Fibers, Volume 12, Issue 3 (March 2024) – 11 articles

The use of bacterial cellulose (BC), having high purity, a high degree of crystallinity, water-holding capacity, tensile strength and adaptability on a broad scale is limited because of the low yield. In this study, the optimal conditions for bio-cellulose production by Komagataeibacter rhaeticus K23 were investigated. Optimal values for temperature, pH, inoculum concentration and incubation time were determined via Taguchi design. The maximum BC production, 9.1 ± 0.66 g·L⁻¹ (dry weight), was obtained from 32 °C, pH 5.5, 8 log CFU·mL⁻¹ and 14 days of incubation. The inoculum concentration was the most significant factor affecting BC yield. A value of 8 log CFU·mL⁻¹ and 14 days of incubation led to significantly higher levels of BC yield than other concentrations (8.5, 9, 9.5, 10 and 10.5 log CFU·mL⁻¹) (p < 0.002) and days (15, 16, 17, 21 and 28) (p < 0.001). The studied features, namely absorption peaks (Fourier transform infrared spectroscopy), pattern and the crystallinity index (X-ray diffraction analysis) of the BC obtained in this study were all in parallel with the characteristics of cellulose I. The study demonstrates that optimized parameters were effective in producing BC with high water-holding capacity, tensile strength, elongation and Young’s modulus (mechanical tests) by K. rhaeticus K23. Full article

The interest and thus the number of publications on the supply chains of bast fiber plants has steadily increased in recent years. A number of specific technical terms related to methods and their use for individual areas of the supply chain are often interpreted and used in very different ways. Therefore, the aim of this publication is to increase the clarity of the description of the operations and to improve the understanding of the sequence and the purpose of the process steps. This is based on a selected review of the relevant literature as well as on suggestions for their classification Full article

Carbon nanofibers based on lignin from wood waste have a promising potential for the ability to produce electrodes that can modernize existing energy storage technology. The most important detail is that the low cost, as well as the availability of the initial products for the production of lignin, will reduce the cost of energy storage devices and contribute to improving the environment. In this study, pine sawdust and elm sawdust were used as raw materials for the production of lignin, which accumulate in large quantities in metal workshops in Almaty. Lignin extraction was carried out using an organosolvent method, which is environmentally friendly, low-cost, uses minimal amounts of strong acids and metal catalysts, does not pollute water, and does not emit sulfur dioxide (SO₂). A comprehensive study of the characteristics of the obtained lignins from wood waste was carried out. Infrared spectroscopy (IR) revealed that the obtained lignin contains aromatic, phenolic, hydroxyl, methyl, and methoxyl groups. The results of nuclear magnetic resonance (NMR) spectroscopy showed the presence of a high number of syringyl (S) links compared to guaiacyl (G), which contribute to increased efficiency in the thermal processing of lignin. Also, this study investigated the use of the obtained lignins to produce continuous fibers by electrospinning. The effect of lignin mass on the viscosity of the lignin/polyacrylonitrile (PAN) solution and the effect of the carbonization temperature on the physico-chemical characteristics of the lignin/PAN solution were investigated. The following research methods were used for this purpose: Raman spectroscopy, thermogravimetric analysis (TGA), electron scanning microscopy, energy dispersion analysis, IR, NMR, and optical microscopy. The conditions for the production of lignin-containing carbon fibers at temperatures of 800, 900, and the carbonation heating rate, is an important parameter in the production of carbon fibers as it strongly affects the characteristics of the resulting carbon fibers. The heating rate affects were studied, and it was found that, at a heating rate of 5 °C/min and a carbonation temperature of 800 °C, porous carbon nanofibers with a diameter of 47 nm are formed in a nitrogen medium for 60 min. Full article

This review is focused on the recent development of various chitosan-based nanofibers (membranes, patches, mats, and scaffolds) that have been designed into core and shell structures using emulsion and coaxial electrospinning techniques. Chitosan, a promising polysaccharide derived from natural sources, holds potential for diverse applications, including nanofiber production, aimed at fostering sustainability. Core/shell chitosan-based nanofibers offer appealing features, including drug encapsulation and sustained release capabilities, with a higher efficiency than uniaxial fibers. The fabrication of core/shell chitosan-based nanofibers, including the co-spinning agents and various spinning parameters, such as spinning voltage, needle size, spinning flow rate, distance from needle tip to collector, temperature, and humidity, is summarized in this work. The review also explores updated applications in various fields, such as textiles, medical dressings, drug release systems, filtration membranes, and food packaging. It highlights the current advancements in core/shell chitosan-based nanofibers produced via electrospinning techniques. The innovative insights presented in the recent literature and the challenges associated with these sustainable materials are thoroughly examined, offering valuable contributions to the field. Full article

