Wood Moisture Content Research Articles

Heuristic study on the interaction between heat exchange and slow relaxation processes during wood moisture content changes

Abstract “Non-Fickian” diffusion of wood moisture refers to the unexplained anomalous behaviour of water vapour sorption in wood. The depression of moisture diffusion rates in thin sections of wood tissue during moisture content change at high relative humidity is one of the least-understood aspects of “non-Fickian” diffusion. In a previous work, a rate-limiting effect by two cooperative couplings of moisture and heat transfer, was shown to generate some signature features of “non-Fickian” diffusion. The present work aims to heuristically study the simultaneous action of this thermal rate-limiting effect and intrinsic slow relaxation processes in wood. Using an analytical non-geometrical model, exact solutions are obtained which show that the thermal rate-limiting effect acts directly and equally on diffusion and all relaxation processes, effectively time-stretching the entire dynamic wood moisture response. The magnitude of the time-scaling effect is proportional to the coupling strength between heat and mass transfer, which increases progressively with the relative humidity.

Mycelia Growth of Shiitake (Lentinula edodes) on 4-Wood Species from Leguminaceae Family

Cultivation of Shiitake mushroom (Lentinula edodes) in Indonesia has not been developed yet, due to its low productivity. It happens because of the limited information of the good ways on cultivation Shiitake in Indonesia. One of the factors that affect the growth of mushroom is the media. In Indonesia, the information about the media composition by using various species of wood have not been found yet. Therefore, this research was conducted to determine the effect of using different wood species to the growth of Shiitake. This study used four wood species from the leguminaceae family, those were: Gamal (Glicidia sepium); Johar (Samanea saman); Leucaena (Leucaena leucocephala); and Sengon (Falcataria moluccana). Those were used as the media by adding 12.5% (w/w) of rice bran and 6% (w/w) of CaCO3, and adjusting the moisture content by adding the distillate water to 65, 70, and 75%. Then, the media was put in to the petridisk (ø 90 mm) and inoculated with Shiitake mushroom. During the mycelia growth, the length of mycelia was measured every 2 days until fifty days, and then glucosamine content was analyzed. In addition, chemical analysis was also conducted to each media. The results showed that different wood species resulted different chemical content of media, except the acid soluble lignin content. The growth rate of mycelia was affected by the moisture content of media, meanwhile the glucosamin content is influenced by the moisture content and various species of wood. The best combination to cultivate the Shiitake mushroom was by using media made of gamal with 70% moisture content. There were positive correlation among the ethanol-toluen extracts content and the mycelia growth, however there was negative correlation among the hemicelullose content the mycelia growth.

ANALYSIS OF RHEOLOGICAL MODELS OF PROCESS OF SELF-FORMING OF GLUED WOODEN

The article considers a promising technology for self-shaping glued wooden elements of curved forms. This method is based on rheological processes occurring in wood, such as dehumidification and swelling of wood and its anisotropic properties.
 To predict the final curved shape of the wooden structure, the authors analyzed existing rheological models of wood and concluded that the rheological model proposed by European researchers includes the most complete list of factors that affect the process of deformation of wood: elastic and plastic deformation, drying and swelling of wood, deformation of viscous-elastic creep and mechanical sorption deformation.
 Based on the results of experimental studies and numerical modeling of the change in the curvature of glued wooden elements, which were made by European researchers, it was found that the proposed rheological model of wood needs to be clarified, namely, the correction of hygro-expansion coefficients depending on the moisture content of wood.
 A further direction of the authors’ research will be aimed at conducting model experiments to determine the hygro-expansion coefficients of different grades of wood depending on the thickness of the wooden elements and the orientation of the layers in the glued structure.

Quality Control of Thermally Modified Timber Using Dynamic Vapor Sorption (DVS) Analysis

The importance of thermal modification is increasing worldwide. Increased use of thermally modified timber (TMT) has resulted in a need for reliable quality control, comprising control of variation of the production within defined limits, allowing third-party control in the case of certification and the regulation of customer complaints and claims. Techniques are thus needed to characterise the modification of quality in terms of improved target properties of TMT during industrial production, and of TMT products that have been in service for an arbitrary time. In this study, we aimed to utilise dynamic vapor sorption (DVS) for this purpose. Norway spruce (Picea abies) and European beech (Fagus sylvatica) samples were thermally modified at different temperatures according to different heat treatment techniques: (1) the Silvapro process based on an initial vacuum; (2) an air heat treatment, whereby samples were wrapped in aluminium foil; (3) thermal modification of wood samples in the ambient atmosphere in a laboratory oven. Wood samples from closed processes were analysed for validation. TMT was characterised with respect to mass loss, colour and density. Mass loss of wood due to modification (MLTM) was correlated with factors derived from DVS analysis. The present DVS measurements suggest that the equilibrium wood moisture content (EMC95% RH), the time to reach 10% wood moisture content (t10% MC), and the elongation factor, c, derived from a logarithmic function, can serve as alternative parameters to characterise the quality of several thermal modification processes. Further studies are recommended using other wood species, different modification processes and further parameters gained from DVS measurements to understand the robustness and the predictive power of the applied technique.

