Finn Englund

Monoterpenes in Scots pine and Norway spruce and their emission during kiln drying.

Summary Scots pine (Pinus silvestris) and Norway spruce (Picea abies) were dried in a laboratory kiln, using conventional schedules with temperatures up to 60°C as well as schedules reaching 110°C. The losses of terpenes, which completely dominate the fugitive emissions from kiln drying of softwoods, were estimated by extraction of pooled subsamples from each batch, before and after drying. The original contents of terpenes were found to be in the ranges of 0.4–0.5% in pine sapwood, 0.8–1.1% in pine heartwood, and 0.02–0.08% in spruce, all calculated relative to the dry weight of the wood. The emissions from pine corresponded to 25–50% of the original content and those from spruce to 10–50%. High temperature drying in the laboratory was accompanied by larger losses, but this tendency was not found in the full-scale drying of spruce. No consistent difference was found between timber from the north of Sweden and from the south. Sampling of the vent exhaust fumes did not give results of sufficient reliability to confirm the extraction analyses.

Spectroscopic studies of surface chemical composition and wettability of modified wood

Abstract Recent advances in spectroscopic methods used in the surface science field may provide new valuable information about the surface chemical composition of engineering materials. Such methods, combined with wettability analyses, have been applied in the development of well-designed adhesives and coating systems for newly developed and commercially available modified wood materials. The main objective of this paper is to demonstrate and present some aspects on the application of two different state-of-the-art spectroscopic methods for surface chemical composition studies of a complex material such as modified wood. The methods are X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), the former generating more quantitative data and the latter more qualitative data. The spectroscopic data are also combined with wettability data obtained from contact angle measurements using the Wilhelmy method. Modified wood samples were prepared from pilot plant or commercially produced acetylated, furfurylated and thermally modified wood. Effects of wood surface ageing, i.e. the time after machining, on the surface chemical composition and wettability were also studied. Results clearly indicate a hydrophobization process due to ageing of the unmodified and certain modified wood, probably mainly related to a migration and reformation of extractives in the surface. The surface composition and wettability of acetylated wood was not appreciably affected by the ageing process. Such findings could be quantified by the XPS measurements, which is further discussed and related to the different wood modification routes. ToF-SIMS is a powerful tool and complementary to XPS for identification of, for example, specific hydrophobic substances in the wood surfaces. In addition, this method provides ion images, mapping the lateral distribution of selected secondary ions signals within an analysed wood surface area.

Association between temperature, relative humidity and concentration of volatile organic compounds from wooden furniture in a model room

Abstract Emissions of volatile organic compounds (VOCs) from wooden furniture in a childs room were investigated. A model room was set up in a 12 m3 test chamber, and in parallel, a scaled-down version was run in a 1 m3 test chamber. The latter had a steady climate of 23°C/50% relative humidity (RH), while the temperature and humidity conditions were varied in the 12 m3 chamber between 18 and 28°C, and 30 and 80% RH. Compounds found were α-pinene, β-pinene, 3-carene, limonene and hexanal. Variations in the climate showed that there is an association between temperature and room concentrations of all found VOCs. Changes in RH showed effect on hexanal concentration, and all monoterpene concentrations remained unaffected.

Moisture buffering, energy potential, and volatile organic compound emissions of wood exposed to indoor environments

The use of wood in built environments has been increasing during the last decades, and more focus has been set on the influence of wood surfaces on indoor environments on the objective and subjective measures of human well-being. In addition, the moisture buffer capacity of hygroscopic materials, such as wood, has been under investigation in order to quantify the impact of wooden surfaces on energy savings in buildings. The current study presents the results of wood surfaces and indoor air temperatures as well as indoor air relative humidity measured in two solid timber test houses. The findings reveal a substantial effect on wood surface temperature under fluctuating indoor relative humidity due to the latent heat of sorption of water vapors. The results were compared with hygrothermal numerical simulations, showing good agreement and the validated numerical model was used in order to quantify the energy performance in a bathroom when the latent heat of sorption is exploited. The combination of wood with a well-controlled HVAC system in rooms with moisture production shows significant potential for indirect energy savings by adjusting the indoor temperature and exploiting the increase of surface temperature in the hygroscopic structure. Furthermore, the emissions of volatile organic compounds from pine wood were studied in laboratory facilities, with focus on the variations of emissions due to diurnal fluctuations in air humidity. Human participants were exposed in a large test chamber to a concealed source of volatile organic compound emissions in the form of fresh pine wood, while the actual exposure reached air levels of monoterpenes up to 18 mg/m3 during the intervention situation. Perceptions of air quality and mucosal irritation effects were reported in a standard questionnaire during this double-blind test with no irritation effects reported.

Mechanism of partial fixation of compressed wood based on a matrix non-softening method

Abstract Three different mechanisms to explain the partial fixation of the compressive deformation of wood are postulated: non-softening, cross-linking and stress relaxation. This study attempted to fix the compressive deformation of wood by the non-softening mechanism of the cell-wall matrix using acetylation of the cell wall making it more hydrophobic. In this method, partial recovery of compressive deformation by wetting decreased at room temperature as the acetyl content increased. However, almost complete recovery occurred by boiling the compressed wood in water or soaking in acetone. This is due to the ability of boiling water or acetone to soften the cell-wall matrix of acetylated wood enough to enable recovery from compression. It is, therefore, possible to partially fix the compressive deformation of wood, preventing the resoftening of the cell-wall matrix in water.

Emission of glycol ethers from medium-density fibreboard surfaces coated by a waterborne lacquer under different drying conditions

Abstract The use of waterborne coatings has become increasingly popular in the furniture industry, as the use of organic solvents is going to be restricted according to a European Union directive. Waterborne coatings commonly need the use of up to 15% organic solvents to achieve proper film formation. The chemicals used usually have a lower vapour pressure than common solvents and may cause elevated emissions of volatile organic compounds (VOCs) during the first few weeks. This article describes the influence of temperature and relative humidity (RH) on later VOC emission during the lacquer drying of medium-density fibreboard. Twenty-seven boards were lacquered with a common industrial waterborne clear lacquer and dried under climatic conditions ranging from 20°C to 40°C, and 20% to 80% RH. The emission of VOCs was measured using a field and laboratory emission cell at 24 h, 72 h, 10 days and 28 days after drying. The cosolvents 2-butoxyethanol and 2-(2-ethoxyethoxy)ethanol were found. Their emission rates ranged from 400 to 16,000 µg m−3. Boards dried at a higher temperature emitted significantly less than those dried at 20°C. Drying at high RH resulted in lower emission levels than drying at low RH. This is explained by a higher mass transfer between the liquid lacquer phase and the air. If the lacquer film is kept wet for a longer period, the organic cosolvent reservoir can be depleted during a longer time. These findings agree with the concept of critical RH derived by Dillon [Journal of Coatings Technology, 1977, 49(634), 38].