Properties Of Flax Fibres Research Articles

Thermoset and thermoplastic polymer composites reinforced with flax fiber: Properties and application—A review

AbstractFlax fibers are a viable material for creating sustainable composites since they have mechanical qualities similar to those of synthetic fibers. Because of their unique hydrophilicity and strong mechanical properties, flax fibers should be taken into specific attention while creating composite materials. Vegetable fibers like flax are highly versatile and are frequently utilized in structural composites. Additionally, flax has shown potential in a variety of other uses, including as shipping, automotive, aerospace, and construction. This study aims to provide a comprehensive overview of the state of advancement in flax fiber reinforcement composite research. The most important research on thermoset and thermoplastic composites reinforced with flax fiber is compiled and analyzed in this article. This article also summarizes the main properties of flax fibers, discusses chemically enhancing their qualities, explains the process of making and analyzing flax fiber composites, and identifies areas that require more research. The article concludes with a few critical ideas and future directions that emphasize the challenges that need to be handled in more in‐depth research and probable composites industrialization.Highlights Flax fibers: Structure, composition, and extraction techniques explored. Polymer matrices in flax fiber composites: Types and processing methods. Mechanical properties of thermoset and thermoplastic flax fiber reinforced composites. Applications of flax fiber composites in automotive, construction, and aerospace. Future potential of flax fiber and hybrid composites in advanced materials.

Predicting transverse thermal conductivity of flax-fiber using micromechanical model based inverse framework

The paper presents an inverse approach using a micromechanical model for predicting the transverse thermal conductivity of flax fiber, addressing the lack of standard testing protocols for characterizing natural fibers. The model predicts the transverse thermal conductivity of the fiber from experimentally measured properties of the flax-epoxy lamina. The inverse approach was validated using data corresponding to carbon-epoxy composite reported in the literature, with an error of less than 5 %. The transverse thermal conductivity of the flax fiber was estimated to be 0.87 W/m K, which is comparable to other natural fibers. The flax fiber properties were used to evaluate the thermal conductivity of the flax-epoxy lamina for a range of volume fractions, and a simplified non-linear regression equation was proposed. The methodology is further extended to predict the elastic properties of the woven fabric laminate using a multiscale homogenization approach. The proposed framework offers a reliable method for predicting the thermal properties of flax-epoxy composites, which forms the basis for thermo-mechanical analysis and design of automotive and aerospace components.

Effect of boron carbide filler on the mechanical properties of flax fiber reinforced epoxy composites

Effect of boron carbide filler on the mechanical properties of flax fiber reinforced epoxy composites

The critical role of size effect on internal damage and mechanical properties of flax fiber reinforced composites

The effect of the size on the strength of laminated artificial fiber reinforced composites has been extensive discussed during the design of large composites structure. With the trial as the structures in aerospace, civil engineering, automobile industry, the scaling of the properties of plant fiber reinforced composite should be studied. In this paper, the size effect and failure mechanism of tensile and impact properties of flax fiber reinforced composites were valuated. The effects of different area, thickness and volume on the tensile properties of composites were explored. Additionally, the failure mechanism of size effect on tensile specimens was proposed through the damage morphologies of composites. It is found that the twist of fiber bundle plays an important role in the size effect of composite thickness. Besides, the relationship between impact properties and size effect of composites was conducted, including the size of hammer, different impact energy and sample size. The curves of different types of impact samples were normalized to verify the linear rule in response stage. The crack length after impact was measured and the size effect of crack length was discussed. The size effect of crack area was studied by calculating the crack area with ultrasonic C-scan. Different “size effects” between flax fibers and artificial fibers were explored. The results are expected to provide a theoretical basis for the structural design of plant fiber reinforced composites.

Atomic force microscopy-based nanoindentation technique for characterizing the transverse and shear moduli of flax fibers

Experimentally evaluating the elastic properties of flax fibers is challenging due to their complex hierarchical structure, and a standard test procedure for measuring their transverse and shear moduli is currently not reported in the literature. Hence, this study presents an atomic force microscopy (AFM) based nanoindentation technique to evaluate the transverse and shear moduli of flax fiber. A high-precision focused ion beam (FIB)-milling process was used to fabricate a flat surface for indentation along the longitudinal fiber cross-section of the fiber and transverse fiber cross-section by polishing the unidirectional (UD) lamina in order to evaluate the indentation modulus. Further, Swanson's numerical contour approach was adopted to evaluate the elastic properties of the fiber from the measured indentation modulus. The accuracy of the experimentally obtained fiber properties is verified by using it in a micromechanics model for predicting the elastic properties of the UD lamina and comparing it with experimental results reported in the literature.

