Search Results (26)

Tannins, present in all plants, are the most abundant polyphenols in the world. Their potential as a raw material for modifying wood alongside furfuryl alcohol (FA) has already been demonstrated in previous studies. This study focused on using large quantities of hydrolysable tannins from chestnut (Castanea sativa) to replace as much FA as possible to chemically modify beech wood (Fagus sylvatica L.). Impregnation was carried out using different concentrations and ratios of both FA and tannins and tartaric acid as catalysts through a vacuum/atmospheric pressure cycle. Copolymerization was carried out for 24 h at 120 °C. Properties such as weight percent gain (WPG), leachability, anti-swelling efficiency (ASE), thermal stability, wettability and durability against brown rot (Coniophora puteana) and white rot (Coriolus versicolor) were analyzed and compared to a furfurylation treatment without the addition of tannins. These treatments were also chemically characterized using FTIR spectroscopy. The results showed that replacing 50% of FA mass by tannins largely increased WPG and demonstrated similar leachability and dimensional stability to standard furfurylation. Above all, the new treatment showed to have better resistance to wood-degrading fungi, in addition to improved wettability and thermal stability. Full article

The combination of different wood-modification technologies to obtain improved performance is increasingly receiving attention in research. In this study, Scots pine (Pinus sylvestris) sapwood was impregnated with furfuryl alcohol (FFA) in pure aqueous 20, 40, and 60% solution strength without adding any catalyst. In a second step, the FFA was polymerized while simultaneously performing thermal modification in a closed system at 130, 150, or 180 °C. After leaching and ageing tests, the nine different combinations were tested in use class 4 applications (in contact with or very close to the ground and frequently wet) according to CEN/TS 15083-2 (2005) decay laboratory test. It was noted that even the minimum-intensity combination of 20% FFA at 130 °C resulted in maximum durability class (DC) 1 performance. On the contrary, DC 4 was assigned to thermally modified control samples, even at the maximum intensity of thermal modification. Similarly, for FFA modifications, previous research has suggested that an uptake of 35% solution strength is required to obtain an adequate durability performance in use class 4 applications. High levels of resistance against termites were also noted by corresponding termite lab tests. Moisture studies showed the combined treatments resulted in improved stability and reduced moisture uptakes. Thus, the results obtained by this study revealed synergistic performance effects, which originate from the combined thermo-chemical modification approach, and which were higher than simple accumulation of the individual performance of purely thermally or chemically modified wood. Thus, the presented findings have provided positive implications for industrial applications of thermo-chemical modification techniques and offers an array of new research opportunities. Full article

Improving the durability of short-rotation wood can be achieved through chemical and thermal modification. Chemical and thermal modification can have an impact on the physicochemical properties of wood, which can affect wood’s surface characteristics and its resistance to weathering. The purpose of this study was to investigate the surface characteristics and artificial weathering resistance of chemically and thermally modified short-rotation teak wood coated with linseed oil (LO)-, tung oil (TO)-, and commercial oil-based coatings consisting of a mixture of linseed oil and tung oil (LT) and commercial oil-based polyurethane resin (LB) coatings. The short-rotation teak woods were prepared in untreated and treated with furfuryl alcohol (FA), thermal treatment (HT) at 150 and 220 °C, and combination of glycerol–maleic anhydride (GMA) impregnation with thermal treatment at 150 and 220 °C. The surface characteristics measured were surface free energy, wettability, Persoz hardness, bonding quality, and color changes before and after artificial weathering exposure. The results showed that chemical and thermal modifications treatment tended to reduce total surface free energy (SFE), hardness, wettability, and bonding quality. FA and GMA at 220 °C treatments provided homogenization effect on surface characteristics, especially in total SFE and wettability. The total SFE of untreated wood ranged from 45.00 to 51.13 mN/m, and treated wood ranged from 40.58 to 50.79 mN/m. The wettability of oil-based coating according to K-value ranged from 0.20 to 0.54. TO presented better photostability than LO. Short-rotation teak wood coated with oil-based commercial coatings presented better weathering resistance compared to pure natural drying oil. Commercial oil-based coatings provided better weathering protection for the chemically and thermally modified teak wood. The application of oil-based coatings on chemically and thermally modified short-rotation teak is being considered for the development of a better wood-protection system. Full article

