The water absorption of sapwood and heartwood of Scots pine and Norway spruce heat-treated at 170 °C, 190 °C, 210 °C and 230 °C

Heat-treatment changes the chemical and physical properties of wood. Wood polymers are degraded, dimensional stability is enhanced, equilibrium moisture content is lowered, colour darkens and biological durability is increased. The properties of heat-treated wood have been researched considerably, but the differences between sapwood and heartwood have not been reported separately. In this research, water absorption differences between sapwood and heartwood of Scots pine and Norway spruce heat-treated at temperatures 170 °C, 190 °C, 210 °C and 230 °C were investigated. The results were compared to industrially kiln-dried reference samples. Water absorption was determined with a floating test based on the EN 927-5 standard. The heartwood of both wood species absorbed less water than sapwood. Heat-treatment evidently decreased the water absorption of spruce and pine heartwood. The higher the heat-treating temperature, the lower the amount of absorbed moisture. However, a very interesting exception was pine sapwood, whose water absorption actually increased with heat-treatment after the three lowest heat-treatment temperatures compared to the reference material. Water absorption did not decrease until the heat-treatment temperature was 230 °C.     

Swelling of polyvinyl alcohol, melamine and urethane treated southern pine wood

Anti-swelling properties of southern pine wood treated with polyvinyl alcohol (PVA) or melamine or urethane were evaluated by measuring the tangential swelling and water uptake using AWPA standards methods. The water-repellency efficiency (WRE) of melamine and PVA treated wafers exhibited values 80% superior to untreated wafers. This study confirms that waterborne solution containing 3% of melamine or 3% of PVA can be used to reduce the swelling of southern pine.     

Optimising the properties of OSB by a one-step heat pre-treatment process

Heat-treatment of solid wood to increase its dimensional stability and durability is well known and established in the industry. To enhance the application of wood-based panels (e.g. for exterior application) their durability against moisture and fungal decay has to be improved. In this paper a possibility is shown, how to adapt a heat treatment process on wood-based panels. Two different temperatures were applied on strands of Scots pine, before hot-pressing oriented strand board. The mechanical properties show an influence of the applied temperature on the strands and of the adhesive used for the panel. The thickness swelling is reduced (Fig. 3), resulting in increased dimensional stability. The process temperature has a major influence; with an increased pre-treatment temperature the thickness swelling is reduced. The internal bond strength was not affected by the pre-treatment.     

Feuchtebeständigkeit und Hydrolyseresistenz von Holz-zu-Holz-Bindungen in Spanplatten,hergestellt mit formaldehydarmen modifizierten Harnstoff-Formaldehydharzen unter Einsatz verschiedener Härtungsbeschleunigersysteme

In continuation of the work conducted in the first and second part of this series one-layer particleboards (pine wood) were made using three different low-emission UF-resins (UF1, UF2, UF4) and various amounts of different catalysts (ammonium sulfate, ammonium nitrate, a mixture of ammonium sulfate and formic acid). Melamine formaldehyde resin, resorcinol, quebracho-tannin and diphenylmethan diisocyanate (PMDI) were used as modifiers. The investigations led to the following results:

1. The use of ammonium nitrate as a catalyst led, compared with ammonium sulfate and the mixture from ammonium sulfate and formic acid, to higher mechanical properties and lower thickness swelling of the particleboards.
2. Particleboards bonded with resin UF1 modified with melamine formaldehyde resin showed, compared with the other investigated modifications, higher resistance in dry state, in the wet state and after water soaking and redrying of the particleboards. Also thickness swelling of these particleboards was lower.
3. Spraying PMDI prior to UF1 resin (preliminary spray method) improved the physico-mechanical properties of the particleboards (second place in the order of precedence after melamine resin).
4. Particleboards bonded with UF1 modified with resorcinol showed the lowest formaldehyde release, though this modification has a negative effect on the physico-mechanical properties of the boards.
5. Modification of UF1 with quebracho-tannin had an adverse effect on all properties of the particleboards.
6. Modification of the resins UF2 and UF4 during the condensation step of the resin led to similar effects on the properties of the particleboards as the modification by mixing modifier and resin prior to the application of the binder.

