Fibers

16 pages, 9757 KiB

Open AccessArticle

Fiber Spinning of Polyacrylonitrile Terpolymers Containing Acrylic Acid and Alkyl Acrylates

by Ivan Yu. Skvortsov, Mikhail S. Kuzin, Andrey F. Vashchenko, Roman V. Toms, Lydia A. Varfolomeeva, Elena V. Chernikova, Gulbarshin K. Shambilova and Valery G. Kulichikhin

Fibers 2023, 11(7), 65; https://doi.org/10.3390/fib11070065 - 24 Jul 2023

Cited by 2 | Viewed by 1768

Abstract

Terpolymers of acrylonitrile with acrylic acid and alkyl acrylates, including methyl-, butyl-, 2-ethylhexyl-, and lauryl acrylates, were synthesized using the reversible addition–fragmentation chain transfer method. In this study, the focus was on the investigation of the impact of different monomer addition methods (continuous [...] Read more.

Terpolymers of acrylonitrile with acrylic acid and alkyl acrylates, including methyl-, butyl-, 2-ethylhexyl-, and lauryl acrylates, were synthesized using the reversible addition–fragmentation chain transfer method. In this study, the focus was on the investigation of the impact of different monomer addition methods (continuous and batch) on both the rheological behavior of the spinning solutions and the mechanical properties of the resulting fibers. Our findings revealed that the method of monomer addition, leading either to non-uniform copolymers or to a uniform distribution, significantly influences the rheological properties of the concentrated solutions, surpassing the influence of the alkyl-acrylate nature alone. To determine the optimal spinning regime, we examined the morphology and mechanical properties at different stages of fiber spinning, considering spin-bond and orientation drawings. The fiber properties were found to be influenced by both the nature and introducing method of the alkyl-acrylate comonomer. Remarkably, the copolymer with methyl acrylate demonstrates the maximum drawing ratios and fiber tensile strength, reaching 1 GPa. Moreover, we discovered that continuous monomer addition allows for reaching the higher drawing ratios and superior fiber strength compared to the batch method. Full article

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12 pages, 2657 KiB

Open AccessArticle

Effect of Hydrolysis Regime on the Properties of Fibers Obtained from Recycling Medium-Density Fiberboards

by Viktor Savov, Petar Antov, Christian Panchev, Muhammad Adly Rahandi Lubis, Seng Hua Lee, Hamid R. Taghiyari, Martina Todorova and Stoyko Petrin

Fibers 2023, 11(7), 64; https://doi.org/10.3390/fib11070064 - 17 Jul 2023

Cited by 2 | Viewed by 1778

Abstract

Unlike the recycling of particleboards, the recycling of medium-density fiberboards (MDF) is not a widespread industrial practice, and currently, most waste MDF panels are landfilled or incinerated after the end of their life cycle. Therefore, it is of great importance to develop cost-effective [...] Read more.

Unlike the recycling of particleboards, the recycling of medium-density fiberboards (MDF) is not a widespread industrial practice, and currently, most waste MDF panels are landfilled or incinerated after the end of their life cycle. Therefore, it is of great importance to develop cost-effective methods for MDF recycling. The extraction of resins used for bonding the panels, mostly urea–formaldehyde (UF) resins, is carried out mainly with hydrolysis. Hydrothermal hydrolysis is a more environmentally friendly and cheaper recycling technique compared to acid hydrolysis and allows obtaining a high yield of recycled fibers. The aim of this research work was to investigate and evaluate the effect of hydrolysis regime applied on its efficiency and on the properties of the recycled MDF fibers. For this purpose, thermal hydrolysis was carried out in an autoclave with saturated steam as a heat carrier. The main novelty of the research is the preliminary preparation of the recyclable MDF in samples with dimensions close to those of pulp chips. The effect of hydrolysis regime characteristics, i.e., process time and temperature on the properties of recycled MDF wood fibers, was studied. The hydrolysis temperatures used were 121 °C (saturated steam pressure of 0.2 MPa) and 134 °C (saturated steam pressure of 0.3 MPa); for each temperature, three durations were applied—30, 45, and 60 min. After hydrolysis, the resulting fiber fraction was refined using a hammer mill. The fractional and elemental composition of the recycled fibers obtained were evaluated. The hemicellulose content after each hydrolysis treatment was also determined. The chemical oxygen demand (COD) was defined as an indicator of wastewater contamination and as an indirect indicator of the quantitative yield of the process. The results revealed no significant changes in the elemental composition of the recycled fibers, and the hydrolysis regimes used showed no decrease in pentosan content. The recycled MDF fibers exhibited similar fiber morphology and fractional composition, being shorter than fibers from industrial pulp. The increased temperature and time of hydrolysis resulted in a significant increase in COD values. Based on the obtained results, with a view to the slightest contamination of wastewater (as determined by COD), the most promising hydrolysis regime was at a temperature of 121 °C and a time of 30 min. It should be emphasized that for a confirmation of this statement, the properties of MDF panels fabricated with fibers recycled in different regimes should be subsequently investigated. Full article

