Influence of temperature of thermal treatment on surface densification of spruce

Spruce (Picea abies L. Karst) wood lamellae, thermally treated at 170, 190, 210 and 230 °C were surface densified by compression at a temperature of 150 °C to three degrees of compression. Immediate springback, set recovery, mechanical properties in 3-point flexure, Brinell hardness and density profiles measurements were used to determine the effect of thermal treatment on the properties of surface densified wood. The highest immediate springback occurred in wood specimens thermally treated at the highest temperature (230 °C) and decreased with decreasing thermal treatment temperature. The untreated samples had the highest set recovery, which decreased with the temperature of thermal treatment. The surface densification increased hardness and bending strength. The highest increase was in the case of untreated wood and decreased with the temperature of thermal treatment. The modulus of elasticity (MOE) and modulus of rupture (MOR) of surface densified wood decreased with increasing thermal treatment temperature. The trend was similar for specimens which were thermally treated but not surface densified. Surface densification increased the density of the specimens in the first few millimetres below the surface. The highest density was achieved in untreated specimens and the lowest in specimens thermally treated at the highest temperature.     

Creep behaviour of commercial wood based boards under long-term loading at room conditions in Taiwan

The purpose of this study was to investigate the creep behaviour of commercial wood based boards (sanded and laminated) under long-term loading at room conditions in Taiwan. Ten types of commercial wood based boards were used to test their physical and mechanical properties in this study. Four types of these boards were used for the same test after laminating with red oak (Quercus spp.) veneer or balanced paper. The bending creep was measured at room conditions with central concentrated loading. The values for creep deflection of commercial wood based boards 18 mm thick decreased from 1.06–1.19 mm ti 1.00–1.12 mm after laminating veneer or balanced paper. The relative creep (120 days) of those specimens decreased from 1.71–3.17 to 1.43–2.04 after laminating with veneer or balanced paper in four months’ loading. The creep deflections of specimens increased with increasing loading time. The linear regression function ist/y=a+bt, wheret is time,y is deflection. When theb value is larger, the boards displayed good creep resistance. The residual bending strength of wood based boards after creep test would be retained at about 80–95%, and the residual bending strength between particleboard proved more significant than between fiberboard.     

Impact of Aspen Log Storage with and without Protection on OSB Performance

Outdoor log storage without protection can change the mechanical and chemical properties of wood due to infection by various fungi. To understand how outdoor log storage affects the wood and, subsequently, the strandboard quality, two piles of aspen logs were set up outside and stored for a period of four months (July to November). One of the piles was treated with a biological solution to prevent fungal growth. The other one was stored without treatment. Both piles contained non-debarked and partially debarked logs. Evaluation of sap stain development indicated that all logs had been colonized by staining fungi with average stain coverage of 9.37 to 57.18% and maximum stain penetration of 3.58 to 7.27 cm over the log cross section. The variation of fungal colonization depended on log treatment and bark condition. The most effective way to prevent stain growth was the combination of biological treatment and partial debarking. A series of strandboard was prepared from fresh and aged aspen logs. All boards made from stored logs were statistically comparable to or superior to the control boards made from fresh aspen logs. The boards made from treated/partially debarked and untreated/non-debarked logs were statistically comparable to each other except for wet MOR. In addition, these two board types were statistically stronger than other boards made from treated/non-debarked and untreated/partially debarked logs in terms of IB and water resistance. Some individual stained strands were observed on the finished board surface. Less staining was found in the boards prepared from biologically treated and partially debarked logs, compared with those made from other stored logs.     

