Mechanical Properties Of Flax Fibres Research Articles

Use of a commingling process for innovative flax fibre reinforced unidirectional composites

Optimisation of textile preforms play a crucial role in the development of high-performance biobased composites materials. In this context, the main ambition of this work is to quantify and assess the mechanical properties and behaviour of biocomposite materials made from unidirectional commingled preforms based on flax and poly-(propylene) fibres. To the best of our knowledge, there is no literature examining the effect of the commingling process on the ultrastructure and the mechanical properties of flax fibres. At the scale of the elementary fibre, fibre mechanical properties are observed to be stable after commingling. However, repeated drawing in the commingling process leads to increased cellulose crystallinity and a larger fraction of elementary fibres exhibiting quasi-linear tensile behaviour. The composite materials produced with these commingled flax/poly-(propylene) preforms contain few cortical residues and show a remarkable degree of fibre individualisation. Moreover, they exhibit high Young's modulus and a stress at break of 24 GPa and 194 MPa, respectively, for a fibre volume fraction of 36 %. A substantial drop in properties is however noted at high fibre fractions due increased heterogeneity of the materials. Remarkably, the biocomposites achieved unprecedented transverse modulus and stress at break of 2.3 GPa and 16.5 MPa, respectively. Our results validate the potential and interest in commingling processes for designing a new family of plant fibre composite materials.

Effect of ozone treatment on the chemical and mechanical properties of flax fibers

The surface of flax fiber is covered by noncellulosic substances, which results in many individual fibers that are bound into bundles. These noncellulosic materials must be removed to extract the usable fiber. In this study, ozone was used to remove the noncellulosic components from the surface of flax fiber. The changing regularity and mechanism of ozone treatment on the lignin content and degree of polymerization (DP) in flax fiber under different operational conditions (pH value, moisture content, ozone feed rate, and reaction time) were fully investigated. Then, the quality of untreated, ozone-treated (ozone 130 mg･L −1 ･min −1 , 20 min), ozone and acid treated (ozone 130 mg･L −1 ･min −1 , 20 min, pH 2.0, moisture content 70%) flax fiber were compared. The effect of ozone treatment on the change in strength, elongation, whiteness, copper number, and thermal stability of flax fiber was systematically tested. The results showed that the lignin content, DP, strength, elongation and thermal stability of flax fiber decreased after ozone treatment. The crystallinity, whiteness, copper number and roughness of flax fiber increased after ozone treatment. This phenomenon was more evident after ozone and acid treatment. Simultaneously, scanning electron microscopy (SEM) analysis showed that the noncellulosic components on the fiber surface were partially removed after ozone treatment and were thoroughly separated after ozone and acid treatment. This study could offer guidance into the removal of noncellulose materials on the surface of flax fiber using ozone treatment. • Ozone treatment was conducted in the gas phase under room temperature and pressure. • The noncellulosic components were removed after ozone treatment. • Lignin content and degree of polymerization was decreased after ozone treatment. • The effect of ozone treatment on flax fibers under acidic conditions were observed.

Exploring the impact of Verticillium wilt disease on the mechanical properties of elementary flax (Linum usitatissimum L.) fibres

Verticillium wilt is a disease caused by the fungus Verticillium dahliae (V. dahliae) which is widespread in flax (Linum usitatissimum L.) cultures. V. dahliae negatively impacts the fibre yield with up to 60% loss at the scutching step of fibre transformation. Yet, little is known about the consequences of V. dahliae on the mechanical properties of flax fibres. In this study, we investigated the tensile characterisation of elementary flax fibres impacted by V. dahlia. Using elementary tensile tests, we observed an important decrease in the mechanical properties of the studied flax fibres, with a 32% decrease of the tensile strength at break and a 15% decrease of the strain at break. Further investigation of the flax fibres cell wall using atomic force microscopy (AFM) in peak-force non-quantitative mechanical mapping mode, showed a 23% decrease in the longitudinal indentation modulus of flax fibre cell walls, measured directly in their cross section. This is arguably due to the important enzymatic arsenal of V. dahliae revealed by a bioinformatic analysis of secreted carbohydrate-active enzymes targeting plant cell wall components. The coupling of this analysis with electron microscopy observations and sugar analysis highlighted the degradation mechanisms of this fungus which significantly affects the mechanical performance of flax fibres

Effect of chemical treatment on the physical and mechanical properties of flax fibers: A comparative assessment

