Technical Fibres Research Articles

Toward the cottonization of hemp fibers by steam explosion. Flame-retardant fibers

The goal is to produce cottonized hemp fibers with improved thermal stability. It was first found that the fine hemp fibers produced from technical non-retted hemp fibers by steam explosion exhibited an enhanced thermal stability. An efficient and low-cost process was developed using a mixture of urea/etidronic acid in aqueous solution in order to achieve a high phosphorus content and produce flame retardant fibers by chemical grafting. ICP, 31P and 13C NMR, SEM, thermogravimetric, Pyrolysis-Combustion Flow Calorimetry analyses and a flame test were used to characterize the grafted fibers. Fibers modified with relatively high P and N contents have been produced (≈ 6 wt % and ≈ 4 wt % respectively) but lower grafting rates (P ≈ 0.5 % and N ≈ 0.35 %) are sufficient to produce non-flammable fibers. A synergistic effect between N and P has been proposed to induce the formation of a stable char.

Multimodal assessment of flax dew retting and its functional impact on fibers and natural fiber composites

Flax (Linum usitatissinum L.) is an economically important fiber crop species as it produces long cellulosic fibers with high tensile strength. The first step in flax fiber extraction occurs after harvest via a process known as dew retting in which pulled (uprooted) plants are placed on the soil. During this process microorganisms from the soil and the phyllosphere develop on the plants, leading to partial decomposition of the stem tissues and facilitated mechanical extraction and improved fiber quality. Despite its importance, the management of dew retting is mainly based on empirical knowledge that makes the process difficult to control. In this study the dynamics of flax dew retting were investigated for the first time by combining targeted-metagenomics (metabarcoding), enzymatic activities and chemical and microscopic characterization of the stem. This multimodal approach indicated that intensive microbial colonization and major chemical changes in the stem cell wall composition occurred during the first weeks of retting leading to progressive fiber bundle decohesion in the outer stem tissues. The main changes could be explained by the degradation of pectin-rich and non-lignified thin walls of both the parenchyma cells surrounding fiber bundles, and the differentiating xylem and cambial cells. Field emission scanning electron microscopy suggested that the ultrastructure of the fiber secondary wall is weakly impacted by dew-retting. Analyses indicated that the mechanical properties of extracted technical fibers were improved during the last retting stages. Overall data on thermoplastic composites produced by a twin-screw extrusion and injection molding processes suggested that the retting degree had a small but significant effect on tensile properties.

Synthesis and Characterization of Aromatic Poly(azomethine ether)s with Different meta- and para-Phenylene Linkage Contents

New aromatic poly(azomethine ether)s (PAMEs) bearing different meta- and para-phenylene linkage ratios in the main chains were synthesized via solution polycondensation reactions of terephthalaldehyde and/or isophthaldehyde with 3,4′-diaminodiphenyl ether. The molecular structures, thermal stability, thermo-mechanical and optical properties of the synthesized PAME homopolymers and copolymers were investigated by using FT-IR, TGA, DMA, and UV-visible/ fluorescence spectroscopy, respectively. The synthesized PAMEs were characterized to be thermally stable up to ~400 °C under nitrogen or air atmosphere and to have high char residues of above 55 % at 800 °C under nitrogen condition. The DMA data revealed that the glass transition temperatures of PMAEs are in the range of 150–200 °C, depending on the relative contents of meta- and para-phenylene linkages. The maximum absorption wavelength of transparent yellowish PAME films was detected at 410±10 nm. In addition, all PAME films exhibited a broad visible emission band at 500–800 nm and two infrared emission bands at 800–1400 nm. The synthesized PAMEs with high thermal stability and thermo-mechanical performance can be thus used as functional polymeric materials for technical fibers, optoelectronic films, and carbon fiber precursors.

