Fibers, Volume 11, Issue 12 (December 2023) – 12 articles

Increasing amounts of waste resulting from over-consumption carry substantial risks for human and environmental health, and disposing of this waste requires enormous amounts of energy. As a result, waste-to-wealth and circular economy approaches have gained attention in both academia and the commercial sector in recent years. Accordingly, this study aims to develop electromagnetic shielding materials by converting non-conductive waste textiles into conductive value-added product and porous fabrics by carbonizing the structure itself rather than by adding any conductive particles. To this end, the novel contribution of the present study is that waste textiles were converted into activated carbon in a shorter time and without compromising the integrity of the fibrous network via microwave pyrolysis without inert gas. Sulfuric acid was used as a dehydration and activation agent, suppressing the release of volatile organic substances and eliminating greenhouse gas emissions. This approach also increased product yield and reduced energy consumption and sample shrinkage. The structures of the activated carbon textile showed EMI shielding within 20–30 dB (99.9% attenuation) in the 1–6 GHz frequency range. The maximum SSE/t value of 950.71 dB·cm²·g⁻¹ was obtained with the microwave post-treated activated carbon textile. Micropores were dominant characteristics of these materials, and pore diameters increased with increased acid concentration. The maximum surface area of 383.92 m²/g was obtained with 8% acid. Ultrasound treatment reduced water-energy consumption and cost. Only 5 min of microwave post-treatment increased textile conductivity and thermal stability and contributed positively to electromagnetic shielding. Full article

The 3D printing process is different from traditional construction methods of formwork casting due to the use of additive manufacturing. This study develops a suitable 3D-printed carbon fiber-reinforced cement mortar (CFRCM) considering the extrudability, fluidity, setting time, and buildability of the CFRCM. The difference in compressive strength and flexural strength between 3D-printed specimens and conventional cast specimens was investigated by varying the amount of carbon fiber added (carbon fiber to cement ratio, 2.5 vol.‰, 5 vol.‰, 7.5 vol.‰, and 10 vol.‰) and the curing times (7th day and 28th day). The results of the experiments indicate that the addition of 6 wt.% cement accelerators to the cementitious mortar allows for a controlled initial setting time of approximately half an hour. The fluidity of the CFRCM was controlled by adjusting the dosage of the superplasticizer. When the slump was in the range of 150 mm to 190 mm, the carbon fiber to cement ratio 2.5 vol.‰ could be incorporated into the cementitious mortar, enabling the printing of hollow cylinders with a height of up to 750 mm. Comparing the 3D-printed specimens with the traditionally cast specimens, it was found that the addition of a carbon fiber to cement ratio of 7.5 vol.‰, and 10 vol.‰ resulted in the optimal compressive strength and flexural strength, respectively. Full article

The potential for sustainable lignocellulosic agro-waste is immense, owing to the fact that it represents the most abundant organic compound on Earth. It is a valuable and desirable source for material production across numerous industries due to its abundance, renewability, and biodegradability. This paper explores the world of barley fibers, which are extracted from the straw of two different cultivars (old Rex or new Barun) and have tremendous potential for use, primarily for technical textiles. The quantity of the extracted fibers depends both on the type of barley used and on climate conditions that influence the plants’ growth, resulting in fiber yields ranging from 14.82% to 19.59%. The chemical composition of isolated fibers revealed an optimal content of cellulose and lignin in barley fibers isolated from the Rex variety. Those results were confirmed with FTIR analysis, which revealed a lower intensity of peaks associated with hemicellulose and lignin and, therefore, indicated their better removal after the chemical maceration process. In terms of fiber density, the quality of the fibers was comparable to that of cotton fibers, but they differed significantly in moisture regain (10.37–11.01%), which was higher. Furthermore, sufficient fiber tenacity (20.31–23.08 cN/tex) was obtained in a case of old-variety Rex, indicating the possibility of spinning those fibers into yarns, followed by their extended usage for apparel. Additionally, our paper reveals the possibility of fulfilling the requirements of the zero waste principle due to the fact that a high percentage of solid waste left after the fiber extraction (26.3–32.3%) was afterwards successfully used for the production of biofuels, enabling the closing of the loop in a circular economy. Full article