In the present study, flax fibers sorted in two batches were considered for treatment. Set one fibers were treated with chemical reagents - KMnO4 and acetone for durations of 10, 20 and 30 min respectively. The second batch of fibers was treated with stearic acid in ethanol for durations of 24 h and 36 h. Physical properties namely diameter and density were determined. The treated fibers were also tested to determine their tensile and interfacial adhesion strength. A comparison was drawn between untreated fibers and fibers treated with different treating media. A decrement in the diameter of the fibers with increasing duration of treatment was observed. Density increased marginally with treatment due to removal of lighter constituents of the flax fiber like hemicellulose and pectin. Treatment had a positive influence on the tensile and interfacial adhesion strengths of the fibers. However, treatment with stearic acid yielded superior values of mechanical properties in comparison to KMnO4. The tensile strength values were 54% higher for stearic acid, compared to that for KMnO4 treatment. Higher strength of about 14% was also noted in case of single fiber pull out test with stearic acid treatment. Scanning Electron Microscopy was used to study the changes on the fiber surface due to treatment. Micrographs revealed reduction in grooves with increased duration of chemical treatment, exhibiting a uniformity along the fiber surface by reducing the variation of the fiber diameter along its length. Due to higher mechanical properties, stearic acid treatment was considered to be the superior method for processing the flax fibers.

Statistical and Experimental Analysis of the Mechanical Properties of Flax Fibers

ABSTRACT In this paper, 400 flax fibers with 10 different lengths (40 fibers at each length) are experimentally characterized (quasi-static tensile behavior) and then the results are statistically analyzed. The quasi-static tensile test results appeared to have a large dispersion, which makes it possible to measure the degree of variability in the ultimate tensile strength (UTS), failure strain, and the Young’s modulus of the fiber, at different gage lengths (10 mm to 500 mm). The variation in mechanical properties at each fiber length is established using two and three Weibull statistics based on maximum likelihood estimation (ML) and least square estimation (LS). Finally, all 10 groups for each tensile property are analyzed by one-way (ANOVA).

Effect of processing temperature on the static and dynamic mechanical properties and failure mechanisms of flax fiber reinforced composites

In this paper, the effects of processing temperatures on both static, dynamic and time-dependent mechanical properties of flax fibers and their composites were investigated. Initially, the chemical component variations of flax fibers processed at different temperatures were ascertained by using Fourier transform infrared spectrometry (FTIR) and X-ray diffraction (XRD). Tensile tests were further conducted to investigate the effect of temperature on the strength, modulus and failure elongation of the fibers and flax fiber reinforced composites (FFRCs). The corresponding fracture mechanisms were characterized by in-situ acoustic emission (AE) technique. The durability and the energy dissipation and absorption capability of these FFRCs were evaluated with tensile-tensile fatigue tests and drop weight impact (DWI) tests. The results showed that there was a vital turning temperature, exceeding which degradation of partial cellulose, hemicellulose and lignin occurs, which introduced damage into the chemical structures of flax fibers and impaired their mechanical performance. The mechanical properties of FFRCs dominated by flax fiber including tensile behaviors, long-term durability and energy dissipation and absorption capability consequently deteriorate when treated temperature exceeds the turning point.

Effect of eco-friendly chemical sodium bicarbonate treatment on the mechanical properties of flax fibres: Weibull statistics

In this work, a chemical treatment with different concentrations of NaHCO3 (sodium bicarbonate) of 5%, 10% and 20% on the surface of the flax fibre for a period of 120 h at room temperature is achieved. The purpose of this study is to observe the effect of different treatment processes on flax fibres, which is to say on its mechanical properties such as strength and strain at fracture and Young’s modulus. An important campaign of the test of more than 480 tests is carried out. Due to the variability of plant fibres, more than 120 samples were tested for each group at a gauge length (GL = 20 mm). The tensile mechanical property values of the flax fibres present a large dispersion of results; this is typical for natural fibres, hence the need for a statistical study. This dispersion has been studied and carried out by means and statistical tools such as the distribution of Weibull at two and three parameters by applying a prediction model to a confidence level at 95% CI and one-way ANOVA analysis of variance.

