Wood Modification Research Articles

Viscoelastic and Thermal Properties of Styrene Modified Fir Wood.

The modification of wood and its surface is one of the challenges that is being perfected with the aim of transitioning to sustainable management. This study investigated the dynamic mechanical and thermal behaviour of unmodified and styrene modified fir wood (Abies alba Mill.). Styrene monomer was chosen and impregnated into the porous structure of fir wood by reversible addition-fragmentation chain transfer (RAFT) polymerisation. Attenuated total reflection Fourier-transform infrared spectroscopy (FTIR-ATR), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA) were employed to characterise the chemical structure, viscoelastic properties, and thermal stability of unmodified and modified (surface-modified) wood. All tests have to be regarded as being preliminary due to the small number of specimens. Fourier transform infrared analysis showed evidence of the phenyl group from styrene at 700 cm−1. DMA results showed that the modified wood caused an increase in the glass transition temperature relative to the unmodified wood. In addition, modification with styrene improves thermal stability, as revealed by thermogravimetric analysis (TGA).

In Situ Construction of Thermotropic Shape Memory Polymer in Wood for Enhancing Its Dimensional Stability.

The extension of wood to a wider field has been restrained significantly due to its dimensional instability that arises from variation in moisture content, which in turn brings about the risk of cracking, warping or distortion. This work proposed a novel strategy to stabilize wood by means of the in situ construction of a thermotropic shape memory polymer (SMP) inside wood. The cross-linked copolymer network (PMP) with good shape memory behavior was first investigated based on the reaction of methyl methacrylate (MMA) and polyethylene glycol diacrylate (PEGDA) in a water/ethanol solution; then, the PMP was constructed inside wood via vacuum-pressure impregnation and in situ polymerization. The weight gain, volume increment and morphology observations clearly revealed that the PMP was mainly present in wood cell lumens, cell walls and pits. The presence of PMP significantly enhanced the dimensional stability of and reduced the cracks in wood. The desirable shape recovery abilities of PMP under heating-cooling cycles were considered to be the main reasons for wood dimensional stabilization, because it could counteract the internal stress or retard the shrinkage of cell walls once water was evaporated from the wood. This study provided a novel and reliable approach for wood modification.

IMPROVEMENT OF MECHANICAL PROPERTIES OF WOOD AT THE ACCOUNT OF THEIR ADHESIVE

High-quality solid wood of deciduous and coniferous species in Ukraine is becoming less and less every year. Therefore it is necessary to use that wood which is available. Various methods and techniques are used to improve the mechanical properties of wood. One of them is gluing wood boards of different thickness. In this article we present the following studies taking into account the actual work of the material.
 The method of researches of glued wood of different breeds by axial compression along fibers by short-term loading at standard humidity (by increase of displacements) is given. Complete deformation diagrams “stress σc - deformations uc” are constructed and the main parameters are established: maximum disturbances, critical deformations, initial modulus of elasticity. The strength of glued wood increases in comparison with the indicators of continuous humidity of 12% at the age of 60 by 13-25%; critical deformations slightly increase or decrease in one direction or another; the initial modulus of elasticity increases by 13–31%.
 This improvement is due to the ingress of glue into the body of wood, ie due to gluing is the modification of wood and the formation of composite material. The strength of such a composition is directly affected by the thickness of the board. The smaller the thickness of the board, the stronger the product.
 It is established that the deformation diagrams of glued wood have two branches: ascending and descending. That is, the work of such composite materials is observed, both in the subcritical stage and in the supercritical stage. Therefore, the samples have a certain residual strength after passing the maximum stress values.
 It has been established that gluing wood increases the strength and initial modulus of elasticity of the composite material and depends on the thickness of the board.

A New Protocol for Ash Wood Modification: Synthesis of Hydrophobic and Antibacterial Brushes from the Wood Surface.

The article presents the modification of ash wood via surface initiated activators regenerated by electron transfer atom transfer radical polymerization mediated by elemental silver (Ag0 SI-ARGET ATRP) at a diminished catalyst concentration. Ash wood is functionalized with poly(methyl methacrylate) (PMMA) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to yield wood grafted with PMMA-b-PDMAEMA-Br copolymers with hydrophobic and antibacterial properties. Fourier transform infrared (FT-IR) spectroscopy confirmed the covalent incorporation of functional ATRP initiation sites and polymer chains into the wood structure. The polymerization kinetics was followed by the analysis of the polymer grown in solution from the sacrificial initiator by proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). The polymer layer covalently attached to the wood surface was observed by scanning electron microscopy (SEM). The hydrophobic properties of hybrid materials were confirmed by water contact angle measurements. Water and sodium chloride salt aqueous solution uptake tests confirmed a significant improvement in resistance to the absorption of wood samples after modification with polymers. Antibacterial tests revealed that wood-QPDMAEMA-Br, as well as wood-PMMA-b-QPDMAEMA-Br, exhibited higher antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) in comparison with Gram-negative bacteria (Escherichia coli). The paper presents an economic concept with ecological aspects of improving wood properties, which gives great opportunities to use the proposed approach in the production of functional hybrid materials for industry and high quality sports equipment, and in furniture production.