Easy maintenance and high durability are expected in structures made with fiber-reinforced cementitious composite (FRCC) reinforced with fiber-reinforced polymer (FRP) bars. In this study, we focused on the bond and cracking characteristics of polyvinyl alcohol (PVA)-FRCC reinforced with braided AFRP bars (AFRP/PVA-FRCC). Pullout tests on specimens with varying bond lengths were conducted. Beam specimens were also subjected to four-point bending tests. In the pullout tests, experimental parameters included the cross-sectional dimensions and the fiber volume fractions of PVA-FRCC. A trilinear model for the bond constitutive law (bond stress–loaded-end slip relationship) was proposed. In the pullout bond test with specimens of long bond length, bond strength was found to increase with increases in both the fiber volume fraction and the cross-sectional dimension of the specimens. Bond behavior in specimens of long bond length was analyzed numerically using the proposed bond constitutive law. The calculated average bond stress–loaded-end slip relationships favorably fitted the test results. In bending tests with AFRP/PVA-FRCC beam specimens, high ductility was indicated by the bridging effect of fibers. The number of cracks increased with increases in the fiber volume fraction of PVA-FRCC. In specimens with a fiber volume fraction of 2%, the load reached its maximum value due to compression fracture of the FRCC. The crack width in PVA-FRCC calculated by the predicted formula, considering the bond constitutive law and the fiber bridging law, showed good agreement with the reinforcement strain–crack width relationship obtained from the tests. Full article

In this paper, the mechanical properties and bond strength of composite samples that consist of a conductive concrete (CC) layer and a self-consolidated concrete (SCC) layer are investigated. The bond strength study includes two parameters: (1) surface preparation and (2) casting and testing directions. The surface preparation study shows that, compared to the other methods in this study, the shear key method is the most suitable surface preparation method to fully utilize the CC in a composite. Moreover, the casting direction study reveals that the strength is heavily dependent on the type of test used along with CC’s layer positioning. The flexural strength study confirms that positioning the CC mix in the tensile region is beneficial since it can increase the flexural strength of a structure because of the hybrid steel fibers included in the mixture. Finally, different codes/specifications and published theoretical results are used to predict the CC’s mechanical properties, and the predictions are not as accurate as the SCC predictions, which can be attributed to the presence of conductive fillers in the CC mix. Full article

The release of microfibres (MFs) from textiles has been observed in various environments, pointing towards the impact of human activities on natural systems. Synthetic textile microfibres, a subset of microplastic fibres (MPFs), are reported to be the primary contributor to microplastic pollution. With the forecasted growth in textile production, the problem of MF pollution is expected to worsen and become more challenging to address. Wastewater treatment plants (WWTPs) are crucial in managing microfibre pollution as they can act as a sink and source of these pollutants. Studies have shown that textile industrial effluent can contain MFs at a rate of up to a thousand times higher than municipal wastewater. As more garments are made than sold and worn, the impact of industrial MF release could be higher than predicted. The detection and quantification of microfibres released in industrial wastewater effluents do not have a standard test method, and legislation to address this issue is not yet feasible. To tackle this issue, it is crucial to raise awareness in the industry and tackle it using a more holistic approach. With its urgency, but still being an underdeveloped research area, priorities for mitigation actions are examined where efforts are needed to accelerate. These include the need to raise awareness and encourage more investigations from industry and academia. A consistent protocol will help us to compare studies and find solutions of high impact and measure MFs in WWTPs, which can help define the maximum limit for MF releases and support legislation implementation. Full article

Microstructured optical fibres (MOFs) are a new type of optical fibres that possess a wide range of optical properties and many advantages over common optical fibres. Those are provided by unique structures defined by a pattern of periodic or quasi-periodic arrangement of air holes that run through the fibre length. In recent years, MOFs have opened up new possibilities in the field of optics and photonics, enabling the development of advanced devices and novel optical systems for different applications. The key application areas of MOFs vary from telecommunications and high-power energy transmission to quantum optics and sensing. The stack-and-draw method is a standard manufacturing technique for MOFs, where a preform is first manually created and then drawn in a sophisticated furnace into a fibre with the required final dimensions and position of the air holes. During the manufacturing process, experimenters can control only a few parameters, and mathematical models and numerical simulations of the drawing process are highly requested. They not only allow to deepen the understanding of physical phenomena occurring during the drawing process, but they also accurately predict the final cross-section shape and size of the fibre. In this manuscript, we assume thermal equilibrium between the furnace and the fibre and propose a functional form of the fibre temperature distribution. We utilise it with asymptotic mass, momentum, and evolution equations for free surfaces already available in the literature to describe the process of fibre drawing. By doing so, the complex heat exchange problem between the fibre and the furnace need not be solved. The numerical results of the whole asymptotic model overall agree well with experimental data available in the literature, both for the case of annular capillaries and for the case of holey fibres. Full article

