Wood-based Composites Research Articles

Comparison of Wood-Based Biocomposites with Polylactic Acid (PLA) Density Profiles by Desaturation and X-ray Spectrum Methods.

Wood-plastic composites (WPCs) represent composite materials that employ shredded wood combined with a thermoplastic substance, such as polylactic acid (PLA), to establish structural cohesion within the product profile. This amalgamation of materials results in a robust structure designed to fulfill specialized roles under the influence of pressure and temperature. Given the nature of the constituent materials, the resultant product can be classified as a biocomposite. The creation of such biocomposites entails a rigorous process necessitating the fine-tuning of specific parameters and suitable technologies. The foundational materials employed in this process must be both natural and biodegradable. However, it is noteworthy that natural components like fibers exhibit anisotropic behavior, wherein their mechanical attributes are contingent on the direction of the applied force. Consequently, predicting their performance during biocomposite production proves challenging. The principal objective of this study was to conduct a comparative analysis of wood-based composites incorporating PLA thermoplastic binding agents. The intention was to discern variations in density profiles arising from distinct measurement methodologies. Two measurement methods were used for the measurement: X-ray and spectrum desaturation. Additionally, the study sought to investigate the impact of introducing PLA additives at 25% and 50% concentrations on the fabrication of WPC from wood chips. The properties of these composites were assessed by considering the inherent traits of the composite materials.

Novel Wood-Based Functional Material with Vibration and Noise Reduction.

As a kind of typical green material, natural materials tend to exhibit excellent performance in the engineering field because of their structure and special functions. The homogeneous vessels of red willow (RW) are potentially unique structures to store lubricants or reinforcing agents to present special functions for engineering applications. A series of novel red willow wood-based composites, which were infused with nano-MoS2 and then reinforced by the epoxy, were developed. Their self-lubricating, mechanical vibration and noise reduction performances were investigated, and the friction, vibration, and noise reduction mechanisms were disclosed. The infusion MoS2 treatment was very beneficial for improving the tribological properties of MoS2-curing epoxy/red willow (MCW), and the coefficient of friction (COF) was reduced by 65.8% under water-lubricated friction after infusing 24 times. Meanwhile, the mechanical performances of MCW were obviously enhanced through the curing treatment of the epoxy. The synergistic effects of the infusion and curing treatments significantly decreased the wear phenomena on the friction surfaces of MCW and weakened the COF and its fluctuation amplitudes, which resulted in the presented excellent vibration and noise reduction performance. The knowledge gained herein could not only develop a novel wood-based composite with low COF and good vibration reduction properties in the engineering field but also provide a new methodology for the design of artificial porous materials with stable and smooth friction processes.

PLATech overview -radiation-heat tailored VOC-free, bio-renewable polylactic acid polymer formulations & methods for multiple industrial adhesion applications

This paper presents an overview of research and results about tailoring crystalline and amorphous form polylactic acid (PLA) polymer resin for use as an adhesive for joining a range of substrates, production of wood-based composites plywood and particle wood-based composites, and, for potential use for elevated temperature applications as for wood structures when subject to fires. The range of substrates successfully joined (with and without bio-plasticizer) ranges from metals, woods, glasses, ceramics, stones, and bricks to synthetic fluoro-polymers. Tensile bond strength for steel-to-steel bonding ranged towards 40+ MPa; superior (over 100%) bonding strength was obtained compared with EVA and other standard adhesives for wood and metal surfaces. Three successful industrial product arenas are described: 3-ply composite plywood panels meeting water soak and shear strength industry metrics; particle boards meeting-exceeding rupture strength, elasticity, and water resistance metrics similar to those expected from urea-formaldehyde based adhesive but without VOC release limitation, PVC-free luxury flooring tiles which meet strict requirements for wear cycles, distortion-free adhesion peel strength; and, production of renewable particle boards with elastic modulus and internal bond strengths comparable with boards made with urea formaldehyde. Thermal and gamma ionizing radiation research results are discussed to tailor key adhesive-relation properties: adhesion strength, viscosity, flow rate, molecular weight, hardness, flexibility, and friability. Scoping studies on radiation-based tailoring with a cross-linking agent were found to permit up to 30% improvements in bond strength as well as for enabling application as an adhesive for elevated (100 °C+) temperature applications with ∼30–50% higher operating temperatures compared with commonly used adhesives. A discussion is included about the remaining challenges and recommendations for further research.