Transportation of Wood Boring Beetles in Wooden Transport Boxes, Wooden Pallets, and Newly Bought Wood in Museums

ABSTRACT In the past, woodborers like A. punctatum and X. rufovillosum were widespread in historic furniture, households, and building structures, but as they need a high wood moisture content and central heating and climate control have become common today their occurrence is rare and often limited to open-air museums, rural museums, and historic buildings. In this paper, we report on the spread and transportation of different wood-boring beetles with wooden pallets, wooden transport boxes used for art transportation, and also the rising problem of different Lyctus species (powder post beetles) in new wood used in museums. Not only the native Lyctus linearis but also the introduced L. brunneus, L. cavicollis, and L. africanus can be found in transport boxes (nine cases in Germany between 2003 and 2015), infestations of new picture frames (three cases in Austria between 2010 and 2015), and new wood sold to carpenters in museum and conservation studios (used for new stretcher and picture frames, two cases in Austria). In some cases (two in Germany) a newly-laid parquet floor was infested by powder post beetles. The house longhorn beetle (H. bajulus), the furniture beetle (A. punctatum), and the Anobiid Oligomerus ptilinoides were all found infesting wooden pallets inside museum stores (five cases in Austria). New wooden pallets and transport boxes are treated once with heat after production, but our examples show that infestation and transportation of wood pests are still possible and are a new challenge for integrated pest management (IPM) in the future. We examine and discuss the materials used to transport art and possible measures to combat and prevent pests (plastic pallets or the use of other wood types). In addition, the biology and life-history of powderpost beetles is described.

Treatability of wood for pressure treatment processes: a literature review

Inadequate and non-uniform penetration of preservatives into refractory wood species is a main concern in the wood preservation industry for pressure processes. Although the treatability of wood is greatly related to its porous structure, it may be influenced by other parameters like wood moisture content, drying technique, preservative formulation and treatment process. General principles of the wood treatability measurement by macro- and microscale approaches as well as by analytical techniques are discussed. Several innovative strategies have been developed to enhance the treatability of wood. Some strategies are currently being used in the industry, some have a potential for industrial upscaling, while others still remain at the laboratory scale. This review also involves a comprehensive review of recent progress to date in improving this physical property of wood.

Real-Time Optimization of Pulp Mill Operations with Wood Moisture Content Variation

In tropical countries, such as Thailand, the variation of tree moisture content can be significant based on seasonal variations in rainfall. Pulp mill operation optimization accounting for wood moisture variation was used to determine optimal operation conditions and minimize production cost. The optimization models were built using empirical modeling techniques with simulated data from the IDEAS software package. Three case studies were performed. First, a base case of nominal annual operation at a fixed production rate was used to calculate production cost that varies with wood moisture content. The second case is annual optimization where production was allowed to vary monthly over an annual cycle to minimize production cost. For the third case, real-time optimization (RTO) was used to determine optimal production rate with the wood moisture content varying every 3 days. The rolling horizon approach was used to schedule production to keep inventory levels within bounds and with a penalty applied to deviations from the annual expected values of inventory. The advantage of RTO in accounting for moisture content variation was confirmed by annual production costs results simulated for 20 years. These results statistically demonstrated that the overall cost was reduced compared to the second case of monthly production targets.

Correlations of Major Flame Characteristics of Some Fire Tolerant Trees in South-East Nigeria by Coefficient of Determination (R2)

