HSLL researchers have recently demonstrated that oxalic acid is the main contributor to the increased acidity in paper during natural degradation. In addition, they demonstrated that lignin, a natural component of historic paper particularly after 1850, is a main source of it. This finding is of key significance to the conservation of libraries and archives as it sidetracks the concerns about volatile organic acids and their contribution to degradation and firmly suggests that deacidification (a conservation treatment) is a method of choice for long-term conservation.
In the study published in Carbohydrate Polymers (Elsevier), titled “Impact of accumulation of organic acids on the degradation of cellulose in historic paper”, Ida Kraševec, Aleksander Kravos, Klara Retko, Hend Mahgoub, Irena Kralj Cigić, and Matija Strlič from the Heritage Science Lab of the University of Ljubljana and the Institute for the Protection of Cultural Heritage of Slovenia explored the impact of non-volatile carboxylic acids on the acidity and degradation of historic paper. Their work reveals, for the first time, the dominant role of oxalic acid in acidic paper conservation.
This study highlights that oxalic acid is the primary contributor to the decrease of pH during natural aging, owing to its high acidity (low pKa values) and low volatility. Its accumulation significantly accelerates cellulose degradation, making it a critical factor in library and archival preservation.
By investigating 89 European paper samples dated between 1844 and 1990 and with the aid of multivariate data analysis, the researchers found that oxalic acid accumulates during ageing and that lignin is either a direct precursor or that it promotes degradation pathways that produce oxalic acid. Further research is needed to clarify these mechanisms.
This research was funded by the Slovenian Research and Innovation Agency (ARIS) through the research core funding P1–0447 and research projects J7–50226, J4–3085, I0–E012, N1–0271, Z1–4404) and European Horizon Framework Programme (Grant No. 101060941).
Read more about the research in the journal article: https://doi.org/10.1016/j.carbpol.2024.123163