# Effect of Various Factors on Plant Fibre-Reinforced Composites with Nanofillers and Its Industrial Applications: A Critical Review

Authors: M. Aravindh; S. Sathish; L. Prabhu; R. Ranga Raj; Murugesan Bharani; Pravin P. Patil; Alagar Karthick; Rafael Luque
Journal: Journal of Nanomaterials
 (2022)

---

## Abstract

The growing awareness of the environmental damage caused by petroleum-based fibres has led to an increase in renewable and biodegradable resources. The continually growing demand for eco-friendly and sustainable materials pushes automakers and material researchers to consider the ecological importance of their materials during fabricating, recovering, and disposal. Natural fibre-reinforced composites (NFRC) have been introduced into the automobile market substantially over the last ten years due to their renewability, eco-friendliness, recyclability, biodegradability, light weight, better specific strength, good resistance to impact and corrosion, abundantly available, ease of processing, and cost-effectiveness. Due to cost-effectiveness and weight reduction, NFRC is becoming a better replacement for petroleum/synthetic fibres like aramid, kevlar, carbon, and glass fibre-reinforced composites, and the transportation sector has instigated the use of these materials in many applications like car interiors and exteriors, dash boards, bumpers, spoilers, seat covers, and mirror casings. NFRC with nanofillers is gaining more attention in the field of engineering, particularly for automotive, defense, building, and construction applications due to better aspect ratio, larger surface area, and attractive properties. The mechanical, tribological, and thermal properties of plant fibre-reinforced composites can be improved through the incorporation of organic or inorganic nanofillers. The present review profoundly explores the effects of various factors influencing NFRC with nanofillers. This paper also summarises the effects of various chemical reagents, fabrication techniques, and industrial applications of NFRC.


---

## Body

## 1. Introduction

Increasing ecological threats and the diminution of petroleum-based products are dynamic forces that cause chemical industries to shift from petrochemicals to eco-friendly resources [1]. Material selection is crucial in the design and manufacture of a sustainable product [2]. Materials are investigated for their mechanical and thermal properties to improve the product efficiency and increase customer satisfaction [3]. Cellulosic fibres derived from plants will play a vital role in this evolution as a significant renewable resource. NFRCs are one such material that offers flexibility during fabrication, desirable properties, and lower cost [4, 5]. Natural fibres act as reinforcing elements (discontinuous phase) in the composites used for various purposes. As a result, they have a more significant impact on a country’s socioeconomic progress. Therefore, the exploitation of natural fibres to make sustainable and renewable products has engendered considerable attention. For example, NFRC has become increasingly important in the transportation segment where better strength characteristics and nondimensional change have to be combined amid less weight [6–8]. Biofibres are often derived from three sources: plants, animals, and minerals. Mineral-based fibres are underutilised in fibre-reinforced composite (FRC) research because they include asbestos, which is harmful to human health [9, 10]. On the other hand, plant-based fibres are endowed with hopeful distinctiveness, for example, cost effectiveness, biodegradability, ease of use, and excellent strength properties [11–15]. Figure 1 shows the classifications of natural fibres based on various categories. The performance of natural fibre is influenced by numerous factors such as plant seed quality, soil performance, fertiliser used, fibre maturity duration and age, fibre retting techniques, cultivation timing, retting degree, climatic change, fibre microfibrillar angle, fibre structure, fibre layer cell dimensions, fibre storage place, and fibre testing procedures [16–24]. Constituents such as cellulose, lignin, hemicellulose, pectin, waxes, oils, and moisture content make up natural fibres. The physical, mechanical, and thermal performance of NFRC can be influenced by many factors, including the selection of reinforcement and matrix, form of reinforcement, manufacturing methods adopted, volume/weight fraction of the reinforcement or matrix, the fibre aspect ratio, fibre matrix interaction, chemical reagents adopted for fibre treatment, stacking sequence, and orientation of the fibres, laminate curing temperature, and time [25–32]. Natural fibres are constructed as chemical constituents like cellulose, hemicellulose, lignin, wax, moisture, and ash content. The chemical constituents considerably vary between fibres to fibres and also affect the overall mechanical properties of the natural fibres. The diameters of the fibres varied considerably from the length of the individual filaments. The disadvantage of cellulosic fibres as reinforcement is that their hydrophilic nature makes them incompatible with thermoset or thermoplastic polymers, resulting in weak adhesion between the matrix and reinforcement because the polymer matrix is hydrophobic in nature [33–35]. However, adhesion between fibre and petroleum-based polymer should be enhanced with appropriate chemical treatment [36–38]. It is critical to building a better interphase for better composites in terms of performance; the external stress should be passed to fibres from polymeric resin. Chemical treatment is one method for natural fibres to maximise the adhesion at the interface. Since it minimises the amount of OH placed over the surface of the fibre and reduces the aspect ratio of the fibre, which improves the adhesion at the interface zone due to superior effective fibre surface area and aspect ratio. The outcome of fibre surface treatment depends on treatment time, type of reagent and its concentration, and temperature [39–44]. Different chemical reagents for various natural fibres include alkaline, benzoylation, acrylation, peroxide, silane, potassium permanganate, dewaxing, maleated coupling agent, stearic acid, graft copolymerization, acetylation, and isocyanate treatment [45–51].Figure 1
Classification of plant fibres.Appropriate manufacturing techniques should be adopted to convert the raw materials into the final product without causing any defects. For the selection of proper manufacturing techniques to develop fibre reinforced composites, design and manufacturing experts would primarily consider a few factors. Such factors are size and shape of the end product, properties of reinforcement and matrix, processing characteristics of raw materials like processing temperature, pressure, curing time and curing temperature, production time, and manufacturing cost [52–57]. Conventionally, fibre-reinforced composites have been fabricated through various methods like autoclave, vacuum bag molding, compression molding, resin transfer molding, injection molding, filament winding, spray-up, and pultrusion [58–66]. The fibre/nanofiller-reinforced polymer composites are used in automobiles, aerospace, construction materials, packaging applications, and medical applications. Nanofillers could belong to organic and inorganic groups in nature. The particles like nanographeme, nanoclay, silica (SiO2), nanomontmorillonite (MMT), titanium dioxide (TiO2), carbon nanotube (CNT), calcium carbonate (CaCO3), and n-SiC are inorganic fillers. However, the fillers, such as rice husk, coconut shell nanofiller, pinecone char, wood shaving char, and cellulosic nanofillers, are extracted from renewable sources and represent organic nanofillers [67–71]. For the nanocomposite preparation, nanofillers are mostly added using a weight fraction method in order to analyse the effect of filler loadings. Wagner et al. [72] revealed that the addition of just below 6 vol.% of polymer nanoparticles as reinforcements to make composite materials improved a wide array of properties like reduction in weight, dimensional stability, heat conductivity, and electrical conductivity. Saba et al. [73] in their research article showed that kenaf and jute fibres have a low density of 1.3 g/cm3 and bond well with thermosets (epoxy) and thermoplastic polymers. They also claimed that nanosized reinforcements develop better properties in the composite materials compared to their microsized counterparts. The review aims to summarise the effects of various factors influencing natural fibre-reinforced composites with nanofillers and various chemical reagents on different natural fibres. Furthermore, it summarises the effects of various manufacturing methods and industrial applications of NFRCs.


