Wood Surface Layer Research Articles

Preparation and application of wood-supported piezocatalyst with high efficiency and stability via partial hydrolysis of wood cellulose and hemicellulose with Lewis acid

The conveniently recoverable piezocatalyst with self-floating and stable performance has drawn wide attention. Herein, MoS2 was anchored on 1-cm-square eucalyptus wood blocks via a facile hydrothermal/solvothermal process to fabricate two floating piezocatalysts, i.e., MoS2/unpretreated wood (MUW) and MoS2/pretreated wood (MPW). FeCl3 solution was used as a Lewis acid to pretreat the wood through partial hydrolyzing cellulose and hemicellulose for an purpose to creat rich micropores for MoS2 loading in the wood and to form MoFe heterojunction. The piezocatalytic properties and performance of the prepared wood were systematically studied. The scanning electron microscopy confirms MoS2 was anchored on wood surface. The macroscopic photos show that MoS2 penetrated through the MPW interior whereas it was only loaded on the wood surface layer. The X-ray photoelectron spectroscopy reveals the shift of Mo 3d and S 2p, verifying the heterojunction formation of MPW. The Fourier transform infrared spectra prove the partial hydrolysis of wood matrix. In comparison to MUW, MPW had excellent piezocatalytic property, wide pH adaptability, convenient recyclability and high stability. Sildenafil and Cr6+ ions could be completely removed in 20 and 15 min, respectively, by MPW. Contrastly, the removal efficiency of sildenafil and Cr6+ by MUW was 78.6 % and 68.3 % in 20 and 15 min, respectively. After five cycles of use, the removal ratio of sildenafil was 62.4 % by MUW and 90.5 % by MPW in 20 min. The mineralization efficiency of sildenafil reached 99.2 % in 30 min by MPW, and various types of N/S-containing intermediates were effectively degraded. The electron spin resonance characterization and active species scavenging experiments displayed that e− and •O2− were major active species responsible for Cr6+ piezoreduction by MUW and MPW, while •O2− and •OH were the dominant species accounting for sildenafil degradation by MUW and MPW, respectively. And •OH was not generated in the MUW piezocatalysis process. MPW had higher piezoelectric current and lower resistance at the electron transfer interface than MUW. Conclusively, this study paves a new pathway for preparing new floating piezocatalysts with easy recyclability and high stability from biomass for wastewater treatment.

Characterization of hygrothermal, gas pressure and stress characteristics for poplar wood during unilateral surface densification

Unilateral surface compression in wood presents notable benefits, including reduced wood volume loss and energy consumption, rendering a highly promising and extensive utilization. However, shortcomings in compressed wood arise due to unclear gas pressure, temperature, and moisture content distribution within the wood during hot pressing. In this paper, the temperature and pressure distribution were analyzed utilizing an optical fiber temperature and pressure measurement system within the wood during hot pressing. Moreover, the moisture content, stress and strain in each layer at the end of hot pressing were discussed extensively. The results showed that the wood surface layer (SL) and subsurface layer (SSL) maximum temperature values were similar even with different layer thicknesses. Under sealing conditions, SL and SSL temperatures were generally 6 ℃ to 7 ℃ higher compared to unsealing conditions. The gas pressure maximum value exhibited an opposite order, gradually transferring to the core layer (CL) and declining as the processing time extended. During compression treatment, moisture migrated from the hot end to the cold within the wood. The moisture content displayed significant differences between the middle and end parts of the wood under unsealed conditions, with the disparity becoming more pronounced further away from the hot end. The transition region of the compressed wood served as a stress concentration area, experiencing the highest levels of stress. The dense region followed with the second highest stress levels, while the un-densified region exhibited the least amount of stress. Under the same process parameters, the thickness had little influence on the distribution of dense layers.

