Wood-based Composites Research Articles

Innovative forest products in the circular bioeconomy.

Background: The forest-based industry has been moving towards the manufacture of bio-based products in response to the increasing concern by consumers and governments regarding the use of non-renewable materials and the generation of residues. Various innovative technologies geared towards reducing the environmental footprint of products and processes are currently being developed and applied in the forest-based industry. This study presents some innovative wood-based products that are about to enter the market or that are already being commercialized but have the potential to expand in market size. Methods: We collected data from interviews and a survey with organisations working with product development and manufacturing, and from the literature. Results: Many innovative products that are already produced at an industrial scale, such as cross-laminated timber, wood-based composites, and lyocell, can still increase their market share in the coming years. Some of the up-and-coming products with high potential to substitute fossil-based materials and will likely enter the market in the near future are wood foam, lignin-based adhesives, glycols, bioplastics, and textile fibres. Our study indicates that, although biomass demand is expected to increase, stakeholders do not consider future supply a limiting factor. Conclusions: The ease of market introduction of innovative products relies heavily on the products' ability to take advantage of existing value chains. Overall, many of the reviewed products have the advantage of being 'drop-in'. This is because products that require adjustments to production lines are less likely to get into the market without strong external drivers that push for bio-based alternatives. According to stakeholders, the economic viability and the market expansion of these products could be encouraged to a certain extent by EU policies, and certain barriers could be alleviated by reducing bureaucracy, increasing the support for pilot-scale to full-scale production, and increasing subsidies for bio-based alternatives.

Exploring the Binding Capacity of Mycelium and Wood-Based Composites for Use in Construction.

Existing research on mycelium-based materials recognizes the binding capacity of fungal hyphae. Fungal hyphae digest and bond to the surface of the substrate, form entangled networks, and enhance the mechanical strength of mycelium-based composites. This investigation was driven by the results of an ongoing project, where we attempt to provide basic concepts for a broad application of a mycelium and chipped wood composite for building components. Simultaneously, we further explore the binding capacity of mycelium and chipped wood composites with a series of experiments involving different mechanical interlocking patterns. Although the matrix material was analyzed on a micro-scale, the samples were developed on a meso-scale to enhance the bonding surface. The meso-scale allows exploring the potential of the bio-based material for use in novel construction systems. The outcome of this study provides a better understanding of the material and geometrical features of mycelium-based building elements.

An overview of regenerable wood-based composites: preparation and applications for flame retardancy, enhanced mechanical properties, biomimicry, and transparency energy saving

An overview of regenerable wood-based composites: preparation and applications for flame retardancy, enhanced mechanical properties, biomimicry, and transparency energy saving

Preparation of transparent wood containing carbon dots for application in the field of white-LED

In this study, the biomass carbon dots (CQDs) with blue and yellow fluorescent colors was prepared by citric acid and urea, and two complementary fluorescent molecules, blue and yellow, were used as the donor-acceptor composite system of white fluorescent emission. Transparent wood-based composites which can emit white fluorescence under the excitation of near ultraviolet light were obtained by encapsulating blue and yellow carbon dots in transparent wood. There is no excessive energy transfer between the donor and the acceptor in this material, and the fluorescence intensity can still be kept at 87.7% or above after 7 days of ultraviolet irradiation, and this material has high mechanical strength and good flexibility. These conclusions confirm that the quantum dot/transparent wood-based composite material prepared in this experiment is a promising encapsulating material for white-light emitting diode (W-LED), which has potential application value in the fields of lighting, monitor, intelligent devices and so on.

New strategy for the preparation of ultra-high-strength wood-epoxy polymer composites

In this study, an ultra-high-strength compressed wood-epoxy polymer composite (CWEPC) was prepared by selective compression followed by epoxy monomer impregnation. Results showed that the flexural strength (343.8 MPa), flexural modulus (20.7 GPa), compressive strength (202.45 MPa), hardness (20.9 kN), and impact strength (47.5 kJ/m2) of the CWEPCs improved by 286.2%, 204.4%, 240.1%, 1050.6%, and 242.1% compared to that of natural wood, respectively. Moreover, no waste was generated during preparation. This study provides a simple and feasible strategy for the preparation of high-strength wood-based composites.

Panel Products Made of Oil Palm Trunk: A Review of Potency, Environmental Aspect, and Comparison with Wood-Based Composites.

