Polymers

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5 pages, 217 KiB

Open AccessEditorial

New Challenges in Wood and Wood-Based Materials

by Lubos Kristak, Ivan Kubovský and Roman Réh

Polymers 2021, 13(15), 2538; https://doi.org/10.3390/polym13152538 - 31 Jul 2021

Cited by 8 | Viewed by 1748

Abstract

Wood and wood-based composites are key engineering materials that can be successfully designed and manufactured with predetermined exploitation properties, making them suitable for a wide range of applications and end uses [...] Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

Research

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15 pages, 1979 KiB

Open AccessArticle

The Evaluation of Torrefied Wood Using a Cone Calorimeter

by Peter Rantuch, Jozef Martinka and Aleš Ház

Polymers 2021, 13(11), 1748; https://doi.org/10.3390/polym13111748 - 27 May 2021

Cited by 7 | Viewed by 2439

Abstract

This study focuses on the energy potential and combustion process of torrefied wood. Samples were prepared through the torrefaction of five types of wood: Ash, beech, oak, pine and spruce. These were heated for 2 h at a temperature of 300 °C under [...] Read more.

This study focuses on the energy potential and combustion process of torrefied wood. Samples were prepared through the torrefaction of five types of wood: Ash, beech, oak, pine and spruce. These were heated for 2 h at a temperature of 300 °C under a nitrogen atmosphere. Torrefied wood was prepared from wood samples with dimensions of 100 × 100 × 20 mm³. These dimensions have enabled investigation of torrefied wood combustion in compact form. The effect of the external heat flux on the combustion of the samples was measured using a cone calorimeter. The observed parameters, include initiation times, heat release rate and combustion efficiency. The results show that increasing the external heat flux decreases the evenness of combustion of torrefied wood. At the same time, it increases the combustion efficiency, which reached an average value of approximately 72% at 20 kW m⁻², 81% at 30 kW m⁻² and 90% at 40 kW m⁻². The calculated values of critical heat flux of the individual samples ranged from 4.67 kW m⁻² to 15.2 kW m⁻², the thermal response parameter ranged from 134 kW s^0.5 m⁻² to 297 kW s^0.5 m⁻² and calculated ignition temperature ranged from 277 °C to 452 °C. Obtained results are useful both for energy production field and for fire safety risk assessment of stored torrefied wood. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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11 pages, 2432 KiB

Open AccessArticle

Chemical and Morphological Composition of Norway Spruce Wood (Picea abies, L.) in the Dependence of Its Storage

by Iveta Čabalová, Michal Bélik, Viera Kučerová and Tereza Jurczyková

Polymers 2021, 13(10), 1619; https://doi.org/10.3390/polym13101619 - 17 May 2021

Cited by 21 | Viewed by 2947

Abstract

Chemical composition and morphological properties of Norway spruce wood and bark were evaluated. The extractives, cellulose, hemicelluloses, and lignin contents were determined by wet chemistry methods. The dimensional characteristics of the fibers (length and width) were measured by Fiber Tester. The results of [...] Read more.

Chemical composition and morphological properties of Norway spruce wood and bark were evaluated. The extractives, cellulose, hemicelluloses, and lignin contents were determined by wet chemistry methods. The dimensional characteristics of the fibers (length and width) were measured by Fiber Tester. The results of the chemical analysis of wood and bark show the differences between the trunk and top part, as well as in the different heights of the trunk and in the cross section of the trunk. The biggest changes were noticed between bark trunk and bark top. The bark top contains 10% more of extractives and 9.5% less of lignin. Fiber length and width depends on the part of the tree, while the average of these properties are larger depending on height. Both wood and bark from the trunk contains a higher content of fines (fibers <0.3 mm) and less content of longer fibers (>0.5 mm) compared to the top. During storage, it reached a decrease of extractives mainly in bark. Wood from the trunk retained very good durability in terms of chemical composition during the storage. In view of the morphological characteristics, it occurred to decrease both average fibers length and width in wood and bark. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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12 pages, 4609 KiB

Open AccessArticle

Experimental Study of Straw-Based Eco-Panel Using a Small Ignition Initiator

by Linda Makovicka Osvaldova, Iveta Markova, Stanislav Jochim and Jan Bares

Polymers 2021, 13(8), 1344; https://doi.org/10.3390/polym13081344 - 20 Apr 2021

Cited by 13 | Viewed by 2417

Abstract

Straw, a natural cellulose-based material, has become part of building elements. Eco-panels, compressed straw in a cardboard casing, is used as building insulation. Eco-panel is a secondary product with excellent insulating properties. If suitably fire-treated (insulation and covering), straw panels’ fire resistance may [...] Read more.

