Lightweight Wood Research Articles

Lightweight, Strong, and Transparent Wood Films Produced by Capillary Driven Self-Densification.

Wood delignification and densification enable the production of high strength and/or transparent wood materials with exceptional properties. However, processing needs to be more sustainable and besides the chemical delignification treatments, energy intense hot-pressing calls for alternative approaches. Here, this study shows that additional softening of delignified wood via a mild swelling process using an ionic liquid-water mixture enables the densification of tube-line wood cells into layer-by-layer sheet structures without hot-pressing. The natural capillary force induces self-densification in a simple drying process resulting in a transparent wood film. The as-prepared films with ≈150µm thickness possess an optical transmittance ≈70%, while maintaining optical haze >95%. Due to the densely packed sheet structure with a large interfacial area, the reassembled wood film is fivefold stronger and stiffer than the delignified wood in fiber direction. Owing to a low density, the specific tensile strength and elastic modulus are as high as 282MPacm3g-1 and 31GPacm3g-1. A facile and highly energy efficient wood nanotechnology approach are demonstrated toward more sustainable materials and processes by directly converting delignified wood into transparent wood omitting polymeric matrix infiltration or mechanical pressing.

Carbonated balsa-based shape-stable phase change materials with photothermal conversion and application in greenhouse

Greenhouse enables to promote plant yield through creating optimal environment. Efficient solar energy conversion and storage is a promising strategy to address energy shortage issue of greenhouse in winter. This paper prepares form-stable composite phase change materials (PCMs) to store solar energy efficiently. Lightweight and porous balsa wood subjected to high-temperature carbonization is designed to simultaneously solve the liquid leakage, enhance the thermal conductivity, and improve the photothermal conversion and thermal energy storage of PCM. OP44E and SEBS are utilized as PCM and thickener, followed by vacuum impregnation into the carbonized balsa wood (CW). Results indicate that carbon content of CW increases with the augment of carbonization temperature. Shaping effects of CW and SEBS endow composite PCMs to have highest adsorption rate of 92.7 wt% with enthalpy over 190 J/g. Composite PCMs reveal reliable thermal properties and thermal stability below 100 °C. Composite PCMs have photothermal conversion larger than 88 % under a xenon lamp radiation. Temperature of PCMs on the shallow layer is higher owing to its photothermal conversion capacity. Greenhouse test indicates that CW/OP44E/SEBS greenhouse gains higher PCM temperature of 71.5 °C at 70 min, compared to 40.3 °C in empty and OP44E/SEBS cases. CW/OP44E/SEBS greenhouse maintaining indoor temperature over 20 °C lasts 15.3 min longer than empty and OP44E/SEBS greenhouses. In addition, form-stable composite PCMs featured with excellent thermal stability and photothermal conversion are capable of maintaining stable indoor temperature of greenhouse, indicating potential in the field of agricultural building temperature regulation.

VOC Emission from Lightweight Wood Fiber Insulation Board

The aim of the presented research work was to determine and analyze emissions of volatile organic compounds (VOCs) from experimental lightweight wood fiber insulation board produced in dry technology. Until now, there have been no rigid insulation materials made of wood fibers produced in such low density and made in dry technology. Among the typical parameters such as thermal conductivity and the mechanical performance of the lightweight board, attention was also paid to their influence on indoor air quality. Therefore, an attempt was made to determine the kind of substances emitting from wood fiber insulation boards produced at defined production parameters as well as the dynamics of emission reduction over time. Additionally, the influence of fire retardants used for protection against lightweight wood fiberboard fires on the emission of VOCs was analyzed. Tests on VOC emissions were carried out using the chamber method according to the applicable ISO 16000 standards. The main components emitting from lightweight insulation fiberboards were acetic acid and aldehydes such as pentanal, hexanal, heptanal, octanal, nonanal, decanal, furfural, and benzaldehyde. The percentage of acetic acid in total volatile organic compounds (TVOCs) was within the limits of 17% to 65%. From the aldehydes group, the most concerning substance was furfural due to a very strict limit value. In the presented research, depending on the variant, the emission of furfural was from 0 up to 10 µg/m3 after 28 days of measurement. Other substances such as terpenes or aromatic hydrocarbons were at a very low level. The reduction in VOCs over a period of 28 days was significant in most cases from 22% up to 61%. The tests carried out also showed a substantial impact of fire retardant, used in the production of lightweight insulation fiberboard, on the emission of VOCs from fiberboards, and thus on their quality.

