Effect of oil impregnation on water repellency,dimensional stability and mold susceptibility of thermally modified European aspen and downy birch wood

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.     

Analysis of the pore-size distribution and fiber saturation point of native and thermally modified wood using differential scanning calorimetry

The aim of this paper was to investigate pore-size distributions in the nano-diameter range of wood and their alteration due to thermal modification of wood using thermoporosimetry, and to find out what consequences can be derived regarding the biological durability. Thermoporosimetry is a technique that is based on the measurement using differential scanning calorimetry (DSC). The method is based on the fact that frozen water contained within small pores is at elevated pressure and therefore has a depressed melting temperature as a function of the appropriate pore diameter. In addition, the fiber saturation points (FSP) were determined by DSC. The former were performed in an isothermal-step method and the latter using the continuous heating-up method. Native and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.), Sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelsior L.) were analyzed. The results clearly show that the pore shares of wood for the measurable diameter range between 4 and 400 nm decrease considerably in all studied wood species due to thermal modification of the wood. Furthermore, thermal modification of wood leads to a decreased FSP for all studied wood species. For evaluation as well as reproducibility of the results of pore-size distribution and FSP, the consideration of sensible heat and specific heat of fusion plays an important role. If this is not done, it can lead to misinterpretations.     

Initial sprouting, growth and mortality of European aspen and birch after selective coppicing in central Sweden

For reasons of aesthetics, sheltering, biodiversity, and children’s need of playgrounds, selective coppicing could be a useful and effective silvicultural method in urban areas. A randomised block experiment was carried out in three broad-leaved coppices situated within the fenced area of Arlanda Airport to compare a selective coppice regime (SCR), where all trees above a certain height limit were cut, with a traditional coppice regime, where all trees were felled. The effects of the treatments of the dominating tree species European aspen (Populus tremula L.) and birch (Betula pendula Roth and B. pubescens Ehrh.) were studied. During three growing seasons after performed treatment, the proportion of sprouting stools and root shooting of European aspen were reduced in SCR. Birch stools had fewer sprouts stool⁻¹, and sprouts of both birch and European aspen tended to be shorter in SCR. There was a tendency that the sprout mortality was lower in SCR for both birch and European aspen. Residual stands of SCR consisted of proportionally less birch, and more rowan, bird cherry, oak and other species. Coppicing with single tree selection from above suppressed light demanding tree species and promoted the more shade-tolerant species compared to traditional coppicing.     

Study of the transverse liquid flow paths in pine and spruce using scanning electron microscopy

Samples of pine (Pinus sylvestris) and spruce (Picea abies) were impregnated with a low-viscous epoxy resin using a vacuum process. The epoxy was cured in situ and the specimens sectioned. Deposits of the cured epoxy was then observed in the wood cavities using a scanning electron microscope. The investigation concentrated on tracing the transverse movements of a viscous liquid in the wood, and special attention was therefore given to the cross-field area between ray cells and longitudinal tracheids. A damage hypothesis is proposed based on the results obtained in the present investigation in combination with those from earlier studies on linseed oil-impregnated pine: In addition to the morphology of the bordered pits, viscous liquid flow in wood is dependent on damage that occurs during the impregnation procedure. For pine sapwood, liquid flow is enabled through disrupted window pit membranes, which divide the longitudinal tracheids and the ray parenchyma cells. A mechanism accounting for the reduced permeability of pine heartwood is believed to be deposits of higher-molecular-weight substances (extractives) in the ray parenchyma cells and on the cell walls. In spruce the thicker ray cells in combination with the smaller pits, which are connected to the longitudinal tracheids, reduce permeability considerably.     

