Special Issue "Selected Contributions from WSE2019—The 15th Annual Meeting of the Northern European Network for Wood Science and Engineering"

A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Wood Science".

Deadline for manuscript submissions: closed (25 May 2020).

Special Issue Editors

Dr. Lisbeth Garbrecht Thygesen
Website
Guest Editor
University of Copenhagen, Department of Geosciences and Natural Resource Management Forest, Nature and Biomass Rolighedsvej 23, DK-1958 Frederiksberg C, Denmark
Interests: wood cell wall structure and chemistry; microscopy; spectroscopy
Dr. Maria Fredriksson
Website
Guest Editor
Lund University, Building and Environmental Technology, Building Materials, PO Box 118, SE-221 00 Lund, Sweden
Interests: wood–water interations; moisture sorption; durability
Dr. Gry Alfredsen
Website
Guest Editor
Norwegian Institute of Bioeconomy Research, Division of Forest and Forest Resources, Wood Technology, PO Box 115, NO-1431 Ås, Norway
Interests: brown rot decay mechanisms; service life prediction; novel wood protection systems

Special Issue Information

Dear Colleagues,

This Special Issue includes selected contributions from the 15th Annual Meeting of the Northern European Network for Wood Science and Engineering—WSE2019, which was held in Lund, Sweden, 9–10 October 2019. The network had its first annual meeting in 2005, and the purpose of the network is to promote collaboration between Northern European researchers within wood science and engineering. Young researchers are especially encouraged to participate in the meetings and present their work. The conference covers the topics: wood physics and mechanics, wood protection and modification, durability, wood engineering, engineered wood products and composites, and application of wood-based materials.

 

Dr. Lisbeth Garbrecht Thygesen
Dr. Maria Fredriksson
Dr. Gry Alfredsen
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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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
  • Durability
  • Moisture
  • Wood modification
  • Wood-based products

Published Papers (8 papers)

