Cellulose最新文献

A facile, efficient, and high yield method for producing chitin nanocrystals (ChNCs) using ultrasound-assisted phosphoric acid (PA) hydrolysis was developed. The hydrolysis was conducted at high chitin loading of 40 wt% and at a mild temperature of 50 °C, with the chitin-PA mixture remaining in a solid paste-like form throughout the reaction. The ChNCs produced showed an average length of ~ 200 nm and a cross-section of ~ 20 nm. Three reaction conditions were compared, at PA concentrations of 65, 75, and 85 wt%. Negligible changes in the sizes of ChNCs and degree of acetylation (DA) of the chitin (~ 96%) were observed, while the ChNC yield varied from 75.1 wt% at 65 wt% PA concentration to 49.6 wt% at 85 wt% PA concentration. The ChNCs were weakly charged, with a ζ-potential of ~  + 27 mV, owing to the inherent deacetylated N-acetyl groups. Overall, ultrasound-assisted PA processing provides an efficient and relatively environmentally-benign method for ChNC production.

Enzyme immobilization has emerged as one of the pivotal technologies in enzyme engineering, offering substantial cost reductions associated with enzyme isolation and utilization. However, efficient catalysis of solid substrates with solid immobilized enzymes remains a challenge, typically exemplified by the hydrolysis of cellulose using immobilized cellulase. In this study, a novel system of reversible release and recycling of cellulase on the surface of low-density polyethylene (LDPE) "hull" was developed, inspired by the operational dynamics of carrier-based aircraft. The reversible formation and disruption of multiple hydrogen bonds between the grafted gelatin molecular chain on the LDPE surface and the modification arm of cellulase (poly (methacrylic acid-propenoic acid; PAA-PMAA) can be achieved through temperature control, thus enabling the reversible release and recycling of modified cellulase molecules on the LDPE surface. Results demonstrated that the release of modified cellulase (PLANE) from the LDPE surface overcame the mass transfer barrier inherent in traditional immobilized enzyme systems for catalyzing insoluble substrates. This was attributed to the dissolution of PLANE in the developed system, rendering its hydrolysis of the insoluble cellulose substrate comparable to that of the free enzyme. Upon completion of the reaction, the PLANE could be reversibly recycled on the surface of the macroscopic LDPE membrane, facilitated by the regeneration of multiple hydrogen bonds. Furthermore, the facile removal of the membrane aided in the convenient recycling of cellulase. Notably, the cellulase molecules in the system retained more than 50% of their biological activity even after 8 batches of reuse, making the process cost-effective. This method addressed the limitations of traditional immobilized enzymes, allowing the catalysis of solid substrates with elevated mass transfer and simultaneous easy recovery, thus standing out as a universal immobilization method.

This paper investigates the production of hydrothermal responsive shape memory filaments with different draw ratios (0.8, 2.0 and 3.2) using microcrystalline cellulose (MCC) as a filler and shape memory polyurethane (SMPU) as a matrix. A mechanical-thermo-aqueous programming test was conducted to study the shape-memory properties of the microcomposite filaments. The effect of draw ratio and triggering temperature on mechanical, physical, thermal, morphological, and shape memory properties was thoroughly studied. Among the microcomposite filaments, SMPU-MCC with a draw ratio of 2.0 exhibited the highest tenacity value of 0.91 cN/dtex in its original shape with an elongation of 385.2%. The differential scanning calorimetry results showed that the glass transition temperature (T_g) of the filaments increased as the draw ratio increased from 0.8 to 3.2, ranging from 38.35 to 41.02 °C. The crystallinity percentages obtained for pure SMPU, SMPU-MCC-0.8, SMPU-MCC-2.0, and SMPU-MCC-3.2 were 27.10%, 30.68%, 38.72%, and 36.88%, respectively. In addition, an optimum draw ratio led to a degradation temperature rise from 372.5 to 391.3 °C which shows the thermal stability of the filaments was significantly influenced by the intermolecular bonding between MCC and SMPU, which intensified as the draw ratio increased from 0.8 to 2.0. Moreover, the filaments exhibited excellent mechanical and thermal properties in six cycles at the optimum draw ratio and triggering temperature indicating their future application for repeated use without experiencing major changes in shape memory properties.

Cellulose acetate (CA) is a semi-synthetic and biodegradable polymer that represents a fair alternative as a structural material for fused filament fabrication (FFF). With very few studies on the subject, the present work aims to broaden and deepen the understanding of FFF of CA with a degree of substitution of 1.7. A fine characterisation of the microstructure and mechanical properties of printed parts and the investigation of the effect of water on this hydrophilic polymer were pursued. Highly dense plasticised CA specimens with a porosity lower than 2% were successfully manufactured. Geometrical discrepancies between the designed and fabricated parts, together with the surface rugosity, inherent from this 3D printing technique, were carefully studied by X-ray microtomography. Ultimately, the printed samples showed no alteration of the intrinsic material’s composition, yield strength and tensile modulus, comforting the potential of FFF of CA-based parts for structural applications. In addition to the geometrical imperfections, the plasticising effect of water on CA was quantified as the elastic and yield properties were significantly decreased after water saturation, evidencing the need to account for the two effects when designing, storing and using FFF CA parts.

