Hygroscopicity Of Wood Research Articles

Modification of the surface of thermally modified wood with ozone when creating glued structures

The greatest interest of researchers is focused on the processes of heat treatment of wood, taking place in an airless environment at temperatures of 180-250 °C, since heat treatment of wood allows increasing its moisture resistance, reduce hygroscopicity, and increase resistance to decay. However, a decrease in the hygroscopicity of wood adversely affects the process of obtaining glued materials due to a decrease in the wettability of thermowood surface and, as a consequence, a decrease in adhesion characteristics. This work is devoted to the study of the effect of ozone on the surface of thermally modified wood to increase the adhesive properties during gluing. It has been determined that the ozonation contributes to an increase in the wettability of the surface layer of thermal wood by more than 15% due to the reactivity of ozone to oxidize and degrade ligno-containing products of wood. It was revealed that the modification of wood, including preliminary volumetric heat treatment followed by surface treatment with ozone, causes an increase in the strength of the glue line when operated in high humidity conditions. In connection with the results obtained, an improved technology for the production of glued load-bearing structures for wooden housing construction is proposed.

Effect of hot-water extraction on the hygroscopicity, shrinkage, and swelling of Paulownia tomentosa wood

Liquid water and water vapor absorption on each separate surface and all surfaces at once, as well as the oven-dry shrinkage before and after the hot-water extraction of the wood, were examined using Korean Standards. The extractives content was examined using American Society for Testing and Materials (ASTM) standards. The highest water absorption and moisture adsorption were found in the transverse sections of both unextracted and extracted wood samples. There was no change in the equilibrium moisture content (EMC) in the unextracted vs. extracted wood samples at a relative humidity (RH) of 75%. However, the EMC in the extracted sample was higher than that in the unextracted sample at a RH of 90%. Swelling per 1% moisture content remained unchanged in the radial direction before and after extraction, while it increased in the tangential direction. The linear and volumetric shrinkage, as well as the coefficient of anisotropy, considerably increased after extraction. There was no difference in the extractive content between sapwood and heartwood. In conclusion, it was confirmed that the extractives in wood considerably affect the hygroscopicity and shrinkage of Paulownia wood.

Physical properties of Tectona grandis (Lamiaceae) juvenile wood thermally modified in a closed system

This paper reports the first results of the effect of an industrial closed-system thermal modification process on the physical properties of fast-growth teak wood (Tectona grandis L.f.). The wood (juvenile) came from thinning a 15–18-year-old plantation located in Mato Grosso state, Midwest Brazil, broken down into plainsawn battens measuring 25 × 70 × 1 070 mm (radial × tangential × longitudinal). The battens were from material close to the pith which was combined heartwood (≈75%) and sapwood. We sampled untreated and thermally modified battens, which were transformed into specimens for testing. The thermal modification was carried out at 160 °C in an industrial scale reactor, according to the parameters of the TanWood process, which is classified as a closed hygrothermal system. Twelve specimens by treatment (25 × 60 × 50 mm3 — radial × tangential × longitudinal) were conditioned in a climatic chamber set up at 35 °C and the relative humidity (RH) was raised stepwise (31%, 49%, 69% and 81%). Apparent density and equilibrium moisture content of the specimens were measured at every step. The latter was used as an index of wood hygroscopicity. For the statistical analysis, only the results of apparent density and moisture content at 35 °C and 69% RH were compared. At the end of the conditioning, the specimens were saturated in water, followed by oven-drying and then the total swelling (from saturated to oven-dried) was calculated. Thermally modified wood became less dense, less hygroscopic and more dimensionally stable than untreated wood. The apparent density and the equilibrium moisture content of wood were reduced by 20% and 18% respectively. With the continuous increase of RH from 31% to 81%, the thermally modified wood proportionally adsorbed less water than the untreated wood. The radial, tangential and volumetric total swelling were reduced by 25%, 5% and 15% respectively.

