Search Results (92)

This work presents the development of two vanillin-based vitrimer epoxy flax fibre-reinforced composites, with both the VER1-1-FFRC (a vitrimer-to-epoxy ratio of 1:1) and VER1-2-FFRC (a vitrimer-to-epoxy ratio of 1:2), via a vacuum-assisted resin infusion. The thermal and mechanical properties of the resulting vitrimer epoxy flax composites were characterised using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical four-point bending tests, alongside studies of solvent resistance and chemical recyclability. Both the VER1-1-FFRC (degradation temperature T_deg of 377.0 °C) and VER1-2-FFRC (T_deg of 395.9 °C) exhibited relatively high thermal stability, which is comparable to the reference ER-FFRC (T_deg of 396.7 °C). The VER1-1-FFRC, VER1-2-FFRC, and ER-FFRC demonstrated glass transition temperatures T_g of 54.1 °C, 68.8 °C, and 83.4 °C, respectively. The low T_g of the vitrimer composite is due to the low crosslink density in the vitrimer epoxy resin. Particularly, the crosslinked density of the VER1-1-FFRC was measured to be 319.5 mol·m⁻³, which is lower than that obtained from the VER1-2-FFRC (434.7 mol·m⁻³) and ER-FFRC (442.9 mol·m⁻³). Furthermore, the mechanical properties of these composites are also affected by the low crosslink density. Indeed, the flexural strength of the VER1-1-FFRC was found to be 76.7 MPa, which was significantly lower than the VER1-2-FFRC (116.2 MPa) and the ER-FFRC (138.3 MPa). Despite their lower thermal and mechanical performance, these vitrimer composites offer promising recyclability and contribute to advancing sustainable composite materials. Full article

The aim of this study is to compare the environmental impact of composites reinforced with flax fiber technical embroidery and traditional woven fabric in order to provide conclusions supporting composite manufacturer management in making technology selection decisions. The research objectives are to identify the key stages in the life cycle of composites, from raw material acquisition to end-of-life; determine the environmental impact of each stage, with a particular focus on processes with the largest contribution to overall result; compare the environmental impact of embroidery-reinforced composites with traditional woven fabric-reinforced composites; propose strategies to minimize the negative environmental impact of composites, including modifying the component set and optimizing the production process. The method involves experimental research including the production of technical embroidery-based composites with varying stitch lengths and woven fabric-reinforced composites. The tensile strength of the composites was evaluated. Subsequently, life cycle assessment was conducted for each material according to the relevant ISO standards. The results presented in this paper provide a comprehensive assessment of the environmental performance of technical embroidery-reinforced composites and identify directions for future research in this field. Full article

The development of lightweight construction is of crucial importance for the development of sustainable technologies and for the reduction in carbon dioxide emissions, especially in the automotive industry. This study aims to address the challenges associated with manufacturing plant fibre-based polymer composites. The investigation focused on two novel formulations of bio-based unsaturated polyester resins, assessing their viability as a matrix in plant fibre-reinforced composites within the context of automotive applications. The study addresses the challenges related to the preparation and processing of the system, leading to the necessity of diluting the resin with (hydroxymethyl)methacrylate (HEMA) to achieve an applicable viscosity. Two different flax fibre textiles, in the form of a short fibre mat and a woven fabric, were used as reinforcement. The composite panels were manufactured using the vacuum-assisted resin infusion (VARI) process. The most efficacious material combination, comprising Bcomp^® ampliTex™ 5040 and STRUKTOL^® POLYVERTEC^® 3831, with viscosity modified by 39% HEMA, exhibited a consistent fibre volume fraction of 40% and a glass transition temperature of 70 °C. In addition, the mechanical behaviour in the 0°-direction demonstrated tensile strength and modulus values of approximately 99 MPa and 9 GPa, respectively, accompanied by an elongation at break of 2%. The flexural modulus was found to be 7 GPa, and the flexural strength 94 MPa. Full article