Oil palm plantations have expanded rapidly in Southeast Asia, particularly in Indonesia and Malaysia. A lot of products, including food and other edible products, oleo-chemicals, cosmetics, personal and household care, pharmaceutical products, and biodiesels are derived from palm oil, thus making them one of the most economically important plants. After 25–30 years of age, the palms are felled and replaced due to declining oil production. Oil palm trunks (OPT) are considered significant waste products. The trunks remain on the plantation site for nutrient recycling or burning. This increases insect and fungi populations causing environmental problems for the new palm generation or air pollution due to the fire. Up till now, OPT has received less attention in research studies. Therefore, this review summarizes the utilization of OPT into products made of oil palm fibers mainly derived from OPT and its application as the substitution of wood panel products. Some research works have been carried out on oil palm fibers that are derived from OPT for exploiting their potential as raw material of composite panel products, which is the objective of this review. Areas of development are processed into various conventional composite panel products such as plywood and laminated board which are usually predominantly made of wood and bonded by synthetic resins, particleboard with binder, or binderless and cement board which is arranged with wood as a minor component. All of the products have been presented and described technically according to best knowledge of the authors and literature review.

Recent developments in the performance of micro/nanoparticle-modified urea-formaldehyde resins used as wood-based composite binders: A review

Urea-formaldehyde resins (UFs) for adhesives have attracted particular interest among other thermosetting polymers applied in the broad area of wood panels technology. UFs are the most common thermoset resins, typical of adhesives formed through polycondensation reactions, extensively applied in the wood-based composites industry. Formaldehyde emission (FE) in UF resins-bonded wood panel products is one of the main drawbacks of UFs resins. The increasing demand for eco-friendly products requires a compelling drive towards the promotion of nano-particles science. Using various types of nanoparticles with their interesting properties due to their large surface area and, occasionally, high aspect ratios can improve the resin's desired properties. Nevertheless, various features of nano-enhanced UFs resins, including the type of nanomaterials, their structure, and performance, which determine the compatibility between UF resins and nanomaterials, should be investigated to guarantee high effectiveness. This critical review, for the first time, emphasizes the importance of recent progress to improve the target properties of UF resins such as mechanical properties, thermal and curing behavior, and formaldehyde emission in the presence of nanoparticles. These and different aspects of such engineered resins are discussed, as well as evaluating their future perspectives. Using nanoparticles in liquid UF polycondensates has the potential to significantly lower environmental and health hazards. This article will also summarize the emerging new nanotechnology features for developing and adapting eco-friendly UF-bonded composites.

Preparation and mechanical failure analysis of wood-epoxy polymer composites with excellent mechanical performances

In this study, wood-epoxy polymer composites (WEPC) with excellent mechanical properties were prepared by adjusting the stress–strain system under mechanical load after introducing epoxy monomers into the cell cavities of plantation wood. The flexural strength, modulus, compression strength, and impact strength of the WEPCs were improved by up to 110.3%, 86.5%, 137.3%, and 110.6%, respectively. The flexure strength (140.5 MPa) was far beyond strength class TB20 (98 MPa), which was higher than that of rosewood. The improvement in mechanical strength was mainly attributed to the change of stress concentration properties by sharing the load with the epoxy polymer and the enhanced cell walls. The enhanced toughness was attributed to the increase in longitudinal cell splitting, as well as the “propagation of cracks” and “debonding” among multilevel structures of cell walls. The mechanical failure mechanism of WEPCs can be used as a reference for the design of wood-based composites.

Synthesis of ultra-high strength structured material from steam-modified delignification of wood

The use of green and renewable raw materials sourced from bio-resources is becoming more urgent to reduce the environmental pollution caused by synthetic materials such as plastics and synthetic fibers. In this work, the hydrogen peroxide (H2O2)/Acetic acid (HAc) steam was employed for delignification of fast-growing wood (poplar wood) in order to produce porous material and to improve compressibility. By using this approach, the delignified wood preserved the cellulose scaffold structure after treatment. Next, a simple and green vacuum-assisted resin transfer molding (VARTM) process was applied to fabricate high-performance wood-based composites from the delignified wood and epoxy resin, named CDW/Ep. Interestingly, the CDW/Ep samples showed unprecedented high mechanical performance. For example, the tensile modulus and strength of CDW/Ep samples were raised to 10.0 GPa and 316.7 MPa, respectively, which are approximately 3 and 5 times higher than those of natural wood (NW) control samples. The flexural modulus and strength of CDW/Ep samples were measured to be 18.2 GPa and 276.8 MPa which improved 198.5% and 603.5%, respectively, compared to that of NW. Furthermore, the CDW/Ep samples presented high dimensional stability after immersing in water for 72 h, as indicated by a 55.6% reduction in water absorption compared with NW samples. In summary, the fabrication of CDW/Ep in this work could prospectively lead to the development of green structural materials.

