Thermal Modification Of Wood Research Articles

Research of the process of water absorption by thermally modified wood

The analysis of the process of thermal modification of wood, which was obtained by a controlled process of pyrolysis of wood heating (> 180 °C), which causes some chemical changes in the structures of cell wall components (lignin, cellulose and hemicellulose), to increase its durability. It is proved that in the process of thermal modification there is a decomposition of hemicelluloses and amorphous part of cellulose, reduction of water absorption, and also the quantity of substances which are the environment for development of fungi decreases. In addition lignin and psevdolihnin formed by the process of polymerization and redistribution in cell volume and cell walls provide higher density, hardness, increase the hydrophobicity (water repelling), thereby reducing their ability to absorb moisture and swell. Polymerised lignin fills the inside of the cell – formed closed porous structure with low ability to bind water. It was established that the most effective option to reduce such substances are temperature and exposure time. The results of water absorption, dependence on which the calculated diffusion coefficient in the water absorption. Thermal modification of wood reduces water absorption by more than 10 times within 6 hours, which allows it to be used on objects with high humidity.

Establishing regularities in the propagation of phase transformation front during timber thermal modification

The creation of environmentally friendly protective materials for building structures made of wood could make it possible to influence the processes of stability and the physical-chemical properties at the thermal modification of hornbeam wood over a certain time. That necessitates studying the conditions for investigating phase transformations when the timber is exposed to high temperature, as well as establishing the mechanism of hornbeam wood thermal modification. Given this, a mathematical model of the phase transformation process during the transfer of heat flux to a sample was built. Based on the derived dependences, it was established that when hornbeam wood is exposed to temperature treatment, it undergoes endothermic phase transformations characterized by the heat absorption and change in the color of hornbeam wood. In particular, at a temperature of 200 °C, the temperature in the wood decreases by 5 % due to the chemical changes in the structure of cell wall components (lignin, cellulose, and hemicellulose). It was found that the process of thermal modification is accompanied by the decomposition of hemicellulose and the amorphous part of cellulose, a decrease in moisture absorption, as well as a decrease in the volume of substances that are a medium for the development of fungi. In addition, lignin and the resulting pseudo lignin undergo a process of polymerization and redistribution throughout the cell volume. At the same time, they give the cell walls higher density, hardness, increase hydrophobicity (water repellency), thereby reducing the ability to absorb moisture and swell. It was established that the most effective parameter of phase transformations is the temperature and aging duration. The results of moisture absorption have been given; it has been found that over 6 hours of modified timber exposure, its moisture absorption decreases by more than 10 times, which allows its application at facilities with high humidity

Quality of Oil- and Wax-Based Surface Finishes on Thermally Modified Oak Wood

In this study, natural linseed oil, hard wax oil, and hard wax, commonly used as finishes for wooden furniture and parquet, were used for surface finishes on Turkey oak wood (Quercus cerris L.), thermally modified at temperatures of 175 °C and 195 °C for 4 h. Several resistance surface properties were investigated. The mechanical resistance properties of all surface finishes were very much allied to interactions between the finish and the type of substrate. The adhesion strength and impact resistance decreased if higher temperature was used for thermal modification of the substrate. The surface hardness and the resistance to abrasion were high and increased slightly with increasing temperature during thermal modification of wood. It was also found that surface adhesion, hardness and resistance to impact were very much related to interactions between the coating film and the substrate. The resistance properties of finishes, such as resistance to cold liquids and mold, were mainly influenced by the type of the surface finish. The resistance to cold liquids increased in the order: surface finish with hard wax < linseed oil < finish system of linseed oil + hard wax oil. The lowest resistance to cold liquids showed up in condensed milk and sanitizer. Resistance to Aspergillus niger and Penicillium purpurogenum was relatively weak, however apparently improved during the first 7 days of the fungal test; the surfaces were covered with a lower distribution density of fungal mycelium after 21 days of the fungal test. Individual surface performances of oil and wax-based surface finishes on native wood were different from thermally modified wood.