Mechanical property enhancement of flax fibers via supercritical fluid treatment

The desire for lightweight, carbon-negative materials has been increasing in recent years, particularly as the transportation sector reduces its global carbon footprint. Natural fibers, such as flax fiber and their composites, offer a compelling combination of properties including low density, high specific strength, and carbon negativity. However, because of the low modulus and high variability in performance, natural fibers can’t compete with glass fibers as structural reinforcements in polymer composites. In this study, flax technical fibers were treated in supercritical CO2 (scCO2), and the effects of this treatment on the morphology and properties of flax fibers are reported. Treatment in scCO2 successfully resulted in higher fiber modulus and strength by 33% and 40%, respectively. Fiber porosity was reduced by 50% and morphological changes to the fibers were observed. Specifically, fiber lumen collapsed during treatment and micro/mesoporosity was reduced by 27%. Treated flax fibers were used to create 30 vol% unidirectional flax-epoxy composites. ScCO2 treatment raised composite modulus and strength by 33% and 25%, respectively. Because of the dependence between technical fiber size and mechanical properties, the relationship between fiber modulus and fiber size were created and applied to the rule-of-mixtures. This relationship were found to be viable representations of the fiber performance within each composite. Overall, the treatment developed in this study has the potential to significantly improve natural fiber properties, enabling their consideration for use in lightweight, semi-structural composites.

Mechanical properties of flax fibers as a green alternative for FRCM systems

In recent years, thanks to policies oriented toward the rehabilitation of existing heritage and the introduction of more environmentally sustainable choices, an increased attention has been devoted to the study of new structural strengthening solutions. With reference to masonry buildings, which constitute a significant part of the built heritage, Fiber Reinforced Cementitious Matrix (FRCM) systems are widely adopted to achieve more effective structural capacity, making use of inorganic matrices and composite grids, the latter being formed of carbon, basalt, glass, or aramid fibers. However, the necessity to reduce the carbon emissions, also considering the new European perspectives on sustainability, have prompted the scientific and engineering community to explore eco-friendly alternatives. In this context, the use of natural fibers as potential alternatives for enhancing the structural performance of a building or part of it, rises as a promising area of study. The present study proposes an analysis on the use of flax fibers within FRCM systems, aimed at reinforcing masonry structures. The mechanical and durability properties of the material are investigated through tensile tests on flax yarns, as well as tests on a fabric composed by flax bundles supported by a mesh of glass fibers. The results obtained in this study shaw how the natural type of fiber studied is so interested when it is treated with coating in terms of mechanical properties and durability.

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.

Experimental study on dynamic properties of flax fiber reinforced recycled aggregate concrete

Recycling waste concrete is critical to land use and reduction of landfills. It is a good option to recycle the waste coarse aggregates from it and add them to the concrete matrix. Due to the existence of new and old interface transition zones (ITZs), the quasi-static compressive strength of recycled aggregate concrete is lower than that of natural aggregate concrete, which limits the widespread application of recycled aggregate concrete. In order to improve its engineering application of recycled aggregate concrete, the dynamic compressive properties were studied. Thus, based on a Split Hopkinson Pressure Bar (SHPB) device, the effects of strain rate and recycled coarse aggregate (RCA) replacement ratio on the failure mode, dynamic compressive strength, critical strain and toughness were investigated. It was found that increasing the strain rate led to the aggravation of the specimen damage and growth of the dynamic compressive strength, toughness and critical strain. At a high strain rate, the strain rate effect changed the failure mode of recycled aggregate concrete. This reduced the performance difference between recycled and natural aggregate concrete, in terms of the dynamic compressive strength. The recycled aggregate concrete had a similar toughness to the natural aggregate concrete. Although the growth of the RCA replacement ratio decreased the dynamic compressive strength and increased the critical strain, it had a little effect on the toughness. In order to reduce the brittleness of the recycled aggregate concrete and improve its deformability, non-synthetic, green and low-consumption flax fibers were incorporated into the concrete matrix, and its dynamic compressive behaviors were studied experimentally accordingly. Tests verified that the addition of flax fibers significantly reduced the damage and increased the critical strain. Especially when the strain rate was greater than 200 s-1, flax fiber reinforced recycled aggregate concrete exhibited a superior energy consumption ability. Based on the experimental data, empirical equations were proposed to describe the dynamic compressive strength, critical strain and toughness at different strain rates.