Background: Bush fire is a common hazard in South East-Nigeria as in other parts of the country during the harmattan. Every year, thousands of hectares of forests as well as suburban lands are severely burnt. These forest fires have been catastrophic, destroying large areas of tropical rain forests and in most cases have claimed many lives and destroyed properties worth millions of naira. However, some of these trees identified by local people and named by taxonomists as Daniellia oliveri, Anacadium occidentale, Vitex doniana, Lonchocarpus griffonianus, Gmelina arborea, Nauclea latifolia, Tectona grandis, Mangifera indica, Delonix regia, Newbouldia laevis, Azadirachta indica, Dialium guineense, Terminalia superba, Manilkara obovata and Irvingia gabonensis have proven to be fire tolerant.
 Aim: The aim is to establish correlations among the physical properties (wood density and moisture content) and flame characteristics (ignition time, flame propagation rate, flame duration, afterglow time, ash formation and limiting oxygen index) of these fire tolerant trees.
 Study Design: An item structured instrument was developed by the researchers which reflected the six points modified Likert scale of strongly agree, agree, somewhat agree, somewhat disagree, disagree, strongly disagree and used to elicit information from the respondents who were mainly seasoned wood dealers of above 60 years of age. Analysis of Variance (ANOVA) was the major tool of analysis used to establish whether the tree species tolerates fire or not while correlation of the parameters was achieved by the application of R2.
 Place and Duration of Study: Determination of both the physical properties and flame characteristics of the tree species was done at the Research Laboratory of the Department of Pure and Industrial Chemistry, Nnamdi Azikiwe University, Awka between June, 2018 and April, 2019.
 Methodology: The physical properties of the tree species as well as their flame characteristics were carried out using their standard methods.
 Results: The values for these parameters vary among the tree species. Correlation among the parameters indicates a determination coefficient range from 0.000 to 0.637.
 Conclusion: There are highly significant correlations between wood density and both ignition time and flame propagation rate as well as wood density and limiting oxygen index. There is also strong correlation between ignition time and both flame propagation rate and limiting oxygen index. Afterglow time depends on limiting oxygen index and vice versa.

Contactless moisture content measurement on green veneer based on laser light scattering patterns

The wood structure anisotropy and moisture content variation within the volume create different patterns of light scattering inside the wood. The objective of this study was to assess the suitability of a laser method for online measurement of green veneer moisture content based on the so-called tracheid effect. Beech and poplar veneers with thicknesses of 1, 2 and 3 mm were subsequently laser scanned and weighed to obtain various humidities. The results show that the measured laser scattering profile, such as the major axis, minor axis and ellipse area on the veneer surface, increases with moisture. The laser scattering profile provides a reliable and precise prediction of the moisture content. Out of the three ellipse parameters evaluated, the ellipse area provides the best prediction of the moisture content of the green veneer for both beech and poplar.

Estimations of the moisture content above the fiber saturation point in sugi wood using the correlation between the specific dynamic Young\u2019s modulus and tangent loss

A novel method for estimating the wood moisture content above the fiber saturation point (FSP) is proposed, and the method performance is confirmed. Previous studies have highlighted that there is a negative linear correlation between the specific dynamic Young’s modulus (log (E/ρ)) and tangent loss (log (tanδ)) of clear small wood specimens. We confirm that this correlation can be obtained for air-dried commercial lumber from Japanese cedar, or sugi (Cryptomeria japonica), via experimental analysis. The best-fit linear regression line of this correlation only changes by the apparent density above the FSP (i.e., only by the moisture content of the specimen) when E and tanδ are kept constant in this high moisture content range. Here, we derive an equation to calculate the moisture content using log (E/ρ) and log (tanδ) based on the regression line of sugi wood at the FSP. A 45-day drying test was conducted on 23 green lumber specimens, with the E/ρ and tanδ values calculated from the natural resonance frequency fr, the logarithmic decrement λ and dimensions at various drying stages. The estimated moisture contents are in good agreement with the measured values, confirming the performance of proposed moisture content method.

Modeling and Monitoring of Wood Moisture Content Using Time-Domain Reflectometry

Time-domain reflectometry (TDR) can monitor the moisture content (MC) of water saturated logs stored in wet-decks where the MC exceeds the range that can be measured using traditional moisture meters (>50%). For this application to become routine, it is required that TDR monitoring of wet-decks occurs after establishment, and tools are needed that automate data collection and analysis. We developed models that predict wood MC using three-rod epoxy encased TDR probes inserted into the transverse surface of bolts (prior wet-deck studies were installed on the tangential surface). Models were developed for southern pine, sweetgum, yellow poplar, hickory, red oak, and white oak using a Campbell Scientific TDR100. For each species, at least 37 bolts were soaked for a minimum of three months and then air dried with TDR waveforms, and MC was periodically recorded. Calibrations were developed between MC and the TDR signal using nonlinear mixed effects models. Fixed effects ranged from excellent (southern pine R2 = 0.93) to poor (red oak R2 = 0.36, hickory R2 = 0.38). Independent of wood species, random effects all had a R2 greater than 0.80, which indicates that TDR detects changes in MC at the individual sample level. Use of TDR combined with a datalogger was demonstrated in an operational wet-deck that monitored changes in MC over 12 months, and in a laboratory trial where bolts were exposed to successive wet-dry cycles over 400 days. Both applications demonstrated the utility of TDR to monitor changes in wood MC in high MC environments where periodic measurement is not feasible due to operational safety concerns. Because a saturated TDR reading indicates a saturated MC, and because of the relatively accurate random effects found here, developing individual species models is not necessary for monitoring purposes. Therefore, application of TDR monitoring can be broadly applied for wet-decks, regardless of the species stored.

