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In spite of being both a one-step solution to several problems associated with woodworking and also energy efficient, the application of microwave (MW) modification in wood research has remained very limited and this promising method has practically no use in wood industries across the globe. Research done so far in this field primarily sheds light on its potential in enhancing wood permeability, treatability and uniform wood drying. While MW treatments are mostly used on wet or green wood, another modification technique, plasma, has potential benefits to synergistically enhance the effects of MW treatment, but so far has not been applied on wet or green wood specimens. This study takes a first step to investigate the effects of plasma treatments (PT) on green wood specimens, as well as combinations of MW and plasma treatments. As a preliminary study, the methodology focuses on water contact angle measurements, since these are most commonly used as indicators for surface modifications in industrial applications. An exponential time dependence was found for the contact angle on the investigated samples of Norway spruce (Picea abies Karst.). Initial contact angles after droplet deposition increased due to drying and migration of organic molecules during treatments. In comparison with the literature, the effect of plasma was significantly less pronounced on wet wood specimens. The initial contact angles showed the lowest statistical variations after MW treatment, whereas plasma increased inhomogeneities. The final contact angles on treated specimens was lowest for PT-only specimens as well as specimens treated with plasma after MW. In contrast to the initial contact angles, the final contact angles showed the lowest variations after PT. Wetting rates were insignificantly improved by plasma, with reduced statistical variations after all treatments. Kljub temu, da je uporaba mikrovalov za modifikacijo lesa energetsko učinkovita in obetavna enostopenjska rešitev za številne probleme, povezane z obdelavo lesa, je ta tehnologija v raziskavah lesa ostala zelo omejena in se v lesni industriji po vsem svetu praktično ne uporablja. Dosedanje raziskave na tem področju osvetljujejo predvsem potencial te metode pri izboljšanju permeabilnosti lesa, kurativne zaščite lesa in enakomernega sušenja lesa. Medtem ko se obdelava z mikrovalovi večinoma uporablja na svežem lesu, izkazuje tehnika obdelave lesa s plazmo potencialne koristi za sinergistično izboljšanje učinkov obdelave z mikrovalovi, vendar se doslej plazma še ni uporabljala za obdelavo svežega lesa. Ta študija je prvi korak k raziskovanju učinkov plazemske obdelave na vzorcih svežega lesa ter kombinacije mikrovalovne in plazemske obdelave. Kot preliminarna študija se osredotoča na meritve stičnega kota kapljic vode, saj se metoda uporablja kot indikator učinkovitosti površinske obdelave tudi v industriji. Na raziskanih vzorcih smrekovine (Picea abies Karst.) je bila ugotovljena eksponentna odvisnost stičnega kota od trajanja omočenja. Začetni stični kot po nanosu kapljic vode se je povečal zaradi sušenja lesa in migracij organskih molekul na površino lesa. V primerjavi z navedbami iz literature je bil učinek plazme na svežih vzorcih lesa bistveno manj izrazit. Začetni stični kot je imel najmanjšo statistično variabilnost po obdelavi z mikrovalovi, medtem ko je plazma povečala nehomogenost. Končni stični kot je bil najnižji pri vzorcih, ki so bili obdelani samo s plazmo, kot tudi pri vzorcih, obdelanih s kombinacijo mikrovalov in plazme. V nasprotju z začetnim stičnim kotom je končni stični kot pokazal najmanjšo spremembo po obdelavi s plazmo. Stopnja omočitve je bila s plazmo neznatno izboljšana, z zmanjšano statistično variabilnostjo po vseh obdelavah.

This research aimed to evaluate the profile of temperature and moisture content in Pinus oocarpa wood being dried with heating oven and microwave oven. The size of samples were (25x70x120) mm3. The temperature profiles in heating oven and microwave oven drying were taken every 10 minutes and 0.5 minutes, respectively. The moisture profiles in heating oven and microwave oven drying were made in every 24 hours and 10 minutes, respectively. The heating oven was set at 60 °C, while microwave oven was set for 2 minutes intermittently with 5 minutes break. In microwave drying, the temperature inside the boards increased faster and higher compared to that in the heating oven, which resulted in a faster moisture movement to the board’s surface. The drying rate of pine increased 48-72 times in microwave compared to that in heating oven. The moisture content in the centre of boards being dried in heating oven was much higher than that of in the outer parts. On the other hand, the moisture profile in the woods being dried in microwave oven distributed more evenly.

