Woven Flax Research Articles

Parametric Study on the Residual Tensile Strength of Flax Natural Fibre Composites after Drilling Operation

The need for hole making on synthetic and natural fibre composites is inevitable due to further requirement of assembly process of different composite parts. However, regardless of the fibre types, the damage cause by drilling operation, namely delamination and matrix cracking around the hole, often deteriorated the long-term mechanical performance of these composites. In this study, the parametric effects of drilling conditions, namely feed rate, spindle speed and drill point angle on residual tensile strength have been investigated. Taguchi technique with statistical analyses was employed as to analyze the residual tensile strength of woven flax epoxy composite after drilling process. A three-axis CNC machine was used to create a hole on the composite specimens based on two levels of drilling parameters and drill bit geometries. Subsequently, static loading tests were performed as specified in the ASTM Standard D3039 (Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials). From the analysis, it is evident that feed rate is the most important parameter that influence the aforementioned output.

Practical solution for improving the mechanical behaviour of the composite materials reinforced with flax woven fabric

This article focuses on finding a practical solution for improving the mechanical behaviour especially in bending in case of the composite materials reinforced with flax fabric. For this purpose, two kinds of composites having the same number of layers are mechanically tested: the flax/epoxy composite and the flax/glass/epoxy composite (hybrid composite). The mechanical tests used were tensile test and bending test (three-point method). Different results corresponding to the weft or warp directions were remarked in case of the hybrid composite: for example, the maximum values of the tensile strength and the flexural strength measured in the weft direction are 40.63% and 34.61% greater, respectively, than the values corresponding to the warp direction. This article reports the improvement of the mechanical properties by replacing the flax reinforcement with glass reinforcement in the two upper and lower layers of the flax composite materials: increasing with 35.19% in terms of Young’s modulus E recorded in the tensile test, with 79.86% of the maximum value of the tensile stress and with 91.08% of the maximum value of the flexural stress. Composite beam theory was considered and theoretical approaches were validated by the experimental results.

Synthesis and mechanical properties of flax fabric reinforced geopolymer composites

Geopolymer composites reinforced with different layers of woven flax fabric are fabricated using lay- up technique. Mechanical properties, such as flexural strength, flexural modulus and fracture toughness of geopolymer composites reinforced with 2.4, 3 and 4.1 wt% flax fibres are studied. The fracture surfaces of the composites are also examined using scanning electron microscopy. The results show that all the mechanical properties of the composites are improved by increasing the flax fibre contents. It is also found that the mechanical properties of flax fabric reinforced geopolymer composites are superior to pure geopolymer matrix. Micro-structural analysis of fracture surface of the composites indicated evidence of various toughening mechanisms by flax fabrics in the composites.

Design of natural fiber composites utilizing interfacial crystallinity and affinity

Butanediol initiated poly(ε-caprolactone) (PCL) has recently been reported as a toughening agent for cationically curing cycloaliphatic epoxides providing plasticized thermosets with excellent properties (Lützen et al., 2013). In this contribution that promising toughening approach was applied for the first time for the development of novel natural fiber composites (NFC). NFCs based on conventional brittle thermosetting polymers often suffer from poor interfacial adhesion and stress cracking. Composites made up of the novel plasticized thermosets and woven flax fiber preserved the elastomer-like properties and increased tensile strength and elongation at break up to 60MPa and 5%, respectively. Furthermore, PCL was shown not only to toughen the epoxide but also to modulate the affinity of the matrix to the fiber. In conclusion, improved interfacial adhesion and the resulting excellent mechanical properties of cationically curable NFCs were achieved by both interfacial crystallization and affinity.