The Use of a Radial Basis Function Neural Network and Fuzzy Modelling in the Assessment of Surface Roughness in the MDF Milling Process.

Wood-based composites are increasingly used in the industry not only because of the shortage of solid wood, but above all because of the better properties, such as high strength and aesthetic appearance compared to wood. Medium-density fiberboard (MDF) is a wood-based composite that is widely used in the furniture industry. In this work, an attempt was made to predict the surface roughness of the machined MDF in the milling process based on acceleration signals from an industrial piezoelectric sensor installed in the cutting zone. The surface roughness parameter Sq was adopted for the evaluation and measurement of surface roughness. The surface roughness prediction was performed using a radial basis function (RBF) artificial neural network (ANN) and a Takagi-Sugeno--Kang (TSK) fuzzy model with subtractive clustering. In the research, as inputs to the ANNs and fuzzy model, the kinematic parameters of the cutting process and selected measures of the acceleration signal were adopted. At the output, the values of the surface roughness parameter Sq were obtained. The results of the experiments show that the surface roughness is influenced not only by the kinematic parameters of the cutting, but also by the vibrations generated during the milling process. Therefore, by combining information on the cutting kinematics parameters and vibration, the accuracy of the surface roughness prediction in the milling process of MDF can be improved. The use of TSK fuzzy modelling based on the subtractive clustering method for integrating the information from many acceleration signal measurements in the examined range of cutting conditions meant the surface roughness was predicted with high accuracy and high reliability. With the help of two tested artificial intelligence tools, it is possible to estimate the surface roughness of the workpiece with only a small error. When using a radial neural network, the root mean square error for estimating the value of the Sq parameter was 0.379 μm, while the estimation error based on fuzzy logic was 0.198 μm. The surface of the sample made with the cutting parameters vc = 76 m/min and vf = 1200 mm/min is characterized by a less concentrated distribution of ordinate densities, compared to the surface of the sample cut with lower feed rates but at the same cutting speed. The most concentrated distribution of ordinate density (for the cutting speed vc = 76 m/min) is characterized by the surface, where the feed rate value was vf = 200 mm/min, with 90% of the material concentrated in the profile height of 28.2 μm. When using an RBF neural network, the RMSE of estimating the value of the Sq parameter was 0.379 μm, while the estimation error based on fuzzy logic was 0.198 μm.

PRODUCTION OF COMPOSITE PARTICLEBOARD FROM WASTE PLUM PITS (PRUNUS DOMESTICA) AND IMPROVEMENT OF ITS CHARACTERISTICS

This paper deals with investigating the feasibility of using waste plum pits in the production of composite particleboard materials and the improvement of their mechanical and physical properties. Biodegradability, flammability and water absorption are the primary disadvantages of wood-based composites, which reduce their service life. In this experimental study, waste colemanite was used to decrease the known flammability of wood composites. Phenol formaldehyde (PF) was used to increase the water resistance and prevent biodegradability of the prepared materials, and hemp fiber was added to increase their mechanical strength. Thus, the objective was to avoid the disadvantages of wood-based materials. Based on the results of the flexural strength test, the optimum polymer composite material production parameters were determined to be as follows: 0.50 filler/binder ratio, 56 kg/cm2 moulding pressure and 0.75 hemp fiber ratio. According to the results of the experiments, the use of waste colemanite in the production of composite materials improves their non-flammability, while decreasing flexural and screw withdrawal strengths. It was determined that waste plum pits could be used to substitute for wood chips, as an alternative filler material in the production of composite materials. As a result, eco-friendly polymer composite materials were produced from waste plum pits, hemp fiber, and waste colemanite. The obtained composite materials are compliant with applicable standards and are suitable for application as building materials for use in both interior and exterior space.

The Thermal and Mechanical Behaviour of Wood-PLA Composites Processed by Additive Manufacturing for Building Insulation.

