Innovative Approaches for Improving Properties of Wood and Wood-Based Materials

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

Deadline for manuscript submissions: 31 May 2024 | Viewed by 18102

Special Issue Editors


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Guest Editor
Faculty of Wood Engineering and Creative Industries, University of Sopron, Sopron, Hungary
Interests: wood modification; wood structure and properties; hygroscopic properties; nanotechnology; durability; biopolymers
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Guest Editor
Institute of Wood Technology and Technical Sciences, Faculty of Wood Engineering and Creative Industries, University of Sopron, Bajcsy-Zsilinszky 4, 9400 Sopron, Hungary
Interests: wood structure and properties; drying and modification of wood; abiotic degradation of wood; hardwoods
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues, 

The forestry-wood chain has developed over the past decades and nowadays, ecosystem services are important in the context of sustainability. Forests aim to provide services for the bio-economy, biodiversity and climate regulation. The increased demand for renewable resources has led to an increased interest in the production of lignocellulosic biomass for both material and energy use, in other words, to an increase in wood production. Whilst the timber sector recognizes these increasing needs, it also realizes that a lot of research and development will be required in overcoming these problems. A manifest way, nowadays, is the development of various new methods to improve the properties of wood and wood-based materials, and with that, to increase the service life of such products. New ways in this field include the use of different physical, chemical or biological effects on wood and wood-based materials to make improvements in targeted properties, such as improving biological durability, dimensional stability, wetting properties, and UV resistance. This Special Issue plans to offer an overview of the most recent advances in the field of the use of nanotechnology, plasma treatments, enzymatic treatments and the use of different combined modifications to obtain high-performance bio-based materials and composites.

Potential topics include, but are not limited to, the following:

  • Wood modification;
  • Use of nanomaterials in wood and wood-based materials;
  • Plasma treatments;
  • Weather resistant wood and wood-based materials;
  • Decay resistant wood and wood-based materials;
  • Dimensionally stable wood and wood-based materials;
  • Future perspectives for innovative approaches in wood modification.

Dr. Miklós Bak
Prof. Dr. Róbert Németh
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 submissions that pass pre-check are 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.

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 2600 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 modification
  • nanomaterials
  • plasma treatment
  • enzymatic treatment
  • high-performance wood-based materials
  • material properties
  • combined modification methods
  • biomaterials

Published Papers (9 papers)