Study on Mechanical Properties of Flax Fibre Textile Reinforced Composites Fabricated Using Bio-Based Epoxy Resin Matrix

Flax fibre reinforced composites were made from non-crimp and woven flax fabric reinforcements using bio-based epoxy resin matrix. The fabrics impregnated with epoxy resin containing 55% biomass carbon were fabricated using vacuum bag technique. The fibre weight content of around 40 wt% was achieved through the vacuum bag technique. The fibre assembly and the morphology of the composites were studied using optical microscope. The influences of different weave type and fibre layup direction on the mechanical properties of composites were studied. It was found that, the woven fabric had lower impact strength values than the unidirectional and biaxial oriented fibres. But the woven fabric had achieved relatively equal impact energies on both directions. The maximum flexural strength (196 MPa) and modulus (13.5 GPa) was observed for the unidirectional non-crimp fabric on 0° fibre layup direction.

Permeability of natural fiber reinforcement for liquid composite molding processes

We investigate the influence of liquid type on the saturated permeability of natural fabrics in liquid composite molding processes. The permeability of flax woven fabric was characterized with two different liquids which have different viscosity, wettability, and sorption characteristics with flax fiber. From the experimental data, it was observed that the saturated permeability values were different for the liquid type. The fiber swell during the mold filling process and the corresponding change of fabric microstructure were assumed to be the main reason for this dependency of saturated permeability on the liquid type. The fiber swell due to the liquid sorption was characterized as a function of time, and the corresponding change of fiber diameter was investigated. The effective fiber volume fraction of wet natural fabric was defined in terms of fiber swelling ratio. The predictions by the classical Kozeny–Carman model and by the modified Kozeny–Carman model with two model constants were compared with the experimental data. It was shown that the modified Kozeny–Carman equation considering fiber swell could predict very well the saturated permeability of natural fabrics regardless of liquid type.

Complex shape forming of flax woven fabrics: Design of specific blank-holder shapes to prevent defects

This study concentrates on the possibility of forming a complex shape such as a tetrahedron using two untwisted commercial flax based fabric reinforcements using the sheet forming process. As some of the defects such as tow buckles or tow sliding cannot be predicted and therefore anticipated using simulation techniques, an experimental approach has been used to optimise the process parameters during forming. Specially designed blank holders were used to apply local adapted pressures to the fabric to reduce the pressure in excessively strained tows and to increase the strain in others. The defects previously encountered using a non-optimised blank holder set have been suppressed to a large extent suggesting that most of the commercial untwisted flax based fabrics that enable the best composite properties and best fibre volume fractions can be used to generate the most complex shapes.

A Mechanical Analysis of In Situ Polymerized Poly(butylene terephthalate) Flax Fiber Reinforced Composites Produced by RTM

This work addresses mechanical characterization in tension of woven flax fabric reinforced in situ polymerized poly(butylene terephthalate) composites, produced by the RTM technique. A brief description of the developed RTM set-up is made and the composite manufacturing details are presented. A morphological analysis of the mechanically characterized materials by Scanning Electronic Microscopy (SEM) is also made. The produced neat polymer (pCBT) showed a brittle behavior and mechanical properties lower than those found in the literature. Its reinforcement with woven flax fabric resulted in an enhancement of both tensile strength and stiffness. The obtained results can be significantly improved by the polymer modifying chemically , optimizing the control of the processing parameters, and subjecting flax fibers to a surface treatment compatible with the CBT 160 resin.

Flame retardancy and mechanical properties of flax reinforced woven for composite applications

This paper investigates the flame retardant and mechanical properties of a flax woven fabric that can be used to prepare biocomposites. The flame retardant properties of the fabric are first considered using different ammonium phosphate salts and intumescent systems. It is demonstrated that satisfactory performances can be achieved using this approach. Better performances were obtained with pure phosphate salts in comparison to intumescent systems. This was attributed first, to the carbonization effect of the flax that could thus react with the phosphate and/or its degradation products leading to a stabilisation of the system and second to the lower phosphorus content when the full intumescent system is considered. On the other hand, despite a loss of biaxial tensile properties, the ability of the fire retardant treated fabric to form complex shape such as a tetrahedron was successfully demonstrated. Finally, the flame retardant properties of one-ply composites, using a bio-based matrix (Bioplast from Biotec), was evaluated. It was shown that good fire retardancy performances could be achieved considering only the flame retardancy of the reinforcement phase. This approach has potential for developing future flame retarded biocomposites.

