Effects of coagulating conditions on the crystallinity, orientation and mechanical properties of regenerated cellulose fibers

Tailoring Polyamide66 Mechanical Performance: A Strategy for Condensed Phase Structure Optimization Through Hydrogen Bond Reorganization

Polymers are widely used in various industries due to their unique properties, but their mechanical strength often falls short compared to other materials. This has spurred extensive research into enhancing their mechanical performance through condensed phase structure regulation. This study investigates the enhancement of mechanical properties in polyamide 66 (PA66) through the introduction of arylamide-based materials (TMB-5) during the melt-spinning process. TMB-5, possessing amide groups like PA66, can reorganize intermolecular hydrogen bonds within PA66, thereby facilitating molecular movement and reducing chain entanglement during fiber formation. Consequently, the synergistic effect of TMB-5 and the stretching field leads to enhanced crystallization and molecular and lamellae orientation in PA66 fibers without post-drawing, resulting in a significant increase in tensile strength and modulus. This work not only offers a novel strategy for adjusting polymer mechanical performance but also sheds light on the importance of molecular interactions in governing polymer properties.

Properties, Production, and Recycling of Regenerated Cellulose Fibers: Special Medical Applications

Regenerated cellulose fibers are a highly adaptable biomaterial with numerous medical applications owing to their inherent biocompatibility, biodegradability, and robust mechanical properties. In the domain of wound care, regenerated cellulose fibers facilitate a moist environment conducive to healing, minimize infection risk, and adapt to wound topographies, making it ideal for different types of dressings. In tissue engineering, cellulose scaffolds provide a matrix for cell attachment and proliferation, supporting the development of artificial skin, cartilage, and other tissues. Furthermore, regenerated cellulose fibers, used as absorbable sutures, degrade within the body, eliminating the need for removal and proving advantageous for internal suturing. The medical textile industry relies heavily on regenerated cellulose fibers because of their unique properties that make them suitable for various applications, including wound care, surgical garments, and diagnostic materials. Regenerated cellulose fibers are produced by dissolving cellulose from natural sources and reconstituting it into fiber form, which can be customized for specific medical uses. This paper will explore the various types, properties, and applications of regenerated cellulose fibers in medical contexts, alongside an examination of its manufacturing processes and technologies, as well as associated challenges.

Continuously enhanced versatile nanocellulose films enabled by sustaining CO2 capture and in-situ calcification

Cellulose possesses numerous favorable peculiarities to replace petroleum-based materials. Nevertheless, the extremely high hygroscopicity of cellulose severely degrades their mechanical performance, which is a major obstacle to the production of high-strength, multi-functional cellulose-based materials. In this work, a simple strategy was proposed to fabricate durable versatile nanocellulose films based on sustaining CO2 capture and in-situ calcification. In this strategy, Ca(OH)2 was in-situ formed on the films by Ca2+ crosslinking and subsequent introduction of OH-, which endowed the films with high mechanical strength and carbon sequestration ability. The following CO2 absorption process continuously improved the water resistance and durability of the films, and enabled them to maintain excellent mechanical properties and promising light management ability. After a 30-day CO2 absorption process, the water contact angle of the films can be increased from 43° to 79°, and the weight gain rate of the films in a 30 h water-absorption process can be sharply decreased from 331.2 % to 52.2 %. The films could maintain a high tensile strength of 340 MPa, and result in a CO2 absorption rate of 3.5 mmol/gcellulose after 30 days. In this study, the improvement of durability and carbon sequestration of nanocellulose films was achieved by a simple and effective method.

