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Influence of thermal modification and sanding parameters on finest particle content in pinewood dust
Interlaboratory study of the operational stability of automated sorption balances
AbstractAutomated sorption balances are widely used for characterizing the interaction of water vapor with hygroscopic materials. These instruments provide an efficient way to collect sorption isotherm data and kinetic data. A typical method for defining equilibrium after a step change in relative humidity (RH) is using a particular threshold value for the rate of change in mass with time. Recent studies indicate that commonly used threshold values yield substantial errors and that further measurements are needed at extended hold times as a basis to assess the accuracy of abbreviated equilibration criteria. However, the mass measurement accuracy at extended times depends on the operational stability of the instrument. Published data on the stability of automated sorption balances are rare. An interlaboratory study was undertaken to investigate equilibration criteria for automated sorption balances. This paper focuses on the mass, temperature, and RH stability and includes data from 25 laboratories throughout the world. An initial target for instrument mass stability was met on the first attempt in many cases, but several instruments were found to have unexpectedly large instabilities. The sources of these instabilities were investigated and greatly reduced. This paper highlights the importance of verifying operational mass stability of automated sorption balances, gives a method to perform stability checks, and provides guidance on identifying and correcting common sources of mass instability.
Kiln-drying effectiveness as influenced by moisture content and density variation within a Scots pine timber batch
Sorption properties of paper treated with silane-modified starch
AbstractSorption properties of paper products are important when applying paper as the packaging material. Hydrophobicity, i.e. reduced affinity of paper surface to liquid water, is of particular importance from the point of view of the direct impact on packed goods. However, hygroscopicity of the material is significant during storage of goods. The analysis of changes in the hygroscopic properties of paper products induced by the treatment with silane modified starch was presented. The results on the hygroscopicity of treated paper were related to the previously published results on the hydrophobicity. The discrete values of equilibrium moisture content allowed constructing adsorption and desorption isotherms. The three-parameter Guggenheim, Anderson, and De Boer (GAB) model, the four-parameter Generalized D’Arcy and Watt (GDW), and Yanniotis and Blahovec (Y-B) sorption isotherm models were used to quantify the hygroscopic properties for all options of untreated and modified paper samples. The effectiveness of silanes for improving hygroscopic properties was determined and compared to their impact on hydrophobicity of the studied materials. It was found that 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane was the only silane improving hydrophobic and hygroscopic properties. The analysis of the applied models of sorption isotherms depicted that the GAB model was not valid for describing water sorption isotherms in the case of the tested materials, while the GDW and Y-B models provided a much more realistic description of water sorption mechanisms. The evaluation of the results of fitting the GDW model indicated that water molecules bonding to the primary sites was the dominating mechanism of sorption.
Interlaboratory study of the quality of water vapor sorption data for wood from automated sorption balances
Abstract Automated sorption balances are widely used for characterizing the interaction of water vapor with hygroscopic materials. This paper is part of an interlaboratory study investigating the stability and performance of automated sorption balances. A previous paper in this study investigated the mass, temperature, and relative humidity (RH) stability of automated sorption balances by looking at the mass change of a non-hygroscopic sample over time. In this study, we examine the mass stability of wood samples held at constant RH for seven to ten days after a step change. The reason for the long hold times was to collect data to “operational equilibrium” where the change in mass is on the order of the inherent operational stability of the instrument. A total of 80 datasets were acquired from 21 laboratories covering absorption with final RH levels ranging from 10 to 95%. During these long hold times, several unusual behaviors were observed in the mass-vs-time curves. Deviations from expected sorption behavior were examined by fitting the data to an empirical sorption kinetics model and calculating the root mean square error (RMSE) between the observed and smoothed behavior. Samples that had a large RMSE relative to the median RMSE of the other datasets often had one of several types of errors: abrupt disturbances, diurnal oscillations, or long-term mass decline during an absorption step. In many cases, mass fluctuations were correlated with changes in the water reservoir temperature of the automated sorption balance. We discuss potential errors in sorption measurements on hygroscopic materials and suggest an acceptable level of RMSE for sorption data.
