Treated Flax Fibers Research Articles

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.

Effect of surface treatment on flax fiber reinforced natural rubber green composite

AbstractThe present work is an attempt to study the effect of different surface treatments of flax fiber on the mechanical properties of the natural fiber reinforced natural rubber (NR) composites. In this study, flax fiber was chopped to 1, 1.25, and 1.5 cm in length and mixed with NR in two roll mill. The composite of 20%, 30%, 40%, and 50% fiber loading was prepared from each fiber length. Tensile analysis showed that a 1.25 cm fiber length composite of volume 40% has higher tensile strength compared to others. Hence, this optimized the fiber length and loading has opted for further study. Flax fiber was treated with NaOH and laccase and reinforced into an NR matrix. Properties like tensile strength, hardness, relative density, water diffusion, scanning electron microscope (SEM) and Fourier‐transform infrared spectroscopy (FTIR) for surface treated and untreated natural fiber‐reinforced NR composites have been investigated and compared. The reduction in the hydrophilic characteristics of the NaOH and laccase treated fiber was evident from FTIR analysis and increase in the crystallinity index of the fiber depicted by X‐ray diffraction (XRD) results. SEM analysis showed the enhanced interfacial interaction of treated flax fiber NR composite compared to untreated composite due to the removal of non‐cellulosic contents in fiber and an increase in the surface roughness after treatments. Further, an increase of 9% and 27.4% in tensile and tear strength was found in NaOH treated flax fiber reinforced NR composite.

Suitability of Surface-Treated Flax and Hemp Fibers for Concrete Reinforcement

The use of vegetable fibres as a sustainable alternative to non-natural sources of fibres applied for concrete reinforcement has been studied for over three decades. The main issues about plant-based fibres pointed out by other authors are the variability in their properties and concerns about potential high biodegradability in the alkaline pH of the concrete matrix. Aiming to minimise the variability of flax and hemp fibres, this research compares a range of chemical surface treatments, analysing their effects on the behaviour of the fibres and the effects of their addition to concrete. Corroborating what has been found by other authors, the treatment using NaOH 10% for 24 h was able to enhance the properties of hemp fibre-reinforced concrete and reduce the degradability in alkaline solution. For flax fibres, a novel alternative stood out: treatment using 1% of stearic acid in ethanol for 4 h. Treatment using this solution increased the tensile by 101%, causing a minor effect on the elastic modulus. Concrete mixes reinforced with the treated flax fibres presented reduced thermal conductivity and elastic modulus and increased residual tensile strength and fracture energy.

Effectiveness of treated flax fibers in improving the early age behavior of high-performance concrete

In recent years, ecoefficiency incentives have recently attracted growing research attention towards the valorization of natural fibers in cement systems. Specific attractive features of natural fibers include cost-effectiveness, abundance, renewability, and non-toxicity while providing several functionalities to concrete such as volumetric stability, strength enhancement, and crack control. This study is aimed at leveraging the hydrophilicity, hygroscopicity, and bridging capacity of flax fibers to design high-performance concrete (HPC) with controlled autogenous shrinkage. The effect of raw fibers and that of alkali-treated fibers on autogenous shrinkage of HPC and its fresh and mechanical properties were investigated and compared to the effect of shrinkage reducing admixture (SRA) and expanded shale lightweight aggregate (LWA). Results show that while SRA was found efficient in reducing autogenous shrinkage at 7 days (64% lower), this option adversely affected mixture flowability and mechanical performance (particularly flexural capacity). Similarly, LWA reduced autogenous shrinkage (by 36%) but without a noticeable effect on mechanical performance. Interestingly, the use of alkali-treated fibers allowed obtaining an HPC mixture with reduced autogenous shrinkage (26% lower) while maintaining improved flowability, compressive strength, and flexural capacity (up to 17% increase). Therefore, alkali-treated flax fibers can be viewed as a viable tool for mitigating autogenous shrinkage, thereby offering a green alternative promoting the sustainability of the built environment.

Investigation of electric properties of flax reinforced polypropylene/strontium titanate composite for multilayer dielectric applications

Electrical properties such as dielectric constant, dissipation factor, capacitance, and conductivity are some of the properties that are required to be investigated when a novel composite is fabricated. This research aims to achieve a low dielectric constant (less than 4.2), lowered dissipation factor, lowered conductivity by fabricating a novel natural fiber reinforced polymer composite and investigating its properties. In this research, polypropylene with 14 wt% of strontium titanate, 8 wt% of treated flax fibers was fabricated using compression molding and tested for their dielectric and conductive properties. The capacitance and dielectric constant were significantly higher (43 percent) than that of pure PP or PP-flax, and a gradual decrease was observed as the frequency was increased. The dissipation factor and conductivity were found to be higher for pure PP. However, the full composite exhibited moderate conductivity showing that delays in charge losses could occur, making it an ideal composite for dielectric multilayer applications.

