Thermally Modified Research Articles

An Integrated Testing Strategy (ITS) to assess the environmental compatibility of wood protection techniques

To quantify the possible impact of different wood protection techniques on the aquatic environment, we applied a tiered Integrated Testing Strategy (ITS) on leachates obtained from untreated (UTW) Norway spruce (Picea abies), specimens treated with a copper-ethanolamine-based preservative solution, complying with the Use Class 3 (UC3), and specimens thermally modified (TM). Different maturation times in water were tested to verify whether toxicant leaching is time-dependent. Tier I tests, addressing acute effects on Aliivibrio fischeri, Raphidocelis subcapitata, and Daphnia magna, evidenced that TM toxicity was comparable or even lower than in UTW. Conversely, UC3 significantly affected all species compared to UTW, also after 30 days of maturation in water, and was not considered an environmentally acceptable wood preservation solution. Tier II (effects on early-life stages of Lymnea auricularia) and III (chronic effects on D. magna and L. auricularia) performed on UTW and TM confirmed the latter as an environmentally acceptable treatment, with increasing maturation times resulting in decreased adverse effects. The ITS allowed for rapid and reliable identification of potentially harmful effects due to preservation treatments, addressed the choice for a less impacting solution, and can be effective for manufacturers in identifying more environmentally friendly solutions while developing their products.

The Effects of Microcrystalline Cellulose Addition on the Properties of Wood-PLA Filaments for 3D Printing.

This paper describes the use of microcrystalline cellulose (MCC) as an additive in wood-polylactic acid (PLA) filaments suitable for 3D printing. Filaments prepared with PLA, thermally modified (TM) wood, and three different MCC loadings (1, 3, and 5 wt%) by two-step melt blending in the extruder were characterized with respect to their rheological, thermal, and mechanical response. The analyses demonstrate that a low MCC content (1%) improves the mobility of the polymer chains and contributes to a higher elasticity of the matrix chain, a higher crystallinity, a lower glass transition temperature (by 1.66 °C), and a lower melting temperature (by 1.31 °C) and leads to a higher tensile strength (1.2%) and a higher modulus of elasticity (12.1%). Higher MCC loading hinders the mobility of the polymer matrix and leads to a rearrangement of the crystal lattice structure, resulting in a decrease in crystallinity. Scanning electron micrographs show that the cellulose is well distributed and dispersed in the PLA matrix, with some agglomeration occurring at higher MCC levels. The main objective of this study was to develop and evaluate a filament containing an optimal amount of MCC to improve compatibility between wood and PLA, optimize melt processability, and improve mechanical properties. It can be concluded that a 1% addition of MCC favorably changes the properties of the wood-PLA filaments, while a higher MCC content does not have this effect.

Effect of thermal modification of wood on the rheology, mechanical properties and dimensional stability of wood composite filaments and 3D-printed parts

ABSTRACT This study investigates the effects of thermal modification (TM) on wood-filled polylactic acid composite filaments for 3D printing. Nine composite formulations with different wood content were analysed. The wood particles came from unmodified and thermally modified beech wood (180 °C or 200 °C). The results showed that the incorporation of thermally modified (TMd) wood changed the filament properties, resulting in lower density and reduced surface roughness. The 3D-printed parts with TMd wood particles had a higher water contact angle, higher storage modulus, lower glass transition temperature, higher modulus of elasticity and higher indentation hardness. However, the tensile strength of the 3D-printed parts decreases, even though the results of parts with TMd wood showed higher strength compared to unmodified wood at the same filler content. Surprisingly, TMd wood had no effect on water absorption under humid conditions. Scanning electron micrographs showed improved interfacial adhesion between TMd wood particles and PLA, with smaller voids in the filament compared to filaments with unmodified wood particles. The study suggests that further research into use of TMd wood particles in composite holds promise for environmentally friendly 3D printing materials with favourable thermal and mechanical properties, impacting the expanding market for sustainable solutions in 3D printing.

An X-ray CT assessment of fungal growth in spruce, poplar and thermally-modified poplar

ABSTRACT Poplar has been gaining attention as a potential material for use in engineered wood products (EWPs). However, poplar wood is not durable against fungal degradation, which is an important factor that needs to be investigated. Previous studies on degradation have mostly focused on evaluating mass loss (ML), while lacking information on the progress of degradation. In this study a recently developed non-destructive X-ray computed tomography (CT) technique was used to investigate the degradation progress within poplar, thermally modified (TM) poplar, and spruce during a 10-weeks fungal degradation experiment. The results showed that degradation led to a significant decrease in density, particularly after 15 days. Based on the X-ray CT scans, it was observed that spruce showed a higher mass loss at the end grain while poplar showed a homogeneous pattern throughout the entire block. Thermally modified poplar specimens were less degraded even at moist conditions. The density of the wood was found to affect the fungal susceptibility of both poplar and TM poplar: a higher density resulted in a lower mass loss of poplar. The use of X-ray CT scanning allowed for a detailed micro-level insight into fungal decay, which can potentially help in protecting poplar in future industrial use for constructions.

