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Special Issue "Wood Properties and Processing"

A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Forest Ecophysiology and Biology".

Deadline for manuscript submissions: 31 May 2019

Special Issue Editor

Guest Editor
Prof. Dr. Miha Humar

Department of Wood Science and Technology, University of Ljubljana, Faculty of Biotechnology, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia
Website | E-Mail
Interests: wood; wood preservation; wood modification; service life prediction; wood-water interactions; performance of wood; weathering

Special Issue Information

Dear Colleagues,

Wood based materials are CO2-neutral, renewable, and considered to be environmentally friendly. The huge variety of wood species and wood-based composites allows a wide scope of creative and aesthetic alternatives to materials with higher environmental impacts during production, use and disposal. Modern building and construction practice would not be possible without use of wood or wood based composites. Use of composites enables use of wood of lower quality for production of materials with engineered properties for specific, target applications. Even more, utilization of reinforcing particles as carbon nano-tubes, nano-cellulose…, enables development of new generation of composites with even better properties. They have a potential to replace other construction materials like steel in many applications. The positive aspect of decomposability of waste wood can turn into the opposite when wood or wood based materials are exposed to weathering, moisture oscillations, different discoloring and degrading organisms. Protective measures are therefore unavoidable for many outdoor applications. These techniques includes: application of biocides, water repellents, surface coatings, wood modification, protection by construction, development of new generation of composites and hybrids… Resistance of wood against different aging factors is always a combined effect of toxic or inhibiting ingredients on one hand, and of structural, anatomical or chemical ways of exclusion of moisture, which is one of the most important factors for deterioration. In order to predict service life of wood various models can be applied.

Prof. Dr. Miha Humar
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Forests is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Wood
  • Wood based composites
  • Performance
  • Properties of wood
  • Building with wood
  • Degradation
  • Protection
  • Water-wood interactions
  • Mechanical properties
  • Fine chemicals

Published Papers (9 papers)