Viscoelastic and thermal behaviour of flax preforms reinforced epoxy composites

This study investigates the thermal and viscoelastic properties of flax preform reinforced epoxy composites. Plain woven flax fabric and 1 × 1 weft rib knitted structures were used as reinforcements and flax preforms reinforced epoxy composites were produced using hand lay-up method. Thermogravimetric analysis (TGA) indicates a decrease in thermal stability of the matrix polymer with the incorporation of flax woven and knitted preforms. The dynamic mechanical analysis revealed a higher storage modulus for woven preform reinforced composite compared to knitted preform reinforced composites. The storage modulus was found to decrease with temperature in all cases. Loss modulus showed shifts in the ( Tg) compared to virgin epoxy, with the addition of flax preforms as reinforcing phase, which indicate that preforms plays an important role with respect to Tg. Single tan δ peaks were observed for all the composite samples tested. The tan δ peak height was maximum for virgin epoxy matrix, indicating that there is a large degree of mobility, thus good damping behaviours. However, lower peaks were observed for both woven and knitted preform reinforced composites. With respect to the viscoelastic properties the rigidity and endurance of the fibres are highly affected by thermal treatment at temperatures above 70℃ and up to 100℃.

Influence of textile treatment on mechanical and sorption properties of flax/epoxy composites

The aim of the present work is to study the effect of conventional textile treatments of woven flax on the mechanical properties and the water sorption of flax/epoxy composites. The flax fabrics are standard 2/2 twills. Various treatments are carried out on fabric such as mercerization, bleaching, and leaching for long fibers or on yarn such as leaching for short fibers. A model, based on a modified rule of mixture applied to composite reinforced with woven fabric, is developed to include the effect of fiber and porosity volume fractions on composite stiffness and strength. Most treatments improve tensile stiffness and strength of flax/epoxy composite and reduce composite water sorption. We prove by X-ray fluorescence analysis, thermogravimetric analysis, and tensile tests of dry fabric that it is due to an improvement in the interfacial bonding between fibers and matrix. The best performances are achieved with bleaching and mercerization treatment. The weakest performances are obtained with the composites made with leached yarns. POLYM. COMPOS., 34:1761–1773, 2013. © 2013 Society of Plastics Engineers

Complex shape forming of a flax woven fabric; analysis of the tow buckling and misalignment defect

With the view to minimise the impact on the environment and to produce structural parts with a good production-rate/cost-ratio, the sheet forming of woven flax based fabric was investigated in this study. A flax fibre plain-weave fabric has been used to form a complex tetrahedron shape. This shape is of particular interest as it contains several geometric singularities required by many automotive parts such as double or triple curvature and low-curvature edges. Globally, the complex tetrahedron shape was obtained, but tow buckling (out of plane bending of tows) was observed in specific zones of the shape. The main mechanism at the origin of this defect has been defined. A reduction of the tow buckle size was obtained by increasing the membrane tension. The influence of fabric architecture at the mesoscopic and macroscopic scales on the appearance of the tow buckles was demonstrated and discussed. Solutions to prevent the appearance of this defect based on the design of the fabric architecture at the tow or fabric scales were successfully proposed. As a consequence, when sheet forming of complex shapes is considered, specific fabric architectures should be chosen to prevent the appearance of the buckling defect.

On the static and dynamic properties of flax and Cordenka epoxy composites

Fibre reinforced composites have excellent specific properties and are widely sought after by engineers seeking to reduce mass. However, end of life disposal is a significant problem and so research into more sustainable natural fibre composites is extremely topical. This paper examines the applicability of natural fibre composites for high performance structural applications. Woven flax and regenerated cellulose (Cordenka) textiles were pre-impregnated with commercially available epoxy resins and consolidated into test laminates in an autoclave to determine their static (compressive, tensile, flexural) and dynamic (energy absorption) properties. The range of compressive strengths was 77.5–299.6 MPa. Tensile strengths ranged from 63 to 92.6 MPa and interlaminar shear strength (ILSS) from 10.7 to 23.3 MPa. Specific energy absorption (SEA) varied between 21.2–34.2 kJ/kg. Biotex flax combined with MTM49 resin matched the SEA of T300 carbon fibre using the same resin system and layup. This work has demonstrated that natural fibre composites have significant scope for use in structural applications but additional work is required on fibre to matrix bonding in order to maximise their properties whilst remaining an environmentally credible option.