Poly(lactic acid)/flax composites: effect of surface modification and thermal treatment on interfacial adhesion, crystallization, microstructure, and mechanical properties

ABSTRACT In this study, unidirectional flax fabrics were used to reinforce poly(lactic acid) (PLA). Flax/PLA composites were produced by thermo-compression using as-received flax fibers and titanium dioxide (TiO2) coated flax fibers. The aim was to investigate the effect of annealing temperature and time, under quiescent or mechanical stress conditions, on the microstructure, interfacial adhesion, crystallization, and mechanical properties of composites. Results showed significant differences between oxidized-TiO2-coated flax fibers/PLA composites (oxi-TiO2-C) and as-received flax fibers/PLA composites (AR-C). Indeed, above the glass transition temperature (Tg) of PLA, the storage modulus (E’) of both composites significantly increased due to PLA crystallization. However, once E’ reached a maximum value, composites with treated flax fibers leveled off while the E’ of composites with untreated flax fibers dropped drastically. This peculiar result was explained by a partial destruction or damage of AR-C interface during PLA crystal growth. This phenomenon was not observed with oxi-TiO2-C, suggesting a good interfacial adhesion. Despite the presence of a trans-crystalline layer for both samples, it was shown that TiO2 coating of flax fibers strengthened the adhesion between flax fibers and the trans-crystalline structure. Interlaminar shear strength measurements revealed a 15% increase in the interfacial strength.

Electrokinetic and sorption properties of hydrogen peroxide treated flax fibers (Linum usitatissimum L.)

Hydrogen peroxide represents an ecologically and economically acceptable agent for bleaching of flax fibers. The influence of hydrogen peroxide treatment under different conditions, i.e. hydrogen peroxide concentrations (1%, 2% and 4% w/v) and treatment temperature (50 °C, 80 °C and boiling temperature), on the chemical composition, electrokinetic and sorption properties and whiteness index of flax fibers, has been studied. The surface properties and water uptake behavior, i.e. swelling of untreated and treated flax fibers, were monitored through zeta potential measurements using the streaming potential method.The present research has found out that hydrogen peroxide simultaneously removes hemicelluloses and lignin from flax fibers. The ratio between the removal of hemicelluloses (hydrophilic component) and lignin (hydrophobic component), as well as changes in crystallinity, pore structure and carbonyl and carboxyl groups content, have a dominant effect on the electrokinetic, i.e. zeta potential versus pH and isoelectric point and sorption properties of the treated flax fiber. An increase of approximately three-to-four-fold in the whiteness index of the treated flax fibers has been observed. The established correlations between the modification conditions and properties of flax fibers, allow the utilization of hydrogen peroxide for bleaching and simultaneous fiber modification with the possibility of tailoringflax fibers properties.

Tensile creep behaviour of unidirectional flax fibre reinforced bio-based epoxy composites

Abstract Composites made of natural fibres are promising in applications of structural components. Their creep resistance is a very important characteristic to be evaluated but is not well understood. This work investigates creep response of a unidirectional flax fibre reinforced bio-based epoxy under various tensile stress levels. Acoustic emission detection and fracture surface morphology analysis were utilized to analyse the creep mechanisms. In addition, a flax fibre pre-treatment using a green chemical (furfuryl alcohol) was applied in order to reduce to creep deformation. The results show that unidirectional flax fibre composites exhibit perceivable creep at low stress levels and have a relatively short creep rupture life at high stress levels. The creep deformation at low stress can be ascribed to the time-dependent shear deformation of matrices at interface area (hemicellulose/pectin matrix at fibrils interface and the epoxy at fibres interface). Creep at high stress are characterized with a development of extensive damage events and doesn't show typical three-stage creep deformation behaviour over creep life. Composites with furfuryl alcohol treated flax fibres displayed a reduced creep deformation of about 30% than their untreated counterparts at the same creep stress, proving that treating flax fibres with furfuryl alcohol is efficient to improve the creep resistance of flax fibre composites.