Straw, a natural cellulose-based material, has become part of building elements. Eco-panels, compressed straw in a cardboard casing, is used as building insulation. Eco-panel is a secondary product with excellent insulating properties. If suitably fire-treated (insulation and covering), straw panels’ fire resistance may be increased. This contribution deals with monitoring the behavior of eco-panels exposed to a small ignition initiator (flame). The samples consisted of compressed straw boards coated with a 40 mm thick cardboard. Samples were exposed to a flame for 5 and 10 min. The influence of the selected factors (size of the board, orientation of flame with the sample) were compared on the basis of experimentally obtained data: mass loss. The results obtained do not show a statistically significant influence of the position of the sample and the initiating source (flame). The results presented in the article confirm the justifiability of fire tests. As the results of the experiments prove, the position of a small burner for igniting such material is also important. Such weakness of the material can also be eliminated by design solutions in the construction. The experiment on larger samples also confirmed the justifiability of fire tests along with the need for flame retardancy of such material for its safe application in construction. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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15 pages, 4161 KiB

Open AccessArticle

Changes of Meranti, Padauk, and Merbau Wood Lignin during the ThermoWood Process

by Danica Kačíková, Ivan Kubovský, Milan Gaff and František Kačík

Polymers 2021, 13(7), 993; https://doi.org/10.3390/polym13070993 - 24 Mar 2021

Cited by 6 | Viewed by 1925

Abstract

Thermal modification is an environmentally friendly process in which technological properties of wood are modified using thermal energy without adding chemicals, the result of which is a value-added product. Wood samples of three tropical wood species (meranti, padauk, and merbau) were thermally treated [...] Read more.

Thermal modification is an environmentally friendly process in which technological properties of wood are modified using thermal energy without adding chemicals, the result of which is a value-added product. Wood samples of three tropical wood species (meranti, padauk, and merbau) were thermally treated according to the ThermoWood process at various temperatures (160, 180, 210 °C) and changes in isolated lignin were evaluated by nitrobenzene oxidation (NBO), Fourier-transform infrared spectroscopy (FTIR), and size exclusion chromatography (SEC). New data on the lignins of the investigated wood species were obtained, e.g., syringyl to guaiacyl ratio values (S/G) were 1.21, 1.70, and 3.09, and molecular weights were approx. 8600, 4300, and 8300 g·mol⁻¹ for meranti, padauk, and merbau, respectively. Higher temperatures cause a decrease of methoxyls and an increase in C=O groups. Simultaneous degradation and condensation reactions in lignin occur during thermal treatment, the latter prevailing at higher temperatures. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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13 pages, 2525 KiB

Open AccessArticle

Experimental Study of Oriented Strand Board Ignition by Radiant Heat Fluxes

by Ivana Tureková, Iveta Marková, Martina Ivanovičová and Jozef Harangózo

Polymers 2021, 13(5), 709; https://doi.org/10.3390/polym13050709 - 26 Feb 2021

Cited by 13 | Viewed by 1689

Abstract

Wood and composite panel materials represent a substantial part of the fuel in many building fires. The ability of materials to ignite when heated at elevated temperatures depends on many factors, such as the thermal properties of materials, the ignition temperature, critical heat [...] Read more.

Wood and composite panel materials represent a substantial part of the fuel in many building fires. The ability of materials to ignite when heated at elevated temperatures depends on many factors, such as the thermal properties of materials, the ignition temperature, critical heat flux and the environment. Oriented strand board (OSB) without any surface treatment in thicknesses of 12, 15 and 18 mm were used as experimental samples. The samples were gradually exposed to a heat flux of 43 to 50 kW.m⁻², with an increase of 1 kW.m⁻². At heat fluxes of 49 kW.m⁻² and 50 kW.m⁻², the ignition times are similar in all OSB thicknesses, in contrast to the ignition times at lower heat fluxes. The influence of the selected factors (thickness and distance from the heat source) was analysed based on the experimentally obtained data of ignition time and weight loss. The experimentally determined value of the heat flux density was 43 kW.m⁻², which represented the critical heat flux. The results show a statistically significant effect of OSB thickness on ignition time. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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12 pages, 2414 KiB

Open AccessArticle

Non-Isothermal Thermogravimetry of Selected Tropical Woods and Their Degradation under Fire Using Cone Calorimetry

by Linda Makovicka Osvaldova, Ivica Janigova and Jozef Rychly

Polymers 2021, 13(5), 708; https://doi.org/10.3390/polym13050708 - 26 Feb 2021

Cited by 6 | Viewed by 1465

Abstract

For selected tropical woods (Cumaru, Garapa, Ipe, Kempas, Merbau), a relationship was established between non-isothermal thermogravimetry runs and the wood weight loss under flame during cone calorimetry flammability testing. A correlation was found for the rate constants for decomposition of wood in air [...] Read more.