The circular economy forces societies to take actions aimed at giving post-consumer products a “second life”. As we know, wood is perfect for this. Moreover, reusing wood helps keep carbon in circulation, thus limiting its emissions into the atmosphere. It turns out that extensive research on determining the durability of wood is very useful and valuable for one more reason. Well, they can be used to create a model to determine the usefulness of wood, which has only apparently lost its utility value during many years of exposure to external factors. The research subject was samples of wood impregnated with protection agents and modified, originating from many years of field tests. The aim of the research was to correlate the results of wood durability determined after a period of exposure in open space with the results of determining the potential usefulness of such wood. On this basis, a model for determining the value of post-consumer wood was created. As a main result of post-consumer wood analysis, the high durabilities against C. puteana with mass loss below 3% were noticed for acetylated, furfurylated, and CCA-treated wood. Moreover, high color stabilities (ΔE < 10) were observed for thermowood and furfurylated wood. Full article

Furfurylation can effectively improve the quality of fast-growing wood, but its leachability is unclear. In this study, fast-growing poplar (Populus sp.) and Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) were impregnated with low concentrations of 5%–20% furfuryl alcohol (FA), and the chemical and microscopic changes during leaching tests were analyzed by UV spectra and confocal laser scanning microscopy (CLSM). The results show that FA impregnation can regulate the weight percentage gain, but its effectiveness in regulating the cell wall bulking coefficient decreased as the impregnation concentration was increased. Impregnation with 15% and 20% FA showed no significant difference in the effect on volume swelling efficiency. The inverse relationship between the concentration of FA and the leaching rate was demonstrated by leaching tests, UV spectra, and CLSM. Notably, the leaching rate of poplar and Chinese fir wood was more than 30% when impregnated with 5% FA. Although the entirety of the furfuryl alcohol was deposited in the cell wall when impregnated with low concentrations of FA, the binding was not stable. The weight percentage gain of furfurylated Chinese fir was greater than that of poplar, but its leaching rate was lower, indicating that the cured furfuryl alcohol resin in poplar was not as stable as that in Chinese fir. Therefore, differences in tree species should be considered in low-concentration FA impregnation, as the improvement effect of concentrations below 10% on the properties of fast-growing wood is weak and the leaching rate of FA is significant. Full article

Prepregs are commonly fabricated with non-renewable petroleum-based materials. To reduce the impact of the manufacturing of these materials and to produce more sustainable prepregs, this research aims to manufacture poly(furfuryl alcohol)/wood veneer prepregs and their posterior molding in laminate composites. For this purpose, the vacuum infusion process was used to impregnate the wood veneers, and compression molding was applied to manufacture three- and four-layer laminate composites. Scanning electronic microscopy was used to evaluate the impregnation. the laminate manufacturing and differential scanning calorimetry were used to predict the shelf-life of the prepregs, Fourier-transform infrared was used to evaluate the induced hydrolysis resistance, and thermogravimetric analysis was used to determine the thermal degradation of the laminates. Moreover, water uptake and flexural, compressive, and tensile properties were evaluated. The kinetic models were effective and showed a shelf life for the laminates of approximately 30 days in storage at −7 °C, which is an interesting result for laminates with lignocellulosic materials. FTIR proved the laminates’ excellent resistance to hydrolysis. The water absorption, thermal stability, and mechanical properties did not differ as the amount of wood veneer increased, but these results were up to ~40% higher compared with unidirectional wood laminates found in the literature, which is probably linked to the excellent interface observed with SEM. Full article