Preparation of chitin twisted fiber and its functional applications

Chitin has garnered significant attention due to its renewable, biocompatibility and biodegradability, while its practical application seriously hindered as the functionality of chitin itself can no longer meet people's increasing requirements for materials. Here, an effective method is successfully built for high-performance chitin fibers fabrication through a multi-step strategy that involved chemical pre-crosslinking, followed by wet-twisting and wet-stretching techniques, combined with physical cross-linking. The as-prepared chitin fiber exhibited a smooth surface, adjustable diameter, and mechanical strong properties (144.6 MPa). More importantly, functional chitin fiber with magnetic or conductive abilities can be easily obtained by spraying Fe3O4 particles or Ag nanowire on the chemical pre-crosslinking chitin gel film before stretching and twisting. The doped functional inorganic particles exist in a continuous ribbon structure in the fiber reduced the decrease in material strength caused by uneven particles dispersion, resulting 88.4 % of stress and 91.6 % of strain retention. This work not only bestow invaluable insights into the fabrication of functional chitin fibers but also provide a novel approach to solve the problem of poor compatibility between organic and inorganic composite materials.

High tensile regenerated cellulose fibers via cyclic freeze-thawing enabled dissolution in phosphoric acid for textile-to-textile recycling of waste cotton fabrics

Recycling of waste cotton fabrics (WCFs) is a desirable solution to address the problems brought up by fast fashion, but it remains challenging due to inherent limitations in preparing stable and spinnable dopes by dissolving high molecular weight cellulose efficiently and cost effectively. Herein, we show that despite the prevailing concerns of cellulose degradation via glycosidic hydrolysis when dissolved in acids, fast and non-destructive direct dissolution of WCFs in aqueous phosphoric acid (a.q. PA) could be realized using a cyclic freeze-thawing procedure, which combined with subsequent adjustment of degree of polymerization (DP) and degassing yielded stable and spinnable dopes. Regenerated cellulose fibers (RCFs) with favorable tensile strength (414.2 ± 14.3 MPa) and flexibility (15.4 ± 1.5 %) could be obtained by carefully adjusting the coagulation conditions to induce oriented and compact packing of the cellulose chains. The method was shown to be conveniently extended to dissolve reactively dyed WCFs, showing great potential as a cheap and green alternative to heavily explored ionic liquids (ILs) and N-methylmorpholine-N-oxide (NMMO)-based systems for textile-to-textile recycling of WCFs.

"Bottom-up" and "top-down" strategies toward strong cellulose-based materials

Cellulose, as the most abundant natural polymer on Earth, has long captured researchers' attention due to its high strength and modulus. Nevertheless, transferring its exceptional mechanical properties to macroscopic 2D and 3D materials poses numerous challenges. This review provides an overview of the research progress in the development of strong cellulose-based materials using both the "bottom-up" and "top-down" approaches. In the "bottom-up" strategy, various forms of regenerated cellulose-based materials and nanocellulose-based high-strength materials assembled by different methods are discussed. Under the "top-down" approach, the focus is on the development of reinforced cellulose-based materials derived from wood, bamboo, rattan and straw. Furthermore, a brief overview of the potential applications fordifferent types of strong cellulose-based materials is given, followed by a concise discussion on future directions.

Structuring restricted amorphous molecular chains in the reinforced cellulose film by uniaxial stretching

The construction of the preferred orientation structure by stretching is an efficient strategy to fabricate high-performance cellulose film and it is still an open issue whether crystalline structure or amorphous molecular chain is the key factor in determining the enhanced mechanical performance. Herein, uniaxial stretching with constant width followed by drying in a stretching state was carried out to cellulose hydrogels with physical and chemical double cross-linking networks, achieving high-performance regenerated cellulose films (RCFs) with an impressive tensile strength of 154.5 MPa and an elastic modulus of 5.4 GPa. The hierarchical structure of RCFs during uniaxial stretching and drying was systematically characterized from micro- to nanoscale, including microscopic morphology, crystalline structure as well as relaxation behavior at a molecular level. The two-dimensional correlation spectra of dynamic mechanical analysis and Havriliak-Negami fitting results verified that the enhanced mechanical properties of RCFs were mainly attributed to the stretch-induced tight packing and restricted relaxation of amorphous molecular chains. The new insight concerning the contribution of molecular chains in the amorphous region to the enhancement of mechanical performance for RCFs is expected to provide valuable guidance for designing and fabricating high-performance eco-friendly cellulose-based films.

