2.  Applications of Woven Natural Fibre Polymer Composites

High strength synthetic fibres like Kevlar, carbon fibre, fibre-glass, Aramid and carbon nanotubes (CNTs) are commonly used in advanced composite structures as composite reinforcing materials. Nevertheless, the world is changing and green materials are in the vanguard due to the depletion and health concerns about inorganic materials, such as petroleum. In addition, the growing demand for natural fibre for composites has increased rapidly due to cost-effectiveness, low density, abundant, good thermal and insulating properties, renewability, biodegradability, high specific strength, etc. ^[2][3][173,174].

These successful benefits have stimulated the interest of numerous researchers in recent years in the development of natural fibres as reinforcement in polymer matrix composites such as kenaf fibre ^[4][5][6][89,175,176], oil palm fibre ^[7][8][177,178], sugar palm fibre^[9][10] [179,180], banana fibre^[11][12] [181,182], pineapple leaf fibre^[13][14] [183,184], flax^[15][16] [185,186], hemp^[17][18] [187,188], sisal^[19][20] [189,190], coir^[21][22] [191,192], jute^[23][24] [193,194], etc, as summarised in Table 4.

The development of loose natural fibre into a woven form improved the natural fibre’s potential and usefulness as a reinforcement in the advanced composite structure. In recent years, an increasing interest in textile composites has been observed. They are progressively used in the fabrication of high mechanical performance structures in many fields as listed in Table 5.

The woven-fibre composite denotes the type of textile composite in which strands form through the weaving process; they are interlaced with each other and impregnated with a resin material in two mutually orthogonal (warp and weft) directions. Particularly, in the form of short and random, composite materials reinforced with woven fabric have better out-of-plane rigidity, strength, and durability properties than laminate composites, although the geometry of this composite class is complex and there is no limit to the choice of possible architectures and components. Many parameters of woven-fibre composite materials can be altered, such as the geometry of microstructures, weave type, and hybridisation or choice of components (e.g., geometric and mechanical parameters of strands and resins)^[57] [223]. Thus, their mechanical performance should be taken into account in the preliminary study for the selection of woven fibre composites with the right blend of weight, cost, toughness, and strength properties.

Biocomposites must have useful characteristics (high-quality performance, durability, and reliability standards) in order to replace synthetic fibre-reinforced composites and extend into other industrial applications, such as traditional petroleum plastics used in automotive applications in particular^{[58][59][60][61]} [4,5,25,224]. The quest for lightweight vehicle parts, together with good end-of-life disposal, has indirectly opened a gateway to solve the issue of fuel consumption in the automotive sector and thus, reduced greenhouse gas emissions^[62] [225]. With this in mind, the European Commission has implemented the “European Guideline 2000/53/EG” which set the objective of improving the vehicle’s recyclability to 85% by weight in 2005. This percentage was increased to 95% by 2015^[62] [225].

Longest fibres, such as jute, can be formed into flexible fibre mats that can be produced by physical entanglement, nonwoven needling, or thermoplastic fibre melt matrix technologies. The two major types are carded and needle-punched mats. In carding, the fibres are combed, mixed and physically entangled in a felted mat. Geotextiles have a wide range of applications. It can be used as a mulch around the freshly planted seedling. With good moisture retention and promoting seed germination of jute fibre mats, low-and medium-density fibre mats can be made and used for soil stabilisation around new or existing constructions to stop soil slopes without roots from soil erosion and topsoil loss. As natural separators between various materials, medium and high-density fibre mats can also be used underground in road building and other forms of construction. Woven jute is commonly used as a “gunny” and tote bag because of the long and strong properties of jute fibre.

Morris et al.^[63]  [32] investigated woven natural fibre-reinforced composites materials for medical imagery. The various woven natural fibre materials, such as silk, cotton, lyocel, bamboo, and carbon fibre (as control), were integrated into a range of various resin materials appropriate for such applications. From examining a variety of resins and natural fibre materials in combination and testing their performance in terms of MRI and X-Ray imaging, the result showed that a woven cotton material impregnated with a two-part epoxy resin increased the passage of X-Rays by 15% and had no effect on the MRI signal (unlike the 40% MRI signal attenuation from carbon fibre) while maintaining a flexural modulus up to 71% of that of carbon fibre. These findings showed that natural fibre composites generated using such materials have attractive properties for use in patient care and positioning devices for multi-modal imaging without the need to substantially compromise the strength of the material.

In biomedical applications, Bagheri et al.^[64]  [226] suggested flax sandwiched with thin carbon sheets on either side for use as an orthopaedic long bone fracture plate because the hybrid’s mechanical properties are closer to the human cortical bone than the clinically used orthopaedic metal plates, rendering the material a possible candidate for long bone fracture fixation. A sandwich-structured composite in which two thin sheets of carbon fibre/epoxy are attached to each outer surface of the flax/epoxy core, resulting in a unique structure compared to other bone plate composite plates. The findings of the mechanical testing showed a significantly high final strength in both tension (399.8 MPa) and flexural loading (510.6 MPa) with a higher elastic modulus in bending tests (57.4 GPa) relative to tension tests (41.7 GPa). In both tension and bending tests, the composite material suffered a brittle catastrophic failure. Compared to clinically use orthopaedic metal plates, current CF/flax/epoxy findings were similar to human cortical bone, making the material a possible candidate for long bone fracture fixation.

