Wood Moisture Research Articles

Predicting wood moisture classes by sound frequency spectra and Explainable Machine Learning during milling

ABSTRACT Varying moisture content in wood lead to problems in the automatic selection of optimised machining parameters. Therefore, production in the wood sector can be improved by the automatic identification of moisture classes during machining. In this work, wood milling was monitored by a novel optical microphone to detect differences in wood moisture classes. A full factorial randomised design was executed along with four moisture classes (dried, conditioned, wet and frozen) and two cutting speeds as independent variables. The measured signals were segmented by extracting information from each cut and were transformed to the frequency domain. A supervised univariate feature ranking based on χ ²-tests was applied to select the most important frequencies. Machine Learning was applied to the selected spectral data to classify the cutting speeds and moisture classes. After testing several classification models, ensemble models with regression-tree learners were the best-performing model type achieved an average validation accuracy of 97.2%. The model explanation was done by Local Interpretable Model-Agnostic Explanation based on regression trees as a simple model, where the frequencies that are responsible for the separation of the data could be identified and were used for retraining the model, achieving a validation accuracy of 90.5%.

Effect of lignin on veneer densification and set-recovery

Wood densification, aimed at enhancing mechanical properties through compression, faces challenges due to set-recovery, where densified wood regains its original shape upon re-moistening. However, understanding the role of lignin in set-recovery remains elusive. In this study, acidified sodium chlorite was applied to achieve approximately 50 % delignification without removing other wood components from 3.2 mm veneers of birch, aspen, and grey alder. The veneers were then densified at 100°C and 6 MPa, with wood moisture contents (MC) of 10 % and 16 %. The morphology, physical properties, and dimensional stability of densified wood are studied in relation to delignification and MC at densification. Delignification with subsequent densification at 16 % MC was better than at 10 % MC, increasing the resultant wood density by 89 %, 148 %, and 146 % for birch, aspen, and grey alder, respectively. In general, delignification and higher moisture content during compression resulted in better compression ratios and lower set recovery. This delignification-densification approach reduced set-recovery across all wood species to a range of 71–86 %, suggesting that under these conditions, lignin has only a marginal impact on shape memory and unrestrained set-recovery in wood. Therefore, cellulose microfibrils are likely playing a dominant role.

Approach to Validate ISPM-15 Compliance for Commercial Treatment Certification of Dielectric Standard Heating of Bulk Solid Wood Packing Materials using Radio Frequency

Abstract To substantially reduce the risk of alien invasive species moving to new geographic areas, phytosanitary treatment of wood packaging materials (WPM) in compliance with the International Standard of Phytosanitary Measures No. 15 (ISPM-15) is required by trading partners. Approved treatments include conventional heating, methyl bromide and sulfuryl fluoride fumigation, and dielectric heating (DH). The DH standard was officially adopted in 2013 but has not been practiced commercially due primarily to insufficient operational validation at commercial scale. In 2022, we converted our 50-kW radio frequency (RF) unit with a 1,200-board foot capacity from an oscillator electromagnetic field power generator to a solid-state power supply, which allows for selective power input adjustments during treatment; we also switched from a five-plate to a three-plate winged electrode system to improve heating uniformity. Each loading cycle can treat sufficient material to build ∼94 standard Grocery Manufacturers Association pallets. Our research team characterized the dielectric heating pattern and options for monitoring wood temperatures over a wide-ranging test matrix of WPM that varied by wood species, dimension, moisture content, and loading configuration. We found that this upgraded RF system markedly reduced treatment times and improved heating uniformity, allowing us to develop methods that can be used to verify compliance with ISPM-15 for improved technology transfer to industry. We also discuss the operational cost of RF treatment and make general cost comparisons to conventional heat treatment for WPM.