For selected tropical woods (Cumaru, Garapa, Ipe, Kempas, Merbau), a relationship was established between non-isothermal thermogravimetry runs and the wood weight loss under flame during cone calorimetry flammability testing. A correlation was found for the rate constants for decomposition of wood in air at 250 and 300 °C found from thermogravimetry and the total time of sample burning related to the initial mass. Non-isothermal thermogravimetry runs were assumed to be composed from 3 theoretical runs such as decomposition of wood into volatiles itself, oxidation of carbon residue, and the formation of ash. A fitting equation of three processes was proposed and the resulting theoretical lines match experimental lines. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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13 pages, 2158 KiB

Open AccessArticle

Eco-Friendly, High-Density Fiberboards Bonded with Urea-Formaldehyde and Ammonium Lignosulfonate

by Petar Antov, Viktor Savov, Ľuboš Krišťák, Roman Réh and George I. Mantanis

Polymers 2021, 13(2), 220; https://doi.org/10.3390/polym13020220 - 10 Jan 2021

Cited by 55 | Viewed by 4873

Abstract

The potential of producing eco-friendly, formaldehyde-free, high-density fiberboard (HDF) panels from hardwood fibers bonded with urea-formaldehyde (UF) resin and a novel ammonium lignosulfonate (ALS) is investigated in this paper. HDF panels were fabricated in the laboratory by applying a very low UF gluing [...] Read more.

The potential of producing eco-friendly, formaldehyde-free, high-density fiberboard (HDF) panels from hardwood fibers bonded with urea-formaldehyde (UF) resin and a novel ammonium lignosulfonate (ALS) is investigated in this paper. HDF panels were fabricated in the laboratory by applying a very low UF gluing factor (3%) and ALS content varying from 6% to 10% (based on the dry fibers). The physical and mechanical properties of the fiberboards, such as water absorption (WA), thickness swelling (TS), modulus of elasticity (MOE), bending strength (MOR), internal bond strength (IB), as well as formaldehyde content, were determined in accordance with the corresponding European standards. Overall, the HDF panels exhibited very satisfactory physical and mechanical properties, fully complying with the standard requirements of HDF for use in load-bearing applications in humid conditions. Markedly, the formaldehyde content of the laboratory fabricated panels was extremely low, ranging between 0.7–1.0 mg/100 g, which is, in fact, equivalent to the formaldehyde release of natural wood. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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18 pages, 3987 KiB

Open AccessArticle

Weathering Stability and Durability of Birch Plywood Modified with Different Molecular Weight Phenol-Formaldehyde Oligomers

by Juris Grinins, Vladimirs Biziks, Brendan Nicholas Marais, Janis Rizikovs and Holger Militz

Polymers 2021, 13(2), 175; https://doi.org/10.3390/polym13020175 - 06 Jan 2021

Cited by 14 | Viewed by 2802

Abstract

This study investigated the effect of phenol-formaldehyde (PF) resin treatment on the weathering stability and biological durability of birch plywood. Silver birch (Betula pendula) veneers were vacuum-pressure impregnated with four different PF resins with average molecular weights (M_w) of [...] Read more.

This study investigated the effect of phenol-formaldehyde (PF) resin treatment on the weathering stability and biological durability of birch plywood. Silver birch (Betula pendula) veneers were vacuum-pressure impregnated with four different PF resins with average molecular weights (M_w) of 292 (resin A), 528 (resin B), 703 (resin C), and 884 g/mol (resin D). The aging properties of PF resin modified birch plywood were analyzed using artificial weathering with ultraviolet (UV) light, UV and water spray, and weathering under outdoor conditions. The same combinations of PF-treated plywood specimens were then tested in soil-bed tests to determine their resistance against soft-rot wood decay. It was not possible to compare weathering processes under artificial conditions to processes under outdoor conditions. However, the weathering stability of birch plywood treated with PF resins A, B, and C, scored better than plywood treated with commercial resin D (regardless of solid content concentration [%]). Results from unsterile soil bed tests showed improvements in resistance to soft-rot wood decay compared to untreated plywood and solid wood. Mass loss [%] was lowest for birch plywood specimens treated with resin of highest solid content concentration (resin D, 20%). Provisional durability ratings delivered durability class (DC) ratings of 2–3, considerably improved over untreated solid wood and untreated birch plywood (DC 5). Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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10 pages, 3280 KiB

