Characterization of Cellulose-Chitosan-Based Materials from Different Lignocellulosic Residues Prepared by the Ethanosolv Process and Bleaching Treatment with Hydrogen Peroxide

Obtaining of a rich-cellulose material from black wattle (Acacia mearnsii De Wild.) bark residues

Black wattle (Acacia mearnsii De Wild.) barks are residues produced by tannin industries in huge quantities, which are normally discharged on environmental or used for energy production. Therefore, this study aimed to evaluate the use of black wattle bark residues as a raw material on obtaining of a rich-cellulose material by alkaline (MET1), acetosolv (MET2), and organosolv (MET3) procedures. The results obtained indicated that the alkaline methodology, followed by a bleaching step (MET1), promoted klason lignin and hemicellulose removals more efficiently. It was possible to observe that better results were achieved using NaOH concentration of 6% (wt%), at 65 °C for 2.5 h, presenting a yield of 63.24 ± 1.25%, and a reduction on klason lignin content of almost 90.45%. Regarding the bleaching step, it was possible to obtain a material free of non-cellulosic compounds with a yield of 78.28 ± 1.48%. Thermogravimetric analysis indicated the removal of lignin and hemicellulose as well as an increase in cellulose degradation temperature, due to changes in crystalline phases. According to X-ray diffraction (XRD), the procedures employed have led to an increase in crystallinity from 66.27 to 91.78% due to the removal of non-cellulosic compounds. Scanning electron microscopy (SEM) showed morphological alterations in accordance with the removal of non-cellulosic compounds.

Optimization of the Sound Absorption Coefficient (SAC) from Cellulose-Silica Aerogel Using the Box-Behnken Design

Noise pollution, which has become a major environmental issue in urban areas, can be minimized using acoustic insulation derived from cellulose-silica aerogel. The raw materials required in the process include waste newspaper-based cellulose, geothermal silica, and NaOH/ZnO solution. Therefore, this study investigates the effect of cellulose, silica, and ZnO concentrations on optimizing the sound absorption coefficient (SAC) using the Box-Behnken design (BBD). The results showed that the optimum conditions were obtained at 39.8578 wt % cellulose, 16.5428 wt % silica, and 0.5684 wt % ZnO. The impedance test for the cellulose aerogel and cellulose-silica aerogel showed SAC values of 0.59 and 0.70, respectively, and were characterized by XRD, FTIR, BET-BJH, SEM-EDX, and TG. The results of XRD and FTIR data indicate that the product was cellulose-silica aerogel, and the SEM micrographs showed that silica particles were attached to the fiber surface. Furthermore, type IV isotherms were observed in the cellulose-silica aerogel, typical of mesoporous materials. The presence of silica strengthened the aerogel structure, improved its thermal stability, and increased the surface area but decreased its pore size.

Physicochemical characteristics of organosolv lignins from different lignocellulosic agricultural wastes

Lignin is a promising alternative to petrochemical precursors for conversion to industrial-needed products. Organosolv lignins were extracted from different agricultural wastes including sugarcane bagasse (BG) and trash (ST), corncob (CC), eucalyptus wood (EW), pararubber woodchip (PRW), and palm wastes (palm kernel cake (PKC), palm fiber (PF), and palm kernel shell (PKS), representing different groups of lignin origins. Physicochemical characteristics of lignins were analyzed by several principal techniques. Most recovered lignin showed high purity of >90 % with trace sugar contamination, while lower purities were found for lignin from palm wastes. Hardwood lignins (EW and PRW) mainly contained guaiacyl (G) and syringyl (S) units with a minor fraction of p-hydroxyphenyl units (H) with high molecular weight, glass transition temperature, phenolic hydroxy group and low aliphatic hydroxy group. Grass-type lignins (BG, ST, CC) and palm lignins (PKC, PF, and PKS) contained three monolignols of H, G, and S units with lower molecular weights and C₅-substituted hydroxy of S unit. Among the grass-type lignins, PKC lignin contained the highest nitrogen and lipophilic components with the lowest molecular weight, thermal stability, and glass transition temperature. This provides insights into properties of organosolv lignin as basis for their further applications in chemical, polymer and material industries.