Effectiveness of Physical and Chemical Methods for Antifungal Protection of Paper

Abstract

Paper-based materials, particularly those of historical, cultural, or scientific value, are highly susceptible to damage caused by microscopic fungi. Micromycetes are capable of inducing both physical destruction of cellulose fibers and chemical degradation through the production of secondary metabolites, including organic acids and pigments. Fungal growth on archival documents and library collections not only results in the loss of informational value but also poses health risks to humans. Therefore, the search for effective antifungal treatments that combine strong biocidal activity with safety for both users and the material substrate remains an urgent task. This study aimed to compare the effectiveness of physical (freezing, freezing followed by drying) and chemical methods (the commercial preparation Valeus D and newly-synthesized compositions of guanidinium-containing oligomers) for the antifungal treatment of different paper types (printing, newsprint, and rag paper) under conditions of high humidity and inoculation with fungal spores. Methods. Ten strains of micromycetes — Alternaria alternata, Acremonium strictum, Aspergillus flavus, A. niger, Chaetomium globosum, Cladosporium cladosporioides, C. sphaerospermum, Fusarium moniliforme, F. poae, and Trichoderma sp. — were used to model biodeterioration. Fungal resistance was assessed according to DSTU IEC 60068-2-10:2015 (IEC 60068-2-10:2005, IDT) using a five-point infection scale, with visual and microscopic examinations on the 14th and 28th days of exposure. Results. Among the physical methods, the combination of freezing with drying showed the highest effectiveness, particularly for newsprint paper. Chemical treatment demonstrated significantly higher resistance to fungal growth, with composition No. 4 (aromatic guanidinium-containing oligomer with branched oligotrimethyl iodide) markedly outperforming the commercial product Valeus D. However, in most cases, fungal growth resumed by the 14th day, indicating a lack of prolonged fungicidal effect. Even in the absence of spore inoculation, the development of background mycobiota (Cladosporium cladosporioides, C. sphaerospermum, Aspergillus flavus, Trichoderma spp., Penicillium spp.) was observed, confirming the high risk of natural contamination during storage under elevated humidity. Conclusions. Newly synthesized guanidinium-containing oligomers, particularly the composition of an aromatic guanidinium-containing oligomer with branched oligotrimethyl iodide, are promising agents for antifungal treatment of paper materials. In particular, the use of physical preservation methods may prove valuable in emergencies situations, when large collections of documents have been excessively moistened, as it can help prevent their rapid colonization by micromycetes. The optimal approach involves combining physical and chemical methods, which produces a more pronounced inhibitory effect on micromycete growth. These findings can be applied in developing preservation protocols for archival and library collections.