Composites from Recycled and Modified Woods – Technology, Properties, Application

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 (15 October 2021) | Viewed by 30363

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Guest Editor
Faculty of Wood Science & Technology, Technical University Zvolen, Zvolen, Slovakia
Interests: wood protection; wood modification; wood composites; material characterization; coatings; biodegradation; non-destructive analysis; service life
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Guest Editor
Faculty of Wood Science & Technology, Technical University Zvolen, Zvolen, Slovakia
Interests: physical-mechanical properties; wood science; wood products; wood composites; wood processing; wood modification; wood-based panels; wood based panels technology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Background and History:

The issue of efficient processing and use of less valuable wood species, bio-damaged logs, sawmill residues, cuttings, chips, sawdust, recycled wooden products, and other lignocellulosic raw materials in the production of wood composites is the focus of several scientific research institutes around the world. Wood composites are mostly produced for a particular application and, therefore, the raw materials, additional additives, production processes, as well as finishing and surface treatments are adapted to this. Research into the optimization of material and technological parameters of the production of wood composites with special properties and applications is still ongoing.

Aim and Scope:

Recycled woods as well as thermally, chemically, or biologically modified woods have the potential to be a base or complementary raw material for (A) construction wood composites used mostly in construction and transport, such as glued prisms (e.g., glulam), glued boards (e.g., blockboards), glued large-area boards from veneers (e.g., plywood, LVL, etc.), or large-area boards from wood particles and fibers (e.g., particleboards, OSB, MDF, etc.), as well as for (B) decorative wood composites used mostly in furniture and building architecture, such as veneered, laminated, coated or plasma-treated large-area boards.

Cutting-Edge Research:

For this Special Issues, we are interested in research on wood composites in the terms of the raw material conditions also encompasses technological processes, including finishing and surface treatments and their individual properties. Development of wood composites with special properties is also of interest.

What kind of papers we are soliciting:

The papers should be focused mainly on material composition (e.g., species, amounts, fractions, and distribution of recycled and modified woods; glues, biocides, fire retardants, other additives), processing, finishing, and properties of wood composites for construction and decorative purposes.

Prof. Dr. Ladislav Reinprecht
Dr. Ján Iždinský
Guest Editors

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Keywords

  • wood composites
  • particleboards
  • plywood
  • recycled wood
  • modified wood
  • processing
  • finishing
  • physical–mechanical properties
  • service life
  • bio-resistance
  • abio-resistance

Published Papers (11 papers)

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Editorial

Jump to: Research, Review

2 pages, 657 KiB  
Editorial
Composites from Recycled and Modified Woods—Technology, Properties, Application
by Ladislav Reinprecht and Ján Iždinský
Forests 2022, 13(1), 6; https://doi.org/10.3390/f13010006 - 21 Dec 2021
Cited by 3 | Viewed by 2011
Abstract
The intention of efficient processing and use of less valuable wood species, bio-damaged logs, sawmill residues, cuttings, chips, sawdust, recycled wooden products, and other lignocellulosic raw materials in the production of wood composites is the focus of several scientific research institutes in the [...] Read more.
The intention of efficient processing and use of less valuable wood species, bio-damaged logs, sawmill residues, cuttings, chips, sawdust, recycled wooden products, and other lignocellulosic raw materials in the production of wood composites is the focus of several scientific research institutes in the world [...] Full article

