Research Articles

Well-crystallized and hexagonal wurtzite ZnO was synthesized with nanocellulose using a facile hydrothermal method. Many highly active (001) facets were retained in the obtained ZnO nanocrystals, presumably due to interaction between the polar facet of ZnO and the nanocellulose. Given its effective surface area, the synthesized ZnO exhibited good photocatalytic activity of degrading methylene blue. Its degradation efficiency reached 94.4% within 30 min (UV irradiation power of 6 W), which was 34% higher than that of Degussa TiO2 P25. The ZnO photocatalyst also exhibited excellent reusability, confirmed by no obvious abatement after its being re-used for 8 cycles. These ZnO nanomaterials were synthesized using renewable nanocellulose derived from cotton. This environmentally friendly and cost-effective approach is anticipated to be applied in the future synthesis of small-sized ZnO photocatalysts.

To illuminate changes in the thermal stability of lignocellulosic biomass by homogeneous chemical modification in ionic liquids, sugarcane bagasse derivatives bearing carboxyl groups were prepared in ionic liquids. Fourier transform infrared (FT-IR) spectroscopy and solid-state nuclear magnetic resonance (NMR) confirmed the chemical structure of the derivatives. Sugarcane bagasse derivatives with degree of substituted OH as high as 9.93 mmol/g were achieved. The homogeneous esterification was demonstrated to be a more efficient approach than heterogeneous ones. Based on thermogravimetric analysis, the onset degradation temperature of sugarcane bagasse decreased dramatically to 185 °C, 160 °C and 140 °C, using succinic anhydride, maleic anhydride, and phthalic anhydride as reagent, respectively. A first-order degradation kinetic model was applied to obtain the degradation activation energies of sugarcane bagasse. The results showed that homogeneous chemical modification significantly decreased the thermal stability of sugarcane bagasse by reducing the onset degradation temperature and degradation activation energies.

In South Africa, approximately 3 × 106 tons of sugarcane bagasse is produced annually by 14 factories located on the north coast of KwaZulu-Natal. It is one of the most readily available lignocellulosic materials for ethanol production through enzymatic saccharification and hydrolysis. Pre-treatment enables disruption of the naturally resistant structure of lignocellulosic biomass to make the cellulose accessible to hydrolysis for conversion to biofuels. In this study, pre-treatment of depithed bagasse and mill-run bagasse was done using acid (3% H2SO4 v/v) followed by alkali (4% NaOH w/v), and the pre-treated solid was subjected to enzymatic hydrolysis. The effects of different conditions for enzymatic saccharification such as enzyme dose, reaction time, and amount of surfactant were studied in detail. The pre-treated substrate (10% w/v) when hydrolysed using 30 FPU/gds/40 FPU/g dry substrate (gds) with 0.4% (v/v) Tween® 80 for 20 h resulted in 608 mg/gds (depithed bagasse) and 604 mg/gds (mill-run bagasse) total reducing sugars.

Torrefaction is an important biomass pretreatment method that impacts fuel characteristics of biomass, specifically during the torrefaction process. Besides improving the fuel characteristics of biomass, torrefaction also contributes to increased quality of liquid and gaseous energy carriers obtained from fast pyrolysis and gasification. In this study, the effect of torrefaction on the solid energy carrier biochar, produced by carbonization, was studied by using solid olive mill residue (SOMR) as raw biomass. The carbonization characteristics of SOMR and torrefied SOMR (tSOMR) were compared by using ultimate and proximate analysis results. The higher heating value (HHV) and energy yields of biochars produced from SOMR and tSOMR were compared. The results showed that torrefaction contributed to the reduction of energy given to the biomass during the carbonization process by decreasing the holding time.

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.