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Degradation of Wood-Based Materials

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: closed (15 November 2020) | Viewed by 43033

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Prof. Dr. Jyh-Horng Wu

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Department of Forestry, National Chung Hsing University, Taichung 402, Taiwan
Interests: bio-based composites; wood modification; functional biomaterials; natural products
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Dear Colleagues,

Wood is a versatile, renewable, basic resource, and natural biopolymer that is widely used in different applications, and it remains indispensable to everyday human life and culture, because of its aesthetic appearance and characteristic properties. In recent years, various wood-based materials have been developed and successfully introduced into the engineering and construction marketplace. However, these lignocellulosic materials have a few undesirable properties, such as photodegradation, combustibility, and susceptibility to biological degradation. These drawbacks have limited their utilization in a variety of applications. To overcome these issues, several physical and chemical approaches have been used to enhance the thermal stability, photostability, and biological and weathering resistances of wood-based materials, and the related mechanisms have also been studied.

The scope of this Special Issue is to cover all of the aspects related to the degradation of wood-based materials. Authors are welcome to submit their latest research on this topic in the form of original research or review articles.

Prof. Jyh-Horng Wu
Guest Editor

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Keywords

Degradation
Wood-based materials
Lignocellulosic materials
Photodegradation
Biological degradation
Weathering
Durability

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Related Special Issues

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Polymer/Biopolymer Stabilization and Degradation in Polymers (6 articles)

Published Papers (11 papers)

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Research

9 pages, 1241 KiB

Open AccessCommunication

Effect of Panel Moisture Content on Internal Bond Strength and Thickness Swelling of Medium Density Fiberboard

by Roberto Magalhães, Beatriz Nogueira, Samaritana Costa, Nádia Paiva, João M. Ferra, Fernão D. Magalhães, Jorge Martins and Luisa H. Carvalho

Polymers 2021, 13(1), 114; https://doi.org/10.3390/polym13010114 - 30 Dec 2020

Cited by 16 | Viewed by 3099

Abstract

Wood-based products usually have serious limitations concerning contact with water, both because wood is a hygroscopic material and because the commonly used binder has low moisture resistance. This paper studies the effect of panel moisture content (MC) on the physico-mechanical properties of medium density fiberboards (MDF). Several commercial MDF boards produced in Europe were stored at room temperature and relative humidity (RH) for 9 weeks (approx. range 15–20 °C and 50–85% RH). Every week, a strip of each MDF board was cut out, divided into 5 × 5 cm test pieces and its internal bond strength (IB) was measured. A strong influence of MDF moisture content on internal bond strength was observed and therefore IB test pieces were stored in a climatic chamber (either at 20 °C, 55% RH and at 20 °C, 70% RH). A decreasing linear relation was established between IB and MC. It was found that this effect is reversible: after drying, internal bond strength rises again (following a slight hysteresis). This work reinforces the importance of conditioned storage before board properties analysis, as described in European Standard EN 319. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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17 pages, 2104 KiB

Open AccessArticle

Cellulose Structural Changes during Mild Torrefaction of Eucalyptus Wood

by Ana Lourenço, Solange Araújo, Jorge Gominho and Dmitry Evtuguin

Polymers 2020, 12(12), 2831; https://doi.org/10.3390/polym12122831 - 28 Nov 2020

Cited by 21 | Viewed by 2905

Abstract

The changes in the cellulose structure of eight Eucalyptus species (E. botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. saligna and E. viminalis) in a mild torrefaction (from 160 °C to 230 °C, 3 h) were studied in situ and after cellulose isolation from the wood by solid-state carbon nuclear magnetic resonance (¹³C NMR), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and by analytic pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS). Changes in molecular weight were assessed by viscosimetry. A small decrease in cellulose crystallinity (ca. 2%–3%) was attributed to its amorphization on crystallite surfaces as a result of acid hydrolysis and free radical reactions resulting in the homolytic splitting of glycosidic bonds. The degree of the cellulose polymerization (DPv) decreased more than twice during the heat treatment of wood. It has been proposed that changes in the supramolecular structure of cellulose and in molecular weight during a heat treatment can be affected by the amount of lignin present in the wood. The limitations of FTIR and Py-GC/MS techniques to distinguish the minor changes in cellulose crystallinity were discussed. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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15 pages, 7589 KiB