This study investigates the novel role of yarn-level fibre hybridisation in tailoring thermomechanical properties and thermal residual stress (TRS) fields in the resin at both micro- and meso-scales of 3D orthogonal-woven flax/E-glass hybrid composites. Unlike previous studies, which primarily focus on macro-scale composite behaviour, this work integrates a two-scale homogenisation scheme. It combines microscale representative volume element (RVE) models and mesoscale repeating unit cell (RUC) models to capture the effects of hybridisation from the fibre to lamina scale. The analysis specifically examines the cooling phase from a curing temperature of 100 °C down to 20 °C, where TRS develops due to thermal expansion mismatches. Microstructures are generated employing a random sequential expansion algorithm for RVE models, while weave architecture is generated using the open-source software TexGen 3.13.1 for RUC models. Results demonstrate that yarn-level hybridisation provides a powerful strategy to balance mechanical performance, thermal stability, and residual stress control, revealing its potential for optimising composite design. Stress analysis indicates that under in-plane tensile loading, stress levels in matrix-rich regions remain below 1 MPa, while binder yarns exhibit significant stress concentration, reaching up to 8.71 MPa under shear loading. The study quantifies how varying fibre hybridisation ratios influence stiffness, thermal expansion, and stress concentrations—bridging the gap between microstructural design and macroscopic composite performance. These findings highlight the potential of yarn-level fibre hybridisation in tailoring thermomechanical properties of yarns and laminae. The study also demonstrates its effectiveness in reducing TRS in composite laminae post-manufacturing. Additionally, hybridisation allows for adjusting density requirements, making it suitable for applications where weight and thermal properties are critical. Full article

This study explores the mechanical behaviour of intra-laminar hybrid flax/E-glass composites, focusing on the role of micro-scale irregularities in flax fibres. By employing computational micromechanics and Monte Carlo simulations, it analyses the influence of flax fibre geometry and elastic properties on the performance of hybrid and non-hybrid composites. A Non-Circular Fibre Distribution (NCFD) algorithm is introduced to generate microstructures with randomly distributed non-circular flax and circular E-glass fibres, which are then modelled using a 3D representative volume element (RVE) model developed in Python 2.7 and implemented with Abaqus/Standard. The RVE dimensions were specified as ten times the mean characteristic length of flax fibres (580 μm) for the width and length, while the thickness was defined as one-tenth the radius of the E-glass fibre. Results show that Monte Carlo simulations accurately estimate the effect of fibre variabilities on homogenised elastic constants when compared to measured values and Halpin-Tsai predictions, and they effectively evaluate the fibre/matrix interfacial stresses and von Mises matrix stresses. While these variabilities minimally affect the homogenised properties, they increase the presence of highly stressed regions, especially at the interface and matrix of flax/epoxy composites. Additionally, intra-laminar hybridisation further increases local stress in these critical areas. These findings improve our understanding of the relationship between the natural fibre shape and mechanical performance in flax/E-glass composites, providing valuable insights for designing and optimising advanced composite materials to avoid or delay damage, such as matrix cracking and splitting, under higher applied loads. Full article

This study aims to investigate the behaviour of thermoplastic composites reinforced with natural fibres. Composite materials were developed using reactive methyl methacrylate (MMA) resin, commercially known as Elium^® (Arkema, Colombes, France), with the incorporation of cellulose nanocrystals (CNCs), dispersed in the matrix at different concentrations. Natural fibres, such as flax, were chemically treated by immersion in an aqueous solution based on NaHCO₃, during different periods of exposure. After this treatment, flax fibres were washed with distilled water and dried. The degree of fibre surface tension was measured in terms of the contact angle. Then, cellulose nanocrystals were incorporated and mixed in the thermoplastic resin, and the samples were developed via the incorporation of intercalated layers of treated flax fibres. The composites were produced using compression moulding. After that, the samples were evaluated, regarding their mechanical performance and morphology. The research results show that flax fibres treated with 9 wt. % NaHCO₃ for 48 h had improved flexural strength as a result of removing impurities and exposing hydroxyl groups that react with Na⁺ ions present in NaHCO₃, which enhances its mechanical properties. The incorporation of 1% CNCs into thermoplastic resin significantly enhanced the fibre/matrix interface, resulting in a remarkable 38% increase in flexural strength. These findings demonstrate the effectiveness of using treated natural fibres and CNCs to improve composites’ performance. Full article