Furfurylated wood has many advantages, such as decay resistance, dimensional stability, hardness, etc. However, furfurylation increases the brittleness and decreases the flexural resistance of wood, which greatly limits its application. Therefore, caprolactam (CPL) is incorporated with furfuryl alcohol (FA) to improve the performance of furfurylated wood. In this study, an FA and CPL combinational modifier was used to treat masson pine (Pinus massoniana Lamb.) earlywood and latewood. The synergistic interaction of both components with the wood cell walls was systematically evaluated via microstructural, chemical, and thermal analysis using scanning electron microscopy (SEM), infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectrometry (XPS), and differential scanning calorimetry (DSC). The SEM images showed that polymerized modifiers were distributed in tracheids, ray cells, and pits, with a higher degree of distribution in latewood tissues. The FA-CPL co-treatment led to the highest degree of distribution in cell cavities as well as of cell wall swelling. The results of the weight percentage gain (WPG) of modified wood agreed with the SEM findings that the FA-CPL co-treatment could more effectively increase the WPG than individual modification. The results of FTIR and XPS revealed that FA and CPL might chemically bind with each other as well as react with lignin and hemicellulose in the cell walls during the curing process. In addition, the interactions between modifiers and cell walls were slightly different for earlywood and latewood. DSC analysis indicated that the wood hygroscopicity decreased and the thermal stability improved after modification. Full article

Furfurylation is an effective and green method for wood or bamboo modification that can significantly improve its physical and mechanical properties and the resistance against biological deterioration and the attack of subterranean termites. To elucidate the effect of furfurylation on the physical and multiscale mechanical properties of bamboo, the conditions of the furfurylation process were modified to cause an independent variation of the physical and multiscale mechanical properties in differently-treated bamboo samples. This was achieved by impregnating bamboo samples with solutions containing 15%, 30%, 50%, or 70% furfuryl alcohol (FA) by either of the two impregnation processes, vacuum pressure (V-P) and soaking (S) impregnation, while applying different curing conditions (wet- or dry-curing). The physical properties we measured included the absorption rate, weight percent gain (WPG), swelling efficiency (SE), and anti-swelling efficiency (ASE); the macro-mechanical properties involved the modulus of rupture (MOR), the modulus of elasticity (MOE), parallel-to-grain compressive strength (CS), and tensile strength (TS); the micro-mechanical properties included the tensile strength of bamboo’s vascular bundle and hardness and the indentation modulus of bamboo’s fiber cell walls. Finally, the correlation between the different physical and mechanical properties of the modified bamboo samples was analyzed. The results indicate that V-P impregnation made bamboo more permissible for the penetration of FA, while wet-curing was more conducive to ensuring a high curing rate. The dimensional stability of the bamboo samples treated with a high FA concentration through V-P impregnation and of those furfurylated by the S-Wet process using either medium or high FA concentrations was significantly increased. However, the dimensional stability of the bamboo samples modified with either low or medium FA concentrations decreased in both dry and wet curing. In terms of mechanical strength, furfurylation had little effect on the macro- and micro-mechanical properties of bamboo and was slightly improved in comparison to untreated samples. The results also showed a positive correlation between the macro- and micro-mechanical strength of the modified bamboo samples and a significant negative correlation between the mechanical strength and ASE. In soaking impregnation, the WPG and ASE were positively correlated, while the WPG and CS were negatively correlated. Interestingly, the correlation between the mechanical properties and ASE was not significant. Finally, both V-P-Wet and S-Wet approaches can be recommended for bamboo furfurylation, the former being time-saving and having a high curing rate in FA resin while significantly improving the moisture absorption and mechanical strength of bamboo. The advantage of the latter process is simplicity, a high utilization rate of FA, and a significant improvement in the dimensional stability of bamboo. Full article