Natural weathering of various surface coatings on five species at four european sites

The natural weathering of surface treatments was compared at four sites and on five wood species; beech, spruce, Scots pine (sapwood), Douglas fir and dark red meranti, for 24 months. The surface treatments were: impregnating stain, film forming stain, pigmented acrylic latex paint and pigmented alkyd paint (solvent based). Despite substantial differences between the four locations, the results of the exposure differed only little. Spruce was shown to be a substantially better substrate for surface treatments than beech or Scots pine, though Douglas fir and meranti were best of all. The impregnating stain weathered uniformly, whereas the film forming stain cracked and flaked, leading to growth of blue stain fungi. Both acrylic latex and alkyd paint showed little or no damage after 2 years of weathering. The dampening effect of surface treatments on the natural changes of wood moisture content was initially quite good for the impregnating-and the film-forming stains, but both lost their efficiency after approximately 12 months. The protection conferred by acrylic latex was somewhat better, though possibly not sufficient for external joinery requiring dimensional stability. The highest level of moisture exchange damping efficiency was shown by the alkyd paint.     

Effect of simulated rainfall and weathering on release of preservative elements from CCA treated wood

The release of arsenic from wood pressure-treated with chromated copper arsenate (CCA) can be decreased by application of wood finishes, but little is known about the types of finishes that are best suited for this purpose. This study evaluated the effects of finish water repellent content and ultraviolet (UV) radiation on the release of arsenic, copper, and chromium from CCA-treated wood exposed to simulated rainfall. Deck boards treated with CCA were either left unfinished or dipped in a finish prepared with 1%, 3%, or 5% water repellent. All specimens were exposed to leaching from simulated rainfall, and a subset of specimens was also exposed to UV radiation. The rainfall was collected and analyzed for total elemental arsenic, copper, and chromium. The water repellent significantly decreased the amounts of these elements in the runoff, but for the short duration of this study there was no difference among the three water repellent concentrations. It is possible that water repellent content would have a greater effect over a longer exposure period. Exposure to UV radiation caused a significant increase in leaching from both finished and unfinished specimens. This effect may be a result of increased surface area during weathering as well as loss of fibers caused by UV-induced surface erosion.     

The influence of material properties on the amount of twist of spruce wood during kiln drying

The development of twist in Norway spruce boards (Picea abies Karst.) during normal temperature kiln drying was researched. Tangentially oriented boards were sawn from diametrical radial planks, from which the basic wood properties, i.e. linear shrinkage and grain angle, were determined. The unrestrained boards were kiln dried using a selected drying schedule. During the controlled drying process the moisture content (MC) and twist of the boards were measured. Twist was generally induced by the shrinkage of wood below the fibre saturation point, and increased in proportional to the decrease in MC. The earlier appearance of twist, with regard to MC and drying time, was confirmed in the case of boards sawn from the central part of logs. The final twist amounted to between 10 and 20°/m in the case of boards close to the pith, and decreased to less than 4°/m in the case of boards sawn at a radius of 70 mm from the centre of the logs. Ring curvature had the highest impact on the final twist of the dried boards, followed by grain angle and tangential shrinkage.     

Phosphate bonded wood composite products from invasive <Emphasis Type="Italic">Acacia</Emphasis> trees occurring on the Cape Coastal plains of South Africa

The feasibility of manufacturing phosphate bonded wood composite board products from four locally occurring invasive acacia tree species (Acacia cyclops, A. saligna, A. mearnsii and A. longifolia) was studied using a formulated magnesium oxide (MgO) and monopotassium phosphate (KH₂PO₄) binder system. The optimization for the manufacturing process was studied using a central composite statistical design, whereupon the following factors were considered, i.e. KH₂PO₄: MgO ratio, the fly ash content as partial replacement for the binder and the wood content as a ratio of wood to the total inorganic content. A fitted response surface plot was used to show the effect of the main factors and their interactions on the measured board properties. A response surface model was developed to predict the parameters leading to the best board properties. All physical properties evaluated met or exceeded the minimum requirements for low density particleboards. The results showed that the variables considered have significant effects on the physical properties of the boards. The optimum composite manufacturing process for making durable products within the scope of the studied species was found to be a KH₂PO₄/MgO ratio of 1.66, an ash content of 2.7% and a wood/inorganic ratio of 0.96 for the selected wood species.     