Effect of woven flax structures on morphology and properties of reinforced modified polylactide composites

Composites composed of polylactide (PLA), modified PLA and woven flax fiber textiles (flax weave style of 2 × 2 twill and 4 × 4 hopsack) were produced by hot press technique. Two structurally different additives were used to modify PLA. The dispersion of the flax in the composites was studied by scanning electron microscopy and computed microtomography system (µCT). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The thermomechanical and creep properties of the composites were determined using thermogravimetric analysis, dynamic-mechanical thermal analysis and short-time creep tests. It was found that the modified PLA and its composite increased the impact resistance compared with the unmodified PLA. Incorporation of flax decreased resistance to thermal degradation and increased water uptake. The impact energy and stiffness value of PLA/flax composites were markedly higher than that of PLA but reflect the effects of composite structures and flax content. The storage modulus master curves were constructed by applying the time–temperature superposition principle. From the master curve data, the effect of modified PLA on the storage modulus was more pronounced in the low frequency range.

Structure and properties of flax/polylactide/alumina nanocomposites

Composites composed of polylactide (PLA), woven flax fiber textiles (weave style of 2 × 2 twill and 4 × 4 hopsack) and boehmite alumina were produced by hot press. The spraying technique served for the pre-dispersion of the alumina nanoparticles. The aqueous alumina slurry was produced by mixing the water with water dispersible alumina. The dispersion of the flax structures and alumina particles in the composites was studied by scanning electron microscopy. The polylactide composites were subjected to water absorption and instrumented falling weight impact tests. The creep and thermomechanical properties of the composites were determined in short-time creep tests (performed at various temperatures), thermogravimetric analysis and dynamic-mechanical thermal analysis, respectively. It was found that the incorporation of alumina particles reduced the water uptake compared to the polylactide/flax blends. The impact energy and stiffness value of polylactide/flax blends was markedly higher than that of PLA but reflected the effects of composite structures. Incorporation of alumina particles enhanced storage modulus and the creep resistance compared to the polylactide/flax blends but slightly incremented thermal resistance at high temperature. No clear trend in the flax weave style-effect was found in the thermal behavior. The creep master curves were constructed by applying the time–temperature superposition principle. The Findley power law could satisfactorily describe the creep compliance versus time traces for all systems studied.

Compression-moulded flax fabric-reinforced polyfurfuryl alcohol bio-composites

Bio-composites (FF-PFA-D) were successfully compression moulded by reinforcing polyfurfuryl alcohol (PFA) with 10 layers of woven flax fabric (FF). FF-reinforced PFA-based bio-composites were then immersed in water to get wet bio-composite samples (FF-PFA-W). Mechanical and impact properties of the bio-composites in dry and wet state were determined. Characterisations of the bio-composites were performed by thermogravimetric analysis, thermomechanical behaviour, and cone calorimeter data. Results indicated the increase in α-relaxation temperature for FF-PFA-W. SEM micrograph showed that the flax fibres were completely coated with the resin indicating complete wetting of the fabrics by the matrix. As expected, time of ignition showed an increase for the bio-composites due to the flame retardant characteristics of PFA. This work gives us simple and effective way to prepare bio-composites from 100 % renewable resources.

Impact, thermal and mechanical properties of high density polyethylene/flax/SiO2 composites: Effect of flax reinforcing structures

Composites composed of high-density polyethylene, woven flax fiber textiles (flax weave style of 2 × 2 twill and 4 × 4 hopsack) and SiO2 were produced by hot press with nanospraying technique. The SiO2 slurries were sprayed on the woven flax fiber followed by drying. The related HDPE/woven flax fibers composites were prepared by hot press. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy. The related high-density polyethylene based composites were subjected to instrumented falling weight impact test. The thermal resistance, stiffness and tensile strength properties of the composites were determined in thermogravimetric analysis, dynamic-mechanical thermal analysis and tensile tests, respectively. It was found that the impact energy and stiffness value of high-density polyethylene/flax composites was markedly higher than that of high-density polyethylene but reflect the effects of composite structures and flax content. Incorporation of SiO2 particles enhanced resistance to thermal degradation. It was established that the linear viscoelastic material principle are fairly applicable to convert from the modulus to the creep compliance results.