## 2. Effect of Various Factors on NFRC with Nanofillers

The influence of fibre length and weight fraction on the mechanical characteristics of agave/polypropylene composites was studied by Jayaraman [74]. He concluded that composite materials with a fibre length of more than 10 mm and a fibre weight fraction of between 15% and 35% revealed excellent mechanical performance. Stalin et al. [75] studied the mechanical properties of vetiver/banana/vinyl ester composites by varying the weight fraction of fibres. The mechanical properties of composites were improved by the hybridization of vetiver and banana fibre. Vinayagamoorthy and Rajeswari [76] examined the mechanical properties of Vetiveria zizanioides/jute/glass composites by varying the weight fraction of fibres. Flexural, impact, compression, and hardness of hybrid composites were increased by 26.8%, 30.44%, 59.1%, and 28.65%, respectively. Sathishkumar et al. [77] analysed the mechanical characteristics of randomly oriented snake grass/banana/coir fibre hybrid composites. They revealed that the snake grass/banana and snake grass/coir fibre composites had better mechanical properties than banana/coir composites. Sanjay and Yogesha [78] studied the physical and mechanical properties of jute/kenaf/E-glass/epoxy hybrid composites. The mechanical properties of the laminates are influenced by the fibre arrangements and adhesion levels of the fabrics and the sequencing of high-strength fibre plies in the laminates. [79] examined the density and thermal stability of Furcraea foetida (FF) fibre-reinforced composites. The density of the Furcraea foetida fibre (778 kg/m3) was relatively reduced in comparison with synthetic fibres, which are useful for making less dense products. FF fibres have a thermal stability of 320.5°C, which is much greater than thermoplastic polymerization temperatures. The effect of the volume fraction of snake grass fibre on tensile and flexural strength was analysed by Sathishkumar et al. [80]. They noticed that an increase in snake grass fibre of up to 25% exhibited the highest properties. Arpitha et al. [81] fabricated five different hybrid composites by using conventional manufacturing methods and varying fibre stacking sequences and studied the water absorption and tensile strength of sisal/glass/epoxy/filler composite laminates. They discovered that adding E-glass and SiC filler to composites can reduce voids and water absorption intake. Also, they revealed that the tensile strength of sisal/glass/epoxy/filler composites increased with an increase in glass fibre volume fraction. Sanjay and Yogesha [82] examined the effect of the fibre stacking sequence of jute, kenaf, and E-glass woven fabric composites on water absorption properties. The water absorption tests were performed on specimens immersed in three different water conditions: normal, distilled, and salt water. They observed that the hybridization of E-glass with jute and kenaf fibres decreases the maximum water absorption. Sanjay et al. [83] investigated the hybridization effect of jute, kenaf, and E-glass fibres-reinforced hybrid composites on mechanical properties as a function of varying fibre layer sequences. They observed that incorporating glass fibre with jute and kenaf fibres enhanced the impact and interlaminar shear strength over pure NFRC. Compared to other laminates, the hybrid laminate with glass and kenaf fibre plies on the outside and jute fibre plies on the inside has improved characteristics. Vijay et al. [84] investigated the tensile strength, thermal stability, and surface properties of untreated and NaOH-treated Tridax procumbens fibres. They found that there was an increase in cellulose level after NaOH treatment and a decrease in hemicellulose, pectin, and wax, which improved thermal stability, tensile strength, and surface roughness. Sanjay et al. [85] assessed the tensile, flexural, and impact characteristics of hemp/glass fibre-reinforced hybrid composites as a function of fibre-layering sequences. They revealed that the incorporation of synthetic fibre with natural fibre decreased the water absorption and increased the mechanical properties of the composites. Murali Mohan Rao et al. [86] studied the tensile and flexural strength of composites made by strengthening vakka fibre into a polyester polymer as a function of the volume fraction of fibre. They revealed that vakka fibre composites had better tensile and flexural properties than banana and sisal fibre composites and were similar to bamboo-composite at the maximum volume fraction of fibre. Okubo et al. [87] analysed the flexural properties of bamboo/polypropylene composites. Due to enhanced bonding at the interface and fewer voids, the composite’s flexural strength and flexural modulus increase by roughly 22% and 40%, respectively. Shanmugam and Thiruchitrambalam [88] studied the dynamic mechanical analysis of palmyra palm/jute/polyester hybrid composites. They observed that combining jute fibres with palmyra palm increased the impact and ILSS by 18% and 25%, respectively. Raghul et al. [89] present a detailed survey on the mechanical behavior of glass fibre reinforced epoxy composites with nanofillers. This composite is manufactured by the compression modelling method in the form of laminates. The weight fraction of the nanofiller in the matrix ranges from 1%wt to 7%wt. This nanocomposite consists of improved mechanical properties suitable for industrial manufacturing. Biswas [90] prepared an effect of silicon carbide (SiC) in bamboo/epoxy composites as a function of weight percentage of filler loadings. The optimum tensile and flexural strengths were observed at 10 wt.% SiC and 5 wt.% SiC, respectively. The highest hardness was found at 15 wt.% SiC. From the SEM analysis, it was concluded that poor adhesion is responsible for low mechanical strengths. Nguong et al. [91] studied the effect of n-SiC on polymer matrix composites with different weight loadings of fillers. They observed that the mechanical properties were increased when 1 wt.