Investigation of the date palm fiber for green composites reinforcement: Quasi-static and fatigue characterization of the fiber

This work describes the quasi-static tensile behavior and cyclic fatigue of technical fibers from date palm tested for the first time according to the authors' knowledge, which can be used in the reinforcement of green composites.The values of the stress and strain at failure and Young's modulus for18 samples tested under quasi-static tensile loading are compared with results reported in the literature for other fibers. Cyclic fatigue tests were performed at a frequency of 2 Hz under sinusoidal solicitation for different loading levels ranging from 0.6 to 0.95 corresponding to maximum recorded forces of 15.36 and 39.82 N, respectively. The evolution of the force as a function of the number of cycles was recorded. This allows us to follow the stiffness degradation. The load-displacement hysteresis curves show the influence of the number of cycles and the loading level on the size and shape of the hysteresis loops, allowing the calculation of the dissipated energy per cycle for the technical fibers.

Study of solutions to optimize the extraction of hemp fibers for composite materials

Fibres from hemp stems can be extracted through different mechanical processes following dew or water retting etc. Extraction processes generally have a significant impact on mechanical and morphological properties of the fibres. In this study, hemp fibres are extracted following three different ways. In the first route hemp fibres are extracted from FUTURA 75 variety stems by performing scutching, hackling and microwave degumming. A second batch of fibres of the same variety was extracted by scutching and hackling after an initial microwave degumming treatment. In the third route, the same variety of hemp fibres are extracted from dew retted stems grown at Piacenza (Italy). Finally, the mechanical properties of single fibres as well as the fineness of technical fibres of all types of extracted fibres are evaluated and compared and the interest of the microwave degumming for hemp stem is evaluated.

Investigation of tensile strength and dimensional variation of T700 carbon fibres using an improved experimental setup

Knowledge of fibre strength is crucial for understanding the failure behaviour of fibre-reinforced composite materials and structures. Measuring the properties of technical fibres has been known to be very challenging, and the different challenges associated with single fibre characterisation are illustrated in this article. An improved and automated experimental methodology for tensile testing of single fibres is described. This process has been used to generate fibre strength data for T700 carbon fibres at three different gauge lengths of 4, 20 and 30 mm. The variability in strength and modulus of short fibres was found to be much larger than that of longer fibres. Statistical analysis of this large data set has also highlighted the limitations of the standard Weibull distribution for representing fibre strength behaviour. The need for a better statistical representation of the fibre strength data in order to provide a more accurate description of the fibre strength behaviour has been emphasized.

Thermal and mechanical behavior of thermoplastic composites reinforced with fibers enzymatically extracted from Ampelodesmos mauritanicus

This work investigates the morphology, the thermal, and mechanical properties of technical fibers extracted from the Ampelodesmos mauritanicus (Diss) grass using a process that combines mechanical, mild chemical, and enzymatic steps. The structure and the thermal stability of Diss fibers make them suitable as a reinforcing filler in polymer composites, which was assessed by manufacturing biocomposites with improved stiffness and a tensile strength not degraded by Diss fibers when compared to those of a commodity polymer and a biodegradable one, namely polypropylene and poly(lactic acid). This work confirms that enzyme mixtures obtained from commercially available products of relatively low cost can represent a simple and environmentally friendly means to extract less common natural fibers. POLYM. ENG. SCI., 59:2418–2428, 2019. © 2019 Society of Plastics Engineers

Bamboo fibres sourced from three global locations: A microstructural, mechanical and chemical composition study

More than 1200 bamboo species are known; therefore, the question arises which species are suited for composites and which microstructural characteristics of the plant are decisive. Three different bamboo species are considered, each of two ages. Technical fibre tensile tests and impregnated fibre bundle tests were performed to characterize the fibres and maceration was applied to determine the length over diameter ratio of the elementary fibres. From the impregnated fibre bundle tests it is concluded that the stiffness of bamboo fibres from tropical species considered in this research is unaffected by the species nor the age of the plant. The strength is more affected by the region of growth, with the temperate bamboo species having lower strength as a result of a lower length over diameter ratio of the elementary fibre. Chemical analysis helped to investigate the age difference and it can be stated that the fibres are mature within one growing season.

