Jonas Stenbæk:
Bio-sustainable Control of the Blue Stain Fungi Aureobasidium pullulans on Exterior Wood Coatings

Date: 04-08-2015    Supervisor: Bo Jensen

Imminent requirements and demands to the composition of protective wood coatings and the use of commercial biocides lead to an increased and necessary interest by the paint industry to find and develop alternative solutions within substitutions of raw materials and new innovative anti-fungal strategies. Besides comprehensive future regulations in the requirements and laws within the use of fossil-based raw materials, companies also have to take the increasing consumer awareness of environmental responsibility into account necessitating the companies to use more environmentally friendly solutions in the production, composition and service life of the protective coatings.

Today’s commercial biocides in the wood coating industry, e.g. IPBC, are proven environmental toxic and exposed to future regulations or indeed complete exclusions so new bio-sustainable alternative solutions are demanded. In this PhD study, a number of alternative and innovative solutions and strategies have been investigated and a number of possible new solutions and reviews are presented. The focus has been on the control of blue stain fungi e.g. Aureobasidium pullulans that lead to discoloration on processed wood and wood protective coatings.

In this study, a number of anionic compounds like fatty acid-based emulsifiers have been screened for anti-fungal properties. The best candidate, a Sodium Caproyl Lactylate, has further been tested in wood panel tests and the mode of action on the fungal cell membrane has been investigated. The compound exhibits promising anti-fungal properties, however, more in-depth investigation on the compound and closely similar compounds are recommended before an actual and useable technology are accessible. Other compounds like silica-encapsulated enzymes and nanoclay have also been investigated and interesting preliminary results makes ground for further studies based on promising anti-fungal properties when added to a standard coating without commercial biocides and tested in environmental mould growth chambers.

As a non-additive biocidal solution the structure of the topography on the surface on the coating has been studied. In this study, manipulation of the micro structure on the coating surface has been performed and revealed that small scratches-structure (between 4-20 μm) had an inhibitory effect on the attachment on fungal conidia from moulds while bigger structure scratches (>50 μm) did not seem to have a notable effect.

A comprehensive study in the role of an interfacial protein, hydrophobin, in the surface growth of Aureobasidium pullulans resulted in bioinformatic identification of two hydrophobin genes, first ever described in a blue stain fungi. The full genome of Aureobasidium pullulans (De Bary) P268 was sequenced and the bioinformatic information led to molecular gene manipulation in the attempt to clarify the role of hydrophobins in surface growth of Aureobasidium pullulans. Overall, this PhD thesis presents a range of studies in alternative and bio-sustainable solutions and strategies in controlling attacks of blue stain fungi on wood protective coatings. The results provide a state-of-art platform for further research and development of alternative options in the control of moulds in coatings.