Wettability performance and physicochemical properties of UV exposed superhydrophobized birch wood

The effect of prolonged ultraviolet (UV) irradiation on the performance of superhydrophobized birch and acetylated birch wood was investigated. The surface modification of the wood was based on a newly developed method using silicone nanofilaments. The combination of surface modification and acetylation of wood showed good wetting resistance also after 600 h of UV exposure, with water contact angles greater than 140° and water uptake 30 times lower by weight than that of the non-surface-modified wood as determined by multicycle Wilhelmy plate measurements. Scanning electron microscopy images revealed that the silicone nanofilaments can still be observed on the wood samples after UV irradiation. The surface-modified wood samples exhibited significant color change after UV exposure. FTIR spectra showed that lignin was degraded on both the non-surface-modified wood surfaces and the wood surface-modified with the silicone nanofilaments.

Temperature, Time, and Interactions between Them in Relation to Colour Parameters of Black Poplar (Populus nigra L.) Thermally Modified in Nitrogen Atmosphere.

Thermal modification of wood in nitrogen atmosphere permits its usability value to be improved. The aim of the research was to determine the impact of technological modification parameters at different levels on the colour of black poplar (Populus nigra L.). Black poplar was thermally modified in nitrogen atmosphere at a range of temperatures from 160 °C to 220 °C, at times between 2 h and 8 h. The parameters of wood colour were measured according to the CIE L*a*b* colour space model. The changes in a* and b* had a non-linear profile. The maximum value of a* for black poplar wood was achieved after a modification at the temperature of 200 °C, while the maximum value of the b* parameter was achieved after modification at 190 °C. Colour changes in the ΔE of black poplar after modification at 160 °C and 170 °C were similar, and the dynamics of changes increased after modification at the temperature of 180 °C. The highest value of ΔE, around 40, was observed after modification at the temperature of 220 °C and time of 8 h. There were no statistically significant differences between the ΔE for radial and tangential sections. Statistical analysis showed that modification temperature was responsible for the variability of the L* value in 90%, and in ca. 70% for the changes in parameters a* and b*. The influence of the modification time on the colour parameters was minor—below 4%. The influence of the interaction between modification temperature and time on the colour parameters was below 10%. As a consequence, in the case of ΔE of black poplar wood, the influence of temperature was at a level of ca. 80%. On the other hand, the influence of time and the interaction between temperature and time of modification was low—below 3%.

Wood modification for the synthesis of MOF@wood composite materials with increased metal–organic framework (MOF) loading

A wood modification with MA and APTES was achieved which enabled an increased MOF loading of MIL-53(Al) and ZIF-8 for a potential application of the MOF@wood composite in continuous filtration and catalysis.

Beech (Fagus orientalis) wood modification through the incorporation of polystyrene-ricinoleic acid copolymer with Ag nanoparticles

Beech (Fagus orientalis) wood modification through the incorporation of polystyrene-ricinoleic acid copolymer with Ag nanoparticles

Exploring volatile organic compound emission from thermally modified wood by PTR-ToF-MS.

Thermal modification of wood is a well-known industrial process performed to increase the durability and dimensional stability or to change the colour of natural wood. The treatment influences many other properties of wood including the emission of volatile organic compounds (VOCs). VOC release ultimately affects the quality of indoor air and the capability of having low VOC emission is often included as a key parameter for the attribution of quality labels. In the present work, wood from six tree species was subjected to different types of treatment and VOC profiling was carried out on both treated and untreated samples by means of PTR-ToF-MS. Different types of thermal treatment were tested, involving either overpressure or vacuum and the effect of different temperature profiles was evaluated. Hardwood and softwood showed different release profiles under all tested conditions: the headspace of softwood was richer in several VOCs, such as terpenes, phenols and C6-C9 aldehydes and carboxylic acids. Upon thermal treatment, terpene emissions decreased, whereas several other VOCs, such as formic acid, formaldehyde, furfural and acetic acid, were released in higher amounts. With its high sensitivity and throughput, PTR-ToF-MS appears to be a very powerful analytical tool, useful in supporting the selection of wood materials for different end uses.

