Flax Fibers Research Articles

Revealing the structural variation and degradation mechanism of cellulose during ozone oxidation treatment

Despite numerous studies on the use of ozone for the removal of non-cellulosic substances from lignocellulosic fibers, the mechanism underlying cellulose degradation and the oxidized group formation during ozone oxidation treatment remain unclear. This study focuses on the extraction of α-cellulose from flax fibers. The effect of ozone oxidation on the degree of polymerization (DP) and oxidized groups in α-cellulose under different operational conditions (ozone concentration, oxidation time, water pick-up value, initial pH value) were thoroughly investigated. Additionally, the quality of α-cellulose oxidized under different phases (gas and liquid) of ozone reaction was systematically compared. Results showed that the DP value of α-cellulose-O3-Gas-80% (130 mg·L−1·min−1, 15 min, WPV 80%, pH 2.0) was lower than that of α-cellulose-O3-Liquid (130 mg·L−1·min−1, 15 min, 1:30 g·mL−1, pH 2.0) and α-cellulose-O3-Gas-0% (130 mg·L−1·min−1, 15 min). However, the carboxyl and carbonyl contents showed the opposite trends. FTIR results showed a new peak (carboxyl peak) for α-cellulose and a reduction of hydrogen bonding interactions in molecules after ozone oxidation. In addition, the crystallinity and thermal stability of α-cellulose decreased after ozone oxidation, with α-cellulose-O3-Gas-80% exhibiting the most significant decline. SEM analysis showed that the morphology of α-cellulose was changed after ozone oxidation. This study provides some guidance to mitigate ineffective degradation of cellulose and assist in the selection of cellulose protectors during the process of extracting lignocellulosic fibers by ozone oxidation.

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.

Design and Fabrication of High-Load Bearing Bio-Composites Reinforced with Flax Fibers

Design and Fabrication of High-Load Bearing Bio-Composites Reinforced with Flax Fibers

Bcomp's flax fibers in NASCAR prototype, ITACA bike and Italdesign Quintessenza™ Concept Car

Bcomp's flax fibers in NASCAR prototype, ITACA bike and Italdesign Quintessenza™ Concept Car

The growing use of flax fibre in transport

Automotive and mobility manufacturers continue to evaluate flax and hemp materials across their model ranges as they look to reduce the overall environmental impact of their products, while taking advantage of their technical properties, says the Alliance of European Flax Linen & Hemp.

Effect of moisture on the sensing capabilities of piezoelectric actuator/sensor pairs on flax fibre reinforced composite laminates

The sensitivity of the piezoelectric actuators’ response to the moisture uptake has been investigated on flax fibre reinforced composite laminates. Non-woven flax fabric was impregnated with epoxy and composite laminates were fabricated using hand lay-up and cured in a compression moulding machine. The laminates were initially impacted with a drop-weight impact machine at a low energy level, with the aim to generate an artificial surface crack that will allow the moisture to enter the fibre-matrix interface more effectively. A set of piezoelectric actuators and sensors were adhered on the surfaces of the composite panels in a specific rectangular arrangement to allow for wave capturing at various directions. The wave characteristics of the samples were extracted in pristine stage and then the samples were impacted and immersed in distilled water until saturation. At regular intervals after the water immersion, the panels’ weight was measured using a laboratory scale and the wave propagation characteristics of the materials ware measured in order to investigate the gradual effect of moisture on the capabilities of the actuators and sensors. The propagation of stress waves in the dry and wet samples was investigated and the effect of moisture absorption was examined experimentally using piezoelectric wafers until the saturation was reached. Finally, a continuum damage mechanics layerwise time domain spectral finite element model, both for the composite laminate and the rich resin layers, was also developed to simulate the materials’ performance under impact and evaluate the wave propagation within the material at the dry state.

LeichtPRO-profiles: development and validation of novel linear biocomposite structural components fabricated from pultruded natural flax fibres with plant-based resin for sustainable architectural applications