Simultaneous detection of density, moisture content and fiber direction of wood by THz time-domain spectroscopy

In the wood product-manufacturing process, the physical properties of wood must be monitored. The terahertz (THz) radiation has a high potential for sensing and imaging wood with a good spatial resolution. This study demonstrates the simultaneous prediction of the density, moisture content, and fiber direction of wood, which are important in determining the wood quality, using THz time-domain spectroscopy. We measured the spectra of 12 kinds of wood at various moisture contents while rotating the sample against the THz wave polarization. The fiber direction was predicted by observing the birefringence, which is the optical property of a material, in which the refractive index depends on the polarization direction. The density and the moisture content were predicted by multiple linear regression using the refractive indices and absorption coefficients obtained from the THz measurement. In a series of THz measurements, we successfully identified the wood fiber direction with an R2 of 0.90 and a root mean square error (RMSE) of 16.51° (total measured range = 0–170°), the density with an R2 of 0.97 and an RMSE of 0.022 (total measured range = 0.25–0.67 g/cm3), and the moisture content with an R2 of 0.78 and an RMSE of 4.06 (total measured range = 0.00–30.98%).

Chemical composition as factor affecting the mechanical properties of thermally modified black poplar (Populus nigra L.)

Black poplar (Populus nigra L.) was thermally modified in superheated steam at 160 °C, 190 °C, and 220 °C for 2 h. The research identified correlations between the chemical composition and selected mechanical properties of thermally modified wood. The higher treatment temperatures significantly lowered the modulus of rupture (MOR) and the Brinell hardness (BH). These correlations were particularly apparent at higher temperatures (190 °C and 220 °C) when thermally modified wood experienced stronger hemicelluloses degradation, which was indicated by an increase in the content of non-structural substances. The wood properties including compressive strength parallel to the grain (CS), modulus of elasticity during bending (MOE), and compressing (MCS) were affected less by the chemical changes caused by the thermal processing of wood. Moreover, the level of wood moisture content also affected these changes.

Wood Density and Moisture Content Estimation by Drilling Chips Extraction Technique.

The novelty of this study is the development of an accurate wood moisture content (MC) estimation method based on a relatively brand-new, non-destructive testing technique (drilling chips extraction). The method is especially important in the assessment of existing timber structures, where non-destructive testing (NDT) results are affected by wood MC and should be adjusted to a reference MC, usually 12%. In the assessment of timber structures, it is not possible to determine MC by oven drying method and this should be estimated. Electrical resistance and capacitance are the conventional methods used for MC estimation. This research work aims to present an accurate MC estimation method based on the drilling chips extraction technique. For that, 99 specimens (90 × 65 × 38 mm3) from three softwood and hardwood species covering a wide range of densities (from 355 to 978 kg m−3) were tested after conditioning at five different MCs (5%, 10%, 15%, 20%, 25%). The Wood Extractor device based on the drilling chips extraction technique was used. The mass of the chips collected (drilling residue) from each drill was recorded. The results show that the MC of the chips extracted was statistically significantly different than the MC of the specimen and cannot be directly used as MC determination. However, the chips MC can be used as an estimator of specimen MC with high determination coefficients (R2 from 71% to 86%). As the main result, models to estimate density directly adjusted to a reference 12% MC from the wet and dry mass of chips extracted were developed with an R2 of 98%. In sum, the drilling chips extractor is a dependable and straightforward method to estimate MC and density from only one measurement. Density adjusted to a reference 12% MC can be directly estimated from a single model.

Moisture-Dependent Strength Properties of Thermally-Modified Fraxinus excelsior Wood in Compression.

