Effect Of Thermal Modification Research Articles

Effect of Thermal Modification on the Density, Durability, Dimensional Stability, and Mechanical Properties of Pinus caribaea

Pinus caribaea (Pine) is an underutilized timber species in Sri Lanka due to its low density, durability, dimensional stability, and undesirable colour. This research aims to examine the enhancements in the physical and mechanical properties of Pinewood through thermal modification (TM) and compare the properties of the TM wood with kiln-dried and untreated wood and with the properties of high-graded timbers of Tectona grandis (teak) and Koompassia malaccensi (kempas). TM is a process that involves heating wood to high temperatures (2000 C) in the absence of oxygen, which removes the moisture and creates changes in the wood at the cellular level. The effectiveness of the thermal modification on density, modulus of rupture (MOR), modulus of elasticity (MOE), moisture content, dimensional stability, durability, and colour was studied. Specific gravity of thermally modified wood was 6% higher than untreated wood, but lower than teak and kempas. MOR and MOE values were 35.75% and 46.46% respectively higher than untreated wood. Equilibrium moisture content was reduced after TM and volumetric shrinkage of TM was reduced to 2.16% and swelling under liquid water contact was reduced to 2.37%. Thermally modified timber was classified as not durable (DC 5) based on field test (EN 252, 2014) results. However, TM timber was slightly durable (DC 4) according to laboratory tests and showed better fungal resistance. The wood underwent a darkening effect as a result of thermal modification, resembling the colour of teak. The cost of TM was 13.1% higher than kiln drying. Improved dimensional stability, enhanced bending strength, and attractive appearance demonstrate the potential of thermal modification as a promising alternative for transforming P. caribaea wood into high-value raw material. TM timber finds suitable applications in indoor furniture and joinery projects. However, due to its lack of termite resistance, preservative treatment is recommended for outdoor ground contact usage.
 
 Keywords: Thermally modified timber, Mechanical properties, Dimensional stability, Durability,
 Pinus caribaea

Effect of thermal modification on axial compression properties and hardness of laminated bamboo

Vacuum thermal modification is an environmentally friendly method to improve the durability and reduce insect infestation of bamboo, which has the advantages of preventing deformation, preventing oxidation of the bamboo surface, and uniformity of thermal conductivity compared to previous studies that used mediums such as nitrogen, air, or oil for heating. This study thermally modified laminated bamboo materials for 1 to 5 h under vacuum conditions ranging from 170 to 230 °C and evaluated their microstructure, surface hardness, water absorption, and axial compression mechanical properties. The results showed that compared with untreated laminated bamboo timber, the colour gradually deepened as the temperature and time of heat treatment increased, while the equilibrium moisture content of heat-treated laminated bamboo timber was reduced by about 4–27% and the density by about 11–18%. This phenomenon indicates that the cell walls of laminated bamboo become denser with increasing temperature, which leads to a significant decrease in the hygroscopicity of laminated bamboo. The dimensional stability of the material was improved. Regarding the macroscopic axial compression test, the results showed that the thermal modification treatment significantly increased the axial compression strength of laminated bamboo, and this improvement in mechanical properties was inversely related to the heat treatment temperature. In addition, through the nanoindentation test, we found that the laminated bamboo's surface hardness and modulus of elasticity showed an inflexion point when the treatment temperature reached 210 °C, indicating that the material properties changed significantly in this temperature range. Investigating the response mechanism between the temperature and time of vacuum thermal heat treatment and the mechanical properties of bamboo will contribute to the development or optimization of the thermal modification process, leading to materials with excellent properties and broadening the application areas.

Bio-Durability and Engineering Characteristics of Heat-Treated Poplar Wood

The aim of this study was to evaluate the effect of brown rot fungus Coniophora puteana activity on physical and mechanical properties as well as biological resistance of heat-treated poplar wood. Two poplar wood species (Populus deltoids and Populus nigra) were heat-treated by thermo-wood (Thermo-D) method. Control and heat-treated specimens were exposed to brown rot fungus C. puteana for 16 weeks. Physical and mechanical characteristics of specimens including density, compression strength parallel to the grain and impact strength were evaluated before and after exposure to fungus. Mass loss of specimens caused by fungal activity (MLF) was also calculated. In addition, the effect of thermal modification on laccase production by C. puteana was assayed. The highest mass loss due to fungal deterioration was observed in control specimens, coinciding with the highest substrate-enzyme interactions and constant decrease in detectable laccase levels. According to the results, thermal modification can be used effectively to protect poplar wood against brown rot fungus attack.