Reconsidering the materials used in construction is crucial within the building industry, particularly in the context of sustainability. Recently, there has been a growing interest in exploring novel materials, with fibre-reinforced composites emerging as a prominent choice with biocomposites standing out as promising for advancing sustainability goals. This paper introduces the development of LeichtPRO-Profiles, continuous linear biocomposite profiles fabricated using the pultrusion technology. A primary focus is the application of these profiles in structural systems as load-bearing elements, emphasising the significance of understanding their mechanical properties. Specifically, an original application involves active-bending structures, necessitating a focus on the material’s bending behaviour. This study discusses the methods employed in developing the pultruded biocomposite profiles which are made from natural flax fibres and an optimised matrix formulation based on a plant-based resin system. This research also outlines the optimisation of the fabrication process of these biocomposite profiles using bio-based ingredients. The results demonstrate the material’s mechanical capabilities through extensive experiments and mechanical tests, revealing a compression strength of 31.2 kN and a flexural strength of 300 MPa, with a bending radius of up to 2.4 m, indicating its suitability for structural applications. Concepts of applications in several systems across different scales and contexts are also presented. The versatility and adaptability of this product make it suitable for a wide range of applications spanning various scales and thematic contexts.

Influence of flax fibers on the curing kinetics of bio-based epoxy resin

Influence of flax fibers on the curing kinetics of bio-based epoxy resin

Experimental analysis of low-velocity impact behaviour on flax-balsa biobased sandwich

This article deals with a detailed experimental study dedicated to the evaluation of the overall mechanical behaviour of a bio-based composite structure used in transportation industries. The sandwich structure is designed to increase the lightening, vibration damping, and composite recyclability. The considered materials consist of a Flax/Elium® laminate composite for skins associated with a balsa core. The sandwich structure was obtained using a one-shot liquid resin infusion process. Low-velocity impact tests were carried out on different sandwich configurations with the aim of characterizing the effects of the stacking sequence and the density and thickness of the core. Furthermore, an experimental comparative analysis was conducted involving two composite laminate types: Glass/Elium and Flax/Elium to enhance the specific behaviour of flax fibre composite to be used as skins in the sandwich structures. The impact tests were carried out at low velocities and at different levels of impact energy using a drop-weight test bench. Notable damage mechanisms have been identified, and a chronological sequence of their development has been suggested. Ultrasonic analyses using C-Scan imaging were applied to the opposite side of the impacted specimen. The research proves the efficient energy-absorbing capability of the biobased sandwich structure during impact. Finally, this study enables a deeper understanding of various parameters that influence the behaviour of sandwiches during low-velocity impacts, thereby facilitating more informed material selection for practical applications.

Reaction Mechanism in Standardized α-Cellulose Content Test: Study from Boehmeria nivea Fiber

In defense industry, α-cellulose is the main component of nitrocellulose propellant. However, a detailed description of the reaction mechanism of each treatment step in SNI 0444-2009 is still very scarce. This study addresses this gap by presenting the reaction mechanisms of each treatment and the symbols used in the SNI 0444-2009 procedure. The separation of lignin from α-cellulose occurred by breaking the C‒O bond linking them. This bond was broken by the ‒OH group of NaOH via a hydrolysis reaction. The reaction was initiated with the elimination of a hydrogen atom from the lignin structure by the hydroxyl ion (‒OH), and the C‒O bond was broken by a hydrolysis reaction. The breaking of this bond was indicated by the disappearance of the IR peaks at wavenumbers 1049 and 1190 cm–1 in the filtrate after extraction. The SNI 0444-2009 method for the α-cellulose content test was carried out by a redox back titration of Cr(VI) with Fe(II) from ferrous ammonium sulfate. This titration was conducted to calculate the amount of Cr(VI) ions in potassium dichromate or Cr(VI) that did not react with lignin or beta cellulose in the filtrate. Understanding the contribution and reaction mechanisms of each compound involved in the SNI 0444-2009 procedure contributed to obtaining accurate data on α-cellulose content. In this study, the calculated α-cellulose content of the flax fiber was 96.75%. Furthermore, the detailed mechanism of the redox reaction was discussed in detail in this paper.

Low-Velocity Impact of carbon, flax, and hybrid composites: Performance comparison and numerical modeling

In recent years, composite materials have assumed an increasingly dominant role in various industrial sectors, combining lightweight with optimal mechanical properties. In this context, natural fibers are essential for the development of eco-friendly composites, ensuring a balance between performance and sustainability via hybridization. This study provides an experimental and numerical analysis on composite laminates subjected to Low-Velocity Impact (LVI) tests at different energy levels, after an initial mechanical characterization of the materials. Carbon and flax fiber fabrics are chosen as reinforcements embedded in a toughened epoxy resin, as well as in two hybrid configurations; two different stacking sequences are also investigated, with the layers placed at 0°and in a quasi-isotropic (ISO) orientation. Hysteresis curves and energy absorption capability – in terms of specific energy absorption (SEA) – are then discussed and compared to each other, along with cross-shaped damage propagation on fracture surfaces. Numerical finite element (FE) models of tensile, compressive, and LVI tests are designed and solved using LS-DYNA software. In particular, tensile and compressive ones are carried out to calibrate the material cards, which have subsequently been adopted in the LVI models. The results obtained not only show an agreement between the experimental response and the simulated one, but also provide a complete investigation of different materials and orientations under LVI in view of future applications, highlighting the possibility of designing structural components to absorb energy in hybrid composites reinforced with natural fibers.