Research

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12 pages, 3255 KiB  
Article
Particleboards from Recycled Pallets
by Ján Iždinský, Ladislav Reinprecht and Zuzana Vidholdová
Forests 2021, 12(11), 1597; https://doi.org/10.3390/f12111597 - 19 Nov 2021
Cited by 11 | Viewed by 2293
Abstract
Worldwide production of wooden pallets continually increases, and therefore in future higher number of damaged pallets need to be recycled. One way to conveniently recycle pallets is their use for the production of particleboards (PBs). The 3-layer PBs, bonded with urea-formaldehyde (UF) resin, [...] Read more.
Worldwide production of wooden pallets continually increases, and therefore in future higher number of damaged pallets need to be recycled. One way to conveniently recycle pallets is their use for the production of particleboards (PBs). The 3-layer PBs, bonded with urea-formaldehyde (UF) resin, were prepared in laboratory conditions using particles from fresh spruce logs (FSL) and recycled spruce pallets (RSP) in mutual weight ratios of 100:0, 80:20, 50:50 and 0:100. Particles from RSP did not affect the moisture properties of PBs, i.e., the thickness swelling (TS) and water absorption (WA). The mechanical properties of PBs based on particles from RSP significantly worsened: the modulus of rupture (MOR) in bending from 14.6 MPa up to 10 MPa, the modulus of elasticity (MOE) in bending from 2616 MPa up to 2012 MPa, and the internal bond (IB) from 0.79 MPa up to 0.61 MPa. Particles from RSP had only a slight negative effect on the decay resistance of PBs to the brown-rot fungus Serpula lacrymans, while their presence in surfaces of PBs did not affect the growth activity of moulds at all. Full article
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15 pages, 5379 KiB  
Article
Particleboards from Recycled Thermally Modified Wood
by Ján Iždinský, Zuzana Vidholdová and Ladislav Reinprecht
Forests 2021, 12(11), 1462; https://doi.org/10.3390/f12111462 - 27 Oct 2021
Cited by 2 | Viewed by 1660
Abstract
In recent years, the production and consumption of thermally modified wood (TMW) has been increasing. Offcuts and other waste generated during TMWs processing into products, as well as already disposed products based on TMWs can be an input recycled raw material for production [...] Read more.
In recent years, the production and consumption of thermally modified wood (TMW) has been increasing. Offcuts and other waste generated during TMWs processing into products, as well as already disposed products based on TMWs can be an input recycled raw material for production of particleboards (PBs). In a laboratory, 16 mm thick 3-layer PBs bonded with urea-formaldehyde (UF) resin were produced at 5.8 MPa, 240 °C and 8 s pressing factor. In PBs, the particles from fresh spruce wood and mixed particles from offcuts of pine, beech, and ash TMWs were combined in weight ratios of 100:0, 80:20, 50:50 and 0:100. Thickness swelling (TS) and water absorption (WA) of PBs decreased with increased portion of TMW particles, i.e., TS after 24 h maximally about 72.3% and WA after 24 h maximally about 64%. However, mechanical properties of PBs worsened proportionally with a higher content of recycled TMW—apparently, the modulus of rupture (MOR) up to 55.5% and internal bond (IB) up to 46.2%, while negative effect of TMW particles on the modulus of elasticity (MOE) was milder. Decay resistance of PBs to the brown-rot fungus Serpula lacrymans (Schumacher ex Fries) S.F. Gray increased if they contained TMW particles, maximally about 45%, while the mould resistance of PBs containing TMW particles improved only in the first days of test. In summary, the recycled TMW particles can improve the decay and water resistance of PBs exposed to higher humidity environment. However, worsening of their mechanical properties could appear, as well. Full article
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21 pages, 5241 KiB  
Article
New Perspectives for LVL Manufacturing from Wood of Heterogeneous Quality—Part 2: Modeling and Manufacturing of Variable Stiffness Beams
by Robin Duriot, Guillaume Pot, Stéphane Girardon and Louis Denaud
Forests 2021, 12(9), 1275; https://doi.org/10.3390/f12091275 - 17 Sep 2021
Cited by 3 | Viewed by 1631
Abstract
This paper presents a new strategy in the use of wood of heterogeneous quality for composing LVL products. The idea is to consider veneers representative of the resource variability and retain local stiffness information to control panel manufacturing fully. The placement of veneers [...] Read more.
This paper presents a new strategy in the use of wood of heterogeneous quality for composing LVL products. The idea is to consider veneers representative of the resource variability and retain local stiffness information to control panel manufacturing fully. The placement of veneers is also no longer random as in the first part of this group of papers but optimized for the quality of veneers according to the requirement of bending stresses along the beam. In a four-point bending test arrangement, this means the high-quality veneer is concentrated in the center of the beam in the area between the loading points where the bending moments are the most important, and the low quality is located at the extremities. This initiates the creation of variable stiffness beams. This is driven by an algorithm developed and tested on representative veneer samples from the resource. Four LVL panels were manufactured by positioning the veneers in the same positions as in an analytical calculation model, which allowed the calculation of beam mechanical properties in four-point bending. The proposed optimization of LVL manufacturing from variable quality veneers should help for more efficient usage of forest resources. This optimization strategy showed notable gains for modeled and experimental mechanical properties, whether in terms of stiffness or strength. The analytical calculation of the local modulus of elasticity from modelized beams was satisfactory compared to the tests of the manufactured beams test results, allowing the reliability of the model for this property to be confirmed. Full article
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22 pages, 7400 KiB  
Article
New Perspectives for LVL Manufacturing from Wood of Heterogeneous Quality—Part. 1: Veneer Mechanical Grading Based on Online Local Wood Fiber Orientation Measurement
