No abstract

There are several biological processes causing aging and damage to buildings. This is partly due to natural aging of materials and excessive moisture. The demands on durability, energy balance, and health of houses are continually rising. For mold development, the minimum (critical) ambient humidity requirement is shown to be between RH 80% and 95% depending on other factors like ambient temperature, exposure time, and the type and surface conditions of building materials. For decay development, the critical humidity is above RH 95%. Mold typically affects the quality of the adjacent air space with volatile compounds and spores. The next stage of moisture-induced damage, the decay development, forms a serious risk for structural strength depending on moisture content, materials, temperature, and time. The worst decay damage cases in North Europe are found in the floors and lower parts of walls, where water accumulates due to different reasons. Modeling of mold growth and decay development based on humidity, temperature, exposure time, and material will give new tools for the evaluation of durability of different building materials and structures. The models make it possible to evaluate the risk and development of mold growth and to analyze the critical conditions needed for the start of biological growth. The model is also a tool to simulate the progress of mold and decay development under different conditions on the structure surfaces. This requires that the moisture capacity and moisture transport properties in the material and at the surface layer be taken into account in the simulations. In practice there are even more parameters affecting mold growth, e.g., thickness of the material layers combined with the local surface heat and mass transfer coefficients. Therefore, the outcome of the simulations and in situ observations of biological deterioration may not agree. In the present article, results on mold growth in different materials and wall assemblies will be shown and existing models on the risk of mold growth development will be evaluated. One of the results of a newly finished large Finnish research project ‘modeling of mold growth’ is an improved and extended mathematical model for mold growth. This model and more detailed research results will be published in other papers.

The effect of two stilbene compounds, pinosylvin and resveratrol, on the growth of several fungi was evaluated in plate tests. Wood decay tests were carried out with birch and aspen samples impregnated with the two stilbenes. In plate experiments, resveratrol had an enhancing effect on growth at concentrations where pinosylvin was already enough to prevent the growth of most fungi studied. Pinosylvin impregnated at 0.2% (w/w) concentration significantly reduced the decay caused by all fungi except Phellinus tremulae. In contrast, a resveratrol content of 0.8%, did not protect the wood from decay. A pinosylvin-synthase-encoding gene from Pinus sylvestris was transferred into aspen ( Populus tremula) and two hybrid aspen clones ( Populus tremulax tremuloides) by Agrobacterium tumefaciens-mediated transformation. Transgenic plants accumulated pinosylvin synthase-specific mRNA and showed stilbene synthase enzyme activity in vitro. Transgenic aspen line H4 showed increased resistance to Phellinus tremulae, while two hybrid aspen transformants decayed faster than the control trees. However, we were unable to detect the accumulation of stilbenes in the transgenic plantlets.

Our purpose was to develop a FTIR spectroscopic method to be used to determine the lignin content in a large number of samples and to apply this method studying variation in sapwood and heartwood lignin content between three fast-growing cutting clones grown in three sites. Models were estimated with 18 samples and tested with 6 samples for which the Klason lignin + acid soluble lignin content had been determined. Altogether 272 candidate models were built with all-subset regressions from the principal components estimated from differently treated transmission spectra of the samples; the spectra were recorded on KBr pellets of sieved and unsieved unextracted wood powder and subjected to four different preprocessings and two different wavenumber selection schemes. The final model showed an adequate fit in the estimation data (R 2 = 0.74) as well as a good prediction performance in the test data (R 2 P = 0.90). This model was based on the wavenumber range of 1850-500 cm -1 of the linesubtraction-normalised spectra recorded from sieved samples. The model was used to predict lignin content in 64 samples of the same material. One of the clones had a slightly lower sapwood lignin content than the two other clones. The fertile growing site with fast growing trees showed slightly higher sapwood lignin content compared with the other two sites. The model was also used to predict the lignin content in the earlywood of 45 individual annual rings. Variation between individual stems and between annual rings was found to be large. No correlation was found between the lignin content and density of earlywood.

The effect of acetic, maleic or succinic anhydride modi®-cations of wood ®ber on the mechanical properties and dimensional stability of differently bonded ®ber boards was studied. The binders for the ®ber boards used in this work were: powdered phenol formaldehyde resin of the novolak type (PF), polypropylene (PP) and a combination of the two. In the second part of the research, birch veneers modi®ed with succinic or phthalic anhydride were laminated with PP ®lms and the effect of the modi®cations on the interfacial bond between the two materials was studied. Signi®cant improvement in the mechanical properties of the PP-bonded boards was generally observed as a result of the anhydride modi®cations. Modi®cation of wood ®bers with maleic anhydride resulted in a reduction in the modulus of rupture of the PF-and PF/PPbonded boards, whereas acetylation and modi®cation with succinic anhydride did not cause any signi®cant changes in the modulus of rupture of the boards. The anhydride modi®cations improved the internal bond strength of the ®ber boards regardless of the binder type used. Dimensional stability of the ®ber boards was observed to increase signi®cantly as result of the modi®cations. Adhesion between the PP ®lms and wood veneer showed an increasing trend as function of the degree of modi®cation. In addition, SEM micrographs of the ®ber boards and PP-coated veneer revealed improved interaction between the two components due to the anhydride modi®cations. Einfluû chemischer Modifikation des Holzes auf die mechanischen und Hafteigen-schafton von Holz-und Polypropylen-Fascrplatten sowie Polypropylen/Furnier-Werkstoffe Der Ein¯uû der Modi®kation von Holzfasern mit Essig-, Malein-und Bernsteinsa Èureanhydrid auf die mechanischen Eigenschaften und die Dimensionsstabilita Èt von unterschiedlich gebundenen Faserplatten wurde untersucht. Als Bindemittel wurden verwendet: Phenol-Formaldehydharz (Pulver) vom Novolak-Typ (PF), Polypropylen (PP) sowie eine Kombiation der beiden. Weiterhin wurde Birkenfurnier mit Bernstein-und Phthalsa Èureanhydrid modi®ziert und mit PP-Filmen beschichtet. Der Ein¯uû der Modi®kation auf die Bindung zwischen den beiden Materialien wurde untersucht. Allgemein konnten signi®kante Verbesserungen der mechanischen Eigenschaften der PP-gebundenen Platten durch die Reaktion mit den Anhydriden erreicht werden. Die Modi®kation der Holzfasern mit Maleinanhydrid fu Èhrte zu einer Verringerung des MOR der PF-und PF/PP-gebundenen Platten. Dagegen blieb der MOR nach Acetylierung oder Modi®kation mit Bernsteinsa Èureanhydrid weitgehend unvera Èndert. Alle Modi®kationen mit den Anhydriden verbesserten die Querzugfestigkeit der Faserplatten unabha Èngig vom Bindemittel. Die Dimensionsstabilita Èt der Faserplatten stieg aufgrund der Modi®kation ebenfalls deutlich an. Die Haftung zwischen den PP-Schichten und dem Furnier verbesserte sich parallel zum Ausmaû der Modi®kation. Zusa Ètzlich konnte anhand von REM-Aufnahmen von Fascrplatten und PP-beschichtetem Furnier die verbesserte Wechselwirkung der beiden Kompon...