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Advances in Wood Composites IV

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Biomacromolecules, Biobased and Biodegradable Polymers".

Deadline for manuscript submissions: closed (31 August 2021) | Viewed by 30780

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Prof. Dr. Antonios Papadopoulos

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Laboratory of Wood Science, Chemistry and Technology, Department of Forestry and Natural Environment, School of Geotechnical Sciences, International Hellenic University, Thermi, Greece
Interests: wood; wood composites; lignocellulosic materials; chemical and thermal modification technologies; nanotechnology and nanomaterilas; adhesives
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Dear Colleagues,

The fibrous nature of wood has rendered it one of the most appropriate and versatile raw materials for various uses. However, two properties restrict its use on a much wider scale, namely, dimensional changes when subjected to fluctuating humidity and susceptibility to biodegradation by micro-organisms. Wood may be modified chemically or thermally in order to enhance selected properties in an almost permanent fashion. An alternative option to improve these properties is to exploit the solutions offered by nanotechnology. The small-size nanoparticles of nanotechnology compounds can deeply penetrate into the wood, effectively alter its surface chemistry, and result in a high degree of protection against moisture and decay. In addition, the use of lignocellulosic materials for the production of advanced wood composites is an innovative avenue for research. This Special Issue on “Advances in Wood Composites” seeks high-quality works on topics including, but not limited to, the latest approaches to the protection of wood and wood composites with chemical or thermal modification technologies; the application of nanomaterials to wood science; the application of carbon fiber fabrics; and the use of lignocellulosic materials for the production of advanced wood composites.

Assoc. Prof. Dr. Antonios Papadopoulos
Guest Editor

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Keywords

wood
wood composites
lignocellulosic composites
chemical or thermal modification
nanotechnology
nanomaterials

Published Papers (9 papers)

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Research

20 pages, 2875 KiB

Open AccessArticle

Properties of High-Density Fiberboard Bonded with Urea–Formaldehyde Resin and Ammonium Lignosulfonate as a Bio-Based Additive

by Petar Antov, Viktor Savov, Neno Trichkov, Ľuboš Krišťák, Roman Réh, Antonios N. Papadopoulos, Hamid R. Taghiyari, Antonio Pizzi, Daniela Kunecová and Marina Pachikova

Polymers 2021, 13(16), 2775; https://doi.org/10.3390/polym13162775 - 18 Aug 2021

Cited by 44 | Viewed by 4183

Abstract

The potential of ammonium lignosulfonate (ALS) as an eco-friendly additive to urea–formaldehyde (UF) resin for manufacturing high-density fiberboard (HDF) panels with acceptable properties and low free formaldehyde emission was investigated in this work. The HDF panels were manufactured in the laboratory with very low UF resin content (4%) and ALS addition levels varying from 4% to 8% based on the mass of the dry wood fibers. The press factor applied was 15 s·mm⁻¹. The physical properties (water absorption and thickness swelling), mechanical properties (bending strength, modulus of elasticity, and internal bond strength), and free formaldehyde emission were evaluated in accordance with the European standards. In general, the developed HDF panels exhibited acceptable physical and mechanical properties, fulfilling the standard requirements for HDF panels for use in load-bearing applications. Markedly, the laboratory-produced panels had low free formaldehyde emission ranging from 2.0 to 1.4 mg/100 g, thus fulfilling the requirements of the E0 and super E0 emission grades and confirming the positive effect of ALS as a formaldehyde scavenger. The thermal analyses performed, i.e., differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and derivative thermogravimetry (DTG), also confirmed the main findings of the research. It was concluded that ALS as a bio-based, formaldehyde-free adhesive can be efficiently utilized as an eco-friendly additive to UF adhesive formulations for manufacturing wood-based panels under industrial conditions. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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14 pages, 5786 KiB

Open AccessArticle

Thermophysical Properties of Larch Bark Composite Panels

by Lubos Kristak, Ivan Ruziak, Eugenia Mariana Tudor, Marius Cătălin Barbu, Günther Kain and Roman Reh