Chemical Composition and Color of Short-Rotation Teak Wood Thermally Modified in Closed and Open Systems

Although the effect of thermal modification (TM) on teak wood color is well documented, few studies have been carried out on closed-system processes, and it remains unclear what the effect is of different processes on the same material. This work aimed to verify the effect of closed- and open-system processes of TM on the color of short-rotation teak wood. Thermally modified wood (TMW) was evaluated in a closed system at 160 °C (CS160) and in an open system at 185 °C and 210 °C (OS185 and OS210). We measured the moisture content (initial and final) of the wood and the corrected mass loss (CML). The chemical analyses encompassed the contents of alpha-cellulose, hemicelluloses, lignin, and extractives (total, in acetone and dichloromethane). Wood color was measured before and after TM according to the CIEL*a*b* color space. It was possible to achieve the same color using different processes of thermal modification (CS160 and OS210). TM reduced wood lightness (L*), red–green chromaticity coordinate (a*), and yellow–blue chromaticity coordinate (b*). L* and a* had the biggest and smallest variations, respectively. TMW color was significantly changed, even at the mildest condition tested (OS185, 0.33% CML).

Effects of thermal modification on the flexure properties, fracture energy, and hardness of western hemlock

Effects of thermal modification on the flexure properties, fracture energy, and hardness of western hemlock

Characterization of the odorous constituents and chemical structure of thermally modified rubberwood

ABSTRACT Rubberwood is a sustainable timber from tropical plantations, and is widely used in human’s daily routine like furniture and interior decoration. The thermal modification technology can effectively make rubberwood preservative, and improve its dimensional stability, while the odorants emitted from thermally modified rubberwood limited its application and recently has attracted people’s attention. In this study, the effects of thermal modification on odor and key odorous constituents of rubberwood were studied. The volatile odorants were identified by sensory evaluation via gas chromatography–mass spectrometry/olfactometry. To gain profound insights into the contribution of single odorants to the overall odor of heat-treated rubberwood, the odor-active constituents were calculated using relative odor activity values (ROAV) on the basis of odor thresholds. It’s revealed that with increasing temperature, the ROAV of 5-methyl-2-furancarboxaldehyde increased from 0.01 to 2.6 and then decreased to 0.7, and 5-methyl-2-furancarboxaldehyde became the important odorant of thermally modified rubberwood ranged from 155°C to 185°C. The odor of 5-methyl-2-furancarboxaldehyde smelled like chocolate and burnt. The identification of odorants from thermally modified rubberwood could provide theoretical guidelines for further controlling the production technology to produce the low odor thermally modified rubberwood.

Effect of thermal modification on the stress relaxation behavior and microstructure of the cell wall

The stress relaxation behavior and cell wall microstructure of sugi were evaluated after thermal modification. Stress relaxation is observed and has a broad relaxation spectrum, implying various relaxation mechanisms. The relaxation was analyzed using a stretched exponential function, namely, the Kohlrausch–Williams–Watts (KWW) function, which contains two parameters. Moreover, the structure of the amorphous phase in the cell wall was examined by small-angle X-ray scattering (SAXS) analysis using the mass fractal dimension. The variation in the relaxation spectrum reduced, and the specific relaxation time increased by thermal modification at 220 °C. The mass fractal dimension in SAXS increased owing to modification, indicating that the structure of the cell wall includes some defects between cellulose microfibrils. The mass fractal dimension was related to the relaxation parameter of the KWW function. Considering the change in crystallinity, the amorphous phase in the cell wall decomposed and condensed by thermal decomposition, which caused a longer relaxation time. Thus, the KWW function may be used to evaluate the stress relaxation behavior of wood, and the mass fractal dimension in SAXS can indicate the amorphous structure in the cell wall.

