Fibers, Volume 10, Issue 2 (February 2022) – 12 articles

The paper presents the results of experimental research on unstrengthened and strengthened laminated veneer beams subjected to 4-point bending. Aramid, glass and carbon sheets with high tensile strength (HS) and ultra-high modulus of elasticity (UHM) glued to external surfaces with an epoxy resin adhesive were used as reinforcement. Two reinforcement layouts were used: (1) sheets glued along the bottom surface and (2) sheets glued to the bottom and side surfaces. Based on the test results, the flexural strength, flexural ductility and stiffness were estimated. Compared to the reference beams, the maximum bending moment was higher by 15%, 20%, 30% and by 16%, 22% and 35% for the Aramid Fiber Reinforced Polymers (AFRP), Glass Fiber Reinforced Polymers (GFRP) and Carbon Fiber Reinforced Polymers (CFRP) HS sheets, respectively. There was no significant increase in the flexural bending capacity for beams reinforced with UHM CFRP sheets. Similar values of bending ductility indices based on deflection and energy absorption were obtained. Higher increases in ductility were observed for AFRP, GFRP and CFRP HS sheets in “U” reinforcement layout. The average increase in bending stiffness coefficient ranged from 8% for AFRP sheets to 33% for UHM CFRP sheets compared to the reference beams. Full article

Lignin is an abundantly occurring aromatic biopolymer that receives increasing attention as, e.g., a biofiller in polymer composites. Though its structure depends on the plant source, it is a valuable component showing biodegradability, antioxidant, and ultra-violet (UV) absorption properties. Lignosulfonates, a by-product of the paper and pulping industries formed as a result of the implementation of the sulfite process, have been used in the presented study as a raw material to obtain a sulfonamide derivative of lignin. Hereby, a two-step modification procedure is described. The obtained materials were investigated by means of FTIR, WAXD, SS-NMR, SEM, and TGA; the results of spectroscopic investigations confirm the formation of a sulfonamide derivative of lignin via the proposed modification method. The obtained modified lignin materials showed significantly improved thermal stability in comparison with the raw material. The internal structure of the lignosulfonate was not altered during the modification process, with only slight changes of the morphology, as confirmed by the WAXD and SEM analyses. The manufactured sulfonamide lignin derivatives show great promise in the potential application as an antibacterial filler in advanced biopolymeric composites. Full article

It is well known that objectionable fibres emerge from the surface of the yarn due to the centrifugal force of the spinning device. Furthermore, the hair removal process is based on the same physical principles. However, the fibres that are >30 µm (PcF) are the fibres that appear in the hairiness of the yarn and are eliminated by dehairing. It has always been presumed that the PcF was linearly correlated with the diameter of the fibre (MFD) in llamas, but not so in alpaca fibres. Nevertheless, there is evidence that this relationship is curvilinear and behaves the same way in both species. The objectives of this study are to explore the relationship between MFD and PcF in both llamas and alpacas, to explore the existence of a breaking point (BP) in this curvilinear relationship, and to determine the frequency of fleeces that do not require dehairing because the PcF ≤ 3.2%. In addition, the existence of a positive bias of coarse fibre content on the hairy surface (CFs) of the yarn to coarse fibre content within the yarn fibres (CFy) was determined, which may explain the effect of the dehairing on the prickle factor of SAC fibres. The relationship of PcF on MFD behaves the same way in alpacas and llamas. It conforms to a power distribution and presents a BP of 23 µm, with PcF being constant before the BP and increasing significantly after it. Most animals (≤91% of alpacas and ≤87% of llamas) are above the threshold (≤3.2%), requiring dehairing to correct it. By means of a shaving technique on the surface of the fabric sample, it was established that the objectionable CFs content is 8.15% higher than the objectionable CFy content. In the evoked-coarse fibre in the dehaired samples, a CFs-CFy difference below 5.9% (p > 0.05) is not significantly detected by panellists. The surface MFD is more than 2.7 µm coarser than the yarn MFD. Full article