(This article belongs to the Special Issue Fiber Recycling)

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17 pages, 6539 KiB

Open AccessArticle

Tailoring Epoxy Composites with Acacia caesia Bark Fibers: Evaluating the Effects of Fiber Amount and Length on Material Characteristics

by Sivasubramanian Palanisamy, Mayandi Kalimuthu, Carlo Santulli, Murugesan Palaniappan, Rajini Nagarajan and Cristiano Fragassa

Fibers 2023, 11(7), 63; https://doi.org/10.3390/fib11070063 - 17 Jul 2023

Cited by 9 | Viewed by 1658

Abstract

In recent years, there has been growing interest in utilizing bark fibers as reinforcements for polymer composites. This study focused on the characterization of epoxy composites reinforced with Acacia caesia bark (ACB) fibers, considering their mechanical, morphological, and thermal properties. Various amounts of [...] Read more.

In recent years, there has been growing interest in utilizing bark fibers as reinforcements for polymer composites. This study focused on the characterization of epoxy composites reinforced with Acacia caesia bark (ACB) fibers, considering their mechanical, morphological, and thermal properties. Various amounts of ACB fibers with three different lengths (10, 20, and 30 mm) were incorporated into the composites, ranging from 10 to 35 wt.% in 5% increments. This resulted in 18 sample categories, which were compared to neat epoxy samples. The findings demonstrated that the introduction of ACB fibers, even at the highest fiber content, led to improved mechanical performance. However, a transition in fiber length from 20 to 30 mm exhibited conflicting effects on the composite, likely due to the tendency of bark fibers to bend and split into fibrils during loading. Regarding thermal degradation, the advantages over neat epoxy were evident, particularly for 20 mm fibers, suggesting enhanced interfacial bonding between the matrix and the reinforcement. The epoxy adequately protected the bark fibers, enabling the composite to withstand degradation at temperatures comparable to pure resin, with minimal structural damage below 320 °C. Full article

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10 pages, 1897 KiB

Open AccessBrief Report

Dispersive Propagation of Terahertz Pulses in a Plasmonic Fiber

by Nikolai I. Petrov

Fibers 2023, 11(7), 62; https://doi.org/10.3390/fib11070062 - 14 Jul 2023

Viewed by 1111

Abstract

The dispersion properties of surface plasmon polaritons (SPPs) during propagation on metal wires with a dielectric coating in the terahertz frequency range were investigated theoretically. An analytical expression was obtained for a pulsed electric field using the solution of Maxwell equations taking into [...] Read more.

The dispersion properties of surface plasmon polaritons (SPPs) during propagation on metal wires with a dielectric coating in the terahertz frequency range were investigated theoretically. An analytical expression was obtained for a pulsed electric field using the solution of Maxwell equations taking into account high-order dispersion terms. The influence of the dielectric coating on the distortion of the pulse shape was investigated. Unlike uncoated wire, the propagation of surface plasmon pulses along a coated wire is highly dispersive. It was shown that the coating leads to the appearance of a long-chirped signal with a propagation of only a few millimeters, i.e., when a terahertz pulse propagates along a coated wire, it acquires a long oscillatory tail, the frequency of which depends on time. Full article

