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Weathering, fungal decay and flame-protection of wood-plastic composites (BAM Innovation Project)
(2011)
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.
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.
Das Interesse für erneuerbare Energieträger ist in den letzten Jahren stark angestiegen.
Im Bereich Biomasse als erneuerbarer Energieträger wird besonders Holz ein großes
Wachstum auf dem Energiesektor prognostiziert (NITSCH 2007). Die Speicherung dieser
Energie erfolgt meist durch Holzhackschnitzelhalden in der Umwelt. Um ein tieferes Verständnis
der in der Halde ablaufenden mikrobiologischen Prozesse erhalten zu können,
wurden in einer neu aufgebauten Kiefernholzhackschnitzelhalde mit den Ausmaßen
15 m x 20 m x 6 m folgende Messungen durchgeführt: a.) Messung der Gaskonzentration
von Sauerstoff, Kohlendioxid als auch der Temperaturentwicklung innerhalb der Halde; b.)
Messung der Veränderung der Holzzusammensetzung innerhalb der Halde über die Zeit;
c.) Charakterisierung der Veränderung der Zusammensetzung der bakteriellen als auch
der pilzlichen Lebensgemeinschaften über die Zeit; d.) Charakterisierung von dominanten
Vertretern der bakteriellen als auch der pilzlichen Lebensgemeinschaften. Die Ergebnisse
zeigen, dass sich die Funktion und die Zusammensetzung der Lebensgemeinschaften
über die Dauer der Holzhackschnitzellagerung ändern, und dass diese Änderungen nur
zum Teil mit den Prozessen bei Kompostierungsanlagen vergleichbar sind.
Fast growing softwood species such as pine are preferred for biomass-based heat as well as electricity production and stored in large quantities. A newly established outdoor pile of freshly cut pine-wood chips was monitored to analyze exothermic processes. Inside the pile, a mean temperature increase of up to 44 °C was measured after six days of piling which was paralleled by a decrease of O2-concentration and an increase of CO2-concentration. Thereafter four additional CO2 maxima were observed, while O2-concentration remained at ambient concentration. The fungal community structure remained almost unchanged after four weeks, while the bacterial community structure was characterized by continuous shifts over time. The rapid heating in the early stage of storage corresponded to high relative abundance of microbial strains belonging to the genera Pseudomonas, Luteibacter and Caulobacter, ascomycetous genera Sphaeropsis and Cadophora and basidiomycetous order Polyporales and genus Sistotremastrum. The late stage was composed by a broader diversity of microorganisms, and heating processes inside the wood pile were attributed mainly to physicochemical processes. Taken together, these observations suggest that the early bacterial and fungal communities are key players in exothermic processes and were replaced by a broader diversity of highly adapted microorganisms.
The white-rot fungus Hypholoma fasciculare coexists with a bacterial community that uses low-molecular weight carbon sources provided by fungal, extracellular enzyme activities. Since fungal development on wood is limited by the availability of nitrogen (N), bacteria could contribute to the N supply. To prove or disapprove an interaction in terms of N transfer, N sources of the fungus and the coexisting bacterial isolates were investigated, and the bacterial N2 fixation was quantified. Fungal, fungal—bacterial and bacterial wood decomposition was analysed by Fourier transform infrared spectroscopy (FTIR), mass loss and surface pH. Microbial N preferences were investigated by elemental analysis isotope ratio mass spectrometry (IRMS). In addition, diazotrophic activity was explored after cultivation under a 15N2/O2 atmosphere. Decomposition was similar with and without bacteria and both H. fasciculare and coexisting bacteria preferred reduced N species, such as urea, ammonium and organic N. In most of the bacteria, the 15N abundance in the biomass increased significantly but to a low extent if they were cultivated under a 15N2/O2 atmosphere. This effect is considered an artefact and attributed to adsorption rather than to bacterial N2 fixation activity. Hence, the bacteria coexisting with H. fasciculare rather competed for the same N sources than supported fungal N supply by diazotrophic activity.