Impact of surface finishing technology on slip resistance of oak lacquer wood floorboards with distinct gloss levels

ABSTRACT The choice of surface finishing technology for floorboards can significantly influence the risk of slipping. This study aimed to assess the impact of surface finishing technology on the likelihood of slippage, focusing on lacquered floorboards made of northern red oak (Quercus rubra L.). Four finishing methods were applied to the floorboard surfaces, with the primary distinction between the tested variants being the level of glossiness in the top layer, ranging from 3 to 20 gloss units (GU). To evaluate slip risk, tests were conducted using the British portable skid resistance tester (BSRT), providing numerical values in the form of the British pendulum number (BPN) and the slip resistance value (SRV) for qualitative comparisons. The analyses revealed that depending on the type of lacquered wood surface layer, the difference in BPN could vary from 46% to 77% for dry tests and from 48% to 60% for wet tests. Matte lacquer finishes, specifically at 19 GU, exhibited the smallest slip risk, while glossy finishes (4 GU) demonstrated the greatest slip risk, especially when the surface was wet. In terms of wet test results, the least slip risk, regardless of wood grain direction, was observed for variant No. 4 (low glossiness at 4 GU), with an SRV value ranging from 51 to 53. Conversely, variant No. 1 (high gloss at a mean of 19 GU) recorded the poorest slip resistance properties, with an SRV between 29 and 31. These findings suggest that matte lacquer finishes generally provide a safer option compared to glossy finishes, and the inclusion of brushing during production can enhance slip resistance. Furthermore, the direction of the wood grain was identified as a contributing factor to slip risk, with a 0° grain orientation presenting the highest risk. These insights can be valuable for flooring manufacturers and installers in selecting and applying finishes that effectively minimize the risk of slipping. These findings can be used by flooring manufacturers and installers to select and apply finishes that minimize slip hazard.

Wood Surface Finishing with Transparent Lacquers Intended for Indoor Use, and the Colour Resistance of These Surfaces during Accelerated Aging.

This work evaluates the effects of accelerated aging on the discolouration of surface-treated spruce wood and oak wood coated with solvent-based polyurethane lacquers, and surface-treated spruce wood coated with water-based transparent coating systems. All concerned coating materials were intended for indoor use. It was also explored how the colour stability of spruce wood and oak wood surfaces treated with solvent-based polyurethane lacquers was affected by wood surface layer modifications with pigment or stain mordants applied before these lacquers. Another issue studied was how the lignin stabilizer admixed into the primer and pigments admixed into the top coating layers affected the stability of water-based coating systems on spruce. The experimental results showed that the accelerated aging process with a simulation of indoor conditions induced significant discolouration of wood surfaces coated with solvent-based polyurethane lacquers and water-based coating systems. There were also confirmed significant impacts of all the studied factors (wood species, lacquer/coating system type, lacquer modification, wood pre-treatment with pigment and stain mordants). The spruce wood surfaces coated with solvent-based polyurethane lacquers were less stable (ΔE = 10-19, dependent on the lacquer type) than the oak surfaces treated in the same ways (ΔE = 4-11). There were also confirmed significant impacts of the particular surface treatment on the colour stability as well as significant impacts of wood surface pre-treatment with pigment and stain mordants (ΔE = 4-17-for spruce wood, and ΔE = 5.5-13-for oak wood). In the case of water-based lacquers, the ΔE values ranged between 3 and 11 (according to the coating system type). The results show that an appropriate UV absorbent combined with an appropriate lignin stabilizer and pigment mordant may enable attaining the required colour stability for a given surface treatment applied on a given wood species.

Development of Microwave Slow-Wave Comb Applicators for Soil Treatment at Frequencies 2.45 and 0.922 GHz (Theory, Design, and Experimental Study)

In agriculture and industry, it is often necessary to heat surface layers of material like soil, timber, concrete, and so on, with microwave (MW) energy. Traditional MW irradiators (antennas) cannot restrain their heating to the surface, with the energy penetrating deeply into the material. Slow-wave comb applicators can provide the required energy distribution in the surface layer. Theoretical analyses of the comb applicators used for heating were carried out and on this basis, three comb applicators were designed and made for soil treatment: two applicators Comb 1 and Comb 2 for frequency 2.45 GHz and Comb 3 for frequency 0.922 GHz. An experimental study of applicators was carried out using two MW plants: 30 kW (2.45 GHz) and 60 kW (0.922 GHz) for heating soil with moisture content in the range from 32% to 173% and density 460 to 1290 kg m−3. The study showed that comb applicators provide the following advantages: reduction in energy dissipation in material depth and release of the significant part of applied MW energy in layers close to the applicator surface. Comb applicators can provide the required soil top layer treatment (sterilization) with reasonable efficiency and can be recommended for practical use in shallow soil treatment for weed seed and pathogen control in agricultural applications. Comb applicators can also be used for effective heating and MW treatment of the surface layers of wood, concrete, bricks, plastics, and other dielectric materials.

