Wood Modification Research Articles

On the"Staple" Effect in the d-Glucose Acetylation by Choline-Chloride Ethylene Glycol and Choline-Chloride Urea Deep Eutectic Solvents.

This work employs hybrid quantum mechanics molecular mechanics simulations coupled with an umbrella sampling technique to investigate the acetylation of d-glucose with acetic anhydride in two deep eutectic solvents (DESs): choline-chloride ethylene glycol (ChCl/Etg) and choline-chloride urea (ChCl/U). The reaction proceeds spontaneously, with activation free energy barriers of 18.19 ± 0.15 and 19.83 ± 0.15 kcal/mol for ChCl/Etg and ChCl/U, respectively. These values align with literature data for similar reactions in ionic liquids, highlighting the potential of DESs as green reaction media for wood modifications, while minimizing lignocellulosic matrix degradation. Energy pair distribution analysis, radial distribution functions, and noncovalent interactions reveal a more solvated transition state compared to the initial reactant state within ChCl/Etg, facilitating the acetylation reaction. Interestingly, combined distribution function analysis unveils a "staple" effect in both solvents, potentially hindering efficient product separation. The work further explores hydrogen bond networks and Kamlet-Taft solvatochromic parameters to elucidate the role of solvents in the reaction mechanism. It was observed that a notable decrease in activation energy is accompanied by increasing net basicity, along with a reduction in the "staple" effect. This suggests that solvent parameters could serve as an effective screening tool for identifying novel and efficient DESs for wood modifications.

Wood Modification—Trends and Combinations

Wood modification is a field that has enjoyed sustained interest over the past two decades, although its history can be tracked back significantly further, to the pioneering work of Alfred Stamm and co-workers at the Forest Products Laboratory in the USA in the 1930s, 1940s, and 1950s [...]

Chemical changes in thermally modified, acetylated and melamine formaldehyde resin impregnated beech wood

Abstract Wood modification (by thermal or chemical treatment) helps to improve the dimensional stability of wood and enhance its resistance to biological agents. Beech wood is non-durable and exposure in exterior settings dramatically shortens its service life. To determine the full potential of beech wood for advanced applications, a better understanding of the chemical changes induced by modification is needed. Two chemical treatments (acetylation and melamine formaldehyde resin impregnation) and three thermal treatments (heating to 180, 200 and 220 °C) were performed on beech wood. The modification effect was examined based on (i) molecular changes in functional groups by Fourier-transform infrared spectroscopy (ATR-FTIR); (ii) extractive content; and (iii) pH changes. Moreover, the explanation of these changes was supported by the FTIR-analysis of isolated main wood components (cellulose, holocellulose and lignin) from the modified wood. The high temperatures applied to samples during thermal modification promoted the deacetylation and degradation of hemicelluloses. Hemicelluloses were targeted also by acetic anhydride and melamine resin, the bonding of which was confirmed by FTIR analysis. The formation of fewer methylene bridges affected the properties of the melamine network. This observation suggests the need to determine optimal curing conditions in future research, to reduce melamine-wood hydrophilicity.

Modifying the radiation ratio of tonewoods through wood degradation

ABSTRACT This work investigates different wood modification techniques to modify the acoustical properties of tonewoods, in particular the sound radiation ratio (R). The treatments used were heat- and fungal exposure, as well as immersion into NaOH and Na2SO3 solution and a combination of the most successful treatments. All initial experiments were performed on pine wood (Pinus patula) due to cost factors, before replicating the best-performing treatment on high-quality spruce tonewood (Picea abies). The main objective was to reduce the hemicellulose content without severely degrading cellulose, which results in a reduction of density, while maintaining, or even improving the elasticity (MOE L ), which results in an increase of R. Overall, the combined heat–fungal and heat–sodium treatments performed best and increased R by up to 20%. Sodium treatment led to the best increases in R, but compromised the wood structure in spruce and the treatment protocol needs to be developed further. Consequently, the most successful wood treatment to improve acoustical properties was determined to be exposure to white rot combined with heat treatment.

