Bilayer Coating Composed of Starch and Methyl Cellulose-Nanoscale TiO2 for the Protection of Historic Paper from UV

Abstract

Among the agents of deterioration considered particularly damaging to cultural heritage objects are light, ultraviolet (UV) and infrared. The high-energy UV is the most damaging of the three, as it can cause irreversible visual, chemical and structural changes in cellulose-based materials. Known for its photocatalytic properties, TiO2 can absorb UV and is thermally and chemically stable. In this study, we propose an innovative bilayer coating composed of starch, methyl cellulose and nano-TiO2 to utilize UV blocking properties of TiO2. The results of the treatments were assessed by determining physical, optical and surface properties, as well as the degradation degree of the samples, prior and post accelerated ageing. The results show that an increase in the weight concentration of TiO2 enhances the colour difference, but the colour of samples coated by lower concentrations of TiO2 after accelerated ageing is closer to the original value than the colour of the uncoated ones. An increase in both the contact angle and the absorption time is also present, but after ageing, both parameters significantly decrease due to the presence of TiO2. To conclude, the presented nanocomposite coating can protect historic paper from UV, but one should bear in mind that a higher weight concentration could lead to a higher water sensitivity after exposure to UV.