Investigation on the effect of castor‐oil based bio‐resins on mechanical, visco‐elastic, and water diffusion properties of flax fiber reinforced epoxy composites

AbstractDue to the depletion of petro‐based sources and environmental consciousness, researchers are striving to replace synthetic fibers and resins in composites with bio‐sourced ones without compromising their properties. In this regard, the present study investigates the effect of partially replacing epoxy moieties with castor oil based bio‐resins on various properties of epoxy resin and its flax fiber reinforced composite system to achieve sustainable materials, thereby encouraging the bio‐based theme. Base‐catalyzed transesterification was used to synthesize epoxy methyl ricinoleate (EMR) as a low viscous reactive green monomer derived from epoxidized castor oil (ECO). The influence of both ECO and EMR bio‐resin on various mechanical, thermo‐mechanical properties, free mode vibration, and water absorption of epoxy and its composites were studied. The composition with 20% of ECO and EMR was optimized based on stiffness‐toughness balance. The inclusion of 20% EMR significantly escalated the tensile, impact, and fracture toughness properties of epoxy composites by 6.45%, 12.8%, and 14.2%, respectively. The strong fiber‐matrix interface was confirmed by increased pullout adhesion by 21% and 35.1% due to the addition of ECO and EMR, respectively. Dynamic mechanical analyzer revealed a 12% higher storage modulus for EMR modified composites than ECO counterparts. Scanning electron microscope morphology revealed superior interfacial adhesion between fiber and matrix in case of EMR modified bio‐composite, which resulted in a lower water diffusion coefficient than ECO modified bio‐composite. These results showed that the 20% EMR customized epoxy composite is dimensionally stable with improved mechanical properties and may act as a green alternative to petro‐sourced epoxy composites in automotive and semistructural applications.Highlights Effects of castor oil based bio‐resins on epoxy composites are studied. Composites with significant bio‐content (~50 wt%) are developed. EMR modified epoxy composites exhibited improved mechanical properties. A strong fiber‐matrix interface was confirmed by increased pullout adhesion. Reduction in pot life of epoxy was observed on adding ECO and EMR.

Tensile properties hybrid effect of unidirectional flax/carbon fiber hybrid reinforced polymer composites

To improve the mechanical properties of flax fiber reinforced polymer composites, flax/carbon fiber hybrid reinforced polymer composites were prepared by wet winding. The effects of carbon fiber volume fraction, carbon fiber monolayer thickness, and hybrid mode (carbon fiber dispersion) on the properties of hybrid composites were studied by tensile tests considering existing theoretical models. The results showed that the minimum repeating unit of flax fiber as skin and carbon fiber as core can yield a positive hybrid effect. In addition, a lower carbon fiber volume fraction reduced the carbon fiber monolayer thickness, and a higher degree of dispersion emphasized the positive hybrid effect of the hybrid composite. The stress–strain curves of the composite did not exhibit pseudo-ductility given the negligible difference in failure strain and large difference in modulus, such that the carbon fiber layer could not fracture multiple times. In an optimized hybrid composite, introducing 26.4% carbon fiber increased the composite strength by 129.3% compared with the flax fiber reinforced polymer and the composite toughness by 32% compared with the carbon fiber reinforced polymer.

Investigation and optimization of wear properties of flax fiber reinforced Delrin polymer composite

Nowadays, the significance of natural fiber hybrid composites shows increasing trend in the automobile industry. New high-performance polymer materials can be produced from natural fibers which are inexpensive, renewable, eco-friendly, and biodegradable. Because of renewability, natural fibers can be an alternative source to synthetic fibers as a reinforcing agent. This research work looks at flax fiber natural composite material reinforced with matrix material. For a wide range of applications, delrin offers viable replacements for metal composites. In the present work, composites were prepared by injection molding and investigated. The composite constituents were chopped natural flax fiber as reinforcement (5%, 10%, 15% and 20%) and delrin as the matrix (95%, 90%, 85% and 80%). Pin-on-disc (POD) wear tests were conducted to reveal wear strength of the composite under various POD parameters, optimization is done through the hybrid grey relational and principal component analysis approach. The results showed that composite material (Flax+Delrin) shows improved wear strength compared to the non-reinforced material.