Design and operational features of an active condensation system for enhanced energy efficiency in a biomass-fired district heating plant

The study addresses the design and operational features of an active condensation (AC) system aimed at improving the energy efficiency of a 3rd generation district heating (DH) plant. Several similar biomass-utilizing plants have recently been built in the Republic of Serbia. The plant is equipped with biomass-fired boilers totaling 2 MW capacity, utilizing varying qualities of wet wood chips. The goals are: (i) to determine optimal constant and variable quench temperatures; (ii) to calculate the electricity consumption of ancillary devices and assess their impact on AC system performance; (iii) to evaluate the effect of biomass moisture variations on system size and performance; (iv) to assess the economic viability of integrating the AC system; and (v) to establish selection and design criteria for the heat pump (HP). For a given commercial HP, an optimal quench temperature exists, dependent on the minimal temperature lift required by the HP. This temperature can be calculated simply by subtracting the minimal HP lift from the lowest possible temperature that the HP can supply to a DH system at the average outdoor temperature. Consequently, an optimal variable quench temperature exists that should be adjusted to enable the HP to operate with its minimal temperature lift.

Analysis of Quality Control for Furniture Production using Pareto Diagram and Fishbone Diagram at PT. SKM Jati

This research aims to describe Quality Control in Improving the Production Efficiency of Tables and Chairs Using Pareto and Fishbone Diagrams at PK. SKM JATI. The type of research used is qualitative descriptive with secondary and primary data, which is intended to collect data and information about a problem and facts related to the object and the research site as they are during the study. This research was conducted in Madiun Regency by interviewing the owner of PK. SKM Jati. Data collection techniques used in this study include in-depth interviews, observations, and documentation techniques to obtain accurate data for creating Pareto and fishbone diagrams. The research results show that PK. SKM Jati still faces obstacles that hinder production efficiency, with defects such as holes in the wood, moist wood, and varnish failures. The highest production failure rate is varnish failure, followed by holes in the wood, and lastly, moist wood. Through fishbone diagram analysis, four main problems are identified: people, materials, machines, and methods.

The Adhesion Performance in Green-Glued Finger Joints Using Different Wood Ring Orientations

Structural lumber is designed to meet the technical standards that ensure safety, cost-effectiveness, and sustainability. However, some tree species face limitations in their growth, which restricts their widespread use. An example of this is Nothofagus alpina, which has excellent mechanical properties but is not utilized much due to the challenges in extracting its timber and poor utilization, mainly because of the length of the wood. There is little information concerned with the uses and better management of small pieces using Nothofagus species, but it is still insufficient. This study investigates the adhesion performance of green-glued finger joints with varying wood ring orientations and moisture contents ranging from 21% to 25% using Nothofagus alpina. The primary aim is to assess how ring orientation and wet timber affect the green gluing process for creating larger wood pieces than sawn wood. The resulting products could meet the standards for wood serviceability number three for native Chilean wood. The findings indicate that finger joint performance improves with higher timber moisture levels. However, the orientation of the wood fibers did not significantly affect the performance under the tested conditions. It is important to note that this effect may become more significant near the fiber saturation point. These findings emphasize the need for a detailed protocol on the green gluing technique for Nothofagus alpina and the associated drying and surface processes in finger joint construction.

Adsorption Dynamics of Disodium Octaborate Tetrahydrate on Clay Minerals: Implications for Construction Wood Protection.

The wood preservative disodium octaborate tetrahydrate (DOT) migration is studied in clay. Using boron analysis by inductively coupled plasma optical emission spectroscopy (ICP-OES), DOT spatial and temporal dynamics are surveyed to show how DOT permeates into the wood and the clay using concentration profiles as a function of depth, initial wood moisture, and direction of filling. Atomic force microscopy and chemical imaging using photoinduced force microscopy are used to show the morphology of the wood samples and the distribution of DOT on their surface. ICP-OES results show that the average DOT concentration in the wood samples is originally 0.8 and 1.5 wt% in the bulk and at the surface, respectively. Conditioning of the wood to a moisture content of 19% in a climatic chamber reduces DOT concentration by 8% for the fir and 17% for the spruce. After one week of contact with the clays, the results showed a rapid decrease of 25-40% in DOT concentration in wood. On longer periods (5 months), the spruce shows a tendency to reabsorb the DOT from the clay and the DOT migration stabilizes at 20%. These results contribute to defining the dosage of DOT when the wood is exposed to clay.