This study was aimed at considering the potential of wood-based composites processed using additive manufacturing as insulators in the building sector. A polylactic acid blend with 30% wood particles was used as a feedstock material in fused filament technology. Its thermal and mechanical properties were determined for various processing conditions, including printing temperature and infill rate. The results showed a minor contraction in its tensile performance as a result of the printing process. The printing temperature had a negligible effect on its stiffness and a limited influence on the other engineering constants, such as the tensile strength and ultimate stress. The thermal properties of printed structures have been found to significantly depend on the infill rate. Although the tested 3D printed wood-PLA material exhibited good thermal properties, which were tuneable using the printing conditions, its performance was still 38% to 57% lower compared to insulators such as the glass wool of the synthetic foams used in the building sector.

Construction of sandwich-structured Cu-Ni wood-based composites for electromagnetic interference shielding

Constructing a controllable electromagnetic gradient toward advanced electromagnetic interference shielding composites has become a development trend. A sandwich-structured Cu-Ni wood composite (CNWC) was successfully fabricated via a simple electroless Cu-Ni procedure. The obtained results showed that the Cu-Ni wood composite material exhibited excellent electromagnetic shielding effectiveness (EMSE) (average value 57.4 dB) in the entire X-band (from 8.2 to 12.4 GHz) in case of low thickness (0.4 mm) and low density (0.87 g/cm3). Herein, the wood-based composites possessed maximum saturation magnetization which was up to 7.7 emu/g and the conductivity increased to 1930 S/cm. The dielectric loss and magnetic loss are important ways of electromagnetic wave attenuation in Cu-Ni-based electromagnetic shielding materials, and are the key to the absorption of most electromagnetic waves by composites. The electromagnetic gradient sandwich-structure can realize multi-dielectric interface loss and multiple reflection loss. When the electromagnetic wave enters the porous structure inside the wood, the electromagnetic wave generates internal scattering and multiple reflections in the hole. The synergistic effect of dielectric loss and magnetic loss to improve the loss ability of electromagnetic wave.

Effects of nanoclay modification with aminopropyltriethoxysilane (APTES) on the performance of urea–formaldehyde resin adhesives

Urea-formaldehyde (UF) resins, as the most common adhesives for wood-based composites, emit formaldehyde, which is forcing producers to find a solution to this problem. Using scavengers is a practical way of reducing formaldehyde emissions, but sometimes these materials change the properties of the adhesive. This study investigated the effect of adding nanoclay and nanoclay modified with aminopropyltriethoxysilane (APTES), as scavengers, on the formaldehyde emission and the properties of the urea-formaldehyde resin. Modification of nanoclay with APTES was confirmed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis. After the addition of nanoclay and modified nanoclay to the urea-formaldehyde resin, the emission of formaldehyde decreased by 22% and 61%, and the physical and mechanical properties were improved. The FTIR, XRD, and differential scanning calorimetry results showed that the addition of nanoclay and modified nanoclay improved the characteristics of the adhesive, reduced the crystalline areas, and delayed the curing of the adhesive. Additionally, according to thermogravimetric analysis results, addition of nanoclay and modified nanoclay increased the thermal stability and reduced the weight loss of urea formaldehyde resin.

A high-performance, full-degradable bioinspired newspaper-based composite enhanced by borate ester bonds

Sustainable construction materials with high performance serve as an important role in our dairy life. However, constructing strong, green and cost-effective structural materials from waste feedstocks is still challenging. Inspired by the borate chemistry in natural plant cell walls, a high-performance, full-degradable and multifunctional newspaper (NP)-based laminated composite was successfully fabricated by boric acid (BA) and poly(vinyl alcohol) (PVA) via borate ester bonds and hydrogen bonds under simple hot-pressing process. Owing to the strong covalent borate ester bonds and abundant hydrogen bonds crosslinking, the resultant b-NP/PVA/BA composite exhibited outstanding tensile strength (147.83 ± 1.60 MPa), elongation at break (15.43 ± 0.56%) and toughness (17.80 ± 0.78 MJ/m3), which exceeded most wood-based composites and all reported NP-based composites. The b-NP/PVA/BA composite also showed excellent self-healing property and could be biodegraded completely within 4 months in soil. Furthermore, the obtained composite was useful for panel overlayers due to its excellent mechanical enhancement effect, antimildew and healthy properties. Notably, the cost-effective and green raw materials, as well as the facile and eco-friendly preparation, offered a competitive strategy to develop high-performance and full-biodegradable composites from waste resources, which can be extensively utilized in the fields of building, furniture and packaging.