Influence of environment, temperature and time of the thermal modification of ash wood (Fraxinus excelsior L.) on the cellulose weight average degree of polymerization

Influence of environment, temperature and time of the thermal modification of ash wood (Fraxinus excelsior L.) on the cellulose weight average degree of polymerization . Using the size-exclusion chromatography (HPLC SEC) method, the weight average degree of cellulose polymerization was determined. The polymer was isolated by the Kürschner-Hoffer method from ash wood (Fraxinus excelsior L.). The wood was thermally modified in different environments (nitrogen, steam and air) at 190°C and modification times of 2, 6 and 10 hours. Depending on the anaerobic atmosphere used, the highest values of the weight average degree of cellulose polymerization were obtained for the nitrogen environment, followed by steam and air. The effect of modification time on the weight average degree of polymerization was observed. The highest values were obtained for wood modified at 2 hours, then 6 and 10 hours of modification. The native wood showed the highest degree of polymerization. On the basis of the results obtained, it can be concluded that for the material studied the oxidation and degradation reactions occurring depend on the environment and time for a given temperature of wood modification.

COMPREHENSIVE APPROACH TO ENSURE DURABILTY OF EXTERNAL WOODEN STRUCTURES

The article deals with durability of wood, durability of wooden structures and surface modification of wood. We are trying to eliminate the factors causing degradation of wood with the use of photocatalytic materials. Those materials are efficient UV absorbers and they are able to destroy biological aggressors also. The planar particles of titanium oxide TiO2 were chosen for the purpose of our research and applied on a wooden surface. In our case, we used a water solution of TiO2. The main goal of our work was to study the interaction between planar particles of TiO2 and wood matter. The samples of pine wood (Pinus sylvestris) were monitored for 255 days and subsequently evaluated using an electron microscope. The use of TiO2 was compared with reference material and a reference commercial coating.

The Influence of Nanoparticles on Fire Retardancy of Pedunculate Oak Wood.

Traditional flame retardants often contain halogens and produce toxic gases when burned. Hence, in this study, low-cost, environmentally friendly compounds that act as fire retardants are investigated. These materials often contain nanoparticles, from which TiO2 and SiO2 are the most promising. In this work, pedunculate oak wood specimens were modified with sodium silicate (Na2SiO3, i.e., water glass) and TiO2, SiO2, and ZnO nanoparticles using the vacuum-pressure technique. Changes in the samples and fire characteristics of modified wood were studied via thermal analysis (TA), infrared spectroscopy (FTIR), and scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The results of TA showed the most significant wood decomposition at a temperature of 350 °C, with a non-significant influence of the nanoparticles. A dominant effect of sodium silicate was observed in the main weight-loss step, resulting in a drop in decomposition temperature within the temperature range of 36–44 °C. More intensive decomposition of wood treated with water glass and nanoparticles led to a faster release of non-combustible gases, which slowed down the combustion process. The results demonstrated that wood modifications using sodium silicate and nanoparticle systems have potentially enhanced flame retardant properties.

Surface and Physical Features of Thermo-Mechanically Modified Iroko and Tauari Wood for Flooring Application

The aim of the study was to determine the selected surface and physical properties of iroko (Milicia excelsa (Welw.) C.C. Berg) and tauari (Couratari spp.) wood after thermo-mechanical treatment (TMT) in relation to extractive content. During TMT, no chemicals are introduced into the wood, which distinguishes this method from a number of wood modification methods. The iroko and tauari wood were subjected to volumetric densification in a hydraulic press. The wood was densified in a radial direction at a temperature of 100 and 150 °C. The wood color parameters were measured using the mathematical CIE L*a*b* and L*C*h color space models. The roughness parameters of Ra and Rz parallel and perpendicular to the grain were investigated. The contact angle (CA) of the wood with distilled water was determined based on the sessile drop method. The equilibrium moisture content (EMC) and dimensional changes of the wood were determined for a climate with a temperature of 20 °C and a relative humidity (RH) of 9%, 34%, 55%, 75% and 98%. The tauari wood was less prone to color changes under the influence of TMT than the iroko wood. After densification, the iroko and tauari wood displayed a different character of roughness changes. The iroko wood featured the lowest level of roughness after TMT at 100 °C, and the tauari wood after TMT at 150 °C. The densified iroko and tauari wood were characterized by weaker dynamics in the changes in their respective contact angles than the non-densified wood. The higher the temperature of the TMT, the lower the EMC of the wood. Higher EMC values were observed for the tauari wood than for the iroko wood. This was due to the lower content of chloroform-ethanol extractives. Similar dependencies were obtained in the case of hot water extractives. The thermo-mechanically treated wood displayed a greater tendency towards dimensional changes in a climate with high relative air humidity, i.e., above 70%, compared to the non-modified wood.