Fine dust after sanding untreated and thermally modified spruce, oak, and meranti wood
AbstractAirborne wood dust poses health and safety risks in the construction and furniture industry. The study verified whether the thermal modification affects the share of fine wood dust particles (< 10 μm) generated during spruce, oak, and meranti wood sanding. The experimental research involved nine material variants, including three wood species in three states: untreated, thermally modified at 160 °C, and thermally modified at 220 °C). To collect at least 200 g of each dust sample, a belt sander with P80 sandpaper and a belt speed of 10 m/s was used, along with a dust collector. The collected dust was then separated into fractions using a set of sieves with aperture sizes of 2000, 1000, 500, 250, and 125 μm. A laser particle sizer was employed to measure the sizes of dust particles in the under-sieve fraction (dust with particle sizes smaller than 125 μm). The under-sieve fraction was decomposed into three subfractions, with particle sizes: <2.5, 2.5-4.0, and 4.0–10 μm. Surprisingly the results indicate that sanding dust from thermally modified wood generates a lower average mass share of potentially harmful fine particle fractions than dust from untreated wood. Oak dust contained a higher mass share of fine particles compared to the spruce and meranti dust samples. Dust from thermally modified oak and meranti wood had a lower content of harmful particle fractions than dust from untreated wood. The average mass shares of these dust fractions for modified wood at 160 and 220 °C showed no statictically significant differences (p < 0.05). Conversely, spruce dust had a low content of fine fractions because spruce particles exhibit a more irregular elongated shape. The study considered the extreme temperatures of 160 and 220 °C used in the thermal modification of wood. Therefore, the above statements are assumed to be valid for all intermediate thermo-modification temperatures.
Analysis of stress development during kiln drying of beech timber
AbstractBefore use, timber must have reduced moisture content. Kiln drying causes cracking risk. This study aims to evaluate the risk of cracking during the drying of beech wood samples using the response surface methodology. Additionally, we aim to develop an empirical model that describes critical tensile stress during the early drying stages and the air parameters commonly used in kiln-drying schedules for beech timber, specifically, the effects of dry-bulb temperature (DBT) and wet-bulb depression (WBD). Nine options of drying conditions were analyzed in the study according to the Central Composite Design assumptions; they were combinations of three options of DBT (30, 40, and 50 °C) and three options of WBD (4, 5, and 6 °C). During the experiments, tangential shrinkage of the wood samples was completely restrained with a load cell that measured generated tensile drying stresses. The results of the ANOVA analysis confirmed that the DBT is the only factor significantly influencing the tensile stress at failure (σf). The second-order effect between DBT and WBD has also been confirmed. The drying condition causing the highest risk of cracking was shown using the multiple contour plots of tensile stresses and the moisture content at failure (MCf). Reliability theory was used to predict the cracking risk of wood tissue. The analysis confirmed the dependence of the cracking risk of wood tissue on drying conditions. When DBT is equal to 30 °C, the cracking risk increases as the air relative humidity (RH) decreases. However, during the drying of beech wood samples at a temperature of 50 °C, decreasing the RH in a range corresponding to the increase of WBD from 4 to 6 °C reduces the cracking risk, which is indicated by the lower moisture content at failure (MCf) of the wood samples. Graphical Abstract
Hydrophobic and hygroscopic properties of cellulose treated with silicone agents
AbstractThe effects of various cellulose treatments on the hydrophobic properties and sorption behavior with respect to liquid water uptake and water vapor sorption were examined within the study. Different hydrophobic agents based on silicon compounds were applied to improve the properties of cellulose-based sheets. The 1H,1H,2H,2H perfluorooctyltriethoxysilane treatment increased hydrophobicity significantly, while N-octyltriethoxysilane and inorganic sodium silicate solution treatments only slightly affected the properties. Silicone-cellulose interaction varied, influencing the fiber saturation and moisture content of the material. The swelling differences between untreated and treated cellulose and, consequently, the uncovering of new active sorption sites during a swelling process and the increase in the content of bound water were confirmed by the T2 relaxation times analysis. The GDW sorption model estimated maximum water content but lacked activation dynamics. The blocking phenomenon of active sorption sites together with silicone improved hydrophobicity had different mechanisms for applied agents. The 1H,1H,2H,2H perfluorooctyltriethoxysilane additionally cross-linked silane structure and restricted cellulose swelling.