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Research

Open AccessArticle
A Mathematical Solution for Calculating the Springback of Laminated Beech Stacks Molded within the Elastic Range
Forests 2020, 11(7), 725; https://doi.org/10.3390/f11070725 - 02 Jul 2020
Abstract
The springback effect in molded wood laminations within the elastic range has, to date, not yet been mathematically described. Once cured, residual internal stresses within the laminations cause the final form to deviate from that of the die. Test pieces of beech laminations [...] Read more.
The springback effect in molded wood laminations within the elastic range has, to date, not yet been mathematically described. Once cured, residual internal stresses within the laminations cause the final form to deviate from that of the die. Test pieces of beech laminations of 1 mm, 2 mm and 4 mm thicknesses and stack sizes of between 2 and 16 laminations were used. The elasticity value of each stack was obtained using non-glued laminations in a three-point bending test within the elastic region. The laminations were glued with polyurethane resin and mounted in a radius form die. The stress induced by the die onto the stack is within the elastic region of the material without any prior chemical or physical plasticisation of the wood. After curing was complete and the laminations removed from the die, the actual radius was calculated using a circular equation within the CAD program, using three measurement points taken from the stack. The radius of the die within the limits of this study has a negligible effect when predicting the springback of the stack. The exponential correlation between springback and the number of laminations, was used to calculate the springback effect on molded laminated stacks. Full article
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Open AccessArticle
Effects of Changes in Biopolymer Composition on Moisture in Acetylated Wood
Forests 2020, 11(7), 719; https://doi.org/10.3390/f11070719 - 29 Jun 2020
Abstract
To investigate the effects of changes in biopolymer composition on moisture in acetylated poplar wood (Populus euramericana Cv.), the acetylation of control wood was compared to the acetylation of wood with reduced hemicellulose or lignin content (about 9% reduction of total specimen [...] Read more.
To investigate the effects of changes in biopolymer composition on moisture in acetylated poplar wood (Populus euramericana Cv.), the acetylation of control wood was compared to the acetylation of wood with reduced hemicellulose or lignin content (about 9% reduction of total specimen dry weight in both cases). Time-domain nuclear magnetic resonance relaxometry of water-saturated wood gave spin–spin relaxation times (T2) of water populations, while deuteration in a sorption balance was used to characterize the hydroxyl accessibility of the wood cell walls. As expected, the acetylation of pyridine-swelled wood reduced hydroxyl accessibility and made the cell wall less accessible to water, resulting in a reduction of cell wall moisture content by about 24% compared with control wood. Hemicellulose loss per se increased the spin–spin relaxation time of cell wall water, while delignification had the opposite effect. The combined effect of hemicellulose removal and acetylation caused more than a 30% decrease of cell wall moisture content when compared with control wood. The acetylated and partially delignified wood cell walls contained higher cell wall moisture content than acetylated wood. An approximate theoretical calculation of hydroxyl accessibility for acetylated wood was in the low range, but it agreed rather well with the measured accessibility, while acetylated and partially hemicellulose-depleted and partially delignified wood for unknown reasons resulted in substantially lower hydroxyl accessibilities than the theoretical estimate. Full article
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Open AccessArticle
Study of Shear-Cutting Mechanisms on Wood Veneer
Forests 2020, 11(6), 703; https://doi.org/10.3390/f11060703 - 24 Jun 2020
Abstract
Multi-material structures made from renewable materials are increasingly being addressed in research and industry. Especially lightweight applications based on wood and polymer materials offer an important opportunity to reduce weight and CO2 emissions, and thus create a sustainable economy. When establishing new [...] Read more.
Multi-material structures made from renewable materials are increasingly being addressed in research and industry. Especially lightweight applications based on wood and polymer materials offer an important opportunity to reduce weight and CO2 emissions, and thus create a sustainable economy. When establishing new material combinations, it is necessary to take economical and efficient manufacturing processes into count to enable the market entry. Therefore, the existing manufacturing processes needed to be adapted and improved in terms of the specific machining characteristic of the wood material. This study targets a combined process where a forming and shear-cutting process is also integrated in an injection-molding tool. The findings on the shear-cutting process of wood veneers are not widely investigated yet. Therefore, process and material-related dependences like cutting velocity, tool shape design, and preconditioning of wood veneers were examined. The target values cutting force and cutting-edge quality were used to describe the relations. The results showed specific damage and fiber fractions of the wood material compared to the isotropic materials (e.g., metal). In addition, low cutting forces appeared by realizing a drawing cut and high cutting speeds. A decrease in the cutting force with a higher moisture content could not be shown for the used wood types. Full article
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Open AccessArticle
The Staining Effect of Iron (II) Sulfate on Nine Different Wooden Substrates
Forests 2020, 11(6), 658; https://doi.org/10.3390/f11060658 - 09 Jun 2020
Abstract