Chemical modification of poplar wood featuring compressible rebound 3D structure as water treatment absorbents

This study investigated compressive strain and water absorption performances of chemically modified poplar wood (Populus tomentosa Carr). Two chemicals used were acidified sodium chlorite (NaClO2) and sodium hydroxide (NaOH) solutions. The Fourier transform infrared spectra confirmed that lignin and hemicellulose in modified wood cell walls were removed, resulting in a compressible rebound 3D structure in modified poplar wood verified through high-resolution scanning electron microscopic image analyses. This 3D structure was approved having excellent properties of compressible rebound and highly Water s absorption. In addition, experimental results indicated the chemically treated poplar wood had better plastic deformation with its strain up to 70% if compared to untreated wood of 14%. The modified wood maintained good resilience performance and no deformation in size after fifty compression-releasing cycles along longitudinal direction. The modified wood had its initial water absorption reaching 404%, and was able to maintain a water absorption at 388% after 20 cycles while still keeping 3D structure intact.

Life Cycle Assessment of Coated and Thermally Modified Wood Façades

Façades—their design, aesthetics, performance, type of cladding material, and understructure—determine architectural expression and form unique appearances of individual buildings. In connection to the sustainable development idea, wood façades provide one of the alternatives of a contemporary building exterior look. Façade cladding made of coated and thermally modified wood can be successfully used for these buildings. In addition, thermally modified wood allows the use of local European wood species, while keeping cladding elements relatively thin. On the other hand, wood has certain structural limitations and disadvantages due to the properties of wood. The main weakness is caused by the surface durability of wood and its related need for maintenance over time. The scope of the study was a comprehensive assessment of coated non-heat-treated and thermally modified wood façades, performed in terms of life cycle assessment. The aim was to identify which type of wooden façade had the lowest environmental impact. According to the EN 15804 + A2 standard, the principle of evaluation of environmental parameters “cradle-to-gate-with options” was used to evaluate wooden façades and coatings and surface preservation methods. Simulations with the SimaPro program showed that the thermal modification of wood has a significant impact on the environment at the product stage. Nonetheless the thermally modified façade without any surface coating showed the lowest environmental impact in a 30 year time-horizon of the “use stage”. It was showed that surface maintenance methods applied, the coatings used, and the frequency of their application play an important role in the environmental impact of the investigated wooden façades.

Influence of juvenile and mature wood on anatomical and chemical properties of early and late wood from Chinese fir plantation

The proportion of juvenile wood affects the utilization of wood seriously, and the transition year of juvenile wood (JW) and mature wood (MW) plays a decisive role in the rotation and the modification of wood. To find out the demarcation of JW and MW, the tracheid length (TL) and microfibril angle (MFA) of early wood (EW) and late wood (LW) from four Chinese fir clones were measured by optical microscopy and X-ray diffraction. Then the data were analyzed by the k-means clustering method. The correlation and the differences among wood properties between JW and MW were compared. Results indicated that the LW showed better properties than that of EW, but the anatomical differences between EW and LW did not influence the demarcation of JW and MW. The cluster analysis of TL and MFA showed that the transition year was in the 16th year and the transition zone of EW and LW was different among clones. The MW has longer and wider tracheid, thicker cell walls, and smaller MFA. In terms of chemistry, MW had a higher content of holocellulose, α-cellulose, less content of extract, but no significant difference in lignin content compared with JW. The stabilization of chemical components was earlier than that of the anatomic properties. Correlation analysis showed that there were strong correlations between the chemical composition and anatomical characteristics in JW and MW. In general, compared with chemical components, anatomical indicators were more suitable for JW and MW demarcation. The differences and correlations between JW and MW properties provide a theoretical basis for wood rotation and planting.

Surface Tuning of Wood via Covalent Modification of Its Lignocellulosic Biopolymers with Substituted Benzoates-A Study on Reactivity, Efficiency, and Durability.