EXPERIENCE OF MODERNISATION OF SORTING TABLES AT THE FLAX PLANT

Modern flax mills are equipped with new production lines for short and long fibres. In particular, the Belgian company Depoortere supplies such lines of various capacities. The equipment allows for continuous processing of flax, complete cleaning of flax seeds. Standard sorting tables are used for sorting flax (manually by length and colour). At the same time, back in the 1980s, based on the modernisation of standard sorting tables, original designs of experimental sorting tables equipped with aspiration devices were created and tested in production conditions. In this paper, an experimental conveyor table with a perforated surface is considered, equipped with a device for removing air contaminated with dust particles. An experimental table with a two-sided arrangement of workplaces with the function of localisation and removal of dust in the process of sorting long flax fibre is presented. The results of testing of experimental tables at Palekh flax plant, comments and suggestions from the employees of the flax plant regarding the design of the tables are presented. The designs of experimental tables equipped with aspiration devices, have significant advantages in comparison with standard tables, can be adapted to modern lines installed at flax plants.

Feasibility of Natural Fibre Usage for Wind Turbine Blade Components: A Structural and Environmental Assessment

There are two key areas of development across wind turbine blade lifecycles with the potential to reduce the impact of wind energy generation: (1) deploying lower-impact materials in blade structures and (2) developing low-impact blade recycling solution(s). This work evaluates the feasibility of using natural fibres to replace traditional glass and carbon fibres within state-of-the-art offshore blades. The structural design of blades was performed using Aeroelastic Turbine Optimisation Methods and lifecycle assessment was conducted to evaluate the environmental impact of designs. This enabled the matching of blade designs with preferred waste treatment strategies for the lowest impact across the blade lifecycle. Flax and hemp fibres were the most promising solutions; however, they should be restricted to use in stiffness-driven, bi-axial plies. It was found that flax, hemp, and basalt deployment could reduce Cradle-to-Gate Global Warming Potential (GWP) by around 6%, 7%, and 8%, respectively. Cement kiln co-processing and mechanical recycling strategies were found to significantly reduce Cradle-to-Grave GWP and should be the prioritised strategies for scrap blades. Irrespective of design, carbon fibre production was found to be the largest contributor to the blade GWP. Lower-impact alternatives to current carbon fibre production could therefore provide a significant reduction in wind energy impact and should be a priority for wind decarbonisation.

MEASURING THICKNESS OF FLAX FIBRES IN A CLUSTER USING COMPUTER VISION

Authors analyse a method of indirect measurement of flax fibre linear density using its thickness, based on computer vision approach and “distance transform” algorithm in particular. A number of flaws of this method are identified. The main reason for the discrepancy is the effect of crossed fibres within the analysed sample. The secondary reason is the specific shape of fibre’s topological skeletonnear its tips. Based on these observations, a software model of the problem has been created. The software produces a simplified image of crossed fibres with specified properties, and measures this image using the above method. The effect of various factors on the discrepancy in the distribution of thickness values appears to match well with theoretical analysis. Additionally, a number of ways to improve the software model are outlined, related to how typicallyfibres are oriented within the analysed sample.

Development of Foam Composites from Flax Gum-Filled Epoxy Resin

In the present work, an innovative range of foams based on flax gum-filled epoxy resin was developed, reinforced or not by flax fibers. Foams and composites with different gum and epoxy resin contents were produced and their mechanical and thermal performances were characterized. To enhance the organic flax gum filler’s cross-linking, we exploited the oxidized components’ reactivity with the amine hardener (isophorone diamine). We compared the materials obtained with those derived from the native components. The flax gum and fibers were primarily characterized by chemical analysis, NMR, and FTIR to evaluate the mild oxidation of the native materials. The formation of chemical bonds between the oxidized polymer chains, epoxy resin, and hardener was evidenced by FTIR, and the materials were then studied by SEM and X-ray computed micro-tomography (CT) and submitted to mechanical and thermal tests. The relevance of the oxidation treatment was highlighted through a significant increase in density and mechanical performance (+36% and +81%, respectively, for the 100% flax gum material). The positive effect of the flax fibers on homogeneity evidenced through micro-CT analysis was also clearly addressed. This set of promising results paves the way for the future development of fully flax-based insulation composite materials.