Flexural and impact properties of flax woven, knitted and sequentially stacked knitted/woven preform reinforced epoxy composites

In this article, plain woven, rib knitted and sequentially stacked rib knitted/plain woven, flax fabric reinforced epoxy composites are investigated for their flexural and impact properties. The effect of lay-up angle and the number of preform layers on the above-mentioned properties are also studied. The composite laminates were processed by hand lay-up technique using 2 and 4 mm thick spacers and cured under pressure of 3 bar for 2 h at 50°C, followed by curing in an oven at 120°C for 1 h. Specimen preparation and testing were carried out as per ASTM standards. The results indicate that the woven preform reinforced laminates perform better in both flexural and impact properties for all the lay-up angles and thicknesses investigated in this study. Among the sequentially stacked knitted/woven preform reinforced laminates, specimen with knitted preform as the skin layers exhibited better flexural and impact properties. The data obtained show a tendency of lower flexural and impact values with increase in number of preform layers for all lay-up angles with the exception of lay-up angle [0°/ + 45°/−45°/0°]. At low fibre volume fraction, the sequentially stacked knitted/woven preform reinforced laminates were found comparable to woven preform laminates.

Natural fibre composite energy absorption structures

Natural fibre composites represent an environmentally sustainable alternative to conventional glass and carbon fibre composites. Fibres derived from plants are renewable and have low levels of embodied energy compared to synthetic fibres. They are also low cost, low density, have high specific properties, are non-abrasive and less harmful during handling. In motorsport the front and rear impact structures are required to act as both load-bearing members and energy absorption devices. The requirement to absorb large amounts of energy means that the specific energy absorption (SEA) of the material is critical to maintaining a low mass. This work focuses on the potential for natural fibres to replace synthetic fibres for future environmentally friendly energy absorption structures. Conical test specimens of jute, flax and hemp were manufactured using vacuum assisted resin transfer moulding (VARTM) and subjected to impact testing. The natural fibre cones exhibited high values of SEA: unwoven hemp 54.3 J/g, woven flax 48.5 J/g and woven jute 32.6 J/g. The SEA was influenced primarily by fibre volume fraction (Vf) where a high Vf leads to high SEA. Significant variability in SEA resulted from the variation in fibre strength and Vf as a result of the VARTM manufacturing process. Natural fibre composites have the potential to be widely applied as low cost, sustainable energy absorption structures.

Flax‐fabric‐reinforced arylated soy protein composites: Brittle‐matrix behavior

AbstractBiocomposites were successfully prepared by the reinforcement of soy protein isolate (SPI) with different weight fractions of woven flax fabric. The flax‐fabric‐reinforced SPI‐based composites were then arylated with 2,2‐diphenyl‐2‐hydroxyethanoic acid (DPHEAc) for 4 h to obtain arylated biocomposites. A new method was proposed to determine the amount of carbon dioxide evolved during the arylation of the soy protein in the presence of DPHEAc. Characterizations of the arylated and nonarylated biocomposites were done by Fourier transform infrared spectroscopy, thermogravimetric analysis, and dynamic mechanical thermal analysis. The results indicate that the arylated soy‐protein‐based composites exhibited mechanical behavior like brittle‐matrix composites, which differentiated them from nonarylated soy‐protein‐based composites, which showed mechanical behavior similar to polymer–matrix composites. In the arylated composites, there was clear evidence of a stick–slip mechanism, which perhaps dominated and, therefore, prevented easy deformation of the reinforced film. Scanning electron microscopy studies revealed cracks in the arylated soy protein composites when they were subjected to tensile tests. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012