Investigation of Microfibril Angle of Flax Fibers Using X-Ray Diffraction and Scanning Electron Microscopy

ABSTRACT Microfibril angle (MFA) of secondary cell wall has an important effect on the mechanical properties of flax fibers. It is therefore essential to study the relationships between MFA and mechanical properties. This paper investigated MFA of seven flax fibers by using X-ray diffraction (0.6T method) and scanning electron microscopy (SEM; direct observation). The results showed that there is no significant difference between MFA obtained by X-ray diffraction (6.2–7.2°) and SEM (5.8–7.3°). Correlation analysis results showed a good linear correlation (>0.9) between two methods.

Screenplay of flax phloem fiber behavior during gravitropic reaction

ABSTRACTFlax phloem fibers act as constitutively formed “muscles” that support the vertical position of the high but narrow stem. The specific mechanical properties of flax fibers and of similar fibers in other plant species are provided by the development of tertiary cell wall with tensed cellulose microfibrils. The work of phloem fibers becomes especially pronounced during the restoration of stem vertical position if it was disturbed. Gravistimulation of flax plants induces considerable modification of phloem fibers at the pulling stem side – the lumen diameter increases, while the cell wall thickness goes down. Here we show that the action of phloem fibers as motors of stem vertical position restoration is coupled to the cell wall remodelling as well as the increase of osmolytes (mainly potassium and malate) content, and accumulation of the γ-amino-butyric acid that may be involved in signalling events. The molecular players that take part in these processes are suggested.

Enhancement of the Mechanical Properties of a Polylactic Acid/Flax Fiber Biocomposite by WPU, WPU/Starch, and TPS Polyurethanes Using Coupling Additives

This work is addressed to the synthesis of bio-based polymers and investigation of their application in a flax-fiber-reinforced polylactic acid. Polyurethane polymers were synthesized from polyphenyl-methane-diisocyanate, poly (ethylene oxide) glycol, and ricinoleic acid, and their structure was examined by the Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. It was established that the introduction of flax fibers and different compatibilizers into the polymers improved their mechanical properties. A vinyl-trimetoxy-silane and polyalkenyl-polymaleic-anhydride derivative with a high acid number produced the best effect on the properties, but samples without additives had the highest water absorption capacity. SEM micrographs showed a good correlation between the morphology of fracture structure of the composites and the mechanical properties of flax fibers.

ANALYSIS OF STRUCTURAL CHANGES OF CELLULOSE COMPONENT IN PROCESS OF ELEMENTARIZATION OF FLAX FIBERS

The comparative research of composition and supramolecular structure of the flax fibers received by methods of a cottonization and a mechanical elementarization under the influence of the cyclic deforming loadings was conducted. It was shown that under the influence of cyclic loadings removal of a considerable part of impurity with the increase in content of cellulose to 80.1% is reached. At the same time, division of complexes onto elementary filament provides the increase in the total surface of material and, as a result, to availability of fibers to the reagents at the subsequent alkaline boiling. X-ray analysis of flax samples with a method of comparison of the normalized parameters of diffraction by crystalline regions of cellulose allowed to establish that degree of crystallinity of a cellulose component of fibers remains constant even at deep purification of raw materials under the influence of cyclic deformations and subsequent boiling. The research of the oriented fibers by X-ray diffraction method has shown that removal of impurity from flax in the course of an elementarization has only weak influence on the sizes of crystallites of cellulose. The increase in the cross sizes of crystallites by 4 – 6% was observed at deep purification of fibers due to the boiling. This phenomenon can be connected with the decrease in influence of a diffraction maximum from impurity on half-width of the equatorial reflex 200 for cellulose Iβ. It should be noted that the longitudinal sizes of crystallites at the same time do not change. It was suggested on possible influence of decrease in content of impurity on supramolecular structure of an amorphous phase of cellulose and as a result on the observed growth of sorption and mechanical properties of flax fibers at an elementarization by method of cyclic deformation.Forcitation:Zavadskii A.E., Stokozenko V.G., Moryganov A.P., Larin I.Yu. Analysis of structural changes of cellulose component in process of elementarization of flax fibers. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 6. P. 102-108.