The increasing use and potential of polylactic acid (PLA) in wood-based composite materials due to its greater performance over common polyolefins provides the justification for a closer examination of the PLA−wood adhesion performance. In PLA-bonded laminates and composites, the optical differentiation between PLA polymer and wood is not possible and necessitates complex techniques such as fluorescence microscopy to characterize the PLA adhesion interface. In this study, spatial chemical imaging via FTIR analysis has been successfully applied to directly identify PLA bondlines within PLA-bonded veneer laminates and to determine the migration of semi-crystalline and amorphous PLAs from the bondline into the wood structure. This method uses involved point contouring line spectra over the bondline area to distinguish the PLA polymer from the wood. From this quantitative analysis, it is revealed that bondline thickness and PLA penetration values depend on pressing temperature, and this has implications for the reinforcement of the adhesion interface and the bondline performance. Furthermore, in developing a methodology for this assessment, this spatial chemical imaging approach can equally be applied to other polyester, amide, and urethane systems used to bond wood laminates. Full article

Lignin has shown a great potential to produce fuels, value-added chemicals, and functional materials due to its high-energy density and intrinsic aromatic-based structure. Yet, the lignin precipitation of different biomasses needs investigation because most of the work has been performed on softwood and much less is known about hardwoods. In fact, the lignin from these two wooden biomasses vary in composition and pulping performance, which can reflect on lignin precipitation. Therefore, the present study investigated the precipitation and composition of 40 distinct kraft lignins obtained from pine, acacia, sweetgum, and eucalyptus black liquors. Two lignin fractions were precipitated at different pHs, according to known industrial lignin separation practices (pH = 9.5 and 2.5) from black liquors taken at different levels of pulping. Overall, lignin recovery increased with increasing lignin concentration in the black liquor, i.e., higher amounts of lignin were obtained at higher levels of delignification. In addition, pine lignins showed superior yields than the hardwoods and were around five times purer. Among the hardwoods, lignin recovery increased with the S–G ratio of the native lignin, and eucalyptus showed the best performance by achieving the highest yields and purities. Finally, the present work compared the lignin recovery yield and the purity of softwood and different hardwood lignins in a systematic way, which will increase awareness of this underutilized green material and could potentially increase the interest in establishing new lignin plants across the globe. Full article

Air filtration has seen a sizable increase in the global market this past year due to the COVID-19 pandemic. Nanofiber nonwoven mats are able to reach certain efficiencies with a low-pressure drop, have a very high surface area to volume ratio, filter out submicron particulates, and can customize the fiber material to better suit its purpose. Although electrospinning nonwoven mats have been very well studied and documented there are not many papers that combine them. This review touches on the various ways to manufacture nonwoven mats for use as an air filter, with an emphasis on electrospinning, the mechanisms by which the fibrous nonwoven air filter stops particles passing through, and ways that the nonwoven mats can be altered by morphology, structure, and material parameters. Metallic, ceramic, and organic nanoparticle coatings, as well as electrospinning solutions with these same materials and their properties and effects of air filtration, are explored. Full article

Enset and sisal fibers are among the most widely used reinforcement to fabricate natural fiber-based composite materials. Hand lay-up techniques were employed in this study to fabricate enset–sisal (E/S) hybrid fiber composite with volume ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 and constant polyester resin. The tensile, flexural, impact strength, water absorption and morphological properties of the fabricated composite were investigated experimentally. The effects of hybridization to volume ratio were determined and the results show that hybrid composites excel in mechanical properties, compared with single composites. For better mechanical properties, the enset fiber has been hybridized with sisal fiber. Tensile and flexural strengths were enhanced by 47.3% and 41.03%, respectively, at 50/50 E/S volume ratio compared with 100/0 E/S composite. The impact strength of sisal fiber composite was improved by adding enset fiber in the composites. The inherent benefits and limitations of these two fibers were balanced out by each other in a positive way. While sisal fiber helped the composite intermesh of tensile, flexural, and reduction of water absorption, enset ensured impact strength. Morphological analysis was carried out in order to observe the fracture behavior and fiber pull-out of the samples by means of scanning electron microscopy. Full article

