Fibers, Volume 10, Issue 9 (September 2022) – 11 articles

In order to improve the strength of concrete structures, the fiber reinforcement of concrete has become an essential factor. This study was conducted as an experimental program to gain a better understanding of how the variance of fiber shape and type affect the structural performance of solid and hollow reinforced concrete beams using four types of fiber (hooked-end, straight, corrugated steel fiber, and polyolefin fiber) under torsion. For this purpose, ten fiber-reinforced concrete beam specimens, five solid and five hollow, with square cross sections were fabricated using the adopted types of fiber. The role of fiber type in the improvement of the mechanical properties of hardened concrete was also investigated. The results revealed that the mechanical properties of the hardened concrete mix was enhanced by using the existing fiber in concrete, and the higher improvement was shown in the splitting tensile strength test and modulus of rapture in specimens with corrugated steel fiber. The torsional behavior of solid and hollow beams was improved significantly, and the capacity of torsional strength was especially improved for the beams strengthened with corrugated steel fiber. Straight and polyolefin fiber showed a slight improvement in the concrete mechanical properties and less enhancement in the torsional capacity of the tested beams. However, the tested beams reinforced by polyolefin fiber provide better ductility under torsion compared with the use of other types of fiber. Full article

The view towards a sustainable bioeconomy is increasing the interest of using renewable natural resources in the production of composites. Until now, the production of sustainable composites has been mainly examined from the point of view of material composition and structure, by replacing petroleum-based components with those that are obtained from renewable resources known as natural fiber composites (NFCs). The usefulness of newly acquired materials is mostly evaluated considering their performance and economic costs, whereas the aspect of environmental protection is underestimated. The impact of composites that are made from renewable resources is examined within the two parts of this study—the first part compares different nitrogen (N) fertilization scenarios for plant origin (hemp and flax) fibers. When compared, hemp crops show higher CO₂ accumulation, (−1.57 kg CO₂ eq) than flax (−1.27 kg CO₂ eq). In addition, the environmental impact of both fiber types is compared to polyamide composites, one of the traditionally used materials in the automotive industry in the second part of this study. According to the conducted life cycle assessment, Flax/PLA emits 1.19 kg CO₂ eq per 1 kg composite, Hemp/PLA 1.7 kg CO₂ eq per 1 kg composite, and PA66/GF 9.14 kg CO₂ eq per 1 kg composite. After the comparison, it was concluded that bio-based composites are able to ensure lower CO₂ emissions, because CO₂ is accumulated and stored in the fibers, however the traditionally used composites are able to provide a lower impact in other environmental categories. Full article

In recent years, the use of hybrid composite stacks, particularly CFRP/Al assemblies, and fiber metal laminates (FMLs) has progressively become a convincing alternative to fiber-reinforced polymers (FRPs) and conventional metal alloys to meet the requirements of structural weight reduction in the modern aerospace industry. These new structural materials, which combine greater mechanical properties with low specific mass, are commonly assembled by riveted and bolted joints. The drilling operation, which represents the essential hole-making process used in the aerospace industry, proves particularly challenging when it comes to achieving damage-free holes with tight tolerances for CFRP/Al stacks in one-shot operations under dry conditions due to the dissimilar mechanical and thermal behavior of each constituent. Rapid and severe tool wear, heat damage, oversized drilled holes and the formation of metal burrs are among the major issues induced by the drilling of multi-material stacks. This paper provides an in-depth review of recent advancements concerning the selection of optimized strategies for high-performance drilling of multi-material stacks by focusing on the significant conclusions of experimental investigations of the effects of drilling parameters and cutting tool characteristics on the drilling performance of aerospace assemblies with CFRP/Al stacks and FML materials. The feasibility of alternative drilling processes for improving the hole quality of hybrid composite stacks is also discussed. Full article