Bound Water Content and Pore Size Distribution of Thermally Modified Wood Studied by NMR

The physical and mechanical properties of thermally modified wood (TMW) have been comprehensively studied; however, the quantitative analysis of water states and cell wall pores of TMW is limited. In this work, Douglas fir and Norway spruce were thermally modified at 180, 200 and 220 °C, and then studied by NMR cryoporometry method. The results show that thermally modified samples had lower fiber saturation point and the bound water content than the reference samples at all the experimental temperatures, indicating the reduced hygroscopicity due to thermal modification (TM). In addition, TM decreased number of hygroscopic groups, which can be implied by the decreased proportion of bound water sites, and TM also increased the proportion of small voids for bound water clusters. An increase in TM intensity resulted in lower bound water content and a smaller number of hygroscopic groups. In summary, the NMR method detected the water states and pore size distribution and confirmed that TM decreased the fiber saturation point and hygroscopicity of wood by reducing the bound water content and proportion of bound water sites in wood cell walls.

Dimensional Stability of Waterlogged Scots Pine Wood Treated with PEG and Dried Using an Alternative Approach

Low-intensity drying is widely believed to protect waterlogged archeological wood against the adverse effects of dimensional alteration and cracking. However, slow drying generates substantial costs for the conservation process. This study compares the effects on conservation of highly-degraded sapwood (SW) and slightly-degraded heartwood (HW) from waterlogged archeological Scots pine wood treated with polyethylene glycol either as a mixture of polyethylene glycol (PEG) 400/4000 or PEG 2000 solution and air-dried using different approaches. The reference air-drying approach, using gradually decreasing air relative humidity (RH), i.e., 96, 86, 75, 66, and finally 44% (multi-stage schedule), was compared to an alternative approach, using constant RH of 44% (single-stage schedule). The Fourier-transform infrared spectroscopy (FTIR) analysis confirmed the decomposition of hydrophilic chemical wood components and revealed differences in the degree of degradation of waterlogged SW and HW. The drying time of PEG-treated waterlogged wood air-dried using a one-stage schedule was shorter compared to the drying time using multi-stage drying. Multivariate analysis (ANOVA) revealed that the drying schedule used after impregnation of waterlogged wood with PEG can have a beneficial effect on wood hygroscopicity and dimensional stability. The drying schedule significantly affected the equilibrium moisture content (EMC) of SW and HW and reduced tangential (ST) shrinkage of SW. These results show the positive effect of the single-stage alternative drying approach on the dimensional stability of highly-degraded Scots pine SW impregnated with PEG 2000. In the case of slightly-degraded HW, the drying approach did not affect wood preservation. These results can be useful for the conservation of highly-degraded waterlogged Scots pine wood.

Effects of Shellac Treatment on Wood Hygroscopicity, Dimensional Stability and Thermostability

Dimensional stability proves to be an important factor affecting the quality of wooden products. As a sort of crude and thermoplastic resin, shellac excreted by lac insects demonstrates water-repellent and environmental-friendly features. The research impregnated shellac with wood at room temperature and with a vacuum-pressure procedure. Efforts were made to examine how shellac treatment affected the dimensional stability, moisture absorption, chemical structure, thermostability, as well as morphological characteristics of wood. Results indicated that shellac treatment was a type of efficient solution useful in the enhancement of the dimensional stability of wood. Shellac solution had good permeability in the wood, and the weight percentage gain reached 13.01% after impregnation. The swelling coefficients of treated wood in the tangential and radial directions decreased by 20.13% and 24.12%, respectively, indicating that impregnation could improve wood dimensional stability. The moisture absorption of shellac-treated wood was reduced by 38.15% under 20 °C and 65% relative humidity. Moreover, shellac treatment significantly modified wood structure, although there were no drastic changes in the spectra. Specimens for shellac treatment ran across two decomposition peaks at 350 and 390 °C, and specimens in the control group saw one more common derivative thermogravimetric curve when the sharp peak approached 355 °C. After impregnation of shellac into wood, the shellac blocked pits and hardened on the intrinsic layer of the wood for fear of hygroscopicity. The practice was applicable to a variety of wood products, such as buildings, furniture, and landscape architecture.

