Industrial applications of natural fibre-reinforced polymer composites – challenges and opportunities

ABSTRACT

The growing industrial demand for sustainable materials has led to a paradigm shift in the focus from synthetic polymers towards natural fibres. This paper deals with the challenges and opportunities associated with the use of natural fibre-reinforced polymer composites in various industrial applications. Natural fibres being biodegradable, light in weight, cost-effective and environment friendly are good candidate materials for modern industrial applications. Use of natural fibres in various industries with a focus on automotive and furniture industry has been discussed. The commonly used natural fibres in polymer composites including jute, hemp, sisal, kenaf, bamboo, cotton, flax, abaca, coir etc. have been dealt with in this paper. The literature revealed that tensile strength and other mechanical properties of these fibres are comparable to synthetic fibres like glass or carbon fibres. However, the temperature stability of polymers limits their extensive use and remains an issue to be addressed.

KEYWORDS:

• Natural fibres
• polymer composites
• sustainability
• automotive
• structural

1. Introduction

In the last decade, natural fibres are being preferred over synthetic fibres as the reinforcement in polymeric composites due to their environmental and economical benefits. Owing to the global energy crisis and quest for sustainability, the unique features of natural fibres like abundance, non-toxicity, high performance, versatility, easy processing at low cost, no irritation to respiratory system, skin, eyes and non-corrosive nature, natural fibre-reinforced polymer composites (NFPCs) have got more attention as compared to synthetic fibre-reinforced polymeric composites. In addition to this, the energy consumption by natural fibres during their production is only 17% as compared to synthetic fibres like glass fibres (Shalwan and Yousif 2013; Holbery and Houston 2006; Dhakal, Zhang, and Richardson 2007). Use of these composites in different sectors has a great potential to improve the pace of manufacturing and recycling with environmental friendliness (Bledzki and Gassan 1999). As suggested by a recent report, NFPC materials market is expected to grow to US$ 531.3 million in the year 2016 from US$ 289.3 million in 2010. The report also revealed that the major increase in the use of NFPC is due to increase of these composites in automotive sector. NFPCs have found considerable applications in the field of automotive and construction due to good specific strength, low density, biodegradability, low density, better tool life and renewability (Caprino et al. 2015). NFPCs offer extensive applications in low-cost housing, consumer goods, civil structures, and different other applications (Satyanarayana, Arizaga, and Wypych 2009; Pandey, Ahn, and Lee 2010). Moreover, NFPCs were found suitable for panelling elements in airplanes and trains (Mohanty, Misra, and Hinrichsen 2000).

The most common natural fibres used in industrial applications include flax, kenaf and hemp, because of their better fibre strength properties. In Table 1, the tensile strength and elastic modulus of the various natural and synthetic fibres have been provided. A comparison of the specific strength (tensile strength/density) and specific modulus (modulus of elasticity/density) of various natural fibres to E-glass reveals that E-glass-specific strength is superior to all natural fibres, although flax fibre is very competitive (1275 vs. 1000, respectively). However, the specific modulus of kenaf (42.9) and flax (54) exceeds to that of E-glass (28). These values imply that the natural fibre characteristics are comparable or, in some cases, better than those of glass fibres (Holbery and Houston 2006). Fowler, Mark Hughes and Elias (2006) and Alix et al. (2008) have opined that cellulose plays a crucial role in strength and durability of fibres, and the percentage of cellulose in fibre directly impacts its strength and durability.

Table 1. Properties of natural and synthetic fibres (Bledzki and Gassan 1999; Holbery and Houston 2006; Hutchinson 2006; Eichhorn et al. 2002; George, Sreekala, and Thomas 2001; Saheb and Jog 1999; Chand and Fahim 2008; Hutten 2007; Khalil et al. 2012; Shinoj et al. 2011; Sen and Reddy 2011; Xiaobo Li 2004; Marrot et al. 2013; Mahjoub et al. 2014; Udoeyo and Adetifa 2012; Ramnath et al. 2014; Berger 1983; Yusriah et al. 2014; Hossain et al. 2014; Paturau 1987; Pothan, Thomas, and Groeninckx 2006; Mwaikambo 2006).