% of n-SiC was reinforced into the epoxy matrix. The tensile strength, flexural strength, and fracture toughness of the composites were significantly increased when fillers were added to the composites. The effect of the addition of silicon carbide to jute fibre-reinforced epoxy hybrid composite was studied by Ramadan et al. [92]. Jute fabric-reinforced epoxy composites with silicon carbide ranging from 2 to 8% were fabricated by the vacuum assisted resin infusion method. The jute fibre-reinforced composites with 4 vol.% SiC exhibited excellent tensile and flexural strength. The mechanical properties of the composite were decreased when the SiC content was exceeded by 4 vol.%. Finally, they observed that the addition of SiC to jute fibre reinforced epoxy composites significantly increased their tensile, flexural, and impact strength. Ali and Ahmad [93] have investigated the compressive strength, thermal stability, and morphology of the empty fruit bunch and nanoclay-reinforced hybrid polyurethane foam composites. The result reveals that the hybridization of empty fruit bunch and nanoclay enhances the mechanical and thermal stabilities of the composites more than the empty fruit bunch alone filled composites. Olumuyiwa et al. [94] have studied the tensile, hardness, and impact strength of the coconut shell powder-reinforced polyethylene composite for different nanofiller loadings (5–25 wt.%). The hardness is found to be increased when the coconut shell filler loadings increase and the tensile strength, modulus of elasticity, impact energy, and ductility of the composite decrease with the increasing coconut shell filler loadings. They have also suggested that coconut shell powder-reinforced polyethylene composites are suitable for interior parts of automobiles. The thermal stability, electrical conductivity, water sorption, and mechanical properties of three different nanofillers (plastic waste char (PWC), wood shavings char (WSC), and pinecone char (PCC)) reinforced epoxy composites are analysed by Ahmetli et al. [95]. The result has revealed that the incorporation of nanochar particles enhances the mechanical and thermal stability of the composites. Among three nanochar-filled composites, plastic waste char-filled composites have produced more thermal stability and decreased the moisture diffusivity of neat epoxy. Table 1 presents the effects of various factors influencing NFRC. Figure 2 shows various factors influencing NFRC. Figure 3 shows various factors influencing the quality of the natural fibre.Table 1
Effect of various factors on NFRC.
S. noFibres usedFactors influencedEffectsReference1Pineapple leafFibre contentTensile and flexural properties increase with fibre content.[96]2BambooMoisture absorptionAn increase in moisture resulted in decreased interfacial shear strength.[97]3PalmyraLength and weight fractionBetter mechanical properties were obtained with a length of 55 mm and a weight of 55%.[98]4JuteWater absorptionAn increase in water absorption resulted in poor flexural and compressive properties.[99]5Banana/sisalLength and weightUp to 50% by weight, mechanical properties increased and water absorption decreased.[100]6Banana/sisalWeight fractionThe highest mechanical properties were obtained at 0.4%.[101]7Chopped snake grassVolume fractionImproved mechanical properties when the volume fraction increases.[80]8AbacaFibre loadingThe mechanical properties showed an increasing tendency up to 40 wt.% of fibre loading.[102]9Banana/sisalMicrofibrillar angle (MFA)High tensile characteristics are seen in fibres with high cellulose content and a low MFA content.[103]10KenafFibre contentImproved mechanical properties at 25% and 30% fibre content.[104]11LuffaVolume fraction of fibresThe mechanical characteristics of treated fibre composites were found to be optimal at 40% fibre volume fraction.[105]12Snake grassVolume fraction and fibre lengthImproved mechanical properties of the short fibre isophthalic polyester composite were achieved at 25%Vf for the 30 mm fibre length.[106]13Luffa cylindricaFibre contentImproved mechanical properties at 40% fibre content.[107]14Oil palmAging and wear behaviorThe wear test was carried out in dry conditions, and it was discovered that the composites immersed in engine oil and diesel performed better than the others.[108]15Lantana camaraLoad and fibre content(1) The proportional wear loss increased in direct proportion to the increase in normal load(2) The optimum wear resistance property was obtained at a fibre content of 40%[109]16AgaveFibre length (3, 5, and 7 mm)3 mm agave fibre reinforcement that has been alkali-treated had better mechanical properties.[110]17Sansevieria cylindricaFibre length and weightThe mechanical characteristics of composites were optimal at 30 mm fibre length and then deteriorated beyond that.[111]18VakkaVolume fractionTensile characteristics improved as the percentage of vakka fibre in the composite increased.[86]19Coir/silkFibre lengthThe mechanical characteristics of composites with 2 cm fibre length were the best.[112]20Palm/coir fibreFibre weight fractionThe mechanical characteristics of composites with 30% fibre reinforcement were the best.[113]21Sisal/nanoclay/polyesterFibre and filler weight fractionImprovement in tensile strength and water absorption when 25% sisal and 3% nanoclay.[114]22Bagasse/nano-SiO2/HDPEFiller loading (2% to 5%)Improvement in tensile strength by 71.46%.[115]23Bagasse/nano-TiO2/vinyl acetateFiller loading (2%)10% improvement in tensile strength.[116]24Ramie/CNT/epoxyFiller loading (0 to 0.6%)Flexural strength and modulus were increased by 34% and 37%, respectively.[117]25Bagasse/nanographene/PPFiller loadingImprovement in mechanical properties such as tensile, flexural, and impact strength.[118]26Jute/nanographeme/epoxyFiller loadingImprovement in mechanical properties such as tensile, flexural, and impact strength.[119]Figure 2
Various factors affecting NFRC.Figure 3
Various factors affecting quality of natural fibres.