Polymers 2021, 13(14), 2287; https://doi.org/10.3390/polym13142287 - 12 Jul 2021

Cited by 17 | Viewed by 2338

Abstract

The effects of using 100% larch bark (Larix decidua Mill) as a raw material for composite boards on the thermophysical properties of this innovative material were investigated in this study. Panels made of larch bark with 4–11 mm and 10–30 mm particle size, with ground bark oriented parallel and perpendicular to the panel’s plane at densities varying from 350 to 700 kg/m³ and bonded with urea-formaldehyde adhesive were analyzed for thermal conductivity, thermal resistivity and specific heat capacity. It was determined that there was a highly significant influence of bulk density on the thermal conductivity of all the panels. With an increase in the particle size, both parallel and perpendicular to the panel´s plane direction, the thermal conductivity also increased. The decrease of thermal diffusivity was a consequence of the increasing particle size, mostly in the parallel orientation of the bark particles due to the different pore structures. The specific heat capacity is not statistically significantly dependent on the density, particle size, glue amount and particle orientation. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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20 pages, 5083 KiB

Open AccessArticle

Enhancement of Flame Retardancy and Mechanical Properties of Polylactic Acid with a Biodegradable Fire-Retardant Filler System Based on Bamboo Charcoal

by Wenzhu Li, Liang Zhang, Weisheng Chai, Ningning Yin, Kate Semple, Lu Li, Wenbiao Zhang and Chunping Dai

Polymers 2021, 13(13), 2167; https://doi.org/10.3390/polym13132167 - 30 Jun 2021

Cited by 17 | Viewed by 2363

Abstract

A cooperative flame-retardant system based on natural intumescent-grafted bamboo charcoal (BC) and chitosan (CS) was developed for polylactic acid (PLA) with improved flame retardancy and minimal decline in strength properties. Chitosan (CS) as an adhesion promoter improved the interfacial compatibility between graft-modified bamboo charcoal (BC-m) and PLA leading to enhanced tensile properties by 11.11% and 8.42%, respectively for tensile strength and modulus. At 3 wt.% CS and 30 wt.% BC-m, the crystallinity of the composite increased to 38.92%, or 43 times that of pure PLA (0.9%). CS promotes the reorganization of the internal crystal structure. Thermogravimetric analysis showed significantly improved material retention of PLA composites in nitrogen and air atmosphere. Residue rate for 5 wt.% CS and 30 wt.% BC-m was 29.42% which is 55.1% higher than the theoretical value of 18.97%. Flammability tests (limiting oxygen index-LOI and UL-94) indicated significantly improved flame retardancy and evidence of cooperation between CS and BC-m, with calculated cooperative effectiveness index(Ce) >1. From CONE tests, the peak heat release rate (pHRR) and total heat release (THR) were reduced by 26.9% and 30.5%, respectively, for 3% CS + 20% BC-m in PLA compared with adding 20% BC-m alone. Analysis of carbon residue morphology, chemical elements and structure suggest CS and BC-m form a more stable char containing pyrophosphate. This char provides heat insulation to inhibit complete polymer pyrolysis, resulting in improved flame retardancy of PLA composites. Optimal mix may be recommended at 20% BC-m + 3% CS to balance compatibility, composite strength properties and flame retardance. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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11 pages, 2559 KiB

Open AccessArticle

Oversized Planer Shavings for the Core Layer of Lightweight Particleboard

by Jakob Gößwald, Marius Cătălin Barbu, Alexander Petutschnigg, Ľuboš Krišťák and Eugenia Mariana Tudor

Polymers 2021, 13(7), 1125; https://doi.org/10.3390/polym13071125 - 02 Apr 2021

Cited by 9 | Viewed by 2304

Abstract

Planer shavings (PS) are side-products generated during the processing of solid wood, typically used for heating, packaging, or insulation purposes. PS has been used for decades in particleboard manufacture, particularly in the core layer. The aim of this research is to investigate the use of PS with a length over 4 mm in low-density one-layer particleboard manufacturing with a thickness of 10 mm, as an option to reduce the raw material demand for wood-based panels. Correlations towards the mechanical properties of the particleboards, fabricated at a density of 475 kg/m³, could be drawn by analyzing the effects of different urea-formaldehyde adhesive contents (6%, 9%, and 12%). Two methods of adhesive application (pouring and spraying) and two types of blending of PS with adhesive (plowshare mixer and drum mixer) were investigated, with the aim that PS will have controlled resin application. The difference between the adhesive application methods was examined by analyzing the mechanical properties as an internal bond, modulus of rupture, and modulus of elasticity as well as indirectly by visualizing the adhesive distribution by adding a green pigment to the adhesive before application. PS demonstrated reduced bending properties in comparison with the EN 312 standard requirements of particleboards for internal use in dry conditions (type P2), due to the low density. The internal bond strength in the case of the particleboard without pigment application (up to 0.5 N/mm²) was higher compared to the P2 requirements (0.4 N/mm²), and significantly lower (0.15 N/mm²) in combination with the pigment (2.5% based on the board weight, compared to 0.1%, specific for such industry applications), but still superior to the values of the reference panel manufactured with wood particles. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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17 pages, 5505 KiB