International audience; There is an increasing interest on wood as it is an environmentally sustainable product (e.g. biodegradable and renewable). Thus, an accurate characterisation of wood properties is of extreme importance as they define the kind of application for which each type of wood can be used. For instance, dry mass of wood is a key parameter itself and is needed to calculate Moisture Content (MC) of wood, which is correlated to its physical properties. Due to the limitations of commonly used drying methods, preliminary work has shown the potential of 1H NMR to measure dry mass of wood but it has never been validated. Here, we performed a critical analysis of 1D and 2D 1H NMR relaxometry methods for obtaining the dry mass of wood and we compared their performance to three commonly used drying methods. This showed that commonly used drying methods do not remove all water from wood. Moreover, we are able to classify them accordingly to their performance. In addition, we showed that MC values obtained by 1H NMR relaxometry methods are higher (up to 20%) than values from commonly used drying methods. This empathizes the importance of accurate values of dry mass of wood and the utility of 1H NMR relaxometry on wood sciences. When comparing both NMR relaxometry methods, 2D should provide the more accurate results but 1D measurements would also be a recommended choice as they are faster than 2D and their results clearly overcome commonly used drying methods in a non-invasive and non-destructive manner.

Oak heartwood usually darkens during and after drying. This darkening can be heterogeneous, leaving non-colored areas in the wood board. These light discolorations have been linked to heterogeneous distribution of tannins, but compelling evidence on the microscale is lacking. In this study Raman and fluorescence microscopy revealed precipitations of crystalline ellagic acid, especially in the ray cells but also in lumina, cell corners and cell walls in the non-colored areas (NCA), which also had higher density. In these denser areas free water is longer present during drying and leads to accumulation of hydrolyzed tannins. When eventually falling dry, these tannins precipitate irreversible as non-colored ellagic acid and are not available for chemical reactions leading to darkening of the wood. Therefore, pronounced density fluctuations in wood boards require adjusting the drying and processing parameters so that water domains and ellagic acid precipitations are avoided during drying.

Drying has a major impact on the viability of sawn timber production, particularly through its influence on productivity, energy usage, and product quality. Traditionally, plantation-grown southern pine structural grade timber from Australia has been dried using high temperature (≥ 180 °C) conventional batch kilns. However, the Australian industry is showing increasing interest in continuous drying kilns because of reported cost savings and potential improvements in product quality. This study investigated the differences between continuous drying and conventional drying schedules on the radial permeability, wettability, gluability, and treatability of southern pine timber from Queensland plantations. The high temperature drying resulted in significantly lower liquid permeability compared to low temperature drying; however, there were no significant differences between drying schedules for gas permeability. For combined wood surface and core data, there were no significant differences in liquid permeability between low temperature drying and continuous drying or between continuous drying and high temperature drying schedules. For earlywood after surface machining, continuous drying resulted in the greatest wettability (based on K-values), whereas for latewood after surface machining, low temperature drying produced the greatest wettability. Earlywood had greater wettability compared to latewood. Continuous drying resulted in better gluability and treatability compared to conventional drying schedules.

The drying process was examined relative to parameters’ influence on the deformation and surface layer color changes of beech wood (Fagus sylvatica L.) and oak wood (Quercus robur L.). The goal was to analyze the impact of drying process conditions, wood and growth rings types, and load on the deformation and surface color changes of drying thin wooden elements. A further aim was to reduce the time of the lamella drying and minimize wood products defects. During each drying, 40 pieces of wood were dried, divided into two groups. For the first group, 30 pieces were dried under a uniformly distributed load of approximately 50 kg, while for the second group, 10 samples were dried without weight. The lamellas dried under load exhibited fewer cup, bow, and twist deformations than the lamellas dried without load. Cracks in the dried lamellas occurred comparably in those dried under and without load. Color changes in the specimens before and after drying were observed and measured. The differences in colorimetric parameters (a, b, and L) between wood without defects and with defects were less marked after drying than before drying. The color changes were only noticed in the surface layers of the specimens.