     

Light medium-density fibreboards (MDFs): does acetylation improve the physico-mechanical properties?

Light medium-density fibreboards (MDFs) with a target density of 580 kg m³ were produced from fibres, which were obtained by defibrillation of chips of commercially available acetylated solid wood (“Accoya^®”). The fibres were produced by thermo-mechanical pulping under industry-oriented conditions in a laboratory refiner. Infrared spectra showed that after the refiner process and board production, the material exhibited the same acetyl content as the initially acetylated solid wood. The fibres were bonded with 4 and 8% (related to the dry fibre mass) polymeric methylene diphenyl isocyanate and the properties of the obtained MDFs were compared with comparable MDFs from untreated Scots pine fibres which were produced under the same conditions. The modulus of rupture tended to be slightly lower for the acetylated boards, while the modulus of elasticity and the internal bond strength (IB) were equal for the respective resin loads. Acetylation clearly reduced the thickness swelling and the water uptake during immersion in cold and boiled water compared to the unmodified boards. IB after the boil test increased with acetylation and with the resin content. The study indicates that acetylated MDFs can be produced with maintained mechanical properties but strongly enhanced moisture-related properties by defibrillation of acetylated solid wood chips in a refiner and subsequent conventional board production.     

Properties of one-layer experimental particleboards from willow (Salix viminalis) and industrial wood particles

The objective of this study was to investigate some mechanical and physical properties of one-layer particleboards made from various willow (Salix viminalis) and industrial pine wood particle mixtures bonded with urea formaldehyde resin. Modulus of elasticity and modulus of rupture decreased, whereas internal bond and screw holding strengths increased with increasing willow particle content. The decrease in bending properties was rather small; these properties of particleboards containing 50 % willow particles were on average smaller by about 10 % than particleboards containing only industrial wood particles. Increasing the willow particle content resulted in improved water absorption and thickness swelling. The willow Salix viminalis can be considered as a substitute for pine wood for manufacturing of particleboards.     

Selected mechanical properties of Scots pine wood from antique churches of Central Poland

Scots pine (Pinus sylvestris L.) wood is the most frequently used building material in old churches of Central Poland. In the article, the density and compressive strength of Scots pine heartwood samples taken from old churches from the sixteenth, seventeenth, and eighteenth century were examined. The properties of the old wood were compared with contemporary wood of similar density. The results showed better quality of the ancient wood as compared to modern wood.     

In-treatment cooling during thermal modification of wood in soy oil medium: soy oil uptake, wettability, water uptake and swelling properties

Thermal modification of wood is a process which has gained wider acceptability as an alternative to chemical treatment in wood preservation. In order to maximize the benefits of this technique several options have been adopted including the use of soy oil in transferring the heat to the wood. Available information on thermal treatment in general and the oil method in particular show that there is need for further investigations on the possibilities of improving the available options in order to evolve new techniques. Thermal treatment of ponderosa pine (Pinus ponderosa P Laws ex C Laws) and black spruce (Picea mariana (Mill) BSP) in soy bean oil was carried out at 220 °C for 2 hours followed by cooling inside the hot oil 180 °C and 135 °C. The surface wettability, (contact angle), amount of oil uptake, water absorption and thickness swelling were determined thereafter. The oil uptake ranged from 88 to 93.3% in the permeable ponderosa pine sapwood and from 6.1 to 11.3% in the refractory black spruce with the uptake increasing with cooling time but decreasing with increasing depth of wood in both species. Thermal modification in soybean oil increased the wettability of the surface to water (reduced contact angle). However, there were no significant changes to the surface energies due to in-treatment cooling, as determined by contact angles of water, glycerol, ethylene glycol, and formamide. There were reductions in the hydrophilic behaviour and swelling of wood as a result of the thermal treatment; in-oil cooling resulted in greater hydrophobicity and dimensional stability in the wood. In both species, there were greater reductions in water uptake and swelling with increasing cooling time.     