Physicochemical and Mechanical Performances of Technical Flax Fibers and Biobased Composite Material: Effects of Flax Transformation Process

Physicochemical and Mechanical Performances of Technical Flax Fibers and Biobased Composite Material: Effects of Flax Transformation Process

CHEMICAL TRANSFORMATION OF TECHNICAL FIBER OF FLAX, HEMP AND JUTE TO CELLULOSE AND THEIR PYROLYSIS

Taking into account the chemical composition and morphological features the technical high purity fibers of flax, hemp and jute were studied as a new potential source of cellulose. The kinetics of the oxidation-hydrolytic method was shown for producing pulp from technical jute fibers in an aqueous alkaline medium containing the active components. The degree of removal of non-cellulosic components from technical jute fibers increases with the concentration of sodium hydroxide in an aqueous medium containing active additives, as well as with the increase in processing time and temperature. With the methods of chemical analysis, wide-angle X-ray scattering, FT-IR spectroscopy, electron microscopy the chemical composition and the supramolecular structure of the samples was studied. The thermal stability of the technical fibers, flax pulp, jute and hemp were determined. It was found that the obtained samples of linen, hemp and jute cellulose have Ib monoclinic modification. The crystallinity of the test samples according to X-ray diffraction method and calculated by limiting adsorption of water was the same within the error. This demonstrates the correctness of using the adsorption method for assessing the degree of crystallinity of cellulose. The obtained cellulose flax, hemp and jute were thermally stable up to 324-337 ° C.

In-depth study of the microstructure of bamboo fibres and their relation to the mechanical properties

The mechanical properties of bamboo technical fibre, from the species Guadua angustifolia, have been studied showing values of strength up to 800 MPa and E-modulus up to 43 GPa, proving their adequate tensile properties that make this natural fibre suitable as reinforcement in composite materials. To fully explore the good mechanical properties and to make an adequate use of this new reinforcement, it is indispensable to comprehensively understand the fibre behaviour as a function of the microstructure. Microscopic observations have provided us with an extensive knowledge of the complex microstructure of this natural fibre from the macroscale down to the microscale level where different features like the distribution of the elementary fibres within the fibre bundle, dimensions and layering pattern of the elementary fibres and the main microfibrillar angles could be measured. The Young’s modulus of the elementary fibre is analysed based on the micromechanics of composite materials, commonly used for unidirectional short fibre composites, and the fibre microstructure. The predicted results are in reasonable agreement with experimental data, showing the appropriateness of the model for describing the elementary fibre stiffness. Also, the failure modes of single fibres after tensile testing are analysed by microscopic observations, to have an indication of the stress development in the elementary fibres and the different failure mechanisms.

Effect of chemical treatments on the mechanical properties of technical flax fibres with emphasis on stiffness improvement

The weak visco-elastic interphase between elementary fibers in a reinforcing technical flax fiber is presumed to play a crucial role in the stiffness reduction during loading. To avoid this stiffness reduction, ethanedial (glyoxal), 3-aminopropyltriethoxysilane (APS) and dimethyloldihydroxyethylene urea (DMDHEU) were investigated as potential fiber treatments in this paper. Tensile tests on single technical fibers show that treating the fibers in an aqueous 3 wt% glyoxal solution was sufficient to increase the technical fiber modulus from 41.6 ± 2.3 GPa to 57.3 ± 2.9 GPa. Further, spectroscopic techniques (FTIR, NMR and XPS) detected increased amounts of acetal and ester bonds after glyoxal treatment. This suggests that cross-linking has taken place between pectin and hemicellulose molecules in the amorphous interphase between elementary fibres. APS and DMDHEU treatments were less successful in improving the technical fibre stiffness due to their lower reactivity towards hydroxyl functionalities compared to glyoxal.

Dynamic In-Situ Observation on the Failure Mechanism of Flax Fiber through Scanning Electron Microscopy

In order to develop and improve bio-inspired fibers, it is necessary to have a proper understanding of the fracture behavior of bio-fibers such as flax fibers from an individual fiber down to the constituent micro-fibrils and nano-fibrils. For investigating the failure mechanism of individual and technical flax fibers, a tensile test bench was placed within a scanning electron microscope, and the entire process of fiber failure was investigated through the capture of an SEM movie. Next, fractographic analysis was performed on the failure surface of single fibers as well as meso-fibrils that failed at a displacement rate of 0.25 mm/min, 0.75 mm/min, and 1.6 mm/min. The analysis also enabled visualization of a few internal details of flax fiber such as the arrangement of meso-fibrils and micro-fibrils (nano-fibrils). It was shown that the crack bridging mechanism and successive fiber pull-out contributed to the high work of fracture of flax fiber and the value may reach as high as 10 6 J / m 2 .

