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Lignocellulosic materials (some natural fibers) have relevant mechanical properties when incorporated in polymeric matrices, being a renewable source to replace synthetic fibers; however, for good adhesion and durability, it is necessary to modify the fibrous surface structure in order to eliminate unwanted compounds. This work aims to evaluate different conditions of alkaline treatment of tobacco stalk waste using 10 and 15 wt% sodium hydroxide (NaOH) during an exposure time of 3 or 5 h. Thermal, chemical, and morphological characterizations as well as kinetic analysis were performed. Through Fourier transform infrared spectroscopy, it was possible to identify the partial removal of compounds such as lignin, hemicellulose, and extractives, increasing the thermal stability, which was proven by thermogravimetric analysis. Furthermore, X-ray diffraction shows a higher crystallinity index from cellulose after the alkaline treatment. Through the kinetic analysis, it is possible to observe that both methods presented similar activation energy values (Ea). In addition, after the alkaline treatment there was a reduction in Ea, the most evident result being observed in the TSW\10\5 sample, which presented an average value of Ea of 223.95 ± 15.79 kJ/mol by the Flynn–Wall–Ozawa method and 218.74 ± 24.69 kJ/mol by the Friedman method. Scanning electron microscopy showed the exposure of the microfibrils and an enhancement of roughness after alkaline treatment. Tobacco stalk wastes has potential application as reinforcing filler in composite materials since surface alkaline modification provides higher fiber/matrix adhesion through the removal of amorphous compounds. [ABSTRACT FROM AUTHOR]

Wet-spun fibers were prepared from plant-based cellulose nanofibers (CNFs) via a novel approach proposed in a previous report. This method is based on the use of a simple NaOH treatment and the minimization of the use of harmful reagents. The CNF gels prepared using an 8% NaOH solution exhibited good preservation of the cellulose I crystal structure, contributing to the high tensile properties of the spun fibers. This study further explored this approach, and a CNF suspension with 8% NaOH was spun into a 2% sulfuric acid coagulation bath at different spinning rates (1–100 m/min). Straight long fibers with a circular cross-section were obtained at all spinning rates. The orientation index of the CNFs and the tensile properties of the CNF spun fibers increased slightly with increasing spinning rate. However, these values were lower than the values expected based on the previous reports. The aggregation of CNFs in the NaOH solution likely affected these properties. Nevertheless, the advantages of this method, namely the lack of use of toxic solvents and the minimal use of organic solvents, were demonstrated. Furthermore, a high wet strength can be expected due to the formation of interdigitated linkages between the CNFs. These CNF filaments are promising for applications in smart textiles, biosensors, and structural reinforcement. [ABSTRACT FROM AUTHOR]

Inferior mechanical properties are hindering the growth of using natural fibre reinforced polymeric composites in many structural applications. One of the popular solutions to this issue being reported in the literature is the addition of nano or micro reinforcements such as carbon nanotubes, ceramic particles, glass particles, clay, rubber additive etc., which is expensive. Furthermore, questions are raised over biodegradability of said composites. The current study investigated the effect of micro-crystalline cellulose (MCC) particles and alkaline treatment on the tensile, bending and impact properties of jute woven fabric reinforced bio-epoxy composite. The composite samples were made by compression moulding using manufacturer provided curing conditions. Alkaline treatment of jute fabric was found to have positive relationships with tensile and flexural properties, whereas it had negative with the impact strength of bio-composite. It is found that up to 7% addition of MCC particles, tensile, bending and charpy impact strength were improved by 48%, 52% and 100% respectively. Beyond this percentage, the mechanical properties were found to be deteriorated. [ABSTRACT FROM AUTHOR]

The effect of alkaline treatment of coir on polypropylene/coir composite properties was investigated, using a two-factor central composite design where NaOH concentration and reaction time were varied. Alkaline treatment favored delignification, and at certain conditions, increased composite stiffness without loss in tensile strength. Increase in cellulose concentration likely increases the number of free hydroxyls, which is less favorable to composite mechanical properties. Treatments with 2 and 9% NaOH for 5 h resulted in cellulose concentration of about 50 and 70%, respectively. Treatments with high concentrations and for long periods are disadvantageous to composite properties, resulting in lower tensile strength likely due to the increased number of free hydroxyls as well as to possible breaks in cellulose structure. A desirability function, used to optimize the delignification process, revealed the highest tensile modulus and strength (3.5 GPa and 31 MPa, respectively) could be obtained at 5.75% NaOH and reaction time of 3 h. [ABSTRACT FROM AUTHOR]

The drying process in typical pulp production generates strong hydrogen bonding between cellulose microfibrils in refined cell walls and increases the difficulty in obtaining uniform cellulose nanofibers. To investigate the efficacy of alkaline treatment for cellulose nanofibrillation, this study applied a bead-milling method in NaOH solutions for the nanofibrillation of dried pulps. NaOH treatments loosened the hydrogen bonding between cellulose microfibrils in dried pulps and allowed preparation of cellulose nanofibers in 8 % NaOH with a width of approximately 12-20 nm and a cellulose I crystal form. Both the nanofiber suspensions prepared in 8 and 16 % (w/w) NaOH were formed into hydrogels by neutralization because of surface entanglement and/or interdigitation between the nanofibers. When the dried pulp was fibrillated in 16 % (w/w) NaOH, the sample after neutralization had a uniquely integrated continuous network. These results can be applied to the preparation of high-strength films and fibers with cellulose I crystal forms without prior dissolution of pulps. [ABSTRACT FROM AUTHOR]

Four types of kenaf bast fibers were prepared via a combination of Wise treatments, for delignification, and alkaline treatments, for the removal of hemicellulose. Each type of kenaf bast fiber with different refining processes were nano fibrillated by grinding. Resulting, cellulose nanofiber (CNF) sheet was obtained from CNF by vacuum filtration (Scheme 1). The structures and properties of these CNF sheets then were investigated to determine how the CNF components had affected these properties. All of the CNFs from different refining processes were classified as a cellulose I type by X-ray diffraction. However, the mechanical properties (Young's modulus, tensile strength and toughness) of the CNF sheet with Wise treatment were higher than the properties of the other three CNF sheets. These results strongly suggested that alkaline treatment was unnecessary for the removal of hemicellulose, and that the application of the Wise treatment effectively imparted high mechanical properties to the cellulose microfiber.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The preparation of high-strength hydrogels from plant-based cellulose nanofibers by simple alkaline treatment is described herein. We isolated the cellulose nanofibers with a uniform width of approximately 15 nm from wood and we prepared two types of hydrogel sheet with different crystal forms (celluloses I and II) in 9 and 15 wt% aqueous sodium hydroxide solutions. Both of the hydrogels exhibited high tensile properties because of the crystalline network in the gels. Especially, the nanofiber hydrogel with a cellulose II crystal structure with the swelling degree of 13.4 achieved a Young's modulus and tensile strength in excess of 35 and 5 MPa respectively, because it had a continuous and strong nano-network formed via the interdigitation of the neighboring nanofibers during mercerization. [ABSTRACT FROM AUTHOR]