by Robin Duriot, Guillaume Pot, Stéphane Girardon, Benjamin Roux, Bertrand Marcon, Joffrey Viguier and Louis Denaud
Forests 2021, 12(9), 1264; https://doi.org/10.3390/f12091264 - 16 Sep 2021
Cited by 5 | Viewed by 2137
Abstract
The grading of wood veneers according to their true mechanical potential is an important issue in the peeling industry. Unlike in the sawmilling industry, this activity does not currently estimate the local properties of production. The potential of the tracheid effect, which enables [...] Read more.
The grading of wood veneers according to their true mechanical potential is an important issue in the peeling industry. Unlike in the sawmilling industry, this activity does not currently estimate the local properties of production. The potential of the tracheid effect, which enables local fiber orientation measurement, has been widely documented for sawn products. A measuring instrument exploiting this technology and implemented on a peeling line was developed, enabling us to obtain the fiber orientation locally which, together with global density, allowed us to model the local elastic properties of each veneer. A sorting method using this data was developed and is presented here. It was applied to 286 veneers from several logs of French Douglas fir, and was compared to a widely used sorting method based on veneer appearance defects. The effectiveness of both grading approaches was quantified according to mechanical criteria. This study shows that the sorting method used (based on local fiber orientation and average density) allows for better theorical quality discrimination according to the mechanical potential. This article is the first in a series, with the overall aim of enhancing the use of heterogeneous wood veneers in the manufacturing of maximized-performance LVL by veneer grading and optimized positioning as well as material mechanical property modelization. Full article
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16 pages, 3744 KiB  
Article
The Impact of a CO2 Laser on the Adhesion and Mold Resistance of a Synthetic Polymer Layer on a Wood Surface
by Ladislav Reinprecht and Zuzana Vidholdová
Forests 2021, 12(2), 242; https://doi.org/10.3390/f12020242 - 20 Feb 2021
Cited by 6 | Viewed by 1956
Abstract
In the wood industry, laser technologies are commonly applied for the sawing, engraving, or perforation of solid wood and wood composites, but less knowledge exists about their effect on the joining and painting of wood materials with synthetic polymer adhesives and coatings. In [...] Read more.
In the wood industry, laser technologies are commonly applied for the sawing, engraving, or perforation of solid wood and wood composites, but less knowledge exists about their effect on the joining and painting of wood materials with synthetic polymer adhesives and coatings. In this work, a CO2 laser with irradiation doses from 2.1 to 18.8 J·cm−2 was used for the modification of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies /L./ Karst) wood surfaces—either in the native state or after covering them with a layer of polyvinyl acetate (PVAc) or polyurethane (PUR) polymer. The adhesion strength of the phase interface “synthetic polymer—wood”, evaluated by the standard EN ISO 4624, decreased significantly and proportionately in all the laser modification modes, with higher irradiation doses leading to a more apparent degradation and carbonization of the wood adherent or the synthetic polymer layer. The mold resistance of the polymers, evaluated by the standard EN 15457, increased significantly for the less mold-resistant PVAc polymer after its irradiation on the wood adherent. However, the more mold-resistant PUR polymer was able to better resist the microscopic fungi Aspergillus niger Tiegh. and Penicillium purpurogenum Stoll. when irradiation doses of higher intensity acted firstly on the wood adherent. Full article
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9 pages, 2749 KiB  
Article
Penetration of Different Liquids in Wood-Based Composites: The Effect of Adsorption Energy
by Hamid R. Taghiyari, Roya Majidi, Mahnaz Ghezel Arsalan, Asaad Moradiyan, Holger Militz, George Ntalos and Antonios N. Papadopoulos
Forests 2021, 12(1), 63; https://doi.org/10.3390/f12010063 - 7 Jan 2021
Cited by 5 | Viewed by 2151
Abstract
The penetration properties of three different liquids on the surface of medium-density fiberboard (MDF) and particleboard panels were studied. Water, as a polar liquid, was compared to two other less polar liquids (namely, ethanol and kerosene) with significantly larger molecules. Measurement of penetration [...] Read more.
The penetration properties of three different liquids on the surface of medium-density fiberboard (MDF) and particleboard panels were studied. Water, as a polar liquid, was compared to two other less polar liquids (namely, ethanol and kerosene) with significantly larger molecules. Measurement of penetration time and wetted area demonstrated significantly higher values for water in comparison with the other two liquids, in both composite types. Calculation of adsorption energies, as well as adsorption distances, of the three liquid molecules on hemicellulose showed higher potentiality of water molecules in forming bonds on hemicellulose. However, comparison of the adsorption energies of cellulose with hemicellulose indicated a higher impact of the formation of bonds between hydroxyl groups in water and cellulose in hindering the penetration of water molecules into the composite textures. It was concluded that the formation of strong and stable bonds between the hydroxyl groups in water and cellulose resulted in a significant increase in penetration time and wetted area. Full article
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16 pages, 4592 KiB  
Article
Particleboards from Recycled Wood
by Ján Iždinský, Zuzana Vidholdová and Ladislav Reinprecht
Forests 2020, 11(11), 1166; https://doi.org/10.3390/f11111166 - 31 Oct 2020
Cited by 39 | Viewed by 3708
Abstract
The effective recovery of wood waste generated in wood processing and also at the end of wood product life is important from environmental and economic points of view. In a laboratory, 16 mm-thick three-layer urea–formaldehyde (UF)-bonded particleboards (PBs) were produced at 5.8 MPa [...] Read more.
