Flax Fibre Composites Research Articles

Fatigue analysis on flax-epoxy composites: insights and implications

This study investigates the performance of flax fiber and epoxy resin composites, focusing on fatigue testing, which is scarcely reported in the literature. Fatigue behavior is evaluated under full reverse bending loading conditions: R = −1. Apart of the definition of the classic S-N curve, the analysis deeply investigated the evolution of the hysteresis leaf generated during each cycle over the entire fatigue life. This approach allows evaluating interesting parameters such as the evolution of the loss factor and the apparent modulus over life, being these informations fundamental for practical application of natural-fiber composites in engineering applications.

Mahua oil cake microcellulose as a performance enhancer in flax fiber composites: Mechanical strength and sound absorption analysis

Mahua oil cake microcellulose as a performance enhancer in flax fiber composites: Mechanical strength and sound absorption analysis

Comparison of the effects of different ageing tests on flexural properties of flax fibre composites

This study investigates the changes in the flexural properties and microstructure of flax fibre thermoset composites induced by accelerated and natural ageing methods. The reductions in flexural strength and modulus of composites, ranging from 14 %–48 % and 6 %–57 %, respectively or even an increase in flexural properties after the cyclic ageing test, show the diverse effects of the tests on the flax composites. Only small differences in the composites' performance were found between the natural ageing under the shade and natural ageing exposed to sunlight. The long-term moisture cycling did not cause progressive damage; instead, the composite's flexural properties increased, likely due to an improvement in both the fibre's and matrix's mechanical properties. The water immersion test seems to be predictive of the long-term durability of uncoated flax composites in natural conditions. Microstructure analysis supports composites' flexural test results, with flax/epoxy showing superior properties compared to flax/polyester. The results suggest that uncoated flax composites can withstand extreme humidity changes, but perhaps not in applications wherein composites come in contact with liquid water for long periods, likely due to the effects of leaching. The varied impacts of the different ageing tests on flax fibre composites underscore the need to thoroughly select testing protocols that simulate service conditions relevant to the composites' intended application.

Damage indicators in unidirectional natural fibre composites under fatigue loading

This paper investigates the occurrence of failure under fatigue loading of unidirectional flax fibre composites with different matrices. Various parameters, such as dissipated energy, residual strain, and stiffness, were measured to evaluate fatigue damage and the fatigue life of composites. The results indicate that absolute dissipated energy may not be the most suitable indicator for assessing damage in natural fibre composites when they are subjected to fatigue before reaching failure. The research proposes to rather consider the “loss factor”, defined as the ratio of dissipated energy to total energy stored in each cycle. This indicator appears to provide a more effective means of evaluating fatigue life of the studied composites, especially when compared to the dissipated energy observed during fatigue tests at low stress levels. Fatigue and acoustic emission results indicate that biocomposites with better fibre–matrix adhesion show a delayed damage initiation and propagation, as well as longer fatigue life.

Examining the performance of eco-friendly flax fiber composites: mechanical, thermal and durability properties—review

Examining the performance of eco-friendly flax fiber composites: mechanical, thermal and durability properties—review

Towards greener wind power: Nanodiamond-treated flax fiber composites outperform standard glass fiber composites in impact fatigue tests

Wind energy is facing two major problems, recyclability of wind turbine blades, primarily made from fiberglass, and rain erosion on the blade’s leading edges. Here, we show that flax fiber reinforced epoxy composites have less impact fatigue damage than glass fiber (GF) composites made with the same resin. The novel treatment of flax with non-toxic nanodiamonds even boosts its outstanding performance. Nanodiamond-treated flax fiber (FFND) composites exhibit a damage incubation period up to 17 times as long as GF composites and have at least 74% less mass loss. This is connected to lower initial impact pressure, less shock wave reflections and better impact absorption of flax composites. The nanodiamonds act as fiber sizing, strengthening the fibers and their matrix interface. This delays fracturing and results in less erosion, making the biodegradable FFND a promising replacement for GF towards a fabrication of more sustainable and longer lasting wind turbine blades.