Scale effect on tribo-mechanical behavior of vegetal fibers in reinforced bio-composite materials

The nature of friction of vegetal fiber and polymeric matrix in bio-composite materials is very important for many industrial applications. In order to design natural fiber composites for structural applications, the scientific understanding of tribo-mechanical phenomena inside the heterogeneous structure of natural fibers and also the overall heterogeneous structure of the bio-composite is required. This implies a special focus on the fundamental aspects of vegetal fiber friction at the macro-, meso-, and microscale. This research paper investigates the multiscale mechanical and friction properties of natural fibers. The mechanical properties of flax fibers, glass fibers (as a reference) and polypropylene matrix has been evaluated at microscale and mesoscale by Atomic Force Microscopy (AFM) and Nanoindenter XP (MTS Nano Instruments), respectively, using nanoindentation technique. At the macroscale, the mechanical behavior has been considered for the global composite structure. The micro-friction response of each composite component has been measured by instrumenting AFM for scratch test technique. The results show the scale dependence of mechanical behavior for flax fibers, unlike glass fibers and polypropylene matrix where their mechanical performances are independent of the analysis scale. Tribological results in terms of dynamic friction coefficient show that flax fibers induce more friction than glass fibers, while polypropylene matrix generates the highest friction. This is sign that vegetal fiber friction is scale dependent property as shown when referring to the contact mechanics theory. The arisen results are very important for many technical applications in PMCs surface engineering based on plant fibers.

Varietal selection of flax over time: Evolution of plant architecture related to influence on the mechanical properties of fibers

The varietal selection of flax (Linum Usitatissimum L.) has always focused on specific criteria fulfilling requirements of farmers and textile workers. Thus, the current development of composites using flax as reinforcement presents new challenges for flax breeders in terms of fiber quantities and quality. However, the impact of the varietal selection on the mechanical properties of resulting fibers is yet to be determined. In the present study, several architectural characteristics of flax stems are defined. Stem transverse sections from four varieties selected from the 1940s to 2011 are compared. Anatomical changes over time are highlighted. The most important ones involve the gap between fiber bundles and the amount of fibers which can be improved with the selection (from 7.8% to 13.4% of the tissue area per section). This trend coincides with the increase in biomass production over time expected from the selection work. Moreover, this study demonstrates that flax fibers preserve their good mechanical performances in spite of the anatomical differences. Thus, through varietal selection, it is possible to increase the biomass yield while preserving the excellent specific mechanical properties of flax fibers. Finally, flax fibers can compete with glass fibers to reinforce composite materials.

Mechanical properties of flax-fibre-reinforced preforms and composites: Influence of the type of yarns on multi-scale characterisations

As the strongest natural fibres, flax fibres are being used increasingly for technical advanced products such as composites with a view to reducing the impact of the material on the environment throughout its life cycle. In order to improve the understanding of the mechanical properties of flax fibres and their reinforced preforms and composites, multi-scale characterisations are carried out to analyse the tensile properties of flax fibre yarns, fabrics and composites. From three types of yarns, quasi-UD fabrics and composites are manufactured with the same process parameters. Tensile tests are performed at each scale to study the effect on the properties of yarn such as the twist level. At the yarn scale a significant variability of the tensile behaviour is pointed out, as described in the literature. The tensile behaviour of un-impregnated fabrics shows the effect of the weaving process. The tensile results at the composite scale indicate the same trend compared to yarn after the weaving and fabric scales. From the experimental results at different scales an analysis is conducted to explain the tensile behaviour, taking into account the different steps of the manufacturing process. In addition, micro-observations through SEM images will confirm the variability of the tensile behaviour of a single flax yarn and emphasize the strong influence of the twist level on the tensile characterisation at different scales.

Surface topography and mechanical properties of flax fibres modified glass ionomer restorative materials

Objectives: Regardless of the excellent adhesive and biological properties of glass ionomer cements (GICs), their poor mechanical properties and abrasion resistance limit their application to non-load bearing areas. This study aimed to investigate the effect of flax fibres incorporation on surface and mechanical properties of GIC filling materials. Methods: Short chopped flax fibres were randomly incorporated into GIC at 0, 0.5, 1, 2.5, 5 and 25 wt%. Surface hardness, distribution of different phases, stiffness map, phase separation and uniformity of the material were investigated. Results: Addition of flax fibres produced no significant change in Vicker hardness number of GIC. Qualitative imaging using atomic force microscopy showed the presence of a single phase in GIC, while biphasic structure was observed for flax fibres modified GICs (FFMGICs). For all tested formulations, the flax fibres, however, were uniformly distributed and well integrated within the GIC matrix without any visible interfacial separation. Incorporation of flax fibres was associated with a significant increase in surface roughness and stiffness. The roughness values obtained for all tested formulations, however, are far below the threshold values for bacterial adhesion and plaque accumulation. Conclusions: Flax fibres modified GICs could be potentially used in high stress bearing areas.