Preparation and characterization of wood plastic composite produced from waste polystyrene with organic filler

In this study, polystyrene (PS) polymer composites were prepared and characterized by mechanically and physically. It was aimed to produce a cheap, lightweight, and eco-friendly wood plastic composite (WPC). Waste PS was melted in a cap by gasoline, and 200 % wheat flour (PS(W)), wheat starch (PS(S)), and medium-density fiberboard (MDF) sawdust (PS(D)) were added into the melted PS. After the mixture was well mixed in a dough-like form, it was placed into wooden molds and molds were kept in the oven at 140 °C for 30 minutes and then taken out, and kept for 20 minutes at 4 °C. After the cooling process, the composites were removed from the molds and were cut to 18 mm x 15 mm x 40 mm dimensions using a diagonal saw. Mechanical characterizations were carried out by Internal bonding (IB), Screw holding resistance for edge (SRE) and surface (SRS), Pressure (PR). Physically characterizations were carried out by Density (DN), Water absorption (WA), Thickness swelling (TS). Results show that PS(D) has the highest mechanical properties despite its lowest density. PS(W) sample has better mechanical properties than PS(S) sample. It has been determined that the wood composite obtained by the combination of MDF waste dust with melted waste PS is close to the mechanical and physical properties of particleboard. Waste PS can be blended with wood dust and used on wood composite.

Experimental research on standardized bamboo culm components for developing prefabricated bamboo building

Bamboo culm structures are useful for areas with limited access to structural wood, especially for remote bamboo forest areas. This study focuses on developing standardized bamboo culm components for the prefabricated bamboo building, which is potential to replace timber components made of dimension lumber used in modern timber buildings. The basic material properties of Moso bamboo and bamboo culm elements were investigated. Test results show that the main mechanical properties of bamboo culm are comparable to some coniferous wood, such as TC-13A grade (in Chinese standard). Several types of simple and reliable connectors were designed for connecting bamboo culms, attempting to provide standardized bamboo culm elements. The prefabricated shear wall elements were designed with bamboo culms as studs and glubam lumber as perimeter frame for regulate the dimension. Three shear wall models were tested under monotonic and cyclic lateral loading. It was found that the lateral resistance capacity of bamboo culm shear wall is about 64% of that of the similar lightweight wood frame shear walls. Three specimens of bamboo culm trusses were also tested to obtain the design capacity of the roof system. Based on the experimental test results, a prototype single-story building was designed and constructed to assess the feasibility of the constructional details. Carbon dioxide emission analysis revealed the environmentally friendly advantages of this type of bamboo building.

“Wood-nacre”: Development of a Bio-inspired Wood-Based Composite for Beam and 3D-Surface Elements with Improved Failure Mechanisms

Following the natural structure of the nacre, the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive. This so-called “wood nacre” consists of macroscopic tiles of birch wood veneer with a thickness of 0.8 mm and a size of 20 or 10 mm in diameter in order to mimic the aragonite tiles and the ductile PUR-adhesive corresponds to the layers of collagen in between. E-modulus (MOE), bending strength (MOR) and impact bending strength of the samples were determined and compared with reference samples of birch laminated wood. The hierarchical layered structure of the tiles does not cause any relevant loss in stiffness. Like nacre, “wood nacre” also shows tough fracture behaviour and a high homogenization effect. However, strain hardening and high fracture toughness of the natural model could not be fully achieved. The reason for this is the insufficient ratio between the strength and stiffness of the veneer layers and the adhesive. By adjusting the size of the tiles, increasing the strength and surface roughness of the veneers, e.g. by densification, and using more ductile adhesives that can be applied in smaller layer thicknesses, it should be possible to better reproduce the natural ratios of nacre and thus achieve a significant improvement in the material properties of “wood nacre”. In addition to the mechanical properties, the high potential of the new material lies in the possibility of producing 3D shell-shaped elements for lightweight wood hybrid construction.

Unlock the myth of low-frequency footstep thumping noise in lightweight wood floors

Major occupants' complaints received in lightweight wood floors of Impact Insulation Class (IIC) above 55, are low-frequency footstep thumping noise. Lack of understanding of fundamentals and solutions motived this study. A series experiments were conducted to answer the following questions: 1) what are the frequency range of the low-frequency footstep thumping noises heard by the occupants in mass timber slab floor and in light frame wood joisted floor when the floors are impacted by the ISO tapping machine, footsteps of a person walking with shoes, and with bare foot? 2) how look like the impact sound spectrums below 50 Hz (ISO) or below 100 Hz (ASTM)? 3) Can the tapping machine excite the low-frequency noise down to the range of wood floor natural frequency around 15 Hz? 3) Can the current measurement system measure the sound signals at such low frequency range reliably? 4) can the measured spectrums of impact sound signals reveal the low-frequency impact noise issues? 5) what are the special construction details of the wood floors contributing to the low-frequency impact noise problem? 6) what are the solutions for the problem? Our experiments answered the questions. The findings and solutions will be shared in the full-length paper.