Type of fibre	Density (g/cm^3)	Tensile strength (MPa)	Elongation (%)	Elastic modulus (GPa)	Specific modulus (GPa cm^3/g)
Jute	1.3–1.5	385–850	1.4–2.1	9–55	6.9–38
Cotton	1.5–1.6	200–800	2.1–12	5.5–15.1	3.3–10.1
Flax	1.3–1.5	340–1600	1.1–3.3	25–81	16.7–54
Hemp	1.1–1.6	285–1735	0.8–4	14.4–70	9.6–29.3
Kenaf	0.6–1.5	223–1191	1.6–4.3	11–60	10–42.9
Sisal	1.3–1.6	400–700	1.9–15	8.5–40	6.5–30.8
Ramie	1.4–1.55	200–1000	1.2–4	41–130	27.3–81
Bamboo	1.2–1.5	500–575	1.9–3.2	27–40	50–67.9
Coir	1.15–1.6	131–593	14–40	3–7	2.5–5
Oil palm	0.7–1.6	50–400	4–18	0.6–9	0.5–7.5
Betelnut	0.2–0.4	120–166	22–24	1.3–2.6	1–1.9
Pineapple	1.56	150–1627	2.4	11–82	7.8–57
Sunhemp	1.07	389	1.6	35	32
Sugarcane bagasse	1.1–1.6	170–350	6.3–7.9	5.1–6.2	3.6–4.1
Abaca	1.5	430–815	1.2–1.5	31.1–33.6	–
Banana	0.5–1.5	711–789	2.4–3.5	4–32.7	3.6–27.3
Softwood Kraft Pulp	1.5	1000	4.4	40	–
E-Glass	2.5–2.55	2000–3500	0.5–3	70–73	26.9–28
S-Glass	2.5	4570	2.8	86	34.4
Aramid (Std.)	1.4	3000–3150	3.3–3.7	63–67	–
Carbon (Std. PAN-based)	1.4–1.78	3400–4800	1.4–1.8	230–425	–

1.1. Sources and properties of natural fibres

Based on the source, natural fibres can be classified into bast fibres (jute, flax, hemp, kenaf, ramie etc.), leaf fibres (sisal, palm, manila, caraua etc.), seed fibres (cotton, kapok etc.), fruit fibres (coconut, coir etc.) and stalk fibres (bamboo, wheat, rice, grass, corn etc.). Natural fibres are generally harvested yearly and in some cases like jute, hemp and kenaf can be harvested two to three times yearly. As reported by Holbery and Houston (2006), all the natural fibres have a high CO₂ assimilation rate i.e. they consume high amount of CO₂, thus helping in reducing the carbon content in atmosphere. The various sources/origin of natural fibres are represented in Figure 1.

Figure 1. Sources of natural fibres (Conceptualized from Ahmad, Choi, and Park 2015; Ashori 2008).

The documented literature suggests that natural fibres when used as reinforcements with polymers result in improved mechanical properties and can act as a suitable replacement to the artificial fibres. Generally, the synthetic fibres have much higher strength than the natural fibre but in case of specific modulus most of the natural fibres are far better than the synthetic fibres as shown in Table 1. As various mechanical properties of natural fibres like tensile strength (σ), breaking strain (ɛ), Young’s modulus (E) etc. have varying cited values mainly due to non-standard testing conditions. The proper compliance to the testing standards for determination of these properties can further bring more clarity and could pave way for widespread use of NFPCs in structural applications (Symington et al. 2009).

Generally, natural fibres are lignocellulosic in nature consisting of cellulose microfibrils in helical form in the matrix of hemicelluloses and lignin (Young 1986; Mohanty, Misra, and Drzal 2001; Zafeiropoulos et al. 2002). Table 2 presents the different chemical compositions of various natural fibres. Plant fibres are mainly composed of lignin, cellulose, hemicellulose, waxes and some other compounds (Sarkanen and Ludwig 1971).