Effect of thermo-vacuum modification on selected chemical, physical, and mechanical properties of Siberian larch (Larix sibirica L.) wood

ABSTRACT The primary aim of this research was to investigate and evaluate the effects of thermo-vacuum modification through forced convection on selected chemical, physical, and mechanical characteristics of Siberian larch (Larix sibirica L.) wood. Larch wood boards were thermally-modified, using press-vacuum plant technology, for three hours at a temperature of 200 °C and a pressure of 350 mBar. In order to characterise the thermally-modified (TH) and unmodified (CTRL) wood samples, the extractives, lignin and holocellulose content, volumetric swellings, compression strength, and modulus of elasticity (MOE) were determined. Gas chromatographic-mass spectrometric (GC-MS) analysis revealed chemical compound changes as a result of the thermal modification process where some extractives became undetectable after treatment while some new extractives were detected. Thermally-modified larch wood exhibited lower volumetric swelling compared to the untreated samples. Markedly, thermally-modified larch wood had lower tendency to absorb moisture. In addition, thermally-treated wood had slightly higher compression strength parallel to the grain, which was 0.29% higher than that of unmodified samples. Meanwhile, a 7.6% reduction in MOE was recorded in the thermally-treated wood.

Characteristics of thermally modified hardwood dust in determining workers’ occupational exposure

Thermal modification of wood changes its mechanical properties, generally reducing its strength, such that it is more easily chipped during processing than untreated hardwood. This study presents specific parameters used in the determination of mass concentration of thermally modified (TM) hardwood by gravimetric and photometric methods. An optical device, the Split 2, was used in the active mode, of which the holder of the inhalable dust IOM (Institute of Occupational Medicine) filter was the input part. Side-by-side determination of the respirable and inhalable mass concentration was made using the Higgins-Dewell respirable dust cyclone and an inhalable dust IOM sampler. Side-by-side determination of inhalable and total dust mass concentration was made using an IOM and open-faced (OF) filter holder to establish an IOM / OF sampling ratio. A correction factor of 1.16 was calculated for applying the photometric method as the ratio of mass concentration determined by gravimetric and photometric methods. Minimal concentrations of respirable and inhalable wood dust (geometric mean: cr = 0.058 mg/m3; cinh = 0.882 mg/m3) and a 12.76% share of respirable dust in the inhalable concentration cr / cinh, had a significant influence on the efficiency of the photometric method. The mass concentration obtained by IOM and OF samplers did not significantly differ (p = 0.36).

Influence of Thermal Modification in Nitrogen Atmosphere on Physical and Technological Properties of European Wood Species with Different Structural Features

The wood of five European species: black poplar (Populus nigra L.), European beech (Fagus sylvatica L.), European ash (Fraxinus excelsior L.), European oak (Quercus robur L.), and Scots pine (Pinus sylvestris L.) was subjected to thermal modification in nitrogen atmosphere at 190 °C during 6 h. Native and modified wood was varnished and oiled in industrial conditions. Thermally modified (TM) wood was characterized by a greater absorption of varnish and oil when applying the first layer to the surface, which finally resulted in higher application values compared to native wood. In particular, after varnishing, there was a significant increase in gloss and radical change of colour. Regardless of the wood species, finishing process (varnishing, oiling), the ΔE values were close to or higher than 6, which proves high colour changes. Modified poplar, ash, and oak after varnishing had a different colour (ΔE higher than 12). The surface colour changes as a result of UV photoaging was individual, depending on the wood species and the method of finishing. In the case of the thickness of varnish coatings, the wood structure was important, i.e., on ring-porous hardwood and softwood they were thicker. In the case of wood species with a lower density, i.e., black poplar and pine, the thermal modification in nitrogen atmosphere process did not reduce the resistance of the varnish coat, and in the case of species with a higher density (oak, ash, beech) it decreased by one level. Thermal modification reduced the Brinell hardness of wood with wide rays (oak and beech) by 11%. The applied process of surface finishing by double varnishing or oiling did not significantly change the hardness of tested wood.