Climate-based prediction of carbon fluxes from deadwood in Australia

Abstract. Deadwood is an important yet understudied carbon pool in tropical ecosystems. Deadwood degradation to CO2 through decomposer (microbial, termite) activities is driven by wood moisture and temperature, which are in turn strongly influenced by local climate. Thus, climate data could be used to predict CO2 fluxes from decaying wood. Given the increasing availability of gridded climate data, this link would allow for the rapid estimation of deadwood-related CO2 fluxes from tropical ecosystems worldwide. In this study, we adapted a mechanistic fuel moisture model that uses weather variables (e.g., air temperature, precipitation, solar radiation) to simulate wood moisture and temperature along a rainfall gradient in Queensland, Australia. We then developed a Bayesian statistical relationship between wood moisture and temperature and CO2 flux from pine (Pinus radiata) blocks and combined this relationship with our simulations to predict CO2 fluxes from deadwood at 1 h temporal resolution. We compared our pine-based simulations to the moisture–CO2 relationships from stems of native tree species deployed at the wettest and driest sites. Finally, we integrated fluxes over time to estimate the amount of carbon entering the atmosphere and compared these estimates to measured mass loss in pines and native stems. Our statistical model showed a positive relationship between CO2 fluxes and wood moisture and temperature. Comparing cumulative CO2 with wood mass loss, we observed that carbon from deadwood decomposition is mainly released as CO2 regardless of the precipitation regime. At the dry savanna, only about 20 % of the wood mass loss was decomposed within 48 months, compared to almost 100 % at the wet rainforest, suggesting longer residence times of deadwood compared to wetter sites. However, the amount of carbon released in situ as CO2 is lower when wood blocks are attacked by termites, especially at drier sites. These results highlight the important but understudied role of termites in the breakdown of deadwood in dry climates. Additionally, mass loss–flux relationships of decaying native stems deviated from those of pine blocks. Our results indicate that wood moisture and temperature are necessary but not sufficient for predicting CO2 fluxes from deadwood degradation. Other factors, such as wood traits (wood quality, chemical composition, and stoichiometry) and biotic processes, should be considered in future modeling efforts.

Water Vapour Resistance of Exterior Coatings—Influence on Moisture Conditions in Ventilated Wooden Claddings

Increasing climate fluctuations and extremes due to climate change are particularly concerning for wooden building envelopes, especially in the Nordic region, which has harsh climatic conditions. The exterior coating’s barrier properties are crucial for maintaining building envelopes’ intended lifespans. Hence, it is unfortunate that the vapor resistance of exterior coatings is not openly accessed for commercial products. This study investigates the influence of the water vapour resistance of exterior coatings on the moisture conditions and mould growth risk of ventilated wooden claddings. The sd-value (vapour diffusion-equivalent air layer thickness) is determined for nine free-standing coatings (alkyds, emulsions, and acrylics); in total, 100 specimens are tested with the wet cup method. Additionally, with WUFI Pro, one-dimensional hygrothermal simulations under Nordic climatic conditions investigate how the coatings’ vapour resistance might influence the moisture dynamics of wood. The mould risk is assessed by the add-on WUFI VTT Model. The determined sd-values for the coatings range from 0.453 to 1.350 m (three layers) and from 0.690 to 2.250 m (six layers), showing a strong correlation with the dry film thickness. The vapour resistance of the coatings does not significantly influence the wood moisture content, but lower resistance may cause slightly faster drying. The importance of surface treatment is confirmed. The mould risk is notably higher in a Stavanger climate on a southwest-facing wall compared to Trondheim on a north-facing wall.

Characterisation of wood combustion and emission under varying moisture contents using multiple imaging techniques

In this study, the complex combustion process of natural wood, with different moisture contents, has been characterised using a pioneering approach that integrated Mid-Wavelength Infrared (MWIR) Hyperspectral Imaging (HSI), Schlieren imaging, Long-Wavelength Infrared (LWIR) thermal imaging and visual imaging. The experiment involved the combustion of oak wood samples with moisture contents varying from dry (defined as 0%) to 30%. This setup enabled a detailed investigation into the combustion process, examining aspects such as weight loss rates, thermal behaviours, spectral radiance of gas emissions and flow structures. Higher wood moisture levels were associated with decreased fuel consumption and sustainability of the combustion. The radiance ratios of CH4/CO2 and CO/CO2 were higher in samples with increased moisture during the initial combustion stages, indicating reduced efficiency in gas-phase combustion. The different combustion stages: flaming and smouldering, were characterised by the thermal profiles. Results demonstrated the moisture level significantly affected the initiation of both flaming and smouldering combustion, as moisture can suppress the thermal pyrolysis of flammable gases during ignition and the evaporation of the residual water can cool the surface locally after ignition. Additionally, the samples with high moisture content transitioned more quickly and directly to smouldering combustion. This transition is further evidenced by lower emissions of flammable gases and a significant decrease in the intensity gradient of flow structures in high moisture conditions. This comprehensive study highlights the potential of multi-wavelength techniques in combustion research. The findings have significant implications for optimising biomass combustion processes in various applications, contributing to the broader field of energy and combustion science.