The effective recovery of wood waste generated in wood processing and also at the end of wood product life is important from environmental and economic points of view. In a laboratory, 16 mm-thick three-layer urea–formaldehyde (UF)-bonded particleboards (PBs) were produced at 5.8 MPa and 240 °C and with an 8 s/mm pressing factor, using wood particles prepared from (1) fresh spruce wood (C), (2) a mixture of several recycled wood products (R1), and (3) recycled faulty PBs bonded with UF resin (R2). Particles from spruce wood were combined with particles from R1 or R2 recyclates in weight ratios of 100:0, 80:20, 50:50 and 0:100. In comparison to the control spruce PB, the PBs containing the R1 recyclate from old wood products were characterized by lower thickness swelling after 2 and 24 h (TS-2h and TS-24h), lower by 18 and 31%; water absorption after 2 and 24 h (WA-2h and WA-24h), lower by 33 and 28%; modulus of rupture in bending (MOR), lower by 28%; modulus of elasticity in bending (MOE), lower by 18%; internal bond (IB), lower by 33%; and resistance to decay determined by the mass loss under the action of the brown-rot fungus Coniophora puteana (Δm), lower by 32%. The PBs containing the R2 recyclate from faulty PBs were also characterized by a lower TS-2h and TS-24h, lower by 45% and 59%; WA-2h and WA-24h, lower by 61% and 51%; MOR, lower by 37%; MOE, lower by 17%; and IB, lower by 33%; however, their biological resistance to C. puteana was more effective, with a decreased Δm in the decay test, lower by 44%. Full article
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10 pages, 1535 KiB  
Article
The Effect of Veneer Densification Temperature and Wood Species on the Plywood Properties Made from Alternate Layers of Densified and Non-Densified Veneers
by Emilia-Adela Salca, Pavlo Bekhta and Yaroslav Seblii
Forests 2020, 11(6), 700; https://doi.org/10.3390/f11060700 - 24 Jun 2020
Cited by 21 | Viewed by 2604
Abstract
In this study the properties of plywood manufactured from densified and non-densified veneer sheets and alternate layers of such veneers with and without densification using low amount of adhesive as a function of densification temperature and wood species were investigated. The plywood panels [...] Read more.
In this study the properties of plywood manufactured from densified and non-densified veneer sheets and alternate layers of such veneers with and without densification using low amount of adhesive as a function of densification temperature and wood species were investigated. The plywood panels were made from rotary-cut birch and black alder veneers using urea-formaldehyde (UF) adhesive. Veneer sheets with thickness of 1.5 mm were subjected to the thermal-compression at three different temperatures while keeping constant the pressure during a same time span. Five-layers plywood panels were produced using a constant hot-pressing schedule using different amounts of glue spread as a function of the plywood type; such as plywood made from non-densified (80 g/m2) and densified (60 g/m2) veneers only; and combination of them (70 g/m2). The bending strength (MOR) and the modulus of elasticity (MOE) along with the shear strength of the plywood samples for bonding class 1 (dry conditions) have been determined. As expected bending strength of the plywood samples increased with the increasing in density. The increase of veneer densification temperature resulted in a gradually decrease of MOR; MOE and shear strength values for the plywood panels made of densified veneers and mixed panels of both species. The temperature of 150 °C for veneer densification seemed to be enough to achieve enhanced bending and bonding properties. All plywood panels in this study were manufactured using reduced glue consumption and they presented satisfactory properties performance for indoor applications. Full article
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11 pages, 1715 KiB  
Article
Development of Wood Composites from Recycled Fibres Bonded with Magnesium Lignosulfonate
by Petar Antov, George I. Mantanis and Viktor Savov
Forests 2020, 11(6), 613; https://doi.org/10.3390/f11060613 - 1 Jun 2020
Cited by 36 | Viewed by 3931
Abstract
The potential of producing ecofriendly composites from industrial waste fibres, bonded with magnesium lignosulfonate, a lignin-based formaldehyde-free adhesive, was investigated in this work. Composites were produced in the laboratory using the following parameters: a hot press temperature of 210 °C, a pressing time [...] Read more.
The potential of producing ecofriendly composites from industrial waste fibres, bonded with magnesium lignosulfonate, a lignin-based formaldehyde-free adhesive, was investigated in this work. Composites were produced in the laboratory using the following parameters: a hot press temperature of 210 °C, a pressing time of 16 min, and a 15% gluing content of magnesium lignosulfonate (on the dry fibres). The physical and mechanical properties of the produced composites were evaluated and compared with the European Standard (EN) required properties (EN 312, EN 622-5) of common wood-based panels, such as particleboards for internal use in dry conditions (type P2), load-bearing particleboards for use in humid conditions (type P5), heavy-duty load-bearing particleboards for use in humid conditions (type P7), and medium-density fibreboards (MDF) for use in dry conditions. In general, the new produced composites exhibited satisfactory mechanical properties: a bending strength (MOR) (18.5 N·mm−2) that was 42% higher than that required for type P2 particleboards (13 N·mm−2) and 16% higher than that required for type P5 particleboards (16 N·mm−2). Additionally, the modulus of elasticity (MOE) of composites (2225 N·mm−2) was 24% higher than that required for type P2 particleboards (1800 N·mm−2) and equivalent to the required MOE of MDF panels for use in dry conditions (2200 N·mm−2). However, these ecofriendly composites showed deteriorated moisture properties, i.e., 24 h swelling and 24 h water absorption, which were a distinct disadvantage. This should be further investigated, as modifications in the lignosulfonate formula used and/or production parameters are necessary. Full article
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Review