## 3. Effect of Chemical Treatments on NFRC with Nanofillers

Plant fibres generally consist of cellulose, hemicellulose, lignin, pectin, water-soluble, and waxy elements [120]. From the chemical point of view, the primary constituents of plant fibres are cellulose, in which Dglucopyranose units are linked together by b-(1-4)-glucosidic bonds; hemicelluloses consist mainly of D-pentose sugar units strongly bonded with cellulose fibrils through hydrogen bonding; and lignin, consisting of aromatic alcohol units such as coniferyl alcohol, sinapyl alcohol, and coumaryl alcohol [121, 122]. Pectin acts as an adhesive to hold fibres together in bundles and bundles to nonfibrous tissues. Hemicellulose, pectin, and lignin act like a matrix, whereas cellulose acts as reinforcement to the matrix, contributing to the strength of the fibre. Plant fibres are amenable to modifications as they bear hydroxyl groups (OH) from cellulose and lignin. The hydroxyl groups may be involved in hydrogen bonding within the cellulose molecules, thus reducing the matrix activity. Surface modifications can either stimulate OH groups or create new moieties that can interconnect with the polymer effectively [123]. Fibre surface characteristics such as adhesion, porosity, surface tension, and wetting can be enhanced upon chemical treatment. Surface modification of natural fibres can result in significant physical changes such as the removal of an oil or waxy layer, changes in fibre structure, density changes, and surface roughness changes [124, 125]. The interfacial adhesion of the composites can be enhanced by altering the fibre surface, altering the matrix, or altering both. Chemical treatment is necessary to improve the adhesion and wettability at the interface [126]. Figure 4 shows the types of various chemical treatments of natural fibres. Mwaikambo and Ansell [127] reported that alkalization improved the characteristics of kapok, sisal, jute, and hemp fibres, resulting in increased fibre–resin adhesion and more incredible interfacial energy. Teli and Jadhav [128] studied the influence of NaOH reagent on the mechanical properties of Agave augustifolia fibres with changing reagent concentrations (i.e., 2, 5, 10, 15, and 20%) for 1 h and found the most extraordinary mechanical properties at 15%. Sawpan et al. [35] showed that the flexural properties of hemp fibre were enhanced by mercerization treatment with a NaOH concentration of 5%.Figure 4
Types of chemical treatments.Dhanalakshmi et al. [129] assessed the alkali treatment effect on the flexural strength of areca fibre-reinforced epoxy composites and observed that flexural strength improved after treatment due to eliminating the hemicellulose, lignin, pectin, and waxes. After mercerization treatment, the characteristics of henequen fibres/high-density polyethylene composites improved owing to the elimination of a few lignin and hemicelluloses from the fibre surface, resulting in a larger contact surface area at the interface zone [130]. The 5% NaOH treatment increased the mechanical characteristics of Borassus fruit fibres by increasing their surface area and improving their interfacial properties [131]. Paul et al. [132] subjected banana fibre to permanganate treatment and investigated the influence of permanganate treatment on the tensile and flexural properties of banana-polypropylene composites. They found that the tensile and flexural properties increased by 5% and 10%, respectively. Lopez Manchado et al. [133] subjected flax fibre to acetylation treatment and analysed the influence of acetylation treatment on the thermal and mechanical properties of flax fibre-reinforced polypropylene composites. They found that the thermal and mechanical properties were enhanced by 50% and 25%, respectively. Singh et al. [134] discovered that an alkali-treated agave reinforced epoxy composite has better fracture strain and interfacial adhesion between fibre and matrix than an untreated fibre. Shanmugam and Thiruchitrambalam [88] revealed that the maleated anhydride-treated jute fibre-reinforced high-density polyethylene composite exhibits improved adhesion between fibre and matrix, which enhances the dynamic and static properties such as tensile, flexural, and impact strength. Singh et al. [134] investigated whether an alkali-treated agave-reinforced epoxy composite exhibits greater fracture strain and interfacial adhesion between the hydrophilic fibre and the hydrophobic matrix than an untreated fibre. Arbelaiz et al. [135] studied that 20 wt% of NaOH-treated flax fibre-reinforced polypropylene (PP) composites exhibited greater maximum interfacial shear strength (ILSS) than untreated flax fibre-reinforced composites. De Rosa et al. [136] observed