Asymmetric ionic bond shielding encountering with carboxylate capturing metal ions for enhancing the flame retardant durability of regenerated cellulose fibers

Enhancing the flame retardancy and durability of cellulose fibers, particularly environmentally friendly regenerated cellulose fibers types like Lyocell fibers, is essential for advancing their broader application. This study introduced a novel approach to address this challenge. Cationic-modified Lyocell fibers (Lyocell@CAT) were prepared by introducing quaternary ammonium structures into the molecular chain of Lyocell fibers. Simultaneously, a flame retardant, APA, containing -COO-NH4+ and -P=O(O-NH4+)2 groups was synthesized. APA was then covalently bonded to Lyocell@CAT to prepare Lyocell@CAT@APA. Even after undergoing 30 laundering cycles (LCs), Lyocell@CAT@APA maintained a LOI value of 37.2 %, exhibiting outstanding flame retardant durability. The quaternary ammonium structure within Lyocell@CAT@APA formed asymmetric ionic bonds with the phosphate and carboxylate groups in APA, effectively shielding the binding of Na+ ions with phosphate groups during laundering, thereby enhancing the durability. Additionally, the consumption of Na+ ions by carboxylate groups further prevented their binding to phosphate groups, which contributed to enhance the durability properties. Flame retardant mechanism analysis revealed that both gas and condensed phase synergistically endowed excellent flame retardancy to Lyocell fibers. Overall, this innovative strategy presented a promising prospect for developing bio-safe, durable, and flame retardant cellulose textiles.

Preparation of Antibacterial Biobased Fibers by Triaxial Microfluidic Spinning Technology Using Ionic Liquids as the Solvents

Bacterial infections have become a serious threat to public health. The utilization of antibacterial textiles offers an effective way to combat bacterial infections at the source, instead of relying solely on antibiotic consumption. Herein, efficient and durable antibacterial fibers based on quercetin and cellulose were prepared by a triaxial microfluidic spinning technology using ionic liquids (ILs) as the solvents. It was indicated that the structure and properties of the antibacterial fibers were affected by the type of IL and the flow rates during the triaxial microfluidic spinning process. Quercetin regenerated from [Emim]Ac underwent structural transformation and obtained an increased water solubility, while quercetin regenerated from [Emim]DEP remained unchanged, which was proven by FI-IR, XRD, and UV analyses. Furthermore, antibacterial fibers regenerated from [Emim]Ac exhibited the highest antibacterial activity of 96.9% against S. aureus, achieved by reducing the inner-to-outer flow rate ratio to 0 and concentrating quercetin at the center of fibers. On the other hand, when [Emim]DEP was used as the solvent, balancing the inner-to-outer flow rate ratio to concentrate quercetin in the middle layer of the fiber was optimal for achieving the best antibacterial activity of 93.3% because it promised both the higher encapsulation efficiency and release rate. Computational fluid dynamics (CFD) mathematically predicted the solvent exchange process during triaxial spinning, explaining the influence of IL types and flow rates on quercetin distribution and encapsulation efficiency. It was indicated that optimizing the distribution of antibacterial agents within the fibers can fully unleash its antibacterial potential while preserving the mechanical properties of the fiber. Therefore, the proposed simple triaxial spinning strategy provides valuable insights into the design of biomedical materials.

Chitosan-modified cotton fiber: An efficient and reusable adsorbent in removal of harmful cyanobacteria, Microcystis aeruginosa from aqueous phases