SEM Analysis of Glued Joints of Thermally Modified Wood Bonded with PUR and PVAc Glues.

This study deals with the scanning electron microscopy (SEM) analyses of the phase interfaces in the glued joints between Norway spruce wood elements thermally modified at 160, 180, 200, and 220 °C/4 h and polyurethane (PUR) and polyvinyl acetate (PVAc) glues with the aim of evaluating various anatomical influences of wood on the quality of joints. Due to cracked regions created in the surface of spruce wood at severe thermal modifications, the penetration depth of glues doubled from 140 to 241 μm for PUR glue, and from 100 to 200 μm for PVAc glue. The thickness of glue lines in joints was apparently higher for PVAc glue, mainly in earlywood regions; however, in joints from thermally modified (TM) woods it increased more apparently for PUR glue from 16.6 to 44.4 μm, probably in connection with formation of micro-bubbles in its structure. The SEM analyses corresponded well with the previous knowledge about lower shear strength of glued joints formed from the more intensively TM spruce elements and mentioned types of glues.

ОПРЕДЕЛЕНИЕ ПЛОТНОСТИ КЛЕТОЧНЫХ СТЕНОК ДРЕВЕСИНЫ И ДРУГИХ ПОРИСТЫХ МАТЕРИАЛОВ МЕТОДОМ ГАЗОВОЙ ПИКНОМЕТРИИ В СРЕДЕ АТМОСФЕРНОГО ВОЗДУХА

The article presents analytical and experimental studies to determine the density of the wood cell walls and other porous materials. From the literature, four main methods have been identified for determining the density of the cell walls of wood and porous materials. Of these, there are three direct methods: suspensions, mercury porosimetry and pycnometry, and one indirect - optical (planimetric). Helium gas pycnometry method is the most common of these ones. Based on the results of the critical analysis, a method for measuring the volume and determining the density of the cell walls of wood and porous materials in the atmosphere of atmospheric air was proposed. The method was theoretically substantiated and does not contradict the basic postulates and laws of thermodynamics. The functional suitability of the proposed method, as well as a high degree of reliability of the results obtained, has been determined experimentally. Volumes and densities of the cell walls of various wood species and other porous materials were measured under various modes of the system functioning using the developed experimental installation. The lowest density values were obtained at an overpressure of +70 kPa, the highest were seen at a vacuum of -90 kPa. The deviations in the results between the highest and lowest density values were, respectively: spruce – 7.02%, aspen – 4.12%, thermally modified (TM) linden – 2.95%, pine rot – 4.93%, shelf fungus – 5.12%, pine bark – 5.27%, birch charcoal – 14.6%.

Photodegradation of Unmodified and Thermally Modified Wood Due to Indoor Lighting

Considering interior applications, sunlight, both direct through open window and through window glass, and artificial lighting are the main sources of radiation possessing sufficient energy to trigger photodegradation processes in wood. LED lamps, which emit mostly visible light, are becoming the dominant artificial light source in various interiors. In the present study, photodegradation of thermally modified (TM) and unmodified (UM) ash (Fraxinus excelsior), aspen (Populus tremula), and pine (Pinus sylvestris) due to exposure to UV radiation and LED lamps was evaluated and compared by analysing wood discolouration (CIELAB colour space), changes in reflectance and FTIR spectra, and formation of water-soluble components. The results show that, apart from UV radiation, LED lamps may cause considerable photodegradation of both TM and UM wood resulting in visually perceptible colour change, alteration in chemical structure and formation of water-soluble components. Improved photo-stability was observed for TM wood exposed to UV radiation, while even more changes in FTIR spectra were detected for TM than UM wood in the experiment with LED lamps. Comparing TM and UM wood, the changes due to photodegradation were quite similar for TM wood of all species while significant differences were observed in the case of UM 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.

