Critical moisture conditions for fungal decay of modified wood by basidiomycetes as detected by pile tests

The aim of cell wall modification is to keep wood moisture content (MC) below favorable conditions for decay organisms. However, thermally modified, furfurylated, and acetylated woods partly show higher MCs than untreated wood in outdoor exposure. The open question is to which extent decay is influenced by the presence of liquid water in cell lumens. The present paper contributes to this topic and reports on physiological threshold values for wood decay fungi with respect to modified wood. In total, 4200 specimens made from acetylated, furfurylated, and thermally modified beech wood (Fagus sylvatica L.) and Scots pine sapwood (sW) (Pinus sylvestris L.) were exposed to Coniophora puteana and Trametes versicolor. Piles consisting of 50 small specimens were incubated above malt agar in Erlenmeyer flasks for 16 weeks. In general, pile upward mass loss (ML) and MC decreased. Threshold values for fungal growth and decay (ML≥2%) were determined. In summary, the minimum MC for fungal decay was slightly below fiber saturation point of the majority of the untreated and differently modified materials. Surprisingly, T. versicolor was able to degrade untreated beech wood at a minimum of 15% MC, and growth was possible at 13% MC. By contrast, untreated pine sW was not decayed by C. puteana at less than 29% MC. © 2016 by De Gruyter 2016

Prirodna trajnost drva izloženoga iznad zemlje – pregled istraživanja

Besides its inherent resistance against degrading organisms, the durability of timber is influenced by design details and climatic conditions, making it difficult to treat wood durability as an absolute value. Durability classification is, therefore, based on comparing performance indicators between the timber in question and a reference timber. These relative values are grouped and related to durability classes, which can refer to a high range of service-lives. The insufficient comparability of such durability records has turned out to be a key challenge for service-life prediction. This paper reviewed literature data, based on service-life measures, not masked by a durability classification. It focused on natural durability of timber tested in the field above-ground. Additionally, results from ongoing aboveground durability studies in Europe and Australia are presented and have been used for further analysis. In total, 163 durability recordings from 31 different test sites worldwide based on ten different test methods have been considered for calculation of resistance factors. The datasets were heterogeneous in quality and quantity; the resulting resistance factors suffered from high variation. In conclusion, an open platform for scientific exchange is needed to increase the amount of available service-life related data.Osim otpornosti drva prema štetnim organizmima, na prirodnu trajnost drva utječe i dizajn detalja na proizvodima od drva te klimatski uvjeti, pa je teško razmatrati svojstvo trajnosti drva kao apsolutnu vrijednost. Stoga je klasifikacija trajnosti drva utemeljena na usporedbi pokazatelja izgleda drva, čija se trajnost određuje prema izgledu referentne drvne građe. Te su relativne vrijednosti grupirane i povezane s klasama trajnosti, što se može odnositi na veliki raspon životnog vijeka drvnih proizvoda. Nedovoljna usporedivost takvih zapisa trajnosti pokazala se kao ključni izazov za predviđanje životnog vijeka drvnih proizvoda. U radu se daje pregled literaturnih podataka utemeljenih na životnom vijeku drvnih proizvoda koji nisu maskirani klasifikacijom trajnosti. Naglasak je na prirodnoj trajnosti drva ispitanoj pri izloženosti drva iznad zemlje. Osim toga, prezentirani su rezultati aktualnih istraživanja prirodne trajnosti drva iznad zemlje u Europi i Australiji te su iskorišteni za daljnju analizu. U obzir za izračun faktora otpornosti uzeta su ukupno 163 podatka o trajnosti drva dobivena s 31 različitoga ispitnog mjesta u svijetu na temelju deset različitih metoda ispitivanja uzeti. Skupovi podataka su heterogeni s obzirom na kvalitetu i količinu, što je rezultiralo velikom varijacijom čimbenika otpornosti. Zaključno, potrebna je otvorena platforma za znanstvene razmjene kako bi se povećala količina dostupnih podataka o životnom vijeku proizvoda

Acetylation of Solid Wood. Wood Properties and Process Development

The influence of acetylation on selected wood properties has been determined for Scandinavian pine and spruce wood, in order to predict the behavior of acetylated wood when it is used in different applications. Only minor differences in both bending strength and the modulus of elasticity were obtained for acetylated wood when compared with unmodified wood, and can, for practical applications, be considered unaltered. The Brinell hardness was found to increase and the tendency of wood to deform under cycled relative humidity conditions was greatly reduced, owing to acetylation of the wood. Acetylated wood was also shown to give strong adhesive bonds, with conventional wood adhesives, and when the laminated wood was tested under wet conditions, the bond strength was higher for the acetylated laminated wood than for unmodified. High dimensional stability in the acetylated laminated wood, was reflected by the absence of radial cracks, after exposure to alternating water soaking and drying. The resistance of acetylated wood against common decay fungi was shown to be in the same order of magnitude when compared with that of CCA preservative treated wood in a field test. Testing of acetylated wood in marine environments showed almost no preserving effect against attack from marine borers. However, a slight decrease in attack with an increase in acetyl content could be observed. The stability of the acetyl groups under conditions of high or cycled humidity shows that acetylated wood can be used for products exposed to changes in humidity. Microwave heating has been shown to be beneficial to the acetylation of solid wood. The penetration depth of microwaves into acetic anhydride impregnated wood is about 10 cm and the reaction temperature (120-130\ub0C) can be rapidly reached. In samples acetylated in the microwave reactor, the acetyl groups were found to be evenly distributed over the wood volume. Microwave heating could also be used for the removal of excess acetic anhydride and by-product acetic acid under vacuum after completed acetylation reaction

Fältprovning av stängselstolpar : Lägesrapport nr 2

This is the second progress report on two field trials with fence posts at SP’s test site in Borås, Sweden. The tests started in 1997 and 2006. The aim of the tests was to comparethe performance of posts of “traditional” materials, such as untreated, fine-textured(narrow growth rings) Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) aswell as spruce posts with charred butt end or butt end immersed in a wood tar productwith preservative-treated posts, Nordic wood preservation class NTR A. Both trials were inspected in 2016 and the conclusions reported in the first progress reportwere further confirmed, namely Preservative-treated material, NTR class A, performs far better than untreated posts, irrespective of material, and posts of “traditional” material. Charred butt end has not improved the durability properties at all in this trial and was the same as for untreated material. The service life of the “traditional” materials was in general from a few years upto between 5 and 10 years. Favorable exposure conditions may give a somewhat longer service life. “Traditional” materials cannot be regarded as realistic alternatives topreservative-treated posts, NTR A class A, even with very low expectations onservice life and cost-effectiveness

Fältprovning av stängselstolpar : Lägesrapport nr 2

This is the second progress report on two field trials with fence posts at SP’s test site in Borås, Sweden. The tests started in 1997 and 2006. The aim of the tests was to comparethe performance of posts of “traditional” materials, such as untreated, fine-textured(narrow growth rings) Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) aswell as spruce posts with charred butt end or butt end immersed in a wood tar productwith preservative-treated posts, Nordic wood preservation class NTR A. Both trials were inspected in 2016 and the conclusions reported in the first progress reportwere further confirmed, namely Preservative-treated material, NTR class A, performs far better than untreated posts, irrespective of material, and posts of “traditional” material. Charred butt end has not improved the durability properties at all in this trial and was the same as for untreated material. The service life of the “traditional” materials was in general from a few years upto between 5 and 10 years. Favorable exposure conditions may give a somewhat longer service life. “Traditional” materials cannot be regarded as realistic alternatives topreservative-treated posts, NTR A class A, even with very low expectations onservice life and cost-effectiveness