•We studied the dynamic wetting behavior of thermally modified wood by wetting models.•We found lower wetting speed of water droplets on thermally modified wood surface.•Dynamic wetting behavior and ...surface chemical components show a strong correlation.
In order to investigate the dynamic wetting behavior of thermally modified wood, Cathay poplar (Populus cathayana Rehd.) and Scots pine (Pinus sylvestris L.) samples were thermally modified in an oven at 160, 180, 200, 220 or 240°C for 4h in this study. The dynamic contact angles and droplet volumes of water droplets on modified and unmodified wood surfaces were measured by sessile drop method, and their changing rates (expression index: K value and wetting slope) calculated by wetting models were illustrated for mapping the dynamic wetting process. The surface chemical components were also measured by X-ray photoelectron spectroscopy analysis (XPS), thus the relationship between dynamic wetting behavior and chemical components of thermally modified wood were determined. The results indicated that thermal modification was capable of decreasing the dynamic wettability of wood, expressed in lowing spread and penetration speed of water droplets on wood surfaces. This change was more obvious with the increased heating temperature. The K values varied linearly with the chemical components parameter (mass loss, O/C ratio, and C1/C2 ratio), indicating a strong correlation between dynamic wetting behavior and chemical components of thermally modified wood.
Ultraviolet (UV)-induced discoloration and cracking pose formidable challenges for thermally modified wood (TMW) when used in outdoor applications. Herein, we propose a novel pretreatment strategy ...using deep eutectic solvent (DES) to enhance the weathering resistance of TMW. DES-assisted TMW (DES-TMW) was prepared by coating wood with choline chloride/citric acid (CA) DES, followed by thermal modification. During the DES-assisted thermal modification process, the cross-linking of the lignin network in DES-TMW was increased as a result of lignin self-polymerization, cross-linking with autologous molecules and furfural, as well as esterified connections caused by CA. This in-situ modification reduces the quantity of photosensitive phenolic hydroxyl groups within lignin by forming cross-linked structures, reducing phenoxy free radical generation during the weathering and obstructing chromophores production pathways, thus enhancing the photostability of lignin. Consequently, the DES-TMW exhibited remarkable resistance to discoloration and cracking compared to TMW. These findings provide evidence that our strategy can effectively enhance the photostability of wood, thereby contributing to the development and production of sustainable outdoor wood products capable of withstanding changing weather conditions.
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•Eco-friendly DES-assisted method for photostable thermally modified wood (TMW).•In-situ lignin modification during treatment created stable cross-linked structures.•DES-assisted method inhibited chromophore formation and photodegradation of lignin.•DES-assisted TMW (DES-TMW) showed excellent resistance to color change and cracking.
The water vapour sorption and viscoelastic characteristic of thermally modified poplar wood (Populus tomentosa Carr.) based upon colour changes were studied to provide insights into the changes in ...hygroscopicity and dimensional stability properties by using dynamic vapour sorption (DVS) and dynamical mechanical analysis (DMA). The thermal treatments at 180, 200, and 220 ℃ for 2, 4, 6, 8, and/or 10 h under air atmosphere were applied to cause the component degradation and crosslinking reactions within the cell wall. As the thermal treatment temperature and time increased, the lightness (L*) value of wood showed a gradual decrease. After the removal of hydroxyl groups, the hydrophobicity and dimensional stability had been significantly improved, especially at low L* value. A gauss function (R2 up to 0.99) relationship was observed between water adsorption property and L* value. Based on the analysis of the multiple sorption parameters against L* value, thermal treatment degraded the hemicellulose and reduced the moisture sorption of wood cell wall and the diffusion of water through the cell wall matrix. As the L* value declined, the trend that slow moving of side chains, increasing glass transition point temperature of hemicellulose, and more additional covalent bonds resulted in increased E″ and decreased E′ values was becoming evident. From these perspectives, it could be deduced that reduced water diffusion and high polymer stiffness confined expansion of the cell wall to endow thermally modified wood with improved hydrophilicity and dimensional stability.
•Hydrophobicity and dimensional stability were improved, especially at low L* value.•A gauss function relationship was observed between water adsorption and L* value.•Physical property was improved by reduced water diffusion and high polymer stiffness.
•The anti-weathering performance of TiO2/paraffin treated thermally modified wood was greatly improved.•TiO2 showed high efficacy on slowing down the photo-degradation of thermally modified wood ...components.•Addition of paraffin emulsion improved the adherence of TiO2 on thermally modified wood surface.
The poor anti-weathering performance of thermally modified wood is always an issue that influences its appearance as well as its service life after exposure in outdoor circumstance. In this study, titania (TiO2) sol, paraffin emulsion, and their combination were used to impregnate thermally modified Scots pine (Pinus sylvestris L.) sapwood, modified at 212 °C, and then the samples were subjected to an accelerated weathering test for up to 1176 h. The time-dependent changes on surface color, gloss and water contact angle (WCA) of control and post-treated samples were investigated during the weathering process. Moreover, the chemical and morphological alterations were analyzed by attenuated total reflected Fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopy (SEM). The results showed that TiO2 was not resistant to water but addition of paraffin emulsion improved the adherence of TiO2 on wood surface. After post-treatment with TiO2 sol and paraffin emulsion, the anti-weathering performance of thermally modified wood improves due to the controlling of negative effects from ultraviolet and water on wood surface, respectively. The degradation of wood components decreased significantly in TiO2/paraffin treated samples, which was confirmed by the FTIR and SEM results.