Assessment of mechanical properties of flax fiber reinforced with Delrin polymer composite

In the material industry, composites are sought after as more affordable and environmentally friendly materials, they play a vital role. Fiber-reinforced polymer composites exhibit excellent mechanical and tribological properties. One of the natural fibers that are both lightweight and biodegradable is flax. However, the mechanical qualities of natural fiber lag behind those of synthetic fiber. To enhance the structural or mechanical application of hybridization, it is therefore important to study the mechanical properties of natural fiber. The mechanical characteristics of natural flax fibre composite materials reinforced with Delrin matrix material are the foundation of the current review. In this work, static mechanical tests like tensile, impact testing and dynamic mechanical tests like wear test, Shore ‘D’ hardness, flexural and compression properties are evaluated for the Delrin as the matrix and the chopped flax fiber as the reinforcement. Measured mechanical test results showed an incremental increase with the addition flax/Delrin. According to the finding’s, non-reinforced epoxy has inferior characteristics to Flax + Delrin composite materials. Making hybrid composites out of natural fiber and Delrin in the future could bring in a new era for composite materials. This improves the performance and degrading life of composite.

Fire reaction and post-fire impact properties of flax fibre reinforced composites containing intumescent flame retardants

The current research aims at investigating the fire reaction and post-fire impact characteristics of flax fibre reinforced composites based on different polymer matrices, such as epoxy resin and polypropylene (PP). The effects of stacking sequences of polymer sheets and flax fabrics within the composites are explored by a cone calorimeter. Heat release and smoke production results indicate that a top surface and number of flame-retardant polymer layers played significant roles in determining the fire reaction properties. Furthermore, post-fire impact properties of flax-epoxy and flax-PP composites depending on burning periods are analysed in this study at the first time. A fully instrumented drop-weight impact testing demonstrates that an increase in heat exposure time led a gradual decrease in impact properties of the composites due to fire-induced damages on fibres and polymers. However, pre-melting and re-consolidation of PP are beneficial to have higher impact energy and force of the flax-PP composite over those of the flax-epoxy counterpart. In addition, the char formation of composites due to intumescent flame retardant enhances the fire reaction properties of composites, whereas there is no significant influence on the post-fire impact characteristics due to highly brittle nature of carbonaceous char.

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.

An investigation of the effect of relative humidity on viscoelastic properties of flax fiber reinforced polymer by fractional-order viscoelastic model

As an environmental-friendly material with eligible mechanical properties, FFRP (Flax Fiber Reinforced Polymer) composites are being widely studied and used in the construction industry. This paper presents an investigation of the effect of environmental humidity on the viscoelastic properties of FFRP. Frequency sweep tests are conducted, and results are re-organized by the Time-Temperature Superposition Principle (TTSP). The Huet-Sayegh viscoelastic model is introduced to describe the relationship between viscoelastic properties and loading frequency. The fractional derivative is applied to the model for more accurate results. It is found both storage modulus and loss modulus decrease with the increase of relative humidity. However, the loss factor does not have a monotonical correlation with the relative humidity of the environment. In general, it can be concluded both the capacity of FFRP to store and dissipate the energy decreases over the hygroscopicity absorption in the air, but there is no specific relationship between the amount of their reduction.

Hybridization effect of cellulose paper and postcuring conditions on the mechanical properties of flax fiber reinforced epoxy biocomposite

AbstractAn ever‐increasing rise in demand for sustainable materials has received significant attention in developing biocomposites for structural applications. In this regard, natural fibers replacing synthetic fibers as reinforcement in epoxy composite could be a significant gain toward sustainability, especially in automobile and structural applications. Herein, flax fiber/cellulose paper–reinforced epoxy biocomposite (FREC‐X) was fabricated via a vacuum infusion process. The influence of postcuring conditions (time and temperature) and cellulose paper density on the mechanical properties of FREC‐X was studied. The tensile strength and modulus of FREC‐X increased by 37% and 64%, respectively, upon the integration of paper. Postcuring FREC‐X further augmented the tensile and flexural properties of the composite, which could be attributed to the increase in cross‐linking of the epoxy and yields a strong polymer network. Fractography analysis confirmed that the composites integrated with paper showed fewer defects with improved interfacial adhesion. In addition, the water absorption and thickness swelling results revealed that the presence of cellulose paper marginally increased the water uptake and thickness swelling of FREC‐X. Furthermore, there was no significant change in the tensile and flexural properties of FREC‐X observed even after immersing in water for >200 h. Such properties of FREC‐X seen as a fascinating alternative to synthetic fibers and petroleum‐based epoxy and are promising material for sustainable development.