Thermal-chemical and biodegradation behaviour of alginic acid treated flax fibres/ poly(hydroxybutyrate-co-valerate) PHBV green composites in compost medium

Abstract In this study, thermal-chemical and biodegradation behaviour of green composites based on flax fibres untreated and treated with alginic acid treated, and poly hydroxybutyrate-co-valerate (PHBV) were studied under composting conditions. The biodegradability of PHBV composites and neat PHBV were assayed by monitoring CO2 production from polymeric carbon under controlled aerobic composting conditions as per ASTM D5338 standard. During the biodegradation process, PHBV composites thermal-chemical and morphology properties were characterized by thermogravimetric analysis (TGA), fourier transform infra-red (FT-IR) and scanning electron microscopy (SEM) techniques. The ultimate biodegradation (mineralization) study results showed alginic acid treated flax/PHBV composites has higher rate of degradation than untreated flax/PHBV composite and neat PHBV. TGA analysis indicated that an increased t-onset temperature for alginic acid treated flax fibres/PHBV composites which was mainly due to the influence of 2% sodium alginate treated with flax fibres. FTIR results showed the increased degradation of PHBV composites was due to the hydrolytic chain scission mechanisms influenced by presence of alginic acid and flax fibres as compared to neat PHBV matrix. Morphological SEM analysis showed PHBV composites biodegradation were readily attacked by fungus but rather PHBV degradation by bacteria. This study found that the incorporation of flax fibres into PHBV matrix provides a benefit to the green composites with enhanced biodegradability.

Strength and Damping Properties of Cementitious Composites Incorporating Original and Alkali Treated Flax Fibers

This experimental investigation focused on the mechanical and damping properties of raw and alkali treated flax fibers reinforced cementitious composites. The objective of this study was to research the influence of flax fiber for the damping properties of cementitious composites. The mechanical strengths were obtained using compressive and flexural tests and damping properties were measured using a dynamic mechanical analysis. Structural modifications to the treated flax fibers were analyzed using scanning electronic microscopy and mercury intrusion porosimetry. Results showed that cement compressive strength was decreased, and flexural strength was increased by the addition of untreated flax fibers. Alkali treatment improved the mechanical strength of flax reinforced cement. The addition of flax fibers improved cement damping properties, and the damping effect of untreated flax fibers was greater than that of alkali treated fibers. The loss tangent of the cementitious composites reinforced with raw and alkali treated flax fibers at an amount of 1 wt % of cement was improved by 45.83% and 37.5% at 20 Hz, respectively. The damping properties of flax fiber was attributed to friction between elementary fibers and between adjacent fiber cell walls and slipping between the fiber and matrix. Callouses, pectin, and lignocellulose in untreated flax fiber contributed to damping and their removal by alkali treatment was the main reason why untreated flax fibers had a greater damping effect as compared to alkali-modified flax fibers.

Flexural and impact properties of flax fibre reinforced epoxy composite with nano TiO2 addition

Recently, there has been renewed interest in the field of natural fibre reinforced composite, where renewability and recyclability of resources comes into attention. There has been substantial research undertaking natural fibre as reinforcement for fabricating composite materials. This study sets out to examine the influence of nano titanium dioxide (15nm size) when added to epoxy matrix in varying weight percentage 2, 4, 6 and 8, and selecting natural flax fibre mat as reinforcement. 0%, 5% and 10%NaOH alkali treated flax fibre woven mats are designated at a weight fraction of 42% with epoxy resin as matrix material. Hand layup is the process used to formulate the composite materials. Flexural strength, impact strength and hardness values were assessed to construe the apposite weight percentage of nano TiO2 addition which will enrich the mechanical properties. From the observations made it is stated that 5% alkali treated flax fibres resulted in better flexural, impact and hardness values when compared to the 0% NaOH-untreated and 10% NaOH treated fibre composites. Among the matrix modified composites 6% TiO2 added composite material projected best flexural strength, impact strength and the hardness value with an increase of 25.05%, 24.29% and 16.01% respectively.

Enhancement of Mechanical Properties of Bio-Resin Epoxy/Flax Fiber Composites using Acetic Anhydride

Chemically treated acetic anhydride (AA) flax fiber mats were investigated. Bio-based epoxy resin and conventional epoxy resin unidirectional fiber composites were manufactured using a vacuum bagging technique. Flax fibers in the bio-resin composites were chemically treated with 1, 2, 3 and 4% (AA), while the fibers used with the conventional resin were not treated. The composites with the conventional resin were compared with the bio-resin in an untreated condition. A 2% AA treatment improved the bio-resin composite tensile strength, stiffness and bond shear strength by 55%, 58% and 7%, respectively. These three properties were evaluated and the results statistically analyzed using ANOVA. The AA reduced moisture absorption intake and improved adhesion of the fiber/matrix interface. The composites treated with 1–2% AA were most successful with a 65% moisture resistance. The scanning electron microscope was used to observe the fiber surface and fractured surfaces of the untreated and treated flax fibers. A chemical pre-treatment has improved the composite mechanical and moisture resistance over the non-treated fiber composites.

