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Ensuring reliability of data on thermal properties of wood-based panels is important for manufacturing processes, especially when it is recommended to shorten the cooling phase and stack the panels in hot conditions. Prediction of the heat transfer during cooling phase and normal or hot stacking based on accurate data is essentially important for attaining panels of required properties. The thermal properties are also required when designing houses, especially low-energy or passive ones. Therefore, a water calorimeter was adequately designed and constructed to ensure improvement in the accuracy of the specific heat measurements. The calorimeter was used to determine the specific heat. The attained accuracy estimated by the relative error was significantly increased, and the error values were less than 2 % for all types of the investigated particleboard and OSB. In case of low-density fiberboard (LDF), the maximum value of the relative error did not exceed 4 %. It was also shown that high accuracy required for the specific heat measurements was achieved for experiments in which high-mass samples were used, in contrast to measurements for such samples in traditional DSC systems. The results for the specific heat were within the range from 1420 to 1450 J/kg K for LDF and all types of particleboard. The effect of the investigated material density on the specific heat was not found. The only exception was in case of OSB for which the specific heat was ca. 1550 J/kg K, and it was approximately 100 J/kg K higher when compared to other panels. [ABSTRACT FROM AUTHOR]

An asymmetrical two-layer laminated densified wood product is prone to cupping when it is placed in a fluctuating moisture environment. This study was aimed at developing a 2D finite element (FE) model to simulate this situation. Two types of specimens with two thickness ratios of 0.18 (type I) and 0.58 (type II) were prepared. A 6-week moisture and temperature treatment was conducted. The cupping value of deformed specimens was measured for verification. The major results were: (1) The cupping value of type I specimens experimentally measured and predicted was 0.307 and 0.327 mm, respectively, while that of type II specimens was 0.440 and 0.396 mm, respectively; (2) FE and experimental results were in good agreement since the FE results lied in the 95 % confidence interval of the experimental results. The developed FE model can be used to predict the moisture-induced cupping of a two-layer laminated wood product. [ABSTRACT FROM AUTHOR]

Cupping is a critical issue that affects the performance of a two-layer laminated densified wood product in service. Many parameters including material properties and product geometry can influence the cupping. It is more efficient to study the influence of these parameters on cupping using a model than by testing. A model sensitivity analysis is helpful in identifying key parameters so that product design can be optimized. This paper expanded the discussion on the finite element model developed and its application. It was found that (1) swelling/shrinkage coefficient and modulus of elasticity in the tangential direction and equilibrium moisture content were three key material parameters; (2) increasing the modulus of elasticity could offset part of cupping; (3) thickness ratio of two wood layers, as a key geometry parameter, was independent of three key material parameters; and (4) the optimal thickness ratio of two wood layers was 0.12. [ABSTRACT FROM AUTHOR]

To clarify the decay resistance effects of wood treated with different preservatives, the thermal behavior of treated samples was investigated. A thermal dynamic model was established using a mathematical method. The results showed that untreated Pinus massoniana had maximum mass loss, and the decay resistance effects of this species treated with different preservatives improved with an increase in the largest mass loss of pyrolysis. The pyrolysis can be divided into primary pyrolysis and secondary pyrolysis reactions in the lower and higher temperature regions, respectively. The activation energy represents a different degree of reduction from the primary pyrolysis reaction to the secondary pyrolysis reaction. The higher the retained cellulose content, the higher the activation energy. The sample's activation energy in the primary pyrolysis reaction can represent the decay resistance effects of wood treated with different preservatives. [ABSTRACT FROM AUTHOR]