Enhancing Thermally Modified Wood Stability against Discoloration

Thermal modification of wood has gained its niche in the production of materials that are mainly used for outdoor applications, where the stability of aesthetic appearances is very important. In the present research, spectral sensitivity to discoloration of thermally modified (TM) aspen wood was assessed and, based on these results, the possibility to delay discoloration due to weathering by non-film forming coating containing transparent iron oxides in the formulation was studied. The effect of including organic light stabilizers (UVA and HALS) in coatings as well as pretreatment with lignin stabilizer (HALS) was evaluated. Artificial and outdoor weathering was used for testing the efficiency of different coating formulations on TM wood discoloration. For color measurements and discoloration assessment, the CIELAB color model was used. Significant differences between the spectral sensitivity of unmodified and TM wood was observed by implying that different strategies could be effective for their photostabilization. From the studied concepts, the inclusion of the transparent red iron oxide into the base formulation of the non-film forming coating was found to be the most effective approach for enhancing TM wood photostability against discoloration due to weathering.

Effect of hemp oil impregnation and thermal modification on European beech wood properties

Thermal modification of wood is an environment-friendly method, which, among others, enhances wood water related properties, whereas the use of hot oil as a heating medium generally leads to better performance. In this study, European beech wood was hemp oil-impregnated, thermally modified at 200 °C and both ways of treatment were combined. Analysis of the treated wood included the determination of the change in important wood characteristics—colour, hygroscopicity, dimensional stability, bending properties, and decay resistance against white rot. The results indicate that heat treatment combined with oil has influenced the properties of beech wood more than heat treatment itself. In certain cases, the high effectiveness is only relative with regard to mass increase caused by high oil retention.

A review on life cycle assessments of thermally modified wood

AbstractThis review compiles various literature studies on the environmental impacts associated with the processes of thermal modification of wood. In wood preservation field, the wood modification by heat is considered as an ecofriendly process due to the absence of any additional chemicals. However, it is challenging to find proper scientific and industrial data that support this aspect. There are still very few complete studies on the life cycle assessment (LCA) and even less studies on the environmental impacts related to wood heat treatment processes whether on a laboratory or on an industrial scales. This comprehensive review on environmental impact assessment emphasizes environmental categories such as dwindling of natural resources, cumulative energy intake, gaseous, solid and liquid emissions occurred by the thermal-treated wood industry. All literature-based data were collected for every single step of the process of wood thermal modification like resources, treatment process, transport and distribution, uses and end of life of treated wood products.

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.

Structural Changes of Oak Wood Main Components Caused by Thermal Modification.

Thermal modification of wood causes chemical changes that significantly affect the physical, mechanical and biological properties of wood; thus, it is essential to investigate these changes for better utilization of products. Fourier transform infrared spectroscopy and size exclusion chromatography were used for evaluation of chemical changes at thermal treatment of oak wood. Thermal modification was applied according to Thermowood process at the temperatures of 160, 180 and 210 °C, respectively. The results showed that hemicelluloses are less thermally stable than cellulose. Chains of polysaccharides split to shorter ones leading to a decrease of the degree of polymerization and an increase of polydispersity. At the highest temperature of the treatment (210 °C), also crosslinking reactions take place. At lower temperatures degradation reactions of lignin predominate, higher temperatures cause mainly condensation reactions and a molecular weight increase. Chemical changes in main components of thermally modified wood mainly affect its mechanical properties, which should be considered into account especially when designing various timber constructions.

Microstructure of thermally modified radiata pine wood

The thermal modification of wood is a potential alternative method for improving wood dimensional stability and increasing the resistance of wood to decay. However, during thermal modification, morphological changes occur within the microstructure of the cell, and these confer different properties to the wood. This study investigated the effects of the thermal modification process on the microstructure of radiata pine juvenile wood. Therefore, anatomical measurements were performed via optical microscopy in selected earlywood and latewood samples after each treatment, and the results were compared to untreated wood samples. In this study, two temperatures (190 °C and 210 °C) were considered for the thermal modification process. The results showed that the level of temperature of modification affected to microstructure of cell wall. The cell wall thickness decreased as treatment temperature increased, whereas the average lumen diameter increased slightly as temperature increased. Thermally modified radiata pine showed signs of damage (cracks, broken cells and deformations in the wood cell wall). The proportion of destroyed area increased as temperature increased, and significant differences were evident for the thermal treatment at 210 °C.