Analysis of chemical properties of thermally treated Pinus roxburghii Sargent wood

Effects of thermal modification were determined relative to chemical parameters of Pinus roxburghii. Thermal modification of wood was carried out at 80, 120, 160, and 200 °C for 2, 4, and 6 h. The chemical properties were different for different temperatures and different heating time. All parameters were similar except for cold water soluble extractives. Among the chemical properties studied, the maximum mean value of cold water extractives (8.20%), hot water soluble extractives (12.7%), holocellulose content (71.8%), and ash content (1.46%) were recorded at 120 °C, whereas the maximum mean values of alcohol benzene soluble extractives (13.9%) and lignin content (33.7%) were observed at 200 °C. The minimum mean value of cold water soluble extractives (5.82%), hot water soluble extractives (9.27%), holocellulose content (65.8%), and ash content (1.03%) were found to be at 200 °C, while the highest value of alcohol benzene soluble extractives 12.2% (control) and lignin content (28.0%) were found to be at 80 °C.

Cross-laminated strand veneer lumber mass timber panels from thermally modified strands

Thin-strand composite panels and subsequent mass timber beams were produced using thermally modified wood strands in a pressurized system. The effects of thermal modification (TM) temperature and dwell time on the mechanical, moisture, and decay performance of panels were studied. TM reduced moisture sorption and increased decay resistance. The thin-strand composites were evaluated in flexure and benchmarked against commercially available structural products. Moreover, the mass timber beams’ out-of-plane bending was accurately predicted with traditionally used laminated beam theory. The study shows that TM, under controlled conditions, enables the production of high-performing wood-strand panels with improved dimensional stability and decay resistance.

Dynamic moisture resistance of chemical and thermal modified plywood

ABSTRACT Time-dependent response of treated and untreated plywood to various modes of water exposure was studied. Treatments included 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU) and phenol-formaldehyde (PF). The effect of thermal modification was also investigated. Water exposure regimes included: one-sided water spray, one-sided water soak, and high humidity – all for a duration of 192 h. Direct measurements of dimensional change were recorded, and digital image correlation (DIC) was used to continuously monitor two-dimensional swelling. Over 90% of thickness swell occurred during the first 24 h of liquid water exposure. Swelling was still progressing under 90% relative humidity exposure after 192 h. DMDHEU and PF were statistically equivalent and improved thickness swell by 64% and 60%, for water spray and water soak, respectively. Chemical treatment improved thickness swell by approximately 41% under high humidity. Thermal modification improved thickness swell by 36%, 28%, and 28% for water spray, water soak, and high humidity exposure after 192 h, respectively. DIC measurements during the first 3 h of exposure revealed the fastest rate of thickness swell occurred with one-sided water spray and the slowest rate during one-sided water soak. Overall, PF-treated plywood exhibited the best initial water resistance. After 24 h DMDHEU and PF were equally effective treatments.

Effects of thermal modification on the separation of clay-containing waste slurries

This paper summarizes the results of studies on the use of thermal modification in the separation of slurries of clay-containing ores. It is currently vital to minimize the environmental footprint of tailings storage facilities of mining and processing enterprises and municipal waste landfills handling liquid wastes and to ensure their respective sanitary and epidemiological safety. The main liquid waste management problems are due to high process water consumption, high energy costs for dewatering and drying of concentrates, caking and congelation of concentrates, complexity and environmental hazards of storing wet waste (tailings), unsuitable for use as mine backfill material, as well as the use of inefficient TSF liner systems with potential soil and effluent contamination risks. This article considers the properties of clay-containing slurries, coal tailings, and halitic potash flotation tailings. It is shown that heat treatment improves waste slurry separation. For dry kaolin separation tailings, heat treatment at 200–400 °C significantly reduces tailings plasticity and fluidity, weakening soil interparticle cohesion and facilitating larger internal friction angles of the particles. The resulting data is used to analyze the potential applications of clay-containing ore processing wastes as a replacement for cement and lime in soil stabilization, land improvement, and mine reclamation, or as components in liner systems of municipal solid waste landfills.This study was carried out under the grant issued by the Russian Science Foundation (project No. 19-79-10114).

Tree species-based differences vs. decay performance and mechanical properties following chemical and thermal treatments

Many thermal and chemical treatments are known to inhibit wood decay despite the wood grade processed, but their impact, e.g., chemicals’ leaching and decay resistance, may not be similar. The aim of this study was to test whether some model treatments retain their performance in different wood species. Additionally, the effects of thermal modification and linseed oil-based varnish treatments as means to mitigate water-soluble chemicals leaching were assessed. The mass loss caused by Trametes versicolor was measured after a 12-week exposure to analyze whether the different treatment approaches prevented the fungal decay after a standard leaching test. The mechanical properties before and after exposure were tested independently to determine whether the mechanical properties of different wood species were affected by the tested treatments and wood decay. The responses of the tested wood species were found to vary by treatments, but thermal and chemical fixation methods for water-soluble tannins were beneficial in all cases considering the mass loss and the degradation of modulus of rupture and modulus of elasticity of treated wood. Varnish was overall the most effective treatment against decay, but the results emphasize the need for testing potential preservation methods and chemicals on several species.