Adhesives based on renewable resources have inferior efficiency compared to the synthetic ones. To improve the adhesive properties of soy protein isolate (SPI) adhesives, a new method of thermally modifying SPI was developed. The commercial SPI powder was thermally modified in a vacuum chamber at different temperatures (50, 100, 150, and 200 °C). Thermally modified and unmodified SPI powders were dispersed in distilled water and stirred at 24, 50 or 90 °C. Dispersions were prepared without and with pH adjustment to 10.0. The viscosity of the resulting adhesives was measured. Effective penetration and bond strength in longitudinal tensile shear were tested with bonded beech specimens. Regardless of the pH value and dispersion preparation temperature, SPI thermally modified at 150 and 200 °C exhibited no adhesive properties, while adhesive bonding was achieved with SPI modified at 50 and 100 °C. Adhesives without pH adjustment had viscosity below 28 mPas and exhibited no adhesive penetration. pH adjustment increased the viscosity and adhesive penetration, which improved the adhesive bond strength. Thermal modification at 50 °C resulted in improved wet shear strength, while the temperature of 100 °C deteriorated it. Increased dispersion preparation temperature to 50 °C increased wet shear strength, while temperature of 90 °C decreased it. The combination of thermal modification at 50 °C, dispersion preparation at 50 °C, and pH increase resulted in an adhesive with the highest shear strength. [ABSTRACT FROM AUTHOR]

Effects of zinc-oxide nanoparticles on physical and mechanical properties, as well as biological resistance of untreated and heat-treated beech wood were investigated in this study. Test specimens were prepared from sapwood and impregnated with a 5,000-ppm nano-zinc-oxide (NZ) suspension with a size ranging from 10 to 80 nm at 2.5 bars of pressure and using the Rueping process for 20 min. Control (C) and nano-zinc-oxide-impregnated specimens after (NZA) and before (NZB) heat treatment were divided into four subgroups of unheated (C and CNZ), heated at 50, 145 and 185 °C. Heat treatment resulted in a significant decrease in mechanical strength at temperatures of 145 and 185 °C. Heat-treated specimens showed less dimensional instability and fungal degradation. Impregnation with nano-zinc resulted in a slight and significant increase in weight loss and biological resistance against Trametes versicolor. The results showed that the impregnation significantly decreased the water absorption of the specimens. Impregnation before heat treatment showed considerable effect on the properties of wood compared to that of untreated ones. [ABSTRACT FROM AUTHOR]

This research work aimed at studying the effects of oleothermal modification of fir wood by using combined soybean oil with maleic anhydride (OHT-MA) to achieve lower treatment temperatures and enhance physico-mechanical properties. Wood blocks were oleothermally treated with soybean oil and OHT-MA at five different treatment temperatures (100, 120, 140, 160 and 180 °C) for three different holding times (30, 60 and 180 min). Afterward, physical and mechanical properties of the treated samples were determined, i.e., density, water absorption and volumetric swelling as the physical properties and bending strength, compression parallel to grain and impact load resistance as the mechanical properties. Results revealed increases in densities and reduction in water absorption as well as volumetric swelling of all treated samples. The mechanical properties were affected by OHT-MA treatment at different temperatures. Bending modulus of elasticity as well as compression parallel to grain was increased due to OHT-MA treatment. In addition, there was less reduction in impact load resistance of the treated samples. It was revealed that the OHT-MA enhanced wood properties at low treatment temperatures as well as shorter holding times. [ABSTRACT FROM AUTHOR]

The effect of the thermo-hydro-mechanical (THM) densification in a closed system on the set recovery and thermal stability of lime ( Tilia cordata) wood was evaluated. The THM densification process consists of four steps: plastification, densification, post-treatment and cooling. The THM-densified wood samples were subjected to three different post-treatment temperatures, and for each one, three different periods were used. Comparison between THM-densified wood sample without and with post-treatment at different temperatures and times was made. The set recovery tests showed that the post-treatment at higher temperatures and times improves the dimensional stability of the samples suggesting a permanent fixation of the transversal compression, but also reduces their thermal stability, by having lower temperatures corresponding to the maximum decomposition rate, lower values for the mass loss at the end of decomposition stage and lower values for the kinetic parameters. The samples with post-treatments at lower temperatures showed high set recovery values and exhibited higher values for the temperatures corresponding to the maximum decomposition rate, lower values for the mass loss at the end of the stage and higher activation energies and reaction orders. [ABSTRACT FROM AUTHOR]