In this work, twin-screw extruder and compression moulding techniques were utilized to fabricate polymer blends: polypropylene (PP), polybutadiene (PB), and composites using glass fibre (GF) and flax fibre (FF). During fabrication, the polymer ratios maintained between PP and PB were 90:10, 80:20, and 70:30. Likewise, the composites were fabricated by varying the ratios between the PP, PB, and GF, which were 90PP:10PB:10GF, 80PP:20PB:10GF, and 70PP:30PB:10GF. Additionally, a hybrid composite was fabricated by adding 20% FF to the 90PP/10PB/10GF blend. The mechanical characterization revealed that the tensile strength and modulus increased by approximately 24% and 23%, respectively, for the hybrid combination (90PP/10PB/10GF/20FF) compared to pure PP (from 21.47 MPa and 1123 MPa to 26.54 MPa and 1382 MPa). Similarly, flexural strength and impact resistance showed significant improvements in hybrid samples, with flexural strength increasing by approximately 15%. Scanning electron microscopy (SEM) was also carried out for impact-tested samples to understand the fibre-to-matrix adhesion behaviour. Regarding the DSC results, PP exhibited a melting peak between 160 °C and 170 °C. When incorporating PP into PB, a reduction in crystallinity was observed. Further, by adding GF to polymer blends, the crystallinity was increased. HDT and Vicat softening temperature results reported that the hybrid samples showed higher values of 79.3 °C and 88.2 °C, respectively, resulting in improvements of approximately 3.9% and 2.9% over standard PP. Findings from this study suggest that the novel combinations offer a promising synergy of flexibility, strength, and thermal resistance, making them suitable for medium engineering applications. Full article

Design and production technology of natural fibre reinforced polymers not only aims to offer products with a lower environmental impact than conventional glass fibre composites but also caters for designers’ needs for the fabrication of lightweight free-formed architectural components. To combine both characteristics, the forming process itself, once scaled up, needs to be based on efficient material moulding strategies. Based on case studies of adaptive forming techniques derived from the composite industry and concrete casting, two approaches for the mass production of customised NFRP profiles are proposed. Both processes are based on foam from recycled PET, which is used as either a removable mould or a stay-in-place (SIP) core. Once the textile reinforcement is placed on a mould, either by helical winding of natural fibre prepregs or in the form of mass-produced textile preforms, its elastic properties allow for the free-forming of the composite profile before the resin is fully cured. This paper investigates the range of deformations that it is possible to achieve by each method and describes the realisation of a small structural demonstrator, in the form of a stool, through the helical winding of a flax prepreg on a SIP core. Full article

Natural fibres have garnered substantial attention because of their eco-friendly attributes and versatility, offering a sustainable alternative to synthetic ones. This review surveys plant fibres, including flax, hemp, jute, banana, and pineapple, emphasizing their diverse properties and applications in nonwoven materials. This research also examines the use of synthetic polymer composites blended with natural fibres to create high-performance nonwoven materials. Furthermore, this review outlines the primary applications of nonwovens manufactured with plant fibres through needle-punching. These applications span geotextiles, automotive interiors, construction materials, and more. The advantages, challenges, and sustainability aspects of incorporating natural fibres in needle-punched nonwovens are discussed. The focus is on mechanical and thermal properties and their adaptability for specific applications. This research provides valuable insights for researchers and industry professionals aiming to leverage the benefits of plant fibres in needle-punched nonwovens across various sectors. Full article

Achieving high-performance 3D printing composite filaments requires addressing challenges related to fibre wetting and uniform fibre/polymer distribution. This study evaluates the effectiveness of solution (solvent-based) and emulsion (water-based) impregnation techniques to enhance fibre wetting in bleached flax yarns by polylactide (PLA). For the first time, continuous viscose yarn composites were also produced using both impregnation techniques. All the composites were carefully characterised throughout each stage of production. Initially, single yarns were impregnated and consolidated to optimise formulations and processing parameters. Solution impregnation resulted in the highest tensile strength (356 MPa) for PLA/bleached flax filaments, while emulsion impregnation yielded the highest tensile strength for PLA/viscose filaments (255 MPa) due to better fibre wetting and fibre distribution. Impregnated single yarns were then combined, with additional polymer added to produce filaments compatible with standard material extrusion 3D printers. Despite a reduction in the mechanical performance of the 3D-printed composites due to additional polymer impregnation, relatively high tensile and bending strengths were achieved, and the Charpy impact strength (>127 kJ/m²) for the viscose-based composite exceeded the reported values for bio-derived fibre reinforced composites. The robust mechanical performance of these filaments offers new opportunities for the large-scale additive manufacturing of structural components from bio-derived and renewable resources. Full article

