Volume 13 Issue 4

Lattice truss cores are used to reduce the mass and increase the strength of sandwich boards. These panels are typically manufactured from metal or carbon composites. As a rule, they do not exhibit auxetic properties. Auxetic structures have several extraordinary mechanical properties. The aim of this study was to manufacture lattice auxetic cores from a biodegradable material and determine their elastic properties. The structures were produced from LayWood Olive, a composite containing polylactic acid and 40% wood dust. The cores had comparable relative densities, but their geometry and number of cells differed. As a result of uniaxial compression in individual lattice truss cores, it was shown that the cores whose cells were square in the top view were isotropic. In contrast, cores with rectangular cells were strongly orthotropic. Moreover, the Poisson’s ratio changed depending on the cell size and rib angle. Among the cores that exhibited isotropic properties, the lowest Poisson’s ratio and modulus of elasticity were recorded for the structure composed of 49 cells with ribs that were 2 mm thick. The highest Poisson’s ratio and modulus of linear elasticity were found with the orthotropic structure composed of 15 cells with ribs that were 3 mm thick. This paper was based on numerical calculations that were verified by experimental studies.

The goal to decrease global dependency on petroleum-based materials has created a demand for bio-based composites. Composites that are reinforced with natural fibers often display reduced strength compared with those using synthetic reinforcement, and hybridizing both types of reinforcement within a common matrix system offers a possibly useful compromise. This research investigated the low-velocity impact performance of glass, kenaf, and hybrid glass/kenaf reinforced epoxy composite plates. The aim of the study was to determine the low-velocity impact behavior of biocomposite material in assessing its potential for application in the radome structures of aircraft. Natural fibers possess low dielectric constants, which is a primary requirement for radome. However, the structural integrity of the material to impact damage is also a concern. Composite samples were prepared via a vacuum infusion method. A drop weight impact test was performed at energy levels of 3 J, 6 J, and 9 J. The Impact tests showed that the impact peak force and displacement increased with the energy level. Hybrid glass/kenaf composites displayed damage modes of circular and biaxial cracking. The former is analogous to the damage observed in glass-reinforced composite, while the latter is unique to woven kenaf reinforced composites. The severity of the damage increased with impact energy and was found to be significant at 3 J.

Two-dimensional materials are promising for use as solid acids in cellulose hydrolysis. However, they suffer from a severe problem of restacking, which leads to poor solid-solid contact and decreased catalytic efficiency. Herein, highly dispersed sulfonated graphene oxide (GO-SO₃H) nanosheets were prepared and used as solid acids to hydrolyze cellulose. The highly dispersed GO-SO₃H was obtained by adding N,N-dimethylacetamide (DMAc). The DMAc improved the dispersibility of the GO-SO₃H nanosheets by increasing the zeta potential. The GO-SO₃H dispersion had the best dispersibility when the water/DMAc volume ratio was 1:10. The good dispersion of the catalysts increased the accessibility of acid sites to the β-1,4-glycosidic bonds in the cellulose, which led to a catalytic performance for hydrolyzing cellulose that was superior to that of any other system. When converting cellulose, the total reducing sugars and glucose yields were 78.3% and 69.7%, respectively, which were obtained within 8 h at 130 °C.

Porous material was prepared by freeze drying of oxidized cellulose microfibrils. Oxidized microfibrillated cellulose was obtained by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-mediated oxidation of bleached bagasse pulp and lapping process, and the influence of cellulose microfibril concentration on the material properties was studied from oxidized cellulose microfibrils within a range of solids concentrations of aqueous suspension. The microscopic morphology, pressure intensity, specific surface area, and pore size were analyzed by scanning electron microscopy (SEM), universal material testing machine, fully automatic specific surface area, and porosity analyzer (BET). The surface elemental composition of the materials was analyzed by X-ray photoelectron spectroscopy (XPS). Results showed that the strength of the porous materials increased with increasing concentration of oxidized cellulose microfibrils, along with decreases of porosity decreases, and increases of specific surface area and pore volume. A higher mass fraction resulted in a smaller pore size of the porous scaffold material and more structure of the material. However, when the concentration reached a certain value, some fiber flocculation occurred.

Correlations between the chemical composition and physical properties of oak wood were studied by correlation analysis. The specimens were produced from thermally treated oak wood at temperatures of 20 °C, 160 °C, 180 °C, 210 °C, and 240 °C. The physical properties were affected by the chemical composition of oak wood. The correlations of equilibrium moisture content (EMC) and oak density at EMC were similar, in accordance with the investigated properties. Oak end hardness was affected by treatment temperature. The depth of indentation significantly affected the hardness. Mass specific heat capacity and effusivity were positively correlated with EMC, sugars, holocellulose, cellulose traits, and ash and negatively affected by total extractives. Thermal diffusivity was slightly affected by treatment temperature.