Effect of acetylation on wood-water interactions studied by sorption calorimetry

Sorption of water has a profound effect on the material properties of wood. The uptake of water vapour in wood and other materials releases more heat than the condensation of vapour to liquid water. This excess energy provides insights to the interactions and energy state of the absorbed water molecules. Modification of wood by acetylation is a common way of altering the wood-water interactions; however, very few data exist on how this and other types of modification affect the energy state of absorbed water in wood. This study is the first to use sorption calorimetry on modified wood to explore the effect of acetylation on wood-water interactions. Acetylation decreased the strength of the interactions between wood and water as seen from a decrease in differential enthalpy of mixing, both overall and in the dry state. It appears that acetylation removes or hinders the most-energetic interactions or bonding configurations of water in wood, perhaps because acetylation reduces the number of water-accessible hydroxyls more than it reduces the amount of absorbed water molecules.

Optimization of mechanical properties and dimensional stability of densified wood using response surface methodology

Wood has gained popularity as a building and decorative material due to its environmentally friendly and sustainable characteristics. Yet, its long maturation time poses a limitation on meeting the growing demand for wood products. This challenge has led to the plantation of fast-growing wood as an alternative solution. Unfortunately, the poor mechanical properties of fast-growing wood hinder its application. In this study, we developed novel densification-modified wood by combining alkali chemical pretreatment, cyclic impregnation, and mechanical hot-pressing techniques. Additionally, the response surface method was employed to rapidly determine the optimal preparation parameters, reducing the cost of preparation under various conditions. The optimized parameters resulted in densification-modified wood with a flexural strength and modulus of elasticity of 337.04 MPa and 27.43 GPa, respectively. Furthermore, the densified wood achieved excellent dimensional stability by reducing the water-absorbing thickness swelling to 1.15 % for 72-h water soaking. The findings indicated that the densification-modified wood possessed high tensile strength and elastic modulus, along with excellent dimensional stability. The proposed densified wood modification technology in this study offers new perspectives and design guidance for the application of outdoor engineering structures, energy-efficient buildings, and decorative materials.

Advanced Molecular Dynamics Model for Investigating Biological-Origin Microfibril Structures.

Understanding the atomic-scale structure of wood microfibrils is essential for establishing fundamental properties in various wood-based research aspects, including moisture impact, wood modification, and pretreatment. In this study, we employed molecular dynamics simulations to investigate the arrangement of wood polymers, including cellulose, hemicellulose, and lignin, with a primary focus on the composition of softwood, specifically Norway Spruce wood. We assessed the accuracy of our molecular dynamics model by comparing it with available experimental data, such as density, Young's modulus, and glass transition temperature, which ensures the reliability of our approach. A key aspect of our study involved modeling the active sorption site for water interaction with wood polymers. Our findings revealed that the interaction between water and hemicellulose, particularly within the hemicellulose-cellulose interphase, was the most prominent binding site. This observation aligns with prior research in this field, further strengthening the validity of our results.

Decay and Termite Resistance of Wood Modified by High-Temperature Vapour-Phase Acetylation (HTVPA), a Simultaneous Acetylation and Heat Treatment Modification Process.

High-temperature vapour-phase acetylation (HTVPA) is a simultaneous acetylation and heat treatment process for wood modification. This study was the first investigation into the impact of HTVPA treatment on the resistance of wood to biological degradation. In the termite resistance test, untreated wood exhibited a mass loss (MLt) of 20.3%, while HTVPA-modified wood showed a reduced MLt of 6.6-3.2%, which decreased with an increase in weight percent gain (WPG), and the termite mortality reached 95-100%. Furthermore, after a 12-week decay resistance test against brown-rot fungi (Laetiporus sulfureus and Fomitopsis pinicola), untreated wood exhibited mass loss (MLd) values of 39.6% and 54.5%, respectively, while HTVPA-modified wood exhibited MLd values of 0.2-0.9% and -0.2-0.3%, respectively, with no significant influence from WPG. Similar results were observed in decay resistance tests against white-rot fungi (Lenzites betulina and Trametes versicolor). The results of this study demonstrated that HTVPA treatment not only effectively enhanced the decay resistance of wood but also offered superior enhancement relative to separate heat treatment or acetylation processes. In addition, all the HTVPA-modified wood specimens prepared in this study met the requirements of the CNS 6717 wood preservative standard, with an MLd of less than 3% for decay-resistant materials.