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Research

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14 pages, 5742 KiB  
Article
Research on the Preparation of Wood Adhesive Active Fillers from Tannin-/Bentonite-Modified Corn Cob
by Linfeng Yang, Haiyang Quan, Jiajun Ji, Haizhe Zhang and Fengwen Sun
Forests 2024, 15(4), 604; https://doi.org/10.3390/f15040604 - 27 Mar 2024
Viewed by 732
Abstract
The artificial plywood industry in our country relies heavily on industrial flour as a filler for adhesives. Using abundant corn cob powder as the main raw material, corn cob powder was modified by impregnation with a sodium-based bentonite/bayberry tannin and used as filler [...] Read more.
The artificial plywood industry in our country relies heavily on industrial flour as a filler for adhesives. Using abundant corn cob powder as the main raw material, corn cob powder was modified by impregnation with a sodium-based bentonite/bayberry tannin and used as filler for urea–formaldehyde resin (UF) adhesive, with NH4Cl as the curing agent and poplar veneer as the raw material to prepare plywood. The results showed that the modified corn cob powder with a particle size of 250 mesh was uniformly dispersed in the UF adhesive. When used as a filler, the modified corn cob powder effectively prevented the premature curing of the UF adhesive and significantly reduced its viscosity. Compared with flour filler, the bonding strength of the prepared plywood increased by 12.1%–19.6% while the formaldehyde emission decreased by 12.7%–27.8%. The cold pressing performance of the plywoods prepared with modified corn cob flour was comparable to the performance of plywood produced with industrial flour. Full article
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12 pages, 8108 KiB  
Article
The Use of Black Pine Bark for Improving the Properties of Wood Pellets
by Charalampos Lykidis, Vasiliki Kamperidou and George I. Mantanis
Forests 2023, 14(6), 1069; https://doi.org/10.3390/f14061069 - 23 May 2023
Cited by 3 | Viewed by 1353
Abstract
The requirement for alternative raw materials for fuel pellets that would enable the use of readily available low-cost renewable resources and waste materials, such as bark, has always attracted interest. The aim of the current work was to assess the effect of black [...] Read more.
The requirement for alternative raw materials for fuel pellets that would enable the use of readily available low-cost renewable resources and waste materials, such as bark, has always attracted interest. The aim of the current work was to assess the effect of black pine (Pinus nigra L.) bark content (0%–100%) as well as densification temperature on the properties of black pine wood pellets produced in a single pellet die. The quality assessment of the pellets was carried out by the determination of radial compression strength, density, moisture content, ash content, and surface roughness. The results showed that adding black pine bark to the pellet feedstock resulted in the production of substantially smoother and moderately denser pellets, which also exhibited higher mechanical strength than that of the respective pellets of pure wood. Finally, it was shown that black pine bark can be a valuable raw material, which can induce improved bonding of biomass particles and may provide the opportunity to create pellets of favorable characteristics at a lower temperature compared to those made of pure wood. Full article
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12 pages, 3048 KiB  
Article
Phytic Acid-Silica System for Imparting Fire Retardancy in Wood Composites
by Chia-Feng Lin, Chi Zhang, Olov Karlsson, Jozef Martinka, George I. Mantanis, Peter Rantuch, Dennis Jones and Dick Sandberg
Forests 2023, 14(5), 1021; https://doi.org/10.3390/f14051021 - 16 May 2023
Cited by 3 | Viewed by 1916
Abstract
Fire-retardant (FR) treated wood-based panels, used commonly in furniture and construction, need to meet stringent fire safety regulations. This study presents a novel treatment for imparting fire resistance to wood composites by applying separate solutions of phytic acid and sodium silicate onto wood [...] Read more.
Fire-retardant (FR) treated wood-based panels, used commonly in furniture and construction, need to meet stringent fire safety regulations. This study presents a novel treatment for imparting fire resistance to wood composites by applying separate solutions of phytic acid and sodium silicate onto wood particles before the hot pressing at 160 °C. A scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analysis revealed that phytic acid and sodium silicate were uniformly distributed throughout the wood particles, and the formation of silica gel resulted in the aggregation of elemental silicon. Fourier-transform infrared spectroscopy (FTIR) displayed that phytic acid caused the thermal degradation of hemicelluloses, which led to a brownish outer appearance of the FR-treated composites. Fire performance was assessed using both limiting oxygen index (LOI) and a cone calorimeter. These techniques showed a higher LOI value and a significant reduction in heat-release rate (HRR), total heat release (THR), smoke-production rate (SPR), and total smoke production (TSP). In addition, cone calorimeter and thermogravimetric (TGA) analyses consistently showed increased char residue in treated wood composites. Moreover, internal bond strength (IB) and modulus of elasticity (MOE) of the wood composite were not significantly changed compared with those of the untreated composite. Surprisingly, in the FR-treated composite, the 24 h-thickness swelling, and the water uptake were slightly decreased. Consequently, this new treatment has the potential to increase the fire retardancy of wood composites, such as particleboard, without deteriorating the key mechanical properties. Full article
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13 pages, 12618 KiB  
Article
One-Step Process for the Fabrication of Hydrophobic and Dimensional Stable Wood Using Functionalized Silica Nanoparticles
by Miklós Bak, Dávid Takács, Rita Rákosa, Zsolt István Németh and Róbert Németh
Forests 2023, 14(3), 651; https://doi.org/10.3390/f14030651 - 22 Mar 2023
Cited by 4 | Viewed by 2579
Abstract
The aim of this research was to improve the dimensional stability of wood through bulk hydrophobization, as a result of impregnation with fluorinated silica nanoparticles. The wood species European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) were used. [...] Read more.
The aim of this research was to improve the dimensional stability of wood through bulk hydrophobization, as a result of impregnation with fluorinated silica nanoparticles. The wood species European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) were used. The characterization of the modified wood was performed using analytical methods, including scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. The effect of fluorinated silica nanoparticles on the anti-swelling efficiency, water uptake, equilibrium moisture content, and water contact angle were investigated. The surface of the cell walls was discontinuously covered with fluorinated silica nanoparticles forming a rough surface coating. The presence of the hydrophobic silica nanoparticles improved the dimensional stability by permanently increasing the hydrophobicity of wood, besides a low weight percent gain. Furthermore, the treatment significantly decreased the equilibrium moisture content and water uptake. The modified wood surfaces showed significantly higher water contact angles, which was the main reason of the improved dimensional stability. Full article
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12 pages, 3781 KiB  
Article
Choline Chloride-Based Deep Eutectic Solvent-Treated Wood
by Ahmet Can, İsmail Özlüsoylu, Petar Antov and Seng Hua Lee
Forests 2023, 14(3), 569; https://doi.org/10.3390/f14030569 - 13 Mar 2023