Preparation and mechanism of lightweight wood fiber/poly(lactic acid) composites

The high density and poor thermal insulation of traditional wood-plastic composites limited the application in the field of building materials. In this paper, wood fiber (WF) and PLA were used as raw materials and azodicarbonamide was used as the foaming agent. Lightweight WF/PLA composites were prepared by the hot-pressing foaming method, aiming to obtain renewable, low-density material with high strength-to-weight ratio and thermal insulation performance. The results showed that after adding 20 % WF into PLA, the cell morphology was excellent and the cell size was uniform. The magnification reached the minimum value of 0.36 g/cm3 and the foaming magnification was 3.42 times. The impact strength and compressive strength were 3.16 kJ/m3 and 4.12 MPa, its comprehensive mechanical properties were outstanding. The thermal conductivity of foamed materials was 0.110–0.148 (W/m·K), which was significantly lower than that of unfoamed materials and common wood. Its excellent mechanical properties and thermal insulation can be suitable for application in the construction field to replace traditional wood.

Lightweight but strong wood armor can fend off bullets

Lightweight but strong wood armor can fend off bullets

Energy Saving Design of Exterior Envelope of Prefabricated Buildings in Alpine Area

In this paper, the exterior envelope of prefabricated buildings in alpine areas is studied. This paper compares the wind resistance of the fabricated structure composed of two different connection modes, connectors with different thickness, lightweight ceramsite concrete peripheral wall panel and wood composite peripheral wall panel. The test results show that the wind resistance of the fabricated structure composed of wood wallboard mainly depends on the thickness of wallboard, connection mode and connector thickness. Whether sand packing is filled or not has no effect on the improvement of wind resistance of this prefabricated enclosure structure. For meeting the wind resistance of the fabricated enclosure used in the support room, it is recommended to use thick wooden wallboard and connect up and down. The wind resistance of the fabricated enclosure composed of wood wallboard mainly depends on the strength of the wood wallboard itself. The use of wood wallboards with higher thickness can improve the wind resistance of this fabricated structure.

Integrative structural design and engineering methods for segmented timber shells - BUGA Wood Pavilion

The presented research describes the holistic development of a modular lightweight timber shell. So-called segmented timber shells approximate curved geometries with the use of planar plates, thus combining the excellent structural performance of double curved shells with the resource-efficient prefabrication of timber modules using only planar elements. Segmented timber shells constitute a novel building system that demands for innovative approaches on structural design and construction technologies. The geometric complexity of plate shells in conjunction with the particularities of the building material wood pose great challenges to the computational design and planning processes as structural requirements and fabrication constraints determine the shell design at early design phases. This paper discusses the design development and construction of the BUGA Wood Pavilion: A segmented timber shell structure made of hollow cassette components. Particular emphasis lies on the technical challenges of the employed building system, notably structural design and analysis, detailing solutions and the construction process. The authors further describe the integrative structural design and optimization methods developed for the timber shell in question. The BUGA Wood Pavilion demonstrates the possibilities of lightweight and sustainable wood architecture merging the merits of integrative design, structural engineering and high-tech robotic fabrication methods.

Notes on the natural history of Stillingia aquatica (Euphorbiaceae): with special attention to reproductive biology

Stillingia aquatica, a wetland shrub in the Southeastern U.S., was profiled in Southeast Florida from a natural history standpoint. The stem has exceptionally lightweight wood in common with other periodically root-inundated woody plants. Pseudowhorled tufts of conspicuous yellow leaves subtend the similarly colored spikelike thyrsoid inflorescences. The plants are monoecious, self-compatible, protogynous with respect to inflorescences, and with a mixed mating system. After a pistillate-only phase, pistillate and staminate phases overlap in time, and are positioned in close physical proximity within inflorescences. Then follows a prolonged phase of only staminate flowers plus maturing fruits. The inflorescences attract ants, bees, and especially abundant wasps, switching from mixed bees and wasps in the dry season to essentially just wasps in the wet season. Wind-pollination is minimal to none. Ants are often abundant in the inflorescences and believed to contribute to geitonogamy but are not necessary for fruitset. Agamospermy is none to negligible. The seeds often fail, with the failure rates varying between populations and between individual plants.