Mid-IR fiber lasers operating at wavelengths near 5 μm are of great interest for many fundamental and industrial applications, but only a few experimental samples based on active chalcogenide fibers have been demonstrated so far. One of the limitations of the power of such lasers may be a fairly low fiber damage threshold. To solve this problem, we developed and numerically investigated in detail a mid-IR fiber laser at 5.3 µm with multi-W output power pumped into the cladding at a wavelength of 2 µm. We proposed using a Tb-doped chalcogenide multicore fiber with 25 single-mode cores arranged in a 5 × 5 square lattice as an active medium. The proposed laser design surpasses the power limit of single-core chalcogenide fibers. When simulating lasers, we specified realistic parameters of Tb-doped chalcogenide glass based on published experimental data. We performed a comprehensive theoretical analysis, studied the influence of various factors on the characteristics of generation, and found optimal system parameters and expected generation parameters. Full article

The quantity of different plastics generated after consumption is an impact factor affecting the environment, and the lack of recycling generates solid waste. The purpose of this work is to incorporate high-density recycled polyethylene fibers (HDPE) for possible use as concrete reinforcement. Physical and mechanical properties from recycled fibers were analyzed, such as density, absorption, and stress resistance, as well as workability, air content, porosity, concrete compression, and flexural strength properties. Samples were prepared with a low fiber content of 0.2% and 0.4%, as a substitution for sand weight, and lengths of 10 and 30 mm. To study corrosion phenomena, the specimens were exposed to a saline environment containing 3% sodium chloride for 365 days, and the electrochemical techniques including half-cell potential (HCP), electrochemical noise (EN), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were applied. The results showed a 4.8% increase in compressive strength with a low fiber percentage and short geometries, while flexural strength increased marginally by 2.3% with small quantities of HDPE fibers. All these factors contribute to greater material durability, less permeability, and crack control. A positive effect of fibers with short dimensions on the corrosion processes of a steel bar was observed, with the fibers acting as a physical barrier against the diffusion of chloride ions. Full article

To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally investigate the impacts of the prestress level and damage in the shear zone on the shear reinforcement effect and analyze the reinforcement mechanism of CFRP tendons. The results show that in the beams reinforced with CFRP, the CFRP tendons could work collaboratively with the stirrups to reduce the strain on the stirrups; the increasing rate in the yield load was 28–70%. After the stirrups yielded, the CFRP tendons did not yet reach their ultimate tensile strength and could still withstand increased shear forces, resulting in an increasing rate of the ultimate load for the reinforced beams with a CFRP content of 56–78%. The enhancements in both the yield load and the ultimate load were positively correlated with the level of prestress in the CFRP tendons. This reinforcement technique efficiently restricts the growth and delays the first appearance of diagonal cracks. The prestress can close the pre-existing diagonal cracks and provide a reserve of shear capacity for the beams. The initial damage in the shear zone decreases the initial shear stiffness and increases the width of the initial diagonal cracks. However, this effect gradually diminishes as the load increases and does not significantly impact the shear capacity. Prestressing can significantly improve the strength utilization rate of the CFRP reinforcement when the reinforced beams fail. The deformation of the CFRP tendon is directly related to the shear deformation. By combining this relationship with the truss–arch model, the shear capacity for the reinforced beam can be predicted. The predicted results exhibit an error of less than 10% when compared to the test results, offering valuable design guidance for reinforced engineering composites. Full article