An enhanced method to determine the Young’s modulus of technical single fibres by means of high resolution digital image correlation

To obtain mechanical tensile properties of materials it is customary to equip the specimen directly with a device to measure strain and Young’s modulus correctly and only within the measuring length defined by the standards. Whereas a variety of tools such as extensometers, strain gauges and optical systems are available for specimens on coupon level, no market-ready tools to measure strains of single fibres during single fibre tensile tests are available. Although there is a standard for single fibre testing, the procedures described there are only capable of measuring strains of the whole testing setup rather than the strain of the fibre. Without a direct strain measurement on the specimen, the compliance of the test rig itself influences the determination of the Young’s modulus.This work aims to fill this gap by establishing an enhanced method to measure strains directly on the tested fibre and thus provide accurate values for Young’s modulus. It is demonstrated that by applying and then optically tracking fluorescing polymeric beads on single glass fibres, Young’s modulus is determined directly and with high repeatability, without a need to measure at different measuring lengths or compensating for the system compliance. Employing this method to glass fibres, a Young’s modulus of approximately 82.5 GPa was determined, which is in the range of values obtained by applying a conventional procedure. This enhanced measuring technology achieves high accuracy and repeatability while reducing scatter of the data. It was demonstrated that the fluorescing beads do not affect the fibre properties.

Influence of Stem Diameter on Fiber Diameter and the Mechanical Properties of Technical Flax Fibers from Linseed Flax

The continued search for sustainable and eco-friendly materials has led to the integration of bio-fibers, such as flax fiber, as reinforcement in composite materials; however, a wide variation in their diameters and mechanical properties poses a considerable challenge for their incorporation in load bearing and structural bio-composite materials. In this paper, a rigorous experimental investigation was performed using two varieties of linseed flax from two growing locations to determine if the variations observed in ultimate tensile strength, Young’s modulus, failure strain and diameter could be attributed to the diameters of the stems that produced the fibers. Tests were performed in two different facilities and the results were compared and analyzed using Welch’s t-tests. Results showed that samples which differed by stem diameter had statistically significant positive correlation with fiber diameter and negative correlation with tensile strength. No correlations for tensile strength, Young’s modulus or fiber diameter were found in samples with the same stem diameter range that were grown in different locations or were of different varieties, that is the effect of location and variety is not statistically significant. Failure strain did not show any statistical significance with respect to differences in stem diameter and only showed one statistically significant result between both facilities for one of the two growing location comparisons.

Effect of discontinuities in bamboo fibre reinforced epoxy composites

This paper performs a systematic study of the effect of various unidirectional fibre patterns, ranging from different overlapping lengths of adjacent fibre bundles to a complete randomization of the position of individual fibre ends. The study is benchmarked with the mechanical behaviour of a fully continuous unidirectional bamboo fibre-epoxy composite and will show the feasibility of using UD discontinuous technical bamboo fibres in continuous preforms for high-end composites applications. The study shows that the tensile stiffness is hardly influenced by the discontinuity patterns, while the introduction of randomized fibre end discontinuities (individual fibres with segment length 50 mm) leads to a preservation of 85% of the longitudinal tensile strength in comparison with a UD continuous bamboo fibre composite.

The adsorption of polystyrene nanoparticles on selected commercially available fibers: a streaming potential study

The article describes the analysis of the adsorption properties of commercially available fibers. Negatively charged polystyrene particles were used for the adsorption on the selected fibers at different pH ranges of the used electrolyte. The streaming potential method proved useful in the assessment of the electrokinetic properties of the fibers. As expected, good adsorption was observed for most fibers that were positively charged in the conditions of the experiments due to electrostatic attraction. Interestingly, for some fibres an increase in zeta potential was observed in the conditions in which both the adsorbent and the adsorbate were negatively charged. An explanation was proposed for this phenomenon, but could not be proved. The adsorption in the conditions of the isoelectric points of the fibers resulted in little to no changes in their zeta potential in most cases. Moreover, in some cases, the adsorption study produced scattered and irreproducible results. This behavior may have its origin in the nature of the selected fibers, which were mostly technical fibers for applications in fields other than adsorption.

