Review on natural plant fibres and their hybrid composites for structural applications: Recent trends and future perspectives

© 2022 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Sustainability and environmental protection have given rise to the use of renewable and biobased materials in several application areas. Fibre reinforced composites are currently gaining a high market value in both structural and semi-structural applications. Making these materials environmentally friendly, renewable and lighter will protect the environment and increase resource use efficiency. Opposed to synthetic fibres such as carbon and glass, natural plant fibres are less expensive, lighter, degradable, easy to produce, non-toxic and environmentally friendly. However, natural plant fibres are inferior to their synthetic counterparts in both mechanical performance and tolerance to harsh environmental conditions. One method of compensating for these disadvantages is to combine natural and synthetic fibres in a single matrix forming a hybrid composite where the disadvantages of one are compensated by the other. In this way, sustainability and cost minimisation are achieved with acceptable mechanical and physical responses. However, successful implementation and advancement in the development of natural plant fibre reinforced polymer (FRP) hybrid composites require the development of workable conceptual design, suitable manufacturing techniques and understanding of the strengthening mechanisms. The main objectives of this review are to critically review the current state of knowledge in the development of natural FRP hybrid composites, outlining their properties and enhancing them while reducing environmental impact of the product through the hybridisation approach.Peer reviewe

Mechanical and Damping Properties of Resin Transfer Moulded Jute-Carbon Hybrid Composites

Hybrid composites with carbon and natural fibres offer high modulus and strength combined with low cost and the ability to damp vibration. This study investigates carbon (CFRP), jute (NFRP) and hybrid (HFRP) fibre reinforced polymers manufactured using the resin transfer moulding process. Tensile strength reduced with increasing injection pressure for NFRP (72.7 MPa at 4 bar, 45.5 MPa at 8 bar) and HFRP (98.4 MPa at 4 bar, 92.4 MPa at 8 bar). The tensile modulus for HFRP (15.1 GPa) was almost double that for NFRP (8.2 GPa) and one third of CFRP (44.2 GPa). Loss factor reduced at small strains (10−4) with increasing pressure for NFRP (0.0123 at 4 bar, 0.0112 at 8 bar) and HFRP (0.0048 at 4 bar, 0.0038 at 8 bar) but all were greater than CFRP (0.0024). Increased injection pressure improved the surface properties and prevented read through of the weave pattern, NFRP (Ra = 2.15 μm at 4 bar, 1.51 μm at 8 bar) and HFRP (Ra = 1.80 μm at 4 bar, 1.42 μm at 8 bar). Hybridisation of low cost, sustainable jute with carbon fibre offers a more sustainable and economic alternative to CFRPs with excellent damping properties

Natural Fiber-Reinforced Hybrid Composites

In the last few decades, natural fibers have received growing attention as an alternative to the synthetic fibers used in the reinforcement of polymeric composites, thanks to their specific properties, low price, health advantages, renewability, and recyclability. Furthermore, natural fibers have a CO2-neutral life cycle, in contrast to their synthetic counterparts. As is widely known, natural fibers also possess some drawbacks, e.g., a hydrophilic nature, low and variable mechanical properties, poor adhesion to polymeric matrices, high susceptibility to moisture absorption, low aging resistance, etc. This implies that their applications are limited to non-structural interior products. To overcome this problem, the hybridization of natural fibers with synthetic ones (i.e., glass, carbon, and basalt) or different natural fibers can be a solution. For this reason, extensive research concerning natural–synthetic and natural–natural hybrid composites has been done in the last years. In this context, this book aims to collect some interesting papers concerning the use of natural fibers together with synthetic ones with the aim of obtaining hybrid structures with good compromise between high properties (e.g., mechanical performances, thermal behavior, aging tolerance in humid or aggressive environments, and so on) and environment care

The Potential of Bast Natural Fibres as Reinforcement for Polymeric Composite Materials in Building Applications