Effect of treatment temperature on structures and properties of flax rove in supercritical carbon dioxide

In this study, flax rove was treated in supercritical carbon dioxide. The effect of different treatment temperatures on the surface morphology, chemical and crystal structures, and thermal properties, as well as isolated compounds of flax rove, were investigated by employing scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal analysis, and nuclear magnetic resonance (NMR), respectively. The results showed that more mild grooves and stripes appeared on the surface of the treated flax fibers after supercritical carbon dioxide treatment. FT-IR spectra showed that hydrolysis of macromolecule of flax fibers occurred, producing a C≡C group. XRD spectra confirmed that the crystallinity of the treated flax samples was gradually increased with the raising of treatment temperature. Simultaneously, thermo gravimetric analyzer (TGA), differential thermal gravity (DTG) and differential scanning calorimetry (DSC) analysis indicated that the thermal properties of flax rove were improved with the increase of treatment temperature. In addition, NMR analysis proved that lignin and the monosaccharide composition of isolated compound were extracted from flax rove. Moreover, a predominance of β–O–4’ arylether linkages, followed by β–5’ phenylcoumaran and β–β’ resinol-type linkages for lignins of isolated compound was shown in NMR. Therefore, the results confirmed that it is technically feasible to using supercritical carbon dioxide to conduct the scouring and bleaching of flax rove.

Development and weatherability of bio-based composites of structural quality using flax fiber and epoxidized sucrose soyate

Composites having high bio-based content with properties and costs rivaling those consisting of synthetic constituents are a goal of much current research. The obvious material choices — vegetable oil based resins and natural fibers — present the challenges of poor resin properties and weak fiber/matrix bonding, respectively. Conventional methods of overcoming poor resin quality involve the incorporation of additives, which dilute the resulting composite's bio-content and increases cost. To overcome these limitations while maintaining high bio-content, in this study, a newly developed biobased resin, epoxidized sucrose soyate (ESS), is combined with surface-treated flax fiber to produce novel bio-composites. Properties of manufactured composites were compared against those using epoxy resin reinforced with flax fiber. In addition to mechanical property evaluation, accelerated weathering was performed on the manufactured composites to evaluate the mechanical properties after exposing to UV and moisture. The results of this study revealed the successful production of bio-composites having properties that meet or exceed those of conventional pultruded members while having 85% bio-content. Moreover, composites using treated flax fiber and ESS resin showed less degradation in properties and appearance after accelerated weathering exposure.

Capillary wicking in flax fabrics – Effects of swelling in water

In this study, wicking in flax fabrics was investigated through an experimental method coupled with Washburn theory. This method was previously shown effective for carbon fabrics (Pucci et al. [21]) to determine morphological characteristics and apparent advancing contact angles. For natural fibers, Washburn equation is not sufficient to describe wicking because of moisture sorption that causes fiber swelling during liquid imbibition. Some flax fabrics were submitted to a thermal treatment known to modify fibers chemistry. Wicking tests with water were performed on both fabrics at different fiber volume ratios. It was observed that wicking trend is very different for these two types of reinforcements: treated fabrics show typical linear trends described by Washburn equation, while untreated flax fabrics lose linearity during wicking. Sorption tests performed on elementary fibers proved that swelling is less significant for treated flax fibers. A model was proposed and was shown to describe properly wicking in natural fabrics undergoing swelling.

Dielectric analysis of the interfacial polarization of alkali treated woven flax fibers reinforced epoxy composites

Dielectric measurements were performed on alkali treated flax fibers reinforced epoxy composites in the frequency range 0.1 Hz–1 MHz and the temperature range 40–170 °C. Two common dielectric relaxations were observed for all composites. The first one appearing at low temperatures was attributed to the water dipoles polarization due to the hydrophilic character of flax fibers. The second one observed at high temperatures was identified to the interfacial polarization. Analysis of this latter using the Havriliak–Negami model showed an improvement of the fibers/matrix adhesion by these alkali treatments. The best adhesion was obtained by the leaching treatment.