Extraction Methods and Their Influence on Yield When Extracting Thermo-Vacuum-Modified Chestnut Wood

Improvements in the yield and solubility of chestnut wood extractives, by using different extraction methods and molybdenum catalysts as support, have rarely been reported in literature. Many studies focus on the different parts of trees, except for the chemical characteristics of the remaining extractives achieved from thermally modified (THM) chestnut (Castanea sativa Mill) wood. This research seeks to better understand the effects of extraction techniques and catalysts on the yield and solubility of extractives. GC-MS analysis of the chloroform soluble and insoluble fractions was also used. Accelerated Solvent Extraction (ASE) 110 °C, Soxhlet, and autoclave extraction techniques were used to obtain extractives from untreated and thermally modified (THM) chestnut wood (170 °C for 3 h). Ethanol/H2O, ethanol/toluene, and water were the solvents used for each technique. A polyoxometalate compound (H3PMo12O40) and MoO3 supported on silica were used as catalysts. The THM induced a change in the wood’s surface color (ΔE = 21.5) and an increase in mass loss (5.9%), while the equilibrium moisture content (EMC) was reduced by 17.4% compared to the control wood. The yields of the extractives and their solubility were always higher in THM and mainly used ASE as the technique. GC-MS analysis of the extractives, without catalyst support, showed different results for each extraction technique and type of wood (untreated and THM). Ultimately, the amount of extractive compound dissolved in each solvent will differ, and the choice of extraction technique will depend on the intended final application of the extracted chemical product.

Thermally modified birch wood interaction with liquids

Large research work is currently being performed concerning different elaborated new wood protection methods. However, combining industrially well-approbated processes is also considered potentially quite promising and such approach is being actively studied. The objective of the present study was to investigate peculiarities of interaction between liquids and thermally modified (TM) birch wood (Betula spp.). This knowledge is essential for proper TM wood post-treatments involving its impregnation as well as for evaluation of potential wood moisture dynamics in outdoor applications. Changes caused by TM (150–170 °C) in a closed system under elevated pressure in wood wettability, permeability, liquid absorption capacity, and drying characteristics were evaluated. The results concerning absorption capacity, which is mainly related to wood anatomical features and is density-dependent, indicated reduced absorption capacity of TM wood compared with unmodified birch of similar density. Permeability, which characterises the ease with which liquid is transported through a wood porous system, was evaluated by capillary absorption tests through the samples’ tangential and radial surfaces. TM made birch wood less permeable through both surfaces as well as less anisotropic regarding transverse absorption rates. Moreover, TM also caused a decrease in drying rates for birch wood impregnated with water. Reduction in permeability influences the impregnation process of boards and no full saturation was detected for TM boards when applying an impregnation schedule providing complete saturation for unmodified boards. On the other hand, less water was absorbed by TM boards exposed to rain on outdoor weathering racks.

Resistance of thermally modified and pressurized hot water extracted Scots pine sapwood against decay by the brown-rot fungus Rhodonia placenta

The thermal degradation of wood is affected by a number of process parameters, which may also cause variations in the resistance against decay fungi. This study compares changes in the chemical composition, water-related properties and decay resistance of Scots pine sapwood that was either thermally modified (TM) in dry state at elevated temperatures (≥ 185 °C) or treated in pressurized hot water at mild temperatures (≤ 170 °C). The thermal decomposition of easily degradable hemicelluloses reduced the mass loss caused by Rhodonia placenta, and it was suggested that the cumulative mass loss is a better indicator of an actual decay inhibition. Pressurized hot water extraction (HWE) did not improve the decay resistance to the same extent as TM, which was assigned to differences in the wood-water interactions. Cross-linking reactions during TM caused a swelling restraint and an effective reduction in moisture content. This decreased the water-swollen cell wall porosity, which presumably hindered the transport of degradation agents through the cell wall and/or reduced the accessibility of wood constituents for degradation agents. This effect was absent in hot water-extracted wood and strong decay occurred even when most hemicelluloses were already removed during HWE.

Water vapour sorption properties of thermally modified and pressurised hot-water-extracted wood powder

AbstractThe objective of the study was to investigate the water vapour sorption behaviour of thermally modified (TM) wood powder, e.g. ground wood prepared from waste streams of TM solid wood, and wood powder that was extracted in pressurised hot water. Solid spruce wood was TM in steam conditions (210°C for 3 h), milled and hot-water-extracted (HWE) at elevated pressure (140°C for 1 h). The results evidence that the hot-water extraction reduced the water sorption and the accessible hydroxyl group concentration by the removal of amorphous carbohydrates. In contrast, the enhanced cross-linking of the cell wall matrix and the annealing of amorphous matrix polymers during thermal modification reduced the sorption behaviour of wood additionally, without further reducing the hydroxyl accessibility. These additional effects of thermal modification were at least partially cancelled by hot-water extraction. The results bring novel insights into the mechanisms that reduce the water vapour sorption of wood by compositional and structural changes induced by heating.