This article presents the effect of the addition of condensed tannins, used as a reticulation agent, on the polymerization of furfuryl alcohol during wood furfurylation, as well as the effect of these condensed tannins on the thermal stability of modified wood. Three kinds of dicarboxylic acids (adipic acid, succinic acid, and tartaric acid), as well as glyoxal, used as model of a wood reticulation agent, were used to catalyze the polymerization of furfuryl alcohol or tannin-furfuryl alcohol solutions. Impregnation of furfuryl alcohol or tannin-furfuryl alcohol solution into the wood, followed by curing at 103 °C for a specific duration, was performed for the wood modification. The thermal stability of the obtained tannin-furfuryl alcohol polymers and their corresponding modified woods was investigated. The leaching resistance and dimensional stability of the modified woods were also evaluated. Results indicated that the partial substitution of furfuryl alcohol by the tannins improved the polymerization reactivity in conditions where furfuryl alcohol alone did not lead to the formation of a solid polymeric material. The thermal stability and leaching resistance of the furfurylated wood in the presence of tannins were improved. Dimensional stability was also improved for furfurylated samples, but the effect of tannin addition was not so obvious, depending on the acidic catalyst used. Full article

The use of lignocellulosic fillers in rigid polyurethane foams (RPUFs) has been receiving great attention due to their good mechanical and insulation properties and the high sustainable appeal of the obtained cellular polymers, although high water uptakes are found in most of these systems. To mitigate this detrimental effect, RPUFs filled with wood flour (2.5% wt) were fabricated with the addition of furfuryl alcohol (FA) to create a polymer grafted with the wood filler. Two concentrations of FA (10 wt% and 15 wt%) were investigated in relation to the wood flour, and the RPUFs were characterized for cell morphology, density, compressive properties, thermal stability, and water uptake. The introduction of wood flour as a filler decreased the cell size and increased the anisotropy index of the RPUFs and, in addition to that, the FA grafting increased these effects even more. In general, there were no significant changes in both mechanical and thermal properties ascribed to the incorporation of the fillers. On the other hand, a reduction of up to 200% in water uptake was ascribed to the FA-treated fillers. Full article

Fast-growing wood has become a major source of materials for the wood industry in recent years, but defects have limited its use. Therefore, modification is urgently needed for the more efficient application of wood products. In this study, a 30 to 50% solution of furfuryl alcohol (FA) was impregnated into Douglas fir sapwood. The microstructure and thermal properties of the specimens before and after furfurylation were evaluated by different techniques. The weight percentage gain (WPG) of modified wood increased up to 22.97%, with the polymerized FA distributed in cell lumens and cell walls, as well as chemically bound to wood components. The polyfurfuryl alcohol (PFA) was mainly located in the tracheids, ray parenchyma cells, and resin canals. In addition, the furfurylated cell walls were greatly thickened. Raman spectra showed that modified wood had significant background fluorescence that covered other peaks. Differential Scanning Calorimetry analysis revealed that the cross-linking reaction between FA and wood changed the shape of curves, with no endothermic or exothermic peaks within the programmed temperature. Moreover, Thermogravimetry and Dynamic Mechanical Analysis results both confirmed that the furfurylation increased the thermal stability of Douglas fir. The percentage of the final mass loss of untreated specimen was 80.11%, while the highest one of furfurylated specimen was 78.15%, and it gradually decreased with increasing FA concentration. The storage modulus (E′) and loss modulus (E″) of the furfurylated wood were both lower, and the damping factor (tan δ) was higher than the untreated one. When the temperature reaches about 75 °C, the untreated specimen began to soften and deform. At 90 °C, it fractured completely while the furfurylatedone remained stable. This study demonstrated that furfurylation can improve wood properties and elongate its service life. Full article