that the composite containing 10% acetic acid-treated okra fibre has less tensile strength and Young’s modulus than those containing untreated okra fibre-reinforced composites. Mwaikambo et al. [137] investigated the effect of alkaline treatment on the tensile and impact strength of hemp/euphorbia composites and reported that the tensile and impact strength increased by 30% each compared to untreated composites. Lopez Manchado et al. [133] examined the influence of alkaline treatment on the tensile and flexural properties of bamboo/polyester composites and found that the tensile and flexural strength increased by 10% and 2%, respectively, over untreated composites. [138] reported the result of alkali treatments on the mechanical properties of a jute/polyester composite. They observed that 10% NaOH-treated fibre composites for 3 h provided an improvement in tensile strength, flexural strength, and impact strength. Shanmugam and Thiruchitrambalam [88] attempted to increase the mechanical properties of palmyra palm/jute/polyester hybrid composites by alkaline treatment with 5% NaOH for a duration of 30 min. They found that the mechanical properties such as tensile, flexural, and impact strength increased by 40%, 55%, and 4%, respectively. The new cane fibres were alkali treated for 24 hours at different concentrations of 2, 4, 6, and 8%, with the highest tensile and flexural strength being revealed at 6% [139]. The effect of mercerization on the flexural and impact strength of coir fibre-reinforced polyester composites was investigated by Prasad et al. [140]. The treated fibre composites outperformed the untreated ones due to stronger interfacial bonding between fibre and matrix after 72 hours of treatment with a 5% NaOH solution. Ragunathan et al. have fabricated rice husk powder-reinforced polypropylene/recycled acrylonitrile butadiene rubber composites by a melt mixing technique. The rice husk-filled composite is fabricated with silane and anhydride. The composites are characterised by mechanical, FTIR, and morphological properties. The composites influenced by anhydride exhibit better mechanical strength than the composites treated with silane. The coupling agent increases the bond between the rice husk filler and the matrix. Table 2 presents the effects of various chemical treatments on NFRC.Table 2
Effect of various chemical treatments on NFRC.
S. noFibres usedType of chemical treatmentEffectsReference1Sisal and roselleAlkalineIncreased mechanical properties.[141]2AlfaAcetylationImproved resistance to moisture absorption[142]3Continuous henequen fibresSilane (0.015 wt. %)Improved mechanical properties.[143]4Borassus fruit fibresAlkalineThermal stability and tensile properties have been slightly improved.[144]5Agave fourcroydesAlkalineImproved fibre matrix adhesion[145]6BagasseMercerization and acrylic acidSuperior tensile and flexural properties and reduced moisture absorption.[145]7Unidirectional Roystonea regiaAlkalineImproved tensile and flexural properties.[146]8SisalAlkalineIntracrystalline lignin and waxy, and resulted in improved mechanical interlocking.[147]9Oil palmAlkaline, acrylonitrile grafting, silane, acrylation, permanganate, acetylation, peroxide treatment(1) Silane treatment-tensile strength reduced(2) Acrylation-enhanced tensile strength(3) Alkali and permanganate-tensile modulus increased(4) Silane and acrylate treatments showed optimum mechanical properties[148]10Coir fibreAlkalineInterfacial adhesion between coir fibre and natural rubber was improved.[149]11SisalAlkalineThe internal structure that resulted in a specific stiffness that was approximately the same as steel.[150]12KenafAlkalineImproved mechanical properties[151]13RamieAlkalineTensile strength of the ramie fibre improved from 4 to 18% compared to untreated fibre while Young’s modulus decreased.Tensile strength increases as a result of a change in microfibrillar angle.[152]14BagasseAlkalineImprovement in tensile, flexural, and impact strength by 13%, 14%, and 16% compared to untreated fibres.[153]15SisalAlkaline and benzoyl chloride treatmentHigher thermal stability.[154]16FlaxBenzoyl chlorideMoisture absorption is reduced, and tensile properties are improved.[155]17JuteAlkalineImproved dynamic mechanical properties.[156]18AlfaStyrene, acrylic acid, and maleic anhydrideThese treatments resulted in reduced water uptake.[157]19KenafAlkaline3% NaOH treatment led to ineffective removal of impurities.9% NaOH cleaned the fibre surface.[158]20CoirAlkali and UV radiationHigher shrinkage of the polymer grafted with fibre resulted in physicomechanical properties.[159]21Sisal/5% nanomontmorillonite (MMT)/PPMaleic anhydride grafted polypropyleneImprovement in tensile strength[160]