Interrelation Between the Variety and the Mechanical Properties of Flax Fibres

Interrelation Between the Variety and the Mechanical Properties of Flax Fibres

Effects of the hygrothermal environment on the mechanical properties of flax fibres

Since flax is the most promising plant for the reinforcement of polymer-based composites in structural applications, we have chosen to investigate its hygrothermal characteristics which can be useful for the understanding of the behaviour of other plant fibres. The flax fibres were exposed to different hygrothermal conditions: in an oven at various controlled temperatures (–40 to 140℃) and measured relative humidity, in a climate chamber at 50% relative humidity for define temperatures between 25℃ and 85℃, or different determined aging conditions. The correlation of these hygrothermal conditions to the evolution of the mechanical properties gives evidence of the prominent influence of water over temperature on the microstructural changes of flax fibres. The mechanical parameters drastically decrease in usually prescribed hygrothermal aging conditions for organic matrix composite materials, the strength being particularly sensitive to the presence of water. These evolutions were correlated to the fibre microstructure modifications induced by water absorption as revealed by electron microscopy analyses. These findings could be useful for understanding the behaviour of polymer matrix biocomposites in severe hygrothermal conditions.

Could oleaginous flax fibers be used as reinforcement for polymers?

Many works deal with the mechanical properties of flax fibers cultivated for textile applications and today used for the reinforcement of polymers. Nevertheless, quantities of oleaginous flax fiber are obtained each year and not promoted. The aim of this work is to study the mechanical properties of single linseed flax fiber as a function of variety, culture year, dew-retting degree and agronomic factors. Five varieties of oleaginous flax have been characterized by tensile tests on elementary fibers and compared to four varieties of textile flax. These tensile experiments have been carried out on with the same equipment, experimental protocol and environmental conditions. The results show that interesting mechanical properties were obtained with the oleaginous variety and are close of those of textile varieties, such as Agatha or Electra. Considering the diameters and specific properties of these oleaginous fibers, we evidenced that they are good candidates for the substitution of glass fibers in composite materials. To increase the development of flax fibers, it is important to have a better control of the spread of their mechanical properties. This point could be observed with the Everest variety cultivated for 4 years and no conclusion could be made. We have evidenced that the retting degree has no influence on the diameters and mechanical properties of the fibers; the same conclusion is obtained with agronomic factors such as seeding rate and plant height.

Strength variability of single flax fibres

Due to the typical large variability in the measured mechanical properties of flax fibres, they are often employed only in low grade composite applications. The present study aims to investigate the reasons for the variability in tensile properties of flax fibres. It is found that an inaccuracy in the determination of the cross-sectional area of the fibres is one major reason for the variability in properties. By applying a typical circular fibre area assumption, a considerable error is introduced into the calculated mechanical properties. Experimental data, together with a simple analytical model, are presented to show that the error is increased when the aspect ratio of the fibre cross-sectional shape is increased. A variability in properties due to the flax fibres themselves is found to originate from the distribution of defects along the fibres. Two distinctive types of stress–strain behaviours (linear and nonlinear) of the fibres are found to be correlated with the amount of defects. The linear stress–strain curves tend to show a higher tensile strength, a higher Young’s modulus, and a lower strain to failure than the nonlinear curves. Finally, the fibres are found to fracture by a complex microscale failure mechanism. Large fracture zones are governed by both surface and internal defects; and these cause cracks to propagate in the transverse and longitudinal directions.

Role of Polysaccharides on Mechanical and Adhesion Properties of Flax Fibres in Flax/PLA Biocomposite

The effect of alkali and enzymatic treatments on flax fibre morphology, mechanical, and adhesion properties was investigated. The multilength scale analysis allows for the correlation of the fibre's morphological changes induced by the treatments with mechanical properties to better explain the adherence properties between flax and PLA. The atomic force microscopy (AFM) images revealed the removal of primary layers, upon treatments, down to cellulose microfibrils present in the secondary layers. The variation in mechanical properties was found to be dependent, apart from the crystalline content, on interaction between cellulose microfibrils and encrusting polysaccharides, pectins and hemicelluloses, in the secondary layers. Finally, microbond tests between the modified fibres and PLA emphasize the important role of the outer fibre's surface on the overall composite properties. It was observed here that gentle treatments of the fibres, down to the oriented microfibrils, are favourable to a better adherence with a PLA drop. This paper highlights the important role of amorphous polymers, hemicellulose and pectin, in the optimisation of the adhesion and mechanical properties of flax fibres in the biocomposite.