Birch wood ( Betula pendula) samples were treated in a thermal regime (140, 160, 180 °C) for 1 h and investigated by means of scanning electron microscopy (SEM). SEM microimages of the wood cross-section were taken from one and the same place before and after the thermal treatment (magnification 100-2,000×). The results of measurements of areas and linear sizes of the birch wood cells show significant changes, which depend on the thermal treatment conditions and the type of the cell: libriform, tracheid, vessel and ray. After the treatment at 180 °C, the integrity of wood morphological structure begins to break up. Voids and cracks are formed between fibres, thus leading to a decline in the mechanical properties of the wood. [ABSTRACT FROM AUTHOR]

The effects of laser incising on the surface of heat-affected zones (HAZs) and liquid uptake of wood were examined. Deep pin holes were incised on the tangential section of the wood with a laser beam of 1 kW in power with varied pulse widths, and the HAZs of the holes were investigated using scanning electron microscopy. The length of liquid uptake passing through HAZs surfaces was then measured. It was observed that the HAZs were unable to maintain normal porous structure, and smooth surfaces such as that of wood charcoal were also not observed. This is because the composite of the middle lamella completely melted, which led to a decrease in the length of liquid uptake. In addition, the release of high gas-pressure and thermal energy during the laser-incising process did not damage the tylose and the aspirated pit in the longitudinal direction. Because of this, the liquid movement remained blocked. However, the incising holes provided additional liquid-intake points, resulting in greater intake capacity. Moreover, it was observed that improvement of liquid impregnation is related to hole diameter. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of heat treatment of untreated and nano-silver-impregnated Populus nigra, Populus deltoides and Fagus orientalis on the physical and mechanical properties. Specimens were impregnated with a 200-ppm aqueous silver nanoparticles suspension. Heat treatment was carried out at temperatures of 135 ± 3 °C and 185 ± 3 °C. Nano-silver impregnation aggravated the effects of heat treatment. Although significant in some cases, nano-silver impregnation did not seem to have great effect on physical properties. It may be concluded that although NS impregnation aggravated the effects of heat treatment on solid woods, other factors may also be involved such as the species and density of the wood. [ABSTRACT FROM AUTHOR]

Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170 °C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species. [ABSTRACT FROM AUTHOR]

Scots pine ( Pinus sylvestris L.) sapwood was impregnated with aqueous solutions of phenol formaldehyde and methylated melamine formaldehyde resins and subsequently cured in an oven. One set of specimens was cured in plastic bags to avoid drying (wet curing) while another set of samples was heated and water was allowed to freely evaporate (dry curing). Macroscopic resin distribution was investigated using X-ray densitometry and infrared spectroscopy (FTIR-ATR). During dry curing, the resins migrated to the wood surface resulting in a gradient. Wet curing resulted in even distribution of the resins because it was immobilized due to condensation and precipitation in the wood. Neither densitometry nor FTIR-ATR was found to be generally applicable for investigating resin distribution in modified wood. Wet curing resulted in low cell wall bulking as compared to dry curing, probably because resin precipitated before drying. Storing impregnated wood prior to curing under non-drying conditions ('diffusion phase') also reduced cell wall penetration and bulking. [ABSTRACT FROM AUTHOR]