## 4. Effect of Various Manufacturing Methods on NFRC with Nanofillers

Shibata et al. [161] investigated the influence of the volume fraction of kenaf and bagasse fibres on reinforced corn starch composites manufactured by compression molding techniques and found that an increase in the volume fraction of kenaf and bagasse fibres led to an increase in the flexural modulus of composites by 60% and 66%, respectively. Barone [162] studied the influence of fibre length on the tensile, impact, and flexural strength of abaca fibre-reinforced phenolic composites manufactured by the compression molding technique and found that the fibre length of 30 mm was optimum for obtaining higher mechanical properties such as tensile, impact, and flexural strength. Kafi et al. [163] assessed the effect of styrene chemical treatment on the crack propagation of jute fibre-reinforced polyester composites manufactured by compression molding technique and reported that the resistance to crack propagation was enhanced when jute fibre was treated with styrene. Sharma and Kumar [164] investigated the effect of the weight fraction of fibre on the flexural strength of banana fibre-reinforced polyurethane composites manufactured by a compression molding technique. They found that a fibre content of 15% by weight was optimum for achieving better flexural strength. Alamri and Low [165] reported that recycled cellulose fibre-reinforced epoxy composites manufactured by compression molding techniques with the weight content of fibre up to 46% had higher fracture toughness. Cao et al. [153] discovered that bagasse fibre-reinforced polyester composites manufactured by compression molding with 65% fibre content by weight had a 30% higher impact strength than other weight fractions of fibre. Jandas et al. [166] studied the effect of the volume fraction of banana fibres on the polylactic acid composite manufactured by the compression molding technique with 25% fibre content by volume, resulting in higher impact strength compared to other volume fractions of fibres. Bledzki et al. [167] studied the influence of volume fraction on the impact strength of jute and flax fibre-reinforced epoxy hybrid composites manufactured by compression molding. They found that the impact strength of the hybrid composite was improved when there was an increase in the fibre content by volume and also reported that flax fibre-reinforced composites had greater maximum impact strength than jute reinforced composites. Yousif and El-Tayeb [168] studied the effect of fibre length and fibre diameter on the wear rate of oil palm fibre-reinforced polyester composites manufactured by hand layup technique and found that the fibre length of 1–1.5 mm and fibre diameter of 350 micro m notably reduced the wear rate by about three to four times compared to pure polyester resin. El-Tayeb [169] investigated the influence of fibre length on the wear resistance of sugarcane fibre-reinforced polyester composites manufactured by hand layup technique and found that the composite with a fibre length greater than 5 mm has increased wear resistance due to less fibre pullout present at that length. Assarar et al. [170] studied the flax fibre-reinforced epoxy composite manufactured by hand layup technique and reported that water aging significantly increased the strain rate by 61% and decreased the Young’s modulus by 40% of the composite compared to the manmade glass fibre. Venkateshwaran et al. [171] analysed the influence of NaOH reagent on the mechanical properties of banana/epoxy composite manufactured by hand layup technique. They concluded that 1% alkaline-treated fibre increased the mechanical properties of untreated fibre composites. Ray et al. [172] analysed the influence of NaOH reagent on the ILSS of a jute/vinyl ester composite manufactured by hand layup technique and concluded that the fibre treated with 5% NaOH for 4 hrs gave 20% progress in the ILSS. Prasad et al. [140] studied the influence of NaOH reagent on the impact and flexural strength of coir/polyester composites manufactured by hand layup technique and noticed that the coir fibre bleached with 5% NaOH for 3 days gave a 40% enhancement in the impact and flexural strength. Gao and Mader [173] fabricated a jute fibre reinforced polypropylene composite using injection molding techniques and noticed that the fibre length was significantly influencing the tensile