Table 2. Chemical composition of common natural fibres (Hutten 2007; Khalil et al. 2012; Shinoj et al. 2011; Han and Rowell 1997; Averous and Le Digabel 2006; Wambua, Ivens, and Verpoest 2003; Xue Li, Tabil, and Panigrahi 2007; Kalia and Sheoran 2011; Ramachandra, Kamakshi, and Shruthi 2004; Mark 1986; Preethi and Balakrishna Murthy 2013).

Fibre	Cellulose (%)	Lignin (%)	Hemicellulose (%)	Pectin (%)	Waxes (%)	Ash (%)	Silica (%)
Fibre flax	64.1–71	2–2.2	16.7–20.6	1.8–2.3	1.5–1.7	13.1	–
Seed flax	43–47	21–23	24–26	–	–	5	–
Kenaf	31–57	8–21	18–24	3–8.9	0.5	2–5.1	–
Jute	45–71.5	0.2–26	12–21	0.2–11.8	0.5	0.5–8	–
Hemp	55–80.2	2.6–13	12–22.4	0.9–3	0.2–0.8	0.5–8	–
Ramie	68–91	0.6–0.7	5–16.7	1.9	0.3	5	–
Abaca	56–63	7–13	15–17	0.3–1	0.1	1–3.2	–
Sisal	47–78	7–14	10–24	0.8–10	0.3–2	0.6–4.2	–
Rice (stalk)	28–48	12–16	23–28	–	–	15–20	9–14
Wheat (stalk)	29–51	16–21	26–32	–	–	4.5–9	3–7
Oat (stalk)	31–48	16–19	27–38	–	–	6–8	4–6.5
Henequen	77.6	13.1	4–8	–	–	–	–
Hardwood	38–50	20–30	19–26	0–1	–	0–1	–
Softwood	40–45	26–36	7–14	0–1	–	0–1	–
Cotton	82.7–90	0.7–28.2	1–5.7	0–5.7	0.6	0.8–2	–
Sugarcane	32–48	19–24	27–32	–	–	1.5–5	0.7–3.5
Bamboo	26–73.8	10.2–31	12.5–73.3	0.37	–	1.7–5	0.7
Oil palm	42.7–65	13.2–25.3	17.1–33.5	–	0.6	1.3–6	–
Betelnut	35–64.8	13–26	29–33.1	9.2–15.4	0.5–0.7	1.1–2.1	–
Coir	19.9–36.7	32.7–53.3	11.9–15.4	4.7–7	–	–	–
Banana	48–60	14.4–21.6	10.2–15.9	2.1–4.1	3–5	2.1	–
Pineapple	57.5–74.3	4.4–10.1	80.7	1.1	3.3	0.9–4.7	–

The strength of natural fibres depends mainly on cellulose content, microfibrillar angle and the aspect ratio. More the value of cellulose content, higher will be the strength of fibre and it is opposite in case of microfibrillar angle i.e. lower value of microfibrillar angle provides higher strength to fibre. Normally, fibres are characterised by the aspect ratio (Mallick 2010; Saravana Bavan and Mohan Kumar 2010). The density of natural fibres has a maximum value of about 1.5 g/cm³. Hollow natural fibres or fibres which are less dense in their natural form like wood can be densified by suitable processing (Saxena et al. 2008). The other parameters which influence the physical properties of NFPCs are fibre–matrix adhesion, volume fraction of the fibres in the composite, fibre dispersion, modulus and strength of fibres and toughness of the matrix (Young 1986; Giancaspro, Papakonstantinou, and Balaguru 2009). The mechanical properties of NFPCs especially the tensile properties improve with the increase in fibre volume fraction (Hull and Clyne 1996). Figure 3 shows various types of degradation for natural fibres and factors responsible.

Figure 2. Current scenario for the applications of NFPCs (Conceptualized from Smith and Wolcott 2006).

Figure 3. Factors responsible of different types of degradation (Conceptualized from Rowell 1998; Amar K Mohanty, Misra, and Hinrichsen 2000).

