Elementary Fibres Research Articles

SPECIFICITY OF CHANGE IN SORPTION CAPACITY OF FLAX FIBER UNDER REGULABLE BIO-CATALYTICAL DESTRUCTION OF NEUTRAL CARBOHYDRATES

Evaluation of the nano sizes of hydrosols from homogeneous cellulosic and industrial products was made using dynamic light scattering method. The influence of the size of the globule of protein catalysts and the duration of their action on the roving of carded flax fiber was compared. The correlation between the change in the equilibrium absorption of sorption marker (methylene blue) and residual content in the fiber of hemicelluloses was monitored. On the basis of a comparative analysis of the efficiency of biocatalysts in industrial homogeneous and cellulosic preparations it was revealed that globule size influences on the efficiency of sorption properties of flax fibers. The use of homogeneous enzymes with differing sized parameters has allowed isolating the contribution of the target enzymatic modification as in the microfibrillar structure of elementary fibers and for modification the hemicelluloses in the binding substance fixing the elementary fibers in the bast bundles (the linen fibrous complexes). The principles of selection of biocatalysts to increase sorption capacity in flax fiber sorbents were revealed. It was found that the sorption capacity of flax fiber sorbents increases due to the development of mezopore space in elementary fibres and regulable amorphization of interfiber binders in the structure of the linen complex. The research revealed that the the amorphization of flax fiber took place only when the cellulases was used. The size of their globules enables the penetration of these enzymes into mesopores of elementary flax fibres. It was established experimentally that the presence of large isoforms of cellulases or hemicellulases can promote as the development of the internal volume into the fibre binders and also conservation the permissible level of reduction of the hemicelluloses amount in flax fibres is not less than 10 mass.%.Forcitation:Aleeva S.V., Lepilova O.V., Kurzanova P.Yu., Koksharov S.A. Specificity of change in sorption capacity of flax fiber under regulable bio-catalytical destruction of neutral carbohydrates. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 80-85

Exploring the link between flexural behaviour of hemp and flax stems and fibre stiffness

Hemp (Cannabis Sativa) and flax (Linum Usitatissimum L) are the most commonly cultivated fibre plants in Europe. The use of their fibres covers a wide range of applications and requires a precise knowledge of their mechanical properties. The aim of this study is to investigate the contribution of fibres to the stiffness of flax and hemp dry stems subjected to bending during a simple three-point flexural test. The analysis is based on measuring the difference of bending stiffness between stems with fibres and stems without fibres after removal by manual peeling. Mechanical characterization shows that hemp and flax fibres contribute 54% and 71%, respectively, on average, to the flexural stiffness of a stem. Then, a microstructural analysis of stems is used to determine fibre distribution and geometry, which leads us to obtain longitudinal moduli of 33.9 ± 13.0 GPa and 55.8 ± 14.5 GPa for hemp and flax, respectively. These values are close to those obtained by tensile tests on elementary fibres (30.0 ± 13.3 GPa and 54.7 ± 13.2 GPa). These results encourage to propose the three-point bending test on stems as a standard test for the estimation of bast fibre stiffness.

Investigation of the Mechanical Properties of Flax Cell Walls during Plant Development: The Relation between Performance and Cell Wall Structure

The development of flax (Linum usitatissimum L.) fibers was studied to obtain better insight on the progression of their high mechanical performances during plant growth. Fibers at two steps of plant development were studied, namely the end of the fast growth period and at plant maturity, each time at three plant heights. The indentation modulus of the fiber cell wall was characterized by atomic force microscopy (AFM) using peak-force quantitative nano-mechanical property mapping (PF-QNM). Changes in the cell wall modulus with the cell wall thickening were highlighted. For growing plants, fibers from top and middle heights show a loose inner Gn layer with a lower indentation modulus than mature fibers, which exhibit thickened homogeneous cell walls made only of a G layer. The influence of these changes in the fiber cell wall on the mechanical performances of extracted elementary fibers was also emphasized by tensile tests. In addition, Raman spectra were recorded on samples from both growing and mature plants. The results suggest that, for the fiber cell wall, the cellulose contribution increases with fiber maturity, leading to a greater cell wall modulus of flax fibers.