Open AccessArticle

Degradation of Mechanical Properties of Pine Wood Under Symmetric Axial Cyclic Loading Parallel to Grain

by Mariana D. Stanciu, Horațiu D. Teodorescu and Sorin Vlase

Polymers 2020, 12(10), 2176; https://doi.org/10.3390/polym12102176 - 23 Sep 2020

Cited by 5 | Viewed by 3440

Abstract

The mechanical properties of wood, respectively the elastic, plastic, and strength properties, depend on a large number of factors, due both to its structural and physical characteristics, as well as to the size, direction, nature, and speed of application of forces. Wood, generally considered to be a viscous-elastic material, has creep deformations over time under the effect of a constant load. In this study the behavior of pine wood samples was investigated due to its large utilization in different finished products, such as roof construction, furniture, outdoor applications, garden furniture, and toys. The paper aims to analyze the viscoelastic behavior of pine wood subjected to cyclically loading to traction-compression with different loads (1 kN; 1.5 kN; 2 kN), applied at different speeds (1 mm/min; 10 mm/min). It was observed that, at low speeds (1 mm/min) and low intensities of the applied force, it was possible to distinguish the three creep regions specific to wood: the primary area (primary flow), the secondary area, and finally the tertiary creep. As the force increases, the law of variation of the wood flow changes. The degradation of longitudinal elasticity modulus occurs with the increase of the number of cycles, so after 20 alternating symmetrical cycles of traction-compression of the pine wood samples, there is a decrease of its values by 35%. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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10 pages, 1374 KiB

Open AccessArticle

Durability of Accoya Wood in Ground Stake Testing after 10 Years of Exposure in Greece

by George I. Mantanis, Charalampos Lykidis and Antonios N. Papadopoulos

Polymers 2020, 12(8), 1638; https://doi.org/10.3390/polym12081638 - 23 Jul 2020

Cited by 15 | Viewed by 3197

Abstract

In this research, acetylated wood (Accoya) was tested in ground contact in central Greece. After ten years of exposure during a ground stake test, acetylated pine wood (Pinus radiata) stakes, with a 20% acetyl weight gain, were completely intact and showed no visual decay (decay rating: 0). However, the key mechanical properties of Accoya wood, that is, modulus of elasticity (MOE) and modulus of rupture (MOR) after 10 years of ground contact, were significantly reduced by 32.8% and 29.6%, respectively, despite an excellent visual result since no evidence of fungal attack was identified. This contradiction could possibly indicate that the hallmarks of decay, i.e., brown-rot decay of acetylated wood can be the significant loss of mechanical properties before decay is actually visible. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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7 pages, 449 KiB

Open AccessArticle

Innovation in Wood Preservation

by Roger M. Rowell

Polymers 2020, 12(7), 1511; https://doi.org/10.3390/polym12071511 - 7 Jul 2020

Cited by 7 | Viewed by 3158

Abstract

The wood preservation industry has depended on toxicity as a mechanism of effectiveness against decay fungi to extend the life of wood used in adverse conditions. An alternative to toxicity, however, is to study and understand the mechanism of fungal attack and stop it before it can start. Knowing that fungi need moisture for colonization, a new approach to wood preservation is to lower the cell wall moisture content below that needed for fungal attack. Acetylation chemistry is known to reduce the moisture content in the cell wall, and it was used to study moisture levels in the bulk cell wall and in the isolated cell wall polymers. Resistance to brown-rot was determined using a 12-week soil block test with Gloeophyllum trabeum. Weight loss was measured and an analysis of what was lost was determined. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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13 pages, 1286 KiB

Open AccessArticle

Pretreatment Affects Activated Carbon from Piassava

by Jonnys Paz Castro, João Rodrigo C. Nobre, Alfredo Napoli, Paulo Fernando Trugilho, Gustavo H. D. Tonoli, Delilah F. Wood and Maria Lucia Bianchi