Wettability of Wood Surface Layer Examined From Chemical Change Perspective

The effect of artificial ageing on spruce (Picea abies), beech (Fagus sylvatica L.), birch (Betula pendula), and sessile oak (Quercus petraea) wood surfaces were investigated using qualitative (total phenolic and total soluble carbohydrate content) chemical examination methods. During ageing (∑240h), the influence of surface chemistry modifications was monitored by contact angle measurements of polar, dispersive (distilled water), and dispersive (diiodomethane) liquids. The results clearly show the relation between the ratio of main chemical components of the wood surface layer and surface wettability during artificial radiation. The identified surface chemistry modifications cause more significant change in the contact angle of polar and dispersive liquid, relative to the change of dispersive liquid contact angle. Chemical changes of the wood surface layer are due to the degradation of the main wood components (cellulose, hemicelluloses, and lignin) which can be properly monitored by total phenolic (TPC) and total soluble carbohydrate content (TSCC) measurements.

Characterization of moisture states and transport in MUF resin-impregnated poplar wood using low field nuclear magnetic resonance

In this study, the spin–spin relaxation time (T2) distributions of free water and bound water, as well as the moisture content (MC) profiles of MUF resin-impregnated poplar wood (Populous tomentosa) sample (RI) were investigated by low-field nuclear magnetic resonance, with the aim of providing insights into how MUF resin impregnation affects the moisture states and moisture transport in modified poplar wood during drying. The T2 curves demonstrated that the resin treatment did not increase the number of peaks in the T2 distributions, but affected the T2 value as compared to the control. Above the fiber saturation point (FSP), the T22 (corresponds to the free water in wood rays and wood fibers) of the RI sample exhibited an increase compared to the control, while the T23 (corresponds to the free water in the vessels) was almost unchanged. Below the FSP, a shorter T21 (corresponding to the bound water) of the RI sample was observed compared to the control. The drying curves and MC profiles indicated a significant difference in the moisture transport in the RI sample as compared to the control. The gradually cured resin system in the wood surface layer during drying provided a barrier for the transfer of water in the center layer toward to the surface, causing the resin curing reactions in the surface and core layers to be out of sync. Therefore, a more significant MC gradient was observed for the resin-impregnated sample.

ОПРЕДЕЛЕНИЕ КИНЕТИЧЕСКИХ ПАРАМЕТРОВ ТЕРМОДЕСТРУКЦИИ И ГРУППЫ ОГНЕЗАЩИТНОЙ ЭФФЕКТИВНОСТИ ДРЕВЕСИНЫ СОСНЫ, МОДИФИЦИРОВАННОЙ БОРАЗОТНЫМ АНТИПИРЕНОМ

Wood is a combustible material. To reduce combustibility, wood is modified with functional compounds of phosphorus, boron and nitrogen, inoculation of which changes the chemical composition of the surface layer of wood and its structure. The mechanism of action of flame retardants is related to their influence on the energy and entropy characteristics of the thermodestruction process. Considering that boron nitrogen compounds are effective flame retardants and react with wood components under “mild” conditions, the effect of grafting of a borax modifier on the kinetic parameters of wood thermal decomposition is studied. The kinetic parameters (activation energy and preexponent value) are determined by thermal analysis using TGA curves (integral method). A 50 % aqueous solution of monoethanolamine (N→B) trihydroxyborate is used as a modifier; samples of unmodified pine wood are used as controls. The experimental data obtained indicate that the surface modification of pine wood with boron nitrogen fire retardant provides the material with group II fire protection efficiency (modifier consumption-150g/m2). The flame retardant effect of the boron nitrogen modifier is associated with a lower value of the activation energy of its thermal destruction process. The contribution of the entropy factor in reducing the combustibility of modified wood is less expressed. The use of monoethanolamine (N→B) trihydroxyborate as a wood flame retardant is advisable in an oxidizing atmosphere.