Thinning is a necessary silvicultural activity for restoring the long-term sustainability of pine forests in much of the southwestern United States. In northern Arizona, a landscape-scale restoration effort, called the Four Forest Restoration Initiative, has been implemented to recover the long-term sustainability of 2.4 million acres on four national forests. Cost-effective and efficient thinning methods are needed due to the scale of the project to help improve habitat, conserve biodiversity, protect old growth, reduce risk of severe wildfire, and restore natural forest structure and function. Mechanical cutting using a feller-buncher is the primary method of thinning in these forests due to the extreme high number of small-diameter ponderosa pine trees. A feller-buncher places harvested trees into small piles known as “bunches.” In this review, we highlight advantages and disadvantages of bunching tree materials in restoration programs and review published studies on transpirational drying of bunches of various tree species in different forest habitats across the United States, including ponderosa pine in Arizona. Studies show that transpirational drying of trees in bunches can be an effective method to allow for wood drying, but this process can be affected by abiotic factors associated with seasonal climate and stand characteristics. Study Implications The Four Forest Restoration Initiative makes up the largest landscape-level collaborative project in the history of the USDA Forest Service with more than 2.4 million acres of forest habitat. Thinning is a necessary silvicultural activity for restoring the long-term sustainability of these forests in northern Arizona. Because of the extremely high number (i.e., average of 720 trees per acre) of small-diameter ponderosa pine (Pinus ponderosa) trees, mechanical cutting is more cost effective than individual saw cutting, which is why a feller-buncher machine is the primary thinning tool. During feller-buncher thinning, small piles of trees known as “bunches” are created. Bunching trees can allow for wood drying in the field that translates into lower operational costs because drier trees are lighter in weight, which reduces transportation costs. In northern Arizona, a 60-day time frame is allotted for transpirational drying before tree materials must be removed from the forest. However, because the drying process through bunching is affected by abiotic conditions, there may be a need to adjust this time frame to account for seasonal weather patterns. For example, during spring, when weather in northern Arizona is hot and dry, less time might be necessary for tree bunches to lose enough moisture while still rendering the thinning operation profitable and simultaneously avoiding bark beetle proliferation given that their life cycle consists of about 40 days. Furthermore, bunching studies should be developed to look at individual tree species in their respective locations and to investigate the effects of the presence, partial presence, or absence of branches and bark on trees within bunches. Studies should also be conducted to look at the effects of bunches on insect communities, particularly those that can cause extensive tree mortality.

In order to generalize the possibilities of using MW radiation in industrial processes, the given paper considers and analyzes various methods of wood drying. Technological and economic advantages of wood drying in an ultra-high frequency electromagnetic field are well justified. Wood drying in the ultra-high frequency range is considered as the most optimal in contrast to traditional methods. This method is based on the penetration of electromagnetic energy into the material and converting it into heat. The paper reveals the possibility of more effective use of MW radiation. It proposes a method for drying wood and large-sized lumber basing on a single-wire transmission line of electromagnetic energy of the surface wave. The paper also describes the advantages of the proposed method: the use of a single wire covered with a thin layer of dielectric material, the use of a vibratory system for surface wave excitation, and the use of a flat reflector. Special attention is paid to the contact area of the wire with a flat reflector since the perfection of this contact largely determines the efficiency of surface wave excitation. The conducted research estimated the influence of the parameters of the vibratory surface wave excitation system in a single waveguide on the efficiency of its excitation. The proposed vibratory excitation device allows quite a simple step-by-step adjustment of the thermal power in the irradiated object. The design of the dissipation load for surface wave lines has been successfully tested during the laboratory works where certain ways of unclaimed electromagnetic energy utilization were suggested. Following the results of the conducted research, we proposed a physical model of a system for microwave drying of wood and large-sized lumber

