The density of wood can be increased by compressing the porous structure under suitable moisture and temperature conditions. One aim of such densification is to improve surface hardness, and ...therefore, densified wood might be particularly suitable for flooring products. After compression, however, the deformed wood material is sensitive to moisture, and in this case, recovered up to 60 % of the deformation in water-soaking. This phenomenon, termed set-recovery, was reduced by thermally modifying the wood after densification. This study presents the influence of compression ratio (CR = 40, 50, 60 %) and thermal modification time (TM = 2, 4, 6 h) on the hardness and set-recovery of densified wood. Previously, set-recovery has mainly been studied separately from other properties of densified wood, while in this work, set-recovery was also studied in relation to hardness. The results show that set-recovery was almost eliminated with TM 6 h in the case of CR 40 and 50 %. Hardness significantly increased due to densification and even doubled compared to non-densified samples with a CR of 50 %. Set-recovery reduced the hardness of densified (non-TM) wood back to the original level. TM maintained the hardness of densified wood at an increased level after set-recovery. However, some reduction in hardness was recorded even if set-recovery was almost eliminated.
Wood modifications are becoming popular as a way to enhance the performance of wood, either to make it more durable, improve the performance of wood, or give it new functionality as a multifunctional ...or smart material. While wood modifications have been examined since the early 1900s, the topic has become a dominant area of study in wood science over the past decade. This review summarizes recent advances and provides future perspective on a selection of wood modifications, i.e., the methods that are currently commercialized (acetylation, furfurylation, and thermal modification), a rediscovered ancient practice (charring), a family of polymerization modifications that have so far made it to the pilot scale, and examples of novel wood-based functional materials explored at laboratory scale.
Black poplar (
L.) was thermally modified in nitrogen atmosphere. The effects of the modification process on poplar wood were evaluated for temperatures: 160 °C, 190 °C, and 220 °C applied for 2 h; ...and 160 °C and 190 °C for 6 h. The percentual impact of temperature and time of modification on the properties of modified wood was analysed. The study permitted the identification correlations between the chemical composition and selected physical properties of thermally modified poplar wood. The dimensional stability of poplar wood was improved after thermal modification in nitrogen. The higher the temperature of modification, the lower the equilibrium moisture content (EMC) of black poplar. At the temperature of 220 °C, EMC was two times lower than the EMC of non-modified black poplar. It is also possible to reduce the dimensional changes of wood two-fold (at the modification temperature of 220 °C), both in radial and tangential directions, independently of the acclimatization conditions (from 34% to 98% relative humidity, RH). Similar correlations have been found for wood that has been soaked in water. Higher modification temperatures and longer processing times contributed to a lower swelling anisotropy (SA).
Wood is a truly sustainable and aesthetically pleasant material used in indoor and outdoor applications. Every material, including wood, is expected to have long-term durability and to retain its ...original appearance over time. One of the major disadvantages of wood is the deterioration of its surface when exposed outdoors, known as weathering. Although weathering is primarily a surface phenomenon, it is an important issue for wood products as it affects their appearance, service life, and wood-coating performance. To encourage the use of wood as a material for joinery and other building components, the results of research into increasing the weathering resistance of wood are extremely significant. The development of weathering protection methods is of great importance to reduce the maintenance requirements for wood exposed outdoors and can have a major environmental impact. There are various methods of protecting wood surfaces against weathering. This paper provides a literature survey on the recent research results in protecting wood from weathering. The topics covered include surface treatments of wood with photostabilizers; protection with coatings; the deposition of thin film onto wood surfaces; treatments of wood with inorganic metal compounds and bio-based water repellents; the chemical modification of wood; the modification of wood and wood surfaces with thermosetting resins, furfuryl alcohol, and DMDHEU; and the thermal modification of wood.
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.
Various thermal modification (TM) treatments using different media have been commercialized, including the commonly practiced TM via steam and hot oil using vegetable or mineral oils. To expand the ...range of oil treatment mediums, this study explored the use of spent cooking oil (used oil from food frying in restaurants), which was centrally collected by a certified hauler and treater of this waste liquid. The effects on the dimensional stability and mechanical strength of giant bamboo Dendrocalamus asper (Schult.) Backer poles subjected to 175°C and 200°C for 30 min and 60 min in steam and oil, respectively were determined. The data were analyzed using a factorial experiment in a completely randomized design with TM treatments, temperature, duration, and presence of nodes as factors.