Brandverhalten von mineralisch gebundenen Platten

The good fire behaviour of mineral bonded boards is due to their low contents of organic material and the crystal water in the binder. Only limited information is available on systematic tests to evaluate the fire behaviour of such boards. Calorimetric, rate of heat release, smoke and toxicity tests in Japan and West Germany show a strong correlation with wood/binder ratio. Board density affects temperature rise in the non-combustibility test methods within the first 15 min only. Standard fire test methods differ widely in individual countries. Basically surface spread of flame and heat release tests are required as well as in some countries smoke development and toxicity tests. Mineral-bonded boards are mostly classed as non-combustible.     

Effects of delayed drying and CO2 application on copper amine fixation in ACQ treated red pine

Fixation of copper and amine in alkaline copper quaternary (ACQ-C) wood preservative was investigated to determine the effects of delayed drying and application of CO₂ gas under pressure. Unlike the fixation of CCA preservative, where the rate of fixation reaction is slowed down by evaporative cooling during drying, delayed drying of ACQ treated wood had no observable effect on the copper fixation rate. However, at 50 °C, delayed drying resulted in a higher degree of copper fixation, while this effect was not observed at 22 °C. Post-treatment of ACQ treated wood with pressurized CO₂ immediately after treatment, reduced the pH of the solution in wood and resulted in rapid fixation of the copper. However, in time, the pH increased as CO₂ dissipated from the solution allowing the copper to re-solubilize.     

Exposure assessment framework for antimicrobial copper use in urbanized areas

Copper is used as an antimicrobial agent in building materials such as algae-resistant roofing shingles and treated wood products for decks, fences, and utility poles used in urbanized areas. Releases from these materials may pose risks to aquatic and terrestrial organisms. Copper exposures in surface water, sediment, and soil were estimated for a hypothetical urban setting using the TREX watershed model. Drainage and soil characteristics were based on an existing watershed. Urban landscape characteristics were developed from data regarding housing densities and copper use in building materials. This setting provides a spatially distributed, upper-bound assessment scenario. Release rates from algae-resistant shingles and treated wood were defined based on surface area and rainfall. Simulations for the urban landscapes were performed for a 10-year period. Simulation results were used to evaluate exceedences of benchmark concentrations for water, sediment, and soil. For algae-resistant shingles, exposures did not exceed benchmarks in any media. For treated wood, exposures did not exceed sediment and soil benchmarks, and surface water benchmarks were exceeded on 2 days in 10 years. Based on this analysis, copper use as an antimicrobial agent in algae resistant shingles and treated wood is not expected to pose significant adverse environmental risks on an individual use basis.     

The effect of silicone on some properties of flakeboard

Waxes are used as water repellent in wood composites, and there are only limited alternative water-repellent systems for wood composites. The aim of this study was to investigate the effectiveness of a silicone compound as a water repellent for flakeboard and to compare the properties of boards made with silicone treated flakes to those made with commercial wax treated flakes. Three levels of silicone and wax application rates were used (0.25, 0.5, and 1%). The hydrophobic nature of silicone-treated flakes was evaluated by measuring the contact angle and the rate of water absorption (WA) on the surface of the wood flake. The internal bonding strength (IB), the modulus of elasticity (MOE) and modulus of rupture (MOR) in bending regime, the WA, and the thickness swelling at edges of boards were evaluated. Results obtained showed that IB, MOE and MOR decreased as the concentration of silicone on the flakes increased from 0.25% to 1%. The IB, MOE and MOR of panels made with 0.25% silicone-treated flakes were comparable to boards made with 1% wax-treated flakes. Thickness swell at edges and WA were significantly reduced as the amount of silicone increased. No significant difference was found for the thickness swelling at edges and the WA between panels made with 1% silicone-treated flakes and 1% wax-treated flakes. The silicone treated flakes had high water repellency.     