Development of lignocellulosic-plastic composite from rice husk and polyethylene

As the demand for wood and wood-based resources keeps outstripping its regeneration, forests are depleting rapidly. To curtail this, it is imperative to shift towards the use of alternative raw materials such as agricultural residues. This study entails the development of lignocellulosic-plastic composites from Rice Husk (RH) and Recycled Low-Density Polyethylene (RLDPE) binder with the potential of augmenting the wood-based composites. Herein, RH was milled, graded into two particle sizes (2 mm and 4 mm), and mixed with RLDPE at two binder ratios (40 wt% and 50 wt%). The obtained composites were evaluated by density, water absorption (WA), thickness swelling (TSW), tensile strength (TS) and bending properties - modulus of elasticity (MOE) and modulus of rupture (MOR). In general, the increase of binder from 40% to 50% resulted in significant improvement of both physical and mechanical properties; while the increment of RH particle size showed slight differences in the properties. Composite with 50% binder content and 4 mm particle size was observed to have the best performance which conforms to the requirements for general-purpose application and door core application.

Robust, Fire-Retardant, and Water-Resistant Wood/Polyimide Composite Aerogels with a Hierarchical Pore Structure for Thermal Insulation.

The use of energy-saving materials is an effective strategy for decreasing energy consumption and carbon emission. Wood is a type of biomass material with a natural hierarchical structure, which results in its high thermal insulation. It has been widely used in construction. However, developing wood-based materials without flammability and dimensional instability is still a challenge. Herein, we developed a wood/polyimide composite aerogel with a well-preserved hierarchical pore structure and dense hydrogen bonds inside, resulting in its excellent chemical compatibility and strong interfacial interactions between its two components. This novel wood-based composite was fabricated by removing most hemicellulose and lignin from natural wood, followed by the fast impregnation using an 'in situ gel' process. The introduction of polyimide into delignified wood substantially improved its mechanical properties, with the compression resistance being improved by over five times. Notably, the thermal conductivity coefficient of the developed composite was approximately half that of natural wood. Furthermore, the composite exhibited excellent fire-retardancy, hydrophobicity, thermal insulation, and mechanical properties. This study provides a novel method for wood modification, which not only aids interfacial compatibility between wood and polyimide but also retains the properties of the two components. The developed composite can effectively reduce energy consumption, making it promising for practical and complex thermal insulation applications.

Green Strategy for Improving the Formation of Reconstituted Wood-Based Composites

In this study, a novel strategy inspired by the low melting temperature of a deep eutectic system (DES) was proposed to improve the efficient formation of reconstituted wood-based composites prepared via hot pressing. Hydrogen bond acceptors were used to prepare DES with lignin and hemicelluloses in a wood matrix in situ to achieve this goal. The feasibility and performance mechanism of this method were investigated in depth. Results show that the glass-transition point, Tg, of the amorphous components could reduce by more than 30 °C after the formation of DES. The dimensional stability and mechanical performances of the reconstituted wood-based composites were synchronously improved. The uniform bonding structure formed due to the efficient distribution of amorphous components (lignin and hemicelluloses) between the bonded interface driven by low-temperature melting of DES was an important reason for this phenomenon. In addition, the re-condensation of the degradation products of the amorphous components in wood also contributed to this. The consumption of a synthetic adhesive for wood interface bonding will be reduced in this situation. This work created a revolutionary approach for the preparation of green wood-based composites.

Performance Analysis of Loose-Fill Thermal Insulation from Wood Scobs Coated with Liquid Glass, Tung Oil, and Expandable Graphite Mixture.