Flax–Reinforced Vitrimer Epoxy Composites Produced via RTM

Composite laminates were produced by RTM using similar glass and flax fabrics and both vitrimer epoxy and aerospace-grade epoxy, both formulated for liquid molding. Tensile and flexural properties were measured and compared, revealing that the vitrimer composites exhibited equivalent performance in flexural strength and tensile modulus, but slightly lower performance in tensile strength relative to reference epoxy composites. In general, glass–fiber composites outperformed flax–fiber composites in tension. However, both glass and flax–fiber composites yielded roughly equivalent flexural strength and tensile modulus-to-weight ratios. Flax fabrics were recovered from composites by matrix dissolution, and a second-life laminate showed full retention of the mechanical properties relative to those produced from fresh flax. Finally, a demonstration of re-forming was undertaken, showing that simple press-forming can be used to modify the composite shape. However, re-forming to a flat configuration resulted in local fiber damage and a decrease in mechanical properties. An alternative forming method was demonstrated that resulted in less fiber damage, indicating that further refinements might lead to a viable forming and re-forming process.

Glass fibre hybridization to improve the durability of circular flax fibre reinforced composites with off-the-shelf recyclable polymer matrix systems for large scale structural applications

Natural fibre composites (NFCs) are not durable in the long run because of the susceptibility of natural fibres to environmental conditions and specifically moisture. Hybridizing NFC laminates externally, with synthetic fibre reinforcements, may improve durability, due to their inherent environmental resistance. This work aims to investigate the effects of glass hybridization, on flax fibre composites, studied via accelerated ageing. In specific, the durability of hybrid flax/glass fibre reinforced polymer composites, with two recyclable polymer matrices was investigated. Unidirectional (UD) flax and UD glass fibre reinforcements were employed to fabricate laminates, with two fully-recyclable off-the-shelf resin systems, as matrix: (i) a bio-based epoxy resin and (ii) an acrylic liquid thermoplastic (Elium®). In addition, a standard petroleum-based epoxy polymer matrix was for reference purposes. Weathering and hygrothermal ageing were used to test the durability of coupons, exposed to UV radiation/condensation/water spray environment (weathering ageing), and full-immersion in distilled water at 23, 40, and 60°C (hygrothermal ageing). In all cases, ageing was performed for a total duration of 56 days. The performance of the unaged and aged composite coupons was assessed and compared in terms of flexural and viscoelastic performance as well as SEM (Scanning Electron Microscopy) analysis. It was revealed that the addition of glass fibres with flax fibres in the hybrid composites improves the performance and better resistance against ageing environments than their neat flax fibre composites.

The Effect of Natural Plant and Animal Fibres on PLA Composites Degradation Process

One of the methods to reduce long-term excessive plastic waste is the development and use of composite materials based on biodegradable polymers and natural fibres. Composites with natural fibres can exhibit very good mechanical properties, and the presence of natural fibres can significantly accelerate the degradation of the material. This study aimed to manufacture and analyse the biodegradation process of composites based on biodegradable polylactide (PLA) filled with flax and sheep wool fibres. The effect of flax and wool fibres and their content on the degradation rate compared to that of pure PLA was investigated. The degradation progress and properties of the composites were studied using an optical microscope, SEM, measurement of surface roughness, and contact angle. Additionally, flexural strength tests, a dynamic mechanical analysis (DMA), and a thermogravimetric analysis (TGA) were conducted. The effect of natural fibres on the phase transition and degree of crystallinity was analysed using differential scanning calorimetry (DSC). The results showed that PLA degrades only under UV light, but not in the composter simulating the natural environment. However, the incorporation of both types of fibres accelerated degradation of PLA/fibres composites in soil. Flax fibre composites exhibited better mechanical properties than pure PLA. For composites with wool fibres, although they showed a significant acceleration of the degradation process in the soil, their large content in the composite caused a reduction of mechanical properties. This research showed the positive effect of the addition of natural fibres on the biodegradation of PLA.

Effect of plasma treatment on hygrothermal creep behaviour of flax fibre composite

Atmospheric plasma activation and plasma coating with 3-aminopropyltriethoxysilane (APTES) were used to investigate the effect of a modified interface on the creep behaviour of flax fibre reinforced polyoxymethylene composite. The wetting parameters and the interfacial shear strength indicate that using air-based plasma activation is superior to plasma coating with APTES when improvement of interface and mechanical properties are concerned. Hygrothermal creep tests within the linear viscoelastic region reveal that the creep resistance of air plasma treated composites is significantly enhanced, evidenced by reduced instantaneous strain and slower viscoelastic flow when compared to the untreated composites. However, creep rupture (run to failure) tests demonstrate that the air plasma treatment extends the creep lifespan only under standard conditions (50 % RH and 23 °C). Under severe conditions (85 % RH and 23 °C), plasma-treated composites exhibit a somewhat shorter lifespan, possibly because some damage induced by the plasma treatment is exacerbated at high humidity.