Study on the Performance of Bamboo Fibre Modified with Different Concentrations of Sodium Hydroxide and Chlorine Containing Agents

In this study, the bamboo fibre bundles (CAN retted fibre bundles) have been treated with sodium hydroxide at different processing conditions, in combination with potassium hydroxide and chlorine containing agent sodium chlorite solution. The purpose of this study was to develop efficient method for the extraction/loosening of bamboo fibres for further textile applications, therefore, lignin content, tensile strength, weight loss, moisture content, whiteness and yellowness indices were measured. Lignin content analysis of the extracted fibre bundles showed that there was a remarkable reduction in lignin content after these treatments. Scanning electronic microscopy of the treated bamboo fibre bundles showed removal of short elementary fibres from their surfaces in appropriate amount which further improved their overall physical properties of treated bamboo fibres.

Influence of hemicelluloses and lignin content on structure and sorption properties of flax fibers (Linum usitatissimum L.)

In this work, alkali and oxidative treatments were employed to obtain flax fibers with different content of hemicelluloses and lignin, in order to study the influence of chemical composition on structure and sorption properties of flax fibers. The flax fibers were characterized using FTIR spectroscopy and FESEM microscopy, and by determination of chemical composition, carboxyl group content, electrokinetic and sorption properties. Adsorption of silver ions was used to evaluate flax fiber sorption properties, but also to obtain antimicrobial fibers whose antimicrobial activity was tested against Gram-negative bacteria Escherichia coli, Gram-positive bacteria Staphylococcus aureus and fungi Candida albicans. The progressive removal of hemicelluloses or lignin influenced the sorption properties through the increased liberation of elementary fibers and accessibility of functional surface groups of flax fibers. Removal of hemicelluloses led to increase of iodine sorption without significant change in functional groups content and electrokinetic properties. On the other hand, lignin removal led to an increase of functional groups content, namely carboxyl groups, which in turn influenced better moisture and silver ions sorption. Flax fibers with incorporated silver exhibit fair antimicrobial activity against Gram (−) E. coli, Gram (+) S. aureus and fungi C. albicans.

Grafting of phosphorus flame retardants on flax fabrics: Comparison between two routes

Flax fabrics were modified through two grafting methods in order to improve their flame retardancy. Vinyl phosphonic acid was used to treat flax fabrics via a condensation reaction between phosphonic acid function and flax hydroxyl groups. It was also grafted under radiation conditions taking advantage of its carbon-carbon double bond. Grafting efficiency of each method was assessed by X-ray fluorescence and scanning electron microscopy. The effect of the phosphorus grafting on fire behavior was studied using thermogravimetric analysis, pyrolysis combustion flow calorimetry and a preliminary fire test. In all cases, the diffusion of the phosphorus molecules into the elementary fibers bulk was observed. Phosphorus content reached 1.4 wt% using radiation grafting, leading to self-extinguishing fabrics.

Radiation-grafting of flame retardants on flax fabrics – A comparison between different flame retardant structures

Three unsaturated compounds bearing respectively phosphate, aryl bromide and sulfenamide moieties were used as flame retardants (FR) for flax fabrics. Due to the presence of carbon-carbon double bonds, radiation-grafting was considered to covalently bond these FR onto fiber structure. Grafting efficiency and location of FR molecules were investigated by weight measurements and SEM-EDX observations. Flammability and especially self-extinguishment were assessed by thermogravimetric analysis, pyrolysis-combustion flow calorimetry and a non-standardized fire test already used in previous studies. All FRs were able to diffuse into elementary fiber bulk. Nevertheless only the phosphonated monomer (noted FR-P) was significantly grafted onto flax. Self-extinguishment was obtained for fabrics containing at least around 0.5wt% of phosphorus. On the contrary the FR content of flax fibers after radiation-grafting procedure and washing was negligible for FR-S and FR-Br, evidencing that these molecules have not been grafted upon irradiation. Moreover, the combination of these molecules prevents the radiation-grafting of other molecules which showed good grafting rate when used alone.