Fracture toughness of wood and wood composites has traditionally been characterized by a stress intensity factor, an initiation strain energy release rate ( G) or a total energy to fracture ( G). These parameters provide incomplete fracture characterization for these materials because the toughness changes as the crack propagates. Thus, for materials such as wood, oriented strand board (OSB), plywood and laminated veneer lumber (LVL), it is essential to characterize the fracture properties during crack propagation by measuring a full crack resistant or R curve. This study used energy methods during crack propagation to measure full R curves and then compared the fracture properties of wood and various wood-based composites such as, OSB, LVL and plywood. The effect of exposure to elevated temperature on fracture properties of these materials was also studied. The steady-state energy release rate ( G) of wood was lower than that of wood composites such as LVL, plywood and OSB. The resin in wood composites provides them with a higher fracture toughness compared to solid lumber. Depending upon the internal structure of the material, the mode of failure also varied. With exposure to elevated temperatures, G for all materials decreased while the failure mode remained the same. The scatter associated with conventional bond strength tests, such as internal bond and bond classification tests, renders any statistical comparison using those tests difficult. In contrast, fracture tests with R curve analysis may provide an improved tool for characterization of bond quality in wood composites. [ABSTRACT FROM AUTHOR]

Effect of artificial weathering on the wettability of three heat-treated North American wood species (jack pine, aspen, and birch) is studied from the point of view of the structural and chemical changes taking place on the wood surface. Weathering increases wettability of all three heat-treated woods by water. Changes in wettability during artificial weathering differ according to heat treatment procedure and wood species and are likely due to combination of structural and chemical changes of the surfaces. Scanning electron microscopic analysis indicates that cracks form due to degradation taking place during weathering. As a result, water has easier entry into the cell wall, which consequently increases wettability. IR spectra suggest that the OH/CH ratio for heat-treated specimens is inversely proportional to the contact angle regardless of the type of wood species. The presence of cellulose-rich layer on wood surface and increasing amount of amorphous cellulose transformed from crystallized cellulose due to weathering result in increase in hydroxyl; consequently, it increases heat-treated wood wettability. [ABSTRACT FROM AUTHOR]

Quality assessment of thermally modified wood has evolved as one of the major fields in the research on thermal modification of wood. This study investigates NIR spectroscopy in combination with the pattern recognition method of soft independent modeling of class analogies (SIMCA). Focus is put on identifying different treatment intensities of thermally modified samples of beech, ash, and Norway spruce. The results indicate that SIMCA classification based on NIR spectroscopy could be used for quality control of thermally modified wood. The method might be applicable for producers (pre-delivery checks) and customers (reception control). However, transfer from laboratory to industrial conditions needs further investigation. [ABSTRACT FROM AUTHOR]

In this study the thermoplastic flow behavior of steamed wood flour was investigated. First it was demonstrated that steamed Japanese beech flour flowed out of the nozzle under compression at high temperature in a thermal flow test with a capillary rheometer. The effects of the steaming temperature, steaming time, compressive pressure, and moisture content of wood flour on the thermal flow temperature were examined. It was shown that the higher the steaming temperature and compressive pressure, the lower the thermal flow temperature. Also, the thermal flow temperature of the sample steamed at 200°C for 20 min became lowest and increasingly higher over time. Furthermore, the thermal flow temperature became linearly low with increasing moisture content of the sample under 15%, whereas it became essentially constant over 15%. It is clarified that compressive pressure and moisture content as well as the steaming conditions profoundly affect the thermoplastic flow behavior of steamed wood flour. [ABSTRACT FROM AUTHOR]

Abstract  Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) specimens were exposed in double layer field trials at 23 different European test sites under different exposure conditions (in total 27 test sets). The material climate in terms of wood moisture content (MC) and wood temperature was automatically monitored over a period of up to 7 years and compared with the progress of decay. The overall aim of this study was to establish dose–response relationships between climate factors and decay as a basis for the service life prediction of wood. The “Scheffer Climate Index” based on weather data collected at official meteorological stations at the different test sites poorly correlated with the corresponding decay progress and was therefore not a suitable tool for estimating site-specific decay potential. In contrast, the use of the combined material climatic parameters MC and wood temperature led to a feasible dose–response function and turned out to be a useful basis for service life prediction of wood. [ABSTRACT FROM AUTHOR]