Cited by 1 | Viewed by 1654
Abstract
Due to their adaptability and low preparation costs, deep eutectic solvents (DESs) have been widely used in a variety of applications. For some potential industrial applications, developing new low-cost DESs is critical. Oxalic acid (OA), acetic acid (AA), urea (Ur), and glycerol (GL) [...] Read more.
Due to their adaptability and low preparation costs, deep eutectic solvents (DESs) have been widely used in a variety of applications. For some potential industrial applications, developing new low-cost DESs is critical. Oxalic acid (OA), acetic acid (AA), urea (Ur), and glycerol (GL) were mixed in various molar ratios to make DES solutions, with choline chloride (ChCL) acting as the hydrogen bond acceptor (HBA). In this work, DES solutions were applied to wood samples of Oriental spruce (Picea orientalis) at 150 °C. The chemical structures of wood samples were significantly altered after impregnation with DES solutions, as revealed by Fourier transform infrared spectroscopy (FTIR). The hemicellulose and cellulose peaks increased around 1700 cm−1, while the lignin peak disappeared completely around 1500 cm−1. After the decay test, mass losses were lower than in the control samples. The decay tests revealed that the leached wood samples were more resistant to decay. DES-treated wood samples, on the other hand, decomposed at lower temperatures. Full article
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13 pages, 2639 KiB  
Article
Heating Rate during Thermal Modification in Steam Atmosphere: Influence on the Properties of Maple and Ash Wood
by Goran Milić, Nebojša Todorović, Marko Veizović and Ranko Popadić
Forests 2023, 14(2), 189; https://doi.org/10.3390/f14020189 - 18 Jan 2023
Viewed by 1296
Abstract
This study aimed to compare two thermal modification (TM) schedules—with short and long heating phases—and their influence on the properties of maple (Acer pseudoplatanus L.) and ash (Fraxinus excelsior L.) wood. Two TM runs were conducted in industrial conditions (open system, [...] Read more.
This study aimed to compare two thermal modification (TM) schedules—with short and long heating phases—and their influence on the properties of maple (Acer pseudoplatanus L.) and ash (Fraxinus excelsior L.) wood. Two TM runs were conducted in industrial conditions (open system, steam atmosphere; substantially longer method compared to the processes usually described in the literature), with the same peak phase (200 °C, 3 h), but with different heating rates—slow (1.1 °C/h) and fast (2.5 °C/h). The results revealed that both TMs significantly reduced hygroscopicity and swelling of wood, but the influence of slow heating rate—through prolonged exposure of wood to relatively high temperatures—on dimensional stability was more pronounced. The modulus of elasticity, compressive strength and Brinell hardness remained mostly unchanged after TM (except for fast-modified maple), while the modulus of rupture was strongly reduced by TM in both species. It is assumed—at least in the case of maple wood—that a combination of initial moisture content above 8% and fast heating rate during TM can cause more intensive degradation of wood polymers. Relatively small differences in colour between slow- and fast-modified wood were found. The results confirmed the hypothesis that the heating phase is an important part of the TM schedule, and it can directly affect (together with peak temperature and time) certain wood properties. Full article
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13 pages, 2486 KiB  
Article
Impregnation Properties of Nigerian-Grown Gmelina arborea Roxb. Wood
by Samuel Oluyinka Olaniran, Sophie Löning, Andreas Buschalsky and Holger Militz
Forests 2022, 13(12), 2036; https://doi.org/10.3390/f13122036 - 30 Nov 2022
Cited by 1 | Viewed by 2979
Abstract
The success of any wood treatment process and the measure of protection conferred on treated wood are determined by the uptake and penetration of the treatment chemicals, in addition to the efficacy of the chemicals used for the treatment. Hence, the level of [...] Read more.
The success of any wood treatment process and the measure of protection conferred on treated wood are determined by the uptake and penetration of the treatment chemicals, in addition to the efficacy of the chemicals used for the treatment. Hence, the level of treatability of wood species should be pre-determined prior to the wood treatment to ensure the overall protection of the treated wood. Gmelina arborea wood, due to its low durability, requires impregnation with chemicals for preservation or chemical modification to enhance its durability. However, more details are required to establish the influence of its anatomy on impregnation to recommend appropriate treatment methods. Therefore, gmelina wood samples were treated under pressure to determine the solution uptake and penetration, while anatomical studies were carried out with light microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) measurements. Variations in stem heights, stem diameters, and samples from other tree stands were considered. The outcome of the study showed that the liquid uptake was generally low for gmelina wood among the selected stands (16%–23%) and there was no significant difference in stem diameters; meanwhile, penetration was less than 4 mm in the axial direction, and very low in the lateral (radial and tangential) direction. Vessels of gmelina wood have abundant tyloses, while crystalline structures with needlelike shapes are present in a large proportion of the ray parenchyma cells, and are confirmed with SEM-EDX to be made up of calcium oxalate. The low liquid uptake and penetration in gmelina wood suggest that the impregnation of chemicals into its microstructure is next to impossible. Hence, alternative treatment methods other than those involving impregnation with chemicals should be sought to enhance its durability. Full article
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15 pages, 4564 KiB  
Article
Biological Durability of Acetylated Hornbeam Wood with Soil Contact in Hungary
by Fanni Fodor, Miklós Bak, András Bidló, Bernadett Bolodár-Varga and Róbert Németh
Forests 2022, 13(7), 1003; https://doi.org/10.3390/f13071003 - 25 Jun 2022
Cited by 4 | Viewed by 2114
Abstract
This test aimed to discover if industrially acetylated hornbeam can tolerate real-field conditions in Hungary, where various microorganisms can attack the wood separately or cooperatively. Untreated samples accompanied the modified wood to assess the degradation capacity of the soil. The test also focused [...] Read more.
This test aimed to discover if industrially acetylated hornbeam can tolerate real-field conditions in Hungary, where various microorganisms can attack the wood separately or cooperatively. Untreated samples accompanied the modified wood to assess the degradation capacity of the soil. The test also focused on weather parameters, the Scheffer index, and soil properties. The untreated stakes showed insect damage, soft rot decay, white rot decay, wasp stripping, moss, and cracks. All of the beech and hornbeam stakes broke after 3.5 years, and the last Scots pine sapwood stakes broke after 6 years. To date, acetylated hornbeam exhibits stronger resistance than untreated hornbeam, beech, and Scots pine sapwood. The acetylated hornbeam stakes showed no decay after 6 years of exposure, and they became dry shortly after being taken from the soil. Acetylated hornbeam stake number 7 had superficial brown rot decay after 18 months, which gradually worsened over the years. The Fourier transform infrared spectroscopy analysis revealed that this stake had lower acetyl content. It was associated with hornbeam wood; it had a wet pocket or a part that was not as permeable and achieved a lower grade of acetylation. Full article
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Review