Leaving wooden façades uncoated has become popular in modern architecture, especially for large buildings like multi-story houses, in order to circumvent frequent maintenance, particularly repainting. To obtain a quick and even artificial graying of the entire façade that gradually turns into natural graying, [...] Read more.
Leaving wooden façades uncoated has become popular in modern architecture, especially for large buildings like multi-story houses, in order to circumvent frequent maintenance, particularly repainting. To obtain a quick and even artificial graying of the entire façade that gradually turns into natural graying, a one-off treatment with iron (II) sulfate may be applied. Its mode of action is commonly ascribed to a reaction with phenolic wood extractives, especially hydrolyzable tannins. This does not however sufficiently explain iron (II) sulfate’s ability to color wood species containing only marginal amounts of phenolic extractives; moreover, little is known about the influence of the wooden substrate and light conditions on the color development of façades treated with iron (II) sulfate. In the present study, we investigated the influence of wood extractives, exposure conditions, and nine different wooden substrates on iron (II) sulfate’s staining effect. Spruce specimens with and without extractives were treated with a 4% iron (II) sulfate solution and exposed to sunlight behind window glass. Both wood types darkened slowly but significantly during 51 weeks of exposure. This shows that artificial graying with iron (II) sulfate (1) does not require precipitation unlike natural graying, (2) takes place without initial wood extractives, and (3) proceeds at a slow rate. Specimens protected from sunlight changed their color only slightly, suggesting that photo-induced phenoxyl and ketyl radicals from photolysis of lignin’s ether bonds oxidize iron (II) to iron (III). Specimens made of spruce, pine, larch, and western red cedar (WRC) and exposed outdoors decreased strongly in lightness during the first two months of exposure. In contrast, a staining effect of iron (II) sulfate in terms of artificial graying was not seen on acetylated radiata pine, possibly because iron ions are hindered from entering the cell wall. Specimens partly protected by a roof overhang showed an uneven color development; this is due to the protection from radiation and not from precipitation as is known for natural graying. Full article
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Open AccessArticle
Leachability and Decay Resistance of Wood Polyesterified with Sorbitol and Citric Acid
Forests 2020, 11(6), 650; https://doi.org/10.3390/f11060650 - 06 Jun 2020
Abstract
Research Highlights: Polyesterification of wood with sorbitol and citric acid (SCA) increases decay resistance against brown-rot and white-rot fungi without reducing cell wall moisture content but the SCA polymer is susceptible to hydrolysis. Background and Objectives: SCA polyesterification is a low-cost, bio-based chemical [...] Read more.
Research Highlights: Polyesterification of wood with sorbitol and citric acid (SCA) increases decay resistance against brown-rot and white-rot fungi without reducing cell wall moisture content but the SCA polymer is susceptible to hydrolysis. Background and Objectives: SCA polyesterification is a low-cost, bio-based chemical wood modification system with potential for commercialisation. Materials and Methods: This study investigates moisture-related properties and decay resistance in SCA-modified wood. Scots pine sapwood was polyesterified at 140 °C with various SCA solution concentrations ranging from 14–56% w/w. Dimensional stability was assessed and leachates were analysed with high-performance liquid chromatography (HPLC). Chemical changes were characterized with attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and spectra were quantitatively compared with peak ratios. Low-field nuclear magnetic resonance (LFNMR) relaxometry was used to assess water saturated samples and decay resistance was determined with a modified EN113 test. Results: Anti-swelling efficiency (ASE) ranged from 23–43% and decreased at higher weight percentage gains (WPG). Reduced ASE at higher WPG resulted from increased water saturated volumes for higher treatment levels. HPLC analysis of leachates showed detectable citric acid levels even after an EN84 leaching procedure. ATR-FTIR analysis indicated increased ester content in the SCA-modified samples and decreased hydroxyl content compared to controls. Cell wall water assessed by non-freezing moisture content determined with LFNMR was found to increase because of the modification. SCA-modified samples resisted brown-rot and white-rot decay, with a potential decay threshold of 50% WPG. Sterile reference samples incubated without fungi revealed substantial mass loss due to leaching of the samples in a high humidity environment. The susceptibility of the SCA polymer to hydrolysis was confirmed by analysing the sorption behaviour of the pure polymer in a dynamic vapour sorption apparatus. Conclusions: SCA wood modification is an effective means for imparting decay resistance but, using the curing parameters in the current study, prolonged low-level leaching due to hydrolysis of the SCA polymer remains a problem. Full article
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Open AccessArticle
Effect of Different Hardwood Species and Lay-Up Schemes on the Mechanical Properties of Plywood
Forests 2020, 11(6), 649; https://doi.org/10.3390/f11060649 - 06 Jun 2020
Abstract
In Estonia, hardwoods form approximately 50% of all forest area, where the main species are birch (30%), gray alder (9%), aspen (6%) and black alder (4%). Birch has been extensively used by the veneer-based industry, but species like black alder, gray alder and [...] Read more.