Analyzing the feasibility of reinforcing new and existing wooden structures is a valid problem, being the subject of numerous scientific papers. The paper presents the preliminary results of a study on reinforcing Laminated Veneer Lumber (LVL) panels with composite materials bonded to exterior surfaces using epoxy resin. Glass-Fiber-Reinforced Polymer (GFRP) sheets, Carbon-Fiber-Reinforced Polymer (CFRP) sheets, and Ultra-High-Modulus (UHM) CFRP sheets were used as reinforcement. The variables in the analysis were the type of reinforcement and the number of reinforcement layers. The tests were carried out on small samples (45 × 45 × 900 mm) subjected to the so-called four-point bending test. Reinforcement positively affected the mechanical properties of composite section. The highest increases in load bearing were 37 and 48% for two layers of GFRP and CFRP, respectively. The bending stiffness increased up to 53 and 62% for two layers of CFRP and UHM CFRP, respectively. There was a change in failure mode from cracking in the tension zone for unreinforced beams to veneer shear in the support zone (for CFRP and GFRP sheets) and sheet rupture (UHM CFRP). Good agreement was obtained for estimating bending stiffness with the presented numerical and mathematical model; the relative error was up to 6% for CFRP and GFRP and up to 20% for UHM CFRP. This preliminary study proved the effectiveness of combining LVL with FRP sheets and indicated their weak spots, which should be further analyzed to improve their competitiveness against the traditional structures. The key limitation was the shear strength of LVL. Full article

Biofibres’ wide application in mortar enhancement has thus far been restricted by factors related to their chemical composition and hygroscopic nature. Their hydrophilic behaviour increases the water demand of mortar mixtures and diminishes their affinity to the matrix, while further moisture-related fibre degradation issues may arise. Additionally, natural fibres seem to be susceptible to degradation caused by exposure to alkaline environmental conditions such as those experienced by cement mortars, restricting their utilisation in the construction industry. Therefore, the current study investigates the potential of fibre modification through treatments that would permanently alter their structure and chemical composition to improve their performance. In this study, wood fibres of black pine and beech species were exposed to mild thermal treatment (140 °C 2 h, under a steam atmosphere), characterised in terms of the physical and chemical properties and incorporated in cement mortars, applying the proportion of 1.5% v/v in the mortar, in order to assess their performance as reinforcement material. The mortars’ workability (at a fresh state) was examined, as well as other physical, hygroscopic, thermal, and mechanical characteristics of the mortars at the ages of 28, 90 and 365 days and weathering performance, by subjecting them to different artificial ageing environments (freeze–thaw cycles or outdoor exposure). The results revealed the beneficial role of the treated fibres in dimensional stability, flexural strength, thermal insulation properties and capillary absorption of the mortar specimens, especially during the ageing process, with the black pine fibres showing the greatest improvement. The hydrothermally treated wood fibres seem to help maintain the integrity of cement mortars under all ageing conditions, proving that they could provide low-cost and eco-friendly mortar enhancement pathways. Full article

Double-layered textile sweat-absorbing underarm pads with a natural antimicrobial treatment can be used to solve the problem of the wetness sensation in the case of increased physical activity or hyperhidrosis. In addition, changeable antimicrobial active underarm pads help to decrease the number of clothing washings, i.e., reducing water consumption and pollution. Another aspect of sustainability is that the underarm pads can be produced from clothing production waste. The moisture absorption capability of six hydrophilic cellulose-based knitted fabrics and two hydrophobic synthetic woven fabrics was investigated. It was found that the best result for next-to-skin moisture absorption and next-to-clothing protection against moisture penetration was achieved by using a double-layered underarm pad composed of a cotton-based fleece knitted structure in the next-to-skin layer and a very thin and tight 100% PA woven fabric in the outer layer. Four samples of impregnated liquid with herbal extracts and essential oils were prepared, and antimicrobial activity was evaluated using the discus method. Textile impregnated with tea tree essential oil, nutmeg, and birch extracts had the highest antimicrobial activity against Gram-positive bacteria—Staphylococcus aureus, Staphylococcus epidermidis, and Bacillus cereus. Full article

Magnetic nanofibers were prepared by electrospinning polymer/metal solutions of poly(acrylonitrile) (PAN) with magnetite (Fe₃O₄) nanoparticles. At a mass ratio of PAN:magnetite of 2:1, the total solid content in the dimethyl sulfoxide (DMSO) solution was varied between 15 wt.% and 25 wt.%, which represents the limits of the spinnable range. The results show that the most homogeneous nanofiber mats were 21 wt.% solid contents. At 15 wt.% solid contents, a nano-membrane with some fibrous regions was produced. Nanofibers at 25 wt.% had a much larger and more inhomogeneous diameter. Nevertheless, the magnetic properties of all samples were very similar, indicating that the distribution of magnetite nanoparticles in the fibers is comparable in all samples. The results also suggested that the samples spun from solutions with near-ideal solid contents (19–21 wt.%) contain agglomerations of the nanoparticles inside the nanofibers. Full article