European ash (Fraxinus excelsior L.) is one of the species commonly used for wood thermal modification that improves its performance. The presented research aimed to investigate a moisture-dependent strength anisotropy of thermally-modified European ash in compression. Wood samples were modified at 180 °C and 200 °C. Their mechanical parameters were determined in the principal anatomical directions under dry (moisture content of 3%) and wet (moisture content above fibre saturation point) conditions. Effect of heat treatment temperature and moisture content on the ash wood mechanical parameters concerning each anatomical direction were determined. The results show that thermal treatment kept the intrinsic anisotropy of wood mechanical properties. It decreased wood hygroscopicity, which resulted in improved strength and elasticity measured for wet wood when compared to untreated and treated samples. Higher treatment temperature (200 °C) increased wood elasticity in compression in all the anatomical directions despite wood moisture content during the measurements. Multivariate analysis revealed that the modification temperature significantly affected the modulus of elasticity perpendicular to the grain, while in the case of compression strength, the statistically significant effect was observed only parallel to the grain. The results obtained can be useful from an industrial perspective and can serve as part of a database for further modelling purposes.

Effects of moisture content on lap-shear, bending, and tensile strength of lap-jointed and finger-jointed southern pine using phenol resorcinol formaldehyde and melamine urea formaldehyde

The bonding performance of the phenol-resorcinol-formaldehyde adhesive (PRF) and melamine-urea-formaldehyde adhesive (MUF) with southern pine as substrates at various moisture contents (MC) was evaluated. The results showed that bonding shear strength with MUF and PRF was negatively related to wood MC, and bonding shear strength with MUF was higher than that of the PRF. The bending and tensile strengths of finger-jointed lumber decreased with wood MC. The bending strength of finger-jointed lumber was affected more by wood than adhesive. However, both wood and adhesive exhibited the same important contribution to the tensile strength.

One-year simulation of a solar wood dryer with glazed walls in a Moroccan climate

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).

Moisture Performance of Façade Elements Made of Thermally Modified Norway Spruce Wood

Wooden façades are gaining in importance. Thermally modified wood is becoming one of the preferred materials for claddings. In spite of the fact that façades made of thermally modified wood have been in use for more than two decades, reports about long-term monitoring have been sparse. The results of three-year monitoring of a façade made of thermally modified wood in Ljubljana are reported. Moisture content measurements of thermally modified façades were taken at 22 locations and compared to the moisture content of untreated Norway spruce wood. Temperature and relative humidity were recorded in parallel. The moisture content of the wood was compared to the average relative humidity before the measurements. The results confirm the lower moisture content of thermally modified wood in comparison to reference Norway spruce. The moisture content of the wooden façade could be best correlated with the average relative humidity and temperature 48 h before the wood moisture content measurement was taken.

Effects of Wood Moisture Content and the Level of Acetylation on Brown Rot Decay

Acetylation is one of the most common types of wood modification and is commercially available throughout the world. Many studies have shown that acetylated wood is decay resistant at high levels of acetylation. Despite its widespread use, the mechanism by which acetylation prevents decay is still not fully understood. It is well known that at a given water activity, acetylation reduces the equilibrium moisture content of the wood cell wall. Furthermore, linear relationships have been found between the acetylation weight percent gain (WPG), wood moisture content, and the amount of mass loss in decay tests. This paper examines the relationships between wood moisture content and fungal growth in wood, with various levels of acetylation, by modifying the soil moisture content of standard soil block tests. The goal of the research is to determine if the reduction in fungal decay of acetylated wood is solely due to the reduction in moisture content or if there are additional antifungal effects of this chemical treatment. While a linear trend was observed between moisture content and mass loss caused by decay, it was not possible to separate out the effect of acetylation from fungal moisture generation. The data show significant deviations from previously proposed models for fungal moisture generation and suggest that these models cannot account for active moisture transport by the fungus. The study helps to advance our understanding of the role of moisture in the brown rot decay of modified wood.

Thermal conductivity and deformation of Taxodium hybrid ‘Zhongshanshan’ during heat transfer process

The thermal conductivity and the deformation of wood from the Taxodium hybrid ‘Zhongshanshan’ were studied in the process of heat transfer. The results showed that the average thermal conductivity of this wood was 0.1257 W/(m·K) under the condition of 12% wood moisture content and 30 °C heat transfer temperature. When the testing temperature exceeded 0 °C, the thermal conductivity increased linearly with both temperature and wood moisture content and was affected by the moisture content of the wood. During the heat transfer process, the deformation of features caused repeated swelling and shrinkage in the longitudinal, radial, and tangential directions. The dimensional change was greatly affected by the wood’s moisture content and was less affected by the temperature. These results are of great meaning for the study of the heat transfer process of Taxodium hybrid ‘Zhongshanshan’ wood. Furthermore, it provides a scientific basis for the heat preservation effect, drying treatment, and pyrolysis treatment of Taxodium hybrid ‘Zhongshanshan’ wood for use as a building material.