Effect of the middle lamella biochemical composition on the non-linear behaviour of technical fibres of hemp under tensile loading using strain mapping

This manuscript describes the effects of alterations in biochemical composition on structural morphology and the mechanical behaviour of technical fibres of hemp used for composite applications. First, the strength and apparent Young’s modulus distribution of technical fibres of hemp of 96 hemp samples, corresponding to 32 different hemp accessions cultivated in 3 locations, were analysed using Weibull distribution. From these, 2 samples (one with high and one with low fibre strength) were selected for further analysis. Next, full-field strain measurement at the micro-scale during tensile loading via digital image correlation analysis was used for evaluating both, the stress-strain behaviour at a global scale and the local mechanical behaviour heterogeneity at a micro-scale, along a technical fibre of hemp. The analysis reveals 2 typical types of tensile stress-strain curves, and a complex and very irregular pattern of strain concentrations, which are associated to the technical fibre strength. The non-linear behaviour of the stress-strain curve is explained by the development of shear strain at the elementary fibre (botanically defined as the individual cell) interphases. Micro tomography and biochemical analysis of the technical fibre microstructure showed that alterations in cell wall composition, in particular substitution of pectin, leads to changes in the non-linear behaviour of technical fibres of hemp under tensile loading.

Changes in hemp secondary fiber production related to technical fiber variability revealed by light microscopy and attenuated total reflectance Fourier transform infrared spectroscopy.

Interest in hemp (Cannabis sativa L.) is increasing due to the development of a new range of industrial applications based on bast fibers. However the variability of bast fiber yield and quality represents an important barrier to further exploitation. Primary and secondary fiber content was examined in two commercial hemp varieties (Fedora 17, Santhica 27) grown under contrasted sowing density and irrigation conditions. Both growing conditions and hemp varieties impact stem tissue architecture with a large effect on the proportion of secondary fibers but not primary fibers. Attenuated total reflectance infrared spectroscopy allowed the discrimination of manually-isolated native primary fibers and secondary fibers but did not reveal any clustering according to growing conditions and variety. Infrared data were confirmed by wet chemistry analyses that revealed slight but significant differences between primary and secondary fiber cell wall composition. Infrared spectroscopy of technical fibers obtained after mechanical defibering revealed differences with native primary, but not secondary fibers and also discriminated samples obtained from plants grown under different conditions. Altogether the results suggested that the observed variability of hemp technical fibers could be partially explained by i) differences in secondary fiber production and ii) differential behavior during mechanical defibering resulting in unequal separation of primary and secondary fibers.

NONWOVEN DEVELOPMENT BY THE MULTILAYER STRUCTURE

The main two directives of the European Commission (EC) has been regulating the automotive industry. The aforementioned directives and education of residents on environmental issues has created the need for new materials that have been produced from renewable resources and should be recycled at the end of product life cycle.
 The objective of this project is to develop a nonwoven materials (NWM) that would incorporate fibers of plants, which could be grown in Latvia because of suitable local climate conditions, for the use in automotive industry. Furthermore, inclusion of polymer fibers in the NWM will expand the areas of use of such material – the NWM can be transformed into a composite material by means of a thermal press.
 Manufacturing process of NWM consist of structure modelling and material samples manufacturing. NWM samples production process to be carried out by fibers preparation, fibers mixing, formation by airlaid method, preparation of fiber webs for fixation with a mechanical needle punching method, mechanical fixation of fiber webs, preparation of fixed fiber webs for NWM manufacturing and manufacturing of NWM by mechanical needle punching method.
 This article reflects the comparison of two compositions NMW (Polylactid (PLA) (60 wt%) and long flax fibres (40 wt%), and PLA (60 wt%) and technical hemp fibres (40 wt%)) with the same structure by visual appearance, geometrical parameters and tensile strength. The average surface density of hemp NWM varies in the range of 792.09 to 958,71 g•m−2 , thickness varies from 6.91 to 9.23 mm. Flax NWM average surface density is higher than hemp NWM and varies in range of 1,064 to 1,260 g•m−2, thickness of the material varies from 12.62 to 15.54 mm. For comparison, the surface density of NWM currently used in automotive industry, depending on the use of the material, varies from 100 to 1,400 g•m−2.