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonNatural fibre composites (NFCs), which are polymers reinforced with cellulosic bast fibres, have the potential to be applied into a range of building products. They are seen as an alternative to glass fibre reinforced plastics (GFRP) in some applications, because of natural fibres (NF) relatively high strength and low density. Moreover, natural fibres have a set of beneficial traits, such as thermal insulation, thermal stability, biodegradability, and are inherently renewable. Those characteristics are of importance when NF are used as reinforcements in polymer composites, but developments in mechanical performance, reliability and economic viability are still required in order to be adopted fully by industry. The goal of this thesis was the development of a processing methodology for NFC laminate and subsequent material characterisation to assess the developed material suitability for building applications. Research objectives included materials selection, processing route development for laminates and tubes, manufacture of NFC laminates and analysis of mechanical properties in order to find an optimal composition. Hemp and flax fibres were selected as the reinforcement, because both have high mechanical properties and are important bast fibre crops in the European region with established cultivation and processing methods. As a matrix, fossil-fuel based and partially bio-derived thermoset resin systems were used. Handling and processing methodologies were developed for laminates and composite tubes based on filament winding and compression moulding techniques. The effects of the selected factors, namely material composition, volume fraction, processing parameters, reinforcement linear density, yarn twist, lamination sequence, yarn waviness and hybrid hemp-wool reinforcement were subsequently described in mechanical properties analysis of laminates. The influence of weathering conditions on the mechanical performance of the NFCs was examined. Furthermore, a study of NFC tubes under compression was performed. Results showed that the developed laminates reinforced with NF yarns have sufficient mechanical properties to be utilised in sandwich panels and/or tubes. However, a low resistance to moisture-related weathering restricts the developed NFCs for indoor applications

The development of natural fibre reinforced composites roof sheet

The study aims to develop natural fibre reinforced bio-epoxy composite for use as roof sheets, manufacturing and characterization to evaluate its suitability for building applications. In this study natural fibres such as flax and kenaf were selected to reinforce bio-epoxy matrix. Different weight ratios of flax and kenaf fibres were processed by needle-punching technique to produce nonwoven mats. The nonwoven mats and bio-epoxy matrix were prepared using vacuum assisted resin transfer moulding (VARTM) at room temperature until dry and cured. The effects of weathering and water aging on the static and dynamic mechanical properties of kenaf and flax composites were investigated. Flax fibre reinforced bio-epoxy composites were found to exhibit higher tensile strength at 25% fibre content of 41.5 MPa in comparison to the composites reinforced with kenaf fibres (33.0 MPa). With regards to the drop weight impact results, flax fibre reinforced bio-epoxy composites exhibited brittle failure. Water aging results showed that kenaf fibre reinforced bio-epoxy composites absorbed less water for all fibre contents in comparison to composites reinforced with flax fibres. The tensile strength and modulus of both the composites reinforced with flax and kenaf fibres were reduced after water aging. However, the composite reinforced with kenaf fibres showed the maximum reduction in tensile strength at 25% fibre content. After UV treatment both composites reinforced with flax and kenaf fibres showed a decrease in tensile strength of 6.25% and 30%, respectively. In comparison to kenaf, bioepoxy composites reinforced with flax fibres showed an increase in tensile modulus. Both composites reinforced with flax and kenaf fibres were found to be brittle and broke easily but no colour fading was observed after UV treatment. The dynamic mechanical analyses results showed that the incorporation of flax and kenaf fibres increases the storage modulus of the composites with the maximum storage modulus value exhibited by flax fibre reinforced bio-epoxy composite at 30% fibre content. The glass transition temperature of composites reinforced with both flax and kenaf fibres shifted to lower temperatures of 79 °C and 69 °C respectively, in comparison to 96 °C for bio-epoxy resin, with the incorporation of fibres

Elevated Temperature Performance of Hybrid Polymer Composites

FRP composites are the most promising and reliable materials in today’s world. Their outstanding properties make them unique and distinct. Apart from many advantages, during application, they start degrading when exposed to harsh environmental condition like elevated temperature. Hybridising a composite using two different reinforcements has proved to be a method for improving their performance in such conditions. Present study aims at evaluating the mechanical performance of GFRP and Glass/Carbon/epoxy (G/C hybrid) composites at ambient and in-situ elevated conditions. When tested for in-situ at +70 oC and +100 oC, significant reduction in inter-laminar shear strength (ILSS) was observed for both the composites as compared to that at room temperature. The ILSS of G/C hybrid was found out to be 28.2 % more than that of GFRP at room temperature, which became nearly equal for both the composite systems when tested at +100 oC and thus the fiber hybridisation effect was completely diminished. On the other hand, incorporation of carbon nanotubes (CNTs) in epoxy resin has also caused drastic improvement in strength over conventional GFRP. In the present study, epoxy of GFRP composite was modified with 0.1 wt. %, 0.3 wt. % and 0.5 wt. % of CNT and laminates were fabricated. Testing was done for these composites at room temperature, 70 oC, 90 oC and 110 oC. Composite with 0.1 wt. % CNT showed the maximum increment in strength by 32.74 % over GFRP at room temperature. Decrease in flexural properties was noted at elevated temperatures for all the composites. Composite with 0.3 wt. % CNT showed the maximum strength at 70 oC and 90 oC among all the fabricated composites. It was found that testing near glass transition temperature caused high reduction in properties and also confirms the ineffectiveness of hybridisation at such temperature