Innovative forest products in the circular bioeconomy

Background: The forest-based industry has been moving towards the manufacture of bio-based products in response to the increasing concern by consumers and governments regarding the use of non-renewable materials and the generation of residues. Various innovative technologies geared towards reducing the environmental footprint of products and processes are currently being developed and applied in the forest-based industry. This study presents some innovative wood-based products that are about to enter the market or that are already being commercialized but have the potential to expand in market size. Methods: We collected data from interviews and a survey with organisations working with product development and manufacturing, and from the literature. Results: Many innovative products that are already produced at an industrial scale, such as cross-laminated timber, wood-based composites, and lyocell, can still increase their market share in the coming years. Some of the up-and-coming products with high potential to substitute fossil-based materials and will likely enter the market in the near future are wood foam, lignin-based adhesives, glycols, bioplastics, and textile fibres. Our study indicates that, although biomass demand is expected to increase, stakeholders do not consider future supply a limiting factor. Conclusions: The ease of market introduction of innovative products relies heavily on the products’ ability to take advantage of existing value chains. Overall, many of the reviewed products have the advantage of being ‘drop-in’. This is because products that require adjustments to production lines are less likely to get into the market without strong external drivers that push for bio-based alternatives. According to stakeholders, the economic viability and the market expansion of these products could be encouraged to a certain extent by EU policies, and certain barriers could be alleviated by reducing bureaucracy, increasing the support for pilot-scale to full-scale production, and increasing subsidies for bio-based alternatives.

A Critical Review on Wood-Based Polymer Composites: Processing, Properties, and Prospects.

Waste recycling is one of the key aspects in current day studies to boost the country’s circular economy. Recycling wood from construction and demolished structures and combining it with plastics forms wood-polymer composites (WPC) which have a very wide scope of usage. Such recycled composites have very low environmental impact in terms of abiotic potential, global warming potential, and greenhouse potential. Processing of WPCs can be easily done with predetermined strength values that correspond to its end application. Yet, the usage of conventional polymer composite manufacturing techniques such as injection molding and extrusion has very limited scope. Many rheological characterization techniques are being followed to evaluate the influence of formulation and process parameters over the quality of final WPCs. It will be very much interesting to carry out a review on the material formulation of WPCs and additives used. Manufacturing of wood composites can also be made by using bio-based adhesives such as lignin, tannin, and so on. Nuances in complete replacement of synthetic adhesives as bio-based adhesives are also discussed by various researchers which can be done only by complete understanding of formulating factors of bio-based adhesives. Wood composites play a significant role in many non-structural and structural applications such as construction, floorings, windows, and door panels. The current review focuses on the processing of WPCs along with additives such as wood flour and various properties of WPCs such as mechanical, structural, and morphological properties. Applications of wood-based composites in various sectors such as automotive, marine, defense, and structural applications are also highlighted in this review.

Physical and Chemical Properties of Acacia mangium Lignin Isolated from Pulp Mill Byproduct for Potential Application in Wood Composites.

The efficient isolation process and understanding of lignin properties are essential to determine key features and insights for more effective lignin valorization as a renewable feedstock for the production of bio-based chemicals including wood adhesives. This study successfully used dilute acid precipitation to recover lignin from black liquor (BL) through a single-step and ethanol-fractionated-step, with a lignin recovery of ~35% and ~16%, respectively. The physical characteristics of lignin, i.e., its morphological structure, were evaluated by scanning electron microscopy (SEM). The chemical properties of the isolated lignin were characterized using comprehensive analytical techniques such as chemical composition, solubility test, morphological structure, Fourier-transform infrared spectroscopy (FTIR), 1H and 13C Nuclear Magnetic Resonance (NMR), elucidation structure by pyrolysis-gas chromatography-mass spectroscopy (Py-GCMS), and gel permeation chromatography (GPC). The fingerprint analysis by FTIR detected the unique peaks corresponding to lignin, such as C=C and C-O in aromatic rings, but no significant differences in the fingerprint result between both lignin. The 1H and 13C NMR showed unique signals related to functional groups in lignin molecules such as methoxy, aromatic protons, aldehyde, and carboxylic acid. The lower insoluble acid content of lignin derived from fractionated-step (69.94%) than single-step (77.45%) correlated to lignin yield, total phenolic content, solubility, thermal stability, and molecular distribution. It contradicted the syringyl/guaiacyl (S/G) units’ ratio where ethanol fractionation slightly increased syringyl unit content, increasing the S/G ratio. Hence, the fractionation step affected more rupture and pores on the lignin morphological surface than the ethanol-fractionated step. The interrelationships between these chemical and physicochemical as well as different isolation methods were investigated. The results obtained could enhance the wider industrial application of lignin in manufacturing wood-based composites with improved properties and lower environmental impact.