Wood drying is the most time- and energy-consuming process in the wood industry. Without proper optimization of the drying process, an attempt to reduce drying time and energy by accelerating the drying rate might easily result in the creation of various defects within the kiln-dried lumber. To overcome this susceptibility, the drying and anatomical characteristics of Mongolian oak (Quercus mongolica) lumber (thickness 30 mm × width 100 mm × length 1900 mm) were investigated in this study. To evaluate the effects of kiln drying, shrinkage and color difference (ΔE) were measured along with warping behavior such as cupping, bowing, crooking and twisting. The formation of tyloses was observed microscopically between one and six months after sawing. To develop value-added products from domestic oaks, the yield rate from standing tree to the flooring board was calculated. Based on the results of this study, it is expected that the present value of commercial oak timber in Korea can be improved by the application of an efficient production plan.

A one-year numerical simulation of a solar wood dryer with glazed walls in a Moroccan climate was developed. This simulation was used to predict detailed and temporal distributions of wood moisture content (MC) and to study the mechanisms and parameters involved in solar wood drying. Calculations were performed for thuya wood (Tetraclinis articulate), which is primarily used in marquetry in the city of Essaouira and is well-known for its aesthetic qualities. Comparisons between the theoretical results and both experimental data and the results reported in pertinent literature were also performed and the results obtained via computer simulation agreed well with the experimental values. Analyses of the studied wood revealed that 15 drying cycles could be achieved within a year for an air velocity of 1 m/s and that the drying process was faster during the hot seasons than in cold seasons (430 h vs. 600 hr). Continued ventilation reduced the drying time, thereby increasing the number of drying cycles (33 vs. 15). Additionally, increasing the air velocity by 100% resulted in more than a 100% increase in the number of drying cycles; doubling the air velocity for thicker boards also resulted in an increase in drying cycles (23 vs. 15).

Predicting kiln-drying schedules for a given wood species is not yet possible, despite many research efforts. This is mainly due to insufficiently considering important spatio-temporal variables such as moisture and temperature gradients, and wood anatomical features during drying in the predictive modelling framework. To understand the influence of aforementioned variables, an experimental measurement set-up was developed consisting of heat-resistant load cells mounted in an oven to record the weight of the wood specimens dried at 100 °C. A camera was mounted outside the oven to acquire images of the end grain through the transparent door of the oven, as such enabling to monitor the occurrence of cracks. Furthermore, custom-made electrodes were inserted as well at different depths in the specimen to measure the electrical resistance, which relates to the moisture content. Specimens were also equipped with thermistors to record the temperature in the specimens at different depths from the surface. Heat-resistant wires from load cells, electrodes and thermistors were connected with data loggers outside the oven. Three specimens of basralocus (Dicorynia guianensis) were selected, measuring 50 mm wide, 50 mm thick and 120 mm long. The results show that it is possible to real-time monitor average moisture loss, local moisture content gradient represented by the electrical resistance gradient and wood temperature gradient as a function of time. These temporally resolved gradients can be related to the occurrence of cracks. This methodology enables to unveil interrelationships between the measured variables and changes of the wood anatomical structure, of utmost importance for the fine-tuning of kiln-drying schedules.

The influence of drying on the microstructure, physical and chemical properties of some tropical wood species has been investigated using thermogravimetric analysis, differential scanning calorimetric (DSC), FTIR-ATR spectroscopy, mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) analysis. Eleven tropical species were used in this study. Results showed that the common Cameroonian wood species can be grouped into three classes: Ga (lightwood) with cross-linking fibers having high volume of macropores, density in the range 0.2–0.4 g cm−3 and high lignin content; Gb (medium dense) with unidirectional fibers packing, density around 0.6 g cm−3 and Gc group showing high densification of unidirectional fibers and low porosity justifying the density > 0.8 g cm−3. Both the Gb an Gc groups have less significant lignin content. A relatively high rate of drying for Ga with respect to low drying rate for Gc was observed in direct relation with their porosity of ~ 72 Vol% and ~ 36 Vol%, respectively. LTF and WG showed similar cumulative pore volume (0.44 mL g−1) with different pore size distribution: 28% and 22% of macropores, 39% and 60% of mesopores and 33% and 18% micropores, respectively. Thermal analysis revealed that lightwoods have the highest amounts of residues and lower thermal stability of chemical components than dense woods. It has been found that the degradation process of hemicellulose, cellulose and lignin occurs mainly at about 200–300 °C, 300–350 °C and 350–500 °C, respectively. The group Ga with low drying rate, a low cycle of reproduction, a high volume of porosity together with large pore sizes appeared promising candidates for the design of ecological, environmental and sustainable management policy of wood transformation in developing countries and even worldwide.

