Topical Collection "Wood Composites"

A topical collection in Polymers (ISSN 2073-4360). This collection belongs to the section "Biomacromolecules, Biobased and Biodegradable Polymers".

Editors

Prof. Dr. Antonios Papadopoulos
E-Mail Website
Collection Editor
Laboratory of Wood Science - Chemistry & Technology, Department of Forestry & 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
Special Issues, Collections and Topics in MDPI journals
Dr. Ľuboš Krišťák
E-Mail Website
Collection Editor
Prof. Dr. Roman Réh
E-Mail Website
Collection Editor
Faculty of Wood Sciences and Technology, Technical University in Zvolen, T. G. Masaryka 24, SK-960 01 Zvolen, Slovakia
Interests: wood-based composites; wood adhesives
Special Issues, Collections and Topics in MDPI journals
Dr. Petar Antov
E-Mail Website
Collection Editor
Department of Mechanical Wood Technology, Faculty of Forest Industry, University of Forestry, 1797 Sofia, Bulgaria
Interests: wood; wood composites; eco-friendly wood-based composites; lignocellulosic composites; wood technology; bio-based wood adhesives; advanced formaldehyde-based wood adhesives; formaldehyde emission; formaldehyde scavengers
Special Issues, Collections and Topics in MDPI journals

Topical Collection Information

Dear Colleagues,

The fibrous nature of wood has made it one of the most appropriate and versatile raw materials for various uses. However, two properties restrict its much wider use, namely dimensional changes when subjected to fluctuating humidity, and susceptibility to biodegradation by micro-organisms. Wood can be modified chemically or thermally so that selected properties are enhanced in a more or less permanent fashion. Another option to improve these properties is to exploit the solutions that nanotechnology can offer. The small nanoparticles of nanotechnology compounds can deeply penetrate into the wood, effectively altering its surface chemistry and resulting in a high 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 collection seeks high-quality works and topics focusing on (among others) 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.

Dr. Antonios Papadopoulos
Dr. Ľuboš Krišťák
Prof. Dr. Roman Réh
Collection Editors

Manuscript Submission Information

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Keywords

  • wood
  • wood composites
  • lignocellulosic composites
  • chemical or thermal modification
  • nanotechnology and nanomaterials

Published Papers (3 papers)

2022

Jump to: 2021

Article
Influence of Lignin Content and Pressing Time on Plywood Properties Bonded with Cold-Setting Adhesive Based on Poly (Vinyl Alcohol), Lignin, and Hexamine
Polymers 2022, 14(10), 2111; https://doi.org/10.3390/polym14102111 - 22 May 2022
Cited by 5 | Viewed by 716
Abstract
The sustainability, performance, and cost of production in the plywood industry depend on wood adhesives and the hot-pressing process. In this study, a cold-setting plywood adhesive was developed based on polyvinyl alcohol (PVOH), high-purity lignin, and hexamine. The influence of lignin content (10%, [...] Read more.
The sustainability, performance, and cost of production in the plywood industry depend on wood adhesives and the hot-pressing process. In this study, a cold-setting plywood adhesive was developed based on polyvinyl alcohol (PVOH), high-purity lignin, and hexamine. The influence of lignin content (10%, 15%, and 20%) and cold-pressing time (3, 6, 12, and 24 h) on cohesion, adhesion, and formaldehyde emission of plywood were investigated through physical, chemical, thermal, and mechanical analyses. The increased lignin addition level lowered the solids content, which resulted in reduced average viscosity of the adhesive. As a result, the cohesion strength of the adhesive formulation with 10% lignin addition was greater than those of 15% and 20% lignin content. Markedly, the adhesive formulation containing a 15% lignin addition level exhibited superior thermo-mechanical properties than the blends with 10% and 20% lignin content. This study showed that 10% and 15% lignin content in the adhesive resulted in better cohesion strength than that with 20% lignin content. However, statistical analysis revealed that the addition of 20% lignin in the adhesive and using a cold-pressing time of 24 h could produce plywood that was comparable to the control polyurethane resins, i.e., dry tensile shear strength (TSS) value of 0.95 MPa, modulus of rupture (MOR) ranging from 35.8 MPa, modulus of elasticity (MOE) values varying from 3980 MPa, and close-to-zero formaldehyde emission (FE) of 0.1 mg/L, which meets the strictest emission standards. This study demonstrated the feasibility of fabricating eco-friendly plywood bonded with PVOH–lignin–hexamine-based adhesive using cold pressing as an alternative to conventional plywood. Full article
Show Figures