Thermally modified (TM) beech wood: compression properties, fracture toughness and cohesive law in mode II obtained from the three-point end-notched flexure (3ENF) test

Abstract The fracture properties of thermally modified beech (Fagus sylvatica) wood (TMW) at 180° and 200°C were evaluated in mode II using the three-point end-notched flexure (3ENF) scheme assisted by three-dimensional (3D) stereovision equipment for obtaining displacements and strains. The compliance-based beam method (CBBM) provided the strain energy release rates (G II) of TMW and cohesive laws for both native wood (W) and TMW. Based on the CBBM and equivalent crack length approach (ECLA), G II was obtained directly from the force-deflection data. The thermal modification (TM) process reduced the compressive strength by 4.4% and increased the compressive elastic modulus by 38.3%, whereas G II was reduced substantially by 40.8% and 67.9% at TM180°C and TM200°C, respectively. TM also increased wood brittleness that was visible on the displacement slip reduction. The resulting mean cohesive models can be used for numerical analyses. The fracture properties of TMW have to be taken into consideration for constructional wood application, when cyclic loading may lead to microcracking and material fatigue.

Effects of thermal modification on the physical, chemical and micromechanical properties of Masson pine wood (Pinus massoniana Lamb.)

Abstract In an attempt to evaluate the effects of thermal treatment on wood cell walls (CWs), Masson pine (Pinus massoniana Lamb.) wood was thermally modified (TM) at 150, 170 and 190°C for 2, 4 and 6 h, respectively. The chemical properties, cellulose crystallinity (C rI) and micromechanics of the control and thermally modified wood (TMW) were analyzed by wet chemical analysis, X-ray diffraction and nanoindentation. The relative lignin content and C rI increased after the TM partly degraded the amorphous wood polymers. The relative lignin content was higher in TMW and the equilibrium moisture content decreased. Moreover, the elastic modulus (E r) and hardness (H) of TMW were lowered along with the creep ratio decrement (C IT) of CWs. However, a severe treatment (e.g. 190°C/6 h) may negatively affect the mechanical properties of CWs caused by the partial degradation of hemicelluloses and also cellulose.

Durability of Thermally Modified Wood of Gmelina arborea and Tectona grandis Tested under Field and Accelerated Conditions

This study evaluated the durability in terms of decay and mechanical resistance of thermally modified (TM) wood of Tectona grandis and Gmelina arborea treated at 160, 180, 200 and 220 °C. The TM wood of both species treated ... | Find, read and cite all the research you need on Tech Science Press

Effect of oil impregnation on water repellency, dimensional stability and mold susceptibility of thermally modified European aspen and downy birch wood

Conventional chemical wood preservatives have been banned or restricted in some applications due to human and animal toxicity and their adverse impact on the surrounding environment. New, low-environmental-impact wood treatments that still provide effective protection systems are needed to protect wood. Thermal modification of wood could reduce hygroscopicity, improve dimensional stability and enhance resistance to mold attack. The aim of this study was to investigate if these properties enhanced in thermally modified (TM) wood through treatments with oils. In this study, TM European aspen (Populus tremula) and downy birch (Betula pubescens) wood were impregnated with three different types of oil: water-miscible commercial Elit Träskydd (Beckers oil with propiconazole and 3-iodo-2-propynyl butylcarbamate, IPBC), a pine tar formulation and 100% tung oil. The properties of oil-impregnated wood investigated were water repellency, dimensional stability and mold susceptibility. The treated wood, especially with pine tar and tung oil, showed an increase in water repellency and dimensional stability. However, Beckers oil which contains biocides like propiconazole and IPBC showed better protection against mold compared with pine tar and tung oil. To enhance the dimensional stability of the wood, pine tar and tung oil can be used, but these oil treatments did not significantly improve mold resistance rather sometimes enhanced the mold growth, whereas a significant anti-mold effect was observed on Beckers oil treated samples.

Wood plastic composites made with thermally modified birch wood residues

Thermally modified (TM) wood production has significantly increased in the last decade. The trend for TM wood residues should be similar – rapidly increasing, which has prompted this research on the possible efficient uses of these residues, such as sawdust. One of the possibilities could be the production of wood plastic composites (WPCs). In this work, three different hydrothermal modification regimes were used to modify birch boards. Modified and unmodified birch boards were milled to obtain sawdust. WPCs were made with a two-roll mill, and they consisted of 50 wt-% wood fibres + 50 wt-% polypropylene. Melt flow index (MFI), flexural properties, impact strength, microhardness water absorption and dimensional stability were tested. WPCs with TM wood showed improvement in flexural properties, MFI and other properties, however there was a decrease in impact strength. Scanning electron microscopy pictures of impact strength samples fracture surfaces were taken.