Effects of flexural configuration and thermal modification on the physical and flexural properties of makino bamboo (Phyllostachys makinoi)

ABSTRACT The effects of thermal modification and flexural configuration on the physical and flexural properties of makino bamboo (Phyllostachys makinoi) with various density ranges were investigated. The density and equilibrium moisture content (EMC) of bamboo significantly decreased with increasing treatment temperature from 140°C to 220°C. Simultaneously, the modulus of rupture (MOR) and ductility factor (DF) of thermally modified bamboo showed a declining trend. In the flexural test, loading on the outer side in tension (OT) and loading on the outer side in compression (OC) of the bamboo specimens were applied using different flexural configurations. The MOR of the nontreated OC specimen (MOROC) was higher than that of the nontreated OT specimen (MOROT), while the MOROC of the 220°C-treated specimen was lower than the MOROT. Additionally, the nontreated OT specimen showed a higher DF than the nontreated OC specimen. Despite the density range and flexural configuration, the DF of the thermally modified specimen decreased when the treatment temperature increased above 140°C. However, the modulus of elasticity exhibited no significant differences among all the specimens under different treatment temperatures and flexural configurations.

Effect of thermal modification on wood properties of 38-year-old Cariniana legalis cultivated at different spacing

Planting spacing influences wood production. However, for tropical species we have scarce information about the effect of spacing on production and wood quality. In general, wood from native species produced in reforestation does not have the same quality compared to that from natural forests. Then, wood thermal modification can help improve the potential for using wood. In this context, our goal was to evaluate the influence of thermal modification on properties of 38-year-old Cariniana legalis wood cultivated at different spacing (3 x 1.5m, 3 x 2m and 3 x 2.5m) at the Luiz Antônio Experimental Station, Luiz Antônio City, São Paulo. We felled 15 trees, five of each spacing, and from each tree, a log, 1 meter in length, a central plank was cut, and from these planks, we cut specimens for anatomical and wood properties investigations according to standard techniques. In the specimens, a thermal modification at a temperature of 200ºC was carried out for one hour and after the specimens were compared with the control specimens. According to the results presented, we found that spacing did not influence vessel diameter, apparent density and volumetric shrinkage significantly. Thermal modification reduced apparent density and volumetric shrinkage. The reduction in vessel diameter can be estimated as a function of the wood thermal modification.

Effect of thermal modification on the surface quality of a coating applied to wood via the electrostatic spray deposition technique

The surface properties of thermally modified ash wood with a powder coating were investigated, and the results were compared to the unmodified wood. The wood specimens were sanded with 80 grit sandpaper and then pre-heated at 80 °C for 5 min in an infrared oven. The surface of the unmodified and the modified wood specimens were coated with an epoxy/polyester (1 to 1 ratio) hybrid coating using an electrostatic corona spray gun at the pilot plant established in the laboratory. The coatings on the wood specimens were cured at different curing conditions in an infrared oven, i.e., 120 °C/15 min, 140 °C/10 min, and 160 °C/10 min. The results showed that the thermal modification (TM) of the wood caused a slight decrease in the mechanical performance of the surface system (wood substrate and coating film). For example, the scratch and abrasion resistance of the unmodified specimens at the curing temperature of 120 °C were 3.33 N and 135 revolutions but were 3.12 N and 120 revolutions after the TM. However, the average surface roughness (1.26 mu) and contact angle (60.8°) of the distilled water on the cured coatings on the modified wood were lower than those on the unmodified wood (1.86 mu and 80.8°, respectively).