Anti-fungal and anti-termite activity of extractives compounds from thermally modified ash woods

Thermal modification of wood is a promising alternative to chemical and biocidal modification processes, increasing the biological durability and dimensional stability of wood. However, the wood-decay resistance properties of heat-treated wood are still not well known. The main objective of this study was to determine the biological resistance of heat-treated ash wood, and assess the antifungal and anti-termite activity of extractive compounds from heat-treated ash woods, depending on the intensity of the modification process (2 hours at 170, 200, 215, 228 (°C) - steam pressure). Untreated and heat-treated wood samples were extracted with water or acetone. The extracts were then used to determine inhibition effectiveness against white-rot (Trametes versicolor) and brown-rot (Rhodonia placenta) fungi. Whatman papers impregnated with extractives were used to evaluate the inhibition of termite feeding. Lastly, the extractives were analyzed by Gas Chromatography - Mass Spectrometry (GC-MS) and compared for their level of anti-termite and antifungal activity. The results showed that the degree of antifungal activity of these extracts depended on the solvent used during the extraction process and varied depending on heat treatment intensity. The extracts were more effective against brown-rot than white-rot fungi. However, the anti-termite activity of heat-treated ash wood extracts was not really significant. A GC-MS analysis showed that the main share of the extractives in untreated wood was removed. In addition, new chemical elements were generated by the thermal degradation of wood polymers (lignin and hemicelluloses), including aliphatic acids, monosaccharides and other products resulting from their dehydration reaction. The most abundant element was syringaldehyde, from lignin derived compounds, which might explain the antifungal activities of thermally treated ash wood extracts.

ДОСЛІДЖЕННЯ ВПЛИВУ РЕЖИМНИХ ПАРАМЕТРІВ ПРОЦЕСУ ТЕР-МІЧНОЇ ОБРОБКИ ДЕРЕВИНИ ЯСЕНА НА ФОРМОСТІЙКІСТЬ КОМБІНОВАНИХ МЕБЛЕВИХ ЩИТІВ

It has been established that the process of thermal modification of wood is an environmentally friendly way of protecting wood. Thermal modification of wood also makes it possible to significantly improve the appearance of wood of low-grade species by changing their color. Method and the results of experimental research of form stability of the combined furniture boards. The influence of mode parameters of the process of heat treatment of wood on the shape resistance of the received boards is determined. The mathematical and graphical dependence of the form stability of the combined furniture boards on the operating parameters of the process of heat treatment of the wood of ash were obtained. It is substantiated that the flatness of furniture panels is greatly influenced by the technological accuracy of the equipment used in the final calibration of finished panels. It has been investigated that the temperature of the thermal modification process is more influenced by the plane of the combined furniture panel than its duration. It is established that the results of experimental studies of the flatness of combined furniture boards, almost all of them do not meet the requirements of the standard. Only combination furniture panels made from a combination of ash wood sections obtained at a modification temperature of 190 ° C and treatment times of 4 and 10 hours with sections of untreated wood meet the requirements of the standard. The deviations from the flatness of the experimental shield data are 0.29 and 0.34 mm, respectively. The justification is made that the unsatisfactory results can be explained by the fact that the individual parts of which the combined shield consists of react differently with the humidity of the environment. It has been found that the combined furniture panels, the sections of which are treated with temperature t = 220 ° C, have the ability to retain their geometric dimensions and shape better than when treated with temperature t = 160 ° C or without treatment. It is recommended to use the results obtained during student preparation and in production conditions to obtain quality products that meet the requirements of the standards.

Interaction of technical and technological factors on qualitative and energy/ecological/economic indicators in the production and processing of thermally modified merbau wood

Abstract Thermal modification of wood is a technological intervention primarily aimed at improving the dimensional stability and decay resistance of wood, making it suitable for outdoor application. Despite the fact that this process is widely used today, there is still a lack of knowledge about the effect of thermal modification on the surface quality of wood processed with conventional milling. This study focuses on two basic areas that significantly influence the economy of production and the quality of thermally modified wood. The first part deals with the evaluation of the effect of modification temperature on the chemical composition of wood. The second part deals with the effect of machining parameters, namely cutting speed, feed rate and rake angle, on selected surface quality parameters (roughness, waviness). The interaction between modification temperature, chemical change and machining parameters was also evaluated. The result of this study suggests the optimal combination of processing parameters necessary to achieve higher surface quality with the lowest energy consumption, considering the intrinsic properties of the studied species.

