Antifungal activity of carvacrol-based solids and their effects on Whatman and Kraft paper

The degradation of cellulose-based materials by fungi represents a menace to the cultural heritage conservation. Carvacrol-based beta-cyclodextrins and cocrystals proved effective antifungal remedies in vitro but their effects on paper structure and properties were not studied. The aim of this study was to investigate possible structural modifications and alterations of the mechanical, optical and chemical properties of artificially aged and unaged Whatman and Kraft paper subjected to the treatment with carvacrol-based beta-ciclodextrins and cocrystals. The pH of the samples did not significantly change after the treatment, as well as no colour-related alterations were detected (1.00<Delta E<2.00). The tensile strength of both Whatman and Kraft paper was not affected by the vapours of carvacrol and spectroscopic analysis (FTIR and XRD) revealed no carvacrol-related damages of paper structure. The antifungal efficacy of the carvacrol-cocrystal was also proved on a book prototype made of Whatman and Kraft paper, kept under 98% of humidity for 28 days, and purposely inoculated with a mix of fungal species (A. alternata, Aspergillus sp. section Nigri, C. cladosporioides, and T. orientale). These results show the applicability of a carvacrol-releasing system, effective as antifungal remedy, and at the same time not harmful to Whatman and Kraft paper, as these materials did not show treatment-induced degradation.