Use of threaded washers in the joints of wooden structures

Introduction. One of the promising types of joints in wooden structures is the joint using glued steel washers. However, the use of adhesive compounds is, for a number of reasons, characterized by lower manufacturability as compared to a threaded connection. Given the relevance of developing new technological types of joints in structures, it is necessary to study the threaded washer connection of wooden elements without the use of adhesives.Aim. To study the performance of a threaded washer connection by conducting a full-scale experiment of specimens exhibiting different parameters of threaded washers in order to assess the prospects for further study of the joint in question and its implementation in construction practice.Materials and methods. The procedure for studying the joint under consideration involves making a series of specimens and conducting an experiment to determine the failure loads and ultimate strains, followed by the visual inspection of these specimens after failure.Results. The experimental study of twelve specimens (four series of specimens exhibiting different parameters of threaded washers, with three specimens in each) yielded failure loads, and graphs showing their deformation were constructed. The performance of the joint in question was examined; its advantages and disadvantages in terms of bearing capacity, manufacturability, and reliability were identified.Conclusions. Threaded washer joints in wooden structures are characterized by high bearing capacity and manufacturability. In spite of such a disadvantage as the effect of wood moisture on the strength and reliability of this joint, its advantages make it promising for further study and use in construction practice.

A discussion on the various aspects of the minimum pressing time for polyurethane adhesives

ABSTRACT For many purposes related to the bonding of wood substrates, one-component polyurethane adhesives (1C-PUR) are of great significance. 1C-PUR adhesives are widely used, especially in the cross laminated timber (CLT) production. One major benefit is their ability to be pressed at room temperature. However, not only pressing temperature but also the pressing time is an important economic aspect for manufacturers. Knowing the minimum possible press time offers an economic advantage, however, there have been only few publications on this topic so far. The aim of this work was to investigate and evaluate various aspects of a 1C-PUR adhesive with regard to the minimum pressing time comparing newly developed knowledge-based approaches. The analysis included the strength development of the advanced curing of the adhesive, the development of the final internal bond strength and the minimum required press time for bonded joints to withstand imposed stress. The influence of the wood moisture content and closed assembly time were also investigated. The present study found that closed assembly time had a favourable influence on the required press time period. With immediate testing of the glued joint it also revealed a quicker strength development with lower strength values at a higher wood moisture content.

Sulfuryl Fluoride Fumigation as a Quarantine Treatment for the Control of Reticulitermes speratus Kolbe (Blattodea: Rhinotermitidae) in Wood.

High-risk termites in wood imported to the Republic of Korea are currently treated with methyl bromide (MB), which has ozone-depleting properties and is highly toxic. This study evaluated the effectiveness of sulfuryl fluoride (SF) as a quarantine treatment against Reticulitermes speratus Kolbe (Blattodea: Rhinotermitidae) in wood, along with its wood sorption and penetration capacity. The LCt50 and LCt99 values for SF were 30.87 and 42.53 mg h/L at 23 °C and 151.62 and 401.9 mg h/L at 5 °C, respectively. The SF Ct values did not significantly differ between dry and wet wood at loading ratios of 10%, 30%, and 50% at both 5 °C and 23 °C (p > 0.05). In a closed wooden cube, the LCt50 and LCt99 for SF for R. speratus were 31.59 and 53.34 mg h/L, respectively, indicating an excellent wood penetration ability. SF caused 100% termite mortality with a 90% loading ratio in the scale-up trials (500 L). The SF concentration during ventilation decreased below the threshold limit value (TLV) of 5 ppm within 30 min, confirming that the working conditions were safe. This study provides a basis for the use of SF as an alternative to MB for the treatment of termites in wood.

Prediction Distribution Model of Moisture Content in Laminated Wood Components.