1.2. Polymer and their composites

Polymer plays the crucial role of matrix phase in the NFPCs. Thermosets as well as thermoplastics both can be used as the resin in polymer composites. Thermoplastics are better than thermosets on different parameters like low processing cost, design flexibility, better mechanical properties etc. Polyester, epoxy, polypropylene (PP), poly vinyl chloride, polybutylene succinate (PBS), polyurethane, phenol-formaldehyde, polyethylene (PE) and polystyrene are the major polymers that have been used as matrix phase in polymeric composites. Properties of composites are governed by matrix–fibre interface, fibre properties and aspect ratio of the fibres. Matrix–fibre interface is very crucial in stress transfer from matrix to fibre (Saheb and Jog 1999).

Matrix–fibre interface can be improved by various surface treatments/chemical treatments like acetone, silane and alkali treatment etc. An alternate way to improve matrix–fibre interface is the use of coupling agents and grafting. Research studies have revealed maleic anhydride as an effective compatibilizer for better matrix–fibre adhesion (John and Anandjiwala 2008; Singha et al. 2009; Mohanty et al. 2004; Gao and Mäder 2006; Samal, Mohanty, and Nayak 2009). Natural fibres when used as the reinforcement in the matrix of petroleum-based polymer result in a partially biodegradable composite; however, if the polymer used is biodegradable, then the resulting composite is green composite. When two or more natural fibres are used with the polymer as reinforcement, then the resulting composite is hybrid composite (Bajpai, Singh, and Madaan 2014). The hybrid composites offer better mechanical and physical properties in comparison to conventional composites. The properties can be tailored by selecting the orientation of the fibres, length of the fibres, content of each reinforcement and chemical treatment of the fibres (Chaudhary, Bajpai, and Maheshwari 2018). Though there are several review articles available on applications of natural fibres, the paper is articulated in a manner to discuss the various industrial applications of NFPCs.

2. Natural fibres in structural automotive applications

With the global trend in the automotive sector towards lightweight materials and with stringent environmental laws, the use of natural fibres is increasingly gaining importance (Anand et al. 2017). Amongst the numerous natural fibres, only a few fibres find automotive applications. In the last decade, NFPCs have been used in European automotive sector. The recent legislation passed by European Union that 80% of a vehicle must be recyclable or reused by the end of 2006 and by 2015 it should be 85%. Use of natural fibres in automotive industries has given more impetus to research in the field of NFPCs. The use of polyester and PP-based natural fibre composites to produce different components for automobiles is already in vogue in German automotive industries (Karus and Kaup 2002; Silva et al. 2006).

Schuh (1999) reported predominant use of natural fibres as reinforcement for door panels, rear parcel shelf, seat coverings and various damping and insulation parts etc. ‘MANACA’ (car panel) banana-reinforced polymer composite was designed and fabricated by Al-Qureshi (1999) who found that fibre and matrix bonding was excellent and there were no clues of debonding or delamination. Davoodi et al. (2010) used Kenaf/glass fibre-reinforced epoxy hybrid composite as structural components in car bumper beams that enhanced the mechanical properties of the said component. Modulus and tensile strength of the hybrid composite were found more than the typical material of car bumper beam and that paved the way for its use as structural components in some car bumper beams.

