Proceedings e report - Firenze University Press

FUNGAL DECONTAMINATION BY COLD PLASMA: AN INNOVATING
PROCESS FOR WOOD TREATMENT
Charlotte Leclaire 1 *, Elodie Lecoq 2 , Geneviève Orial 3 , Franck Clement 2 , Faisl Bousta 3
1 Cercle des Partenaires du Patrimoine, LRMH, Champs-sur-Marne, France
2 Université de Pau et des Pays de l’Adour, Laboratoire d’Electronique des Gaz et des Plasmas, Pau, France
3 Laboratoire de Recherche des Monuments Historiques, Champs-sur-Marne, France
Abstract
Cold plasma technology offers an environmental approach to decontaminate wood surfaces, alternative to
conventional methods such as biocides applications. Decontamination effect of plasma discharge is evaluated on
a blue-stain fungus Aureobasidium pullulans, responsible for bluish discoloration of wood material causing
aesthetical and economical damages. Several gas mixtures and exposure times were assessed. These results
suggest that fungal spores are inactivated after an afterglow exposure of 15 minutes.
1. Introduction
In the last years, biological decontamination by afterglows issued from plasma devices has shown
promising results [1-3]. Efficiency of plasma discharges as a sterilisation process has been proved on
bacteria contamination, in several industrial activities.
Wood material exposed to natural outdoor conditions is subject to biological development. In the case
of fresh maritime pine (Pinus pinaster), bluish discoloration due to blue-stain fungi development
causes aesthetical damages, limiting its use according to safety issues. Nowadays, preventive chemical
treatments are performed to delay fungal growth, but new environmental issues impose to develop
alternatives to conventional biocides.
According to industrial requirements, flowing afterglow which is a clean dry process offers numerous
advantages and may answer to specific needs regarding preservation of cultural heritage.
The present study focuses on the assessment of atmospheric pressure afterglow efficiency as a curative
treatment. In order to better understand the mechanisms involved between the excited gas and
microorganims, efficiency of plasma afterglow is initially assessed directly on fungal cultures of
Aureobasidium pullulans, set on a membrane filter. After recalling plasma characteristics, the main
objective is, in the first place, to set up the experimental device and the characterisation means to find
better plasma parameters to inactivate Aureobasidium pullulans. Finally, first promising results are
presented.
2. Gas plasma
2.1. Definition and characteristics of gas plasmas
Cold plasmas, in reference to their low gas temperature, are partially ionised gases generated from the
introduction of sufficient energy to ionise a molecular or atomic gas. For instance the application
between two electrodes, in the gas, of an electric field leads to such environments. Thanks to the
supplied energy, numerous reactive species are created, resulting from collisions between electrons
and present neutral species. As a consequence, a cold plasma is composed of electrons, ions,
molecular and atomic neutral particles. Moreover, ions and neutral particles are constituted of a very
large number of excited states, themselves responsible for the formation of new elements as photons,
radicals, etc. This complex composition suggests that cold plasmas are potential energy tanks which
may interact with material surfaces in order to obtain physical and/or chemical modifications.
The Dielectric Barrier Discharge (DBD) technology provided for the experiments is a particular way
to generate cold plasmas. In this system, a dielectric coating on one or more electrodes is realised in
* Contact : charlotte.leclaire@culture.gouv.fr
Joseph Gril (edited by), Wood Science for Conservation of Cultural Heritage –Braga 2008: Proceedings of the International
Conference held by COST Action IE0601 (Braga - Portugal, 5-7 November 2008, ISBN 978-88-6453-157-1 (print)
ISBN 978-88-6453-165-6 (online) © 2010 Firenze University Press