Equations for estimating above- and belowground biomass of Norway spruce,Scots pine,birch spp. and European aspen in Latvia

This study aims to derive allometric functions to estimate the above- and belowground biomass components of the most important tree species in Latvia. The study material included a total of 81 Norway spruce (Picea abies [L.] Karst), 102 Scots pine (Pinus sylvestris L.), 105 birch spp. (mainly silver birch (Betula pendula Roth)) and 84 European aspen (Populus tremula L.) trees sampled in 124 forest stands. The suitability of three mathematical models for the prediction of total aboveground biomass, stem biomass, total live and dead branch biomass, belowground biomass and small root biomass was evaluated. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change mean default values for the root-to-shoot ratio recommended for temperate and boreal ecological zones leads to the overestimation of root biomass of young trees, especially Scots pine and Norway spruce. Our findings indicate that biomass functions recommended for other Baltic Sea countries are not appropriate for the assessment of the biomass stock in Latvia’s forests because these lead to biased estimates. The biomass functions derived in our study are recommended for reporting the biomass stock in Latvia.     

Gluability of thermally modified beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.) wood

Abstract

One of the main disadvantages of wood is hygroscopicity resulting from its polar character. The sorption–desorption of water causes unwanted swelling and shrinkage in wood. Thermal modification substantially reduces this inconvenient feature. Unfortunately, the same chemical changes that reduce water sorption alter the polar character of the material and result in poorer wetting of thermally treated wood by waterborne adhesives. Gluability of thermally modified beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.) wood with two commercial amino resins, melamine–urea–formaldehyde (MUF) and melamine–formaldehyde (MF), and a two-component polyurethane (PUR) adhesive was investigated. Both wood species were modified according to two temperature regimes: 160°C and 190°C. Shear strengths of the joints were then determined according to EN 205:2003 standard. The results showed that thermally modified beech and birch wood can be effectively glued not only with commercially available PUR adhesives, but also with aqueous MF and MUF resins. The resultant shear strengths of the joints were limited by the strength of the thermally modified substrate.     

Microdistribution of metal elements in wood impregnated with a copper-chrome-arsenic preservative as determined by analytical electron microscopy

Summary The distribution of Cu, Cr and As in the walls of tracheids of Scots pine impregnated with Tanalith C at a retention of 2.5 lb/ft³ has been examined at the submicroscopic level in the electron microscope microanalyser, EMMA-4, using the absolute method, as well as in the conventional electron microscope. All three elements are present in all regions examined (probe area 0.2 m diameter). The concentration of Cu ranges from 0.4–0.9% (w/w), that of Cr is about 0.8%, while As ranges from 2%–2.6%. The morphology of this fine deposit is clearly dictated by the run of the cellulose microfibrils. There is in the wall an occasional coarse deposit, almost entirely copper, and the inner face of the tracheid wall is covered by a thin layer 20–30 m thick which contains all these elements at high concentration.     

Evaluation of thermally modified beech and spruce wood and their properties by FT-NIR spectroscopy

Quality assessment of thermally modified spruce (Picea abies (L.) Karst) and beech (Fagus sylvatica L.) wood and of the corresponding reference samples was carried out by means of non-destructive FT-NIR spectroscopic measurements and PLS regression. Oven-dry and basic density as well as MOE and MOR determined by 3-point bending tests were evaluated. The focus was put on specimens produced from material that had been thermally modified in an industrial scale kiln. Modelling results range from poor to very good. The results of the spectra taken from the spruce samples resulted in better prediction results than the spectra of the beech samples. This could be due to different proveniences or variation in the industrial modification process. The results indicate that FT-NIR surface measurements of sound thermally modified wood samples could be applied to evaluate several characteristics before and after the modification process. The method could be used for screening during pre-sorting of thermally modified wood.     

Three-dimensional imaging of a sawn surface: a comparison of confocal microscopy,scanning electron microscopy,and light microscopy combined with serial sectioning

The three-dimensional structure of a transverse sawn wood surface was investigated using several methods, to compare techniques, and to study the types of deformation in tracheids at the saw cut. A sample of spruce sapwood was cut with a fret saw across the grain. The transverse sawn surface was imaged by confocal microscopy, field emission scanning electron microscopy (FESEM), and by light microscopy combined with serial sectioning and three-dimensional (3D) reconstruction. Both confocal microscopy and FESEM were restricted to visualising the cut surface of the wood. However, serial sectioning was able to reveal the internal structure below the cut surface providing more information on the types of cell deformation present. The wood structure was deformed to depths of more than 600 μm below the surface with twisting, crushing and tearing deformations. Near the outer surface, gaps were formed between groups of tracheids where the cell walls had been torn away to form saw dust. The deformation tended to form groups of tracheids that were twisted relative to each other. Latewood was less distorted, forming a dense solid surface compared to the highly fibrous earlywood.     