In Estonia, hardwoods form approximately 50% of all forest area, where the main species are birch (30%), gray alder (9%), aspen (6%) and black alder (4%). Birch has been extensively used by the veneer-based industry, but species like black alder, gray alder and aspen have not been commonly used by the veneer-based products industry due to the lower quality of this resource. The aim of this research is to determine the effect of different lay-up schemes and usages of gray alder, black alder and aspen on the mechanical properties of plywood, by replacing birch veneer in the plywood core with alternative wood species. The main veneer and plywood characteristics will be evaluated according to the current standards, e.g., veneer strength perpendicular to grain, plywood bonding and bending strength, and modulus of elasticity. All processing parameters will be kept similar to those used generally by birch plywood manufacturers. The results showed that birch and black alder plywood panels had generally the highest bending strength properties, followed by grey alder and aspen. It was also found that, for proper gluing, birch veneers had the lowest glue consumption, 152 g/m2, and aspen had the highest glue consumption, 179 g/m2. It was found that when lower density wood was used in the plywood, the product density increased. Low density wood veneers had higher glue consumption, and also higher compaction in thickness than birch veneers under the same pressure. Overall, it was shown that the wood species used in this study have slightly lower strength properties, but with proper lay-up schemes, these wood species could be successfully used by the veneer-based products industry. Full article
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Open AccessArticle
Natural Weathering of Bio-Based Façade Materials
Forests 2020, 11(6), 642; https://doi.org/10.3390/f11060642 - 05 Jun 2020
Abstract
Although there is a global awareness that the exploitation of non-renewable materials is unsustainable, there has been limited interest in fully utilizing natural, renewable resources like wood and its products because of the service durability concerns. One such issue is the aesthetical degradation [...] Read more.
Although there is a global awareness that the exploitation of non-renewable materials is unsustainable, there has been limited interest in fully utilizing natural, renewable resources like wood and its products because of the service durability concerns. One such issue is the aesthetical degradation of wooden facades due to the impact of weathering. This research was carried out as an international cooperation project to ascertain the weathering resistance of bio-based façade materials under the Estonian climate. In total, 120 bio-based façade materials obtained from 31 different companies, universities and research institutions from 17 countries were investigated. The specimens were placed on an exposure rack, inclined at an angle of 45° located at 59°23′50.6″ N 24°39′24.0″ E and then subjected to accelerated natural weathering for 2 years. Parameters such as precipitation, UV index, temperature and relative humidity were measured during the period of the natural weathering. The influence of the weathering on the colour change and cracks on the surface of test specimens was evaluated using Minolta Chroma Meter CR-121 (Konica Minolta INC., Tokyo, Japan) and Avongard Check Width Gauge (Avongard Ltd., Gloucestershire, UK), respectively. The results showed that the untreated natural wood façade materials presented the least resistance to weathering, while 63 of the tested materials developed checks. The outcome of this study is essential to the optimization of software-simulating changes in the appearance of façade materials in outdoor conditions. Full article
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Open AccessArticle
Mapping the Decay Hazard of Wooden Structures in Topographically Divergent Regions
Forests 2020, 11(5), 510; https://doi.org/10.3390/f11050510 - 01 May 2020
Abstract
The service life of exposed wooden structures depends on many endogenous and exogenous factors with moisture being key for fungal degradation. Climate parameters are therefore important input variables for modelling fungal decay in wood. In recent years, different approaches aimed at modelling climate-induced [...] Read more.
The service life of exposed wooden structures depends on many endogenous and exogenous factors with moisture being key for fungal degradation. Climate parameters are therefore important input variables for modelling fungal decay in wood. In recent years, different approaches aimed at modelling climate-induced dosage on the material climate (i.e., exposure models) and the effect of the latter on fungal decay (i.e., decay models). Based on maps of Europe, North America or Australia, the decay hazard can be assigned to zones and used for estimating the relative decay potential of an arbitrary location. However, especially in topographically divergent regions, the climate-induced decay hazard can vary strongly within a small area. Within this study, decay hazards were quantified and mapped for a mountainous region where topography-induced differences in local climate and corresponding exposure dosage can be expected. The area under investigation was Switzerland. In addition to the Scheffer Climate Index (SCI), two exposure models were combined with two decay models and used to quantify the relative moisture- and temperature-induced exposure dose at 75 different weather stations in Switzerland and adjacent regions. The exposure was expressed as relative dosage with Uppsala (Sweden) as a reference location. Relative dose values were calculated for locations between weather stations using an ‘inverse distance weighted (IDW)’ interpolation and displayed in maps for the entire country. A more detailed analysis was undertaken for the Lötschental area, which is the largest valley on the northern side of the Rhône valley in the canton of Valais. The relative dose differed strongly within small areas and altitude was well correlated with the average annual temperature and the resulting relative dose. It became evident that small-scale mapping with high resolution is needed to fully reflect the impact of topography and other local conditions on the moisture- and temperature-induced decay risk in wooden components. Full article
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