Alves et al. (2010) used jute fibres as a replacement to glass fibres in frontal bonnet of a vehicle to check on different aspects like environmental, social, technical and economical. Except technical aspect, jute fibres provide better performance than glass fibres in this structural application. Kim et al. (2011) reinforced poly lactic acid (PLA) and PBS (biopolymers) with pineapple and cassava flour to check total volatile organic compound emissions and it was compared with synthetic polymers like PP and PE. Significant reduction in odour emissions was found for pineapple, cassava/PLA, PBS-based composites and this property is very useful in automotive interior components. Ramnath et al. (2014) investigated mechanical properties of abaca, jute and their hybrid composites along with glass fibre in all three cases. The maximum volume fraction of fibres in all three composites was set to 0.4. The study revealed that tensile strength of hybrid composite was much higher than other composites. Moreover, the impact and flexural strength of abaca-based composite as reported by the authors are also higher than that of jute and hybrid composites. The authors also concluded that hybrid composite is good replacement for various application. Moreover, abaca-based composite can be used in cases of higher impact strength requirement. The authors also suggested that abaca and jute fibres can be used as reinforcement in polymeric composites to make automotive components like mudguard and engine cover. Zhong, Lv and Wei (2007) developed sisal/urea-formaldehyde composite through compression moulding technique. The authors investigated the effect of fibre loading on mechanical properties. The researchers have concluded that composites with 30 wt.% sisal fibre exhibited best results for flexural strength and composites with 50 wt.% sisal fibre exhibited maximum impact strength. Abdellaui et al.(2015) studied the effect of number of jute layers on mechanical properties of jute/epoxy laminated composite prepared using compression moulding technique. The researchers observed that a number of fibre layers have a significant effect on the mechanical properties. The study revealed that composites with five layers of fibre exhibited better mechanical properties.

The study carried out by Saxena, Nandan and Ramakrishan (2011) revealed that NFPCs possess significant advantages in various structural applications in Indian railways. In railway industry, floor/roof panels, berths, partitions, modular toilets are made up of NFPCs. Use of natural fibres in railways is critical in achieving high speed, low power consumption, weight reduction, lesser inertia, lower track wear etc. The authors also suggested that sisal fibre is also a potential candidate for these applications.

DaimlerChrysler’s efforts towards sustainability paved the way for technology transfer initiatives which involve use of green materials in South America, Philippines and South Africa. The organisation emphasised upon the use of renewable energy sources over conventional fuels to promote global sustainability network wherein a bio-based automotive supply chain system would be developed which shall start from the farmer and shall end at automotive distributor (Elliott-Sink 2005). Presently, almost all the major automotive manufacturers are using NFPCs to make different components as listed in Table 3.

Table 3. Automotive parts produced from natural fibres (Pandey, Ahn, and Lee 2010; Singh, Verma, and Gupta 1998; Das 2009; Nakamura et al. 2009).

Vehicle part	Material used
Glove box	Wood/Cotton, flax/sisal
Door panels	Flax/Sisal with thermoset resin
Seat coverings	Leather/Wool backing
Seat surface/backrest	Coconut fibre/natural rubber
Trunk panel	Cotton fibre
Trunk floor	Cotton with polypropylene/PET fibres
Spare tyre covers	Kenaf/PLA
Insulation	Cotton fibre
Floor panels	Flax mat with polypropylene
Headliners	Jute fibre
Dashboards	Jute fibre
Parts in railway coach	Jute fibre
Floor protection	Abaca/Polypropylene

PET: Polyethylene terephthalate; PLA: poly lactic acid.

3. Natural fibres in building applications

The use of NFPCs is growing rapidly to meet today’s requirement of the world like low-cost building (Chandramohan and Bharanichandar 2013). Lumen/Voids present in the natural fibres helps these composites to have better acoustic and thermal insulation characteristics especially in construction industries (Holbery and Houston 2006; Taylor 2002). Structural beams and panels were fabricated and tested for NFPCs especially on bio-based polymers (Dweib et al. 2004, 2006). Saravana and Mohan (2010) reported use of Straw in polymer composites as building material. Literature revealed that straw bales are good candidates for building construction material.