Effect of a Combination of Moderate-Temperature Heat Treatment and Subsequent Wax Impregnation on Wood Hygroscopicity, Dimensional Stability, and Mechanical Properties

Wood is an environmentally friendly material, but some natural properties limit its wide application. To study the effect of a combination of heat treatment (HT) and wax impregnation (WI) on wood hygroscopicity, dimensional stability, and mechanical properties, samples of Pterocarpus macrocarpus Kurz wood were subjected to HT at a moderate temperature of 120 °C and a high temperature of 180 °C, for a 4 h duration. Subsequently, half of the 120 °C HT samples were treated with WI at 90 °C. The results showed that 180 °C HT and WI decreased the capacity of adsorption and liquid water uptake and swelled the wood significantly, while WI had the biggest reduction. The effect of 120 °C HT was significant only on decreasing the capacity of adsorption and the swelling of liquid water uptake. The bending strength (MOR) of wood decreased only after 180 °C HT, and 120 °C/4h HT and WI had no significant influence on MOR. The bending stiffness (MOE) increased significantly after 180 °C HT and WI, while 120 °C/4h HT had no significant influence on MOE. Therefore, the combination of moderate-temperature HT can act synergistically in the improvement of certain aspects of wood properties such as capacity of water adsorption and liquid water uptake. WI effectively improved wood hygroscopicity, dimensional stability, and mechanical properties.

The Effect of Contact-Drying on Physical Properties of European Beech (Fagus sylvatica L.)

Beech wood is mainly used for furniture, plywood, decorative veneer manufacturing or packaging. Timber or lumber is traditionally dried in kilns by processes often taking several weeks. This research deals with more rapid process called contact-drying process. Drying was performed using the heating plates with a temperature of 160 °C and pressures of 1.0 MPa, 1.4 MPa and 1.8 MPa. The results were compared to conventional warm-air drying. The warm-air drying mode was divided into two phases, with and without free water and bound water in the dried wood. The density of the samples increased remarkably during the contact-drying. The effect of the pressure of the heating plates was substantial. The difference in the average density between the pressure of 1.0 MPa and 1.8 MPa was more than 22 kg·m−3. The pressure of the heating plates affected the process and the resulting change in the sample thickness. The change in the sample thickness was more considerable in the case of the tangential samples. The thickness did not increase significantly after air conditioning. During contact-drying, the hygroscopicity and absorptivity of wood reduced on average by 21.24% and 25%, respectively, compared to warm-air drying.

Effect of Degradation on Wood Hygroscopicity: The Case of a 400-Year-Old Coffin

The hygroscopicity and thermodynamic properties of Pinus sylvestris L. wood from a coffin allegedly holding the remains of famous Spanish author Miguel de Cervantes Saavedra (1547–1616) were studied using the 15 °C and 35 °C isotherms fitted to the Guggenheim–Anderson–de Boer model and comparing them with the isotherms of recently felled wood of the same species. In addition, using infrared spectroscopy (FTIR-ATR) and X-ray diffractograms, the functional groups were determined and the crystallinity and organization of the cell wall components were analyzed. The absence of the 1740 cm−1 group indicates hemicellulose degradation in the archaeological wood, and the X-ray diffractograms show a considerable decrease in cellulose crystallinity and disorganization of the cellulose crystallites. The greater availability of active –OH groups means that the archaeological wood isotherms are above the juvenile and mature wood isotherms, and therefore the thermodynamic balance in the sorption of the archaeological wood is greater.

FTIR analysis of chemical changes in wood induced by steaming and longitudinal compression

Pleating is an optimal way to increase bendability of wood used in diverse industrial applications. It results in the excessive buckling of cell walls and modifications of constitutive polymers. However, thoughtful understanding of the physical–chemical mechanisms of that modification process is very limited. The main purpose of the present study was to identify changes in functional groups of wood polymers induced by longitudinal compression. Four types of wood samples prepared from beech and sessile oak (untreated, steamed, longitudinally compressed and fixated for 1 min as well as longitudinally compressed and fixated for 18 h) were assessed by infrared spectroscopy. The spectra interpretation revealed that changes can be observed in hydroxyl as well as in carbon–oxygen single and carbon-hydrogen functional groups of polysaccharides and lignin. Beech wood seems to be more susceptible to investigated modification processes as compared to oak. Detailed interpretation of infrared spectra allows identification of changes in the hygroscopicity of wood as well as alterations in the linkage between structural elements in the polymer matrix of wood induced by the applied treatments.Graphic

Moisture-Dependent Strength Properties of Thermally-Modified Fraxinus excelsior Wood in Compression.