Analysis of the influence of instrumental and regime factors on the quality of wood grinding

The grinding tool does not have a solid cutting edge, in most cases the front angles for abrasive grains are negative, the grains have rounded vertices and an irregular geometric shape. Grinding should be considered as a process of cutting-scratching the surface layer of wood with a large number of abrasive grains of the grinding tool. The main purpose of the grinding process is to prepare the surface for finishing by eliminating irregularities and defects of the previous processing. The effectiveness of grinding to a greater extent depends on the processing conditions, characteristics and properties of the grinding tool. Theoretical studies and analysis of the derived equations for determining the critical values of the rake angle, cut thickness and cutting speed show that all of the above parameters have a significant effect on the amount of lifting of the processed material by abrasive grain and the intensity of the appearance of contact fractures. An increase in the critical thickness of the slice leads to an increase in the deformation of the surface layers of the processed material, and, consequently, to an increase in the depth and number of contact fractures. The increase in the absolute value of the rake angle leads to the need to increase the critical cutting speed to ensure the conditions of chip formation. In general, an increase in cutting speed always has a positive effect on chip formation conditions and on the quality of the machined surface. An increase in the modulus of the rake angle leads to a deterioration in the conditions of chip formation and surface quality. An increase in the radius of curvature of the cutting edge of the grain leads to an increase in the critical thickness of the slice, which entails an increase in contact deformations and fractures.

Application of Confocal Raman Microscopy for the Analysis of the Distribution of Wood Preservative Coatings

The distribution of wood preservative coatings in wood surface layer was assessed at the cellular level using confocal Raman microscopy. Raman images were created based on the fingerprint Raman bands of the different wood polymers and coating components (resin and pigment). The wood cell walls and the distribution of the resin and pigment were clearly visualized at the same time. It was concluded that confocal Raman microscopy is suitable for the evaluation of the microdistribution of wood coatings, providing valuable information for the improvement of wood coating technology.

Kinetic Parameters of Smoke Aerosols during Combustion of Modified Wood

The most dangerous factors of fire are formation of smoke and thermal decomposition of toxic products. In case of fire, smoke spreads to evacuation routes. In this case, a person may be disoriented and feel panic. Smoke is an aerosol produced by the thermal decomposition of materials. The study object is the wood, which is widely used in construction. Up to date, the influence of wood species and wood surface layer modifiers on the smoke-forming ability has been studied. The effect of wood surface layer modifiers on the properties of aerosols remains insufficiently studied. The objective is to evaluate the effect of the wood surface layer modifiers on the formation and stability of smoke aerosols. In the course of work, the ultimate analysis method was used to assess the modifying effect of selected phosphoric acid esters. It is known that these compounds constitute effective flame retardants and are able to provide the biological stability of the wood. Granulometric analysis was additionally performed to evaluate the aerosol’s properties. To evaluate the energy characteristics of the modified wood surface, the “neutral drop” method was used. As a result of the studies, a percentage phosphorous content was obtained in the surface layer of the wood before and after thermal decomposition. This data made it possible to conclude that the thermal effect of diethyl phosphite is very effective and stable when it is used as a modifier. Based on the granulometric analysis, the size distribution of solid aerosol particles was obtained. When using the selected modifiers, the maximum particle size of the aerosol is reduced, which in turn reduces the optical density of the smoke. Phosphoric acid esters affect the kinetic parameters of the aerosol, which were obtained on the basis of mathematical calculation. Diethyl phosphite produces the greatest effect on the decrease in the aerosol’s stability. The formation of an aerosol having a smaller particle size occurs during thermal decomposition of the modified wood having a thermally stable surface. Therefore, the modification of wood by phosphoric acid esters reduces its propensity to smoke-generating ability, which determines the reduction in death rate of humans in the event of fire.

