Questions and AnswersIn this section, we answer questions brought forward by the community. These are questions about conservation, preservation, storage, etc. They are answered either by a board member or an expert in the particular field, whom we will address on behalf of you. Questions concerning the research centre itself are answered here. Please do not hesitate to send your question to firstname.lastname@example.org. This service is for free.
- The use of ethanol in neutralising moulds and the differences between ethanols from various suppliers. In fact, we realised that depending on the supplier, the ethanol has varying properties (more or less "wetting", more or less smelling, more or less disinfectant). We even saw a non-biocide ethanol which is the opposite of what we want for neutralising mold...
- Do you know about neutralising mold on paper using ethanol vapour? This is a technique that we are using more and more over here which is very interesting on many points but we would need chemists' support on the composition of different ethanols available. Would you be able to advise me?
- There are a couple of comprehensive papers on the use of alcohol against moulds on paper:
- Nittérus, M. (2000a) ‘Ethanol as Fungal Sanitizer in Paper Conservation.’ Restaurator, 21(2) pp. 101– 115.
- Sequeira, S. O., Phillips, A. J. L., Cabrita, E. J., & Dinis, M. F. M. A. D. M. (2017). Ethanol as an antifungal treatment for paper: short-term and long-term effects. Studies in Conservation, 62(1), 33-42. https://doi.org/10.1080/00393630.2015.1137428
Summarising their results and my knowledge, ad answering your questions: Ethanol is a nonspecific antimicrobial, ranked among the membrane-active agents, which means that it acts through coagulation/denaturation of proteins and membrane damage, interfering with metabolism and causing cell lysis in bacteria and some fungi.
It can be used in a water:alcohol solution (best: 70% PURE ethanol – 30% pure water) to stop fungal growth. The presence of water is a crucial factor in destroying or inhibiting the growth of microorganisms with alcohol. Water acts as a catalyst and plays a key role in denaturing the proteins of vegetative cell membranes. 70% solutions penetrate the cell wall more completely which permeates the entire cell, coagulates all proteins, and therefore the microorganism dies. Extra water content slows evaporation, therefore increasing surface contact time and enhancing effectiveness. Alcohol concentrations over 90% coagulate proteins instantly.
Consequently, a protective layer is created, which stops other proteins from further coagulation. In most real situations (not in vitro testing), alcohol does not work against fungal spores, especially the thick and resistant ones (i.e. Chaetomium and other fungi with ascospores). When alcohol concentration is below 50%, usefulness for disinfection drops sharply, while an alcohol concentration higher than 70% doesn’t generate better bactericidal, virucidal, or fungicidal properties.
Therefore, different levels of effectiveness of the ethanol solutions on the market are to be found in the fungi and microorganisms treated (they can be very different in how they react), and especially in the water-alcohol ratio of the same solution and commercial formulations. Please always remind that ethanol is not preventing biodeterioration, it only stops actively growing fungi, without killing all of them. The different effects coming from the quality and supplier of the alcohol is all in the % of water in the sold solution, its purity, the presence of eccipients in the formulation. Any added chemicals can change the effects on fungal and bacterial cells, increasing the efficacy (i.e. some products sold for conservation contain small amounts of quaternary salts or other biocides that are themselves antimicrobial, some include glycerol or other stabilisers especially added when also perfumes are enclosed in the formulations that limit the effectiveness since these might protect microbial cells)
- The use of alcohol vapours is feasible and the mode of action is the same as with alcoholic solutions. Vapours should be used in closed chambers with a slightly negative pressure applied to facilitate the compound's vaporisation. In fact, ethanol ebullition point depends on the atmospheric pressure and the environmental temperature. In this case (use as a vapour) the PURE ethanol 100% (actually sold as 99%-98% since there is always a small percentage of constitutive water in the distilled product) ethanol should be used.
Some alcohols act better than ethanol (i.e. isopropanol) and are more easily evaporated. Isopropanol is more toxic if inhaled than ethanol. If you need more specific advice and details on the vapours, the effects of excipients in the formulation and their behaviour, please ask an organic chemist. There are few studies on the effects and efficacy of ethanol or isopropanol vapours (and in comparison with liquid treatments).
Here are some papers published on the topic:
- Bacílková, B. 2006. Study of the effect of butanol vapours and other alcohols on fungi. Restaurator 27 (2006): 186–199
- Dao, T., Dejardin, J., Benoussan, M., Dantigny, P. 2010. Use of the Weibull model to describe inactivation of harvested conidia of different Penicillium species by ethanol vapours. Journal of Applied Microbiology 109: 408–414
- Benedetta Favaro, Eleonora Balliana, Federica Rigoni, Elisabetta Zendri. (2021) A preliminary evaluation of chemical interaction between sanitising products and silk. Journal of Cultural Heritage 51, pages 1-13