Shrinkage cracks are some of the most common defects in timber structures obtained from woods with an uneven distribution of moisture content and are subject to external dynamic environmental changes. To accurately predict the changes in the moisture content of wood components at any time and position, this study first applied the principles of food drying and established a moisture field model for laminated wood based on the analogy between heat and humidity transfer. A model for predicting the moisture content of wood that considers time and spatial distribution was then proposed. Second, by collecting relevant experimental data and establishing a finite element analysis model, three moisture absorption conditions (0-9.95%, 0-13.65%, and 0-17.91%) and four desorption conditions (34-5.5%, 28-8.3%, 31-11.8%, and 25.5-15.9%) were analyzed. In the moisture absorption comparison, the time needed to reach 95% equilibrium moisture content was 2.43 days, 4.07 days, and 6.32 days. The rate at which the internal components reached equilibrium moisture content exceeded 10 days. The temporal and spatial distribution of wood moisture content revealed the correctness of the proposed wood moisture field model. Finally, the moisture content prediction model was applied in the order of characteristic equation solutions, moisture content gradient difference, and laminated wood size. The results revealed that the established humidity field model can predict the wood moisture content and how it changes over time and in space. Notably, 1-2 orders for the solution of the characteristic equation are recommended when applying the prediction model. The greater the difference in moisture content, the faster the equilibrium moisture content is reached. The moisture content varies greatly based on the component size and position. Notably, the influence of moisture gradient and wood size on the average wood moisture content cannot be ignored.

Production of greenhouse gases by logging residue in boreal clear-cut forests

AbstractForest deadwood is an important carbon reserve, estimated to contain 8% of the total forest carbon. This type of woody debris is recognized as a source of carbon dioxide (CO2), as the carbon is released back into the atmosphere by microbial decomposition. Production of methane (CH4) and nitrous oxide (N2O) has also been reported. In managed forests, logging residues form a major source of fine deadwood, but its role in the greenhouse gas exchange of forest ecosystems is poorly understood. We studied the greenhouse gas production of spruce and birch left-over fine woody debris and estimated the residence time of these residues at 18 spruce-dominated boreal forest sites in Central Finland. The study areas consisted of clear-cut forest stands, totally covering approximately 47 hectares, with logging residue ages varying between 0 and 10 years. The research was carried out over eight months from May to December 2019. We observed that CO2 dominated the greenhouse gas production of the logging residues, with the production being regulated by air temperature, tree species, residue age, and wood moisture. Emission of CO2 continued throughout the research period with a clear seasonal pattern. Production of CH4 and N2O was also observed, but not in climatically-relevant amounts. Deadwood half-life was estimated at 18 years for spruce and 9 years for birch. Our study demonstrates that logging residues form a mid-term carbon reserve and suggests that global warming could reduce the lifetime of the residues as a result of elevated and temperature-dependent CO2 release in the studied Myrtillus type forest stands.

Impact of Wood-Boring Larvae of Xylotrechus arvicola (Coleoptera: Cerambycidae) on Mechanical Properties of Vitis vinifera Plants

Xylotrechus arvicola represents a significant insect pest impacting Vitis vinifera within the principal wine-producing territories of the Iberian Peninsula. The larvae of this species bore into grapevine wood, resulting in significant structural and biomechanical deterioration to the plant. Compressive and flexural tests were conducted to assess the mechanical properties of wood affected by X. arvicola. Compressive and flexural strength exhibited a decline with the escalation of the Total Damaged Surface Area (TDSA) of the samples, ranging from 0.31% to 0.73% in trunks and from 0.04 to 0.76% in branches, irrespective of the wood moisture content (fresh and dry). The most significant reduction in resistance occurred in affected dry trunks and branches. Notably, the deflection at break for dry samples was lower compared to fresh samples (65.00 and 97.85 mm, respectively). Moreover, the deflection at break for affected fresh samples (164.37 mm) significantly surpassed that of unaffected fresh samples (72.58 mm) and affected dry samples (37.50 mm). It is noteworthy that a higher percentage of TDSA coincided with diminished wood resistance. The percentage of fungal growth symptoms observed in affected wood samples was 66.66% for dry trunks, 75.00% for fresh branches, and 60.00% for dry branches. The damage inflicted by larvae facilitated the spread of grapevine diseases via emergence of holes created by insects upon exiting the wood and through the larval galleries connected to them. This damage also altered the mechanical properties of grapevine plants, with fresh branches exhibiting the most pronounced effects.