The current study presents the results of monitoring the behavior of loose-fill thermal insulating material for buildings made of wood scobs (WS), which were coated with one, two, and three component-based coatings from liquid glass (LG), tung oil (TO), and expandable graphite (EG). The thermal conductivity of samples in the dry state and under normal laboratory conditions, short-term water absorption by partial immersion, surface wettability, and water vapor permeability were evaluated, and regression equations describing the variations in numerical values of specified properties under different amounts of each coating component were presented. It was shown that LG and TO act as hydrophobic layers that, in conjunction, reduce water absorption by a maximum of 274%, have a contact angle equal to 86°, and lower thermal conductivity by 55% in the dry state due to the specifics of the layer formed on the surface of WS. The addition of EG to LG coating resulted in insignificantly changed water absorption and thermal conductivity values, indicating the potential of this material to be used to improve the fire resistance of wood-based composites in the future. The results showed that the three-component layer of LG/TO/EG reduces water absorption by a maximum of 72%, increases thermal conductivity in the dry state by a minimum of 0.4%, and increases the contact angle to 81° at 100 wt.% LG. The changes in water vapor permeability of all compositions were determined to be insignificant.

Preparation and characterization of hybrid resin from used urea-formaldehyde and isocyanate resin

Hybrid resins composed of polymeric 4-4 diphenyl methane diisocyanate (pMDI) and used urea-formaldehyde (UUF) resins were prepared and studied. In these hybrid resins, high ratios of pMDI (e.g., 20%) were evenly dispersed in UUF resins by using acetone as a solvent for pMDI. The viscosity of the hybrid resin containing 15% of pMDI only changed from 216 to 424 mPa s with 30 h of storage. Chemical composition analysis showed that the free isocyanate groups were reacted with hydroxyl groups in the hybrid resins within 2 h. From a curing kinetics analysis, even without obvious active isocyanate groups, these hybrid resins still showed lower curing peak temperatures and Kissinger activation energies than the UUF resin. Moreover, the hybrid resins presented significantly higher dry and wet tensile shear strengths than the UUF resin. The effective use time of the hybrid resin with 15% pMDI reached up to 12 h. This study provided a new method for modifying UF resin with pMDI. These results also proved the feasibility of applying the hybrid resins in wood-based composites manufacturing.

Effects of nano manganese dioxide on performances of urea-formaldehyde resin

In cured urea-formaldehyde (UF) resin with low molar ratio of formaldehyde/urea (F/U), existent crystalline regions are believed to affect the properties of wood-based composites bonded with UF resins. The effects of crystalline regions on physicomechanical properties and formaldehyde emission of the plywood bonded with UF resin modified by nano Manganese dioxide (MnO2) were studied in this work. Results show that the modified UF resins with 0.9% MnO2 has a higher ratio of crystalline regions than those of neat resins. They resulted in a 79% improvement in the wet shear strength and a 70% reduction in the formaldehyde emission. The X-ray diffraction (XRD) results show that the crystallinity in the cured UF increases with the amount of MnO2 added. No change in the structure of the cured UF was found in the Fourier transforms infrared spectroscopy (FT-IR) with the addition of MnO2.

DEPENDENCE OF POLYURETHANE CONTENT ON PHYSICAL AND MECHANICAL PROPERTIES OF WOOD FIBER/PALM KERNEL SHELL COMPOSITES

Wood-based composites with different ratiosof wood fiber (WF)/palm kernel shell (PKS) and polyurethane (PU) content have been prepared using the wet-process method. Samples of WF85/PKS15 and WF75/PKS25 were fabricated where each sample was applied with 20% and 70% of PU contents and itsphysical and mechanical properties had beenstudied. The physical results show that the samples with 70% of PU content were denser, had low porosity, low moisture content,and low water absorption. Surface morphology observation shows both series samples with high PU content tend to form tube-like shape with different diameter. Inmechanical studies, generally, the sample with high PKS and PU possesseshigh flexural strength, flexural modulus, tensile strength, tensile modulus,and hardness. However, theincreased of PKS content in the composite reduces the tensile strength for both sampleswith 20% and 70% of PU. The effects of the binder and palm kernel shell in the composite were also explained. Based on the Japanese Industrial Standard (JIS) A 5905 standard, the sample composites meet therequirement under medium density fiberboard (MDF) category and classified as board type 5 which suitable as furniture, house,and automotive interior design and construction materials.