Polymers 2020, 12(7), 1483; https://doi.org/10.3390/polym12071483 - 2 Jul 2020

Cited by 5 | Viewed by 3084

Abstract

The specificity of activated carbon (AC) can be targeted by pretreatment of the precursors and/or activation conditions. Piassava (Leopoldinia piassaba and Attalea funifera Martius) are fibrous palms used to make brushes, and other products. Consolidated harvest and production residues provide economic feasibility for producing AC, a value-added product from forest and industrial residues. Corona electrical discharge and extraction pretreatments prior to AC activation were investigated to determine benefits from residue pretreatment. The resulting AC samples were characterized using elemental analyses and FTIR and tested for efficacy using methylene blue and phenol. All resulting AC had good adsorbent properties. Extraction as a pretreatment improved functionality in AC properties over Corona electrical discharge pretreatment. Due to higher lignin content, AC from L. piassaba had better properties than that from A. funifera. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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15 pages, 2100 KiB

Open AccessArticle

The Effect of Environmental Conditions on the Degradation Behavior of Biomass Pellets

by Hamid Gilvari, Luis Cutz, Urša Tiringer, Arjan Mol, Wiebren de Jong and Dingena L. Schott

Polymers 2020, 12(4), 970; https://doi.org/10.3390/polym12040970 - 21 Apr 2020

Cited by 24 | Viewed by 4419

Abstract

Biomass pellets provide a pivotal opportunity in promising energy transition scenarios as a renewable source of energy. A large share of the current utilization of pellets is facilitated by intensive global trade operations. Considering the long distance between the production site and the end-user locations, pellets may face fluctuating storage conditions, resulting in their physical and chemical degradation. We tested the effect of different storage conditions, from freezing temperatures (−19 °C) to high temperature (40 °C) and humidity conditions (85% relative humidity), on the physicochemical properties of untreated and torrefied biomass pellets. Moreover, the effect of sudden changes in the storage conditions on pellet properties was studied by moving the pellets from the freezing to the high temperature and relative humidity conditions and vice versa. The results show that, although storage at one controlled temperature and RH may degrade the pellets, a change in the temperature and relative humidity results in higher degradation in terms of higher moisture uptake and lower mechanical strength. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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14 pages, 2804 KiB

Open AccessArticle

Effects of Brown Sugar Water Binder Added by Spraying Method as Solid Bridge on the Physical Characteristics of Biomass Pellets

by Kexin Zhang, Shuangyan Song, Zhongjia Chen and Jianbo Zhou

Polymers 2020, 12(3), 674; https://doi.org/10.3390/polym12030674 - 18 Mar 2020

Cited by 6 | Viewed by 2974

Abstract

The binder can improve the physical characteristics of biomass pellets by forming solid bridges and increasing the adhesion of biomass materials. Taking pine sawdust as raw material and brown sugar water with different concentration as a binder, this study adopted spraying and stirring methods, respectively, and mixed brown sugar water with biomass in diverse proportions. The characteristic of pellets such as durability, relaxation ratio and compressive strength were studied by orthogonal design. Through range analysis, BP (Back Propagation) neural network factor significance analysis and mapping the relationship between physical properties and factors according to the importance of each factor, the effect of densification variables on the physical characteristics of biomass pellets was studied, and the outcome of adding brown sugar water binder to raw material by spraying method in improving the densification quality of biomass was explored. Results showed the brown sugar water binder added to pine sawdust by spraying method could mix the binder and biomass raw material more evenly compared with the stirring method. The relaxation ratio of pellets obtained by spraying method was reduced by 13.47%. The optimal densification conditions of pine sawdust were when the compaction pressure was 100 MPa, the mass ratio of brown sugar to water was 2:1, the proportion of brown sugar water to biomass material was 3%, and the adding method was spraying. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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10 pages, 2023 KiB

Open AccessArticle

Effects of Acetylated Veneer on the Natural Weathering Properties of Adhesive-Free Veneer Overlaid Wood‒Plastic Composites

by Ying-Ying Chao, Ke-Chang Hung, Jin-Wei Xu, Tung-Lin Wu and Jyh-Horng Wu

Polymers 2020, 12(3), 513; https://doi.org/10.3390/polym12030513 - 27 Feb 2020

Cited by 7 | Viewed by 3851

Abstract

The purpose of this study is to investigate the natural weathering properties of unmodified and acetylated veneer overlaid wood‒plastic composites (vWPCs) manufactured by one-step hot press molding. The results show that the water absorption and thickness swelling of vWPC with acetylated veneer were lower than those of unmodified vWPC. In addition, the surface tensile strength of vWPC increased with increasing weight gain of acetylated veneer, and the flexural properties of vWPC were not significantly different. Furthermore, the results of natural weathering demonstrated that not only the photostability but also the modulus of elasticity (MOE) retention ratio and surface tensile strength of vWPC with acetylated veneer were significantly higher than those of vWPC with unmodified veneer. Thus, better dimensional stability, surface tensile strength, and weathering properties can be achieved when the vWPC is made with acetylated veneer, especially those containing veneers with a higher weight percent gain. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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12 pages, 1949 KiB