Effect of Thermal Modification on the Nano-Mechanical Properties of the Wood Cell Wall and Waterborne Polyacrylic Coating

Masson pine (Pinus massoniana Lamb.) samples were heat-treated at different treatment temperatures (150, 170, and 190 °C), and the nano-mechanical properties of the wood cell wall, which was coated with a waterborne polyacrylic (WPA) lacquer product, were compared. The elastic modulus (Er) and hardness (H) of wood cell wall and the coating were measured and characterized by nanoindentation, and the influencing factors of mechanical properties during thermal modification were investigated by chemical composition analysis, contact angle analysis, and colorimetric analysis. The results showed that with the increase in the heat treatment temperature, the contact angle of the water on the wood’s surface and the colorimetric difference increased, while the content of the cellulose and hemicelluloses decreased. After thermal modification of 190 °C, the Er and H of the wood cell wall increased by 13.9% and 17.6%, respectively, and the Er and H of the WPA coating applied to the wood decreased by 12.1% and 22.2%. The Er and H of the interface between the coating and wood were lower than those near the coating’s surface. The Er and H of the cell wall at the interface between the coating and wood were lower than those far away from the coating. This study was of great significance for understanding the binding mechanism between coating and wood cell walls and improving the finishing technology of the wood materials after thermal modification.

Crack formation, strain distribution and fracture surfaces around knots in thermally modified timber loaded in static bending

The effect of thermal modification (TM) on the chemistry, anatomy and mechanical properties of wood is often investigated using small clear samples. Little is known on the effect of growth-related and processing defects, such as knots and checks, on the bending strength and stiffness of thermally modified timber (TMT). Nine boards of Norway spruce with different combinations of knot types were used to study the combined effects of checks and knots on the bending behaviour of TMT. Digital image correlation (DIC) measurements on board surfaces at sites of knots subjected to bending allowed to study strain distribution and localise cracks prior to and after TM, and to monitor development of fracture (around knots) in TMT to failure. DIC confirmed that checking in knots was increased after TM compared to kiln-dried timber, specifically for intergrown knots and intergrown parts of encased knots. Effects appear local and do not affect board bending stiffness at these sites. Bending failure in TMT initiated mainly at knot interfaces or besides knots and fractures often propagated from checks. Scanning electron microscopy analyses of fracture surfaces confirmed this, and fractures were typically initiated around knots and at knot interfaces due to crack propagation along the grain in the longitudinal–radial plane (TL fracture) under mixed mode I and II loading, such that boards failed in simple tension like unmodified timber. Images of fracture surfaces at the ultrastructural level revealed details of the brittle behaviour of TM wood. This was especially apparent from the smooth appearance of transwall failure under mode I loading across the grain.

Effect of the thermal modification and nano-ZnO impregnation on the deterioration of Caribbean pine wood

This study aimed to investigate the effect of thermal modification and nano-zinc oxide (nano-ZnO) particle impregnation on the deterioration of Caribbean pine wood under field conditions. Samples were thermally-modified at various temperature levels (control, 180 °C, 200°C, and 220 °C). Nano-ZnO impregnation was done with an aqueous solution at 1,5 % in an autoclave under two-steps of pressure and vacuum. Unmodified and thermally-modified, non-impregnated and nano-ZnO impregnated samples were exposed to deterioration for five months in field tests. A deterioration index was used to evaluate the health condition of the samples. The mass loss and occurrence of termite tunnels in percentage were also determined. The nano-ZnO impregnation improved the resistance of unmodified wood to field-deterioration. The thermal modification at 180oC, and 200oC increased the wood deterioration and nano-ZnO impregnation did not improve their resistance. Unmodified and 220 oC modified samples had a lower mass loss by xylophages than other thermal treatments regardless of the nanoparticle impregnation. The nano-ZnO impregnation decreases the occurrence of termite tunnels in unmodified, 200 oC and 220 oC-modified samples

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.

Effects of thermal modification on selected physical properties of sapwood and heartwood of black poplar (Populus nigra L.)

Black poplar (Populus nigra L.) was subjected to thermal modification in superheated steam. The modification was performed at 160 °C, 190 °C, and 220 °C for 2 h. The equilibrium moisture content of the black poplar wood was examined when it was exposed to 76% ± 2% relative humidity at a temperature of 20 °C ± 2 °C. The thermal modification of the poplar wood changed its moisture-exchange-related physical properties to a large extent. The effects of temperature on individual properties (density, mass loss, hygroscopicity, swelling, and water absorption) were diverse, and the intensity of these effects increased with increasing temperature of the thermal treatment process. In most cases, no significant differences were observed between the changes in properties of the sapwood and the heartwood.