Green bio-derived epoxidized linseed-oil plasticizer improves the toughness, strength, and dimensional stability of furfuryl alcohol-modified wood

Furfuryl alcohol (FA) modification represents a sustainable approach to wood modification; however, it significantly reduces the toughness of the wood, limiting its practical applications. This study introduced epoxidized linseed oil (ELO) as an environmentally friendly and bio-derived plasticizer to enhance the toughness and mechanical properties of FA-modified wood. Microstructural analyses confirmed the integration of FA and ELO into the cellular structure of the wood. The chemical interactions between the epoxy groups of ELO and hydroxyl groups of FA were characterized using Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy, illustrating that a ring-opening reaction occurred that grafted the long flexible aliphatic chains of ELO onto the FA chains, thereby enhancing the chain mobility and flexibility. This interaction significantly decreased the crosslinking density, thereby achieving toughening. FA–ELO modification resulted in significantly enhanced dimensional stability and mechanical properties. Specifically, the anti-swelling efficiency exceeded 80 %, while the modulus of elasticity, modulus of rupture, and along-grain compressive strength increased by up to 35.0 %, 36.8 %, and 45.7 %, respectively. Additionally, significant enhancements in the elongation at break and impact strength were achieved, at 369.1 % and 72.4 %, respectively. The loss factor also increased. The optimal ELO content was 20 wt%. This study effectively demonstrated how ELO mitigates the brittleness of FA-modified wood and supports its application in high-value fields such as construction.

Moisture and Temperature Profiles of Heartwood Pinus pinaster Ait. Wood Specimens during Microwave Drying

Microwave (MW) drying of wood has gained popularity in the field of wood modification. The rise in temperature during MW drying leads to increased steam pressure, enhancing wood permeability but potentially decreasing mechanical properties. Understanding temperature and moisture behaviors during MW drying is crucial for its industrial application in wood drying. Therefore, this study aimed to characterize the temperature and moisture behaviors during MW drying of small Portuguese maritime pine (Pinus pinaster Aiton.) wood samples to support a wider use of this technology. The effects on water uptake and the compressive strength parallel to the grain were also investigated. The results indicated three distinct phases in the MW drying rates, with an average of 0.085% of water removed per second. Moreover, the temperature underwent three distinct stages: an initial rapid increase, a period of constant temperature, and a slight decrease until drying was complete. At the beginning of MW drying, the temperatures were below 100 °C, with average temperatures ranging from 126 to 145 °C. Specimens with lower initial moisture content had higher temperatures, and a positive correlation was found between initial moisture content and drying time. In contrast, negative correlations were found between the initial moisture content and average temperature, as well as average temperature and MW drying time. Additionally, the operating condition parameters used in MW drying of pine samples enhanced water impregnability by 65%, generating a slight reduction of 11% in compressive strength. It was also noticed that the initial moisture content did not impact MW-dried samples’ water uptake or compressive strength. Finally, although small clear wood samples of maritime pine were utilized, the temperature and moisture patterns observed closely matched real-scale specimens. Thus, the findings corroborate a wide utilization of MW technology for wood drying, mainly demonstrating positive possibilities for structural-sized wood specimens.

Oil Heat Treatment of Wood-A Comprehensive Analysis of Physical, Chemical, and Mechanical Modifications.

Wood, a natural material with versatile industrial applications, faces limitations such as low dimensional stability and decay resistance. To address these issues, there has been significant progress in wood modification research. Oil heat treatment has emerged as an effective method among environmentally friendly wood treatment options. Studies have indicated that treating wood with hot vegetable oils yields superior properties compared to traditional methods involving gaseous atmospheres, which is attributed to the synergistic effect of oils and heat. This comprehensive review investigates the physical, chemical, and mechanical modifications induced by the oil heat treatment of wood, along with its impact on biological durability against biotic agents. The review synthesizes recent research findings, elucidates underlying mechanisms, and discusses the implications for wood material science and engineering.