Durability of Basalt/Hemp Hybrid Thermoplastic Composites

The Achilles heel of thermoplastic natural fibre composites is their limited durability. The environmental degradation of the mechanical properties of hemp and hemp/basalt hybrid-reinforced high-density polyethylene (HDPE) composites has been investigated with a special focus on the effects of water ageing and accelerated ageing, including hygrothermal and UV radiation. Modification of the matrix was carried out using a maleic anhydride high-density polyethylene copolymer (MAPE) as a compatibilizer. Hybridization of hemp fibres with basalt fibres and the incorporation of MAPE were found to significantly decrease the water uptake (up to 75%) and increase the retention of mechanical properties after accelerated ageing. Secondary crystallization phenomena occurring in the composites, as confirmed by differential scanning calorimetry (DSC) analysis, were able to counteract the severe combined effects of hygrothermal stress and UV radiation, with the exception of hemp-fibre composites where permanent damage to the fibres occurred, with 2% and 20% reduction in tensile strength and modulus, respectively, for a 30 wt % hemp fibre-reinforced HDPE

Polymer fibre composites : investigation into performance enhancement through viscoelastically generated pre-stress

In this research, the performance and further development of viscoelastically pre-stressed polymer matrix composites (VPPMCs) was investigated. Pre-stressed composite samples with continuous unidirectional fibres are produced by applying a tensile load to polymeric fibres to induce tensile creep. After removing the load, the fibres are moulded in a polyester resin. Following resin curing, compressive stresses are imparted by the viscoelastically strained fibres as they attempt to recover their strain against the surrounding solid matrix material. Prior to this study, VPPMCs using nylon 6,6 fibres increased impact energy absorption and flexural modulus by 30-50% relative to control (un-stressed) counterparts. The current work contributes to ongoing efforts in VPPMC research by expanding the knowledge of existing VPPMC materials and identifying the potential for an alternative, mechanically superior polymeric fibre.For nylon 6,6 fibre-based VPPMCs, the effects of Charpy impact span settings and fibre volume fraction (3-17% Vf) were investigated. The effects of commingling nylon pre-stressing fibres with Kevlar fibres to produce hybrid VPPMCs was also evaluated. Moreover, as an alternative to nylon fibre, the viscoelastic characteristics and subsequent VPPMC performance of polyethylene (UHMWPE) fibre was investigated. Charpy impact and three-point bend tests were used to evaluate VPPMC samples against control (un-stressed) counterparts. In addition, microscopy techniques were applied to impact-tested samples, to analyse fracture behaviour.For the nylon fibre-based VPPMCs, it was found that improvements in impact energy absorption from pre-stress depended principally on shear stresses activating fibre-matrix debonding during the impact process. Scanning electron microscopy of impact-tested samples revealed visual evidence of pre-stress impeding crack propagation. A short span setting (24 mm) showed greater increases in energy absorption of 25-40%, compared with samples tested at a larger span (60 mm) which gave increases of 0-13%. The results suggest that there is an increasing contribution to energy absorption from elastic deflection at larger span settings; this causes lower energy absorption as well as reducing any improvements from pre-stress effects. However, this effect was suppressed by the addition of Kevlar fibres (to produce hybrid VPPMCs), which promoted more effective energy absorption at the larger span. Moreover, bend tests on the hybrid composites demonstrated that pre-stressing further enhanced flexural modulus by ~35%.The viscoelastic characteristics of UHMWPE fibres indicated that these fibres could release stored energy for pre-stressing over a long time period. This was effectively demonstrated with UHMWPE fibre-based VPPMCs using three-point bend tests, i.e. flexural modulus increased by 25-35% from pre-stressing with no deterioration observed over the time scale investigated (~2 years). Also, these VPPMCs absorbed ~20% more impact energy than their control counterparts, with some batches reaching 30-40%. Although fibre-matrix debonding is known to be a major energy absorption mechanism, this was not evident in the UHMWPE fibre-based VPPMCs. Instead, evidence of debonding at the skin-core interface within the UHMWPE fibres was found. This is believed to be a previously unrecognised energy absorption mechanism.This work contributes to a further understanding of the viscoelastic properties of polymeric fibres and insight into the field of pre-stressed composite materials. The findings support the view that VPPMCs can provide a means to improve impact toughness and other mechanical characteristics for composite applications