Volume 11 Issue 3

A facile approach for producing fluorescent composite paper containing nitrogen-doped graphene quantum dots (N-GQDs) and graphene on the surface of the modified fibers was implemented from the exfoliation of graphite oxide (GO) using a one-step hydrothermal method. The properties of the composite paper were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV), photoluminescence spectroscopy (PL), and confocal laser scanning microscopy (CLSM). The results indicated that the GO was reduced to graphene sheets, and the N-GQDs nanoparticles were deposited on the surface of these sheets. The composite paper remained undamaged, with a three-dimensional structure and smooth fibers during the hydrothermal process, and the average particle size of N-GQDs was less than 10 nm. Photoluminescence measurements showed that the composite paper had a strong ultraviolet absorption in the range of 200 to 340 nm, and the band edge emission occurred at 475 nm. The CLSM image of composite paper exhibited a well-defined excitonic emission feature with an excitation wavelength of 405 nm.

Thermo-gravimetric analyses of three cellulosic substances, namely, microcrystalline and amorphous cellulose, and treated Japanese cypress (JC) sawdust were carried out in this study. The thermal degradation temperature of crystalline cellulose decreased with increasing ball-milling time, while that of amorphous cellulose barely changed. However, small differences in the derivative thermo-gravimetric (DTG) curves between crystalline cellulose (i.e., before ball milling) and amorphous cellulose (i.e., after ball milling) were observed. The DTG curves of high-crystalline cellulose were sharp and similar to those of low-crystalline samples. The thermal degradation temperature of JC was decreased by ball milling, and its DTG peak shape became broad and low. These effects could be caused by the denaturing of non-cellulosic substances such as hemicellulose and lignin. The thermal degradation behaviors revealed by the DTG curves may serve as indicators of crystalline cellulose purity and other physical properties of lignocellulosic biomass.

Polyurethane (PU) films were prepared by solution casting using a three-component system, namely, a novel solvolytic lignin, polyethylene glycol (PEG), and tolylene 2,4-diisocyanate (TDI), with dibutyltin dilaurate as a catalyst. An important objective was to incorporate as much lignin as possible. To this end, PU film synthesis was optimized by varying the lignin content (30 to 70 wt.% with respect to PEG), isocyanate-to-hydroxyl (NCO/OH) stoichiometry (0.8, 1, 1.2, 1.5, and 1.8), and PEG molecular weight (400, 600, and 1000). The results showed that the films derived from PEG 600 and a NCO/OH ratio of 1.5 were synthesized with a maximum content of 70% lignin, with respect to PEG. The effects of lignin content on the tensile properties and the thermostability of the PU films were studied. The onset decomposition temperature (TOD) of the lignin PU films reached an average limit of 310 °C, regardless of the lignin content, and 260 °C for a PU film without lignin. Thus, the addition of lignin, as a PEG substitute in polyurethane films, leads to better thermal stability. Furthermore, breaking stress, Young’s modulus, and Shore hardness of PU films increased constantly with lignin content, without reaching a maximum.

A barrier plasma, created at atmospheric pressure, was used to improve the surface and adhesive properties of polyester (PES) film with respect to wood using polyurethane adhesives. The modification of PES film surfaces using barrier discharge plasma is attractive for various applications. Plasma pre-treatment initiates and participates in grafting, polymerization, or cross-linking reactions on the PES surface. This method of surface modification is clean, dry, ecological, and very efficient. The enhancement of the wettability of the polyester film was necessary for promoting higher adhesion to wood with water-based adhesives. The treatment of polyester films by barrier plasma led to a considerable increase in the surface free energy of the film and subsequently an increase in the peel strength of the adhesive joint of PES film-oak wood with polyurethane adhesive.

