An evaluation of changes induced by wet cleaning treatments in the mechanical properties of paper artworks

Wet cleaning of ancient papers is a common treatment performed for the removal of degradation products, external contaminants and salts, which can promote the degradation of cellulose (i.e., hydrolysis, oxidation). In this research, the effects on the mechanical properties of paper samples caused by wet cleaning treatments were evaluated by considering the changes induced in the ultimate tensile strength, deformation at break and flexibility. For this purpose, samples were subjected to different aqueous cleaning treatments such as immersion in deionised water and the application of rigid gels of agar and gellan gum at different concentrations was carried out. Tensile tests were run, and morphological observations of paper by means of light microscopy and scanning electron microscopy were recorded. Contrary to the significant changes in the mechanical properties of paper samples after immersion treatment (an increase in flexibility as the elongation at break), the use of gelled systems caused slight improvement in the mechanical properties of paper (in both the ultimate tensile strength as well as in the breaking strain). Changes in the mechanical properties of paper were also correlated with slight changes in the diameter of the cellulose fibres as a consequence of the swelling action of water molecules, especially in the case of immersion treatment. Finally, the tensile tests performed on the paper samples after thermo-hygrometric accelerated artificial ageing (70 °C and 65 % RH) demonstrated that cleaning treatments by rigid gels did not seem to accelerate any sort of paper degradation in the mid to long term.