Swamy et al. (2004) investigated use of areca fibre as reinforcement in polymeric composites and found as a good acoustic material for structural applications. Polymeric composites reinforced with jute fibre are used in structural applications like ceiling, window panels, floor and wall partition, mobile or pre-fabricated buildings and panels for partition etc. (Das 2009). Li and Matuana (2003) used wood fibre-reinforced polymer composites in making window frames, moulded panel components. Maheswari et al. (2013) suggested that borassus/High Density Poly Ethylene (HDPE) composites can be used as a good packaging material and in various secondary structural applications. Further some researchers have investigated jute/PP composites for structural and manufacturing feasibility for insulated panelised construction, used as skin in the panels (Uddin and Kalyankar 2011; Kalyankar and Uddin 2012). Moreover, some authors have manufactured cellular beams and plates with jute, hemp and flax fibre-reinforced unsaturated polyester as load bearing structural components, wherein it was revealed that NFPCs can be used as load bearing components with some improvement in their efficiency as structural components by arranging the cellular material (Burgueno et al. 2004; Burgueño et al. 2005; Burgueno et al. 2005a, 2005b). Ramnath et al. (2014) found abaca and jute fibre-based composites suitable for housing and packaging industry. Ghavami (2005) has reported the use of bamboo fibre to make structural concrete elements. Green composites have found various applications in building materials like door, bridge, fencing etc. (Golbabaie 2006). Some other natural fibres that are used as reinforcement are jute fibre (Chakraborty et al. 2013a; Zhou et al. 2013; Chakraborty et al. 2013b), coir fibre (Ali et al. 2012; Ali and Chouw 2013; Saravanan and Sivaraja 2012), flax fibre (Yan and Chouw 2013), corn stalk (Jarabo et al. 2013) and hemp fibre (Jarabo et al. 2012).

4. Natural fibres in decking/furniture applications

The wood like appearance and minimal maintenance of NFPCs make them a suitable replacement of wood in various applications like window systems and decking. Banana fibre is a potential replacement for wood-based products like plywood and medium density boards (Bavan and Kumar 2010). Rethinam and Sivaraman (2001) investigated the acoustic properties of areca fibre and have reported better properties in comparison to wood-based plywood, thereby making it more suitable for various furniture applications. Arecanut-based products can be used in preparation of hardboards and paperboards etc. Das (2009) reported the use of jute/polymer in making of products like tables, chairs, kitchen cabinets etc. Li and Matuana (2013) used wood fibre-reinforced polymer composites to form decks, docks. Figure 2 summarises the various applications of NFPCs.

5. Challenges in using natural fibres

Use of natural fibres in polymeric composites involves various issues related to moisture absorption, durability, weak interfacial adhesion of fibre and matrix and poor mechanical properties etc.(Gassan and Gutowski 2000; Hirai, Hamada, and Kim 1998; Irfan Ul Haq et al. 2018). NFPCs face the critical issue of degradation when exposed to external environment. There are different degradation modes pointed out in Figure 3. These include biological, mechanical, water, weather and fire degradations. Different degradation reactions are also mentioned in Figure 3. Biological degradation of NFPCs takes place due to attack by biological organisms. Organisms/Enzymes attack hemicelluloses first and hydrolyse them into digestible units (Rowell 1998). This weakens the fibre–matrix interface resulting in lowered strength of composites. Biodegradation also occurs due to oxidation and reduction reactions by enzymes. It can be avoided by using toxic chemicals (Golbabaie 2006).

Water degradation is the next challenge associated with these composites. As NFPCs are hydrophilic in nature, therefore, they absorb moisture in outdoor environment. It is governed by void content of natural fibres and content of non-crystalline parts. Rain, sea, dew and ice are the major sources for this absorption. The main constituent of fibre that absorbs moisture is hemicelluloses. The fibre swells due to this and also shrinks when it dries. Those NFPCs which are exposed to water frequently have wetter and drier areas within the composite leading to differential swelling and ultimately cracking (Rowell 1998).

Absorbed water bonds with fibre’s hydroxyl group weaken the bonding of fibre and matrix resulting in lesser mechanical strength (Azwa et al. 2013). The moisture absorption behaviour of natural fibres limits the outdoor applications of NFPCs. There are several methods like chemical treatment, coupling agents that are used to reduce moisture absorption and enhance mechanical properties (Ahmad, Choi, and Park 2015; Saheb and Jog 1999; Riccieri, Vázquez, and De Carvalho 1999; Luo and Netravali 1999). Percentage of moisture absorption is shown in Table 4. It can be seen that the lower the moisture content, the better will be the physical and mechanical characteristics of fibres and composites.

Table 4. Moisture absorption by different natural fibres (Bledzki and Gassan 1999; Khalil et al. 2012; Averous and Le Digabel 2006; Wambua, Ivens, and Verpoest 2003; Mark 1986; Preethi and Balakrishna Murthy 2013).