Lamellation in the S2 layer of softwood tracheids as demonstrated by scanning transmission electron microscopy

Summary Ultrathin cross sections of the tracheid wall in black spruce and silver fir have been examined at high resolution by scanning transmission electron microscopy (STEM) and by conventional transmission electron microscopy (TEM). For both softwoods, lamellation of the S2 layer was evident but the lamellae were seen more clearly in the STEM photomicrographs. The interlamellar distance was 7.1 nm in the case of spruce and 8.4 nm for silver fir.     

Early growth of planted yellow and paper birch and European birches in Vermont

Twelve native yellow birch (Betula alleghanensis Britt.) and paper birch (B. papyrifera Marsh.) sources and 9 European white birch (B. pendula Roth.) sources were planted on three sites in Vermont. Significant differences in growth were found among sources within two of the sites, and differences between sites were significant. Birch from Latvia appeard to be the best source on favorable sites attaining a total height of 5.18m, a total 6-year height increment of 4.29 m, and good stem form. Birches from Finland also showed good growth potential. Six yellow birch seed sources grew well on the best site and yellow birch ranks best there as a species group. European white birches do best as a group on the poor site. Silver birch (Betula pubescens Ehrh.) from Scotland grew poorest of the European birches.     

Z-Directional distribution of fiber orientation of Japanese and western papers determined by confocal laser scanning microscopy

Confocal laser scanning microscopy was applied to visualize inside fibers stained with a fluorescent dye, and the fiber orientation distribution in the thickness direction was determined by image analysis from optically sliced images. Fiber orientation angle and anisotropy were determined by the fast Fourier transform method, which holds advantages over the conventionally applied Hough transform with regard to evaluation of fiber width-weighted contribution and intrafiber segmental contribution. An orthogonally layered Japanese paper handmade by the flow-sheet forming method resulted in a clear change of fiber orientation angle from 0° to 90°. Machine-made wood-containing printing paper showed the highest anisotropy, while copier paper showed a low anisotropy. Thick papers like the wood-free paperboard and recycled packaging board showed that the maximum measured thickness was about 150 μm. The depth limit to detect fluorescence was considered to depend on the apparent density of the paper and the light absorption character of the fibers. Part of this study was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, Japan, August 2004     

Homoplastic occurrence of perforated pit membranes and torus-bearing pit membranes in ancestral angiosperms as observed by field-emission scanning electron microscopy

Recent studies demonstrated that perforated pit membranes (i.e., pit membranes with a large opening in their central portion) are commonly present between wood fibers in core eudicots. It is unclear whether this type of pit membranes might also occur in ancestral angiosperms. Therefore, structure of interfiber pit membranes was examined by field-emission scanning electron microscopy in nine species representing seven families that are located at more ancestral position than core eudicots. We found perforated pit membranes in three of the nine species. Our observations indicate that perforated pit membranes are relatively common even in ancestral groups of angiosperms. In the non-perforated pit membranes of the other six species, we found a range of structural variations. Thin-walled pit membranes without apparent intercellular layers were always found in three of the six species and the porosity of sheet-like pit membranes differed among the three species. Unlike the thin-walled pit membranes, interfiber pit membranes of Buxus microphylla var. japonica were thick-walled with obvious intercellular layers, and in Schisandra chinensis, we often observed torus-bearing pit membranes. Such variations in layered structure of pit membranes and homoplastic occurrence of torus-bearing pit membranes have not yet been reported for ancestral angiosperms. Our observations indicate that the structure of interfiber pit membranes might be more complicated than previous studies might suggest.     