In sporting good uses, a multitude of flax preforms have been used: woven flax prepregs, containing epoxy resin, were combined with carbon prepregs in the hybrid material concepts used in tennis rackets, bicycles, fishing rods, or ski. Glass fibres are still used in the latter and in one particular technology^[65] [227], the core of the ski sandwich structure is reinforced with strips ± 45° flax, located in the thickness direction of the core (balsawood), facilitating more weight reduction and damping capability improvement. In ski poles, braided flax is used, making them a bio-based and light alternative to poles reinforced with carbon or glass fibre.

Wambua et al.^[66] [228] found that flax composites had higher energy absorption compared with hemp and jute composites. However, the ballistic qualities of hemp composites were improved greatly when a mild steel plate was used to protect and support the body armour. Radif et al.^[67]  [229] noticed that the use of a woven ramie Kevlar-reinforced polyester composite as a material to manufacture body armour, in particular, to reduce the amount of Kevlar used, created a potential cost-effective product and could also contribute to a reduction in its cost of production. Furthermore, the armour was comparable to the third level of protection of the ballistic limits in accordance with the International Standard of the National Institute of Justice (NIJ).

A multilayer armour system (MAS) in which traditional Kevlar^TM  was substituted by either an epoxy matrix composite reinforced with 30 vol% jute fabric or a plain epoxy plate following an NIJ trauma limit after ballistic testing with 7.62 mm ammunition was manufactured and characterised by Luz et al.^[68] [230]. Within the statistical deviation, the ballistic output for the three investigated MAS second layer materials were found to be identical. Generally, lesser energy was dissipated by the aramid fabric in perforating individual ballistic tests, while the jute fabric composite and the plain epoxy were more effective. While not indicative of what happened in the MAS tests, the energy dissipated by each particular substance led to the exploration of the ballistic significance of the epoxy rupture mechanism. Referring to them, evidence of the massive collection of post-impact fragments by the composite of jute fabric and also the aramid fabric, which has also been recently reported, has been suggested as the main mechanism for energy dissipation. Additional fragment capture and brittle epoxy spalling (plain or composite matrix) contributed significantly to the dissipation of post-impact energy. Despite comparable ballistic efficiency and a negligible difference in weight, the considerably lower cost associated with environmental and societal advantages of natural fibre in practice favoured the replacement of jute fibre composite for both aramid and plain epoxy in MAS.

Woven bamboo fabric is similar to silk in softness. The fibres, which are not chemically treated, are generally smoother and more round without sharp spurs to irritate the skin making bamboo fabric hypoallergenic and ideal for people who have allergic reactions to other natural fibres like wool or hemp. A comparative analysis by Tausif et al. ^[69][231] on their comparative study of bamboo viscose fibre as an eco-friendly alternative to cotton fibre in knitted polyester-cellulosic blends was performed. Conventional cotton is not known to be eco-friendly, since it needs a significant quantity of water and pesticides during its processing. The eco-friendly quality of bamboo viscose is subjected to the manufacturing process used. Polyester-bamboo (PB) and polyester-cotton (PC) blended yarns were prepared using open-ended spinning techniques and the yielded yarns were single jersey weft-knitted. The results indicated that the PB blend outperformed the PC blend in mechanical properties and demonstrated lower thermal resistance than the PC blend, which is advantageous for summer clothing. Although at higher proportions of bamboo viscose fibre in the PB blend, the moisture management characteristics of PB blended fabrics were expected to be comparable to those of PC blended fabrics.

3. Challenges and Future Perspective on Woven Natural Fibre Composites

Under the Industrial Revolution 4.0 (IR4.0), the development of woven natural fibre composites remains in a very high challenge. The woven polymer composites are normally fabricated with thermoset matrices, although thermoset composites are well-known for their superior strength^[70] [86]. However, the fabrication processes in innovative ways are hardly ever reported^[71] [232]. Additives manufacturing (AM) coves the 3D printing production from a thermoplastic polymer, ceramic to metal materials. It reduces waste materials, labour monitoring and energy used^[72] [233]. The insertion of natural fibre reinforcements in powders and yarn forms, into PLA polymer composites, were reported as FDM or SLS 3D printing materials^[73] [234]. Unfortunately, there is no room is available for woven natural fibres composites in additives manufacturing, at least not to date. From a future perspective, woven natural fibres should be involved in AM to produce strong composites at a minimum cost.

Despite the intense research conducted on woven natural fibre composites, the use of woven natural fibre in aircraft interior components are not yet seen. Aircraft components have strict regulations on their durability and performance, especially with regards to flame retardancy^[74] [235]. However, woven natural fibres behave similarly as wood materials, with high flammability and low thermal stability in general^[75] [236]. Although numerous treatments and flame-retardant fillers were included in the woven natural fibre composites’ design and enhanced thermal and flame properties were achieved, but compliance with aviation materials’ requirements seems still challenging. Therefore, pushing the woven natural fibre composites as the alternative aircraft interior materials would be a prior task that needed to be done instead of continuous research without commercialisation.

As commercialization is a part of the future schedule, the popularisation of woven natural fibre composites is important. Without knowing and understanding from the public, commercialising woven NF composite products shall be a tough challenge. Publicity on the woven natural fibre composites should be a collaborative effort between universities, government and industrial partners. Woven natural fibre composites have been innovative materials among researchers for at least decades, however, the public has zero or limited information about these woven natural fibre composite materials. This makes it challenging for companies to use woven natural fibre composites in their products. This is because consumers are not going to select the products with which they are not familiar or confident. Hence, the government should take the initial step to introduce and promote the achievements of woven natural fibre composites conducted by local universities, via social media and newspapers. Through this approach, good products made from woven natural fibre composites can be delivered to consumers.