Open AccessArticle

The Characteristics of Natural Rubber Composites with Klason Lignin as a Green Reinforcing Filler: Thermal Stability, Mechanical and Dynamical Properties

by Jutharat Intapun, Thipsuda Rungruang, Sunisa Suchat, Banyat Cherdchim and Salim Hiziroglu

Polymers 2021, 13(7), 1109; https://doi.org/10.3390/polym13071109 - 31 Mar 2021

Cited by 16 | Viewed by 4388

Abstract

The objective of this work was to investigate the influences of Klason lignin as a filler on the thermal stability and properties of natural rubber composites. The modulus and tensile strength of stabilized vulcanizates were measured before and after thermo-oxidative aging. It was determined that lignin filled natural rubber had significantly enhanced thermo-oxidative aging and mechanical properties compared to those of controlled samples. The reinforcement effect of lignin increased stress with lignin loading but it decreased at 20 phr, suggesting that the reinforcement mechanism of lignin was via strain-induced crystallization. The composite samples with 10 phr filler loading had the highest mechanical properties as well as thermo-oxidative degradation resistance. Such a finding could be due to interactions between the Klason lignin filler and natural rubber matrix. Based on the findings in this work, the degradation temperature of Klason lignin occurred at 420 °C. The absorption peaks at wavenumbers 1192 and 1374 cm⁻¹ indicated that C–O stretching vibrations of the syringyl and guaiacyl rings of hardwood lignin existed. It was also found that the Klason lignin–rubber composite containing 10 phr had the highest stress–strain, 100% modulus, and tensile strength, while lignin showed increasing aging resistance of the composite comparable with commercial antioxidant at 1.5 phr. It appears that Klason lignin from rubberwood could be used as a green antioxidant and alternative reinforcing filler and for high performance eco-friendly natural rubber biocomposites. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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14 pages, 1533 KiB

Open AccessArticle

Eco-Friendly Fiberboard Panels from Recycled Fibers Bonded with Calcium Lignosulfonate

by Petar Antov, L’uboš Krišt’ák, Roman Réh, Viktor Savov and Antonios N. Papadopoulos

Polymers 2021, 13(4), 639; https://doi.org/10.3390/polym13040639 - 21 Feb 2021

Cited by 51 | Viewed by 4938

Abstract

The potential of using residual softwood fibers from the pulp and paper industry for producing eco-friendly, zero-formaldehyde fiberboard panels, bonded with calcium lignosulfonate (CLS) as a lignin-based, formaldehyde free adhesive, was investigated in this work. Fiberboard panels were manufactured in the laboratory by applying CLS addition content ranging from 8% to 14% (on the dry fibers). The physical and mechanical properties of the developed composites, i.e., water absorption (WA), thickness swelling (TS), modulus of elasticity (MOE), bending strength (MOR), as well as the free formaldehyde emission, were evaluated according to the European norms. In general, only the composites, developed with 14% CLS content, exhibited MOE and MOR values, comparable with the standard requirements for medium-density fiberboards (MDF) for use in dry conditions. All laboratory-produced composites demonstrated significantly deteriorated moisture-related properties, i.e., WA (24 h) and TS (24 h), which is a major drawback. Noticeably, the fiberboards produced had a close-to-zero formaldehyde content, reaching the super E0 class (≤1.5 mg/100 g), with values, ranging from 0.8 mg/100 g to 1.1 mg/100 g, i.e., equivalent to formaldehyde emission of natural wood. The amount of CLS adhesive had no significant effect on formaldehyde content. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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15 pages, 4887 KiB

Open AccessArticle

Natural Tannins as New Cross-Linking Materials for Soy-Based Adhesives

by Saman Ghahri, Xinyi Chen, Antonio Pizzi, Reza Hajihassani and Antonios N. Papadopoulos