In the present study, to remove harmful cyanobacterial species Microcystis aeruginosa from aqueous phases, adsorption-based strategy was utilized. For this strategy, the surface of cotton fiber was modified using chitosan molecules to develop a highly efficient and ecofriendly adsorbent in removal of Microcystis aeruginosa from aqueous solution. The pristine cotton fiber could not remove M. aeruginosa, while the chitosan-modified cotton (CS-m-Cotton) showed the 95% of cell removal efficiency within 12 h. The surface characteristics of chitosan-modified cotton compared to the pristine cotton fiber was examined by various surface analysis methods. In addition, the pre-treatment of pristine cotton using sodium hydroxide solution was an important factor for enhancement of chitosan modification efficiency on the cotton fiber. The developed chitosan-modified cotton fiber could be reusable for M. aeruginosa cell removal after the simple desorption treatment using ultrasonication in alkaline solution. During the repeated adsorbent regeneration and reuse, the chitosan-modified cotton maintained its M. aeruginosa removal efficiencies (>90%). From the acute toxicity assessment using the chitosan-modified cotton and, the measurements of chemical oxygen demand and microcystin level changes in the M. aeruginosa treatment process using the adsorbent, the environmental safety of the adsorption strategy using the developed adsorbent could be confirmed. Based on our results, the chitosan-modified cotton fiber could be proposed as an efficient and ecofriendly solution for remediation of harmful cyanobacterial species occurring water resources.

Structure and properties variations of regenerated cellulose fibers induced by metal ion impurity

In the ionic liquids (ILs) method for processing regenerated cellulose fiber (RCF), which is a high-performance ecologically benign product, metal ion impurities (such as Fe3+ and Cu2+) of cellulose might inevitably remain in the recycled ILs and coagulation bath. The presence of metal ions might negatively impact the properties of the manufactured RCFs and obstruct their applications, which are urgent to be made clear. For this research, the solvent for dissolving wood pulp cellulose (WPC) was 1-ethyl-3-methylimidazolium diethyl phosphate ([Emim]DEP) with various metal ion concentrations. The effect of metal ions in IL on the dissolution of cellulose was investigated by Molecular Dynamics simulations. Rheological analysis and degree of polymerization (DP) analysis were adopted to evaluate the influence on fiber spinnability of different spinning solution metal ion concentrations and various dissolving times. Further, the morphology and mechanical performances of the RCFs variation regulation were also thoroughly researched. The findings showed that the presence of metal ions in the spinning solution affected the DP, crystallinity, and orientation factor of RCFs, which will influence their stress more sensitively than the strain. These findings can serve as a practical guide for the commercial manufacture of emerging fiber.

Cellulose dissolution and regeneration behavior via DBU-levulinic acid solvents

Most organic solvents are unable to dissolve carbohydrates due to the lack of hydrogen bonding ability. The development of solvent systems for dissolving cellulose is of great importance for its utilization and conversion. In this study, four new cellulose solvents were designed using inexpensive levulinic acid (LevA) and 1,8-diazabicyclo [5,4,0] undec-7-ene (DBU) as raw materials. The results showed that the prepared DBU-LevA-2 solvent was able to dissolve up to 7 wt% of bamboo cellulose (DP = 860) and 16 wt% of microcrystalline cellulose (DP = 280) at 100 °C and regenerated without derivatization. Also, the molar ratio of each component of this solvent has a significant effect on the dissolution properties of cellulose. The regenerated cellulose had the typical crystalline characteristics of cellulose II. Subsequently, the interactions and microscopic behaviors of solvent and cellulose during the dissolution process were thoroughly investigated by using NMR spectroscopy combined with density functional theory. The systematic study showed that the hydrogen bond-forming ability provided by DBU, a superbase, plays an indispensable role in the overall solvent system.

Bioinspired Thermochromic Textile Based on Robust Cellulose Aerogel Fiber for Self-Adaptive Thermal Management and Dynamic Labels