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22 pages, 57123 KiB

Open AccessArticle

Flexural Strength of Damaged RC Beams Repaired with Carbon Fiber-Reinforced Polymer (CFRP) Using Different Techniques

by Abbas Yahya Turki and Mahdi Hameed Al-Farttoosi

Fibers 2023, 11(7), 61; https://doi.org/10.3390/fib11070061 - 14 Jul 2023

Cited by 3 | Viewed by 2646

Abstract

In this study, an experimental program was developed to investigate the flexural behavior of pre-damaged reinforced concrete (RC) beams that had been repaired and strengthened using carbon fiber-reinforced polymer (CFRP) laminates under a monotonic load. Two techniques were used: externally bonded reinforcement (EBR) [...] Read more.

In this study, an experimental program was developed to investigate the flexural behavior of pre-damaged reinforced concrete (RC) beams that had been repaired and strengthened using carbon fiber-reinforced polymer (CFRP) laminates under a monotonic load. Two techniques were used: externally bonded reinforcement (EBR) and near-surface-mounted (NSM) reinforcement, to repair and strengthen the tested beams. The experimental program involved casting and testing nine simply supported RC rectangular beams; one beam was considered as the reference beam and did not undergo additional strengthening, and the remaining beams were strengthened using CFRP laminates. These eight beams were divided into two main groups for the purposes of strengthening: beams for which the EBR technique was used, and beams for which the NSM technique was used. The primary variables observed in the EBR and NSM groups included four damage percentages obtained according to the preload (20, 40, 60, and 80%) from the ultimate load carried by the reference beam. The experimental results show that decreasing the damage percentage leads to an increase in ultimate strength from about 3.6% to 17.2% for the beams repaired using the EBR technique and from 27.6% to 57% for the beams repaired using the NSM technique; additionally, the NSM method was more effective than the EBR method in terms of the flexural strength and mode of failure. However, using CFRP laminates enhances the flexure capacity of strengthened RC beams. Full article

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12 pages, 2167 KiB

Open AccessArticle

Hi-Accuracy Method for Spectrum Shift Determination

by Nadezhda Pavlycheva, Ayna Niyazgulyyewa, Airat Sakhabutdinov, Vladimir Anfinogentov, Oleg Morozov, Timur Agliullin and Bulat Valeev

Fibers 2023, 11(7), 60; https://doi.org/10.3390/fib11070060 - 10 Jul 2023

Cited by 1 | Viewed by 1538

Abstract

A new hi-accuracy method for slight-shift determination of low-resolution spectra is proposed. The method allows determining a spectrum shift with an accuracy exceeding the spectrum analyzer resolution to more than three orders of magnitude due to the mathematical post-processing. The method is based [...] Read more.

A new hi-accuracy method for slight-shift determination of low-resolution spectra is proposed. The method allows determining a spectrum shift with an accuracy exceeding the spectrum analyzer resolution to more than three orders of magnitude due to the mathematical post-processing. The method is based on representing the spectrum as a continuous and everywhere differentiable function; expanding it into the Taylor series; approximating all the function derivatives by finite differences of a given order. Thereafter, the spectrum shift is determined using the least-squares method. The method description, its mathematical foundation and the simulation results are given. The advantages of the application of the proposed method are shown. Full article

(This article belongs to the Special Issue Optical Fibers as a Key Element of Distributed Sensor Systems II)

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12 pages, 1107 KiB

Open AccessArticle

Post-Cracking Behaviour of Fibre-Reinforced Shotcrete: A Numerical Comparison between Beams and Panels

by Lina Östlund, Andreas Sjölander and Elin Brodd

Fibers 2023, 11(7), 59; https://doi.org/10.3390/fib11070059 - 4 Jul 2023

Viewed by 1786

Abstract

Fibre-reinforced shotcrete is an essential part of the support of hard rock tunnels. Due to the complexity of the design, a combination of empirical and numerical analysis is commonly used in the design. The required dosage of fibres for structural purposes is determined [...] Read more.