Heat Treatment of Wood in Liquids

Modern alternative to chemical methods of wood modification is heat treatment, which allows to increase biological stability, to reduce the hygroscopicity of the material and to improve the appearance of products. One of such technologies is heat treatment in liquids. However, this method is characterized by a considerable duration of the process because of cooling the material directly in the liquid. The aim of this work is to improve the technology of thermal modification of wood in liquids by reducing the duration of cooling phase without additional energy consumption. The results of experimental studies of the proposed technology of heat treatment of wood are presented. The obtained data on changes in wood density show that at increasing the average density of the material, there is a reduction in the density of its central layers that is explained by impregnation of the surface layers of wood with wood agent. It can be stated, basing on the analysis of the depth of impregnation of different wood species, that the rate of flow of impregnating liquid is directly proportional to the temperature of heat treatment, in the same time the depth of penetration of the treatment agent into the lumber depends not on treatability of natural wood but its basic density. Therefore, heat treatment of wood in hydrophobic liquids is more rational to use for hard species with greater density, and consequently, a smaller depth of penetration of the treatment agent, which will reduce the flow rate of hydrophobic liquid when carrying out the process and avoid large losses of material during subsequent mechanical processing.

Influence of modifiers on coked foam structure and properties formed with thermal decomposition of wood

Wood is a material that forms a surface layer of coke when burning. Properties of the coke layer significantly impact the fire resistance of structures due to the change of the structure working section reduction rate. This paper discusses the research of how the wood surface layer modifiers influence the structure and properties of the coke layer formed with thermal decomposition of wood. As modifiers have been used phosphorus flame-retardants. To evaluate how the modifiers influence the coke layer formation process, the source and modified samples of pine have been analyzed before and after thermal decomposition using the element analysis, electron microscopy, and adsorption. Thermal analysis has been accomplished using the thermogravimetry (TG), differential thermogravimetry (DTG), and differential scanning calorimetry. To evaluate the fire protection efficiency of the modified wood, fire tests have been accomplished. Such tests were tests to determine the magnitude of weight loss during combustion, flame spread index and the coefficient of smoke-ability. Based on the acquired data, it was identified that when the modifiers are used, and these modifiers enter into efficient superficial chemical reaction with wood under mild conditions, the thermal decomposition occurred under mild conditions - the first stage of thermal decomposition transits to the lower temperatures zone. This reduces the thermal effect of thermal decomposition reaction. There is a decrease in weight loss during thermal decomposition. This results in formation of the strong and structured, thermally stable surface, which is less adsorption ability, specific surface area and porosity reduction. This explains high rate of fire protection and low smoke-generating capacities.

Sandwich-structured wood flour/HDPE composite panels: Reinforcement using a linear low-density polyethylene core layer

Sandwich-structured panels, composed of two surface layers of wood flour/high-density polyethylene composite (WPC) and a core layer of linear low-density polyethylene (LLDPE), were prepared by hot-press. The single-layer WPC panels were used as controls, with wood flour contents ranging from 55 to 84%. The sandwich-structured panels showed an improvement in both flexural and impact strength of up to 42% and 77%, respectively, and water absorption was considerably reduced compared to the controls. The LLDPE core layer did not cause substantial change in creep and relaxation behavior, but resulted in an increase in the linear coefficient of thermal expansion.

The kinetic parameters of aerosols formed during combustion of modified wood

The paper studies kinetic properties of aerosols formed in thermal degradation of wood. The impact of modifying agents in wood surface layer on the quantitative composition of smoke aerosol solids was analyzed. For this purpose, grain-size of aerosol solids was analyzed, and the physical and chemical properties of source and modified wood were assessed.