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Research

Open AccessArticle Artificial Neural Network Modeling for Predicting Wood Moisture Content in High Frequency Vacuum Drying Process
Forests 2019, 10(1), 16; https://doi.org/10.3390/f10010016
Received: 5 December 2018 / Revised: 24 December 2018 / Accepted: 26 December 2018 / Published: 29 December 2018
Cited by 1 | PDF Full-text (2933 KB) | HTML Full-text | XML Full-text
Abstract
The moisture content (MC) control is vital in the wood drying process. The study was based on BP (Back Propagation) neural network algorithm to predict the change of wood MC during the drying process of a high frequency vacuum. The data of real-time [...] Read more.
The moisture content (MC) control is vital in the wood drying process. The study was based on BP (Back Propagation) neural network algorithm to predict the change of wood MC during the drying process of a high frequency vacuum. The data of real-time online measurement were used to construct the model, the drying time, position of measuring point, and internal temperature and pressure of wood as inputs of BP neural network model. The model structure was 4-6-1 and the decision coefficient R2 and Mean squared error (Mse) of the training sample were 0.974 and 0.07355, respectively, indicating that the neural network model had superb generalization ability. Compared with the experimental measurements, the predicted values conformed to the variation law and size of experimental values, and the error was about 2% and the MC prediction error of measurement points along thickness direction was within 2%. Hence, the BP neural network model could successfully simulate and predict the change of wood MC during the high frequency drying process. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Nondestructive Characterization of Dry Heat-Treated Fir (Abies Alba Mill.) Timber in View of Possible Structural Use
Forests 2018, 9(12), 776; https://doi.org/10.3390/f9120776
Received: 14 November 2018 / Revised: 4 December 2018 / Accepted: 11 December 2018 / Published: 15 December 2018
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Abstract
The use of heat-treated timber for building with wood is of increasing interest. Heat treatment improves the durability and dimensional stability of wood; however, it needs to be optimized to keep wood’s mechanical properties in view of the possible structural use of timber. [...] Read more.
The use of heat-treated timber for building with wood is of increasing interest. Heat treatment improves the durability and dimensional stability of wood; however, it needs to be optimized to keep wood’s mechanical properties in view of the possible structural use of timber. Therefore, dry vacuum heat treatment varying the maximum temperature between 170 °C and 230 °C was used on fir (Abies alba Mill.) structural timber, visually top graded according to EN 338, to analyze its final weight loss, hygroscopicity, CIELAB color, and dynamic elastomechanical properties. It turned out that weight loss and total color difference of wood positively correlates with the increasing intensity of the heat treatment. The maximum 40% reduction of the hygroscopicity of wood was already reached at 210 °C treatment temperature. The moduli of elasticity in longitudinal and radial direction of wood, determined by ultrasound velocity, increased initially up to the treatment temperature of 210 °C, and decreased at higher treatment temperature. Equally, the Euler-Bernoulli modulus of elasticity from free-free flexural vibration of boards in all five vibration modes increased with the rising treatment temperature up to 190 °C, and decreased under more intensive treatment conditions. The Euler-Bernoulli model was found to be valid only in the 1st vibration mode of heat-treated structural timber due to the unsteady decrease in the evaluated moduli of elasticity related to the increasing mode number. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Investigation of Bamboo Grid Packing Properties Used in Cooling Tower
Forests 2018, 9(12), 762; https://doi.org/10.3390/f9120762
Received: 1 November 2018 / Revised: 2 December 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
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Abstract
Due to its advantages of good heat-resistance, environmental-friendliness, and low cost, bamboo grid packing (BGP) has become a promising new type of cooling packing. It is being increasingly used in Chinese industrial cooling towers to replace cooling packings made of polyvinyl chloride, cement, [...] Read more.
Due to its advantages of good heat-resistance, environmental-friendliness, and low cost, bamboo grid packing (BGP) has become a promising new type of cooling packing. It is being increasingly used in Chinese industrial cooling towers to replace cooling packings made of polyvinyl chloride, cement, and glass fiber reinforced plastic. However, mechanical properties and fungal resistance are a concern for all bamboo applications. In this study, the modulus of rupture (MOR), modulus of elasticity (MOE), density, crystallinity, and environment scanning electron microscope (ESEM) properties were compared between fresh BGPs and those that had been in service for nine years in the cooling towers. The results showed that the MOR, MOE, density, crystallinity, and the crystal size of the used BGPs decreased to some extent, but still met the requirements for normal use in a cooling tower. The ESEM observation showed that the used BGPs were not infected by fungi. The decrease in mechanical properties could be caused by the decrease of density, crystallinity, and the decomposition of the chemical components of bamboo, but not by fungal infection. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Acoustic Velocity—Wood Fiber Attribute Relationships for Jack Pine Logs and Their Potential Utility
Forests 2018, 9(12), 749; https://doi.org/10.3390/f9120749
Received: 18 October 2018 / Revised: 15 November 2018 / Accepted: 23 November 2018 / Published: 30 November 2018
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Abstract
This study presents an acoustic-based predictive modeling framework for estimating a suite of wood fiber attributes within jack pine (Pinus banksiana Lamb.) logs for informing in-forest log-segregation decision-making. Specifically, the relationships between acoustic velocity (longitudinal stress wave velocity; vl) and [...] Read more.