properties of the composite. Karmaker and Schneider [174] fabricated jute and kenaf fibre-reinforced polypropylene hybrid composites using injection molding techniques and reported that the hybrid composite had higher mechanical properties with maximum jute fibre than kenaf fibre. Bledzki et al. [175] analysed the influence of acetylation treatment on the mechanical characteristics of a flax fibre-reinforced polypropylene composite fabricated by injection molding technique. They concluded that the mechanical characteristics of the treated fibre composite increased by up to 35% compared to untreated fibre. Yang et al. [176] investigated the influence of maleated anhydride treatment on the tensile strength of a rice husk fibre-reinforced polypropylene composite fabricated by injection molding technique and noticed that the tensile strength of the treated fibre composite was improved due to enhanced adhesion between the hydrophilic fibre and the hydrophobic matrix. Pickering et al. [177] analysed the influence of fungal and NaOH reagents on the mechanical characteristics of a hemp/polypropylene composite fabricated by injection molding technique. They noticed that the mechanical characteristics of fungal-treated and combined fungal/alkaline-treated composites were increased by 22% and 32%, respectively. Wielage et al. [178] fabricated flax and hemp fibre-reinforced polypropylene composites using injection molding techniques and noticed that maleated anhydride-grafted treatment significantly enhanced the dynamic mechanical properties of the composites compared to untreated fibre composites. Figure 5 shows the classifications of manufacturing methods for the NFRC. Table 3 presents the effect of various manufacturing methods on NFRC. Figure 6 presents the merits, demerits, and applications of NFRC.Figure 5
Classifications of manufacturing methods.Table 3
Effect of various manufacturing methods on NFRC.
S. noFibre/matrixManufacturing method usedEffectsReference1Long discontinuous kenaf and jute-reinforced polypropyleneHot-pressMaximum tensile strength and modulus were obtained at 40% fibre weight fraction.[179]2Short bamboo fibreInjection moldingImproved mechanical properties.[180]3Chicken feather fibre/PLAInjection moldingThe SEM image indicated that an even distribution of CFF in the PLA matrix existed.[181]4Sisal, banana, jute, and flax/propyleneExtrusion and compression moldingEnhanced the mechanical properties.[182]5Silk/gelationCompression moldingMechanical properties were increased.[183]6Agave/epoxyHand layupWear properties were improved.[184]7Luffa/coir/PPInjection moldingMechanical properties were improved.[185]8Luffa/thermoplastic starchCompression moldingMechanical properties were improved.[107]9Luffa and groundnut/epoxyHand layupMechanical properties were improved.[105]10Alfa/polyesterHand layupMechanical properties increased up to 5% NaOH treatment.[186]11Snake grass/polyesterHand layupMechanical properties were improved.[187]12Tea/epoxyCompression moldingMechanical properties were improved.[188]13Cissus quadrangularis stem fibre/unsaturated polyesterCompression moldingMechanical properties were improved.[189]14Short Sansevieria cylindrica/polyesterCompression moldingMechanical properties were improved.[111]15Tapsi fibreHand layupMechanical properties were improved.[190]16Prosopis juliflora/epoxyHand layupMechanical properties were improved.[14]17Tea leaf fibreCompression moldingMechanical properties were improved.[191]18FlaxCompression moldingMechanical properties were improved.[192]19Long jute fibre yarnInjection moldingMechanical properties were improved.[173]20Short date palm leavesInjection moldingMechanical properties were improved.[193]21Wood flour/6% MMT/PPInjection moldingTensile and flexural strength were improved by 20% and 13%, respectively.[194]22Sisal/2-5% MMT/epoxyCompression moldingTensile strength and tensile modulus were improved by 27% and 47%, respectively.[195]23Sisal/5% nanoclay/epoxyCompression moldingWater absorption was reduced by 1/3 times.[195]24Hemp/nanoclay/polyesterCompression moldingWater absorption and tensile strength were reduced by 8% and 20%, respectively.[196]25Bamboo/MMT/HDPEMelt compoundingMechanical properties were decreased.[197]26Bamboo/CNT/epoxyHand layupTensile strength and flexural strength were increased by 6.67% and 5.8%, respectively.[198]Figure 6
Merits, demerits, and applications of NFRC.