Effect of hygrothermal aging on mechanical properties of continuous flax fiber composites

AbstractThe influence of hygrothermal aging on the mechanical properties of flax fiber‐reinforced polymer (FFRP) composites was studied by examining the mechanical properties and failure mechanism of the composite laminates exposed in distilled water at different temperatures. The resin transfer molding (RTM) process was used to manufacture FFRP laminates, which were then subjected to accelerated aging tests in distilled water at different temperatures. The moisture absorption characteristics of FFRP were analyzed by a water absorption test. Tensile, bending, and low‐velocity impact tests of laminates after different aging conditions were performed. Combined with DSC and FTIR tests, the failure mechanism of FFRP exposure to hygrothermal aging was analyzed. The result indicated that the increase in temperature will accelerate the moisture absorption process of FFRP, and the hygroscopic behaviors at different temperatures conform to Fick's law. In the early stage of hygrothermal aging, the composites undergo post‐curing, and the tensile and bending strengths increase. After that, the tensile and bending strengths are decreased because of the thermo‐oxygen aging of materials and fiber/matrix interface damage. After hygrothermal aging, the impact peak force of FFRP decreases obviously while the absorbed energy increases due to the increase of internal defects and plasticization of composites. The increase of hygrothermal aging temperature aggravates the aging of materials, resulting in a more obvious decline in the tensile, bending, and impact properties of the composites.Highlights The effect of hygrothermal aging on the mechanical properties of FFRP is investigated. With the increase of hygrothermal aging time, the tensile and bending strength of FFRP increased at the early stage of aging and then decreased. After hygrothermal aging, the impact peak force of FFRP decreases and the absorbed energy increases due to the increase of internal defects and plasticization of composites.

Failsafe layer for wind turbine blades: Erosion protection of glass fiber composite through nanodiamond-treated flax composite top layer

Wind turbine blades are mainly made from E-glass fiber (GF) epoxy composites, because of their good ratio of strength to weight and costs. With the increase in blade length and tip speed, the problem of leading edge erosion is becoming more severe, reducing annual energy production and raising maintenance cost. It was recently shown that nanodiamond-treated flax fiber (FFND) composites have significantly less erosion than GF composites and could be an alternative for GF in the turbine blade aeroshells. However, FFND alone might not be suitable for manufacturing turbine blades at the large scale of modern wind turbines. Here, we show that a hybrid composite with a thin layer of only 1.5 mm of FFND on a GF base, can achieve the same superior results as bulk material FFND composite. In addition, we show and explain why aramid fibers, that are known for impact resistance, do not perform well as erosion protection. Our research shows the great potential of this technology to be implemented as a low-cost, lightweight skin layer on the leading edge. Acting as damage-tolerant failsafe layer, negligible ∼0.04% extra weight of the FFND could increase the blade’s base erosion resistance by a factor of 60±20 compared to plain GF, expanding the repair window, reducing costs, and enhancing reliability.

Influence of sodium hydroxide, silane, and siloxane treatments on the moisture sensitivity and mechanical properties of flax fiber composites

AbstractNatural fibers are a sustainable alternative to synthetic fibers due to their high weight‐specific Young's moduli and strengths. However, the mechanical properties of natural fibers are very sensitive to their moisture content. Therefore, chemical treatments are often applied to natural fibers to lower their water absorption and enhance fiber‐matrix interaction. The aim is to study the effects of fiber modifications with sodium hydroxide, silane, and siloxane on the water uptake and tensile properties of flax fiber composites produced via prepreg technology. In addition, the effect of moisture on the composites' tensile properties was investigated by conditioning one part of the tensile specimens according to DIN EN 2823 (at 70°C and 85% relative humidity). The NaOH treatment was the only modification that had positive effects on the Young's modulus and tensile strength in the unconditioned and conditioned state. The increase of the tensile modulus and strength are most likely due to changes in flax fiber composition, crystallinity of the cellulose and the rougher fiber surface of NaOH modified fibers. This shows that chemical treatment of natural fibers may improve the performance level of natural fiber composites and prevent a loss in their mechanical properties in humid environments.Highlights Flax fiber modifications with sodium hydroxide, silane, and siloxane. Flax fiber composite production via prepreg technology. Water uptake after conditioning at 70°C and 85% relative humidity. Tensile tests before and after conditioning. SEM images of modified flax fibers.

