Search

Cellulose is one of the most abundant biopolymers on Earth and is of most significant interest due to its properties and uses. Cellulose can be obtained from agro-industrial residues, such as rice husk, whose cellulose content is approximately 30%. In this study, cellulose microfibers were extracted from rice husks. Fibers were obtained by submitting the biomass to alkali (NaOH) and bleaching treatments. These treatments have already been reported in the literature; however, variables such as the concentration of reagents, the time, and the temperature of the chemical treatment have yet to be optimized. A factorial design of experiments with 3 factors and 2 levels for each factor was proposed to optimize the chemical processes. It was determined through the analysis of variance (ANOVA) that the factors evaluated significantly influenced the elimination of non-cellulosic compounds, and that the chemical treatment was more efficient when the factors took high level values. Ultraviolet-visible spectroscopy (UV-Vis) analysis showed the successful removal of undesired components during the alkaline treatment. The effect of the treatments on the morphology upon removing hemicelluloses, lignin, and inorganic material was evaluated through Scanning Electron Microscopy (SEM). The increase in the thermal stability in the alkali-treated rice husk and in cellulose microfibers, compared to the raw rice husk, was established by thermogravimetric analysis (TGA). X-ray diffraction (XRD) indicated that the treatments increased the percentage of crystallinity. [ABSTRACT FROM AUTHOR]

Cellulose microfibrils were isolated from coffee parchment through acid hydrolysis, alkaline hydrolysis, and bleaching. Factorial design experiments allowed studying the influence of the chemical precursor concentrations and reaction times on the mass losses. TGA, SEM, XRD, and FT-IR techniques allowed for characterizing the coffee parchment hydrolyzed and bleached. Obtained results suggest that acid hydrolysis breaks down the lignocellulosic compounds from the coffee parchment, and alkaline hydrolysis allows the solubilization of lignin and hemicellulose. Lignocellulosic compound dissolution produces a reduction/disappearance of some vibrational bands. This dissolution enhances the crystalline index and decreases the microfibril's diameter. However, in coffee parchment, the microfibrils are twisted, giving the appearance of fibers with a minor diameter. The design of the experiment results suggests that the main factors during acid and alkaline hydrolysis are the concentration of the chemical precursors. In the bleaching process, a variation in the factors does not significantly influence the response variable. However, for brightness, the precursor concentration affects the cellulose quality. The optimal conditions for cellulose extraction from coffee parchment are 5% (v/v) of HNO3 by 2 h, 3% (m/v) NaOH by 60 min, and a 1:1 mass of NaClO:CH3COOH by 45 min for bleaching. [ABSTRACT FROM AUTHOR]