Conventional chemical wood preservatives have been banned or restricted in some applications due to human and animal toxicity and their adverse impact on the surrounding environment. New, low-environmental-impact wood treatments that still provide effective protection systems are needed to protect wood. Thermal modification of wood could reduce hygroscopicity, improve dimensional stability and enhance resistance to mold attack. The aim of this study was to investigate if these properties enhanced in thermally modified (TM) wood through treatments with oils. In this study, TM European aspen (Populus tremula) and downy birch (Betula pubescens) wood were impregnated with three different types of oil: water-miscible commercial Elit Träskydd (Beckers oil with propiconazole and 3-iodo-2-propynyl butylcarbamate, IPBC), a pine tar formulation and 100% tung oil. The properties of oil-impregnated wood investigated were water repellency, dimensional stability and mold susceptibility. The treated wood, especially with pine tar and tung oil, showed an increase in water repellency and dimensional stability. However, Beckers oil which contains biocides like propiconazole and IPBC showed better protection against mold compared with pine tar and tung oil. To enhance the dimensional stability of the wood, pine tar and tung oil can be used, but these oil treatments did not significantly improve mold resistance rather sometimes enhanced the mold growth, whereas a significant anti-mold effect was observed on Beckers oil treated samples.
The aim of this experiment was to impregnate thermally modified wood using an easy and cost-effective method. Industrially processed thermally modified European aspen (Populus tremula L.) and birch (Betula pubescens Ehrh.) were collected and secondarily treated at the laboratory scale with the preservatives tung oil, pine tar and Elit Tra ¨skydd (Beckers) using a simple and effective method. Preservative uptake and distribution in sample boards were evaluated using computed tomography (CT) and scanning electron microscopy (SEM) techniques. Preservative uptake and treatability in terms of void volume filled were found the highest in Beckers and the lowest in tung oil-treated samples. Thermally modified samples had lower treatability than their counterpart control samples. More structural changes after thermal modification, especially in birch, significantly reduced the preservative uptake and distribution. The differences of preservatives uptake near the end grain were high and then decreased near the mid position of the samples length as compared with similar type of wood sample. Non-destructive evaluation by CT scanning provided a very useful method to locate the preservative gradients throughout the sample length. SEM analysis enabled the visualization of the preservative deposits in wood cells at the microstructural level.
Scots pine (Pinus sylvestris L.) sapwood lumber was collected after kiln drying and preservative treatment with Celcure AC 800 (a copper-amine wood preservative). Distribution of the preservative throughout the lumber was visually examined. Not all, but some samples showed specific localized areas without any preservative distribution throughout their entire length. Those samples were assessed further for anatomical properties, specifically in impregnated and unimpregnated areas. Additional study was conducted on the morphological nature and redistribution of lipophilic extractives using three different histochemical staining methods. Intrinsic wood properties – especially the frequency of axial resin canals and the percentage of canals blocked – were found to be responsible for the irregular distribution of the preservative. Furthermore, the inability to create continuous and frequent interstitial spaces due to the collapse of thin-walled ray cells throughout the lumber resulted in un-even distribution of preservatives. Staining techniques were useful to localize places with more or less abundance of extractives (e.g., fats) in impregnated and unimpregnated wood, which varied considerably. Histochemical observations revealed information pertaining to the kiln dry specific distribution and redistribution of extractives between the areas. Moreover, resin reallocation and modification in ray parenchyma and resin canals induced by kiln drying would be another reason for the impregnation anomalies.
SubjectThe effect of three different drying procedures on moisture and dimensional changes for Scots pine and Norway spruce during subsequent climate changes has been studied.Material and methods Matched samples of 15 mm thick cross sections from 10 individual green planks (50´100 mm 2 ) of pine and spruce respectively, were dried at three different temperature levels: LT, LHT and HT. In every case during the initial drying phase, the samples were kept in tight glass jars to extend the capillary phase. The drying procedures were performed as follows: LT drying with 48 hours in glass jars at +55°C dry bulb followed by 48 hours at +80°C/8% EMC. LHT drying with 48 hours in glass jars at +55°C dry bulb followed by 12 hours at +120°C in dry oven, and ®nally HT drying with 12 hours in glass jars at +120°C followed by 12 hours at 120°C in dry oven. After drying all samples were equalized in a climate chamber at +30°C/8% EMC for 109 days. After equalization the material was exposed to 6 cyclic climate changes followed by oven drying to 0% MC. In green state, after drying and after every climate change the specimens of the test series were weighed and dimensional changes were measured on digital scanned greyscale images. Maximal radial and tangential shrinkage, changes in MC and dimension from green state during cyclic climate changes were calculated and evaluated statistically in order to ®nd if signi®cant differences at 5% level exist between drying methods and species. Results and discussionThe results are summarized as follows:· Maximal shrinkage during drying in one step from green to 0% MC at +103°C for 12 hours was measured on a reference material. No difference exists between pine and spruce in maximal radial or tangential shrinkage for this reference material. · LHT and HT dried materials show, for both pine and spruce, signi®cantly higher maximal radial and tangential shrinkage after ®nal oven-drying to 0% MC, compared with reference material. · HT dried spruce shows signi®cantly higher maximal shrinkage at 0%MC compared with HT dried pine. · During cyclic climate changes the HT dried material shows a signi®cantly lower MC compared with LT and LHT series for both pine and spruce. · The changes in shrinkage from green state (Ds rad ) during cyclic climate changes, i.e. the real displacement, show no obvious dependence on the drying method. In case of signi®cant differences, the LT dried materials show least changes i.e. are more dimensionally stable as opposed to the results from Sandlands (1999) investigation. · During climate changes the change in shrinkage from green state/change in MC(Ds rad /DMC) shows no dependence on drying method or species according to Fig.
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