The numerical modeling of transverse laminar flow past a new type of hollow-fiber membranes with external profiling has been performed. A model system of parallel fibers with symmetrical parallel protrusion obstacles or grooves is considered. The absorption of point particles (solute or gas molecules) from a laminar transverse flow of a viscous incompressible liquid (gas) is calculated for a row of fibers, and the dependences of the efficiency of retention of particles by fibers on the Peclet (Pe), Reynolds (Re), and Schmidt (Sc) numbers and on the distance between neighbor fibers in a row are determined. The flow velocity and concentration fields are calculated by numerical solution of the Navier–Stokes equations and the convective diffusion equation in a wide range of Peclet numbers Pe = 0.1 − 10⁵ for Sc = 1, 10, 1000 and Re ≤ 100. Full article

Cotton is one of the most-used natural fibres in the world due to its relative comfort and strength compared with other natural fibres. However, the processing of cotton for manufacturing products consumes a lot of water, while harvesting cotton uses significant amounts of pesticides. One solution to this ecological problem is to recycle cotton waste. This study investigated the effect of blending virgin cotton with two categories of denim cotton waste—sourced during the winding and dyeing processes and used in various ratios—on the quality of blended denim cotton. The study was realised in collaboration with a large manufacturer of denim fabrics in Tunisia and a producer of preparation machines in Italy and aimed to use an adequate process to recycle cotton yarn waste and to obtain fibres with acceptable quality. The research aimed at providing a solution to the great demand for denim with the use of reclaimed fabric, which accompanies the increased need for denim with a fancy effect and the obligation of denim producers to follow environmental standards required by many brands The results show that it is possible to obtain a good quality of blend yarn using virgin cotton and cotton waste even when the waste content exceeds 50%. These results are significant for textile mills. Reprocessing fibres from denim colour-processing waste has a lot of advantages, including reductions in wastewater treatment and the consumption of energy, chemicals and water. In addition, the process eliminates the need for the dyeing and finishing processes of these coloured fibres. Full article

Nanotubes (NTs) are mainly known as materials made from various substances, such as carbon, boron, or silicon, which share a nanosized tube-like structure. Among them, carbon-based NTs (CNTs) are the most researched group. CNTs, due to their nonpareil electrical, mechanical, and optical properties, can provide tremendous achievements in several fields of nanotechnology. Unfortunately, the high costs of production and the lack of unequivocally reliable toxicity data still prohibit their extensive application. In the last decade, a significant number of intriguing nanotubes-like structures were identified in bacteria (BNTs). The majority of experts define BNTs as membranous intercellular bridges that connect neighboring bacterial cell lying in proximity. Despite recent contrasting findings, most evidence suggested that bacteria exploit NTs to realize both antagonistic and cooperative intercellular exchanges of cytoplasmic molecules and nutrients. Among other consequences, it has been proposed that such molecular trade, including even plasmids, can facilitate the emergence of new non-heritable phenotypes and characteristics in multicellular bacterial communities, including resistance to antibiotics, with effects of paramount importance on global health. Here, we provide an enthralling comparison between CNTs, which are synthetically producible and ubiquitously exploitable for improving the quality of human life, and BNTs biosynthetically produced by prokaryotes, whose functions are not still fully clarified, but whose greater knowledge could be crucial to better understand the mechanisms of pathogenesis and combat the phenomenon of resistance. Full article

This paper provides a review of recent studies on the weave factor along with the effect of weave parameters and particularly the weave structure on various properties of woven fabric. The weave structure can be considered as one of the prime parameters that contributes to the dominant physical and qualitative properties of the woven fabric. This study analyzed not only the parameters that significantly influence the properties of the woven fabric, but also the weave factors for the estimation of the weave that were proposed by earlier scientists. This review paper highlights the impact of weave structure on the physical and mechanical, thermo-physiological and comfort properties, and some special application properties of woven fabrics. This work seeks to serve as a future reference for related research. Full article