Fibre-reinforced shotcrete is an essential part of the support of hard rock tunnels. Due to the complexity of the design, a combination of empirical and numerical analysis is commonly used in the design. The required dosage of fibres for structural purposes is determined based on minimum energy absorption or residual flexural strength. The latter is derived from tests on beams, while energy absorption is tested on panels. It is widely known that tests on beams suffer from a large scatter in results due to the short fracture zone in combination with the natural variation in the number and orientation of fibres which bridge the crack. This impacts the characteristic strength derived from these tests negatively. This paper presents a numerical study to investigate how the test method affects the required dosage of fibres. First, a non-linear model for shotcrete based on continuum damage mechanics is presented. Thereafter, the model is tuned against test results for beams and panels. A model tuned on beams is then used to simulate the response of a panel and vice versa. The results indicate that the size of the fracture zone has a significant effect on the post-cracking behaviour and that the required dosage of fibres could be decreased if specimens with longer fracture zones, i.e., panels or slabs, are used. Full article

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23 pages, 3024 KiB

Open AccessReview

Use of Sawdust Fibers for Soil Reinforcement: A Review

by Carlos J. Medina-Martinez, Luis Carlos Sandoval Herazo, Sergio A. Zamora-Castro, Rodrigo Vivar-Ocampo and David Reyes-Gonzalez

Fibers 2023, 11(7), 58; https://doi.org/10.3390/fib11070058 - 3 Jul 2023

Cited by 6 | Viewed by 6447

Abstract

A frequent problem in geotechnics is soils with inadequate physical–mechanical properties to withstand construction work, incurring cost overruns caused by their engineering improvement. The need to improve the engineering properties of soils is not recent. The most common current alternatives are binders such [...] Read more.

A frequent problem in geotechnics is soils with inadequate physical–mechanical properties to withstand construction work, incurring cost overruns caused by their engineering improvement. The need to improve the engineering properties of soils is not recent. The most common current alternatives are binders such as cement and lime. The climate change observed in recent decades and the uncontrolled emission of greenhouse gases have motivated geotechnical and geoenvironmental researchers to seek mechanisms for soil reinforcement from a more sustainable and environmentally friendly approach by proposing the use of recycled and waste materials. An alternative is natural fibers, which can be obtained as waste from many agro-industrial processes, due to their high availability and low cost. Sawdust, as a by-product of wood processing, has a rough texture that can generate high friction between the fiber and the matrix of the soils, leading to a significant increase in its shearing strength and bearing capacity. This concept of improving the properties of soils using natural fibers distributed randomly is inspired by the natural phenomenon of grass and/or plants that, when growing on a slope, can effectively stabilize the said slope. Full article

(This article belongs to the Special Issue Natural Fiber Competitiveness and Sustainability)

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Graphical abstract

11 pages, 2596 KiB

Open AccessArticle

Numerical Study of Efficient Tm-Doped Zinc-Tellurite Fiber Lasers at 2300 nm

by Elena A. Anashkina and Alexey V. Andrianov

Fibers 2023, 11(7), 57; https://doi.org/10.3390/fib11070057 - 26 Jun 2023

Cited by 2 | Viewed by 1238

Abstract

Fiber laser sources operating near 2300 nm in the atmospheric transparency window are interesting for different applications, such as remote sensing, lidars, and others. The use of Tm-doped fiber lasers based on tellurite fibers is highly promising. We propose and theoretically study a [...] Read more.

Fiber laser sources operating near 2300 nm in the atmospheric transparency window are interesting for different applications, such as remote sensing, lidars, and others. The use of Tm-doped fiber lasers based on tellurite fibers is highly promising. We propose and theoretically study a highly efficient diode-pumped Tm-doped zinc-tellurite fiber laser operating at two cascade radiative transitions at 1960 nm and 2300 nm, with additional energy transfer between these laser waves due to the Raman interaction. We demonstrate numerically that a dramatic increase in the slope efficiency up to 57% for the laser wave at 2300 nm, exceeding the Stokes limit by 22% relative to the pump at 793 nm, can be obtained with optimized parameters thanks to Raman energy transfer from the laser wave at 1960 nm to the wave at 2300 nm. Full article

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Fibers, Volume 11, Issue 7 (July 2023) – 9 articles

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