Color change and emission of volatile organic compounds from Scots pine exposed to heat and vacuum-heat treatment

Heat treatment improves the dimensional stability and durability of wood. Thermal modification of wood has been extensively studied in the last two decades as it is an environmentally friendly method. Thermally treated wood has been industrialized under different brand names such as ThermoWood, Plato wood and Retified wood. These products differ from each other according to their process technology. During the heat treatment process, wood is chemically changed due to the higher temperature. This is followed by increased color change and the wood becomes darker. In addition, various volatile organic compounds (VOCs) in different quantities are emitted during or after heat treatment. In this study, evaluation of VOC emissions of Scots pine sapwood and heartwood was carried out after heat and vacuum-heat treatment. Higher mass loss occurred in sapwood samples with heat treatment as compared to vacuum-heat treatment. Lightness decreased and color change increased after the heat treatment, but these results were inhibited with vacuum-heat treatment. Vacuum-heat treatment increased the sum of emitted compounds (TVOC) when heartwood samples were used. Pentanal, hexanal and α-Pinene were emitted from air-dried samples in higher quantities than other compounds, with α-Pinene being the most frequently emitted compound from the air-dried or treated wood samples.

Gaseous decomposition products from wood degradation via thermogravimetric and fourier transform infrared analysis during thermal modification of beech and pine woods

Wood thermal modification is an environmentally friendly method used to improve wood characteristics, and its degradation mechanism directly influences its application in construction, building, and home decoration. Combined thermogravimetry and Fourier transform infrared (TG–FTIR) studies were conducted to evaluate the hardwood and softwood on-site at 160 °C and 220 °C. The results indicated that the mass loss rates (MLRs) for both hardwood and softwood samples decreased over time and ultimately became constant. The total mass loss increased with an increase in temperature. The total mass loss was about 3% at 160 °C, and about 4.7% to 6.5% at 220 °C. Decomposition also occurred much more easily in the hardwood than in the softwood. More species of gas products were emitted from hardwood than softwood, and the number of species of gas products increased with an increase in temperature and processing time. The FTIR spectra of softwood were similar, whereas those of hardwood were remarkably different at different temperatures. Water and alcohol were generated from both the hardwood and softwood, whereas contents of these gaseous products were visible in hardwood decomposed at 220 °C during the thermal treatment. Ketones, ethers, acids, and aromatics were found in both hardwood and softwood, whereas CO2 was only found in the hardwood that underwent thermal treatment.

New Perspective on Wood Thermal Modification: Relevance between the Evolution of Chemical Structure and Physical-Mechanical Properties, and Online Analysis of Release of VOCs.

Thermal modification (TM) is an ecological and low-cost pretreated method to improve the dimensional stability and decay resistance of wood. This study systematically investigates the relevance between the evolution of chemical structure and the physical and mechanical properties during wood thermal modification processes. Moreover, the volatility of compounds (VOCs) was analyzed using a thermogravimetric analyzer coupled with Fourier transform infrared spectrometry (TGA-FTIR) and a pyrolizer coupled with gas chromatography/mass spectrometer (Py-GC/MS). With an increase of TM temperature, the anti-shrink efficiency and contact angle increased, while the equilibrium moisture content decreased. This result indicates that the dimensional stability improved markedly due to the reduction of hydrophilic hydroxyl (–OH). However, a slight decrease of the moduli of elasticity and of rupture was observed after TM due to the thermal degradation of hemicellulose and cellulose. Based on a TGA-FTIR analysis, the small molecular gaseous components were composed of H2O, CH4, CO2, and CO, where H2O was the dominant component with the highest absorbance intensity, i.e., 0.008 at 200 °C. Based on the Py-GC/MS analysis, the VOCs were shown to be mainly composed of acids, aldehydes, ketones, phenols, furans, alcohols, sugars, and esters, where acids were the dominant compounds, with a relative content of 37.05−42.77%.

Influence of Different Modifications on Bending Strength of Wood

Despite intensive research in wood protection, no simple wood treatment method is available for satisfactory wood protection that could ensure appropriate strength and bio-resistance of wood products during their service life. The present study is a part of a project that is aimed to improve wood service properties by combining wood thermal treatment and impregnation with copper containing preservatives. The objective of the present study was to investigate the effect of conventional modifications (thermal modification at relatively mild temperature range (150 - 180°C) and impregnation) and double-treatments (impregnation after thermal treatment and vice versa) on the bending properties of birch (Betula spp.) and pine (Pinussylvestris L.) wood. Bending strength considerably decreased after thermal modification of wood, however MOE values generally did not significantly change. Moreover, impregnation had no effect on the bending properties for both unmodified and thermally modified wood specimens. For double-treatment in which impregnation was carried out before thermal modification no changes in bending strength were observed comparing to thermally modified wood. However, MOE values of these specimens were 10 % for birch and 19 % for pine smaller comparing to just thermally modified wood. The results of double-treatment tests imply that, regarding wood bending properties, wood impregnation after thermal modification is more appropriate.