Recycling medium-density fiberboards (MDF) presents notable technological challenges, primarily due to the deteriorated properties of the recycled wood fibers obtained from MDF waste. On the other hand, the enhanced valorization of recycled wood in the manufacturing of wood composites represents a viable approach for implementing the principles of a circular bio-economy in the wood-based panel industry and lowering its carbon footprint. This research aimed to investigate and evaluate the impact of the hydrothermal hydrolysis regime on the physical and mechanical properties of recycled MDF panels (rMDF). The hydrolysis temperature was varied from 121 °C (saturated steam pressure 0.2 MPa) to 134 °C (saturated steam pressure 0.3 MPa), and three hydrolysis durations, i.e., 30, 45, and 60 min, were applied. A control MDF panel, manufactured in laboratory conditions from industrial pulp, was used to perform the comparative analyses. It was observed that the degradation of the rMDF panels occurred when the hydrolysis temperature was increased from 121 °C to 134 °C. The research confirmed the deteriorated physical and mechanical properties of rMDF compared to the panels manufactured from natural wood fibers. Markedly, no significant differences were detected between the density profiles of the rMDF panels and the control boards fabricated from industrial pulp. As a result of the study, it was found that the hydrolysis temperature has a more significant effect than the processing time. It was also established that, in the preliminary preparation of the MDF panels into samples with dimensions similar to those of pulp chips, the optimal hydrolysis regime is at a temperature of 121° C (saturated steam pressure 0.2 MPa) and a time of 30 min. Full article

The aim of this paper is to present the influence of the modification of polypropylene (PP) fibers on the sorption capabilities of the fibers. The physical modification of the PP fibers was made with inorganic nanoadditives in the mass, with a view to improving the properties of silicate composites used in the construction industry. The compositions of the modified PP fibers using two different nanoadditives were based on previous work, as well as the work presented in this paper. The prepared modified PP fibers were compared with pure PP fibers, and their mechanical and thermomechanical properties were evaluated. Another task of this work was to evaluate and compare the sorption capabilities of these fibers without the preparation of concrete blocks. Therefore, the Washburn method was used. However, the obtained results led us to the conclusion that the given method points to the excellent transport properties of PP fibers if such properties are used to evaluate the sorption of the fibers. However, the sorption of the prepared modified fibers could be associated with the nanoadditives used, which have a higher water sorption capacity compared to pure PP fibers, and this could also ensure the higher adhesion of the modified PP fibers with inorganic additives to the cement matrix compared to the adhesion of the hydrophobic PP fibers. Full article

A significant increase in the consumption of recycled fiber products has been observed worldwide, and the industry is forced to solve the challenges of recycled fiber quality and add strength agents and/or virgin fibers to reach sufficient properties. In order to investigate whether the mechanical and air permeability properties of waste fiber (WF) material can be significantly improved by adding wood kraft fibers (KF), hemp soda fibers (HF), and ammonium persulfate oxidated cellulose nanofibrils (CNF), different fiber blends were prepared and tested. Results revealed the excellence of hemp fibers over wood fibers regarding the improvement of WF products. The results of WF after the addition of 10% mixed fibers (KF + HF) were higher than the results of a 50% KF addition. The impact of CNF depended on fiber composition and properties. A formula for modeling the CNF impact on different fiber compositions was proposed. Obtained fiber material samples showed suitability for home composting, thus contributing to the goals of the European Green Deal regarding reducing landfill waste and the development of cleaner products. Full article

Wind turbine blades in excessive wind conditions present extreme deflection problems. For this reason, an analysis of the structural response of composite reinforced box beams is developed. For this purpose, reinforced box beams were fabricated to improve the bending strength in the flapwise direction of the wind turbine blades. The box beams were analyzed with three-dimensional models using the Finite Element Method (FEM) and validated with bending tests at four-points and two-points. The box beam meets the characteristics of lightness and mechanical strength. Experimental four-point bending results showed that reinforced cross-sections decrease displacements by 30.09% and increase their stiffness to 43.41% for a box beam without structural reinforcement. In addition, the two-point bending results showed a difference of 18.98% between the displacements of the beams with structural reinforcements. In the FEM analysis, a maximum error of 11.24% was obtained when correlating the maximum displacement value with the experimental results of the beams. Full article

The purpose of this study was to detect changes in the structure and chemical composition of undyed and dyed cotton fabrics under the influence of six popular agents for disinfection, sterilization, and DNA degradation with different chemical compositions. The original and exposed fabrics and their constituent fibers were subjected to comparative analysis using various optical microscopy methods, infrared spectroscopy, and UV–Vis microspectrophotometry in order to differentiate the exanimated material due to the agents applied. Differences in color, from a slight change to complete discoloration, and in the structure of the tested fabrics, which became more rigid, brittle, or, for example, compact, were noticed. With the use of ATR FTIR, it was possible to identify the presence in the exposed fabrics of residues of these agents that contained quaternary ammonium salts. Bright-field microscopy made it possible to show, above all, changes or lack thereof in the fluorescence properties of single exposed fibers in relation to control ones. With the use of UV–Vis microspectrophotometry, changes in colored fibers following the action of a specific agent on the examined fabrics were monitored. A case study was presented as an application aspect of the research, in which the use of concrete disinfectants was recognized based on changes observed in cotton clothing. Full article