Capillary effects on flax fibers – Modification and characterization of the wetting dynamics

Introducing bio-based composites has now become an opportunity of development for industry. Accordingly, Liquid Composite Moulding (LCM) processes are increasingly used for manufacturing those composites, mainly in the transportation industry, since they are considered as effective and low cost routes to manufacture bio-based composites fitting high quality requirements, even for parts with complex shape. However observations of a large amount of voids in bio-based composites call for an improved understanding of the local wetting phenomena that occur during impregnation of the natural reinforcements. The purpose of the present work is to study the influence of flax fiber surface chemistry on the local wetting dynamics. Flax reinforcements were submitted to a thermal treatment to modify the chemical composition of fiber surface. In order to analyze the fiber’s wetting behavior, some methods for measuring apparent static contact angles and surface energy were firstly validated on solids of defined geometry, and subsequently applied to untreated and treated flax fibers. The Owens–Wendt’s approach was used to determine both components of apparent surface energy, indicating polar and dispersive interactions in materials. Subsequently dynamic tests were carried out on both types of chopped flax fibers in order to evaluate apparent advancing dynamic contact angles. Considerations about morphological effects have also been included. Finally bio-based composite plates reinforced with untreated and treated flax quasi-UD were simultaneously fabricated by LCM process, and observation of the porosities highlighted some benefits of using treated flax fibers.

Novel Hybrid Flax Reinforced Supersap Composites in Automotive Applications

Flax fibre bio-epoxy composites have not found many commercial uses in structural applications on account of their lack of cost efficiency and high susceptibility to environmental changes. Non-woven flax mats were subjected to alkali, acetylation, silane and enzymatic treatment, and then combined with untreated unidirectional (UD) flax fabrics to make hybrid flax bio-epoxy composites. Mechanical and environmental resistance (aging) tests were performed on the treated flax fibres. The glass transition temperature was detected at about 75 °C with little effect of treatments. Untreated composites were found to have a tensile strength of 180 MPa while no significant improvement was observed for any of the treatments, which are also not environmentally friendly. The amiopropyltriethoxysilane (APS) composites after Xenon aging, retained the tensile strength of 175 MPa and a modulus of 11.5 GPa, while untreated composites showed 35% reduction in elastic modulus.

Effect of Alkali, Esterification and Silane Surface Treatments on Properties of Flax Fibres

In the recent decades, flax fibres can be used as laminate reinforcements with polymer matrix materials to form natural composites, providing outstanding environmental benefits and other characteristics such as reduced cost and light weight. The composite properties are limited by the poor natural fibre/polymer matrix adhesion, which could be improved by chemical modifications. The fibre properties, such as thermal and mechanical properties, after the treatments have a direct effect on the composite behaviors. In order to investigate the effect of treatments on fibre properties, non-woven flax fibre mats were subjected to alkali, esterification and silane treatment. Fourier transformation infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and tensile tests were conducted on the virgin and treated flax fibres. It was found that all the treatments resulted in the removal of pectin and lignin component within the primary cell wall as evidenced by the characteristic IR peak change. The results showed that the thermal stability of non-cellulose part of flax fibres was highly improved by esterification modifications. However, the decrease (20-30%) in fibre tensile properties after the treatments was possibly offset by the improvement in fibre/matrix adhesion.

Properties of alkali treated short flax fiber reinforced poly(lactic acid)/polycarbonate composites

The main focus of this study is to investigate the properties of alkali treated flax fiber reinforced poly(lactic acid)/polycarbonate (PLA/PC) composites. Characterization of these composites was performed by conducting tensile strength, dynamic mechanical analysis (DMA), differential scanning calorimeter (DSC) and scanning electron microscope (SEM) analyses. Tensile strength results revealed that the highest mechanical performance was observed for 2 % sodium hydroxide (NaOH) treated flax fiber reinforced PLA/PC composites. DMA analysis also supported the results of the tensile tests. Tan delta (δ) curves were used for evaluating the fiber-matrix adhesion in flax fiber reinforced composites. The lowest peak magnitude and consequently the best fiber-matrix adhesion were also observed for 2 % NaOH treated flax fiber reinforced composites. DSC results showed that slight changes occurred in glass transition and melting temperature values. Moreover, crystallinity of PLA was affected by the flax fiber reinforcement. The maximum crystallinity value was observed in 2 % NaOH treated flax fiber reinforced composites. Furthermore, SEM analysis showed that 2 % NaOH treated flax fibers have better interfacial bonding with PLA/PC matrix among the flax fibers.