Electron-induced structural changes in flax fiber reinforced PLA/PCL composites, analyzed using the rule of mixtures

The paper presents the effect of electron treatment on the various properties of flax fibers (20 wt%; 5 mm in length) reinforced PLA/PCL (70:30) composites. To enhance the intensity of the electron-induced cross-linking reactions, triallyl isocyanurate (TAIC) as a cross-linking agent was also added (up to 3 wt%). The composites were manufactured by conventional extrusion, granulation, and injection molding techniques, and then electron irradiated at doses of up to 60 kGy. The structural changes were determined using mechanical testing (tensile strength, impact strength, dynamic mechanical analysis), gel content analysis, thermogravimetry, and differential scanning calorimetry (DSC). The modified composites were also subjected to enzymatic biodegradation and industrial composting. An important novelty aspect of the presented research, additionally to the new material composition, is the use of the rule of mixtures in the assessment of the effect of electron treatment on the interfacial interactions of dispersed PCL in the continuous phase of PLA, in the presence of flax fibers. PCL was dispersed in the PLA phase with an average phase size of a few micrometers. Based on the rule of mixtures, it was found that without TAIC, the predominantly degraded PLA phase-initiated cross-linking of the dispersed PCL phase, contributing to the interphase adhesion enhancement reflected in improved mechanical properties. To apply this model, it was required to refer to the previously published results of analogous composites with homopolymer matrix (PLA or PCL). • PCL was an effective impact modifier of flax fiber reinforced PLA /PCL composites. • The continuous phase was PLA with small-size 5 µm PCL lamellar inclusions. • Electron radiation increased the tensile strength and modulus of elasticity. • Effects of electron radiation were elucidated using the rule of mixtures. • The adhesion between PLA and PCL phases improved as a result of electron treatment.

Developing aligned discontinuous flax fibre composites: Sustainable matrix selection and repair performance of vitrimers

Sustainability of fibre reinforced polymer composites has become vital for reaching the global sustainable development goals. Natural fibres, particularly flax, and bioderived matrices are possible sustainable solutions for the composites industry, due to the constituents’ embedded environmental impact reduction. According to the circular economy paradigm, sustainability can also be achieved by delaying the disposal of materials. This work reports the interfacial properties of flax fibres with three potentially sustainable advanced matrices, i.e., a vitrimer that combines the beneficial properties of both thermosets and thermoplastics, an entirely bio-based thermoset, and an advanced thermoplastic resin. Each of the selected matrices offers the potential for either recyclability, repairability, reusability, or the use of renewable sources and a reduction in the emissions of volatile organic compounds. Microbond tests were used to evaluate the interfacial shear strength and critical fibre length. It was found that the vitrimer and the bio-based thermoset matrices had a higher level of adhesion with flax fibres (∼20 and ∼24 MPa, respectively) compared to a traditional epoxy matrix (∼12 MPa); the advanced thermoplastic resin (∼6 MPa) shows the poorest adhesion. The vitrimer matrix was selected as a candidate for a sustainable and repairable discontinuous flax fibre reinforced composite. Mechanical and low-temperature rapid repair performance of an aligned discontinuous flax fibre composite, produced using the HiPerDiF method, were investigated. End-to-end and single patch repair methods were performed: vitrimer matrix composites show the potential for a mechanical strength recovery (∼%50-70) that would allow them to be reused over several life cycles, enabling a circular economy.

Residues from Cajanus cajan Plant Provide Natural Cellulose Fibers Similar to Flax

ABSTRACT With an annual production of about 5 million tons, Cajanus cajan (pigeon pea) generates at least 20 to 25 million tons of stems as residues. These residues are generally disposed of as waste leading to environmental pollution and loss of a valuable raw material. In this report, we demonstrate that the stems of pigeon pea could be used as a source for developing natural cellulose fibers. Fibers were extracted from the stems using only water and also with water followed by alkali treatment. Fibers with high strength (984 MPa) and elongation (3.4%) similar to the properties of flax fibers were obtained. The physical and morphological properties of the fibers were similar to the common fibers. The fibers had good thermal stability and showed potential to be useful for textile, composite, and other applications. Such applications will provide a considerably high value addition to the stems of C. cajan and also be a renewable and sustainable source for fibers.