The degradation of paper is an inevitable process, as the paper is composed of organic compounds which decompose due to the processes of natural ageing. The papermaking process has changed through centuries. Between 1850 and 1990, wood and aluminum sulfate were used for the paper production, which caused paper acidity, brittleness and its limited durability. Conservators and conservation scientists are trying to find solutions to slow down the degradation of historical paper to preserve the cultural heritage. Deacidification is an important and widely used conservation treatment to slow down the degradation of paper due to acid hydrolysis and consequently increase its longevity.
The aim of this study was to evaluate the effectiveness of various non-aqueous deacidification dispersions during thermally accelerated degradation on model lignocellulose papers.
The effectiveness of commercially available nano calcium hydroxide dispersions in ethanol or 2-propanol (Nanostore Paper, CaLoSiL), Bookkeeper deacidification dispersion (containing submicron MgO particles in organic solvent perfluoroheptane) and laboratory prepared nano calcium carbonate dispersions in ethanol or 2-propanol was evaluated.
FE-SEM and SEM-EDS analyses were performed to determine the size of CaCO3 particles in the dispersion and distribution of calcium ions on the paper surface. The effectiveness of non-aqueous dispersions after deacidification of paper was evaluated by determinations of pH value, alkaline reserve, and spectrometric determination of the color changes. The kinetics of paper degradation was studied by size-exclusion chromatography. The degree of polymerization of cellulose was determined before and after 4, 9 and 14 days of accelerated thermal degradation. During thermally accelerated degradation, the changes of paper color were followed. For all treated paper samples, the degradation rate constants decreased in comparison to the untreated control paper sample.
Deacidification of paper samples with Bookkeeper dispersion and with nano calcium hydroxide dispersion in ethanol or 2-propanol had a noticeable effect on color stability of model paper samples.
Therefore, it can be concluded that deacidification for such lignocellulose papers, where color stability is important (manuscripts, paintings, etc.) with Bookkeeper and calcium hydroxide dispersions is not recommended. To preserve such objects, the use of less invasive and milder alkaline deacidification agent, such as dispersion of nano calcium carbonate is recommended.
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