Jump to: Editorial, Research

10 pages, 1571 KiB  
Review
Expandable Graphite as a Fire Retardant for Cellulosic Materials—A Review
by Bartłomiej Mazela, Anyelkis Batista and Wojciech Grześkowiak
Forests 2020, 11(7), 755; https://doi.org/10.3390/f11070755 - 13 Jul 2020
Cited by 31 | Viewed by 5298
Abstract
A diversity of chemicals is used to produce fire retardants (FRs); some of the main group of chemicals are hazardous to the environment as well as to human life; however, expandable graphite (EG) can be a gateway to a more environmentally friendly FRs [...] Read more.
A diversity of chemicals is used to produce fire retardants (FRs); some of the main group of chemicals are hazardous to the environment as well as to human life; however, expandable graphite (EG) can be a gateway to a more environmentally friendly FRs or intumescent fire retardants (IFRs). Researchers define intumescent as the swelling of a particular substance placed between a heat source and an underlying substrate when they are heated. EG is a material with extraordinary thermophysical and mechanical properties. The referred EG properties are unparalleled. EG is a low-density carbon material having a series of unique properties: developed specific surface, binder-free pressing capacity, stability to aggressive media, and low thermal conductivity. Therefore, EG is a promising material both for research work and for industrial applications. The primary goal of this literature review was to report current knowledge on the use of EG as a fire retardant for cellulose and cellulose-modified materials. EG is produced, among other methods, by thermal shock of graphite oxide under forming gas. When exposed to heat, EG will expand. The expansion mechanism was presented in this review. Equally important to this review is the knowledge related to cellulose thermal degradation and cellulose impact on the development of science and technology. Full article
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