Moving towards the era of bio fibre based polymer composites

1. Introduction

Bio fibres based products are materials that are derived from a biological origin, such as, crops, plants or other renewable agricultural, or forestry materials. These products provide alternative material options to conventional petroleum-based materials by using renewable carbon as feedstock reported by (Morão and de Bie, 2019). Bio fibres and their composites are the recent trends in the global context. Bio fibres (jute, hemp, flax, cotton etc.) are a potential substitute for different synthetic materials due to their eco-friendly behaviour, considerable mechanical and physical properties as studied by (Chaudhary and Ahmad, 2020). Current researchers focus their research on novel materials which has a minimal impact on the environment which could replace the conventional composites as they cause ecological problems which was investigated by (Ramesh et al., 2017). Plant fibres are the primary choice for such composites as synthetic fibres have severe problems such as they cause skin irritation, allergies, etc (Ramesh et al., 2020). The addition of bio-fillers with plant fibres increases the strength of the composites significantly as presented by (Das and Chaudhary, 2021a) To maintain the balance of our nature and to prevent irreversible damage to natural resources on Earth, sustainable means ‘to uphold’ or ‘to maintain’ and sustainable development means establishing those principles and practices on industrial processes as mentioned by (Bogoeva-Gaceva et al., 2007). Sustainability Consumer requirements in many fields, from automobiles, aerospace, the military, and much more, live in an eco-conscious era. Consumers are looking for eco-friendly products, knowing environmental issues which was reviewed by (A. K. Mohanty et al., 2002). Today, people have started looking for ‘‘Green Products’’ everywhere as presented by (Das et al., 2021). Renewability is an ecological footprint of the resource and the use of any chemical to produce/process the product ready for use are requirements for judging products as being “environmentally friendly” as presented by (Chaudhary et al., 2018). Various plastic waste is being released directly to the environment which is coming from different industries ranging from automobile, textile, power plants, and many more presented by (Bajpai et al., 2019). These plastic/synthetic waste release various toxic gases to the environment, which are causing a serious problem to mankind. Due to this environmental pollution, various airborne diseases are also get initiated which leads to health hazards which was studied by (Das and Chaudhary, 2021b). A green economy is also an important prospect of health environmental condition. A green economy is characterized in terms of low carbon, productive capital and social inclusion which was presented by (Loiseau et al., 2016). In the green economy, public and private investment drive growth and incomes through these business practices, infrastructures and assets that minimize carbon emissions and pollution, boost energy and resource quality and avoid biodiversity loss and ecosystem services as investigated by (Moynihan, 2011). Fig. 1 (Chaudhary and Ahmad, 2020) shows some of the bio fibre mats used as reinforcement. The benefits of green economy due bio fibre based polymer composites and broad classification of bio fibres are shown in Fig. 2 and Fig. 3 (Petroudy, 2017), respectively. Land pollution occurred due to the landfill of synthetic fibre reinforced composites upon completion of their life-cycle. Usage of bio-degradable resin with plant (bio) fibres has been the current trend as they render bio-degradable, eco-friendly and they can be easily disposed of upon completion of their life-cycle which was presented by (Ramesh et al., 2020).

The present work highlights the major contribution in the area of bio fibre based polymer composites. Recycling and disposal mechanism along with the sustainability of bio fibre based polymer composites and how bio fibre based polymer composites will play an important role in the coming future with their potential applications have been reviewed and presented. At last, the future market trend of bio fibre based polymer composites is also addressed in this present article.