Jute and Flax Fiber Composites Enhancement through Carbon Nanotube Filler

This investigation primarily focuses on enhancing the sustainable jute/flax/epoxy nanocomposite with the use of carbon nanotubes (CNTs) as filler. The flax and jute natural fibres were treated with sodium hydroxide solution. The compression moulding technique was preferred for better fabrication. The CNTs were thoroughly mixed with epoxy resin with the help of a ball milling-type mixture. The nanocomposite samples were prepared by varying the reinforcement and filler content. Jute fibre varied from 59 to 99 wt%, Flax Fiber varied from 0 to 40 wt% and the filler was maintained as constant of 1 wt%. The five types of laminated and fabricated composites were characterized in terms of tensile strength, flexural strength and modulus of elasticity. The SEM examinations were carried for the composite samples to analyse the fibre diameter (µm), CNT dispersion and interfacial adhesion. The results revealed that the sample fabricated with 69 jute fibre, 30 wt% flax fibre, and 1 wt% CNT filler outperformed with 60.1 MPa tensile strength, 79.3 MPa flexural strength, 8.1 GPa modulus of elasticity.

The Influence of the Chemical Composition of Flax and Hemp Fibers on the Value of Surface Free Energy.

The article presents the exploration of flax and hemp fibers' surface free energy depending on the chemical composition of the fiber, which is closely related to the plant variety and the method of extracting the fiber. For this purpose, tests of the surface free energy (SFE), evaluation of the percentage content of individual fiber components and FTIR analyses were conducted. The research was carried out with the use of fibrous materials prepared in three different ways: 1. To analyze the effect of subsequent stages of flax fibers refining process on chemical composition and SFE, 2. to explore the dependence of fiber SFE on hemp variety, the water-retting hemp fibers were used, 3. To evaluate the influence of the retting method of hemp fibers BIAŁOBRZESKIE variety on SFE, the fibers extracted with the use of dew and water retting were used as the research material. The study confirmed that the content of individual components in the fiber influenced its sorption capacity and therefore determined its hydrophilic properties. The values of Pearson's linear correlation coefficients determined in the statistical analysis proved that the surface free energy was strongly correlated with the content of individual components in the fibers. Understanding the wettability characteristics of bast fibers will allow modeling the properties of products made of these fibers and designing surface modification processes in order to obtain specific functionality of textile products, depending on their intended utilization.

Tensile, impact, and the damping performance of woven flax‐carbon hybrid polyamide biocomposites

AbstractFiber hybridization is suggested to enhance the properties of fiber‐reinforced composites. Regarding the matrix, thermoplastic alternatives to conventional thermosets are needed to balance mechanical performance and sustainability. We combined woven flax and carbon fibers with a polyamide 11 matrix into a hybrid biocomposite and studied its manufacturing process as well as its impact, tensile, and damping properties. Mechanical damage was investigated using scanning electron microscopy and X‐ray computed tomography. Hybridization significantly improved the tensile properties: 233% higher modulus and 432% higher strength than pure flax composites and 19% higher failure strain than pure carbon composites. Additionally, the hybrid composites exhibited a positive hybrid effect with respect to the impact resistance, characterized by higher displacement at maximum impact force and occurrence of combined damage mechanisms. Although the damping behavior of the hybrid composites remained inferior to that of pure flax composites, their damping factor was 20% higher than that of pure carbon composites. These results provide valuable insights into the mechanical performance of carbon‐flax hybrid composites.Highlights Enhanced mechanical performance and impact resistance in woven flax‐carbon/PA11 hybrid biocomposite compared to nonhybrid reference composites. Superior tensile modulus and strength of hybrid biocomposite than pure flax fiber composite, and greater failure strain than pure carbon fiber composite. A positive hybridization effect in impact properties with a greater displacement at maximum force and higher dissipated impact energy, indicating enhanced ductility and fracture toughness. Improved damping behavior in hybrid biocomposite compared to the pure carbon composite.

Hybridization Effect on Interlaminar Bond Strength, Flexural Properties, and Hardness of Carbon-Flax Fiber Thermoplastic Bio-Composites.