This study presents an acoustic-based predictive modeling framework for estimating a suite of wood fiber attributes within jack pine (Pinus banksiana Lamb.) logs for informing in-forest log-segregation decision-making. Specifically, the relationships between acoustic velocity (longitudinal stress wave velocity; vl) and the dynamic modulus of elasticity (me), wood density (wd), microfibril angle (ma), tracheid wall thickness (wt), tracheid radial and tangential diameters (dr and dt, respectively), fiber coarseness (co), and specific surface area (sa), were parameterized deploying hierarchical mixed-effects model specifications and subsequently evaluated on their resultant goodness-of-fit, lack-of-fit, and predictive precision. Procedurally, the data acquisition phase involved: (1) randomly selecting 61 semi-mature sample trees within ten variable-sized plots established in unthinned and thinned compartments of four natural-origin stands situated in the central portion the Canadian Boreal Forest Region; (2) felling and sectioning each sample tree into four equal-length logs and obtaining twice-replicate vl measurements at the bottom and top cross-sectional faces of each log (n = 4) from which a log-specific mean vl value was calculated; and (3) sectioning each log at its midpoint and obtaining a cross-sectional sample disk from which a 2 × 2 cm bark-to-pith radial xylem sample was extracted and subsequently processed via SilviScan-3 to derive annual-ring-specific attribute values. The analytical phase involved: (1) stratifying the resultant attribute—acoustic velocity observational pairs for the 243 sample logs into approximately equal-sized calibration and validation data subsets; (2) parameterizing the attribute—acoustic relationships employing mixed-effects hierarchical linear regression specifications using the calibration data subset; and (3) evaluating the resultant models using the validation data subset via the deployment of suite of statistical-based metrics pertinent to the evaluation of the underlying assumptions and predictive performance. The results indicated that apart from tracheid diameters (dr and dt), the regression models were significant (p ≤ 0.05) and unbiased predictors which adhered to the underlying parameterization assumptions. However, the relationships varied widely in terms of explanatory power (index-of-fit ranking: wt (0.53) > me > sa > co > wd >> ma (0.08)) and predictive ability (sa > wt > wd > co >> me >>> ma). Likewise, based on simulations where an acoustic-based wd estimate is used as a surrogate measure for a Silviscan-equivalent value for a newly sampled log, predictive ability also varied by attribute: 95% of all future predictions for sa, wt, co, me, and ma would be within ±12%, ±14%, ±15%, ±27%, and ±55% and of the true values, respectively. Both the limitations and potential utility of these predictive relationships for use in log-segregation decision-making, are discussed. Future research initiatives, consisting of identifying and controlling extraneous sources of variation on acoustic velocity and establishing attribute-specific end-product-based design specifications, would be conducive to advancing the acoustic approach in boreal forest management. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Bending Stiffness, Load-Bearing Capacity and Flexural Rigidity of Slender Hybrid Wood-Based Beams
Forests 2018, 9(11), 703; https://doi.org/10.3390/f9110703
Received: 19 October 2018 / Revised: 3 November 2018 / Accepted: 9 November 2018 / Published: 13 November 2018
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Abstract
Modern architecture suggests the use of opened spaces with large transparent envelope surfaces. Therefore, windows of long widths and large heights are needed. In order to withstand the wind loads, such wooden windows can be reinforced with stiffer materials, such as aluminium (Al), [...] Read more.
Modern architecture suggests the use of opened spaces with large transparent envelope surfaces. Therefore, windows of long widths and large heights are needed. In order to withstand the wind loads, such wooden windows can be reinforced with stiffer materials, such as aluminium (Al), glass-fibre reinforced polymer (GFRP), and carbon-fibre reinforced polymer (CFRP). The bending stiffness, load-bearing capacity, and flexural rigidity of hybrid beams, reinforced with aluminium, were compared through experimental analysis, using a four-point bending tests method, with those of reference wooden beams. The largest increases in bending stiffness (29%–39%), load-bearing capacity (33%–45%), and flexural rigidity (43%–50%) were observed in the case of the hybrid beams, with the highest percentage of reinforcements (12.9%—six reinforcements in their tensile and six reinforcements in their compressive zone). The results of the experiments confirmed the high potential of using hybrid beams to produce large wooden windows, for different wind zones, worldwide. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Effect of Rotation Age and Thinning Regime on Visual and Structural Lumber Grades of Douglas-Fir Logs
Forests 2018, 9(9), 576; https://doi.org/10.3390/f9090576
Received: 24 July 2018 / Revised: 8 September 2018 / Accepted: 8 September 2018 / Published: 18 September 2018
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Abstract
Douglas-fir, the most important timber species in the Pacific Northwest, US (PNW), has high stiffness and strength. Growing it in plantations on short rotations since the 1980s has led to concerns about the impact of juvenile/mature wood proportion on wood properties. Lumber recovered [...] Read more.
Douglas-fir, the most important timber species in the Pacific Northwest, US (PNW), has high stiffness and strength. Growing it in plantations on short rotations since the 1980s has led to concerns about the impact of juvenile/mature wood proportion on wood properties. Lumber recovered from four sites in a thinning trial in the PNW was analyzed for relationships between thinning regime and lumber grade yield. Linear mixed-effects models were developed for understanding how rotation age and thinning affect the lumber grade yield. Log small-end diameter was overall the most important for describing the presence of an appearance grade, generally exhibiting an indirect relationship with the lower quality grades. Stand Quadratic Mean Diameter (QMD) was found to be the next most uniformly important predictor, its influence (positive or negative) depending on the lumber grade. For quantity within a grade, as log small-end diameter increased, the quantity of the highest grade increased, while decreasing the quantity of the lower grades differentially. Other tree and stand attributes were of varying importance among grades, including stand density, tree height, and stand slope, but logically depicted the tradeoffs or rebalancing among the grades as the tree and stand characteristics change. Structural lumber grade presence was described best by acoustic wave flight time, log position (decreasing presence in upper logs), and an increasing presence with rotation age. A smaller set of variables proved useful for describing quantity within a structural grade. Forest managers can use these results in planning to best capture value in harvesting, allowing them to direct raw materials (logs) to appropriate manufacturing facilities given market demand. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Surface Changes of Selected Hardwoods Due to Weather Conditions