Experimental study of material properties of modified Scots pine

The mechanical and physical properties of modified timber were assessed by experimental work. The timber was modified using three different methods: acetylation with acetic anhydride, modification with methylated melamine formaldehyde resin and heat treatment in an oil bath. The wood material was sapwood of Scots pine (Pinus sylvestris) with dimensions of 45×70×1100 mm. A total of 99 specimens were included in this study. The following properties and their inter-relations were studied: density, modulus of elasticity (MOE), bending creep deflection and relative creep. It was found that all the modifications successfully reduced the relative creep. However, the performance properties of modified timber ought not to be calculated on the basis of density, as is the case for untreated wood. On the other hand, the long-term performance of modified timber can be assessed by its initial MOE and the difference in equilibrium moisture content (EMC) between two climates.     

The boron fixation to the cellulose, lignin and wood matrix through its reaction with protein

This paper is an attempt to determine the actual boron adsorption and retention in wood and its isolated components: cellulose and lignin. The rate of boron retention in cellulose, lignin and wood powder of Scots pine Pinus silvestris L. was investigated using denaturing properties of protein contained in reaction solutions. Both animal and plant origin protein was used in this study. In order to determine the reactivity of the analyzed formulation the reactions of cellulose, lignin and wood powder with protein borates were carried out. The aim of the analyses was also to compare methods of protein denaturation: thermal and chemical with the use of tannic acid solution. The obtained products were subjected to water extraction at 20 °C. Boron content in the solid and water extracts was analyzed using atomic absorption spectrometry (AAS). The results showed that the method of protein denaturation played the crucial role in the rate of boron retention. The type of protein used in the reaction solution had also significant effect on the boron retention.     

A comparative study on brown-rot fungus decay and subterranean termite resistance of thermally-modified and ACQ-C-treated wood

The resistance of thermally-modified and Alkaline Copper Quaternary type C (ACQ-C) treated aspen (Populus tremuloides Michx), jack pine (Pinus banksiana Lamb.), yellow-poplar (Liriodendron tulipifera L.), and Scots pine (Pinus sylvestris L.) against the brown-rot fungus (Gloeophyllum trabeum) and Eastern U.S. subterranean termite (Reticulitermes flavipes) was studied. Wood materials were thermally-modified at a temperature of 210 °C for 15 min. ACQ-C was impregnated into yellow-poplar and jack pine wood at three different retention levels and at each level both leaching and non-leaching procedures were conducted. Results indicate that ACQ-C-treated yellow-poplar and jack pine became significantly more resistant to the brown-rot fungus compared to the thermally-modified wood and the untreated control. Thermally-modified yellow-poplar and jack pine were more resistant to this fungus than untreated wood. For aspen and Scots pine, the resistance to G. trabeum was improved after the thermal modification, but it remained susceptible to this brown-rot fungus decay. Termite susceptibility of thermally-modified aspen, jack pine, and yellow-poplar was comparable to that of untreated controls. Significantly greater termite attack occurred on thermally-modified Scots pine wood than it did on untreated wood. This likely is attributed to some compounds contained in Scots pine wood that inhibited termite attack.     

Tanninformaldehydharze aus den Rindenextrakten von Fichte (Picea abies) und Kiefer (Pinus sylvestris)

Bark extracts from sproce and pine obtained with water or organic solvents were used as adhesives partly as binder additives, for manufacturing wood based boards. For plywood the extracts replaced about 60% (pine extracts) or 80% (spruce extracts) of PF-resin. The addition of more than 20% of extract reduced the wet bonding strength. Extracts were further used together with cold setting PRF-resin as adhesive for solid beech boards. They could replace the resin up till 30% without falling the boiling-water-resistance below the minimum values of DIN 68602. The mechanical properties of partieleboards bonded with unmodified extracts were low. The addition of PF-resin of düsocyanate as fortifier increased the strength values and reduced thickness swelling.     