European ash (Fraxinus excelsior L.) is one of the species commonly used for wood thermal modification that improves its performance. The presented research aimed to investigate a moisture-dependent strength anisotropy of thermally-modified European ash in compression. Wood samples were modified at 180 °C and 200 °C. Their mechanical parameters were determined in the principal anatomical directions under dry (moisture content of 3%) and wet (moisture content above fibre saturation point) conditions. Effect of heat treatment temperature and moisture content on the ash wood mechanical parameters concerning each anatomical direction were determined. The results show that thermal treatment kept the intrinsic anisotropy of wood mechanical properties. It decreased wood hygroscopicity, which resulted in improved strength and elasticity measured for wet wood when compared to untreated and treated samples. Higher treatment temperature (200 °C) increased wood elasticity in compression in all the anatomical directions despite wood moisture content during the measurements. Multivariate analysis revealed that the modification temperature significantly affected the modulus of elasticity perpendicular to the grain, while in the case of compression strength, the statistically significant effect was observed only parallel to the grain. The results obtained can be useful from an industrial perspective and can serve as part of a database for further modelling purposes.

Organosilicons of different molecular size and chemical structure as consolidants for waterlogged archaeological wood \u2013 a new reversible and retreatable method

Ineffectiveness of the chemicals applied so far for waterlogged wood conservation created the need to develop new more, efficient and reliable agents. As an alternative, a new method with the use of organosilicon compounds differing in chemical composition and molecular weight has been investigated. The results obtained show the potential of organosilicons as consolidants in waterlogged wood conservation able to effectively stabilise wood dimensions upon drying. The best wood stabilisers were low-molecular organosilicons enable to penetrate the cell wall as well as chemicals with functional groups capable of interacting with wood polymers and forming stabilising coatings on the cell wall surface. The best anti-shrink efficiency values were obtained for (3-Mercaptopropyl)trimethoxysilane, (3-Aminopropyl)triethoxysilane, 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, reaching 98, 91 and 91%, respectively. Most of the applied organosilicons reduced wood hygroscopicity, which limits the risk of further dimensional changes of wood exposed to a variable air moisture content and potentially reduces wood biodegradation. In the light of our studies, the proposed method of waterlogged wood conservation with organosilicons is potentially reversible in the case of siloxanes and amino-silanes as well as retreatable, which complies with the requirements of the conservation ethics.

Changes in the wood-water interactions of mahogany wood due to heat treatment

Abstract Mahogany wood (Swietenia macrophylla King) was thermally modified by heating at various temperatures. The wood-water-related parameters of the heat-treated wood, including fiber saturation point, equilibrium moisture content, moisture excluding efficiency, hygroscopic hysteresis, swelling, anti-swelling efficiency, water adsorption, and surface wettability were determined to clarify the mechanism of heat treatment to reduce wood hygroscopicity. The wood treated at a higher temperature demonstrated a more significant decrease in hygroscopicity. The reduction in hygroscopicity of the heat-treated wood was partially diminished as the moisture excluding efficiency decreased in the absorption and desorption processes caused by the changes in environmental temperature and relative humidity. The fiber saturation point (determined by nuclear magnetic resonance spectroscopy), surface free energy, and the surface wettability of wood were reduced by heat treatment, resulting in the decreased hygroscopicity of the heat-treated wood. Mahogany wood became more insensitive to the influence of moisture due to the heat treatment, and this effect was more distinct for wood treated at a high temperature.