Study on Alcoholysis of Waste PET and Its Application in Wood Modification

Study on Alcoholysis of Waste PET and Its Application in Wood Modification

Aqueous modification of waterlogged archaeological wood by phenylboronic acid to reduce hygroscopicity and improve the dimensional stability

Aqueous modification of waterlogged archaeological wood by phenylboronic acid to reduce hygroscopicity and improve the dimensional stability

Древесно-композитные плиты с низким коэффициентом линейного теплового расширения

A number of industries require materials with a low coefficient of linear thermal expansion (CLTE), in particular, in the production of satellite spherical antennas. The latter are formed from composites containing carbon fibers and synthetic resins. The composition is cured by heating up to 180 °C. This leads to a thermal expansion of the mold and a change in the geometric characteristics of the product. Therefore, specific requirements are imposed on the materials for making molds. The high cost of special materials used for molds determines the need to search for other materials with a low CLTE. Wood is a possible solution to this problem. Its CLTE along the fibers is less than that of the vast majority of materials, and is approximately 3 ‧ 10-6 K–1, which is comparable to special materials. However, the expansion of wood across the fibers is much higher than the longitudinal one, which excludes the use of solid wood. Anisotropy can be reduced by creating a composite in which the fibers are uniformly oriented in all structural directions, bringing the value of wood expansion across the fibers closer to the value of expansion along the fibers. The traditional approach to producing wood composites, based on the use of synthetic adhesives, fails to achieve a noticeable reduction in thermal expansion due to the high CLTE of adhesives The use of boards made of hydrodynamically activated wood particles without binders is promising. Three series of experiments have been carried out: with varying the density of the boards, preliminary thermal modification of the original wood and the use of alkali during hydrodynamic processing. The thermal expansion study has been carried out using the NETZSCH DIL-402 C induction dilatometer in dynamic mode with a heating rate of 2 K/min. It has been established that thermal expansion increases with increasing density.The average CLTE at a density of 950 kg/m3 is 12 ‧10–6 K–1 and at a density of 1,100 kg/m3 it is 17‧10–6 K–1. At a comparable density, the thermal expansion of boards without binders is significantly lower than that of fiberboards (MDF). Preliminary thermal modification of wood does not significantly affect the CLTE of the boards. The use of alkali in the hydrodynamic treatment also has no effect.

Super-stable modified wood for enhanced autonomous indoor humidity regulation

The crucial development of materials that automatically adjust indoor humidity, a significant factor in human health and daily life, has gained importance due to the emphasis on energy conservation. Wood, with its natural hygroscopic properties, is effective in this regard but faces challenges of deformation and cracking due to moisture content changes. Herein, we introduced an innovative in-situ wood modification strategy, which integrated deep eutectic solvent (DES) impregnation with heat treatment, producing dimensionally super-stable modified wood for enhanced autonomous indoor humidity regulation. This modification process focused on creating more robust cross-linking structures within the amorphous regions of the wood cell wall. As a result, water-induced deformation of natural wood was significantly reduced, as evidenced by an anti-swelling efficiency exceeding 80%, ensuring the long-term reliability of DES-modified wood in varying humidity environments. Additionally, the introduction of additional pores and hygroscopic sites in the cell wall enhanced the natural wood’s moisture buffering value by 2.5 times, showcasing the superior ability of DES-modified wood to control indoor humidity effectively. Moreover, the DES-modified wood also exhibited commendable flame retardancy and antibacterial properties. Consequently, this novel modified wood emerges as a reliable material for indoor humidity regulation, promoting healthier indoor conditions and offering a sustainable alternative for energy-efficient construction practices.

Coatings Adhesion on Chemically Modified Scots Pine (Pinus sylvestris L.) Woods

Synergizing coating and wood modification is a promising concept to develop wood products that have multi-qualities that include excellent dimensional stability, durability, and weathering resistance. However, the nature of the modified substrate is a critical parameter for coating adhesion. Chemical modification of wood impacts the physicochemical properties of the wood, which could in turn impact the adhesion of coatings. Therefore, this study investigated the adhesion of seven different coatings to Pinus sylvestris L. woods chemically modified through esterification with acetic anhydride (acetylated), etherification with 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU), and esterification with sorbitol/citric acid formulation (SorCA). The selected coatings include water-based and solvent-based examples with different binder constituents that include acrylate, alkyd, natural oil, and hybrids. Coating adhesion to the modified wood was evaluated in terms of crosscut resistance to detachment, wear-resistant hardness, and pull-off strength. Chemical modifications yielded positive impacts on coating adhesion compared to unmodified wood. Coatings adhered better to acetylated and DMDHEU-modified P. sylvestris wood than on SorCA-modified wood. Solvent-based coatings had higher adhesion strength on the acetylated, DMDHEU-modified, and unmodified woods than water-based coatings. On the other hand, water-based coatings mostly adhered better to SorCA-modified wood compared to solvent-based coating. Overall, the coating of chemically modified P. sylvestris wood is promising for the development of an enhanced wood protection system.