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35 pages, 33570 KiB  
Review
A Review of Wood Compression along the Grain—After the 100th Anniversary of Pleating
by Mátyás Báder and Róbert Németh
Forests 2023, 14(4), 763; https://doi.org/10.3390/f14040763 - 7 Apr 2023
Cited by 2 | Viewed by 2226
Abstract
This study focuses on the compression of wood along the grain (also known as pleating), a modification that improves the pliability of higher-density hardwoods with a moisture content above 20%. Pleated wood can be bent into small curves in any direction. The success [...] Read more.
This study focuses on the compression of wood along the grain (also known as pleating), a modification that improves the pliability of higher-density hardwoods with a moisture content above 20%. Pleated wood can be bent into small curves in any direction. The success of the industrial pleating process in some parts of the world is influenced by many factors, such as wood species, wood quality, moisture content, compression ratio, fixation time, etc. Pleating by 20% causes the modulus of elasticity to decrease to one-third for oak and beech, and the bending ratio can be increased above ½. Bending stress decreases and the absorbed energy increases multiple times. The impact bending strength also increases significantly. The walls of cells crinkle by pleating and the microfibrils of the fibres become distorted. Many patents, articles, and books on this subject have been published since 1917, and this review attempts to introduce and, where necessary, critically analyse them. Full article
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