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Eingeladener Vortrag
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The biodeterioration of water-based manufactured formulations, such as polymer dispersions, is a major problem for the producing companies and the users of such products. Industrial preservatives, also known as biocides, are therefore used to protect these and similar products from the effects of microorganisms, predominantly bacteria and yeasts. In the absence of internationally recognised standard methods for determining the resistance of polymer dispersions to microbial growth and the efficacy of biocides used in them, protocols for testing other products, e.g., paints, have been adapted, and other methods produced by manufacturing companies, test laboratories, and academic institutions have been used. Often these do not take into account the specific nature of the materials being tested, the types of organism commonly causing contamination, and the conditions that the polymer dispersions will be exposed to during manufacture, storage, and use. By conducting a series of round-robin, collaborative tests, the member organisations of the International Biodeterioration Research Group Polymer Dispersion Working Group have identified the bacteria that commonly infect polymer dispersions, defined the main parameters necessary for a standard method of test, and developed a protocol that is robust, repeatable, and reproducible. The recommended test involves three repeat inoculations of the material with a previously determined mix of seven Gram-negative bacteria and evaluation of living cells by a simple plating technique. The work reported here, carried out by nine participating laboratories, is a final statistical validation and suggests that the method is eminently suitable as a standard test method.
Decay resistance of pine sapwood treated with titanium alkoxide solutions was tested against the brown-rot fungi Coniophora puteana and Poria placenta for exposure times of 10 and 16 wk. In practice, wood-specimens were vacuum-impregnated by alcoholic solutions of titanium alkoxide with concentrations in the range of 5–16 mass % (solid content in solution) and subsequently cured under different humidity conditions. Results reveal that treated wood degraded up to 5% in comparison to untreated one that deteriorated 38% and 50%, respectively against both wood-decay fungi. Even full protection (mass loss below 3%) was achieved against brown rot with titanium alkoxide solution containing solid content of around 5 mass% with a weight percentage gain (WPG) of 9 mass%. With increased concentration, fungal resistance decreased slightly which was associated with more cracks and imperfections formed in the deposited layers of titanium dioxide in the adjacent wood matrix. Thermal analysis verified that a considerable amount of precursor remained in the wood structure as un-hydrolyzed organic residues. These organics, being bioactive, had the tendency to induce similar fungicidal effects as those of conventional fungicides. The amount of organic residues is correlated with the decay resistance of the tested samples. In a prolonged decay test, mass losses of 16-wk incubated samples do not show behavior different from that of the wood samples incubated for 10 wk. This result implies that the decay protection is permanent and confirms further the fungicidal activity of titanium-alkoxide-treated wood.
The antileaching efficacy of sol-gel-derived TiO2- and SiO2-based precursors has been evaluated through laboratory leaching trials with pine sapwood in two different ways. In a one-step process, wood was vacuum impregnated by the precursor solutions containing CuCl2. The copper (Cu) emission rates of the sol-gel-based impregnated woods were up to 70% lower than that of wood treated with pure CuCl2 solution at the same level of concentration. More improvement (80%) could be achieved in a two-step process, in which sol-gel precursors were introduced into an already CuCl2-treated wood. The refinement was attributed to several effects. In the one-step approach, Cu was embedded in the TiO2/SiO2 gels formed in the wood texture. During a two-step impregnation, gel layers that were formed in the wooden interior acted as an effective diffusion barrier. The sol-gel impregnations made wood more hydrophobic; therefore, the low amount of water that penetrated the cell wall was less efficient to leach out Cu.