Simultaneous evaluation of bending and shear stiffness of wood I-joists by transverse vibration tests

Prefabricated wood I-joists are widely used in lightweight wood constructions. Accurate and efficient measurements of their elastic properties are of great importance for predicting their mechanical behaviour during structural design. In this study, an alternative algorithm for simultaneous measurement of bending and shear stiffness of wood I-joists was developed for transverse vibration techniques based on Timoshenko beam theory. Sixty-five wood I-joists with thirteen configurations were tested by using the proposed modal testing method as well as traditional third-point bending tests. Based on the test results, the influences of section properties of wood I-joists on the shear rigidities were studied. It was found that the transverse vibration tests can be simply and efficiently implemented to determine the true and apparent bending stiffness of wood I-joists. In addition to the I-joist depth, the shear rigidities are also influenced by the web thickness and flange width. More importantly, shear deflection coefficients of tested wood I-joists are significantly larger than those theoretical values currently used by wood I-joist manufacturers.

Lightweight Insulation Boards Based on Lignocellulosic Particles Glued with Agents of Natural Origin.

In this study, the possibility of using adhesives of natural origin for the manufacture of wood fiber-based lightweight panels was investigated. The boards, of a density ranging from 150 to 250 kg/m3, were glued together using commercial urea–formaldehyde resin (control board), solutions of rye flour and potato starch and two types of starch: oxidized and gelatinized. The density and density profile, compressive strength, modulus of elasticity, acoustic properties and thermal conductivity were determined in the produced boards. These studies show that when food components are used as binding agents in the manufacture of lightweight wood fiberboards, the properties obtained can be comparable with those of commercial boards manufactured using synthetic agents.

Photochromic holo-cellulose wood-based aerogel grafted azobenzene derivative by SI-ATRP

Wood is actually a natural polymers composite that is easy to process, mainly constituted of cellulose, hemicellulose and lignin. However, most wood-based functional materials are prepared by physical methods, which undoubtedly limit the application of wood-based materials. Herein, the wood aerogel (WA) was obtained from wood by delignification and freezing dried. The WA then was fabricated into an unexpected photochromic wood aerogel (PWA) via surface-initiated atom transfer radical polymerization (SI-ATRP) covalently grafting poly{6-[4-(4-methoxyphenyl-azo)phenoxy]hexyl methacrylate} (PMAZOM). Both WA and PWA showed good compression resilience. The hydrophobicity of PWA was obviously enhanced because of the surface modification. The color of PWA can change from yellow to orange-red after being irradiated by UV light for 30 s. The color of sample can be reversibly changed to yellow under sunlight for 200 s. The lightweight and photosensitive wood aerogel is potential to apply for optical information storage materials and photosensitive devices.

Sensor-based Particle Size Determination of Shredded Mixed Commercial Waste based on two-dimensional Images

To optimize output streams in mechanical waste treatment plants dynamic particle size control is a promising approach. In addition to relevant actuators – such as an adjustable shredder gap width – this also requires technology for online and real-time measurements of the particle size distribution. The paper at hand presents a model in MATLAB® which extracts information about several geometric descriptors – such as diameters, lengths, areas, shape factors – from 2D images of individual particles taken by RGB cameras of pre-shredded, solid, mixed commercial waste and processes this data in a multivariate regression model using the Partial Least Squares Regression (PLSR) to predict the particle size class of each particle according to a drum screen. The investigated materials in this work are lightweight fraction, plastics, wood, paper-cardboard and residual fraction. The particle sizes are divided into classes defined by the screen cuts (in mm) 80, 60, 40, 20 and 10. The results show assignment reliability for certain materials of over 80%. Furthermore, when considering the results for determining a complete particle size distribution – for an exemplary real waste – the accuracy of the model is as good as 99% for the materials wood, 3D-plastics and residual fraction for each particle size class respectively as assignment errors partially compensate each other.

Influence of Adding Lignin and Wood as Reactive Fillers on the Properties of Lightweight Wood–Polyurethane Composite Foams

Abstract In this study, bio-based rigid polyurethane (PU) composite foams were prepared by a free-rising method, with the addition of wood particles (10 and 20 weight percent by the foam mass) and kraft lignin (5 and 10 weight percent by the polyol mass) as reactive reinforcing fillers. The resultant PU composites were evaluated for chemical structure, density, morphology, compressive properties, water uptake, and thermal stability. Fourier-transform infrared analysis confirmed the formation of characteristic urethane bonds in all foam samples. The foaming process was slowed down by the incorporation of lignin and wood particles. The apparent density of lignin-incorporated wood–PU composite foam ranged between 77 and 105 g/cm3. Compared with the neat PU foam, addition of wood particle resulted in decreased compressive properties and increased water uptake of the foams, whereas incorporation of lignin had a positive effect on the compressive properties and water resistance. In general, the PU foam sample with the incorporation of only 5 percent lignin (PUL5) exhibited the optimal physical–mechanical properties, with the compressive strength increased by 74 percent and 24-hour water uptake decreased by 28 percent compared with the control PU foam. Thermogravimetric analysis showed that the incorporation of lignin and wood particles did not significantly affect the thermal degradation pattern of foam but rather increased the mass of char residue.

