Integrating phosphotungstic acid-assisted prerefining with cellulase treatment for enhancing the reactivity of kraft-based dissolving pulp

A novel process for efficient utilization of bamboo fiber resource in dissolving pulp production by fiber fractionation: Laboratory study and mill trials

The rational use of bamboo to make dissolving pulp can offer up new opportunities for cellulose production, alleviating wood scarcity. Bamboo contains a high content of non-fiber cells, which presents technical challenges in dissolving pulp production by the conventional process. In this study, a process concept of separating hemicelluloses is presented by fiber fractionation and purification for cleaner production of bamboo dissolving pulp: bamboo kraft pulp was fractionated into long-fiber and short-fiber fractions. The cellulose-rich long-fiber fraction was converted to dissolving pulp by further purification treatment with acid hydrolysis and cold caustic extraction. The hemicellulose-rich short-fiber fraction was used for papermaking. The laboratory results were confirmed by those from mill trials. The combined pulp yield (dissolving pulp + paper-grade pulp) reached 49 %, which was significantly higher than that of the conventional pre-hydrolysis kraft pulping process. Furthermore, the quality of dissolving pulp was higher due to inherently higher cellulose content of long-fiber fraction.

Nano-copper ions assembled cellulose-based composite with antibacterial activity for biodegradable personal protective mask

The current SARS-CoV-2 pandemic has resulted in the widespread use of personal protective equipment, particularly face masks. However, the use of commercial disposable face masks puts great pressure on the environment. In this study, nano-copper ions assembled cotton fabric used in face masks to impart antibacterial activity has been discussed. To produce the nanocomposite, the cotton fabric was modified by sodium chloroacetate after its mercerization, and assembled with bactericidal nano-copper ions (about 10.61 mg·g-1) through electrostatic adsorption. It demonstrated excellent antibacterial activity against Staphylococcus aureus and Escherichia coli because the gaps between fibers in the cotton fabric allow the nano-copper ions to be fully released. Moreover, the antibacterial efficiency was maintained even after 50 washing cycles. Furthermore, the face mask constructed with this novel nanocomposite upper layer exhibited a high particle filtration efficiency (96.08% ± 0.91%) without compromising the air permeability (28.9 min·L-1). This green, economical, facile, and scalable process of depositing nano-copper ions onto modified cotton fibric has great potential to reduce disease transmission, resource consumption, and environmental impact of waste, while also expanding the range of protective fabrics.

Rapid and massive fractionation of hemicelluloses for purifying cellulose at room temperature by tetramethylammonium hydroxide

The fractionation of hemicelluloses is a promising method to improve the comprehensive utilization of lignocellulosic biomass. However, the effective fractionation of hemicelluloses is always limited by the structural complexity and easy degradability. In this study, tetramethylammonium hydroxide (TMAH) was developed to fractionate hemicelluloses from poplar holocellulose with high molecular weights and high yields at room temperature. Approximately 90% of hemicelluloses could be dissolved at room temperature in 1 h, and the yield was up to 81.9%. Compared with the fractionation using NaOH solution, the hemicelluloses isolated by TMAH solvent showed a more complete structure and higher purity. Meanwhile, the retention rate of cellulose after treatment with TMAH was up to 90.2%, and the crystal structure of cellulose in the residues was practically unchanged. Moreover, the TMAH solvent could be recycled to fractionate hemicelluloses. The work provides an elegant and significantly efficient method towards hemicelluloses fractionation and cellulose purification.

Simultaneous microwave-assisted phosphotungstic acid catalysis for rapid improvements on the accessibility and reactivity of Kraft-based dissolving pulp

Improving the cellulose accessibility and reactivity in an efficient and convenient way has become the focused issue in the field of dissolving pulp manufacturing. We herein demonstrate a simple yet efficient strategy, namely a simultaneous microwave (MW)-assisted phosphotungstic acid (PTA) catalysis (MW-PTA_sim). The MW-PTA_sim treatment was efficient to improve Fock reactivity from 49.1 % to 85.8 % and decrease viscosity from 561 to 360 mL/g within 10 min, which was superior to the single MW treatment and the sequential MW-PTA_seq treatment. Besides, the MW-PTA_sim treated fiber had rougher and more fibrillated surfaces with an enhanced fiber accessibility, showing increased specific surface area (SSA) from 1.43 to 6.31 m²/g, mean pore diameter (MPD) from 6.92 to 11.20 nm and water retention value (WRV) from 101 % to 172 %. These positive enhancements are mainly due to a synergy that MW-enhanced rotation of PTA mediums was served as "spinning cutters" to attack the fibers, plus MW-accelerated PTA transfer and catalytic hydrolysis further improved the fiber accessibility. Moreover, PTA also demonstrates a high reusability and chemical stability. This process offers an effective and sustainable alternative for manufacturing a premium dissolving pulp.