Characterization of suberinic acids from birch outer bark as bio-based adhesive in wood composites

Huge amounts of synthetic binders and polymers are used for the production of wood-based composites which are toxic to humans during the production and exploitation of products because of the risk of harmful vapor emissions. The bio-based society requires new value chains for the production of bio-based materials. Suberinic acids (SA) have a high potential to replace synthetic binders and polymers due to the unique structure. In this study, hydrolytic depolymerization of birch outer bark in alkaline environment was carried out. To evaluate the adhesive properties, the chemical composition and structure were analyzed using chemical and instrumental methods. To set independent variables for the design of experiments (DOE), the following preliminary parameters were investigated: filtered and unfiltered SA; impact of the depolymerization agent; the fractional composition of the raw material. Based on the obtained results, DOE with three independent variables (depolymerization time, pH after acidification, alkali concentration) was used for the selection of optimal depolymerization parameters. It has been concluded that, with increasing concentration of KOH in the depolymerization solution and the reaction time, suberin is depolymerized to a higher extent and thus there is a higher amount of monomeric SA, monosaccharides and polyphenolic compounds in the resulting adhesive, which positively affects the physico-mechanical properties of the obtained particleboards. These substances together form cross-linked structures that provides not only the mechanical strength but also water resistance of the resulting particleboards. The optimal SA-based adhesive was improved by increasing the KOH concentration to 4%, acidifying to the pH 3 and reducing the reaction time to 0.5 h. The obtained particleboards' properties (modulus of rupture – 19.0 N mm−2, modulus of elasticity – 2604 N mm−2, thickness swelling – 14.3% and internal bonding – 2.25 N mm−2) meet the requirements of the particleboard standard EN 312 type P3. Still, this is an experimental work and the hot-pressing parameters must be decreased to consider the possibility to introduce the adhesive in the large-scale industry.

Mechanical properties of particleboards produced from wasted mixed sengon (Paraserianthes falcataria (L.) Nielsen) and bagasse particles

This study investigated the possibility of using the mixing bagasse and sengon wood (Paraserianthes falcataria (L.) Nielsen) wastes combined with urea formaldehyde (UF) and polyester (PE) as binders for particleboards application. The tested composite materials included the baggase-sengon powder mixed with two kinds of polymers separately, UF and polyester. One-UF composite were examined the volume fraction by comparison of sugarcane baggase (SCB), sengon wood (SW), and UF with 8:0:2, 6:2:2, 4:4:2, 2:6:2, and 0:8:2, respectively. While another one, polyester composites were manufactured by ratio of volume fraction of SCB, SW, and PE with 6:0:4; 4:2:4; 3:3:4; 2:4:4; 0:6:4, respectively. Those lignocellulosic materials were treated with 5% alkalization (NaOH) for 2 h then mixed with a specified binder before conduction hot press compression molding at 100 °C and 40 bar was carried out. The boards were tested for their modulus of rupture (MOR), modulus of elasticity (MOE), internal bond, and Scanning Electron Microscopy (SEM) after being subjected to the bending test. The results showed that in specific tests, all lignocellulosic mixed powders may serve as partial substitutes for wood-based composites in the particleboards. The presence of these materials was particularly favourable for the internal bond. SCB was the useful part of mixing powder, as the boards supplemented with the material met the requirements of the Indonesian Standard SNI 03–2105-2006 in terms of the internal bond and therefore it can be potentially used for non-structural boards such as furniture.

Recent Advances on the Development of Protein-Based Adhesives for Wood Composite Materials-A Review.

The industrial market depends intensely on wood-based composites for buildings, furniture, and construction, involving significant developments in wood glues since 80% of wood-based products use adhesives. Although biobased glues have been used for many years, notably proteins, they were replaced by synthetic ones at the beginning of the 20th century, mainly due to their better moisture resistance. Currently, most wood adhesives are based on petroleum-derived products, especially formaldehyde resins commonly used in the particleboard industry due to their high adhesive performance. However, formaldehyde has been subjected to strong regulation, and projections aim for further restrictions within wood-based panels from the European market, due to its harmful emissions. From this perspective, concerns about environmental footprint and the toxicity of these formulations have prompted researchers to re-investigate the utilization of biobased materials to formulate safer alternatives. In this regard, proteins have sparked a new and growing interest in the potential development of industrial adhesives for wood due to their advantages, such as lower toxicity, renewable sourcing, and reduced environmental footprint. This work presents the recent developments in the use of proteins to formulate new wood adhesives. Herein, it includes the historical development of wood adhesives, adhesion mechanism, and the current hotspots and recent progress of potential proteinaceous feedstock resources for adhesive preparation.