## 5. Industrial Applications of NFRC

Composites reinforced with natural fibres are gaining more attention in the market right now, as demand for high strength-to-weight ratios for industrial applications grows. The NFRC material has a high strength-to-weight ratio, moderate stiffness, impact resistance, durability, improved corrosion resistance, and excellent fatigue strength. Because of these numerous benefits, NFRC has found applications in construction, aircraft, defense, hockey sticks, homes, surgical equipment, leisure, ship hulls, and automobile parts [199–203]. Snake grass, bamboo, kenaf, flax, vetiver, areca, and ramie fibres are used in various applications like office furniture, textile products, ropes, home appliances, fishing nets, the paper industry, packing materials, and building materials [204]. Textiles, households, oil pipes, packing products, and structural panels were all made with hemp/epoxy composites. The roof cover, electronic panels, trunk panels, seatback covers, packing items, and support insulation are all made from kenaf. Fibre-reinforced composites in the bast and seed category were used in the glove box, back rest panels, filter cloths, wheel boxes, and household furnishings [205]. The pineapple and sisal fibre-reinforced hybrid composites were used in underfloor-body panels, partition panels, door cladding, parcel shelves, two-wheeler bumpers, crates, drainage pipe, table mats, fishing boats, and automobile body building [206]. The coir/epoxy composites were used in the seat cushions, mirror casings, storage tanks, postboxes, helmet casings, brushes, ropes, bags, brooms, door shutters, and building panels [207].Daimler Chrysler used flax, cotton, sisal, and banana fibres for floor panels, dashboards, seat back rests, door panels, and pillar cover panels of A, C, and E class models. Lotus Peugeot used hemp and sisal fibre reinforced composites for packaging trays, door panels, interior mats, seat backs, and body panels of the eco-elsie 406 [208]. The coir/natural latex rubber-reinforced hybrid composites were used in seat belt lining, soundproofing panels, particle boards, and parcel shelves. Flax, sisal, and coir fibres with thermoplastic matrix such as PP, PE, PS, and PVC were used in automobile components, containers for logistics, interior parts, and household products. Nippon Electric Company (NEC) used kenaf fibres to reinforce PLA biocomposite for mobile phone casings. Museeuw Bikes used flax and hemp fibres reinforced with epoxy composites for racing bicycle frames and casings for musical instruments [209]. Flax/sisal/epoxy composites were used in parcel shelves, curtains, seat backs, back cushions, floor mats, and interior panels for top-class vehicles [210]. Door bolsters, centre consoles, carriers for covered door panels, seat back panels, covered components for instrument panels, rear deck trays, pillars, covered inserts, seat backs, carriers for hard and soft armrests, door panels, headliners, side and backwalls, load floors, and trunk trim were all made from bast fibre-reinforced PP/polyester composites [211].The sisal/glass/filler/epoxy-reinforced composites were used in the frames, toys, and electronic panels [81]. The flax/epoxy composites were used in the aerospace-military aviation fuselage, rudder, slats, and wings [212]. Figure 7 presents various automobile applications of NFRC. Figure 8 shows industrial applications of NFRC. Table 4 presents applications of NFRC in various fields.Figure 7
Automobile applications of NFRC [213–217].Figure 8
Industrial applications of NFRC [218–220].Table 4
Applications of NFRC in various fields.
S. noFibreComponentsReference1Flax/sisalDoor trim panels and cable linings[221]2KenafAutomobile dashboards, carpet padding, and products as rope, twine, bagging, and rugs[222]3JuteBrake pad and car insulation[223]4SisalRopes, mats, carpets, and fancy articles[15]5Soybean oilHigh-quality paint enamel[224]6CoconutInterior trim and seat cushioning[225]7BananaHousehold telephone stand[226]8Soy oilStructural panels[227]9Kenaf/glassCar bumper[228]10CoirLiquid storage tanks[229]11Sugar palm fibreBrushes, ropes[230]12Mature coconutTextiles (mats and carpets), building (thermal insulation), and automobile (cushion and seat covers)[231]13Ichu fibreConstruction material[232]14Tapsi/karaya gumFood and pharmaceutical industries[233]15Date palmInsulation material in buildings[234]16Azadirachta indicaCar roofing, interior and exterior panels, home appliances, container boxes, particle boards, and parcel shelves.[235]17Tridax procumbensAyurvedic medicines to treat liver disorders[84]


## 6. Conclusions

The exploitation of natural fibre-reinforced composites by using an emerging technology transforms the future of the coming days. The hydrophilic nature of natural fibres affects bonding to a hydrophobic polymer, which results in poor mechanical properties. To overcome this issue, the natural fibre surface must be modified to promote better interaction between fibre and matrix. The innovative and commercial applications of natural fibre-reinforced composites can help develop new revolts to maintain our natural properties. Natural fibres such as flax, snake grass, ramie, vetiver, areca, kenaf, hemp, kenaf, pineapple, and bamboo are gifted to the transportation industry because of their renewability, sustainability, eco-friendliness, and biodegradability. Composites reinforced with natural fibres are gaining traction in the market as the market’s demand for high strength-to-weight ratio for industrial applications grows. This extensive range of different benefits has led fibre-reinforced composites to find more applications in the automobile, aerospace, marine, biomedical, construction, household, and sports industries. Incorporating nanofillers to plant fibre-reinforced composites introduces a positive effect on physical and mechanical properties. Many investigations are revealed, reviewed, and presented in this article concerning the effects of various factors influencing different types of chemical treatment and manufacturing methods and industrial applications of natural fibres and reinforced composites.



---

*Source: 4455106-2022-07-05.xml*