Moisture Properties of Heat-Treated Scots Pine and Norway Spruce Sapwood Impregnated with Wood Preservatives

An experiment was conducted on commercially heat-treated (HT) Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) sapwood collected from Ht Wood AB, Arvidsjaur, Sweden. Secondary treatment on HT wood was performed in laboratory scale by impregnating with water-repellent preservatives (a commercial one and pine tar) to evaluate their retention and different moisture-related properties. Preservative solutions were impregnated using a simple and effective method. Wood samples were heated at 170°C in a dry oven and were immediately immersed in preservative solutions. Considerable retention was observed in HT wood, particularly in pine. Moisture adsorption properties were measured after conditioning in a high-humidity environmental chamber (4°C and 84% RH). Experimental results showed that secondary treatment enhanced moisture excluding efficiencies by decreasing equilibrium moisture content, suggesting better hydrophobicity. Soaking test in water showed that antiswelling and water repellence efficiencies improved, especially in tar-treated wood. In addition, this type of treatment significantly decreased water absorption. It was also possible to decrease volumetric swellings. Thus, secondary treatment of HT wood with preservative, in particular with tar, improved dimensional stability and water repellency

Implementation of adaptive control systems in industrial dry kilns

Capacity optimisation of Norway spruce, 150x50 mm2 was carried out in a full-scale kiln dryer starting at 50 °C wet bulb temperature. The objective was to reach as high capacity as possible. Maximum allowed moisture content (MC) standard deviation was 10% of the end moisture content value with 2 % maximum allowed amount of checks. An adaptive control strategy for the process control of a kiln dryer was used to optimise the drying process. The temperature drop across the load (TDL) was used to achieve a constant moisture flux from the drying batch. The drying time was 56 h and the total cycle time was 66. 7 h. The end moisture content was 15. 6 % with a standard deviation of 1. 4 %-units. It was concluded that adjustments in TDL due to the amount of heartwood need to be done using this control strategy. Optimising start parameters for different wood species and board dimensions considering maximum allowed checking is important to achieve maximum capacity with this control strategy.Godkänd; 2003; 20071010 (ysko

Determination of the surface emission factors in wood sorption experiments

Fukttransporten i trä kan med god approximation beskrivas som en diffusionsprocess, åtminstone när temperaturen är under vattnets kokpunkt. Ytemissionsfaktorn anger hur långt ytfuktkvoten befinner sig från den omgivande luftens jämviktsfuktkvot och är mycket viktig att ta med i analysen av sorptionsförsök. I denna artikel diskuteras tidigare utförda mätningar och analyser av ytemissionsfaktorn och jämförs med de värden som fås från inverkan av luftgränsskiktet närmast virkesytan. In this paper some previously published data and results from new direct measurements of the surface emission factors are discussed and compared with values obtained from the boundary layer theory

Colour stabilization of heat modified Norway spruce exposed to out-door conditions

Wood boards from Norway spruce (300 mmx125mmx10mm) were heat modified in a pilot chamber corresponding to Thermowood-D quality. The surface of boards was sprayed with diluted solutions of ferrous sulphate alone or in combination with subsequent spraying of a 30% solution of hydrogen peroxide. The boards were exposed to outdoor conditions during summer 2009 (45o facing south). Colour coordinates were measured using a colorimeter.Only small changes in colour of boards were observed directly after the surface treatments. Lightness increased for boards with no surface treatments during out-door exposure (seven weeks). Increase in lightness was delayed when ferrous sulphate was applied to the board. Lightness was essentially unchanged during the out-door exposure period when ferrous sulphate and hydrogen peroxide was used to modify the wood surface (at low hydrogen peroxide charge a small increase of lightness was, however, observed). Chroma decreased for boards with surface treatments but levelled out after a couple of weeks. On the other hand a decrease in chroma of boards with no surface treatments started after about four weeks exposure. Hue increased for all the boards until the fourth week. After that hue of untreated boards and boards treated with both ferrous sulphate and hydrogen peroxide continue to increase.Godkänd; 2010; 20100302 (ysko

Förstudie: värmebehandling av trä : slutrapport

Projektet har bedrivits som en förstudie till en större ansökan inom området Värmebehandlat trä för interiört bruk. Projektet inleds med studier av olje- och tjärupptagning i värmebehandlat trä genomen speciell impregneringsmetod som bygger på förvärmning och undertryck i materialet. Tanken är att med denna metod kunna tillföre ytterligare en egenskap som skyddar trä och gör det attraktivt för inomhusbruk genom att t ex blockera den något besvärande luft som kommer från värmebehandlat trä. Projektet syftar till att undersöka möjligheten att med en förenklad impregneringsmetod erhålla tillräcklig penetrering av impregneringsmedel (Becker olja och trätjära) och i samband därmed studera fördelningen av impregneringsmedel i trä

Influence of heat transferring media on durability of thermally modified wood

Studies on the durability and dimensional stability of a series of hardwoods and softwoods after thermal modification in vegetable oils and in steam atmospheres have been performed. Mass loss after exposure to Coniophora puteana (BAM Ebw. 15) for 16 weeks was very low for European birch, European aspen, Norway spruce, and Scots pine thermally modified in a linseed oil product with preservative (for 1 hour at 200 degrees C). Fairly low mass losses were obtained for wood thermally modified in linseed-, tung-and rapeseed oil, and losses were related to the wood species. Low mass loss during rot test was also found for Norway spruce and Scots pine modified in saturated steam at 180 degrees C. Water absorption of pine and aspen was reduced by the thermal treatments and the extent of reduction was dependent on wood species and thermal modification method. Thermally modified aspen was stable during cycling climate tests, whereas pine showed considerable cracking when modified under superheated steam conditions (Thermo D). At lower modification temperature (180 degrees C) an increase in mass after modification in rapeseed oil of spruce, aspen and sapwood as well as heartwood of pine was observed, whereas at high temperature (240 degrees C) a mass loss could be found. Oil absorption in room tempered oil after thermal modification in oil was high for the more permeable aspen and pine (sapwood).Validerad; 2011; 20110415 (ysko

