Volume 13 Issue 2

The effect of high-pressure (HP) densification (30, 90, and 150 MPa for 3, 30, and 300 s) on the moisture sorption properties of Paulownia wood was investigated. After the densification, samples were conditioned at three temperatures (20, 30, and 40 °C) and five equilibrium moisture contents (from 11.20 to 95.62%) during the study, after which the equilibrium moisture contents of the control and treated samples were measured. The HP-treated groups had higher equilibrium moisture contents than the controls at higher relative humidity levels. The hysteresis phenomenon and the scanning electron microscopy observations were explained by the transformation of the structural elements by the HP treatment. Finally, two moisture sorption isotherm (MSI) models (a linear polynomial model for adsorption and a quadratic polynomial model for desorption) were established with good performance to describe the relationship between HP treatment parameters, environmental conditions, and equilibrium moisture contents.

Bamboo is one of the most important raw materials for pulp and paper production in several countries due to its abundance and cost-effectiveness. However, the difficulties in bleaching and low brightness of bamboo chemo-mechanical pulp (CMP) has limited the expansion of its utilization. In this study, the low-cost twin-screw extruder (TSE) was used instead of the high-cost common extruded model screw device (MSD) before chemical impregnation to improve the brightness of the bamboo CMP. There were minor differences in the holocellulose, lignin, and pentose contents in the extruded materials between the two devices. The absorbency of the TSE extruded materials was 4.50 g/g, which was three times that of the material extruded by MSD. Alkali optimization was conducted at levels of 12% H₂O₂. The TSE-CMP achieved the highest brightness, at 57.6% ISO with 6% sodium hydroxide (NaOH), while the MSD-TMP only reached approximately 49.6% ISO with 3% NaOH. At the same time, the physical properties of paper-sheets made from bleached TSE-CMP and MSD-CMP were tested. When bleached at 12% H₂O₂ with 6% NaOH, the tensile index of TSE-CMP was higher compared with that of MSD-CMP, while the other strength properties were nearly unchanged.

Fly-ash (FA) /wood-flour (WF) geopolymer composites (FWGCs) were prepared to investigate the influence of WF on the properties of FA-based geopolymer composites at different curing times. The crystallization, surface morphology, geopolymerization, interface analysis, and mechanical properties were characterized. The results indicated that the curing time exerted positive effects on the mechanical strength of the FWGCs. Noticeably distinct microstructures and mechanical properties were observed with different WF contents. The FWGCs with low WF loading (1 wt% and 5 wt%) presented almost unchanged or even improved mechanical properties compared to the pure FA-based geopolymer due to the existence of bonds between the WF and geopolymer matrix in the interface. However, the addition of WF to a higher content (10 wt%, 15 wt%, and 20 wt%) posted a negative influence on mechanical properties with insufficient polymerization of geopolymer and degradation of WF detected by morphology and elemental microanalysis. This study will facilitate a better understanding of the interaction between geopolymers and wooden materials, and serve as a basis for further research and applications.

The influence of laser radiation was evaluated relative to the color and major chemical component changes of three hardwood species. The surfaces of maple (Acer pseudoplatanus L.), beech (Fagus sylvatica L.), and lime (i.e. linden, Tilia vulgaris) wood were exposed to radiation from a CO2 laser (wavelength = 10.6 µm, output power = 45 W). It was observed that increased doses of irradiation resulted in a decrease in the lightness (L*), increase in the total color difference, and a drop in the total polysaccharide content. Compared with the non-irradiated specimens, the ΔL* values at the highest irradiation doses were −56 (maple), −46.8 (beech), and −50.5 (lime). The trends observed in the FTIR spectra also showed there was a relationship between the breaking of C=O and C=C bonds in important functional groups in the lignin, hemicellulose, and carbohydrates. A highly linear correlation (R2 from 0.902 to 0.987) was observed between the increase in the ΔL* and decrease in the hemicellulose content, which degrades faster than other basic wood components. Such a phenomenon may have been related to the formation of new chromophore structures, which caused the color changes in the wood.

Stress wave testing has been applied in the nondestructive evaluation of wood for many years. However, the anisotropy property of wood and the limited number of sensors prevent an accurate stress wave velocity measurement and the high resolution of tomographic inversion. This paper proposes a tomographic imaging algorithm (IABLE) with a velocity error correction mechanism. The proposed algorithm computed the wave velocity distribution of the grid cells of wood cross-sections by the least square QR decomposition (LSQR) iterative inversion, and then optimized the tomography with a velocity error correction mechanism (ECM). To evaluate the performance of the proposed algorithm, several healthy and defective logs and live trees were selected as the experimental samples, and the nondestructive testing procedures were finished. With the stress wave velocity data sets measured via a PiCUS 3 stress wave testing instrument, the IABLE algorithm was implemented, and the tomographic images of the log samples and live trees were generated. The experimental results demonstrated the effectiveness of the proposed imaging algorithm for the nondestructive evaluation of wood.