Sugarcane bagasse was treated to obtain sawdust, in addition to mechanical, thermomechanical, and chemical-thermomechanical pulps. The obtained fibers were used to obtain reinforced polypropylene composites prepared by injection molding. Coupling agent contents ranging from 2 to 10% w/w were added to the composite to obtain the highest tensile strength. All the composites included 30% w/w of reinforcing fibers. The tensile strength of the different sugarcane bagasse fiber composites were tested and discussed. The results were compared with that of other natural fiber- or glass fiber-reinforced polypropylene composites. Pulp-based composites showed higher tensile strength than sawdust-based composites. A micromechanical analysis showed the relationship of some micromechanical properties to the orientation angle, critical length, the intrinsic tensile strength, and the interfacial shear strength. The pulps showed similar intrinsic tensile strengths and were higher than that of sawdust. The properties of the sugarcane bagasse composites compared well with other natural fiber-reinforced composites.

As a clean and green alternative fuel to replace fossil fuels, hydrogen could be an ideal fuel for the future. Supercritical water gasification of lignocellulosic agricultural residues results in H2 production with zero CO2 emission, which makes this technique an attractive technology for hydrogen generation from biomass. Structural analyses were performed to determine the lignin, cellulose, and hemicellulose contents in feedstock. The effects of different process variables (temperature, reaction time, and feed concentration) on supercritical water gasification of Iranian rice straw (IRS) were evaluated. IRS, which has a high content of cellulose and hemicellulose, has significant potential for gaseous product generation under the supercritical water condition. The maximum H2 production of 5.56 mmol/gr of biomass was achieved at 440 °C (temperature), 20 min (reaction time), and 2 wt. % (feed concentration).

A robust process of purification, characterization, and application of endoglucanase from the agro-industrial waste was performed using solid state fermentation (SSF). Trichoderma harzianum as a micro-organism and wheat straw as a growth supportive substrate were used in SSF under pre-optimized conditions. The maximum activity of 480 ± 4.22 U/mL of endoglucanase was attained when a fermentation medium was inoculated using 10% inoculum size and 3% substrate concentration with pH = 5.5 at 35 °C for an optimized fermentation period. In comparison with crude extract, enzyme was 1.83-fold purified with a specific activity of 101.05 U/mg using Sephadex-G-100 column chromatography. Sodium dodecyl sulfate (SDS) poly-acrylamide gel electrophoresis revealed that the enzyme exhibited a low molecular weight of 43 kDa. The purified enzyme displayed maximum activity at pH = 6 and a temperature of 50 °C, respectively. The maximum activity (Vmax) of 156 U/mL and KM value of 63 µM were observed. Ethylenediaminetetraacetic acid (EDTA), SDS, and Hg2+ inhibited enzyme activity, while Co2+ and Mn2+ enhanced enzyme activity at 1 mM concentration. The maximum substrate affinity and specific activity of biosynthesized endoglucanase revealed that it can be potentially useful for industrial applications.

The fire properties of particleboard coated with calcite and a variety of fire-retardants (FR) was investigated. Four different chemicals, boric acid (BA), borax (BX), dolomite (DOL), and melamine (MEL), were added at the concentration of 1.0%, 3.0%, and 5.0% by oven-dry weight of calcite. The particleboard panels were tested according to the ASTM-E 69 standard to investigate their fire-retardant properties. The determination of weight loss, temperature, and the release of O2, CO, and NO by the samples was measured and recorded over 30 s intervals during combustion of the materials. The results indicated that the BA coatings exhibited better thermal stability than the other chemicals. Consequently, the lowest weight loss and temperature was found for specimens treated with 5.0% BA. These chemicals were effective relative to the fire properties of coated particleboard surfaces, depending on the type and ratio of the chemicals to the calcite.

Wood shrinks anisotropically as it loses hygroscopic moisture. While longitudinal shrinkage (parallel to the grain) is nearly negligible in normal wood, transverse shrinkage (across the grain) is significant and characterized as tangential and radial shrinkage. The application of average tangential shrinkage values to a rectangular cross section results in errors, especially for boards cut from near the center of the log. In addition, using a Cartesian coordinate system to calculate shrinkage cannot provide an estimate of cup. Calculating shrinkage and cup deformation using a previously developed model, this Excel model can provide a more realistic image of the final cross section and a more accurate estimate of shrinkage. The model is dependent on wood species, initial and final moisture contents, and location of the board within the log. This paper describes and illustrates uses of the model.