Damage mechanisms in defected natural fibers

A novel experimental setup is presented to reveal damage mechanisms in bast fibers. 3D imaging at submicronic scale based on X-ray micro-tomography is combined with in-situ tensile experiments of both elementary fibers and bundles. The results reveal that the relevant scale that drives failure of hemp lignocellulosic fibers is submicronic. In-situ tensile experiments assisted by X-ray micro-tomography shows complex damage mechanisms involving the constitutive sub-layer structure, fiber extraction defects like kink bands, and the tubular porosity of the natural fiber.

A micromechanical model of interfacial debonding and elementary fiber pull-out for sisal fiber-reinforced composites

The interfacial failure behavior of sisal fiber-reinforced composites (SFRCs) was studied experimentally and theoretically. The residual pull-out strength of the SFRCs was observed to gradually decrease during the single sisal fiber pull-out test, after which the SFRCs presented multiple failure modes, including at the interface between technical fiber and matrix and at the interface between elementary fibers. To further investigate the failure mechanisms of SFRCs, using the traditional shear lag model, a double-interface model tailored to the unique multi-layer interface structure of plant fibers was developed to describe the fiber pull-out behavior and the interfacial adhesion status of single plant fiber-reinforced composites (PFRCs). By comparison with other existing models, using the experimental applied stress as reference, the proposed double-interface model was found to provide a more accurate quantitative theoretical prediction of the interfacial failure behavior of PFRCs during multi-stage fracture of the two interfaces.

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.

Bioactive nanofibrous structures based on hyaluronic acid

AbstractStudies related to selection of molar mass of hyaluronic acid and analysis of rheological properties of hyaluronic acid solutions modified with bioactive substances, used in spinning, were undertaken within the presented work. A cephalosporin group antibiotic, Biofuroxime®, was used, together with the nanoadditives zinc oxide (ZnO) and hydroxyapatite (HAp). Electrospinning studies were performed on selected solutions using a large scale laboratory station, allowing the process to be performed using three nozzles supplying the spinning solution. Optimum electrospinning conditions were selected on the basis of the performed study, which allow fibrous structures made of elementary fibres with diameters below 200 nm to be obtained. Studies showed that the most preferred distance between the nozzle and the collecting manifold was 450 mm and the most preferred applied voltage was 30 kV. The obtained, modified nanofibres of hyaluronic acid comprise structures for use in the production of biomaterials with a wide range of applications in tissue engineering.

Toward the cottonization of hemp fibers by steam explosion – Part 1: defibration and morphological characterization

Fine hemp fibers (cottonized hemp) were processed using steam explosion. The quantification of the defibration rate was performed by image processing. Based on this method, the hemp defibration was optimized using a response surface methodology based on three-variable central composite design for the production of elementary fibers with low variability. Optimal parameters for the steam processes were as follows: time = 4.1 min; temperature = 191℃. Biomass was impregnated with a solution of NaOH (8%) before treatment, leading to a defibration rate of 91.2%, which is producing ≈50% fibers with length <3 mm, in good agreement with the experimental data. Damaged fibers originating from the conjugated effect of steam explosion and alkali hydrolysis were also observed.

Impregnated fibre bundle test for natural fibres used in composites

In this study, the impregnated fibre bundle test, a common method used by carbon and glass fibre manufacturers to determine the properties of fibres used in composites, was adapted for natural fibres and validated by a round robin test on one type of natural fibres, namely flax fibres. Five European laboratories have carried out in parallel the impregnated fibre bundle test, on the same batch of hackled flax (long fibres), to check the applicability and reliability of this modified method on natural fibres. The results were compared to the more traditional single fibre test on elementary fibres. The back-calculated fibre stiffness shows a very low scatter between the five laboratories of less than ±5% (59.8 ± 2.4 GPa, as measured between 0 and 0.1% strain). The fibre ultimate tensile strength of 527 ± 138 MPa has a higher scatter, compared to stiffness values, as this property is highly sensitive to imperfections and flaws.