A major drawback of current hair styling treatments is their use of toxic chemicals, such as thioglycolates, sulfites, formaldehyde, and others. Exposure to such chemicals is not only harmful to hairstylists but also to the millions who routinely receive hair treatments. The present research discusses the development of a benign sucrose-based crosslinker consisting of aldehyde groups to stabilize hair via crosslinking amine groups in keratin. ATR-FTIR and ¹H-NMR were used to confirm functional groups on sucrose. Hair straightening was carried out by crosslinking via flat ironing. Crosslinked hair swatches were hung in a high humidity environment and subjected to repeated washings with shampoo to characterize the permanency of the treatment. Hair straightening through crosslinking was found to be durable to high humidity and repeat shampoo washings. The tensile characteristics of hair, such as fracture stress, strain, and Young’s modulus, were unaffected by the treatment. SEM images showed no damage to surface scales. The sucrose-based crosslinker could be used to create curls in straight hair as well. Full article

Vascular disease in elderly patients is a growing health concern, with an estimated prevalence of 15–20% in patients above 70 years old. Current treatment for vascular diseases requires the use of a vascular graft (VG) to revascularize lower or upper extremities, create dialysis access, treat aortic aneurysms, and repair dissection. However, postoperative infection is a major complication associated with the use of these VG, often necessitating several operations to achieve complete or partial graft excision, vascular coverage, and extra-anatomical revascularization. There is also a high risk of morbidity, mortality, and limb loss. Therefore, it is important to develop a method to prevent or reduce the incidence of these infections. Numerous studies have investigated the efficacy of antibiotic- and antiseptic-impregnated grafts. In comparison to these traditional methods of creating antimicrobial grafts, nanotechnology enables researchers to design more efficient VG. Nanofibers and nanoparticles have a greater surface area compared to bulk materials, allowing for more efficient encapsulation of antibiotics and better control over their temporo-spatial release. The disruptive potential of nanofibers and nanoparticles is exceptional, and they could pave the way for a new generation of prosthetic VG. This review aims to discuss how nanotechnology is shaping the future of cardiovascular-related infection management. Full article

In the present study, the mechanical behavior of Fiber-Reinforced Concrete (FRC) beams was studied under bending until rupture. Each beam was reinforced with a hybrid mix of short fibers randomly distributed in its volume. Concrete beams with three different fiber combinations were investigated, namely, beams reinforced with (1) a homogeneously distributed mix of short polypropylene fibers (PP) and steel fibers, (2) PP fibers and Alkali Resistant Glass (ARG) fibers, and (3) PP and composite fibers (CF). The amount of short PP fibers was the same in all FRCs. The investigation focused on the fracture mechanisms and the load-bearing capacity of FRC beams with the developing macro cracks. In total, 12 FRC composite prismatic specimens were casted and tested in four-point bending experiments (4PBT). The current load value versus the Crack Mouth Opening Displacement (CMOD) for all FRCs was analyzed. The crack opening relationship and the influence of fibers on the fracture energy and flexural tensile strength were determined. Rupture surfaces of all samples were investigated using an optical microscope. Full article

The effect of using basalt fibers on the fresh, mechanical, durability, and corrosion properties of reinforced concrete was investigated in this study. The study was performed using different basalt fiber volume fractions of 0.15%, 0.30%, 0.45%, and 0.50%, while two different water/cement (w/c) ratios of 0.35 and 0.40 were utilized. The results were compared to conventional concrete (PC) as well as steel fiber concrete (SFC) with 0.30% and 0.50% steel fibers volume fractions. An extensive experimental program of 336 samples was conducted in four stages as follows: testing for fresh properties included slump and unit weight tests; mechanical properties testing included compressive strength tests, split tensile strength tests, flexural strength tests, and average residual strength tests; durability testing included unrestrained shrinkage and surface resistivity tests; and a Rapid Macrocell corrosion evaluation test for corrosion properties. The test results showed that the use of basalt fibers reduces slump values as the fiber volume fraction increases; however, with the use of the appropriate amount of High Range Water Admixture (HRWA), target slump values can be achieved. Moreover, a considerable improvement in the compressive, tensile, flexural, average residual strength and durability properties was achieved in case of using basalt fibers. On the other hand, corrosion rates increased with the increase in fiber volumes. However, it can be concluded that utilizing a 0.30% fibers volume fraction is the optimum ratio with an overall acceptable performance with respect to mechanical and corrosion properties. Full article