Comparing predictability of board strength between computed tomography,discrete X-ray,and 3D scanning of Norway spruce logs

Strength graded boards of Norway spruce (Picea abies (L.) Karst.) are important products for many Scandinavian sawmills. If the bending strength of the produced boards can be predicted before sawing the logs, the raw material can be used more efficiently. In previous studies it is shown that the bending strength can be predicted to some extent using discrete X-ray scanning of logs. In this study, we have evaluated if it is possible to predict bending strength of Norway spruce boards with higher accuracy using computed tomography (CT) scanning of logs compared to a combination of discrete X-ray and 3D scanning. The method was to construct multivariate models of bending strength for three different board dimensions. Our results showed that CT scanning of logs produces better models of bending strength compared to a combination of discrete X-ray and 3D scanning. The main reason for this difference was the benefit of knowing the position of where the boards were cut from the logs and therefore detailed knot information could be used in the prediction models. Due to the small number of observations in this study, care should be taken when comparing the resulting prediction models to results from other studies.     

Variations in phenology and growth of European white birch (Betula pendula) clones

Phenology can have a profound effect on growth and climatic adaptability of northern tree species. Although the large interannual variations in dates of bud burst and growth termination have been widely discussed, little is known about the genotypic and spatial variations in phenology and how these sources of variation are related to temporal variation. We measured bud burst of eight white birch (Betula pendula Roth) clones in two field experiments daily over 6 years, and determined the termination of growth for the same clones over 2 years. We also measured yearly height growth. We found considerable genetic variation in phenological characteristics among the birch clones. There was large interannual variation in the date of bud burst and especially in the termination of growth, indicating that, in addition to genetic effects, environmental factors have a strong influence on both bud burst and growth termination. Height growth was correlated with timing of growth termination, length of growth period and bud burst, but the relationships were weak and varied among years. We accurately predicted the date of bud burst from the temperature accumulation after January 1, and base temperatures between +2 and -1 degrees C. There was large clonal variation in the duration of bud burst. Interannual variation in bud burst may have important consequences for insect herbivory of birches.     

Quantification of urea formaldehyde resin in wood fibers using X-ray photoelectron spectroscopy and confocal laser scanning microscopy

The potential merits of X-ray photoelectron spectroscopy (XPS) technique for the quantification of nitrogen on the wood fiber surface before and after resination with UF resin was investigated and the resin content was calculated. The bulk nitrogen content of the fibers obtained by XPS after grinding was compared with those obtained by combustion and Kjeldahl methods. Four different fluorescence staining agents were tested by UV spectroscopy. Their λ_max shifted to longer wavelengths when reacted with UF resin. Appropriate analysis conditions were tested for a satisfactory analysis of wood fibers by the confocal laser scanning microscopy (CLSM). The result obtained by CLSM was compared with that obtained by XPS.     

Durability of thermally modified Norway spruce and Scots pine in above-ground conditions

Abstract

One of the main objectives of thermal modification is to increase the biological durability of wood. In this study the fungal resistance of Norway spruce and Scots pine, thermally modified at 195°C and 210°C, was studied with a lap-joint field test. Untreated pine and spruce and pine impregnated with tributyl tin oxide (TBTO) and copper, chromium and arsenic (CCA) were selected as reference materials. The evaluations were carried out after 1, 2 and 9 years of exposure. After 1 and 2 years of exposure mainly discoloration was detected. Only the untreated pine was slightly affected by decay fungi. There were significant differences in the decay ratings of untreated and thermally modified wood materials after 9 years in the field. While the untreated wood materials were severely attacked by decay fungi or reached failure rating, only small areas of incipient decay were detected in the thermally modified samples. Thermally modified pine was slightly more decayed than thermally modified spruce. The only wood material without any signs of decay was CCA-treated pine, since some of the TBTO-treated pine samples were also moderately attacked by fungal decay. The results of the lap-joint test had a good correlation with mass losses in a laboratory test with brown-rot fungi.