1,721,198 research outputs found
Basalt grid reinforcement of lightweight plywood
No full textAbstract By using basalt fibre grids as a reinforcing material, lightweight plywood with improved bending properties could be produced by using low density hardwood veneers and phenol-formaldehyde (PF) adhesives. The improvement in flexural strength would allow it to be used in a wider range of load-bearing applications. In this study, acrylate-coated basalt fibre grids with a grammage of 200g m - 2 and uncoated basalt fibre grids with a grammage of 116g m - 2 were inserted into the outer glue joints of five-layer lime ( Tilia cordata ) plywood as reinforcement. The plywood was bonded with two formulations of PF adhesive. The evaluation of the mechanical properties showed increases for the modulus of rupture (MOR) and the modulus of elasticity (MOE). The increase in MOR was up to 25% in the parallel direction of the top layers and up to 49% in the perpendicular direction of the top layers for plywood reinforced with the acrylate-coated basalt fibre grid compared to the unreinforced reference in a raw density-adjusted comparison. After treatment to evaluate moisture resistance under cyclic test conditions (MR), the reinforced plywoods exhibited similar bending strength to the unreinforced reference after standardised climate conditioning. At the same time, the addition of coated basalt fibre grid had no effect on surface soundness (SS). Therefore, the use of coated basalt grid as a reinforcing material could be a good way to produce high-strength plywood using low-density hardwood veneers.Fachagentur Nachwachsende Rohstoffe e.V.Georg-August-Universität Göttingen 50110000338
Modification of wood with silicon compounds. inorganic silicon compounds and sol-gel systems: a review
No full textThis review describes the treatment of wood with various inorganic silicon compounds. Among these compounds silicofluorides represent one of the long-known classes of wood preservatives based on silicon. Data on an organic fluorosilicon compound ("silafluofen") are additionally presented. The mode of action of these fluorides is based on their biocidal action. "Water glass", an alkali silicate, was able to enhance the durability of wood but showed some important drawbacks. Because of its high hygroscopicity and its high pH values, increased moisture absorption and strength loss of wood was frequently observed. Wood treated with tetraalkoxysilanes showed an enhanced dimensional stability, especially when the hydrolysis and the condensation of the silanes was controlled to react within the cell wall. Durability and fire resistance were improved to a certain degree and could be significantly enhanced by addition of boron compounds
Treatment of wood with silica sols against attack by wood-decaying fungi and blue stain
No full textPine sapwood was treated with various types of silica sols. Whereas alkaline sols were not able to penetrate deeper into wood, neutral and acidic sols showed good penetration. The weight percent gain of treated specimens amounted to 20-25%; bulking was negligible or even slightly negative. All silica sols in the treated specimens were stable against water leaching. A water submersion test revealed hydrophobation of the wood only after treatment with a cationic silica sol; all other silica sols increased the rate of water uptake. The addition of 2% cationic sol to a malt-agar growth medium caused growth inhibition of 40-50% of the wood decay fungi Coniophora puteana and Trametes versicolor, whereas the other silica sols did not inhibit growth. Pine sapwood and beech wood blocks treated with the cationic sol showed a strong reduction in mass loss compared to the control samples after incubation with C. puteana (pine) and T. versicolor (beech) according to EN 113 and CEN/TS 15083-1; all other silica sols did not inhibit fungal decay. The cationic silica sol reduced blue staining by Aureobasidium pullulans compared to the untreated control but did not fully prevent it; all other silica sols did not inhibit blue staining
Mode of action of brown rot decay resistance of thermally modified wood: resistance to Fenton's reagent
No full textThe resistance of heat treated (HT) wood to brown rot fungi has been investigated, while the role of the Fenton reaction (FR) in the initial phase of degradation was in focus. Micro-veneers made of Scots pine, were HT with various intensities and their mass losses (MLHT) were determined before soaking with a solution of Fenton's reagent containing Fe ions and hydrogen peroxide. The mass loss of the veneers treated that way (MLFT), their tensile strength loss (TSLFT) and the H2O2 decomposition were observed. The MLFT, TSLFT, and H2O2 loss decreased with increasing MLHT of the veneers. Soaking of the veneers in acetate buffer containing only Fe without H2O2 revealed that the heat treatment (HT) strongly reduces the Fe uptake by the cell walls. FTIR spectroscopy indicated oxidation of the unmodified control veneers but did not reveal predominant decay of cell wall components; the HT veneers were not changed at all due to FR. It was concluded that the reason for the enhanced resistance of HT wood to FR is attributable to hindered diffusion of Fe ions into the wood cell wall.German Academic Exchange Service (DAAD
Water vapour sorption of wood modified by acetylation and formalisation analysed by a sorption kinetics model and thermodynamic considerations
No full textThe water vapour sorption data of untreated (W-untr), acetylated (W-ac) and formaldehyde-treated (W-FA) Scots pine (Pinus sylvestris L.) sapwood were analysed in terms of their sorption kinetics and were transformed into excess surface work (ESW) isotherms. The sorption kinetics were studied by fitting the non-linear parallel exponential kinetics (PEK) model to the experimental data in which the sorption kinetics curve is composed of two processes (fast and slow components). W-ac and W-FA showed evident differences in their sorption kinetics and their thermodynamic sorption behaviour. In contrast to acetylation, formalisation influenced both the extent of the slow sorption process and the shape of its pseudoisotherm. For W-untr and W-ac, it appears that some water associated with the slow process is adsorbed at sites for fast sorption newly generated upon swelling (previously postulated as extra water) and subsequently desorbed by the fast process. For W-FA, the formation of extra water hardly occurs. ESW was reduced through acetylation with a constant factor over the whole hydroscopic range, whereas the ESW of W-FA was reduced only after reaching the monolayer capacity compared to its control. The sorption behaviour of W-ac was solely determined by cell wall bulking, whereas that of W-FA was governed by the increased matrix stiffness due to cross-linking of the cell wall polymers