Influence of resin content and pulping temperature on the formaldehyde release from medium density fibreboards (MDF)

Increasing the binder content from 12?% to 20?% in medium density fibreboards (MDF) using a slightly melamine modified (3?% melamine) UF-resin of a molar ratio F:U of 1:1 causes a decrease in the formaldehyde release from the boards prepared under the same conditions. The formaldehyde emanation was measured using the perforator (EN120) and the flask method (EN 717-3) after a reaction period of 3?h and 24?h. The results apply for boards made from thermo-mechanical pulps (TMP) prepared by pulping wood at 140?°C and 175?°C. The pulping temperature of wood also impacts the formaldehyde release from MDF prepared therefrom. Ascending the pulping temperature from 140?°C to 175?°C has a positive, but less significant influence on the formaldehyde release compared to that of increasing the binder content from 12?% to 20?%. Insofar, it becomes evident from the results that the conclusions drawn in the literature pertaining to the influence of resin content in case of high molar ratio resins do not necessarily apply to low molar ratio resins.     

Mechanical properties of wood treated with PF-pyrolytic oil resins

Jack pine and sugar maple wood samples were treated in a two-step process that involved first a copper chloride or a copper chloride-sodium borate mixture and then a phenol-formaldehyde resin containing a certain percentage of softwood bark pyrolytic oil. Various controls were also prepared for comparison. The modulus of rupture (MOR) of jack pine samples was generally negatively affected by the treatment, the observed values being lower than those of the controls. These values were statistically lower or equal to those of untreated samples. On the other hand, the modulus of elasticity (MOE) of treated jack pine samples was not found to be statistically different from that of the untreated wood. Mechanical properties behaved in a similar way for sugar maple wood. Unlike the other treatments, copper chloride–sodium borate and the resin containing 85% of pyrolytic oil as phenol substitute appeared to slightly improve the mechanical properties of both wood species even if not significantly so. Treatment with PF-pyrolytic oil resin resulted in similar or slightly better mechanical properties when compared to CCA-treated wood. The amount of treating water soluble salts retained in samples after the first treatment had a significant impact on MOR of both wood species and on MOE of sugar maple.     

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.     

Lignin as binder in particle boards using high frequency heating

This paper reports the results of a study exploring the possibility of employing unmodified Kraft (sulphate) lignin as a binder in particle boards manufactured using high frequency (27 MHz) heating. The mechanical parameters of the samples varied substantially with their density. For instance, the modulus of elasticity increased from 2.5 to 6.1 GPa when density changed from 700 to 1200 kg/m³. Similar results were obtained when replacing the lignin component with some thermoplastic binders (PVCAC, PVC, LDPE, PA 11, and an acrylic copolymer). The water resistance of the samples was relatively low. For instance, a sample containing 20% lignin and having a density of 700 kg/m³ exhibited after 2 h exposure to water a thickness swelling of 40%. With a similar sample containing PVCAC as binder, the corresponding value was 13%. It was possible to reduce the degree of swelling with hydrophobizing additives or by using acetylated wood flakes. An addition of 5% of a polyethylene wax thus reduced the swelling of lignin bound samples to below 5%. Similar results were obtained with PVCAC as binder. Supplementary experiments were carried out with adding hollow microspheres (Expancel) to the material. Reduced swelling was recorded also in this case. Predictions of the modulus values based on the Halpin-Tsai concept produced a fair degree of agreement with the experimental data, provided the density and the binder content were sufficiently high.     

Zum Sorptionsverhalten von Holzspanplatten

The sorptional behaviour of particleboards made from wood species of widely differing morphological structure and chemical composition was investigated. Diisocyanate (MDI), urea-formaldehyde (UF), and alkaline phenol-formaldehyde resins (PF) were used as binders. In the case of UF- and MDI-boards the sorption isotherms reveal that, using the same binder, differences in the equilibrium moisture content (E. M. C) between particleboards from different wood types were generally more or less of the same order as among the wood species themselves. More pronounced differences were found between the thickness swelling of the boards. Increasing the pressing time had no bearing on the sorption behaviour of particleboards. Also with PF-resins, the used wood species and the pressing time had practically no influence on the equilibrium moisture content. Consequently, no correlation seems to exist between bonding strength of particle boards and their sorptional behaviour.     