2. Need for bio fibre based polymer composites

A significant environmental concern is the Green Economy (GE). GE is a health, prosperity, and well-being healthy and environmentally sustainable economy which was studied by (Robinson and Robinson, 2015). The development of sustainable and environmentally friendly green materials based on renewable resources, recyclable and biodegradable has led to global awareness of environmental issues as directed by (Rahman and Gakpe, 2008). Bio fibres such as hemp, flax, jute, kenaf and sisal were used in polymer-based green composites as a replacement for traditional/synthetic plastic fibres which was investigated by (Nabi Saheb and Jog, 1999). On the other hand, bio-resins have been derived to replace oil-based polymers with starch, vegetable oils, and protein. Composites based on cement use new binders such as geopolymers and recycled aggregators. The introduction of renewable and recycled energy decreases petrochemicals and minerals and eliminates the loss of natural energy. Such bio fibre based polymer composites also have consumer products and applications. Bio fibre based polymer composites are important for both academia and industries as the next generation of sustainable composites which was concluded by (Bismarck et al., 2005). The scientists/researchers are looking for alternatives to replenish synthetic composites in an increasing understanding of petrochemical resources and their limited reserves and to reduce the carbon footprint as presented by (Faruk et al., 2012).

Many of the major synthetic polymers issues are as presented in (Synthetic Polymer-Polymer Composites, 2012):

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Generation and recycling of enormous plastic waste as non-biodegradable.
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The manufacture of composites and synthetic fibres is energy-intensive because heat and pressure are very important.
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The fact that the recycling methods for polymer composites are very underdeveloped
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Limited reserves of petroleum

For many of the reasons listed above, researchers are now investigating polymers synthesized with more accessible and renewable raw materials. This led to the use of natural fibres and matrices for polymer composite production. Research shows that more than half of the energy necessary to synthesize synthetic fibres is the energy involved in the production of natural fibres. Light in weight, non-abrasion, non-irritation, non-toxic, biodegradable and ecology are the advantages of natural fibres as presented by (John and Thomas, 2008). We will soon achieve a green economy for healthy economies using renewable composites and have a renewable world in the future as presented by (La Mantia and Morreale, 2011). Various mechanical and chemical properties of various bio fibres are presented in Table 1.

Table 1. Mechanical and chemical properties of various bio fibres.

Types of bio Fibres	Physical Properties		Mechanical Properties				Chemical Properties				References
Types of bio Fibres	Density (gm/cm3)	Length (mm)	Tensile strength (MPa)	Specific strength	Young's modulus	% elongation	Cellulose (wt. %)	Lignin (wt. %)	Hemicellulose (wt. %)	Moisture content (wt. %)	Empty Cell
Agave	1.2	–	5.69	4.74			68.42	4.85	15.67	7.69	Hargitai et al. (2008)
Sansevieria cylindrica	0.915	1000–2000	658	719.12	6.69		79.7	3.8	10.13	6.08	Sreenivasan et al. (2011)
Kenaf	1.2	40–300	223	185.8	15	2.5–3.5	44.4	20.1			Fiore et al. (2015)
Fiber frax	–		1400			˂1					Avérous & Le Digabel (2006)
Broom grass	0.864	10	297	343.75	18	2.87					Ramanaiah et al. (2012)
Bamboo	0.68	1.5–2	1.79	2.63	12.02					1.4	Yu et al. (2014)
Jowar	0.922	300–320	302	327.5	6.99					4.32	Prasad & Rao (2011)
Elephant grass	0.817	150–200	185	226.4	7.4					2.5	Rao et al. (2007)
Jute	1.5–1.6	1000–4000	393–773	364.3	26.5	1.16–1.5	40–50	12–25		1.5–1.8	Wambua et al. (2003)
Ramie	1.55	130–150	400–938		61.4–128		68–76	0.6–0.7		3.6–3.8	Holbery & Houston (2006)
Coir	1.2	350	593	494.1	4.0–6.0					30	Chand & Fahim (2020)
Softwood	1.5		1000	666.6	40		40–45	34–36		4.4	Chand & Fahim (2020)
Flax	1.5		344		27	1.5–1.8	65–85	1–4		8–12	Khan et al. (2018)
Hemp	1.07		389		35	1.6	70–74	3.7–5.7		6–12	Avérous & Le Digabel (2006)