Fire Behavior of Wood-Based Composite Materials.

Wood-based composites such as wood plastic composites (WPC) are emerging as a sustainable and excellent performance materials consisting of wood reinforced with polymer matrix with a variety of applications in construction industries. In this context, wood-based composite materials used in construction industries have witnessed a vigorous growth, leading to a great production activity. However, the main setbacks are their high flammability during fires. To address this issue, flame retardants are utilized to improve the performance of fire properties as well as the flame retardancy of WPC material. In this review, flame retardants employed during manufacturing process with their mechanical properties designed to achieve an enhanced flame retardancy were examined. The addition of flame retardants and manufacturing techniques applied were found to be an optimum condition to improve fire resistance and mechanical properties. The review focuses on the manufacturing techniques, applications, mechanical properties and flammability studies of wood fiber/flour polymer/plastics composites materials. Various flame retardant of WPCs and summary of future prospects were also highlighted.

Wood-Based Composites: Innovation towards a Sustainable Future

The term wood-based composite (WBC) is used to define a wide range of products in which wood is bonded together with other wooden or non-wooden materials [...]

Rotational Stiffness and Carrying Capacity of Timber Frame Corners with Dowel Type Connections.

With the development of wooden structures and buildings, there is a need to research physical and numerical tests of wood-based structures. The presented research is focused on construction and computational approaches for new types of joints to use in wooden structures, particularly glued lamella elements made of wood and wood-based composites. This article focuses on improving the frame connection of a wooden post and a beam with the use of fasteners to ensure better load-bearing capacity and stiffness of the structure. In common practice, bolts or a combination of bolts and pins are used for this type of connection. The aim is to replace these commonly used fasteners with modern ones, namely full thread screws. The aim is also to shorten and simplify the assembly time in order to improve the load-bearing capacity and rigidity of this type of frame connection. Two variations of the experimental test were tested in this research. The first contained bolts and pins as connecting means and the second contained the connecting means of a full threaded screw. Each experiment contained a total of two tests. For a detailed study of the problem, we used a 2D or 3D computational model that models individual components, including fasteners.

Toward Strong and Tough Wood-Based Hydrogels for Sensors

The purpose of this research is to develop strong and tough wood-based hydrogels, which are reinforced by an aligned cellulosic wood skeleton. The hypothesis is that improved interfacial interaction between the wood cell wall and a polymer is of great importance for improving the mechanical performance. To this end, a facile and green approach, called ultraviolet (UV) grafting, was performed on the polyacrylamide (PAM)-infiltrated wood skeleton without using initiators. An important finding was that PAM-grafted cellulose nanofiber (CNF) architectures formed in the obtained hydrogels under UV irradiation, where CNFs themselves serve as both initiators and cross-linkers. Moreover, an alkali swelling treatment was utilized to improve the accessibility of the wood cell wall before UV irradiation and thus facilitate grafting efficiency. The resulting alkali-treated Wood-g-PAM hydrogels exhibited significantly higher tensile properties than those of the Wood/PAM hydrogel and were further assembled into conductive devices for sensor applications. We believe that this UV grafting strategy may facilitate the development of strong wood-based composites with interesting features.

Dimensional Stability of Modified Wood Composite Panels

Dimensional stability of wood-based composites with changing moisture content remains an important challenge in the industry for many applications. Wood identification technologies have shown significant promise to improve dimensional stability. The main objective of this research project was to study the effectiveness of impregnation and heat treatments on wood composites when exposed to selected moisture environments. Moisture exposure conditions included one-sided water spray, one-sided liquid water contact, constant high RH, and cyclic exposure to high and low RH. Commercial moisture-resistant medium-density fiberboard (MDF) and birch plywood panels, as well as laboratory manufactured birch plywood panels, were modified by impregnation with phenol-formaldehyde (PF) resin, 1,3-dimethylol-4,5-dihydroxyethylenurea (DMDHEU) resin, or subjected to heat treatment at 205oC for 2 h to improve dimensional stability. All treatments improved moisture resistance. Plywood impregnated with PF or DMDHEU resin showed the lowest thickness swelling values, with maximum values not higher than 5% after 192 h of exposure. Heat-treated MDF and heat-treated plywood samples resulted in 11% and 6% thickness swell after water spray exposure, respectively. The heat-treated plywood resulted in lower linear expansion (LE) than untreated plywood, with an average reduction of 54%; whereas the heat-treated MDF material did not show improvement of LE relative to control MDF samples.