The drying of sawn lumber is one of the major processing steps in sawmills with high production volumes. Existing publications on kiln drying analyse and improve technological conditions, while this paper focuses on the scheduling and loading planning with time availability of the individual dried packages. To improve dry kiln scheduling for multiple and identical kilns in large softwood processing sawmills, heuristic approaches are developed that generate kiln allocation plans according to existing production specifications. The aim is to minimise total tardiness for the drying of all sawn lumber packages while considering technological and capacity restrictions. These heuristics calculate the position, time and kiln for each package, thus solving scheduling and loading problems caused by capacity and stacking limitations. Several heuristic approaches are illustrated and tested with actual production data. In addition, the difference between static and dynamic scheduling for group and batch generation is analysed. Further improvements are possible through: drying of different lumber assortments in one batch, outsourcing the drying of special assortments or investing in supplementary kilns for drying smaller volumes within more flexible time slots.

Wood drying is an important stage in the woodworking process. After drying, wood is subject to a re-sawing process, for which a high quality surface, low material loss, and high efficiency are often required. In this paper, forecasted values were presented of cutting power for the re-sawing process of pine and beech wood that were dried with four different methods. Forecasting of cutting power for an industrial band saw machine that works daily in a Polish sawmill was determined. Values of cutting power were forecasted for a full range of feed speeds of the analyzed band saw machine. The achieved results allowed the observation of noticeable changes in the forecasted cutting power for a given sawing process as a function of the wood drying method applied. Significant changes were observed for pine wood, especially between air-dried pine wood and wood dried with warm air-steam mixture, and between pine wood dried in a conventional kiln and with warm air-steam mixture.

Wood moisture content (WMC) is an important technical index used in the wood drying process, and assessing its change accurately and reliably is the key to improving wood drying quality. In order to improve the accuracy and reliability of WMC forecasting, a modeling method is proposed that uses a modified ant colony algorithm (MACA) to optimize the least square support vector machine (LSSVM). The MACA combines the large-step size global search with the small-step size local fine search to obtain the optimal parameter combination automatically and are tested by five standard functions. Then the MACA-LSSVM model is proposed to predict the WMC and compared with back propagation neural network (BP-NN), LSSVM model, and ant colony optimization LSSVM (ACO-LSSVM). The drying data from a small-sized wood drying kiln independently developed by Northeast Forestry University are taken as the samples for analyzing. The results indicate that the root mean square relative error (RMSRE) obtained by the proposed method (MACA-LSSVM) is only 1.82%, which is 0.77%, 0.50%, and 0.20% less than those of the BP-NN, LSSVM, and ACO-LSSVM models. The forecasting time are 0.0070 s, 0.0030 s, and 0.0010 s shorter, respectively. The relative error (RE) and the mean absolute error (MAE) are also lower than those of the latter three models. The MACA-LSSVM shows the characteristics of low computational complexity, fast convergence speed, high prediction accuracy and strong generalization ability, and the prediction effect is ideal. This model can provide the theoretical support for intelligent control of the wood drying process.