Wetting and swelling property modifications of elementary flax fibres and their effects on the Liquid Composite Molding process

Flax fibres were thermally treated, to prove that in the same manufacturing conditions, modifying wetting and swelling properties of fibres changes the flow during LCM processes and thus could enhance the final material health of composite parts. Swelling of untreated and treated fibres was measured with optical and tensiometric methods proving that the thermal treatment increases the dimensional stability of flax fibres. A methodology to minimise the dispersion of contact angle values was also developed, and surface energy components of untreated and treated fibres were then determined in the frame of the Owens and Wendt theory. It was evidenced that the thermal treatment makes fibres less hydrophilic. Composite half plates reinforced with untreated and treated flax fabrics were then simultaneously manufactured by Liquid Composite Molding (LCM) process (resin infusion) and finally, a reduction of porosity was observed in composites reinforced with treated flax fabrics.

Nonlinear tensile behaviour of elementary hemp fibres: a numerical investigation of the relationships between 3D geometry and tensile behaviour

Experimental observations have shown that most of plant fibres are characterised by an intricate structure, morphology and organisation. This complex geometrical characteristics may affect the mechanical behaviour of this kind of natural fibres and contribute to the high variability of their mechanical properties. So, this study proposes a numerical investigation on the relationship between the cross-sectional shape of primary hemp bast fibres and their tensile behaviour. A 3D viscoelastic model based on finite element method is used for this study. Real and elliptical simplified cross-sectional shapes are considered. Results of the tensile test simulations clearly show the strong influence of the degree of ellipticity on the tensile response of the fibre, and more exactly on the shape of the nonlinearity of the response. Results also show that this morphologic effect is strongly related and coupled to structural parameters and physical mechanisms, such as the cellulose microfibrils angle and the viscoelastic behaviour of the material of the fibre wall. Geometric issues could then contribute to explain the different types of tensile behaviour experimentally observed and deserve to be taken into account in plant fibre models.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ЩЕЛОЧНОЙ ОБРАБОТКИ НА СОСТАВ И СВОЙСТВА ЭЛЕМЕНТАРИЗОВАННОГО ЛЬНЯНОГО ВОЛОКНА

The possibility of modification of linen fibers according to the essentially new technological scheme which includes purposeful destruction of connective tissues by the action of cyclic de-forming loads (elementarization) with the subsequent chemical processing is proved. The analysis of properties of the obtained elementary fibers of natural origin has shown that geometrical indicators of flax elementary fibers are close to the ones of cotton and wool fibers, and their du-rability is considerably higher, that gives the prospects to create innovative products for technical, textile and medical purposes on their basis. The influence of chemical processings, modeling the processes of modification and upgrading of flax materials, on the composition of basic admixtures and properties of elementarized fibers is investigated. It is shown that the high extent of purification of elementarized fibers raises the possibility of cellulose destruction. The selection of chemical reagents and concentration and time parameters of the process, which provide the optimum extent of purification of elementarized fibers without the destruction of its cellulose component, is carried out. It is determined that chemical processings of elementarized flax fibers in comparison with the cottonized ones have to be carried out in softer conditions: the concen-tration of alkali – to 2 g/l, the processing duration – up to 60 min. As the alkaline reagent the bases weaker than sodium hydroxide can be applied, in particular, sodium carbonate. The insig-nificant destruction of cellulose noted during the subsequent influence of an oxidizer is confirmed by small contents of carboxyl and aldehyde groups in it and also by the durability indexes of new type of fibers: the durability of fibers before and after the chemical processings has no significant differences and is within the limits 40,4–42,0 sn/tex.