Forests 2018, 9(9), 557; https://doi.org/10.3390/f9090557
Received: 14 August 2018 / Revised: 6 September 2018 / Accepted: 7 September 2018 / Published: 11 September 2018
Cited by 2 | PDF Full-text (18082 KB) | HTML Full-text | XML Full-text
Abstract
The study is focused on the surface changes of five hardwoods (oak, black locust, poplar, alder and maple) that were exposed to natural weathering for 24 months in the climatic conditions of Central Europe. Colour, roughness, visual and chemical changes of exposed surface [...] Read more.
The study is focused on the surface changes of five hardwoods (oak, black locust, poplar, alder and maple) that were exposed to natural weathering for 24 months in the climatic conditions of Central Europe. Colour, roughness, visual and chemical changes of exposed surface structures were examined. The lowest total colour changes (ΔE*) were found for oak (23.77), the highest being recorded for maple (34.19). Roughness differences after 24-month exposure (ΔRa) showed minimal changes in poplar wood (9.41); the highest changes in roughness were found on the surface of alder (22.18). The presence of mould and blue stains was found on the surface of maple, alder and poplar. Chemical changes were characterized by lignin and hemicelluloses degradation. Decreases of both methoxy and carbonyl groups, cleavage of bonds in lignin and hemicelluloses, oxidation reaction and formation of new chromophores were observed. In the initial phases of the degradation process, the discoloration was related to chemical changes; in the longer period, the greying due to settling of dust particles and action of mould influenced the wood colour. The data were confirmed by confocal laser scanning microscopy. The obtained results revealed degradation processes of tested hardwood surfaces exposed to external environmental factors. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Preferences for Urban Building Materials: Does Building Culture Background Matter?
Forests 2018, 9(8), 504; https://doi.org/10.3390/f9080504
Received: 24 July 2018 / Revised: 13 August 2018 / Accepted: 14 August 2018 / Published: 17 August 2018
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Abstract
A fast-growing global population, increasing urbanization, and an increasing flow of people with different building cultural backgrounds bring material use in the housing sector into focus. The aim of this study is to identify material preferences in the building environment in cities and [...] Read more.
A fast-growing global population, increasing urbanization, and an increasing flow of people with different building cultural backgrounds bring material use in the housing sector into focus. The aim of this study is to identify material preferences in the building environment in cities and to determine if the building cultural background impacts those preferences. The data in this study consisted of responses from two groups of dwellers in Norway, including immigrants from countries where wood is an uncommon building material and native Norwegians from a building culture where wood is common. We found that the most preferred materials were often the same as the most common materials currently used in city buildings. Only small differences were found between the two groups of dwellers that were studied. Most differences were related to concerns about material choice in general and where individuals wanted to live. Respondents who preferred city living preferred commonly used city materials, such as concrete and steel. For cladding materials, stone/bricks were the most preferred. However, stained or painted wood was one of the most preferred, even though it is not commonly used in city buildings. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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Open AccessArticle Influence of Natural and Artificial Weathering on the Colour Change of Different Wood and Wood-Based Materials
Forests 2018, 9(8), 488; https://doi.org/10.3390/f9080488
Received: 1 July 2018 / Revised: 6 August 2018 / Accepted: 8 August 2018 / Published: 10 August 2018
Cited by 7 | PDF Full-text (6997 KB) | HTML Full-text | XML Full-text
Abstract
The importance of the aesthetic performance of wood is increasing and the colour is one of the most important parameters of aesthetics, hence the colour stability of twelve different wood-based materials was evaluated by several in-service and laboratory tests. The wood used for [...] Read more.
The importance of the aesthetic performance of wood is increasing and the colour is one of the most important parameters of aesthetics, hence the colour stability of twelve different wood-based materials was evaluated by several in-service and laboratory tests. The wood used for wooden façades and decking belongs to a group of severely exposed surfaces. Discolouration of wood in such applications is a long-known phenomenon, which is a result of different biotic and abiotic causes. The ongoing in-service trial started in October 2013, whilst a laboratory test mimicking seasonal exposure was performed in parallel. Samples were exposed to blue stain fungi (Aureobasidium pullulans and Dothichiza pithyophila) in a laboratory test according to the EN 152 procedure. Afterwards, the same samples were artificially weathered and re-exposed to the same blue stain fungi for the second time. The purpose of this experiment was to investigate the synergistic effect of weathering and staining. The broader aim of the study was to determine the correlation factors between artificial and natural weathering and to compare laboratory and field test data of fungal disfigurement of various bio-based materials. During the four years of exposure, the most prominent colour changes were determined on decking. Respective changes on the façade elements were significantly less prominent, being the lest evident on the south and east façade. The results showed that there are positive correlations between natural weathering and the combination of artificial weathering and blue staining. Hence, the artificial weathering of wood-based materials in the laboratory should consist of two steps, blue staining and artificial weathering, in order to simulate colour changes. Full article
(This article belongs to the Special Issue Wood Properties and Processing)
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