Hybridizing carbon-fiber-reinforced polymers with natural fibers could be a solution to prevent delamination and improve the out-of-plane properties of laminated composites. Delamination is one of the initial damage modes in composite laminates, attributed to relatively poor interlaminar mechanical properties, e.g., low interlaminar strength and fracture toughness. This study examined the interlaminar bond strength, flexural properties, and hardness of carbon/flax/polyamide hybrid bio-composites using peel adhesion, three-point bending, and macro-hardness tests, respectively. In this regard, interlayer hybrid laminates were produced with a sandwich fiber hybrid mode, using woven carbon fiber plies (C) as the outer layers and woven flax fiber plies (F) as the inner ones (CFFC) in combination with a bio-based thermoplastic polyamide 11 matrix. In addition, non-hybrid carbon and flax fiber composites with the same matrix were produced as reference laminates to investigate the hybridization effects. The results revealed the advantages of hybridization in terms of flexural properties, including a 212% higher modulus and a 265% higher strength compared to pure flax composites and a 34% higher failure strain compared to pure carbon composites. Additionally, the hybrid composites exhibited a positive hybridization effect in terms of peeling strength, demonstrating a 27% improvement compared to the pure carbon composites. These results provide valuable insights into the mechanical performance of woven carbon-flax hybrid bio-composites, suggesting potential applications in the automotive and construction industries.

Flax fiber-chitosan biocomposites with tailored structure and switchable physicochemical properties

A facile and sustainable synthesis of unique flax fiber composites (FFCs) is reported, where raw flax fiber (FFR) was immobilized with variable chitosan content. FFCs were structurally characterized via TGA, XRD, SEM analysis, and spectroscopy (IR, NMR, and Raman mapping). Physicochemical characterization of FFCs enabled estimation of the point-of-zero-charge (PZC), solvent swelling at variable pH. Dye adsorption with Rose Bengal (RB) and Methylene Blue (MB) afforded characterization of the surface chemistry of the materials. This contribution study is a first reported example that highlights the unique structure-property relationships of FFC materials and the role of electrostatic interactions between the pristine fiber substrate and chitosan. FFCs with incremental chitosan content display the following trends: (i) greater solvent swelling at variable pH (350 % for FFCs and ca. 100 % for FFR and commercial absorbents), (ii) two-fold enhanced adsorption of RB (FFC 0.5 to FFC 2.0) and (iii) 1.5-fold decreased adsorption of MB (FFC 2.0 to FFC 0.5). The unique “switchable” sorption properties of the FFCs toward solvent and dyes was revealed upon facile and noncovalent immobilization of chitosan onto FFR. The sustainable composites reported herein offer a potential adsorption-based technology suitable for filter-based applications in “smart textiles” to biomedical sorbents for wound healing.

Influence of processing and matrix parameters on the manufacturing of unidirectional flax/polypropylene composites

The manufacturing by thermocompression of flax fiber composites requires a good understanding of process parameters. This work focuses on the influence of key parameters in the manufacture of quality unidirectional flax/polypropylene composites by thermocompression. To this effect, a number of matrix and process parameters have been studied and ranked according to their influence on composite morphology and tensile properties. Among tested parameters, process time and temperature tend to decrease tensile strength as they increased from 3 to 11 min and from 180 to 200 °C. As a result, decrease of cooling speed from 15 to 5 °C min−1 also decreased tensile strength. Temperature of 180 °C also led to composites with no dispersion of fibers. Using a compatibilized agent, maleic anhydride grafted polypropylene (PP), also increased tensile strength of composites. Increasing its percentage from 3 to 5% increased tensile properties in the 90° direction. Pressure had no significant effect on mechanical properties, though lower pressures increase fiber dispersion.

Effect of e‐waste materials as filler in the flax woven fiber reinforced polymer composite for a sustainable environment

AbstractThe main aim of the present investigation is to fabricate waste printed circuit board (WPCB) particles and woven bidirectional flax fiber mat reinforced polymer matrix composite through a hand layup technique followed by vacuum bagging technique and examine its mechanical properties using the Universal Testing Machine (UTM), compression testing machine, and Shore D hardness tester. The WPCB particles with weight percentages of 0, 5, 10, 15, and 20 were used as reinforcement along with five layers of flax fiber mat to improve the adhesion behavior of epoxy resin with reinforcements and thereby improve the properties. The XRF (X‐ray fluorescence) investigation of the prepared WPCB particles confirmed the existence of various toxic elements in the processed printed circuit board (PCB). The scanning electron microscopy (SEM) analysis confirmed the presence of WPCB particles in the composite, along with flax fiber and resin. The tensile, compression, impact test shows that that the 15 wt.% WPCB particles reinforced flax fiber polymer composite gave betters properties, and the reduction of properties was seen thereafter. The percentage of water absorption increased with the weight percentage of the WPCB particles from 0% to 20%. Results indicate that the biodegradable flax fiber composites impregnated with WPCB filler can be utilized for many engineering and domestic applications.