Modification of wood with silicon compounds. Treatment systems based on organic silicon compounds - a review
No full textA wide variety of organo-silicon compounds has been described for application on wood. Some compounds such as organo-functional silanes which are mostly applied in combination with tetraalkoxysilanes (sol-gel process) as well as chlorosilanes and trimethylsilyl derivatives were proposed for a full impregnation treatment of wood. Other systems have been developed for surface treatment of wood such as plasma coating with hexametyldisiloxane and micro-emulsions which mainly contain silane/siloxane mixtures. The effects related to the various treatments vary from an increase in dimensional stability, durability and fire resistance to an enhanced hydrophobation of wood. In the cases of decay and fire resistance a combination of silicon based systems with other chemicals was required to obtain satisfactory results. Due to the excellent water repellent ability and weathering stability of some treatments, application of silicon treated wood under conditions of hazard class III (EN 335 outside above ground exposure) is recommended
Hydrolysis of cellulose and wood powder treated with DMDHEU by a hydrolase enzyme complex, Fenton's reagent, and in a liquid culture of Trametes versicolor
No full textCellulose was treated with various concentrations of 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU) to obtain different DMDHEU contents in the cellulose preparation. The release of sugars due to hydrolysis by a cellulase enzyme complex clearly decreased with increasing DMDHEU content. When the cellulose preparation with the highest DMDHEU content was subjected to pretreatment with Fenton's reagent (Fe2+, H2O2), the sugar release increased 4.5-fold. Incubation of modified cellulose with only H2O2 did not increase sugar release by cellulase. Compared to cellulose, the sugar release from milled wood powder induced by cellulase was very low but still decreased due to treatment with DMDHEU. Sole incubation of wood powder with Fenton's reagent did barely cause more sugar release compared to the storage of wood powder in buffer, but when the pretreated wood was incubated with cellulase the sugar release was higher than without pretreatment. Release of sugar from untreated cellulose in liquid cultures of the white-rot fungus Trametes versicolor was detected after 7 days and increased linearly with incubation time. Sugar release from DMDHEU-treated cellulose was much lower and was not detectable before 21 days of incubation. Total protein content in the cultures was low, but was slightly higher in the cultures of untreated cellulose. Laccase activity was not different in the presence of untreated and DMDHEU-treated cellulose after 7 and 14 days, but increased with increasing DMDHEU content after 21 and 28 days.German Science Foundation (DFG) [Mi 934/1-3
Mechanical properties of lightweight gypsum composites comprised of seagrass Posidonia oceanica and pine (Pinus sylvestris) wood fibers
No full textMode of action of brown rot decay resistance in phenol-formaldehyde-modified wood: resistance to Fenton's reagent
No full textThe mode of action of phenol-formaldehyde (PF)-modified wood has been investigated with respect to its resistance to brown rot decay. The Fenton reaction is assumed to play a key role in the initial brown rot decay. Pine microveneers were modified to various weight percent gains (WPG) with low molecular weight PF and exposed to a solution containing Fenton's reagent. The mass loss (ML) and tensile strength loss (TSL) as well as the decomposition of hydrogen peroxide within the incubation time decreased with the increasing WPG of the veneers. Incubation of untreated and PF-modified veneers in acetate buffer containing ferric ions without H2O2 revealed that the modification strongly reduces the uptake of iron by the wood cell wall. Further studies indicated that lignin promotes the decay of wood by Fenton's reagent. The reason for the enhanced resistance of modified wood to the Fenton reaction is attributable to the impeded diffusion of iron ions into the cell wall rather than to the blocking of free phenolic sites of lignin, which accelerate redox cycling of iron.German Academic Exchange Service (DAAD
Effects of acetylation and formalization on the dynamic water vapor sorption behavior of wood
No full textThe dynamic water vapor sorption of untreated, acetylated (W-ac), and formaldehyde-treated (W-FA) Scots pine (Pinus sylvestris L.) sapwood was studied in a dynamic vapor sorption apparatus to assess the effects of cell wall bulking and cross-linking. Both modifications resulted in a considerable reduction of reduced equilibrium moisture content (EMCR), the corresponding equilibrium times, and hysteresis in the hydroscopic range of wood. Acetylation reduced the adsorption and desorption of water at each given relative humidity (RH) step from 0% to 95% RH, whereas formalization affected the sorption behavior of wood solely above 20% RH. From 20% to 95% RH, the EMC ratio of W-FA to its control steadily decreased, whereas the EMC ratio of W-ac was still constant in this RH range. Below 20% RH, the sorption behavior of W-ac was governed by hydroxyl blocking, whereas that of W-FA was hardly influenced compared with the control. Above 20% RH, the sorption behavior of W-ac was solely determined by cell wall bulking, whereas that of W-FA was governed by the increased matrix stiffness due to the cross-linking of cell wall polymers
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