Bamboo–Alginate Composite as a Sustainable Structural Material

In the current context of environmental concern and energy crisis, wood-based composites are attracting attention as sustainable materials; however, their mechanical properties require improvement. Herein, we report a novel method for the preparation of bamboo composites with excellent mechanical properties and formability. After delignification of bamboo, an alginate solution was filled into the voids of delignified bamboo (DB) under reduced pressure to obtain alginate-impregnated DB (ADB). Then, the alginate was subjected successively to ionic and chemical cross-linking by adding CaCl2 and glutaraldehyde, respectively. The mechanical strength of the resulting dually cross-linked ADB (DCB) was improved by removing unfilled voids via a hot-press forming process. The tensile and flexural strengths of the hot-pressed DCB (HP-DCB) showed the highest values ever reported for wood composites, i.e., 1.12 GPa and 678 MPa, respectively, which can be attributed to the strong adhesion and effective load transfer stemming from the dual cross-linking of alginate between the bamboo fibers. In particular, the presence of flexible and adhesive alginate enabled the reshaping of HP-DCB into desired shapes through rehydration and molding, demonstrating its potential for various applications requiring ecofriendly, high-strength, and lightweight materials.

Towards circular economy by valorization of waste upholstery textile fibers in fibrous wood-based composites production

The aim of the research was to utilize textile waste by adding upholstery fabric fibers with different content (0, 5, 10, and 20% by weight referred to dry wood fibers) to high density fiberboards (HDF) and analyze selected physical and mechanical properties of the obtained boards. Tests of mechanical (modulus of elasticity in bending and bending strength, surface soundness, internal bond, screw withdrawal resistance) and physical (density profile, swelling in thickness after immersion in water, water absorption) properties were performed. The results show that the increasing content of textile fibers in HDF panels has the strongest negative influence on mechanical properties, especially internal bond, and screw withdrawal resistance. Modulus of elasticity and modulus of rupture also decreased, but still fulfilled the requirements of European standards. No significant influence of rising content of textile fibers on HDF thickness swelling and water absorption has been found. It can be concluded that, depending on further application of HDF, it is possible to utilize the recovered upholstery textile fibers as a reasonable addition to wood fibers when producing HDF panels. It is also a step toward carbon storage extension, which is fixed in textile fibers.

Synthesis of Cu-Doped TiO2 on Wood Substrate with Highly Efficient Photocatalytic Performance and Outstanding Recyclability for Formaldehyde Degradation.

Photocatalytic oxidation is considered one of the most effective ways to remove formaldehyde from indoor air. However, the use of powder photocatalysts is limited by their low adsorption capacity and strong aggregation tendency. Hence, there is a need for a composite material with good cycling stability and high degradation efficiency. In the present study, a unique wood-based composite is produced by arranging Cu-TiO2 nanoparticles on porous structured wood. The porous structure of wood can adsorb formaldehyde, and the abundant functional groups on the surface can act as a reaction platform for anchoring the Cu-TiO2 nanoparticles. Cu doping facilitates electron interaction between TiO2 and Cu, promotes the transfer of charge carriers, lowers the electron-hole recombination rate, and improves the photocatalytic degradation efficiency of formaldehyde. The photocatalytic efficiency of the wood-based composites was highest (85.59%) when the n(Cu)/n(Ti) ratio was 7%. After nine cycles, the wood composites still had a high degradation rate, indicating good recyclability. Overall, this wood composite is an eco-friendly and promising material for indoor air filtration.

Application of Finite Element Method for Mechanical Characterization of Wood and Reconstituted Lignocellulosic-Based Composites – A Review

Performance evaluations of wood and other lignocellulosic-based composites involve complex scenarios of several factors such as material heterogeneity and geometry that often leads to complicated, expensive, and time-consuming experimental procedures. Hence, the application of computational modeling and simulation is desirable to mitigate these biocomposites’ performance testing challenges. This review paper, therefore, presents an outlook on the finite element method (FEM) application in probing performance characteristics of wood and solid wood-based composites as well as reconstituted wood and other lignocellulosic-based composites. Notwithstanding the complex nature of wood and other lignocellulosic biomass, the feasibility of FEM application in characterizing their performances has been favorably demonstrated. Going forward, broader applications of FEM combined with the design of experiments would further establish developing protocols. More exploration of FEM-based parametric and optimization studies would facilitate comprehensive, cost-efficient, and swift biocomposites design and performance optimization processes thereby enhancing their acceptance and implementation in target applications.