Investigation of the effect of aging on wood hygroscopicity by 2D 1H NMR relaxometry

Abstract Two-dimensional proton nuclear magnetic resonance (2D 1H NMR) relaxometry is increasingly used in the field of wood sciences due to its great potential in detecting and quantifying water states at the level of wood constituents. More precisely, in this study, this technique is used to investigate the changes induced by “natural” and “artificial” aging methods on modern and historical oak woods. Two bound water components are detected and present differences in terms of association to the different wood polymers in cell walls: one is more strongly associated with wood polymers than the other. The evolution of the two bound water types is discussed in regard to aging methods and is related to the structure of the cell wall, especially with the S2 layer and the evolution of wood chemical composition (cellulose, hemicelluloses and lignin). The evolution of hydric strains is also discussed taking into account the effect of aging methods on the two bound water components. The obtained results confirm the ability of 2D 1H NMR relaxometry to evaluate the effect of aging at the molecular level and on hydric deformation. Furthermore, this method shows that it is possible to determine the moisture content of wood without the necessity to oven-dry the wood material.

Changes of water related properties in radiata pine wood due to heat treatment

Wood is a green and renewable building material, however, the hygroscopicity restrict its use in the field of construction and building. To study the effect of heat treatment (HT) on wood hygroscopicity and other water related properties, radiata pine wood was subjected to HT at four temperature levels of 185, 200, 215 and 230 °C, for the duration of 4 h. Overall, the equilibrium moisture content, moisture adsorption, water absorption and volume swelling ratio were all decreased, while hygroscopic hysteresis was enhanced with increasing HT temperature. The surface wettability was clearly weakened after HT, reflected as the increased contact angle and reduced surface free energy.

Effects of Tung oil treatment on wood hygroscopicity, dimensional stability and thermostability

It is commonly known that wood is a limited renewable material, and its low dimensional stability characteristics limit its ability to be more widely used. Tung oil, which is characterized by environmentally friendly and water-repellent features, is used in this study as a modifier to improve the properties of wood. Wood is impregnated with Tung oil at room temperature, and the effects of Tung oil on the dimensional stability, moisture absorption, chemical structure, thermostability, and morphological characteristics of the wood are studied. The results show that Tung oil treatment is an effective technique to improve wood dimensional stability. The weight percentage gain was found to attain up to 60.56%, and Tung oil treatment decreased the wood tangential and radial swelling coefficients by 30.8% and 29.6%, respectively. Tung oil treatment also decreased the moisture absorption by 51.53%. Specimens treated with Tung oil presented two sharp peaks of decomposition around 376 °C and 421 °C, while the control specimens exhibited a more common DTG curve with a sharp peak at 376 °C. Tung oil can be impregnated into wood and occluded pits, and solidifies at the internal surface of wood to prevent moisture absorption. This method can be implemented in buildings, furniture, and landscape architecture to broadly expand the application of wood products.

Study on Formalization of Oil Palm Trunk Modified by Melamine Formaldehyde

The structure, composition and water content of a oil palm wood influence its dynamic mechanical properties. These are very important to study in relation to wood applications. The quality of oil palm wood can be improved through formalization treatment in acid and alkaline conditions and then impregnated by melamine formaldehyde. Variation of formalization time and curing temperature after impregnation on specimens were investigated. Based on physical properties and FTIR characterizations, the formalization time of both acidic and alkaline conditions with the melamine formaldehyde impregnation treatment, showed improving in physical properties of the samples after treatment and this is also indicated with a shift in wave numbers and emergenced a new functional group on FTIR spectra of the samples. The curing temperature has also led to increase density and decrease water content of the specimen, so therefore revealing a decrease of the hygroscopicity of wood.