Open AccessArticle

Structural Changes of Oak Wood Main Components Caused by Thermal Modification

by Ivan Kubovský, Danica Kačíková and František Kačík

Polymers 2020, 12(2), 485; https://doi.org/10.3390/polym12020485 - 21 Feb 2020

Cited by 202 | Viewed by 7712

Abstract

Thermal modification of wood causes chemical changes that significantly affect the physical, mechanical and biological properties of wood; thus, it is essential to investigate these changes for better utilization of products. Fourier transform infrared spectroscopy and size exclusion chromatography were used for evaluation of chemical changes at thermal treatment of oak wood. Thermal modification was applied according to Thermowood process at the temperatures of 160, 180 and 210 °C, respectively. The results showed that hemicelluloses are less thermally stable than cellulose. Chains of polysaccharides split to shorter ones leading to a decrease of the degree of polymerization and an increase of polydispersity. At the highest temperature of the treatment (210 °C), also crosslinking reactions take place. At lower temperatures degradation reactions of lignin predominate, higher temperatures cause mainly condensation reactions and a molecular weight increase. Chemical changes in main components of thermally modified wood mainly affect its mechanical properties, which should be considered into account especially when designing various timber constructions. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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13 pages, 3130 KiB

Open AccessArticle

Feasibility of Manufacturing Strand-Based Wood Composite Treated with β-Cyclodextrin–Boric Acid for Fungal Decay Resistance

by Lili Cai, Hyungsuk Lim, Nicholas C. Fitzkee, Bojan Cosovic and Dragica Jeremic

Polymers 2020, 12(2), 274; https://doi.org/10.3390/polym12020274 - 29 Jan 2020

Cited by 8 | Viewed by 4219

Abstract

The feasibility of using β-cyclodextrin (βCD) as an eco-friendly carrier of boric acid for the protection of strand-based wood composites against decay fungi was evaluated. The formation of a βCD–boric acid (βCD–B) complex was confirmed by the appearance of the boron–oxygen bond by using attenuated total reflection–Fourier transform infrared spectroscopy. Chemical shifts of around 6.25 and 1.41 ppm were also observed in ¹H Nuclear Magnetic Resonance (NMR) and ¹¹B NMR spectra, respectively. The βCD–B preservatives at two levels (5 and 10 wt.%) were uniformly blended with southern pine strands that were subsequently sprayed with polymeric methylene diphenyl diisocyanate (pMDI) resin. The blended strands were formed into a loose mat by hand and consolidated into 25 × 254 × 12 mm oriented strand boards (OSB) using a hot-press. The OSB panels were cut to end-matched internal bonding (IB) strength and fungal decay resistance test specimens. The vertical density profiles (VDPs) of the IB specimens were measured using an X-ray based density profiler and the specimens with statistically similar VDPs were selected for the IB and decay tests. The IB strength of the treated specimens was lower than the control specimens but they were above the required IB strength of heavy-duty load-bearing boards for use in humid conditions, specified in the BS EN 300:2006 standard. The reduced IB of preservative-treated OSB boards could be explained by the destabilized resin upon the addition of the βCD–B complex, as indicated by the differential scanning calorimetry (DSC) results. The resistance of the OSB panels against two brown-rot fungi (i.e., G. trabeum or P. placenta) was evaluated before and after accelerated leaching cycles. The treated OSBs exposed to the fungi showed an average mass loss of lower than 3% before leaching, while the untreated OSBs had 49 and 35% mass losses due to decay by G. trabeum or P. placenta, respectively. However, upon the leaching, the treatment provided protection only against G. trabeum to a certain degree (average mass loss of 15%). The experimental results suggest that protection efficacy against decay fungi after leaching, as well as the adhesion of the OSB strands, can be improved by increasing the amount of pMDI resin. Full article

(This article belongs to the Special Issue Degradation of Wood-Based Materials)

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