Thermal modification of birch using saturated and superheated steam

During the thermal modification, wood is normally exposed to temperatures between 160 - 220°C. As a result physical and chemical changes are taking place and some of the wood properties are changed. Dimensional stability and weather resistance are improved. On the other hand the mechanical strength properties are usually negatively affected by the treatment. The visual appearance is also changed. There were two different types of thermal modification processes used in this study. One of them was using saturated steam and the other one superheated steam. Treatment temperature was 160°C in saturated steam process and 185°C in superheated steam. The wood specie used in this study was Silver birch (Betula pendula). In the chemistry part the acid content was investigated. Despite the 25°C lower treatment temperature, birch modified in saturated steam was more acidic compared to birch modified in superheated steam. Some differences in equilibrium moisture content (EMC) and dimensional stability were found mainly in the environment T=20°C and RH=85%. The colour of birch treated in saturated steam at 160°C was darker than the colour of birch treated in superheated steam at temperature 185°C

Absorption of liquid water in pine, birch and spruce and the effect of heat treatment on the microstructure

Heat-treated and matched boards dried at 60°C of Scots pine (Pinus silvestris), Norway spruce (Picea abies) and Birch (Betula pubescens) were submerged into water, allowing for water absorption in the longitudinal direction during two weeks in room climate. Heat treatment was performed according to the Thermo-wood process at 170°C and 200°C. Boards from pine and spruce boards contained both sap- and heartwood. During water absorption computer tomography scanning, CT-scanning, was performed intermittently in order to measure the ascent of capillary water. Longitudinal water absorption in heat-treated pine sapwood was substantial larger compared to untreated sapwood. In pine heartwood the ascent of water was low in heat-treated as well as in untreated boards. Spruce showed low water absorption in sap- and heartwood in heat-treated as well as in untreated boards. In birch the water absorption was lower in heat-treated wood compared to wood dried at 60°. SEM-studies of the anatomical microstructure, pits and pit membranes were performed on heat-treated as well as on untreated material. SEM-studies revealed damages in heat-treated and dried pine sapwood mainly in pit membranes in the fenestriform cross-field pits connecting longitudinal tracheids with radial ray parenchyma cells. These damages are believed to play an important role in explaining the differences in water absorption between pine and spruce since the piceoid cross field pits in spruce seemed to be unaffected by heat treatment. In birch no striking, visible observations were found when comparing the three different treatment temperatures that could shed light to the observed big difference in capillary water absorption.Godkänd; 2006; Bibliografisk uppgift: Sider: 8; 20070501 (ysko

In Situ CT-Scanning of Checking and Collapse Behaviour of Eucalyptus nitens During Drying

Eucalyptus nitens has become a commercially important species in Chile and it isrepresenting one of the fastest growing wood-stock in the country. Today, it is widelyused for pulp and paper production, but the interest in using the solid wood has increasedin recent years. Before the sawn timber can be utilized, its moisture content must bereduced. Often during drying, hydrostatic tension forces within the cell exceed thecompressive strength of the thin cell wall of Eucalyptus nitens and the cell collapses. Thisphenomenon usually leads to severe surface deformation and both surface and internalcracks (honeycombing). Yield and quality of the final product, and thereby sawmills’profitability, are decreased by these cracks and deformations. The aim of this study wasto investigate, by CT-scanning samples throughout the drying process, if it is possible todetect when and how cracking and deformation occurs and develops in specimens ofEucalyptus nitens from Chile. Based on this knowledge, better drying schedules canhopefully be developed to improve the yield and provide a higher end-quality of the sawntimber

Heat treatments of high temperature dried norway spruce boards : Saccharides and furfurals in sapwood surfaces

Carbohydrates that migrate to wood surfaces in sapwood during drying might influence properties such as mould susceptibility and colour. Sugars on the surface of Norway spruce boards during various heat treatments were studied. Samples (350mm×125mm×25mm) were double-stacked, facing sapwood-side outwards, and dried at 110°C to a target moisture content (MC) of 40%. Dried sub-samples (80 mm × 125 mm × 25 mm) were stacked in a similar way and further heated at 110°C and at 130°C for 12, 24, and 36 hours, respectively. Glucose, fructose, and sucrose as well as 5-hydroxymethylfurfural (HMF) and furfural in the sapwood surface layer of treated wood were analysed using HPLC (RI- and UV-detectors). Carbohydrates degraded to a lower extent at 110°C than at 130°C. Furfural and to a larger extent HMF increased with treatment period and temperature. Heat treatment led to a decrease in lightness and hue of the sapwood surface of sub-samples, while chroma increased somewhat. Furthermore, considerably faster degradation (within a few minutes) of the carbohydrates on the surface of the dried spruce boards was observed when single sub-samples were conductively hot pressed at 200°C. Treatment period and initial MC influenced the presence of the carbohydrates in wood surface as well as colour change (ΔE ab) of the hot pressed sub-samples.Validerad; 2012; 20120807 (ysko