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.

Archaeometric characterization of a textile fragment recovered from a Byzantine Period tomb in Nysa ad Maeandrum in the light of archaeological and anthropological evaluations

Nysa ad Maeandrum (also known as the ancient city of Nysa) is an ancient city located in Western Anatolia of today’s Türkiye. It was determined during the excavations that an uninterrupted life continued in the ancient city of Nysa from the Hellenistic Period (330 BCE-30 CE) to the Byzantine Period (330–1453). The aim of this study is the anthropological evaluation of the skeleton in tomb chamber-11 (T-11) found during the excavations in 2023 and the characterization of the well-preserved textile fragment on the coin unearthed from the individual’s skull. In this study, the textile sample underwent analysis using a polarized optical microscope (OM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), and high-performance liquid chromatography with photodiode array detection (HPLC-PDA). As a result of the analysis, it is thought that the textile fragment has a tabby weave and the fiber is a cellulosic bast fiber, which is most likely flax fiber. In the dyestuff analysis, alizarin and ellagic acid dyestuffs were detected, and it was determined that the textile fragment was dyed by using the madder plant (Rubia tinctorum L.), which we frequently encounter in Anatolia, and a plant containing tannins. In addition, according to anthropological studies, it is thought that the individual in T-11 belongs to a female between the ages of 30–40 and was engaged in weaving based on the marks on her teeth.

A multicriteria approach to quantify contaminant shives in industrial batches of flax fibres

Residual shives have a major impact on the quality and performance of flax textile and composite preforms. Quantifying the content of shives in batches of scutched flax fibres is a time-consuming and operator-dependent process. Although the shive content can be estimated from the chemical composition, our aim here is to explore a series of effective, reliable and complementary approaches to quantifying shives. Various methods are presented: microscopic observations, analytical biochemistry (monosaccharides, lignins), indirect methods (infrared spectroscopy) and dynamic morphological analysis (QICPIC). A reference standard was first analysed and then compared with batches of flax tow fibre of unknown shive content from current industrial production. This approach shows that calibration curves can be established by applying each selected method to batches with known fibre and shive content. In addition, a database was generated to determine the shive content of industrial batches using partial least squares (PLS) regression. Finally, a detailed study of shives in industrial batches is presented, comparing the different analytical methods.

Experimental and numerical approach to understand the role of defects in damage mechanisms of flax fibers at bundle scale

Flax fibers represent a valuable reinforcement in composite materials. However, the presence of defects known as kink-bands in flax fiber has the capacity to influence their mechanical properties. The primary objective of this research is to gain a comprehensive understanding of the damage mechanism in flax fiber bundles presenting a novel aspect due to the intricate structure of bundle fibers, which is more complex compared to elementary fibers. The study specifically explores flax fiber bundles under tensile loading and investigates the impact of kink-bands on their failure through a combined approach, utilizing both experimental and numerical methods. In the experimental part, X-ray microtomography in situ tensile testing is carried out, which reveals complex failure mechanisms. Furthermore, a 3D-Finite Elements (FE) model is implemented utilizing 3D reconstructed fiber and used for numerical tensile analysis. Our findings highlight that the kink-band region acts as prominent failure site in fiber bundles with significant stress concentration at the kink-band region, mainly induced by local porosity.

Mechanical behavior and apparent stiffness of flax, hemp and nettle fibers under single fiber transverse compression tests

While plant fibers find extensive use across numerous applications, their transverse behavior and mechanical properties lack direct and fiber-scale characterization, posing a significant knowledge gap. This paper investigates, for the first time, the transverse behavior of flax, hemp and nettle fibers through Single Fiber Transverse Compression Tests (SFTCTs). Finite element analysis is used to study the influence of time-dependent and irreversible inelastic behavior on the fiber’s response and identify configurations fit for the identification of apparent elastic properties. SFTCTs are performed experimentally with a repeated progressive loading protocol using a custom micro-mechatronic setup. An apparent fiber transverse elastic modulus of 1 to 3 GPa is identified by inverse method for all tested fibers, demonstrating high fiber anisotropy. Important inelastic features are also observed on fiber behavior. Their origin is discussed with both material behavior and structural mechanisms such as lumen collapse, identified as the main potential causes.