Structure–property relationships of elementary bamboo fibers

Natural fibers are promising alternatives to synthetic fibers because of their sustainability, low environmental footprint and specific properties desirable for a wide range of technical engineering applications. The industrial implementation of fine grade natural bamboo fibers, including technical (100–200 microns) and elementary fibers (<30 microns) has been of increasing interest in recent times because these fibers offer a unique set of properties including high tensile strength, antibacterial and UV absorption. However to date, very little scientific effort has been devoted to fully understand the inter-correlation between their mechanical, physico-chemical, microstructural and morphological properties. In this paper, we report for the first time the structure–property relationship of elementary bamboo fibers. The impact of the inner microstructural organization of fibers (including the micro-fibrils angle) and physico-chemical factors such as the cellulose content and crystallinity index, on the tensile performance of these fibers is discussed in detail. This work also provides an insight into the application of bamboo fibers as natural and low-cost sorbent material for the removal of Cu2+ metal ions from model industrial wastewater. The metal ion adsorption properties of the fibers are correlated to surface energy analysis obtained from inverse gas chromatography.

A probabilistic model of the tensile strength of a UD flax–fabric‐reinforced polymer composite

In order to fully realize the efficiency of bast fibers or their yarns as reinforcement of polymer composites, they should be aligned. Tensile strength of such composites in the direction of reinforcement has been found to exhibit size effect commensurable with that of unidirectionally reinforced (UD) composites with inorganic fibers, necessitating a probabilistic modeling approach. Strength distribution of a polymer matrix composite reinforced with aligned twisted bast fiber yarns is considered allowing for the strength scatter of elementary fibers, the presence of defects in the form of adjacent fiber breaks, and twist of the yarns. The model is applied to predicting the strength of flax/acrylated epoxidized soy oil resin composite specimens of different sizes. The theoretical prediction is found to be in a reasonable agreement with strength test results. POLYM. COMPOS., 39:2101–2109, 2018. © 2016 Society of Plastics Engineers

Microstructural analysis using X-ray computed tomography (CT) in flax/epoxy composites

Among natural fibres which have recently become attractive to researchers, flax is probably the most commonly used bast-type fibre today. Due to its properties and availability, flax fibre has potential to substitute glass in polymer composites. A flax fibre has a complex structure; it can be classified into elementary fibres, which are grouped into so-called technical fibres. These technical fibres themselves are actually composite structures. Several works [1, 2, 3] were focussed on the study of damage behaviour in unidirectional flax fibres reinforced composites, where materials were subjected to tensile loading. At the microscopic level and at low stress, microcracks arise within the material and by growing they may lead to other forms of damage such as delamination, fibre breakage, interfacial debonding...etc. In order to better understand the damage phenomena and to better control the parameters which lead to the failure, several methods and techniques have been developed on natural fibre reinforced composites [2, 3]. In the present work, X-ray computed tomography (CT) technique has been used to observe damage in flax/epoxy quasi-unidirectional woven laminates, loaded in uniaxial tension. The tensile tests show that these composites offer good mechanical properties. X-ray computed tomography technique allowed us, on the one hand to determine the microstructure parameters of the studied composites and to observe the damage occurring during loading, on the other. The inspection of the several tomography images showed cracks on interface of the yarns and technical fibres.

Development of Methodology to Assess the Failure Behaviour of Bamboo Single Fibre by Acoustic Emission Technique

Acoustic emission (AE) was used as a tool for detecting, evaluating and for better understanding of the damage mechanism and failure behavior in composites during mechanical loading. Methodology was developed for tensile test of natural fibres (bamboo single fibre). A series of experiments were performed and load drops (one or two) were observed in the load versus time graphs. From the observed AE parameters such as amplitude, energy, duration etc. significant information corresponding to the load drops were found. These AE signals from the load drop occurred from such failure as debonding between two elementary fibre or from join of elementary fibre at edge. The various sources of load at first load drop was not consistent for the different samples (for a particular sample the value is 8 N, stress: 517.51 MPa). Final breaking of fibre corresponded to saturated level AE amplitude of preamplifier (99.9 dB) for all samples. Therefore, it was not possible to determine the exact AE energy value for final breaking. Same methodology was used for tensile test of three single fibres, which gave clear indication of load drop before the final breaking of first and second fibre.