Acrylic hydrogels have been used in agriculture to increase the availability of water in the soil; cause faster plant growth and increase plant survival to water stress; allow controlled release of fertilizers; and, therefore, increase crop yields. On the other hand, Aloe vera gel production generates a large amount of solid waste as cuticles, which is currently underutilized despite that it is a good source of cellulose nanofibers that could be used to improve the swelling capacity of commercial acrylic hydrogels. In this work, both morphology (SEM) and particle size (TEM) of the cellulose nanofibers obtained from A. vera cuticles by the acid hydrolysis method combined with ultrasound were analyzed; as well as the presence of functional groups (FITR) and thermal stability (TGA). Then, acrylic hydrogels were synthesized by the solution polymerization method, and nanofibers were added to these hydrogels at different concentrations (0% w w⁻¹, 3% w w⁻¹, 5% w w⁻¹, and 10% w w⁻¹). These concentrations had a nonlinear relationship with the swelling capacity, and the hydrogel reinforced at 3% cellulose nanofiber was chosen as the best formulation in this work, as this one improved the swelling capacity of hydrogels at equilibrium (476 g H₂O g hydrogel⁻¹) compared to the hydrogel without nanofiber (310 g H₂O g hydrogel⁻¹), while hydrogels with 10% nanofiber had a similar swelling capacity to the non-reinforced hydrogel (295 H₂O g hydrogel⁻¹). Therefore, cellulose-based superabsorbent hydrogels with potential application in agriculture were developed in this work. Full article

This study investigates the quasi-static axial crushing tests of eco-hybrid composites based on flax and E-glass fibres strengthened with polyester resin. Five different configurations of self-supporting webs were fabricated to investigate the crushing behaviours of this eco-hybrid composite with different stacking sequences based on intercalation and sandwich-like sequences. The effect of different open-section web profiles was also investigated. The results were plotted in load-displacement curves and the specific energy absorption (SEA), as well as the crushing force efficiency (CFE), were calculated to evaluate the crushing response of each configuration. The test results verified the crushing mechanisms related to the energy absorption depending on the stacking sequence as well as the frontal profile. In this study, all specimens with the intercalation stacking sequence have achieved higher SEA and CFE than specimens with a sandwich-like stacking sequence. In terms of the frontal profile, the sine wave hat shape had the highest CFE, up to 80% compared to other web profiles. Thus, it demonstrated the capability of a sine wave hat-shape eco-composite based on flax fibre to be applied as a crashworthy material. Full article

A popular water pipe system used in many countries is one formed by prestressed cylindrical concrete pipes (PCCPs) formed by identical precast moduli joined together in situ. This technology was and still is quite popular in many water supply systems internationally. This technology was mainly selected at the time due to its cost-based comparative advantage. However, over the years, numerous incidents of structural failures have been reported for this type of pipeline, causing, in some cases, serious disruption of the water supply. This study summarizes the results of an experimental investigation on ten (10) PCCP specimens taken from an existing water pipeline with the objective of investigating their bearing capacity under either three-edge bending or internal hydraulic pressure loads. Moreover, there is a need to check the capability of specific retrofitting/strengthening schemes to upgrade this bearing capacity and thus enhance the operational period. Provided that the prestressing wires are fully active according to design specifications, the original specimen performed satisfactorily for the set internal hydraulic pressure limit of 8.5 bar. Specimens retrofitted with either internal or external CFRP or RC jacketing performed satisfactorily for internal hydraulic pressure levels well above this 8.5 bar limit. A critical factor is, as expected, the loss of prestress. Full article

To obtain composite fiber materials with antibacterial properties, the samples of bacterial cellulose (BC), polylactide (PLA) and usual fibers (FM) were modified by poly-ε-caprolactone or polyhydroxybutyrate and then functionalized by the enzyme-polyelectrolyte complex of quorum-quenching enzymes, such as hexahistidine-tagged organophosphorus hydrolase with poly(glutamic acid) or by suspension of tantalum nanoparticles (Ta NPs) in ethanol. The structures of the composite fibers were analyzed using scanning electron microscopy. It was shown that the introduction of additional natural polymers into the matrix of BC, PLA and FM resulted in decreasing of the structural porosity. Comparative studies of the antibacterial activity of the composite materials were carried out using Escherichia coli and Bacillus subtilis cells. The decrease of adenosine triphosphate concentration in cell samples loaded onto fiber materials was applied as a measurable characteristic of antibacterial effect typical for the new fiber materials. The profound improvement of antibacterial activity was determined in composite materials with polyhydroxybutyrate and Ta NPs. Full article