Table 1 presents the various important properties of bio fibres. The internal structure of bio fibres are hollow and comprises lignin, cellulose, pectin etc. Most of the natural fibres have good mechanical properties but lower than synthetic fibres. Bio fibres such as flax, hemp, jute, bamboo, jowar, kenaf, ramie, coir etc. have comparable mechanical properties such as high specific strength, stiffness and are sustainable as these are easily available, low in cost and completely biodegradable without harming the eco-system. All these favourable properties make bio fibres popular among researchers and scientists to enhance their applicability which was studied by (Nair and Joseph, 2014). Observing the physical and mechanical properties of the natural fibres and synthetic fibres as shown in Table 1, it is clear that the density of bio fibres is lesser as compared to synthetic fibres which enhance the specific properties of these fibres, though the strength is lower as compared to bio fibres. The chemical composition of bio fibres given in Table 1 shows that cellulose is the main content of bio fibres which governs its all over properties.

3. Recycling and disposal mechanism of bio fibre-based polymer composites

Recycling, as well as degradation mechanisms, plays an significant role in reducing environmental pollution as the world's increasing environmental pollution caused using plastic/synthetic waste (Amar K. Mohanty et al., 2005). Traditional waste management is focused on recycling which was presented by(Monteiro et al., 2009) as shown in Fig. 4. For the disposal of waste materials, various disposal approaches are used.

To manufacture and effectively use bio fibre based polymer composites, waste treatment improves long usability. To order to enhance the lives of fibre-based polymer composites, reprocessing and recycling processes of fibre-reinforced polymers must be understood which was concluded by (Baillie, 2004). The recycling of reinforced polymer composites employing recycled polymer composite components offers a clear alternative to manufacturing a new product. Fibre-reinforced polymer composite recycling helps control plastic waste and leads to an atmosphere that is green and renewable. Recycling also leads to a green economical era as well which was studied by (Bakar et al., 2017). Bio fibre based polymer composites reprocessing, or reuse degrades the mechanical properties of the recycled product produced. Different controlling factors like shearing forces, which produce internal residual stresses in polymer composites at high temperatures in mechanical recycling as well as high temperatures, contribute to the decomposition of the polymer chain which was investigated by (Cestari et al., 2018).

3.1. Mechanical recycling

Mechanical plastic recycling applies, without substantially altering the chemical composition of the material, to converting plastics waste into secondary raw material or goods as studied by (Yang et al., 2012). All types of thermoplastics can be recycled mechanically, with little to no reduction in inefficiency. Waste streams, which can easily supply clean plastic of a single type, are ideal for mechanical recycling and represent an environmental and economic win-win situation. It is a method of recovery for traditional plastics, such as polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) and polystyrene (PS), which was well known. The steps involved in mechanical recycling is shown in Fig. 5.

Waste treatment increases performance for a long time to produce and safely use fibre-enhanced polymer composites. Reprocessing and recycling methods for fibre-reinforced polymers should be known to boost the lives of fibre-based polymer composites (Le et al., 2008). investigated recycling effects on mechanical characteristics of polylactic acid composites reinforced with flax fibre. A single screw extruder was used for processing the composites and an injection moulding system was used to mode them. The effects of the injection cycles on the mechanical, rheological, and morphological properties were studied during the recycling process using six injection moulding cycles. The authors concluded that injection numbers do not affect the rigidity of the recycled composite material, whereas after processing cycles, the molecular weight of the recycled composite material decreases, and the crystallinity of the developed composite increases. Several other researchers (Hamad et al., 2013), (S. J. Pickering, 2006), (Goodship, 2009) have carried out the same research work, who saw the effects of methods of recycled materials on the efficiency of recycled composite mechanics, rheological and thermo-mechanical properties. Since mechanical recycling is restricted in each process e.g. due to the high demands for sorting and the reduction in material quality, chemical recycling is considered as presented by (Ávila and Duarte, 2003).