Properties of Forest Tree Branches as an Energy Feedstock in North-Eastern Poland

Tree branches from forest tree harvesting for the timber industry are an important energy feedstock. Solid biofuel in the form of wood chips, produced from branches, is an excellent renewable energy source for generating heat and electricity. However, the properties of wood chips as a solid biofuel produced from forest tree branches can vary greatly depending on the species from which they have been produced. Therefore, this study aimed to assess the thermophysical properties and elemental composition of fresh branches harvested from nine tree species (pedunculate oak, silver birch, European ash, common aspen, grey alder, Norway maple, Scots pine, European larch and Norway spruce) over three consecutive years (2020–2022). The branches of the tree species most commonly found in Polish forests (Scots pine) were characterized by the highest heating value (an average of 20.74 GJ Mg−1 DM), the highest carbon content (an average of 55.03% DM), the lowest ash (an average of 0.60% DM) and nitrogen contents (an average of 0.32% DM), and low sulfur (an average of 0.017% DM) and chlorine contents (an average of 0.014% DM). A cluster analysis showed that the branches of all three coniferous tree species (Scots pine, Norway spruce and European larch) formed one common cluster, indicating similar properties. The branches of the European ash were characterized by the lowest wood moisture content (an average of 37.19% DM) and thus the highest lower heating value (an average of 10.50 GJ Mg−1). During the three years of the study, the chlorine and ash contents of the branches of the tree species under study exhibited the highest variability.

An Adjusted Waveguide Antenna with A Woodpile-Shaped EBG for Eucalyptus Wood Moisture Content Measurement

An Adjusted Waveguide Antenna with A Woodpile-Shaped EBG for Eucalyptus Wood Moisture Content Measurement

Species-specific prediction model of wood moisture content based on electromagnetic wave propagation time

Laboratory and field experiments were performed to examine the feasibility of using Time Domain Reflectometry (TDR) to monitor moisture content (MC) of wood and standing trees. The TDR was used to detect the electromagnetic wave propagation time of four tree species (Betula platyphylla, Tilia tuan, Picea asperata, and Fraxinus mandshurica) at different MCs. During the TDR test, effects of probe insertion depths on MC predictive accuracy were considered. The best results were obtained at an insertion depth of 8 cm. At the selective 8 cm insertion depth, a species-specific MC prediction model (0.94 ≤ R2 ≤ 0.98), a generalized model for the four species (R2 = 0.65), and a hybrid model for the species with similar densities (0.80 ≤ R2 ≤ 0.96) were constructed, respectively. Overall, the species-specific MC prediction model showed good predictive ability for both tree and wood disc samples, including that TDR can be used to detect wood and standing tree MC. If possible, the hybrid model can be used for species with similar density.

An environmentally friendly multifunctional soy protein adhesive composed of rosin acid derivative inspired from organic-inorganic hybrid structure

Soy protein adhesives have the advantages of low price and renewability but are limited by terrible bonding strength and poor water resistance, which restricts the practical application. Herein, inspired by the structure of mussels and organic-inorganic hybrid strengthening mechanism, a novel and bio-based soy protein adhesive (SPI-RA-CSA) based on rosin acid derivative and calcium sulfoaluminate was generated. According to the optimization of response surface methodology (RSM), the best proportion of adhesive SPI-RA6-CSA1 was chosen. The dry and wet shear strengths of SPI-RA6-CSA1 adhesive reached 1.92 and 1.35 MPa, respectively, which were 120% and 210% higher than original soy protein adhesive. Meanwhile, SPI-RA6-CSA1 adhesive showed excellent coating performance even if it was coated on wet wood veneer. In addition, SPI-RA6-CSA1 adhesive effectively inhibited the formation of mold and exhibited outstanding antimicrobial ability for Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) with antimicrobial rates of 87.36% and 85.73%, respectively. What's more, SPI-RA6-CSA1 adhesive demonstrated prominent flame retardant properties reducing the harm of fire accidents. SPI-RA6-CSA1 adhesive also possessed the characteristics of low energy consumption and environmentally friendliness by Life Cycle Assessment (LCA). Therefore, this simple strategy provides workable guidance for the production of multifunctional and green soy protein adhesive.