Polymers 2021, 13(4), 595; https://doi.org/10.3390/polym13040595 - 16 Feb 2021

Cited by 38 | Viewed by 3514

Abstract

Human health problems and formaldehyde emission from wood-based composites are some of the major drawbacks of the traditional synthetic adhesives such as urea formaldehyde resins. There have been many attempts to decrease formaldehyde emission and replace urea formaldehyde resins with bio-based adhesives for wood-based composites. Because of some weakness in soy-based adhesive, chemicals have been used as modifiers. Modified soy-based adhesives without any formaldehyde have been successfully used to prepare wood panels. To achieve this, different synthetic cross-linking chemicals such as phenol formaldehyde resins and polyamidoamine-epichlorohydrin were used. However, in reality, what we need are totally green adhesives that use natural materials. In our previous research work, the use of tannins in combination with soy-based adhesives to make wood composites was investigated. Thus, in this research work, the feasibility of using three types of natural tannins (quebracho, mimosa and chestnut tannins) as cross-linking materials for soy adhesive was studied. The chemical bond formation and adhesion behaviors of tannin-modified soy adhesives were also investigated by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-ToF-MS) and thermo-mechanical analysis (TMA). The results showed that at ambient temperature, both ionic and covalent bonds formed between tannin constituents and amino acids; however, at higher temperature, covalent bonds are largely predominate. Based on the results obtained from the thermo-mechanical analysis, the modulus of elasticity (MOE) of soy adhesive is increased by adding tannins to its formulation. In addition, the chemical bond formation was proved by MALDI-ToF-MS. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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12 pages, 3954 KiB

Open AccessArticle

Characterization of Zinc Oxide-Urea Formaldehyde Nano Resin and Its Impact on the Physical Performance of Medium-Density Fiberboard

by Waheed Gul, Syed Riaz Akbar Shah, Afzal Khan and Catalin I. Pruncu

Polymers 2021, 13(3), 371; https://doi.org/10.3390/polym13030371 - 25 Jan 2021

Cited by 12 | Viewed by 2627

Abstract

The main purpose of this research work is to characterize zinc oxide-urea formaldehyde nano resin and identify the physical performance of medium-density fiberboard (MDF). Considering the dry weight of natural fibers, the ZnO nanoparticles were added to urea formaldehyde (UF) glue at four levels—0.0%, 1.0%, 2.0% and 3.0%—and their effects were investigated in terms of the physical properties of MDF. The surface morphology and crystalline structure of ZnO, UF and UF-ZnO nanofillers were characterized using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) analysis and significant improvements were achieved as a result of the addition of nanoparticles. Thermal properties were analyzed by means of differential scanning calorimetry (DSC) and thermogravemetric analysis (TGA) and it was observed that increasing the concentration of ZnO nanoparticles ultimately enhanced the curing of UF-ZnO nanofillers. Finally, density, thickness swelling and water absorption properties were investigated and it was observed that thickness swelling and water absorption properties were improved by 38% and 12%, respectively, when compared to control MDF. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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12 pages, 4156 KiB

Open AccessArticle

Potential of Brewer’s Spent Grain as a Potential Replacement of Wood in pMDI, UF or MUF Bonded Particleboard

by Marius Cătălin Barbu, Zeno Montecuccoli, Jakob Förg, Ulrike Barbeck, Petr Klímek, Alexander Petutschnigg and Eugenia Mariana Tudor

Polymers 2021, 13(3), 319; https://doi.org/10.3390/polym13030319 - 20 Jan 2021

Cited by 17 | Viewed by 2858

Abstract

Brewer’s spent grain (BSG) is the richest by-product (85%) of the beer-brewing industry, that can be upcycled in a plentiful of applications, from animal feed, bioethanol production or for removal of heavy metals from wastewater. The aim of this research is to investigate the mechanical, physical and structural properties of particleboard manufactured with a mixture of wood particles and BSG gradually added/replacement in 10%, 30% and 50%, glued with polymeric diisocyanate (pMDI), urea-formaldehyde (UF) and melamine urea-formaldehyde (MUF) adhesives. The density, internal bond, modulus of rupture, modulus of elasticity, screw withdrawal resistance, thickness swelling and water absorption were tested. Furthermore, scanning electron microscopy anaylsis was carried out to analyze the structure of the panels after the internal bond test. Overall, it was shown that the adding of BSG decreases the mechanical performance of particleboard, due to reduction of the bonding between wood and BSG particles. This decrease has been associated with the structural differences proven by SEM inspection. Interaction of particles with the adhesive is different for boards containing BSG compared to those made from wood. Nevertheless, decrease in the mechanical properties was not critical for particleboards produced with 10% BSG which could be potentially classified as a P2 type, this means application in non-load-bearing panel for interior use in dry conditions, with high dimensional stability and stiffness. Full article

(This article belongs to the Special Issue Advances in Wood Composites IV)

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