3.2. Chemical recycling

Chemical Recycling is defined as the technology for reprocessing which affects, for original or other purposes, either the formulation of the polymer waste or its polymer and transforms it into chemical substances and/or product, except the recovery of energy as investigated by (Collins and Metzger, 1970). Chemical recycling can lead to reducing the amount of plastic waste that is discarded or incinerated which was concluded by (Srebrenkoska et al., 2008). Fossil resources can be replaced with recycled plastic waste material by chemical recycling for chemical production as directed by (Edeerozey et al., 2007). The chemical reactions that take place in recycling to transform polymer recycled into small molecules, such as monomers, oligomers, and other compounds of hydrocarbon, are shown in Fig. 6 (Grigore, 2017).

3.3. Thermal recycling

The combustion of diverse non-recycled material from municipal waste streams (garbage) for the generation of steam for electricity is known as thermal recycling and also known as waste to energy conversion (S. Pickering, 2009). Pyrolysis is the most widely used thermal recycling method, in which the fuel plastics which converts non-recycled plastics from municipal solid waste (garbage) into synthetic waste as presented by (Blazsó, 2009). Pyrolysis decreases greenhouse gas emissions by 14%, and water consumption by 58%, and decreases to up to 96% in classic energy use compared with traditional petrol, by transforming non-pyrolysis of non-recycled plastics into ultra-low sulphur diesel (ULSD). This helps to create an atmosphere that is environmentally sustainable and green because of the high emissions in the atmosphere as investigated and concluded by (Cicala et al., 2017). Various recycled green composites are also gaining a lot of importance in various automotive industries, which will eventually lead to a green society.

3.4. Biodegradation by micro-organism

Biodegradation is known as the mechanism by which micro-organisms invade and break into smaller components. Under-ground biodegradation is partly anaerobic and partly aerobic of polymer composite fibre. The polymer form and microorganism activity impact the degradation of bio fibre based polymer composites. This has a molecular weight, crystallinity degree, attached functional group and other ingredients which was studied by (Stepczyńska and Rytlewski, 2018) that influence polymer declines. Polymer degradation occurs in four steps. In the first step, the microorganism attacks the surface of the polymer, in the second stage, the growth and continuous multiplication of the microorganism by using carbohydrate; and in the third step the division of the polymer chain into monomers. Types of organisms and climate, such as soil pH, temperature and humidity, are factors that affect the degradability of fibre-reinforced polymer composites in their growth as presented by (Oliveux et al., 2015). (Liu et al., 2010) developed hybrid-screw hybrid composite starch/wood-flour reinforced PLA. Starch and wood-flour effects on biodegradation and thermal degradation were analyzed by burying under compost soil and thermal gravimetric analysis (TGA). The test reveals, in contrast to cellulose, that composites made of starch/PLA and wood-flour/PLA are less biodegradable than neat PLA (Yussuf et al., 2010). developed compression composite jute fibre-reinforced polypropylene (PP) and natural rubber jute fibre. The authors studied the mechanical properties and deterioration of generated composites. The findings have shown that, as compared with polypropylene, the mechanical properties and degradation of natural rubber improved with jute fibre reinforcement.

3.5. Photodegradation mechanism

Under ultraviolet (UV) radiation, bio fibre based polymer composites degrade. As UV light falls on the polymer composite surface it is heated, and a polymer reaction begins. This leads to the breakup of the bonds between the polymer, the creation of monomer units, and the decrease in the molecular weight.

Different scholars have studied how the composite surface degrades and the behaviour of the substance (Mumtahenah Siddiquee et al., 2014). studied on glass/epoxy composites. The authors performed an experimental and numerical simulation survey to track ultraviolet (UV) light effects on the morphology of the composites produced. The results showed that composite surface degradation depends on UV light's intensity, wavelength and duration (Pandey et al., 2012). investigated the mechanical characteristics of the composite compressor moulding through degradation. For 672 h kenaf/polyethylene terephthalate (PET) was exposed for tensile, flexural and impact strength before and après degradation to environmental conditions (moisture, water spray, U V-penetration). The authors found that the stress intensity decreased by 40% for kenaf/POM and 8% for hybrid composites because of environmental conditions. The author concluded that substantial decreases in mechanical properties have been achieved due to deterioration.