Study of the mechanical behavior of a lightweight wood concrete

Today, the development of building materials based on toxic or non-toxic industrial waste is a topical issue for the productive structures in industrialized countries. In this article, non-toxic wood waste (wood chips) is used to improve the characteristics of ordinary concrete (lightness, thermal insulation, acoustic absorption, rigidity under stresses, etc.) for the purpose of eventually developing light wood concrete. The present experimental study aims at conducting a comparative behavioral analysis between concretes based on non-toxic wood waste of natural origin on the one hand, and ordinary concrete on the other.In order to achieve this goal, a series of test pieces were made, with five different formulations. Four of them are lightweight wood-concretes obtained by the substitution of a volume of aggregates; the fifth formulation is ordinary concrete. A number of tests were carried out at the Construction Technical Control Laboratory at different ages, i.e. 7, 14, 21 and 28 days. Interesting results were obtained with respect to the evolution of the mechanical characteristics of light wood-concrete at early age. Some of these features, such as the long-term compressive strength of concrete, are essential parameters in civil engineering.

Mechanical properties and water resistance of Vietnamese acacia and rubberwood after thermo-hygro-mechanical modification

Low density and poor mechanical performance often limit utilisation of sawn wood from fast-growing plantation forests. Thermo-hygro-mechanical modification (THM) of timber is one innovation for improving the properties of light-weight wood species. The objective of this study was to determine the effects of THM and subsequent thermal treatment on dry density, modulus of elasticity (MOE), compression strength, Brinell hardness, and swelling behaviour in immersion tests on two fast-growing Vietnamese species, acacia (Acacia mangium) and rubberwood (Hevea brasiliensis). Test boards were modified in an industrial kiln, in which a tangential thickness compression of 14% and 12% were aimed for acacia and rubberwood, respectively, either with or without subsequent thermal treatment at 210 °C. Dry density, MOE, Brinell hardness, compression strength, and dimensional changes in water immersion tests of specimens were measured from the modified and unmodified reference materials, the latter ones being kiln dried at 50 °C. The results showed that the responses of the mechanical properties were more evident for rubberwood than for acacia. In rubberwood, the MOE and compression strength of wood thermo-hygro-mechanically modified with or without thermal treatment were higher than those of kiln-dried reference specimens throughout the thickness profile. In case of acacia, similar differences between the modified and reference specimens were observed only in the surface layer. Density and Brinell hardness of thermo-hygro-mechanically modified rubberwood were higher than those of reference specimens, but after thermal treatment they did not differ from (acacia) or were lower (rubberwood) than those of THM specimens. Post-compression thermal treatment increased the hydrophobicity of THM specimens.

Lightweight and Construable Magnetic Wood for Electromagnetic Interference Shielding

Currently, due to the rapid development of communication technology, electromagnetic interference (EMI) and irradiation have become an emerging environmental pollutant. Herein, hierarchical and porous structured wood is used as the lightweight three‐dimensional organic scaffold for the incorporation of magnetic iron oxide nanoparticles through an in situ mineralization process that endows the woodblock with favorable appearance as well as magnetic and EMI shielding properties. The two‐step process involves the removal of lignin from natural wood via cooking and bleaching followed by inorganic mineralization. The resultant magnetic wood displays an optical brown appearance and possesses a typical magnetic hysteresis behavior with a saturation magnetization of 4.5 emu g−1 for the whole wood. More importantly, the obtained magnetic wood is much lighter than traditional magnetic metal and construable for versatile applications. Notably, the 3 mm thick magnetic wood shows 5–10 dB (or 7–10×) enhanced electromagnetic wave attenuation across the X‐band of 8–12 GHz compared with nonmagnetic wood with the same thickness. The enhanced electromagnetic wave absorption of magnetic wood is mainly due to its enhanced magnetic loss tangent compared with nonmagnetic wood. This work provides an inspiring strategy to develop sustainable, lightweight, and environmentally friendly wood for multifunctional magnetic applications.