Laminated veneer lumber (LVL) is an engineered wood product that is commonly used for joists in wooden buildings. Holes in joists are often necessary to allow piping systems to pass through. Introducing a hole into an LVL joist remarkably changes the distribution of stresses in the vicinity of the hole. Tensile stresses occur perpendicular to the grain, and the capacity of the joist can be decreased accordingly. This study presents the experimental results of LVL joists with holes and reinforcement methods around the holes. The results showed that cutting a large enough hole contributed substantially to the strength reduction of LVL joists. Holes with a diameter-to-joist depth ratio of 0.4, 0.5, and 0.6 reduced the load-capacity 50.1%, 59.6%, and 68.8%, respectively. Glued plywood and glued-in threaded rods were both effective methods for reinforcing LVL joists with holes having a diameter-to-joist depth ratio of less than 0.5. The reinforcement effect of nailed plywood was relatively poor, increasing the load-capacity less than 30%. The reinforcement effect of all of the methods depended on the effective joint with the LVL. The thickness of the plywood, the number of nails, and the withdraw strength were also important factors.

The lateral load-slip behavior of a single-shear metal-to-particleboard single-screw connection (SMPSC) was investigated. The connection consisted of a layered particleboard main member fastened to a metal plate as a side member using a 4.8-mm diameter sheet metal screw. A mechanics-based approach was used to evaluate critical factors on the lateral load resistance performance of SMPSCs. Experimental results indicated that ultimate screw-bearing strengths in face and core layers of evaluated particleboard materials were 100.0 and 29.9 MPa, respectively. This significant difference of screw-bearing strength in material layers significantly affected the lateral resistance load capacity of SMPSCs. The proposed mechanical models considering material layer effects on screw-bearing strengths were verified experimentally as a valid means for deriving estimation equations of lateral resistance loads of SMPSCs evaluated in this study.

Particleboard was manufactured using dialdehyde starch (DAS) as the adhesive and corn stalk as the matrix. The adhesive was prepared via the oxidation of tapioca starch in sodium periodate. The DAS was characterized by Fourier transform infrared (FTIR) spectroscopy. The effect of the hot pressing temperature, board density, and DAS dosage on the physical properties of particleboard was studied. The cross-section morphology of particleboard was observed via scanning electron microscopy (SEM). The absorption peak of the aldehyde group appeared at 1731 cm^-1 after the tapioca starch was oxidized by sodium periodate, indicating that DAS had formed. Both the modulus of rupture (MOR) and modulus of elasticity (MOE) increased first and then decreased, with the increase of hot pressing temperature, board density, and DAS dosage. Within a certain range, the increase of hot pressing temperature, board density, and DAS dosage reduced the thickness swelling (TS) and improved the particleboard water resistance. During the particleboard hot pressing process, DAS filled the spaces of the corn stalk and acted as an adhesive to bind the corn stalks tightly together, thereby improving the physical, mechanical, and water resistance properties of the particleboard.

Cellulose was successfully isolated from poplar wood chips using a two-step treatment for controlled times. The treatment included nitric acid-ethanol pretreatment and mechanical dispersion. The cellulose specimens were then dissolved in an ionic liquid and cast to prepare cellulose films. The prepared samples and films were examined using scanning electron microscopy (SEM), High Performance Liquid Chromatography (HPLC), Fourier-transform spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and ultraviolet-visible spectroscopy (UV-Vis). The results showed that lignin and hemicellulose reacted and dissolved in the nitric acid-ethanol mixture solution, which broke the biomass recalcitrance and promoted cellulose dispersion in the solvent for preparing uniform films. However, a large amount of cellulose was hydrolyzed within the fourth treatment, resulting in a remarkable decrease in the tensile strength of the films. After three repetitions of treatments, the cellulose had a better average degree of polymerization, crystallinity, and thermal stability. The films had the highest tensile strength of 32.8 MPa, elongation at break of 47.5%, and transmittance that exceeded 80% at the wavelength range of 600 nm to 800 nm, which indicated that the samples were more suitable for film fabrication.

The aim of the research was to evaluate the impact of various temperatures of thermal modification and sanding treatment on the color change of sessile oak, Norway spruce, and Red meranti. Thermal modification was carried out at various temperatures. Subsequently, one side was sanded. The measurements were recorded using a BFS 33M-GSS-F01-PU-02 color reader. A Konica Minolta CR-10 Plus colorimeter and Nikon D3200 camera were used in conjunction with the Matlab program. The assessments were conducted in the color space of CIE L* a* b*. The measured values confirmed that the decrease in lightness from natural to thermally modified wood (220 °C) was the largest for non-machined spruce samples (ΔL = 42.47) and the smallest was for sanded spruce samples (ΔL = 31.64). The relative change in sample lightness was the largest for sanded oak samples (51%). The trends of the color values a* and b* were different for individual wood species. Overall, the average color change ΔE was the lowest for the non-machined meranti species (ΔE = 33.06), and the largest for the non-machined spruce (ΔE = 43.06). Comparing the individual methodologies, it was found that all methodologies provided relevant results and can be used in practice.