ВЛИЯНИЕ МОДИФИКАТОРОВ НА ХАРАКТЕРИСТИКИ ПЕНОКОКСА, ОБРАЗУЮЩЕГОСЯ ПРИ ТЕРМИЧЕСКОМ РАЗЛОЖЕНИИ ДРЕВЕСИНЫ

Introduction. Currently, wood-based construction materials are in high demand in the field of construction around the globe. The study of the original wood composite in order to improve its characteristics through various methods is scientific pre-requisity for such development. When wood burns, it forms a surface coke layer, which can differ in mechanical and thermal stability. These parameters produce a significant effect on the fire resistance rating of building structures due to a change in the reduction rate of the structure useful cross section. Materials and methods. The studies carried out during the work are related to the evaluation of the characteristics of coke layer formed during thermal decomposition of wood. Thermal analysis methods, the scanning electron microscopy method and the water adsorption method were used. The original sapwood of pine, as well as the wood modified with effective fire-retardant agents were used in the course of work. Results. Based on conducted experiments process graphic dependences of thermal decomposition have been obtained, as well as images, obtained by an electronic microscope. In addition, the dependence of adsorptive capacity of wood after thermal decomposition has been obtained. Discussions. As a result of the study, it was found that with the use of modifiers based on organophosphorous compounds, entering into effective reaction with wood, structuring of the surface layer occurs after thermal decomposition while reducing the size of specific surface area of wood. Conclusions. Based on the analysis of experimental data, we can conclude that because of the use of efficient wood surface layer modifiers, thermal decomposition takes place under “mild” conditions that is the shift of the first stage of thermal decomposition to the area of lower temperatures with non-severe exothermic effects. The loss of weight of samples during combustion is significantly reduced. This causes high fire-retardant efficiency and low smoke-generating capacity.

Analysis of the process of wood plasticization by hot rolling

In this research, a mathematical model is derived to enable analytical determination of effective ultimate forces in the process of plasticization of the surface layer of wood. The experimentally determined thermo-mechanical properties of the material subjected to the process of plasticization are used in defining the structure of the model. The analysis of plastic strain in the layer in consideration is based on a generalised model of an ideally rigid-plastic medium, including certain modifications. Considering the anisotropic properties of wood, the Azzi-Tsai-Hill (ATH) strength criterion is applied which takes into account variation in the response of the loaded material depending on the direction. The article presents also results of FEM analysis of the same process of hot rolling of wood.

Surface thermodynamic parameters of modified wood

Energy characteristics of modified wood are studied in the paper. Application of this approach during the study of wooden materials allows forecasting the efficiency of modifiers for surface layer of wood. Phosphites, the efficient fire-retarders, were applied as modifiers. Using the example of a number of ethers with various alkoxy substituents of phosphorus atom, we have made an attempt to associate surface thermodynamic properties of modified wood and formation of properties for fire-, bio- and smoke protection. The dependence of change of energy characteristics and surface structure of wood on the nature of modifiers is determined. To study energy characteristics of wood, modified by various compounds, the following characteristics were used: σ surface tension and ΔG free enthalpy gradient. Easy Drop setting and the corresponding software were used to determine these values. According to the obtained data, the conclusion is made about the influence of modifiers on energy characteristics of wood. The high degree of modification (% P) causes bigger change of Gibbs energy, which determines formation of high-level fire-, bio- and smoke protection. Diethyl phosphite is the most efficient modifier. Formation of fire-protective properties stipulates long-term operation of wood and wood-based materials.

A Study on Capillary-porous Structure of Wood Modified with Boron-Nitrogen Compounds

Capillary-porous structure of wood modified with boron-nitrogen compounds was studies by sorption methods. Specific surface area of the suport was found to be reduced up to three folds.Changes of structure of the wood surface layer treated with aqueas solutions of boric acid and ethanolamines as well as the possibility of forming 4-coordinate boron-nitrogen compounds in situ, directly on the wood surface, were investigated. Stepwise treatment of wood surface with boric acid and ethanolamines in different order was found not to cause significant changes in the capillary-porous structure, which is apparently due to the difficulties of formation of 4-coordinate boron-nitrogen compounds in situ.

Diffusion-model-based risk assessment of moisture originated wood deterioration in historic buildings

The paper deals with investigating the response of wood artefacts to relatively fast changes of ambient air humidity and temperature and with estimating the wood stress and strain variations due to the moisture content changes. The moisture content dynamics are described by a specially developed model based on the Fick's second law and further transformed into a state space model. The surface boundary conditions are tied up with a model of equilibrium moisture content. As the final objective of the diffusion model application the moisture induced stress and strain in the wood artefact is assessed. The obtained stress amplitudes are compared with the yield point stress as the boundary of elastic deformations. The model application has particularly confirmed that the concerned transfer phenomena have to do with only a thin surface layer of wood while the deeper layers are not touched by them. For a given set of data provided from unheated historical churches the stress and strain responses are evaluated and compared with their admissible limits in order to estimate the risk of potential moisture originated damage.