The interest in natural fibres and biopolymers for developing bio-composites has greatly increased in recent years, motivated by the need to reduce the environmental impact of traditional synthetic, fossil fuel-derived materials. However, several limitations associated with the use of natural fibres and polymers should be addressed if they are to be seriously considered mainstream fibre reinforcements. These include poor compatibility of natural fibres with polymer matrices, variability, high moisture absorption, and flammability. Various surface treatments have been studied to tackle these drawbacks, such as alkalisation, silane treatment, acetylation, plasma treatment, and polydopamine coating. This review paper considers the classification, properties, and limitations of natural fibres and biopolymers in the context of bio-composite materials. An overview of recent advancements and enhancement strategies to overcome such limitations will also be discussed, with a focus on mechanical performance, moisture absorption behaviour, and flammability of composites. The limitations of natural fibres, biopolymers, and their bio-composites should be carefully addressed to enable the widespread use of bio-composites in various applications, including electronics, automotive, and construction. Full article

The integration of natural fibre thermoplastic composites, particularly those combining flax fibres with polypropylene, offers a promising alternative to traditional synthetic composites, emphasising sustainability in composite materials. This study investigates the mechanical properties of flax/polypropylene composites manufactured using flashlamp automated tape placement and press consolidation, individually and in combination. Tensile, compression, three-point bending, and double cantilever beam tests are utilised for comparing these manufacturing processes and the mechanical performance of the resulting composites. The microstructure of the tapes is investigated using cross-sectional microscopy, and the thermophysical behaviour is analysed utilising thermogravimetric analysis and differential scanning calorimetry. The temperature during placement is monitored using an infrared camera, and the pressure is mapped with pressure-sensitive films. The natural fibre tapes show a good aptitude for being manufactured with automated tape placement. The tensile performance of tapes manufactured with automated tape placement is close to that of press consolidated samples. Compression, flexural properties, and the mode I fracture toughness critical energy release rate all benefit from a second consolidation step. Full article

Recent pressure on scientists and industries to use renewable resources, as well as the need to produce environmentally friendly materials, has led researchers and manufacturers to use natural fibres as possible reinforcements for their composites. Although they seem to be “ideal” due to their low cost, light weight and interesting energy absorption properties, they cannot be compared to synthetic fibres. To solve this problem, hybridization techniques can be considered, since the combination of synthetic and natural fibres allows for good performances. The aim of this study was to characterize the delamination and in-plane crashworthiness behaviour of carbon, flax and hybrid composites from experimental and numerical points of view. Double Cantilever Beam and Four-Point End Notched Flexure tests were carried out to determine the interlaminar fracture modes. In-plane crashworthiness tests were then performed to investigate the delamination phenomenon and the energy absorption capacity considering two different geometries: flat and corrugated. Numerical models were created and validated on both geometries, comparing the obtained load–displacement curves with the experimental ones. Crush force efficiency and specific energy absorption were quantified to provide a proper comparison of the investigated materials. The good results achieved represent a promising starting point for the design of future and more complex structures. Full article

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. Full article

This study investigates the impact of lignin on the durability and performance of polypropylene-based biocomposites (PP–flax and PP–pine) under environmental stresses such as UV radiation and moisture. The findings indicate that pine fibres, with their higher lignin content, are significantly more resistant to thermal degradation than flax fibres. Differential scanning calorimetry (DSC) showed that lignin influences crystallinity and melting temperatures across the composites, with variations corresponding to fibre type. Acoustic emissions analysis revealed that increasing the lignin content in pine fibres effectively reduces surface microcracks under UV exposure. Overall, these results underscore the importance of fibre composition in improving the performance and longevity of biocomposites, making them better suited for durable construction applications. Full article