Metal accumulation in root crops grown in planters constructed from copper azole treated lumber

Preservative treated wood is often used to construct planters, but there are concerns about components migrating from the wood into the surrounding soil where they might be selectively absorbed by plants. Potential for selective accumulation was evaluated by growing radishes, carrots and potatoes in copper azole (CA) treated Douglas-fir planters. Copper levels were higher in soil adjacent to CA treated wood, but did not differ in roots or tubers grown in treated or non-treated wood. Copper levels were elevated in carrot foliage which is not normally consumed.     

The protective effect of 23 paint systems on wood against attack by decay fungi

A laboratory method was used to evaluate the protective effect of 23 different paint systems on Norway spruce wood against decay fungi. Weather-o-meter treated and non-treated paint films on wood were tested. Results were compared to those obtained on unprotected spruce wood. Finishes included in the study were primer oils, solvent-borne alkyd paints, water-borne acrylic paints, water-borne mixed alkyd/acrylic paints, alkyd emulsions and stains in different paint system combinations with one to four coats. The growth of the decay fungi of the paint films was estimated by visual inspection. After 5 months of incubation, microbial activity in the wood below the paint films was evaluated. Growth of the fungi in the wood below the paint film was measured by an indirect chemical method for estimation of microbial activity. Paint systems including a solvent-borne alkyd coat usually had a good performance when tested without prior weathering but degenerated most during the weathering process as judged from the altered water absorption and fungal growth rate. Paint systems including a treatment with a primer oil exhibited low moisture uptake also after weathering. A clear effect of fungicide additions was also seen. A water-borne penetrating oil with an acrylic top coat exhibited no visual surface attack before weathering, and low microbial activity in wood for all decay fungi before and after weathering.     

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 part of this series one-layer pine wood particleboards were made using two different low-emission UF-resins (UF 1 and UF 2) using various amounts of different catalysts (ammonium chloride, ammonium sulfate, ammonium nitrate, a mixture of ammonium sulfate and formic acid) and tested regarding their properties. From the results the following conclusions can be drawn:

1. With increasing amount of catalyst in the range between 0.8% and 2.4% ammonium chloride and 0.8% and 3.2% ammonium nitrate the physical-mechanical properties of the boards deteriorated. In contrast, the formaldehyde release decreased with increasing amount of catalyst.
2. Compared with ammonium chloride ammonium nitrate led to higher mechanical properties and lowered thickness swelling of the boards.
3. Particleboards containing UF 1 as a binder showed, compared with those boards bonded with UF 2, higher mechanical properties and lower thickness swelling in water. However, the formaldehyde release of the boards bonded with UF 1 was above that of boards bonded with UF 2.
4. Particleboards bonded with UF 1 and UF 2 as a binder and containing ammonium nitrate as a catalyst showed, in general, the highest mechanical properties, those prepared with ammonium sulfate or a mixture of ammonium sulfate and formic acid as a catalyst the lowest.

     

Use of UF-bonded recycling particle- and fibreboards in MDF-production

The work is related to the use of thermomechanical pulps (TMP) prepared from recycling UF-bonded particle- and fibreboards as a partial substitute for TMP made directly from wood in MDF. The results reveal that TMP from recycling boards show striking differences in their morphological characteristics and chemical properties compared to TMP prepared directly from wood. TMP from recycling boards are of shorter fibre length and higher content of fine fraction. Moreover, their cold water extractives are of higher pH-value and contain appreciably higher amounts of acetate and formate ions. TMP from recycling boards releases also more formaldehyde compared to TMP made directly from wood. Moreover, the results clearly show that TMP from recycling boards can be used up to 30% as a partial substitute for TMP from wood in making UF-bonded MDF without any noteworthy deterioration of the physical-mechanical board properties. Also, the formaldehyde release of the boards made using TMP from recycling boards experiences no negative change. Only small differences were found in the content of formate and acetate ions as well as in the release of volatile acids from MDF made from recycling fibre- and particleboards on the one side and boards directly made from wood on the other side. All the results indicate that chemical interaction seems to take place between the chemically degraded resin in UF-bonded recycling boards and the new binder used in making MDF.