Einfluß der Lagerung von Industrierestholz der Klefer und Fichte auf seine Eignung für die Herstellung von Spanplatten und mitteldichten Faserplatten (MDF)

Particle- and medium density fibreboards (MDF) were prepared from chips of spruce and pine, a byproduct of sawing wood in a saw mill with a profiling unti. The wood residues were stored in piles of 40 m³ volume for different time periods. The physical-technological properties of the particle- and fibrebroads prepared therefrom were evalutated and the formaldehyde release of the boards was assessed. The results reveal: In general, there is a positive influence of storage on the thickness swelling and internal bond strength of UF-bonded particleboards; the bending strength of UF-bonded particleboards showed no pronounced response to storage. The prositive influence of storage onthe thickness swelling and internal bond strength was much higher in case of boards made from pine chips than in case of spruce boards. On using PMDI as a binder for particleboards no significant influence of storage on the thickness swelling, internal bond strength and bending strength was detected. The influence of storage on the thickness swelling of UF-bonded MDF from pine fibres was much less pregnant than on that of UF-bonded particleboards. On UF-bonded MDF from spruce the influence of storage, if any, was negligible. On using PMDI as a binder for MDF there was no detectable change in the thickness swelling due to storage. The internal bond strength of UF-bonded MDF experiences only subtle positive change due to storage of pine wood chips. However, no notable change was detected in case of MDF from spruce. Storage has almost no influence on the chemical properties of boards.     

Effect of oil type, temperature and time on moisture properties of hot oil-treated wood

This paper focuses on the moisture properties of wood treated in palm oil-, soy oil- and slack wax for different processing times and temperatures. Also, the relative importance of oil uptake and thermal modification on the wood moisture properties is investigated. Slack wax was better than palm oil or soy oil in improving the moisture performance of thermally treated wood, and treatment at 220 °C was superior to treatment at 200 °C, with 4 h being generally better than 2 h treatment. Water absorption in samples treated with wax at 100 °C or 160 °C was similar to that in samples treated at high temperatures while improved anti-shrink efficiencies (ASE) and lower hygroscopicities occurred only for the high temperature treatments. Chloroform extracted samples treated at high temperature with palm oil or soy oil had relatively similar hygroscopicity and ASE properties compared to unextracted samples, but had greatly increased water absorption properties. These results confirm that chemical reactions in wood resulting from the heat treatment account for the main improvements of wood properties in reduced hygroscopicity and improved dimensional stability, while the oil absorbed by wood reduces the rate of water absorption.     

Tall oil/water – emulsions as water repellents for Scots pine sapwood

Like classic wood preservatives, many water repellents have the drawback of being detrimental to the environment. Hence interest in environment-friendly, even biodegradable, substances has increased. Natural oils (e.g. tall oil, linseed oil) appear to be capable of preventing water uptake by wood. However, in order to achieve total sapwood penetration, the amount of oil needed is high. The aim of this study was to investigate the water repellent efficiency of crude tall oil and crude tall oil water emulsions (oil-in-water and water-in-oil emulsions), and the possibilities of reducing the amount of oil needed with the emulsion technique. Scots pine sapwood samples were impregnated with tall oil formulations. The levels of water absorption and the degree of water repellent efficiency were determined with cyclical wetting and drying tests. The results showed that tall oil treatments reduce the water uptake of pine sapwood. With tall oil emulsion treatments almost equal water repellent efficiencies were reached as with pure tall oil, even when the oil retentions were considerably lower. The total amount of oil required could be halved. The emulsion technique is a potential method of decreasing the amount of oil needed in order to protect wood from water uptake.     

Swelling kinetics of thermally modified wood

European Journal of Wood and Wood Products - The swelling kinetics of native and thermally modified wood was studied. Norway spruce, Scots pine, European beech, and English oak specimens of...     

