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

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

Deadline for manuscript submissions: closed (31 May 2024) | Viewed by 23761

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Special Issue Editors

Dr. Miklós Bak

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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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Prof. Dr. Róbert Németh

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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

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Keywords

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

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Published Papers (10 papers)

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Research

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18 pages, 5066 KiB

Open AccessArticle

Charring of and Chemical Changes in Historical Wood under Thermal Loading

by Katarína Dúbravská, Viera Kučerová, Jaroslava Štefková and Ol’ga Mišíková

Forests 2024, 15(7), 1189; https://doi.org/10.3390/f15071189 - 9 Jul 2024

Viewed by 692

Abstract

Research in historical timber assessment is hindered by the limited availability of samples, yet understanding the fire resistance of historic wood is crucial for preservation efforts. There is an opinion that historic wood behaves similarly to contemporary wood in terms of fire resistance. The aim of this paper is to observe the rate of charring of historical pine wood during the experiment, the color changes in the sample that occurred due to thermal loading, and the changes in the chemical composition of pine wood. Test samples made from historic pine wood were loaded with a 50 kW∙m⁻² radiation panel for 60 min. The charring process was faster at the beginning of the charred layer formation. The charring rate at the beginning of the test at a depth of 10 mm from the exposed side reached values from 1.28 mm∙min⁻¹ to 3.16 mm∙min⁻¹. At a depth of 30 mm from the exposed side, the individual charring rates approached a value of 1 mm∙min⁻¹ (0.99 mm∙min⁻¹ to 1.08 mm∙min⁻¹). Observations during medium-scale testing revealed distinct layers forming on the exposed side: a charred layer, charring base, pyrolysis layer, and intact wood. The chemical composition of the wood changed under the influence of the thermal load. The relative contents of extractives and holocellulose decreased with the increasing temperature while the lignin content increased. The highest value of combustion heat was measured in the charred layer of the sample. Correlation analysis demonstrated a negative relationship between the combustion heat and holocellulose, while a positive correlation was found with the lignin content. Chemical changes were also monitored using the FTIR method. These findings provide valuable insights into the behavior of historic pine wood under thermal loading, which is essential for understanding and preserving historical structures. Full article

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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14 pages, 5742 KiB

Open AccessArticle

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

Cited by 2 | Viewed by 1177

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 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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12 pages, 8108 KiB

Open AccessArticle

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 5 | Viewed by 1815

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 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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12 pages, 3048 KiB

Open AccessArticle

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 6 | Viewed by 2449

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 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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13 pages, 12618 KiB

Open AccessArticle

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 6 | Viewed by 3141

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. 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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12 pages, 3781 KiB

Open AccessArticle

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 3 | Viewed by 2275

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) 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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13 pages, 2639 KiB

Open AccessArticle

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 1567

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, 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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13 pages, 2486 KiB

Open AccessArticle

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 3625

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 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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15 pages, 4564 KiB

Open AccessArticle

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 2606

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 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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Review

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35 pages, 33570 KiB

Open AccessReview

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 3 | Viewed by 2937

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 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

(This article belongs to the Special Issue Innovative Approaches for Improving Properties of Wood and Wood-Based Materials)

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