Furfurylation with a low concentration of furfuryl alcohol (FA) promotes the improvement of the properties and the effectiveness of FA on cell–wall action without darkening the furfurylated wood to the point that it affects its applications. In this paper, the effects of furfurylation on the hygroscopicity and water uptake dimensional stability of poplar (Populus sp.) and Chinese fir (Cunninghamia lanceolata) were analyzed. Meanwhile, the distribution of FA resin, the relationship between wood and water, the change in pore size distribution, and the weight percentage gain and cell wall bulking coefficient of wood were also investigated. The results were as follows: (1) A low concentration of FA could better enter the cell walls of the Chinese fir than the poplar, as FA resin was almost cured in the secondary walls, cell corners, and compound middle lamellae when a 10% concentration of FA was applied to the Chinese fir and poplar. When the FA concentration was increased to 30%, there were no significant increases in the amount of FA entering the cell walls and the amounts of FA cured in the cell lumen of the poplar were greater than those of the Chinese fir. Meanwhile, the modification of cell walls was more suitable in poplar than in Chinese fir. (2) The pointed ends of the pit chambers and the pit apertures (800–1000 nm) in the poplar and the small pores of the pit membranes and the pit apertures (1–6 μm) in the Chinese fir were partially deposited by the FA resin, which formed new pores in the size ranges of 80–600 nm and 15–100 nm, respectively. The porosity of the poplar was greater than that of the Chinese fir, and the bulk density of the poplar was less than that of the Chinese fir before and after modification. (3) Furfurylation with a low concentration of FA was able to better reduce the equilibrium moisture content, improve the anti-swelling efficiency, and enhance the dimensional stability of the poplar wood compared to the Chinese fir. Furfurylation effectively reduced water uptake due to the hydrophobic property of the FA resin. The water uptake of the Chinese fir increased by 17%–19% in second cyclic water soaking when treated with FA with various concentrations, which indicated the loss and leaching of FA resin during the test. Low-field NMR was used to demonstrate that the furfurylation not only reduced the amount of water but also affected the combination state of bound and free water with wood. Thus, furfurylation at a low concentration is a feasible method by which to extend applications of furfurylated wood. Full article

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. Full article

Guanyl-urea phosphate (GUP) was introduced into furfurylated wood in order to improve fire retardancy. Modified wood was produced via vacuum-pressure impregnation of the GUP–furfuryl alcohol (FA) aqueous solution, which was then polymerized at elevated temperature. The water leaching resistance of the treated wood was tested according to European standard EN 84, while the leached water was analyzed using ultra-performance liquid chromatography (UPLC) and inductively coupled plasma–sector field mass spectrometry (ICP-SFMS). This new type of furfurylated wood was further characterized in the laboratory by evaluating its morphology and elemental composition using optical microscopy and electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX). The chemical functionality was detected using infrared spectroscopy (FTIR), and the fire resistance was tested using cone calorimetry. The dimensional stability was evaluated in wet–dry soaking cycle tests, along with the mechanical properties, such as the Brinell hardness and bending strength. The fire retardancy of the modified furfurylated wood indicated that the flammability of wood can be depressed to some extent by introducing GUP. This was reflected in an observed reduction in heat release rate (HRR₂) from 454.8 to 264.9 kW/m², without a reduction in the material properties. In addition, this leaching-resistant furfurylated wood exhibited higher fire retardancy compared to conventional furfurylated wood. A potential method for producing fire-retardant treated furfurylated wood stable to water exposure has been suggested. Full article

Dimensional stability is a commonly targeted property for improvement through wood modification. Here four different tests have been performed on three types of modified wood to compare methods of measuring dimensional stability behavior. These tests cover long and short time periods, as well as dimensional changes caused by contact with liquid water, or from changes in air humidity. All the tests showed increased dimensional stability of the modified samples relative to the unmodified controls; however, the relative behavior of the different modifications varied between tests. Soaking in water until maximum swelling showed no differences between thermally modified and furfurylated samples, but a subsequent test showed large differences in the rate of swelling for each wood type, with the furfurylated samples swelling very slowly. Long-term swelling in humid air showed similar results to soaking in water, but with the thermally modified samples having significantly greater dimensional stability than the furfurylated samples. Swelling for a short period in humid air showed no difference in swelling between the modified wood types, but there was a threefold reduction in swelling compared to the unmodified controls. For a more complete understanding of dimensional stability, several tests employing different test conditions should be used. Full article