Figure 1

2021

Jump to: 2022

Article
The Effect of Varying the Amount of Short Hemp Fibers on Mechanical and Thermal Properties of Wood–Plastic Composites from Biobased Polyethylene Processed by Injection Molding
Polymers 2022, 14(1), 138; https://doi.org/10.3390/polym14010138 - 30 Dec 2021
Cited by 2 | Viewed by 466
Abstract
Biobased HDPE (bioHDPE) was melt-compounded with different percentages (2.5 to 40.0 wt.%) of short hemp fibers (HF) as a natural reinforcement to obtain environmentally friendly wood plastic composites (WPC). These WPC were melt-compounded using a twin-screw extrusion and shaped into standard samples by [...] Read more.
Biobased HDPE (bioHDPE) was melt-compounded with different percentages (2.5 to 40.0 wt.%) of short hemp fibers (HF) as a natural reinforcement to obtain environmentally friendly wood plastic composites (WPC). These WPC were melt-compounded using a twin-screw extrusion and shaped into standard samples by injection molding. To improve the poor compatibility between the high non-polar BioHDPE matrix and the highly hydrophilic lignocellulosic fibers, a malleated copolymer, namely, polyethylene-graft-maleic anhydride (PE-g-MA), was used. The addition of short hemp fibers provided a remarkable increase in the stiffness that, in combination with PE-g-MA, led to good mechanical performance. In particular, 40 wt.% HF drastically increased the Young’s modulus and impact strength of BioHDPE, reaching values of 5275 MPa and 3.6 kJ/m2, respectively, which are very interesting values compared to neat bioHDPE of 826 MPa and 2.0 kJ/m2. These results were corroborated by dynamic mechanical thermal analysis (DMTA) results, which revealed a clear increasing tendency on stiffness with increasing the fiber loading over the whole temperature range. The crystal structure was not altered by the introduction of the natural fibers as could be seen in the XRD patterns in which mainly the heights of the main peaks changed, and only small peaks associated with the presence of the fiber appeared. Analysis of the thermal properties of the composites showed that no differences in melting temperature occurred and the non-isothermal crystallization process was satisfactorily described from the combined Avrami and Ozawa model. As for the thermal degradation, the introduction of HF resulted in the polymer degradation taking place at a higher temperature. As for the change in color of the injected samples, it was observed that the increase in fiber generated a clear modification in the final shades of the pieces, reaching colors very similar to dark woods for percentages higher than 20% HF. Finally, the incorporation of an increasing percentage of fibers also increased water absorption due to its lignocellulosic nature in a linear way, which drastically improved the polarity of the composite. Full article
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Figure 1

Article
Efficiency of High-Frequency Pressing of Spruce Laminated Timber Bonded with Casein Adhesives
Polymers 2021, 13(23), 4237; https://doi.org/10.3390/polym13234237 - 03 Dec 2021
Viewed by 526
Abstract
This study identifies the importance of reducing press times by employing high-frequency pressing of spruce-laminated timber bound with sustainable casein adhesives. Spruce lamellas with dimensions of 12 × 10 × 75 cm were bonded into five-layered laminated timber and then separated into single-layer [...] Read more.
This study identifies the importance of reducing press times by employing high-frequency pressing of spruce-laminated timber bound with sustainable casein adhesives. Spruce lamellas with dimensions of 12 × 10 × 75 cm were bonded into five-layered laminated timber and then separated into single-layer solid wood panels. Three types of casein (acid casein from two sources and rennin) were used. To compare the effectiveness of the casein formulation, two control samples bonded with polyvinyl acetate (PVAc) adhesive were pressed at room temperature (20 °C) and also with high-frequency equipment. The tests included compression shear strength, modulus of rupture, modulus of elasticity and screw withdrawal resistance on the wood panel surface and in the glue line. The average values of casein-bonded samples compression strengths ranged from 1.16 N/mm2 and 2.28 N/mm2, for modulus of rupture (MOR) were measured 85 N/mm2 to 101 N/mm2 and for modulus of elasticity (MOE) 12,200 N/mm2 to 14,300 N/mm2. The screw withdrawal resistance (SWR) on the surface of the wood panels ranged from 91 N/mm to 117 N/mm and in the adhesive line from 91 N/mm to 118 N/mm. Control samples bonded with PVAc adhesive did not perform better for compression shear strength, MOR and MOE, but for SWR in the adhesive line with 114 N/mm. Casein-bonded spruce timber pressed with HF equipment represents a sustainable new product with reduced press times, hazardous emissions and improved workability. Full article
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