Gross adhesive penetration in furfurylated, <Emphasis Type="Italic">N</Emphasis>-methylol melamine-modified and heat-treated wood examined by fluorescence microscopy

This study investigated the radial penetration of three conventional cold-set wood adhesives [emulsion polymer isocyanate (EPI), poly (vinyl acetate) (PVAc), one-component polyurethane (PU)] into various degrees of furfurylated and N-methylol melamine-modified (NMM) Scots pine, and heat-treated Scots pine and beech based on measurements of effective (EP) and maximum penetration (MP) from microscopic observations. EP of EPI adhesive decreased after modification with higher concentration of furfuryl alcohol while an improved penetration was recorded for PVAc into furfurylated wood. A deeper penetration was observed for all adhesives into wood treated with lower concentration of furfuryl alcohol. The EP of EPI and PU adhesives reduced after NMM treatment but it increased in the case of PVAc. In spite of reduction of EP of PU after NMM treatment, it represented a deeper penetration among all adhesives possibly due to its lower molecular weight. For Scots pine, increasing the treatment temperature improved EP of all adhesives while for beech, the EP of PU and PVAc increased largely in the case of samples treated at 195 °C. Visual analysis of fluorescence microscopy pictures provided more detailed information on modality of penetration. The results are useful for understanding the interaction among common adhesives and modified materials, and can be used in future research to explain the bonding behavior of modified wood.     

Untersuchungen zur Optimierung des Oberflächenschutzes von Holzbauteilen

T-shaped specimens, jointed by mortise and tenon, simulating a critical part of window frames, were exposed to open air weathering for three years. The parameters tested were various wood species and surface treatments, including pretreatments by dipping in water repellent preservatives. The evaluation criteria were the changes of moisture content in time, measured by weighing over a period of two years, and the state of conservation of the specimens after three years. The capillary absorption of rain water by the wood species subjected to the treatments proved to be a significant factor for the intensity of changes in moisture content, as well as for decay resistance. Scots pine and beech showed the largest variations, spruce medium, and sipo and meranti only little change in moisture content, few cracks and low deformation. Most beech and pine, and a few of the spruce specimens showed substantial decay, whereas sipo and meranti (dark red) resisted quite well. Fungicide and water repellent pretreatments as well as film forming surface coatings of relatively low permeability to water vapor offered the best protection against moisture damage.     

Zur Bestimmung von Holzschutzmittelwirkstoffen in Wasser—Ein Beitrag zur Umweltanalytik

After a short review of important publications in the field of the chemical analysis of woodpreservatives in waste water a new method is described for the determination of organo-chlorine compounds in water samples. Spruce and pine sapwood samples were treated with an oil-borne wood preservative containing pentachlorophenol, dichlofluanide and lindane and leached with water serveral times after impregnation. The active substances were separated from the leaching water by solid phase extraction using Empore^TM extraction disks C18 Octadecyl. This method allows to extract very small amounts of active substances from large volumes of water relatively quickly and therefore this technique is suited for the type of extractions routinely run in the environmental analysis.     

Einfluß der Lagerung von Industrierestholz der Kiefer und Fichte auf seine Eignung für die Herstellung von Spanplatten und mitteldichten Faserplatten (MDF)

Particles and fibres were prepared from saw mill wastes (chips) after different storage periods. The particles and fibres were chemically analysed regarding the change in their pH-value, buffering capacity, extractive content, release of volatile acids and formaldehyde release. Furthermore, the physical-mechanical properties of UF- and PMDI-bonded particleboards and fibreboards prepared therefrom were assessed. The results reveal:

1. Storage leads to an improvement in the properties of UF-bonded particleboards prepared from pine chips as the internal bond strength increases and the thickness swelling decreases.
2. Particleboards made from spruce prior to storage show in general better mechanical properties and lower thickness swelling compared to those prepared from pine wood. However the differences dwindle upon storage.
3. Storage seems to have almost no influence on bending properties of particles bonded with PMDI, as no significant change in the properties of the boards due to storage was detected.
4. Storage of chips from wood felled in spring has less impact on the properties of the boards than that of chips from winterfelled wood (Schäfer und Roffael, 1997).
5. The properties of MDF made from spruce using UF-resin as a binder show higher mechanical strength properties and less thickness swelling compared to those prepared from pine wood. However, after storage only subtle differences between boards made from spruce and pine were detected.
6. On using PMDI as a binder no significant changes in the properties of the MDF due to storage under the boundary conditions indicated in the work were detected.