Open AccessArticle

An Additive Manufacturing Method Using Large-Scale Wood Inspired by Laminated Object Manufacturing and Plywood Technology

by Yubo Tao, Qing Yin and Peng Li

Polymers 2021, 13(1), 144; https://doi.org/10.3390/polym13010144 - 31 Dec 2020

Cited by 18 | Viewed by 4892

Abstract

Wood-based materials in current additive manufacturing (AM) feedstocks are primarily restricted to the micron scale. Utilizing large-scale wood in existing AM techniques remains a challenge. This paper proposes an AM method—laser-cut veneer lamination (LcVL)—for wood-based product fabrication. Inspired by laminated object manufacturing (LOM) [...] Read more.

Wood-based materials in current additive manufacturing (AM) feedstocks are primarily restricted to the micron scale. Utilizing large-scale wood in existing AM techniques remains a challenge. This paper proposes an AM method—laser-cut veneer lamination (LcVL)—for wood-based product fabrication. Inspired by laminated object manufacturing (LOM) and plywood technology, LcVL bonds wood veneers in a layer-upon-layer manner. As demonstrated by printed samples, LcVL was able to retain the advantageous qualities of AM, specifically, the ability to manufacture products with complex geometries which would otherwise be impossible using subtractive manufacturing techniques. Furthermore, LcVL-product structures designed through adjusting internal voids and wood-texture directionality could serve as material templates or matrices for functional wood-based materials. Numerical analyses established relations between the processing resolution of LcVL and proportional veneer thickness (layer height). LcVL could serve as a basis for the further development of large-scale wood usage in AM. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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17 pages, 12130 KiB

Open AccessArticle

The Impact of Wood Waste on the Properties of Silicone-Based Composites

by Maciej Mrówka, Małgorzata Szymiczek and Magdalena Skonieczna

Polymers 2021, 13(1), 7; https://doi.org/10.3390/polym13010007 - 22 Dec 2020

Cited by 11 | Viewed by 2822

Abstract

The impact of wood waste on the mechanical and biological properties of silicone-based composites was investigated using wood waste from oak, hornbeam, beech, and spruce trees. The density, abrasion resistance, resilience, hardness, and static tensile properties of the obtained WPC (wood–plastic composites) were [...] Read more.

The impact of wood waste on the mechanical and biological properties of silicone-based composites was investigated using wood waste from oak, hornbeam, beech, and spruce trees. The density, abrasion resistance, resilience, hardness, and static tensile properties of the obtained WPC (wood–plastic composites) were tested. The results revealed slight changes in the density, increased abrasion resistance, decreased resilience, increased hardness, and decreased strain at break and stress at break compared with untreated silicone. The samples also showed no cytotoxicity to normal human dermal fibroblast, NHDF. The possibility of using prepared composites as materials to create structures on the seabed was also investigated by placing samples in a marine aquarium for one week and then observing sea algae growth. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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11 pages, 4148 KiB

Open AccessArticle

Investigation of 3D-Moldability of Flax Fiber Reinforced Beech Plywood

by Johannes Jorda, Günther Kain, Marius-Catalin Barbu, Matthias Haupt and Ľuboš Krišťák

Polymers 2020, 12(12), 2852; https://doi.org/10.3390/polym12122852 - 29 Nov 2020

Cited by 8 | Viewed by 1745

Abstract

The current work deals with three dimensionally molded plywood formed parts. These are prepared in two different geometries using cut-outs and relief cuts in the areas of the highest deformation. Moreover, the effect of flax fiber reinforcement on the occurrence and position of [...] Read more.

The current work deals with three dimensionally molded plywood formed parts. These are prepared in two different geometries using cut-outs and relief cuts in the areas of the highest deformation. Moreover, the effect of flax fiber reinforcement on the occurrence and position of cracks, delamination, maximum load capacity, and on the modulus of elasticity is studied. The results show that designs with cut-outs are to be preferred when molding complex geometries and that flax fiber reinforcement is a promising way of increasing load capacity and stiffness of plywood formed parts by respectively 76 and 38% on average. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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