Chemical modification of wood applying benzotriazolyl-activated carboxylic acids has proven to be a versatile method for the durable functionalization of its lignocellulosic biopolymers. Through this process, the material properties of wood can be influenced and specifically optimized. To check the scope and limitations of this modification method, various benzamide derivatives with electron-withdrawing (EWG) or electron-donating (EDG) functional groups in different positions of the aromatic ring were synthesized and applied for covalent modification of Scots pine (Pinus sylvestris L.) sapwood in this study. The bonded amounts of substances (up to 2.20 mmol) were compared with the reactivity constants of the Hammett equation, revealing a significant correlation between the modification efficiency and the theoretical reactivity constants of the corresponding aromatic substitution pattern. The successful covalent attachment of the respective substituted benzamides was proven by attenuated total reflection infrared (ATR-IR) spectroscopy, while the stability of the newly formed ester bond was proven in a standardized leaching test.

Dimensional Stability of Treated Sengon Wood by Nano-Silica of Betung Bamboo Leaves

Sengon (Falcataria moluccana Miq.) is one of the fastest growing wood that is broadly planted in Indonesia. Sengon wood has inferior wood properties, such as a low density and dimensional stability. Therefore, sengon wood requires a method to improve its wood quality through wood modification. One type of wood modification is wood impregnation. On the other hand, Betung Bamboo leaves are considered as waste. Betung Bamboo leaves contain silica. Based on several researches, nano-SiO2 could improve fast-growing wood qualities. According to its perfect solubility in water, monoethylene glycol (MEG) is used in the study. The objectives are to evaluate the impregnation treatment (MEG and nano-silica originated from betung bamboo leaves) in regard to the dimensional stability and density of 5-year-old sengon wood and to characterize the treated sengon wood. MEG, MNano-Silica 0.5%, MNano-Silica 0.75%, and MNano-Silica 1% were used as impregnation solutions. The impregnation method was started with 0.5 bar of vacuum for 60 min, followed by 2.5 bar of pressure for 120 min. The dimensional stability, density, and characterization of the samples were studied through the use of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results show that the treatment had a significant effect on the dimensional stability and density of sengon wood. Alterations in the morphology of treated sengon wood were observed through the full coverage of the pits on the vessel walls (SEM analysis results) and the detection of ethylene (FTIR analysis results) and silica (XRD and FTIR analysis results). Overall, the 0.75% MNano-Silica treatment was the most optimal treatment for increasing the dimensional stability and density of 5-year-old sengon wood.

Investigating the surface wettability and surface free energy of sodium silicate-impregnated poplar wood

The surface free energy of wood is an important property that influences later manufacturing process, such as wood gluing and finishing. Sodium silicate modifications of poplar wood inevitably alter wood’s surface free energy. The purpose of this study was to determine the effect of various impregnation times on the resulting surface free energy of radial and tangential sections of poplar wood specimens. The contact angles of standard probe liquids (i.e. distilled water, diiodomethane, formamide) on the surface of the wood were measured by contact angle goniometer, and a geometric average method and acid–base interaction method were applied to calculate and analyze the changes in the surface free energy. In addition, Fourier transform infrared spectroscopy was used to analyze the changes in the functional groups on the wood surface; after finishing the wood surface with water-based or oil-based paint, the paint film adhesion properties were also evaluated. The results indicate that sodium silicate modification can effectively improve the surface wettability and surface free energy of poplar wood. The modification treatment gradually creates hydrophilic groups (e.g. hydrogen bonds, free hydroxyl groups) on the wood surface, and their contents increase with increasing impregnation time. Additionally, by introducing Si-O–C moieties, the polarity, dispersion, and acid–base components of the wood surface all increase to varying degrees. Finally, the sodium silicate modification treatment worsens the adhesion of the paint films on the wood surface, although not to a significant extent.

Magnetron Sputtering Construction of Nano-Al Metallized Wood and Its Functional Research

The magnetron sputtering method was used to deposit nano-Al film on the wood surface of Pinus sylvestris L. var. mongholica Litv., and the material structure, electrical conductivity, mechanical properties and wetting properties were tested and characterized. When the sputtering time was 60 min, the average cross-grain sheet resistance of metallized wood was 695.9 mΩ, and the average along-grain sheet resistance was 227.2 mΩ. Load displacement decreased by more than 88%,elastic modulus increased by 49.2 times, hardness increased by 46 times andsurface hydrophobic angle was close to 130°. The grain size of the Al film on the wood surface was presented as nanoparticles, and the arrangement was uniform and dense. The results indicate that without any burden on the environment, the use of magnetron sputtering can quickly and efficiently achieve Al metallization on wood surfaces, so that the wood surface can obtain conductivity and hydrophobic properties. The elastic modulus and hardness of the wood surface were improved, the mechanical properties of the wood were effectively improved and the functional improvement of the wood was realized. This study provides a feasible method and basis for the study of the simple, efficient and pollution-free modification of wood.