization, following a coupling reaction as well as an autoxidation reaction on the long aliphatic unsaturated side chain. And, the lacquer drying process requires severe and specific conditions (about 80-90% relative humidity at 20-30℃). Additionally, when the laccase is inactivated (we call it dead lacquer), the lacquer can not dry, so these limit the applications of lacquer. To fabricate fast drying lacquer or to be free of the restriction of relative humidity and temperature, many efforts have been performed in this field. However, these methods still need a few hours to form lacquer films. To further improve the drying rate of lacquer saps is of high importance for the protection and restoration of archeological findings coated by lacquer or excavated lacquer wares and the development of new application of this lacquer.In this work, the UV-curing technology was introduced to dry Chinese lacquer quickly by using a high-pressure mercury lamp of 365 nm wavelength as a UV source. The effects of mainly specific components and the role of each reactive group of urushiol in the course of UV exposure were well-studied. The UV-induced polymeric behavior of Chinese lacquer was also investigated by FT-IR,1H NMR, SEM, TGA, and Py-GC/MS. In addition, the UV curing waterborne Chinese lacquer films were fabricated. Furthermore, the UV curing PU/MS nanocomposties were prepared by in situ method.It was found that the UV-cured Chinese lacquer films could be completely dried within 2 min in the absence of any additional photoinitiator, and that urushiol was the main component to form Chinese lacquer films, and decomposed to generate the urushiol semiquinone radicals, which sequentially induced the polymerization of Chinese lacquer by radical polymerization, as well as radical substitution under UV irradiation. In addition, the TG analysis suggested that polysaccharide and glycoproteins were integrated with the UV-cured films by covalent bonding. Furthermore, this method could be suitable to fast cure other phenol bearing long aliphatic unsaturated chain, such as CNSL. At the same time, the UV-cured Chinese lacquer films and the UV curing waterborne Chinese lacquer films had excellent properties. MS nanoparticles were homogeneously dispersed in the polymer matrix.Free of the restriction of relative humidity and temperature, this fast curable technology would bring bright and significant prospects into the field of the protection and/or restoration of archeological findings coated by lacquer or excavated lacquer wares and the new application of this lacquer. More interestedly, the dead lacquer, urushiol-based polymers, together with other long aliphatic unsaturated chain phenol derivatives such as CNSL, could also be rapidly dried within 2 min by using this method without an additional photoinitiator.