Potential use of condensate generated by cooling the steam obtained during high-frequency/vacuum drying step of hardwood lumber was investigated. The liquid condensates were obtained from oak, beech and walnut wood. This liquid condensate was then used as a replacement for deionized water in the synthesis of Urea-Formaldehyde (UF) resin (5 wt% of total resin) using a laboratory scale reactor. Medium Density Fibreboards (MDFs) were produced using control and modified resins. Emissions of Volatile Organic Compounds (VOCs) from the MDFs were determined by Mcro Chamber method. The bonding properties of the MDFs were determined according to European standards. The main VOC emissions from MDFs produced using UF resin containing the condensate were a-Pinene, b-Pinene, careen, and acetic acid, which were lower than those of the control MDF, except for the acetic acid emission of MDF with oak condensate. In the tree species, the beech wood condensate gave the lowest VOC emissions (732 μgm-3) from the MDFs, followed by the MDFs containing walnut wood condensate (852 μg·m3), oak wood condensate (998 ugnf3), and control MDF (3529 μg-3), respectively. However, the internal bond strength of MDFs containing the condensate was negatively impacted by the condensate (0.70 N·mnf-2 to 0.54 N·mm-2 depending on the tree species). The results showed that the liquid wood-drying condensate which generally released to the ground could be efficiently used as an alternative to expensive VOCs scavenger used in the production of UF resin bonded MDF. This may be one of the most efficient uses of the condensate in high value-added materials.

Aim of study: The adsorption properties of the samples of full-dry Eastern Spruce (ES) [Picea orientalis (L). Link.] with 12.5 mm, 25 mm, 37.5 mm and 50 mm thick is to determine under the climate conditions with 42%, 65% and % 78 of relative humidity and at a constant temperature of 20 °C.Material and method: The wood samples used in this study were the Eastern Spruce woods which were obtained from Forestry Process Management in the city of Trabzon/Turkey. With regard to mathematical modeling used to determine the wood moisture content (MC), the equation constants in case of adsorption was determined. Experiments were conducted at three different equilibrium moisture content (EMC); 8%, 12% and 16%.Main results: Cross section had no crucial effect on the rate of accessibility to the final MC. However, EMC and thickness have been effective.Research highlights: In practice, since dried wood is kept at outside weather conditions for a certain time before operation, an increase can be observed in the wood MC. It is practically important that under the influence of climate conditions until its utilization, the tendency of water adsorption of wood is determined as a function of time., Çalışmanın amacı: Tam kuru Doğu ladini [Picea orientalis (L). Link.] örneklerinin 12.5 mm, 25 mm, 37.5 mm ve 50 mm kalınlıkta, 20 ° C sabit bir sıcaklıkta ve % 42 ,% 65 ve %78 farklı bağıl nem koşullarında adsorpsiyon özelliklerini belirlemektir.Materyal ve yöntem: Bu çalışmada Maçka Orman İşletme Müdürlüğü’nden alınan Doğu Ladini örnekleri kullanılmıştır. Odun rutubet içeriğini belirlemek için kullanılan matematik modelleme ile adsorpsiyon durumunda denklem sabitleri belirlenmiştir. Deneyler, % 8, % 12 ve % 16 olmak üzere üç lif doygunluk noktası için gerçekleştirilmiştir.Sonuçlar: Kesitin, denge rutubetine erişilebilirlik oranı üzerinde önemli bir etkisinin olmadığı, bununla birlikte denge rutubet miktarı ve kalınlığın etkili olduğu belirlenmiştir.Araştırma vurguları: Kurutulmuş odunun, kullanım öncesinde belirli bir süre dış hava şartlarında tutulduğunda rutubet içeriğinde bir artış gözlemlenebilir. Kullanıma kadar iklim koşullarının etkisi altında, odunun rutubet alma eğiliminin zamanın bir fonksiyonu olarak belirlenmesi pratik olarak önemlidir.