Due to various factors, there is evidence that there will be a future lack of wood materials in the woodworking and energy sectors, as well as other sectors. This has been confirmed definitively through the most recent developments. Possible solutions include the partial replacement of wood in composite materials by post-harvest remnants of agricultural crops. Unlike wood matter, however, these stems need surface pre-treatment before they can be used to produce composite materials. In this study the effects were compared for two pre-treatments of stems (alkaline and hydrothermal) of rapeseed (Brassica napus L.), maize (Zea mays L.), and wheat (Triticum aestivum L.). The effects were compared using the contact angle between water and the surfaces of the stems. Hydrothermal modification yielded a statistically significant reduction in the contact angle between water and the stem surfaces of winter rapeseed and maize; likewise, alkaline modification yielded a statistically significant reduction in the contact angle between water and the stem surface of maize. The possibility of using winter rape to produce composite materials was further evaluated and comprehensively assessed using SWOT analysis.

A revenue-sharing contract was introduced into a three-echelon wood processing residue-based reverse supply chain model to maximize the supply chain profit and realize a win-win situation for all participants. The optimal expected supply chain profits under different decision policies and the acceptable range of revenue-sharing coefficients were analyzed. Finally, the model was applied in a case study where sawdust was recycled to produce black fungus. Results showed that revenue-sharing can effectively enable supply chain coordination. Within the domain of the revenue-sharing coefficients, the production cost decreased by 5.91% and the corresponding demand increased by 16.09%, resulting in an increase of 7.73% in the supply chain profit. A comparison was made between the three-echelon and a two-echelon supply chains, and the results showed that the two-echelon supply chain would become less competitive than the three-echelon supply chain with the increase of recycling cost. Additionally, the profit shares of all parties in the three-echelon supply chain depended mainly on the revenue-sharing coefficients, which were determined by the positions of the parties and their bargaining power.

Polylactic acid (PLA) and bamboo fiber are both green and biodegradable materials. However, the bonding of PLA and bamboo fiber is poor, which limits the physical properties of paper. The effects of polyvinyl alcohol (PVOH) on PLA fiber/bamboo fiber composites were studied by measuring the tensile strength, tear resistance, and breaking length of the paper. In addition, the morphology of paper comprised of PLA fiber and bamboo fiber were investigated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The tensile index, tear index, and breaking length of paper made with the 4 wt% PVOH-treated bamboo fiber and the untreated PLA fiber compared favorably with the paper made of the untreated bamboo fiber and PLA fiber increased 21.0%, 8.6%, and 20.8%, respectively. However, compared with the paper made of the untreated bamboo fiber and PLA fiber, the tensile index, tear index, and breaking length of the paper made with the treated PLA fiber and the treated bamboo fiber with 4 wt% PVOH solution were dramatically reduced by 30%, 18%, and 30%, respectively.

Fillers can greatly affect the properties of adhesives, and this research aimed at enhancing the performance of adhesives by using different concentrations of fillers. This paper describes the influence of using recycled polyurethane particles (powder of particle size from 10 µm to 50 µm) as a filler on some properties of polyurethane adhesives for the gluing of wood. Two kinds of one-component, moisture-curing polyurethane adhesives were used. The observed properties were the contact angle between the wood and adhesive droplet, and the strength of bonded joints (shear strength). From the results, it was concluded that the contact angle increased with an increase in filler (in the entire observed range from 0% to 15% filler). The content of filler also affected the strength of bonded joints and their thermal stability. The strength of bonded joints decreased with an increase in filler content when samples were conditioned in cold water. However, the strength of bonded joints increased with an increase in filler content when samples were boiled in water.

Invasive Teline monspessulana can be an important source of biomass to supply fibers for the rising demand of cellulose bioproducts, especially for the development of advanced materials. Its fibers can be extracted via a thermo-alkaline process at 170 °C with 40 g/L of sodium hydroxide (NaOH) and characterized by crystallographic, thermo-analytical, and mechanical techniques. The cellulose proportion in the wood of this species is approximately 47.6 wt.% ± 1.05 wt.%. However, its fibers are relatively small, and they have a wide range of aspect ratios from 25 to 287, with an average diameter of 9.3 μm ± 2.5 μm. These characteristics and mechanical properties make the fibers unattractive for the textile and paper industries. Meanwhile, crystalline cellulose was prevalent in the monoclinic phase, with a crystalline index and crystalline portion of 78 and 41%, respectively, observing crystal domains of c.a. 3.2 nm. Nanoindentation tests revealed favorable values of elastic modulus and hardness of c.a. 16 GPa and 0.28 GPa, respectively. Thus, this bioresource is expected to see promising applications in materials engineering, such as reinforcement in material composites, in drug delivery carrier, and electronic devices, among other biomultifunctional components.