Ultrafast process of microwave-assisted deep eutectic solvent to improve properties of bamboo dissolving pulp

Viscosity control and reactivity enhancement are critical to produce high-quality cellulose products, such as dissolving pulp, yet remain challenging. In this work, an ultrafast process, namely microwave-assisted deep eutectic solvent (MW-DES), is proposed for this purpose. It is based on the hypothesis that the MW-DES process can deliver an enhanced synergy: a simultaneous fiber swelling and cellulose depolymerization via hydrogen-bonding break-up and acid hydrolysis from the actions of polar and acidic DES further boosted under MW irradiation. Results showed that after the MW-DES (Choline chloride- oxalic acid, ChCl-OA) treatment for only 40 s, the pulp viscosity decreased from 715 to 453 mL/g, and the reactivity increased from 43.0 % to 84.6 %, which is ultrafast in comparison with those reported work. Furthermore, DES in the process shows a high reusability and chemical stability, thus offering a simple, sustainable and effective alternative for upgrading of dissolving pulp, particularly, using non-wood materials of bamboo.

Purification and enzymatic properties of a new thermostable endoglucanase from Aspergillus oryzae HML366

Aspergillus oryzae HML366 is a newly screened cellulase-producing strain. The endoglucanase HML ED1 from A. oryzae HML366 was quickly purified by a two-step method that combines ammonium sulfate precipitation and strong anion exchange column. SDS-PAGE electrophoresis indicated that the molecular weight of the enzyme was 68 kDa. The optimum temperature of the purified endoglucanase was 60 ℃ and the enzyme activity was stable below 70 ℃. The optimum pH was 6.5, and the enzyme activity was stable at pH between 4.5 and 9.0. The analysis indicated that additional Na⁺, K⁺, Ca²⁺, and Zn²⁺ reduced the catalytic ability of enzyme to the substrate, but Mn²⁺ enhanced its catalytic ability to the substrate.The Km and Vmax of the purified endoglucanase were 8.75 mg/mL and 60.24 μmol/min·mg, respectively. In this study, we report for the first time that A. oryzae HML366 can produce a heat-resistant and wide pH tolerant endoglucanase HML ED1, which has potential industrial application value in bioethanol, paper, food, textile, detergent, and pharmaceutical industries.

Production of rayon fibres from cellulosic pulps: State of the art and current developments

The increasing demand for cellulosic fibres is continuously driven by the growing earth population and requirements of the textile industry. The annual cotton production of ca. 25 million tons is no longer enough to meet the market demands. This market gap of cellulosic fibres is progressively filled by regenerated cellulosic fibres derived from the dissolving pulp. The conventional industrial process of viscose production is far from being environmentally friendly due to the use of hazardous reagents. Alternatively, new trends in the production of regenerated fibres are related to the direct dissolution of cellulose in appropriate environmentally sound recyclable solvents, allowing high quality rayon fibres. This article reviews the sources of dissolving pulps used for the production of viscose and its quality parameters related to the performance of viscose production. The prospective cellulose regeneration processes, both commercialized and under development, are reviewed regarding current and future developments in the area.

Dissolving pulp production: Cellulases and xylanases for the enhancement of cellulose accessibility and reactivity

Dissolving pulps are high-grade cellulose pulps that have minimum amount of non-cellulosic impurities. Dissolving pulps are the basic source for the manufacturing of several cellulosic products such as viscose, lyocell, cellulose acetates, cellulose nitrates, carboxymethyl-cellulose, etc. Dissolving pulps are mainly manufactured by pre-hydrolysis kraft and acid sulphite pulping. A high reactivity of dissolving pulps is desirable for its eco-friendly utilization for several purposes. Several approaches including mechanical, chemical, ultrasonic, and enzymatic treatments have been employed for the improvement of pulp reactivity. This review mainly focussed on pulp reactivity improvement through enzymatic approaches. Cellulases and xylanase have been proved effective for the improvement of pulp reactivity of dissolving pulp from different sources. The different combinations of cellulase, xylanase, and mechanical refining have been tested and found more effective rather than the single one.

Cellulose-assisted construction of high surface area Z-scheme C-doped g-C3N4/WO3 for improved tetracycline degradation

The preparation of heteroatom doping heterojunction photocatalysts with nontoxic carbonaceous materials and simple method still remains a challenge. Herein, ternary Z-scheme C-doped graphitic carbon nitride/tungsten oxide (C-doped g-C₃N₄/WO₃) was successfully fabricated via the hydrothermal impregnation with cellulose nanocrystal, high-temperature calcination, and electrostatic self-assembly with WO₃ nanocuboids in turns. Benefiting from the porous structure, high specific areas (57.20 m² g^-1), C-substitution, and the formation of Z-scheme heterojunction, the resulting photocatalyst exhibited narrower band-gap, enhanced visible-light absorption and separation of charge carrier, faster interfacial charge transfer, good oxidation/reduction capacities, and thus improved the photocatalytic activity performance. As such, this investigation will provide an effective route for not only incorporating semiconductors and heteroatoms into g-C₃N₄ but also developing more heterojunction with markedly improved photocatalytic performance.