In this study, a method suitable for on-line rapid species classification of western hemlock and amabilis fir (hem-fir) green mix of timber was developed and tested with the use of near infrared spectroscopy (NIRS) and chemometrics. The spectra of 600 wood specimens obtained from each species were collected over the wavelength range of 350–2500 nm. They were thereafter pretreated by smoothing; first derivative, second derivative and standard normal variate and calibration models were developed using the wavelength range of 800–1800 nm by partial least squares-linear discriminant analysis (PLS-LDA) and least squares-support vector machines (LS-SVM). The effects of wood surface (transverse, tangential and radial), wood zone (heartwood and sapwood) and sample moving speed (0, 0.5 and 1 m/s) were also explored. LS-SVM is superior to PLS-LDA in terms of classification performance at moving conditions. The best results were obtained using the LS-SVM method when spectra were collected on the transverse surface at a speed of 1 m/s and pretreated by smoothing. The sensitivity, specificity, and accuracy for both calibration and validation sets were all 100%. Collectively, NIR spectroscopy combined with LS-SVM is capable of on-line species separation of green hem-fir mix prior to wood drying.

Funding Information: Open access funding provided by Aalto University. This work received funding from the Academy of Finland (Grant No. 315768) and FinnCERES Flagship Programme of the Academy of Finland (Projects No. 318890 and 318891). Funding Information: This work was a part of the Academy of Finland’s Flagship Programme, under Projects No. 318890 and 318891 (Competence Center for Materials Bioeconomy, FinnCERES). P.A.P. thanks the Academy of Finland for funding (Grant No. 315768). Institut Laue-Langevin (ILL) (instrument D11, proposal DIR-175) is thanked for provision of facilities and technical assistance. The authors wish to acknowledge CSC – IT Center for Science, Finland, for computational resources. Dr. Ralf Schweins is thanked for assistance with the neutron experiments. Dr. Jukka Ketoja is thanked for valuable discussions. Publisher Copyright: © 2021, The Author(s). Structural changes of cellulose microfibrils and microfibril bundles in unmodified spruce cell wall due to drying in air were investigated using time-resolved small-angle neutron scattering (SANS). The scattering analysis was supported with dynamic vapor sorption (DVS) measurements to quantify the macroscopic drying kinetics. Molecular dynamics (MD) simulations were carried out to aid in understanding the molecular-level wood-water interactions during drying. Both SANS experiments and simulations support the notion that individual cellulose microfibrils remain relatively unaffected by drying. There is, however, a significant decrease in fibril-to-fibril distances in microfibril bundles. Both scattering and DVS experiments showed two distinct drying regions: constant-rate drying and falling-rate drying. This was also supported by the MD simulation results. The shrinking of the fibril bundles starts at the boundary of these two regions, which is accompanied by a strong decrease in the diffusivity of water in between the microfibrils.

The relationships between free shrinkage and actual shrinkage of different layers in Mongolian Scotch pine (Pinus sylvestris var. mongolica Litv.) were explored to provide basic data for the further study of drying shrinkage properties. The free shrinkage coefficients at different temperatures and the actual shrinkage strain of each layer were examined under conventional drying. The results showed high precision of free drying shrinkage of corresponding layers of thin small test strips in each layer of sawn timber. The free shrinkage increased linearly as moisture content declined. At the same temperature, the free shrinkage coefficient reached the largest values for the first layer (above 0.267%), while the smallest values were recorded for the ninth layer (below 0.249%). Except for the ninth layer, the free shrinkage coefficients in width directions of other representative layers decreased as temperature increased. At constant temperature, the difference in free shrinkage coefficient of test materials in the length direction of sawn timber was small for the first layer, but slightly larger and changed irregularly in the fifth and ninth layer direction. At the end of conventional drying, the plastic deformation of each layer in the early stage of drying showed a reducing trend or even reversal due to the effects of reverse stress and later damp heat. In sum, these findings look promising for future optimization of wood drying process.

The influence of the impregnation process of pine wood (Pinus sylvestris L.) samples on the electrical resistance changes and the moisture-content measurement accuracy is presented in this paper. In this study, the resistances of impregnated and nonimpregnated green pine timber harvested from northern Poland were compared. An impregnation method based on a vacuum-pressure chamber was used. Copper salts were applied as the impregnated solutions. The obtained results of the electrical resistance comparison showed a dependence of wood resistance on the moisture content. Higher conductivity occurred in impregnated wood samples filled with copper salt compared with wood samples without impregnation. Noticeable differences in the electrical resistance values were observed when the wood moisture content was significantly above the Fibre Saturation Point (FSP).