In the context of sustainable development, the escalating need for hazardous wastewater treatment underscores the importance of developing innovative cellulose adsorbents for pollutant removal and separation. This study introduces a novel aerogel composed of a vinyl-functional covalent organic framework (COFs) and cellulose nanofibrils synthesized via in situ growth of COFs on aminated cellulose nanofibers (ACNFs). The aerogel’s surface is enriched with active functional groups (hydroxyl, amino, aldehyde, benzene, etc.), enabling diverse physical and chemical interactions with pollutants. Furthermore, a simple post-modification strategy involving thiol-ene click reactions was employed to modify the surface vinyl groups, resulting in two new aerogels (ACNF/COF-COOH and ACNF/COF-SH) to enhance interactions with different aqueous pollutants, specifically by targeting the removal of cationic dyes such as methylene blue (MB) and heavy metals. ACNF/COF-COOH aerogel exhibited a maximum adsorption capacity of 563.0 mg/g for MB, while ACNF/COF-SH aerogel demonstrated high selectivity for heavy metal ion removal, with a mercury ion (Hg²⁺) distribution coefficient (K_d) of 22,782.0 mL/g. This novel cellulose-based aerogel offers significant potential for removing pollutants from water bodies.

Functional aerogels have attracted intensive attention due to their large specific surface area and light weight. In this study, liquid metal (LM) was uniformly dispersed into carboxymethyl cellulose nanofiber (CCNF) for fabricating sustainable CCNF/LM aerogel using a freeze-drying method. The as-fabricated CCNF/LM aerogel was characterized to understand its morphology, chemical components, crystal structure and surface structure, and the sound absorption together with thermal insulation of the aerogel were measured. The CCNF/LM aerogel exhibited good sound absorption, which can be attributed to the unique three-dimensional layered structure. Furthermore, the surface temperature of the CCNF/LM aerogel can be effectively decreased due to the heat absorption, reflection, and radiation of liquid metal. This work provides strategies in developing LM-aerogels toward application of in noise reduction and thermal insulation.

The need for natural fibers has increased in recent years due to more environmental consequences, which led to the exploration of novel biofibers. This research deals with extracting and characterizing fiber extracted from Cymbopogon nardus roots. The C. nardus root fibers were obtained from the roots of the C. nardus plant by manually retting. The C. nardus root fibers were analyzed for physio-chemical, morphological, thermal, crystalline, and mechanical properties. The test results elucidated that the cellulose contents of C. nardus root fibers were 65.67%, and the density was 1192 kg/m³, which was less than synthetic ones to prove its lightweight behavior. The crystallinity index of C. nardus Root fibers was 59.16%, demonstrating the extracted fiber’s higher-order crystal nature. Fourier Transform Infrared Spectroscopy proved the various crystalline and amorphous contents in the C. nardus root fibers. Scanning Electron Microscope elucidated the multiple features of the C. nardus root fibers, demonstrating its suitability as reinforcement for the composite to suit versatile, lightweight, medium-load applications.

The hypothesis was that low residual alkali after cooking would cause lignin re-precipitation during washing and in turn affect the subsequent oxygen delignification stage negatively. To test the hypothesis, kraft cooks were performed in lab-scale to different residual alkali levels, ranging from 5 to 15 g/L and the pulps were subjected to washing with either water or 0.1 M NaOH and then oxygen delignified. The results show that even at low residual alkali and washing with water, the pH in the liquor after washing was above 11 which is sufficiently high to keep lignin in solution. No effect of residual alkali level was observed on the performance of the oxygen delignification stage.

Over the last years, the potential of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) as fillers in polymers for mechanical reinforcement and extending the operation lifespan of materials is highlighted. Here, we investigate the inclusion of CNCs and CNFs with two distinct functional groups (TEMPO-oxidized, or solely having hydroxyl groups) as nanofillers into cellulose acetate films. Solution blow spinning has been utilized as a novel approach to fabricate composite materials from renewable carbon feedstocks, and the resulting structural, morphological and mechanical properties were evaluated. A maximum concentration of 5 wt% was found for CNCs while this was lower for CNFs, 2.5 wt%, to achieve uninterrupted processing of composite materials via SBS. All-cellulose composites showed differences in morphological features depending on the nanofiller type. Interestingly, a low loading of CNCs (1.5 wt%) increases the strength at break by 30%, while the inclusion of CNFs in a same amount deteriorates the mechanical properties. However, further increase to 2.5 wt% CNFs provides enhanced tensile strength and elastic modulus values. The largest improvements in elongation at break and strength at break is achieved with the inclusion of 2.5 wt% TEMPO-oxidized cellulose nanofibrils. Microscopic analysis after fracture reveals coral-like structured films,  providing a unique mechanical behavior. Overall, the results point out that TEMPO-oxidized CNFs are efficient reinforcements to fabricate renewable carbon-containing composite materials with improved mechanical performance. The proposed SBS processing offers a unique advantage in the fabrication of highly flexible cellulose-based films, eliminating the need for plasticizers or additional additives.

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