Characteristics of Chitosan Films with the Bioactive Substances—Caffeine and Propolis
Chitosan is a natural and biodegradable polymer with promising potential for biomedical applications. This study concerns the production of chitosan-based materials for future use in the medical industry. Bioactive substances—caffeine and ethanolic propolis extract (EEP)—were incorporated into a chitosan matrix to increase the bioactivity of the obtained films and improve their mechanical properties. Acetic and citric acids were used as solvents in the production of the chitosan-based films. The obtained materials were characterized in terms of their antibacterial and antifungal activities, as well as their mechanical properties, including tensile strength and elongation at break. Moreover, the chemical structures and surface morphologies of the films were assessed. The results showed that the solution consisting of chitosan, citric acid, caffeine, and EEP exhibited an excellent antiradical effect. The activity of this solution (99.13%) was comparable to that of the standard antioxidant Trolox (92.82%). In addition, the film obtained from this solution showed good antibacterial activity, mainly against Escherichia coli and Enterococcus faecalis. The results also revealed that the films produced with citric acid exhibited higher activity levels against pathogenic bacteria than the films obtained with acetic acid. The antimicrobial effect of the chitosan-based films could be further enhanced by adding bioactive additives such as caffeine and propolis extract. The mechanical tests showed that the solvents and additives used affected the mechanical properties of the films obtained. The film produced from chitosan and acetic acid was characterized by the highest tensile strength value (46.95 MPa) while the chitosan-based film with citric acid showed the lowest value (2.28 MPa). The addition of caffeine and propolis to the film based on chitosan with acetic acid decreased its tensile strength while in the case of the chitosan-based film with citric acid, an increase in strength was observed. The obtained results suggested that chitosan films with natural bioactive substances can be a promising alternative to the traditional materials used in the medical industry, for example, as including biodegradable wound dressings or probiotic encapsulation materials.
Chitosan Films with Caffeine and Propolis as Promising and Ecofriendly Packaging Materials
This study addresses challenges faced by the packaging industry in finding suitable natural and biodegradable materials that can replace plastics while preserving the superior quality and freshness of the items contained within. Chitosan, a biodegradable natural polymer, shows great potential as a matrix for ecofriendly and biodegradable composite materials. In the present study, bioactive substances such as caffeine (CAF) and propolis extract (EP) were used for the enhancement of the bioactivity of chitosan-based films. Two acidic solvents, acetic acid and citric acid, were used to produce chitosan films. The study examined the antioxidant capabilities of the solutions used for film formation; similarly, the characteristics of the resultant films were also examined, encompassing antimicrobial, barrier, and mechanical characteristics. The findings suggested that the use of additives exhibiting antioxidant activity, such as CAF and EP in the chitosan matrix can be an effective method to counteract oxidative stress in food packaging. The study also showed that films produced with citric acid exhibit antimicrobial activity against many strains of bacteria, including foodborne pathogens. In addition, the antimicrobial activity of chitosan/citric acid film can be increased by adding CAF and EP. The results confirmed that both the additives and the acids used affect the mechanical and barrier features of the obtained chitosan-based films. This study suggests that chitosan films supplemented with natural bioactive substances have the potential to serve as viable replacements for traditional plastics in the packaging sector.
Transient water vapor diffusion in paper treated with methyltrimethoxysilane modified starch
Abstract The interaction of cellulose paper with water is a major hindrance to its broader application. This study, which introduces a novel approach to understand water vapor diffusion in both untreated and treated paper, aims to identify the diffusion coefficient, a crucial property in improving the hydrophobicity of paper. The treatment process utilized an aqueous solution of starch or starch modified with methyltrimethoxysilane (MTMS). While the initial sorption method is frequently used to determine the diffusion coefficient, this study found that it could lead to significant errors due to the non-Fickian behavior exhibited by lignocellulosic materials. This behavior causes that the hygroscopic equilibrium is not instantly obtained by surface of paper. It also induces slowing down moisture diffusion in its final stage due to molecular relaxation. For the first time, the modified convective boundary condition was introduced into the moisture diffusion model in paper materials. The results from vapor sorption experiments demonstrated this non-Fickian behavior, particularly at high values of air relative humidity. The study also revealed that the commonly applied first kind boundary condition is not applicable, even for thin paper samples, inhibiting the use of the initial sorption method for determining the diffusion coefficient. While the treatment with starch and MTMS significantly improved the hydrophobic properties of paper, it didn’t alter substantially its hygroscopic properties, potentially due to not blocking active sorption sites of cellulose fibers. This research underscores the need for further investigation into the chemical modification of cellulose fibers to improve the hydrophobicity of paper.