The elasticity in bending of European oak (Quercus robur L.) and Norway spruce (Picea abies (L.) Karst.) timber was evaluated before and after thermal modification and related to the changes in ...chemical composition of the wood as a result of the modification. A new software was developed (MATESS) and used to identify characteristic points on the force-deformation diagram. The modulus of elasticity (MOE), stress at the limit of proportionality (LOP) and elastic potential (PE) were used to describe the wood properties. Extractives, lignin, cellulose, holocellulose, and hemicelluloses were analysed to reveal the patterns that occur during the loading of the specimens. Thermal modification lowers the mechanical properties (MOE, LOP and PE) of oak and spruce wood, and the reduction increases with increasing modification temperature. Changes in chemical composition of thermally modified wood show a strong relationship to the reduction in elasticity properties for bot species.
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•TiO2 efficiently improves the surface durability of coated thermally modified wood.•The addition of ZnO leads to poor adhesion strength, cracking and peeling of coating.•The addition ...of TiO2 helps to maintain sufficiently good adhesive of coating on TMT.•Discoloration of TMT out of doors cannot be eliminated, but can be reduced by addition of TiO2.
In this research the samples of thermally modified (TMT) beech wood samples, finished with waterborne polyacrylate clear coatings modified with nano-sized ZnO and TiO2-rutil were naturally and artificially exposed to weathering conditions. To extend the lifetime of wood and maintain its natural look, the research and development of clear coatings with minimal use of harmful chemicals has become very important. Therefore nano-sized inorganic UV absorbers are increasingly used to enhance the durability of the coating and wood substrate, still retaining the transparency of the coating. During exposure the visual inspection was performed, further the changes of colour, gloss and adhesion were recorded. Interaction of the film with the thermally modified substrate surface were studied. Results showed that the addition of TiO2-rutil and ZnO nanoparticles to the waterborne polyacrylate coating improved the colour stability of thermally modified beech-wood. However, nano-sized ZnO increased the cracking and peeling, and caused the loss in adhesion strength of the film on thermally modified beech wood.
•Carnauba wax/organoclay emulsion was synthesized and organoclay was well dispersed.•Carnauba wax/organoclay emulsion could overcome drawbacks of thermally modified wood.•This emulsion enhanced the ...strength and photostability of thermally modified wood.•This emulsion decreased the metal corrosiveness in thermally modified wood.•1.0 %wt organoclay-formulation had the best performance for quality improvement.
Thermally modified wood (TMW) presents several disadvantages, such as poor mechanical properties and vulnerability to ultraviolet exposure, which limit the application of TMW in the construction industry. To address the aforementioned shortcomings, carnauba wax emulsions containing efficiently dispersed organoclay (0, 0.5, and 1.0 wt%) were prepared as modifiers for the post-treatment of thermally modified loblolly pine (Pinus taeda). Morphological observation confirmed that the carnauba wax/organoclay complex coating was formed in the tracheid lumen, and organoclay layers successfully penetrated into the wood cell wall. The efficiency of the carnauba wax/organoclay emulsion in improving the quality of TMW was evaluated. The results showed that carnauba wax/organoclay emulsion positively affected TMW, reducing its water uptake, increasing its bending and compressive strengths, maintaining its constant color and gloss under weathering, and decreasing metal corrosiveness. In most cases, the higher the organoclay loading, the better the performance of TWM. Thus, TMW impregnated with carnauba wax/organoclay emulsion shows potential as a potential construction material for outdoor applications.
The increasing demand for wood with enhanced flame retardant characteristics in construction applications necessitates strategic interventions. This study explores the fire behaviour and chemical ...characterisation of
Robinia pseudoacacia
wood subjected to thermal modification and flame retardant treatments. Thermal modification was carried out at three different temperatures (160 °C, 180 °C and 240 °C). The fire properties of wood coated with Flame Gard (F), a commercial flame retardant, arabinogalactan (A), a natural flame retardant, melamine adhesive (MF) with ammonium polyphosphate (AP), nanosilica (NS), nanoclay (NC) (MF-AP-NS and MF-AP-NC) and arabinogalactan with AP, NS and NC (A-AP-NS and A-AP-NC), were assessed using cone calorimetry in terms of the weight loss rate, ignition time and heat release rate. The commercial flame retardant Flame Gard outperformed the natural and fortified flame retardants in terms of the weight loss rate, heat release rate (HRR) and ignition time (t
ig
). Unmodified samples exhibited superior fire properties in terms of t
ig
and HRR compared to thermally modified samples. The peak heat release rate (kW.m
− 2
) and time to peak heat release rate (s) showed a moderate degree of dependency on the chemical constituents of the wood.
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