Aerogel fiber has emerged recently for incorporation in personal thermal management textiles due to its flexibility, scalability, and ultrahigh porosity, which allows the body to keep warm via thermal isolation without energy consumption. However, the functionalization and intellectualization of cellulose-based aerogel fibers have not yet been fully developed. Herein, we propose a biomimicking design inspired by polar bear and Siamese cat hair that combines porous cellulose aerogel fiber (CAF) with reversible thermochromic microcapsules to mimic biological sensory and adaptive thermoregulation functions. The produced CAF has a controllable pore structure, a large specific surface area (230 m2/g), and excellent mechanical strength (∼15 MPa). Low-temperature darkening microcapsules have been incorporated into the robust CAF to spontaneously adjust color by perceiving the ambient temperature. The functional aerogel fiber fabric achieves high thermal insulation and photothermal modulation simultaneously at temperatures below 18 °C. The temperature of the thermochromic fabric was higher by 6 °C than that of the sample without the microcapsules at a light intensity of 0.2 W/cm2. In addition, the aerogel fibers mixed with two types of thermochromic microcapsules exhibit three color switches with fast response, a color-control precision of 0.2 °C, and good cycling performance. This smart aerogel fibers hold great promise for self-adaptive thermal management, temperature indication, information transfer, and anticounterfeiting in textiles.

Recent Advances in Cellulose-Based Hydrogels Prepared by Ionic Liquid-Based Processes

This review summarizes the recent advances in preparing cellulose hydrogels via ionic liquid-based processes and the applications of regenerated cellulose hydrogels/iongels in electrochemical materials, separation membranes, and 3D printing bioinks. Cellulose is the most abundant natural polymer, which has attracted great attention due to the demand for eco-friendly and sustainable materials. The sustainability of cellulose products also depends on the selection of the dissolution solvent. The current state of knowledge in cellulose preparation, performed by directly dissolving in ionic liquids and then regenerating in antisolvents, as described in this review, provides innovative ideas from the new findings presented in recent research papers and with the perspective of the current challenges.

Eco-friendly materials knitting by different yarn ply for high-performance garments

Purpose

Synthetic materials have many drawbacks in high-performance garments because they absorb less moisture and cause allergies to sensitive individuals. Cotton materials cannot satisfy all the requirements and cannot provide the required high performance. This study aims to use eco-friendly materials with a common structure to analyse their suitability for high-performance garment application.

Design/methodology/approach

This study used two eco-friendly yarns (bamboo, modal and bamboo: modal 50:50) and yarns per needle (two- and four-ply yarns). with a single jersey knit construction and gauge of 7. The physical, mechanical, appearance, comfort, thermal and ultraviolet protection factor (UPF) protection characteristics were evaluated using 15 tests.

Findings

The produced knitted fabrics showed high performance for use as garments with physical, mechanical, appearance, comfort, thermal and UPF protection characteristics that were achieved, tested and analysed. The highest-achieved samples with a good UPF (<15) were made from bamboo material, which has other high-performance characteristics such as antibacterial characteristics, a soft surface, thermal insulation and others.

Research limitations/implications

The single jersey structure was used for producing fabrics as it is the common structure in the garment. Also, only gauge 7 was used for its economics and ease of production.

Effects of Glucose and Coagulant on the Structure and Properties of Regenerated Cellulose Fibers

Regenerated cellulose fiber (RCF) is an environmentally friendly material with outstanding mechanical properties and recyclability, which has been used in a large number of applications. However, during the spinning process using ionic liquids (ILs) as solvents, the dissolved cellulose continues to degrade and even produces degradation products such as glucose, which can enter the recycled solvent and coagulation bath. The presence of glucose can seriously affect the performance of the produced RCFs and hinder their applications, so it has become critical to clarify the regulation and mechanism of this process. In this study, 1-ethyl-3-methylimidazolium diethyl phosphate ([Emim]DEP) with different glucose contents was selected to dissolve wood pulp cellulose (WPC) and obtained RCFs in different coagulation baths. The effect of glucose content in spinning solution on fiber spinnability was investigated by rheological analysis, and the influence of coagulation bath composition and glucose content on the morphological characteristics and mechanical properties of the RCFs was also studied in depth. The results indicated that the morphology, crystallinity, and orientation factor of RCFs were influenced by the presence of glucose in the spinning solution or coagulation bath, resulting in corresponding changes in mechanical properties, which can provide practical reference and guidance for the industrial production of new type fiber.