Results revealed significantly improved dimensional stability in modified bamboo as indicated by reduced moisture content, dimensional shrinkage/swelling, and water loss/absorption at higher temperatures. While treatment duration moderately affected dimensional stability, oil-treated samples exhibited greater enhancement.
In terms of mechanical strength, bamboo treated at 175°C exhibited enhanced flexural (modulus of rupture or MOR, and modulus of elasticity or MOE) and compressive strength (CS). However, treatments at 200°C led to marked reductions in these properties. Node presence generally weakened bamboo, except for CS. Oil-treated samples demonstrated superior mechanical strength, although there was a slight reduction in MOR with extended exposure.
In conclusion, steam and oil-based TM improve the dimensional stability and mechanical strength of giant bamboo at 175°C. For optimal properties, a 30-min treatment is recommended. This research underscores the viability of spent cooking oil in enhancing bamboo's physico-mechanical attributes, contributing to sustainable applications.
•Thermal modification enhances bamboo stability, reducing moisture content and dimensional changes.•Oil treatment at 175°C improves mechanical strength, especially compressive strength.•Mechanical strength diminishes at 200°C, emphasizing the importance of optimal treatment.•Spent cooking oil proves effective in enhancing giant bamboo's physico-mechanical properties.
The effects of the TanWood thermal modification process on the resistive properties of Tectona grandis juvenile wood were verified, and the best setting for the use of a resistive moisture meter was ...determined for both untreated and thermally modified wood (TMW). Sixteen treatments were assessed for both untreated and TMW according to three factors: moisture meter scale (four levels), electrode length (two levels), and grain direction (two levels). Moisture content was measured in four steps with equilibrium moisture contents of 6.0%, 8.6%, 12.2%, and 15.6%. For statistical analysis, the oven-drying moisture content was used as the standard. Statistical analysis included the statistics bias, mean absolute difference, mean square error, tests of linear correlation, and comparison of means. The TanWood process of thermal modification significantly changed the resistive properties of Tectona grandis juvenile wood once different results were found for untreated and TMW regarding the meter’s scale of use and the reliable ranges of moisture content measuring.
Wood of poplar (Populus sp.) and black pine (Pinus nigra) species was subjected to thermal treatment under variant conditions of temperature, 180 ºC and 200 ºC, and duration of 3 h, 5 h, 7 h, and its ...resistance to natural weathering was investigated through the determination of crucial properties, such as the colour and surface roughness, while the appearance of the boards was assessed both visually and through a microscope, prior to and after their exposure outdoors. Prior to the outdoors exposure, it was observed that, as the intensity of heat treatment increases, wood tends to darken, with the parallel decrease of L* index, referring to tangential, radial and cross-sectional surface of both species specimens. The surface roughness of both wood species was found decreased only in the boards of the mildest treatment, while as the treatment intensity increases, the roughness degree demonstrated a strong increase compared to unmodified wood. After the 100-day exposure of poplar and pine boards to external conditions, they acquired a wilder look and new checks and cracks emerged in the boards surface, while fungi infestation signs appeared, most apparent in control and boards treated at milder treatments, with modified poplar boards to demonstrate more dense defects patterns on their surfaces, compared to modified black pine boards. A similar degree of discoloration recorded on unmodified boards was observed also on the thermally modified boards, which was except for the visual assessment, confirmed by the recorded progress of L*, a* and b* colour indexes of poplar and pine surfaces and is probably attributed to leaching of the water soluble extractives. The roughness of all of the exposed boards surfaces was found higher than the respective values recorded prior to the exposure and among the treated boards only those of the milder treatments presented lower roughness values than the unmodified ones. Thermal treatment enhanced the biological durability and dimensional stability of both species, but it did not adequately protect wood from the weathering effect when it was exposed outdoors. Nevertheless, wood modified at short-term heat treatments exhibited enhanced properties compared to unmodified wood and taking into account that the milder treatments did not cause mechanical strength loss, these materials could be utilized in applications where structures are not continually and directly exposed to aging factors, such as under shelter applications, or after the application of a thermal and surface modification with protective preservatives combination.
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