Modeling and simulation of heat-mass transfer and its application in wood thermal modification

Abstract Wood is a type of renewable and natural material, with most of its end application related to building materials. However, hygroexpansion and anisotropy in wood markedly shorten its service life and value. In this study, wood thermal modification was used to improve wood quality, and a heat-mass transfer model was established based on practical production process. The software COMSOL Multiphysics was used to solve this coupling transfer model. Relationships between temperature and moisture content, temperatures of the medium under thermal treatment, and treatment time, were established. Results indicated that this coupling model and method can be used to simulate and solve heat-mass transfer during wood thermal treatment, and the simulation results were found to be consistent with the measured results. The temperatures at the wood surface could achieve the target temperature within a considerably short time, whereas that at the wood central point was difficult to obtain. The cross-section of the heat convection boundary obtained the highest temperature and the lowest moisture content, whereas the cross-section of the symmetry boundary obtained the lowest temperature and the highest moisture content. These results can be used to devise a wood thermal treatment schedule, determine the heat and moisture distribution, and control the wood heat treatment process. Consequently, guidance for wood thermal treatment is provided to reduce energy and time consumption.

Technologies for Manufacturing of Moisture-Resistant Products from Modified Wood

Wood, as a finishing and building material, has always been given special attention. Wood has many positive properties, but it's no secret that faced with its shortcomings such as fragility, instability of form and susceptibility to decay, people often prefer synthetic materials, putting aside the ecology and useful properties of wood and choosing the long life of non-natural materials. In this regard experts around the world are constantly searching for new solutions aimed at improving the physical, mechanical and operational properties of wood, which would allow a person to limit the use of artificially created analogs of natural materials and enjoy the atmosphere of tranquility and appeasement in a house that can create a tree. Analyzing the knowledge and skills of previous generations the author of the article took as a basis various technologies of deep processing with the aim of improving the quality, extending the service life and expanding the scope of its use, thanks to which a new modern moisture resistant "hardened" tree is created for furniture, interior, finishing elements for garden houses and plots. Experiments have been carried out to investigate the biological resistance of wood thermo modified in five different technologies: vacuum-convective thermal modification in a superheated steam, convective thermal modification in a saturated high-pressure steam environment, thermal modification of wood in hydrophobic liquids, thermal modification of wood in a flue gas environment and vacuum-conductive thermal modification. The degree of moisture resistance of the samples is calculated, which makes it possible to conclude that the mass of thermo-modified wood is significantly lower, caused by the destructive effect of fungi, as compared to untreated samples. The most optimal technology for structures involving close contact with water or soil is determined.

Resistance of Scots pine (Pinus sylvestris L.) after treatment with caffeine and thermal modification against Aspergillus niger

Various natural products are potentially suitable for wood protection, particularly against fungi attack. Caffeine is a well-known compound of natural origin, commercially and economically available, which could facilitate its future use for wood protection. This work investigated the antifungal resistance of the sapwood of Scots pine (Pinus sylvestris L.) treated with a water solution of caffeine and then thermally modified. The samples after impregnation were thermally modified at different temperatures selected on the basis of thermogravimetric analysis (TGA) of caffeine. The paper presents preliminary results of resistance of treated pinewood towards Aspergillus niger van Tieghem (ATCC 6275). The treated samples were subjected to both a leaching procedure and to the artificial aging procedure imitating natural weather conditions. Thermal modification of wood treated with caffeine improved the fungistatic properties of samples after artificial aging. It occurred through partial elimination of caffeine leaching from the wood structure.

Thermal modification of wood by the method of thermo-mechanical dehydration with pressure drop

Thermal Modification of Wood by the Method of Thermo-Mechanical Dehydration with Pressure Drop. The results of experimental research of thermal wood processing by the method of high temperature drying with pressure drop are presented. Drying was carried out cyclically by heating the material under pressure to the temperature 100-140 oC followed by pressure drop. After that the temperature was raised up 160-210 oC and the samples were processed briefly in those conditions. This treatment is shown to be effective for largesized wood.