Deacidification of Acid Paper with Organic Base in Supercritical Carbon Dioxide

As one of valuable cultural assets, paper materials have been conserved in museums and libraries. However, a solvent, water employed in conventional processes has danger of destroying the paper due to deformation occurred during wet and dry treatments. In this study, supercritical carbon dioxide (scCO(2)), that is a fluid beyond critical point of pressure and temperature was used as a new solvent. The scCO(2) can penetrate in micro- and nanospace owing to its extremely low surface tension with carrying substances while it does not adsorb on hydrophilic materials causing no swelling of them. Therefore, the use of scCO(2) is expected to neutralize acid paper without damage. In the experiments, an acid paper without printing was accumulated in multi-layers and treated on batch processing with three organic bases, monoethanolamine, triethanolamine that are applied in conventional methods and triethylamine that is relatively dissolved in scCO(2). The pH of the paper increased from 5.5 to 7.0 or 7.5 after 1 hr-treatment, suggesting deacidificaiton of the paper by all organic bases in scCO(2) containing methanol. The acid paper handled with triethylamine in scCO(2)/methaol was neutralized faster without yellowing as compared with ethanolamines or by a vapor- and liquid phase methods. In addition, the tensile strength of the paper was not significantly influenced by the base treatment in scCO(2). The buffering effect of triethylamine impregnated in the acid paper lasted more than six months. Furthermore, fifty sheets of the acid paper were uniformly neutralized by scCO(2) method using triethylamine.