Natural fibre	Moisture absorption (%)
Abaca	5–10
Coir	0.2–10
Ramie	7.5–17
Sisal	10–22
Hemp	6–12
Flax	7–12
Cotton	7.5–20
Jute	10–13
Bamboo	11.7
Banana	2–3

Degradation is also caused by ultraviolet (UV) radiations when these composites are exposed to outdoor environment. Lignin constituent of fibre is responsible for this weather degradation. Fresh layer of lignin is exposed to UV radiations after first layer degradation. This results in significant loss of fibres at the surface of composite. Mechanical degradation of NFPCs is caused by wind, dust, snow and hail etc. leading to stress, fracture, cracks and abrasion.

Another major challenge for the use of NFPCs in various structural applications is their poor fire resistance. Moreover, very less information is available for this behaviour of these composites. NFPCs undergo fire degradation due to pyrolysis reactions (oxidation, hydrolysis, oxidation). These reactions take place as the temperature increases. First, hemicelluloses degrade, then cellulose followed by lignin. The thermal degradation is a two-stage process one starting in the range of 220–280°C and the another starting in the range of 280–300°C. The lower temperature range is linked with the degradation of hemicellulose and the higher range is associated with lignin degradation. Thermal degradation effects colour, odour and also deteriorates mechanical properties of natural fibres (Saheb and Jog 1999).

As represented in Figure 3, there are four degradation reactions which include oxidation, reduction, hydrolysis and dehydration which points to a similar degradation chemistry (Rowell 1998).

Fibre consistency/quality throughout the composite is also a big concern. Diameter of fibre is also not constant throughout its length and sometimes, it is not perfectly circular also. Natural fibres have low impact strength and high concentration of fibres cause defects in the composite. Poor matrix–fibre interface is a major challenge in NFPCs. Fibre degradation taking place during the composite processing leads to lower durability which can be improved by the chemical treatment up to a considerable amount.

6. Conclusion and outlook

The stringent environmental regulations and the quest towards sustainable materials have led researchers towards development of eco-friendly materials. NFPCs with outstanding properties have potential applications in the modern industry in general and the automotive industry and civil infrastructure sector in particular. The comparable mechanical properties of natural fibres with synthetic fibres, low production cost, good thermal and acoustic characteristics and eco-friendly processing make them a good alternative as reinforcement in polymeric composites. Owing to the excellent properties, NFPCs have good potential in load bearing applications. There seems a tremendous scope as many of the natural fibres and their polymer blends are unexplored. Additionally, the various indigenous species of a lot of natural fibres also needs to be explored. The hybrid polymer composites and the synergetic effect of various natural fibres are an area towards which future studies could be focused. The issues of thermal stability and the moisture absorption need to be addressed so as to widen the applications of NFPCs. This paper will serve as a catalyst and to initiate further advancements in the field of polymer composites

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Rajiv Kumar

Rajiv Kumar is specialized in Industrial and Production. He is currently working as as Assistant Professor at School of Mechanical Engineering, Shri Mata Vaishno Devi University, Katra. He is pursuing his doctoral program in the field of polymer composites.

Mir Irfan Ul Haq

Mir Irfan Ul Haq is specialized in Mechanical System Design. He has worked previously with Mahindra Research Valley, Chennai. He is currently pursuing his Ph.D. in the field of Materials and Tribology. He is currently working as Assistant Professor at School of Mechanical Engineering, Shri Mata Vaishno Devi University, Katra.

Ankush Raina

Ankush Raina is specialized in Mechanical System Design. He is pursuing his doctoral program in the field of lubricating oils used in Mechanical Industry. He is currently working as Assistant Professor at School of Mechanical Engineering, Shri Mata Vaishno Devi University, Katra.

Ankush Anand

Ankush Anand is specialized in the field of sustainability and design . He is currently working as Associate Professor in the School of Mechanical Engineering. He has published numerous articles in journals of high repute. He has guided numerous Masters and PhD candidates. Dr. Anand is also member of various international bodies.