Solid Wood Modification toward Anisotropic Elastic and Insulative Foam-Like Materials.

The methods used to date to produce compressible wood foam by top-down approaches generally involve the removal of lignin and hemicelluloses. Herein, we introduce a route to convert solid wood into a super elastic and insulative foam-like material. The process uses sequential oxidation and reduction with partial removal of lignin but high hemicellulose retention (process yield of 72.8%), revealing fibril nanostructures from the wood's cell walls. The elasticity of the material is shown to result from a lamellar structure, which provides reversible shape recovery along the transverse direction at compression strains of up to 60% with no significant axial deformation. The compressibility is readily modulated by the oxidation degree, which changes the crystallinity and mobility of the solid phase around the lumina. The performance of the highly resilient foam-like material is also ascribed to the amorphization of cellulosic fibrils, confirmed by experimental and computational (molecular dynamics) methods that highlight the role of secondary interactions. The foam-like wood is optionally hydrophobized by chemical vapor deposition of short-chained organosilanes, which also provides flame retardancy. Overall, we introduce a foam-like material derived from wood based on multifunctional nanostructures (anisotropically compressible, thermally insulative, hydrophobic, and flame retardant) that are relevant to cushioning, protection, and packaging.

Dimensional Stability and Mechanical Properties of Gmelina arborea Roxb. Wood Thermally Modified through Open Reactor and Low-Pressure Closed Reactor Systems

This study focused on the thermal modification of Gmelina arborea Roxb. wood following processes using the open reactor and low-pressure closed reactor systems. The aim is to determine the optimum treatment conditions suitable for gmelina wood due to its poor drying characteristics using the low-pressure closed reactor thermal modification. Subsequent to thermal modification under both processes, the dimensional stability and mechanical properties of gmelina wood were investigated. Effects of the thermal modifications under the open and low-pressure closed reactor systems on mechanical properties were additionally reported. The outcome of this investigation revealed that mass loss increased with increasing treatment temperatures, but minimal mass losses were observed for samples modified in the low-pressure closed reactor system. Due to the low-pressure regime used in the closed reactor system, a lesser improvement was found in volumetric shrinkage, fibre saturation point and tangential-to-radial swelling compared to the improvement in these properties in the open reactor system. Results further revealed that the mechanical properties of gmelina wood deteriorated more rapidly after modification in the open reactor system. Since the properties of modified gmelina wood are comparable at 180 °C under both systems, the closed reactor system will be investigated further to arrive at a suitable treatment condition under higher pressure variations. The thermal modification of gmelina wood with the closed reactor system is more promising in delivering a better quality of modified gmelina wood.

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.

Utilizing pyrolysis cleavage products from softwood kraft lignin as a substitute for phenol in phenol-formaldehyde resins for modifying different wood species

Phenol-formaldehyde resins can be used for wood modification through an impregnation process and subsequent curing within the wood cell wall. Phenol is gained from non-renewable resources, and its substitution by renewable chemicals has been a research goal. A promising example for renewable phenol substituents are lignin-derived organic chemicals. Phenol-formaldehyde resins with such substitutions have been studied, however, knowledge of their application for wood modification is deficient. While there are attempts to modify pine and beech wood with this method, studies on other wood species are scarce. Considering the increasing use of different wood species in wood industry, determining the influence of the wood species on the modification quality is an important research goal. Therefore, in this study, vacuum-pressure impregnation of five wood species – Scots pine sapwood (Pinus sylvestris), Norway spruce (Picea abies), European beech (Fagus sylvatica), Silver birch (Betula pendula), and European aspen sapwood (Populus tremula) – with phenol-formaldehyde resins is described. Here, up to 45% of the phenol in the synthetic resin is substituted by vacuum low-temperature microwave-assisted pyrolysis cleavage products from commercial softwood kraft lignin. The solution uptake, weight% gain, leaching, and anti-swelling efficiency of the modified wood are analyzed and compared. The results indicate that up to 30% of the phenol can be substituted without significant decreases in the performance of the modification. The method gives comparable results for most of the wood species described herein, with exception of beech wood, for which the modification had a lower quality. The results could help to develop more environmentally friendly wood modification methods for several common European wood species.