ISO 846 - Part A and B, Resistance to Fungi; Documentation and discussion of ring-test results
(2013)
Flame retarded wood-plastic composites (WPCs) should allow safe application in areas of fire risk. Halogen-free flame retardants can contain high amounts of nitrogen, phosphorus or sulphur, which may serve as nutrition source for wood degrading fungi and accelerate wood decay. Therefore, the material resistance of WPCs with each of four flame retardants against both fire or fungal decay was examined in comparison to WPC without flame retardant. Expandable graphite showed the best performance against fire in cone calorimetry and radiant panel testing. Two ammonium polyphosphates and a third nitrogen-containing flame retardant were not as effective. Contrary to the possibility that flame retardants might enhance fungal decay of WPC, the opposite effect occurred in case of the wood-degrading fungi Trametes versicolor and Coniophora puteana according to determination of mass loss and decrease of bending modulus of elasticity. Only the surface mould Alternaria alternata slightly increased the degradation of WPCs with nitrogen-containing flame retardants compared to WPC without flame retardant according to mass loss data and FTIR-ATR analyses. Finally, WPC including expandable graphite as flame retardant was effective against both fire and fungal decay.
As the results of a 14 weeks outdoor exposure of a series of automotive coatings in South Florida, the panels were found to be overgrown with an almost closed layer of mildew. Pinholes remained as permanent surface damage after removing the mildew mycelium. The extent of the damage differed in dependence of the kind of the coating. By tracing the images and profiles of the coating surfaces systematically over all phases of weathering and the subsequent cleaning procedure, a connection between formation of pinholes and mildew growth could be found. Outdoor weathering tests in other regions of Florida as well as in Europe and Australia showed that pinholes caused by mildew attack could also be found in all other locations, but always to a lower extent than in South Florida. The standardised mildew tests EN ISO 846 and MIL-STD 810F for laboratory exposure failed to reproduce the formation of pinholes.
Material performance testing of wood-plastic composites (WPC) requires adequate and time-efficient evaluation of the resistance against fungal colonisation and decay. This study investigates the effects of weathering on WPCs and subsequent material degradation by fungi. Weathering using UV radiation, water spray and repeated frost incidents caused micro- and macro-cracks. Fourier transform infrared spectroscopy (FTIR) demonstrated delignification of wood particles at the weathered WPC surface. Despite of increased surface area, accessibility for fungal hyphae and moisture content, weathering enhanced mass loss due to fungal decay only subtly but not significantly. These potentially enhancing effects for fungal decay are assumed to be outbalanced by delignification due to photo-oxidation and leaching of degradation products resulting in loss of nutrient sources essential for fungal growth.
Unterschiedliche Befeuchtungssysteme für Vitrinen, die die Ausstellungsobjekte bei definierter Luftfeuchtigkeit vor externen Einflüssen wie Staub bewahren sollen, wurden im Hinblick auf die Möglichkeit der potenziellen mikrobiologischen Kontamination untersucht. Ergänzend hierzu wurden Parameter wie pH-Wert und Leitfähigkeit des Wassers im Befeuchter untersucht und die mikrobiellen flüchtigen organischen Verbindungen (MVOC, microbial volatile organic compounds) in der Modellvitrine bestimmt. Die Leitfähigkeitsmessung kann als Indikator für den Verunreinigungsgrad des Wassers dienen, weil sie mit der mikrobiologischen Belastung korreliert. Weiterhin war eine mikrobiologische Belastung der Luft in der Modellvitrine auch bei relativ hoher Verunreinigung des Befeuchtungswassers nicht nachzuweisen.
During their growth on wood many fungi produce characteristic volatile organic compounds as secondary metabolites. These microbial volatile organic compounds (MVOCs) can be used as indicators of fungal growth even when such growth is concealed. In order to investigate the formation of these volatile metabolites on building materials, specimens of pine sapwood on agar media colonized by the dry-rot fungus Serpula lacrymans and a mixture of six moulds were examined. MVOCs from this fungal growth were studied over a period of up to half a year by ion mobility spectrometry (IMS) headspace analysis using a sensitive, portable IMS mini-device. The IMS headspace spectra from the growing fungal specimens obtained during this time span are differed from non-incubated wood specimens and indicate the presence of a mixture of MVOCs. The composition and amount of volatile metabolites of the fungi changed during cultivation. This was confirmed by a principal component analysis (PCA). Identification of different MVOCs in the headspace according to drift time and the mobility of ionized gaseous species in reference to GC-MS investigations were proposed. It was concluded that IMS can be used as a rapid and sensitive on-site method to indicate actively growing fungi concealed within wood.