Effects of zinc chloride\u2013silicone oil treatment on wood dimensional stability, chemical components, thermal decomposition and its mechanism

The hygroexpansion and anisotropy of wood limit its application in construction and wood products industry. Zinc chloride–silicone oil was use to decrease the hygroscopicity and improve the dimensional stability of wood at 80 °C, 140 °C, 160 °C and 180 °C. The effects of the treatment on the dimensional stability, chemical structure, thermal degradation, morphology of wood were evaluated, and the mechanism was determined. Results indicated that the zinc chloride–silicone oil treatment at 80 °C improved the dimensional stability and decreased the hygroscopicity of wood. The tangential, radial, and volumetric swelling coefficients of the treated wood decreased by 9.7%, 33.5%, and 18.2%, respectively, relative to those of the untreated wood. Zinc chloride–silicone oil treatment also changed the chemical structure of wood by degrading the wood components and decreasing the moisture absorption groups. Moreover, zinc chloride–silicone oil treatment significantly influenced the thermal degradation of wood, as samples treated with zinc chloride–silicone oil at 140 °C, 160 °C and 180 °C presented sharp peaks around 511 °C, 501 °C and 473 °C. The control group exhibited a more common derivative thermogravimetric curve with a sharp peak at 375 °C. In addition, the silicone oil could impregnate wood, occlude moisture passage, and prevent the movement of moisture in wood. This method can be applied in building and wood industries to expand the applications of wood products.

CARACTERIZAÇÃO E AVALIAÇÃO DA RESISTÊNCIA BIOLÓGICA DA MADEIRA SOBRE O ATAQUE DE FUNGOS

Resumo: O tratamento termomecânico consiste em um processo que combina tratamentotérmico com compressão mecânica sobre a madeira, com a finalidade de se produzir um materialcom menor higroscopicidade. O objetivo neste trabalho é caracterizar e avaliar a resistênciabiológica da madeira perante o ataque de fungos causadores de podridão parda e de podridãobranca. A fim de delinear melhor o objetivo, as amostras de madeira submetidas a tratamentotermomecânico foi feito em uma prensa hidráulica a temperaturas de 140°C e 180°C, tempos deum e dois minutos e pressão constante de 2,7 N/mm2. Foi avaliada a resistência biológica dessespainéis sobre o ataque de fungos causadores de podridão parda (Gloeophyllum trabeum) e depodridão branca (Trametes versicolor). Depois, as amostras foram caracterizadas por análises deFTIR (espectroscopia de infravermelho com transformada de Fourier), MEV (microscopiaeletrônica de varredura) e TGA (análise termogravimétrica). A análise de FTIR identificouclaramente nos espectros, uma redução do pico em 1700 cm-1com o tratamento termomecânicoe atacados pelos fungos, ocorrendo à diminuição da lignina. A caracterização por MEV mostroumudança na morfologia das amostras. As curvas termogravimétricas (TG) mostraram boaestabilidade térmica para as amostras com tratamento termomecânico. Mostrou também umadiminuição do teor de umidade de equilíbrio, mostrando que o tratamento foi eficiente emreduzir a higroscopicidade da madeira, podendo assim melhorar as propriedades mecânicas.Palavras-chave: Tratamento termomecânico, madeira, resistência biológica.

Nondestructive Characterization of Dry Heat-Treated Fir (Abies Alba Mill.) Timber in View of Possible Structural Use

The use of heat-treated timber for building with wood is of increasing interest. Heat treatment improves the durability and dimensional stability of wood; however, it needs to be optimized to keep wood’s mechanical properties in view of the possible structural use of timber. Therefore, dry vacuum heat treatment varying the maximum temperature between 170 °C and 230 °C was used on fir (Abies alba Mill.) structural timber, visually top graded according to EN 338, to analyze its final weight loss, hygroscopicity, CIELAB color, and dynamic elastomechanical properties. It turned out that weight loss and total color difference of wood positively correlates with the increasing intensity of the heat treatment. The maximum 40% reduction of the hygroscopicity of wood was already reached at 210 °C treatment temperature. The moduli of elasticity in longitudinal and radial direction of wood, determined by ultrasound velocity, increased initially up to the treatment temperature of 210 °C, and decreased at higher treatment temperature. Equally, the Euler-Bernoulli modulus of elasticity from free-free flexural vibration of boards in all five vibration modes increased with the rising treatment temperature up to 190 °C, and decreased under more intensive treatment conditions. The Euler-Bernoulli model was found to be valid only in the 1st vibration mode of heat-treated structural timber due to the unsteady decrease in the evaluated moduli of elasticity related to the increasing mode number.