3.6. Hydrolytic degradation

Bio fibre-based polymer composites continue to be researched for their use in medical applications such as heart stents, bones etc. Polymer degradation is categorized as thermal, mechanical, biodegradable, and degradation of chemicals. The chemical degradation of medical biopolymer composites. The hydrolytic essence of degradation is discussed in this section. Hydrolytic degradation of the composite polymer due to moisture attacks is known as degradation. When the water molecule enters the biopolymer, it starts to degrade and voids into (Shogren et al., 2003). These voids are the site from where the actual degradation takes place gradually as also the formation of other smaller monomer units of the polymer composite. Approaches of polymer compounds to water, the molecular weight of the polymer, the various polymer-related groups, temperature, and the existence of the polymer compound are factors that impact hydrolytic decline which was studied by (Elsawy et al., 2017).

The rice husks/PLA composites were manufactured by (Ndazi and Karlsson, 2011). Through thermal and chemical analysis, the authors investigated the influence of temperature on hydrolytic degradation. Tests have shown that at 25 cm, the properties are not changed too much, but at 51 and 69 cm, the properties dramatically change. Gonzalez et al. (Sánchez-González et al., 2018) developed a phase inversion method of composite reduced graphic oxide enhanced polycaprolactone (rGO/PCL). The authors researched the hydrolytic degradation of the composite produced for scaffolding. Studies have shown that the molecular weight of pure PCL and 27 kDa (kilodalton) of rGO and PCL was off from 80 to 33 kDa during a year's analysis. The four composite forms for dental application were studied by (Martos et al., 2003). The authors studied the effect on the microhardness of formed composites of hydrolytic degradation. It has been shown that the microhardness of the four composites has decreased after 30 days.

As seen in Fig. 7, Reusing is the most popular and most advertised methods of recycling. In the past decade, publications chose to reuse natural fibres as the most popular of their methods with polymer recycling and fibre recycling being the second-best consecutively. Reusing is considered to be the best of the methods because it helps in waste management. Secondly, the use of the same product over and over again for other purposes creatively eliminates its need to be broken down to make raw material for some other new product. It promotes the availability of quality products for consumers and organisations with a tight budget or deficiency of means hence contributing to the economy.

4. Bio fibre based polymer composites for sustainable environment

The widespread environmental consciousness of the quality of the product has spurred significant efforts in product design with more environmentally friendly products. One of the most promising ways to address the needs is the use of natural fibres as reinforcement and filler materials for polymer composite building to reduce their dependence on synthetic fibres. Over the years, the production of bio fibre based polymer composites has increased significantly.

By 2024, a combined annual growth rate of 10 per cent is expected to hit 4.8 billion USD, which illustrates strong bio fibre based polymer composite materials growth for customers globally. The use of bio fibre based polymer composite is rising, especially compared to synthetic composites as concluded by (El-Shekeil et al., 2014) and (Holbery and Houston, 2006). In addition to the size, the size and cost of composites, the other advantages of green composites use especially for car applications include improved light and hot properties, improved acoustic isolation, and allow CO2 neutrality due to greenhouse gas consumption during plant cultivation which was presented by (Brosius, 2006). The automotive industry has taken up the task of green composites to achieve better environmental results of green property vehicles, less energy use, and thus the promotion of cleaning manufacturing processes and highly recyclable material through the part disposal phase. The recyclability benefit also enables the green composite based product to develop an environmental marketing strategy. Other sectors that benefit from using green composites are, such as lower processing temperatures, a reduction of energy usage, a reduction of process cycle times up to 25%, reducing the use of composite reinforcement material per unit volume due to the low defined weight of natural fibre, lower shipping costs due to the better lightweight as concluded by (S.M. et al., 2010). The regular use of different goods, therefore, leads to some part of the environmental harm over the entire life of the product which was studied by (Song et al., 2009). This is why different stakeholders must consider both the resulting product impact and the environmental performance of each product to improve its sustainability situation. Nowadays, i.e., LCA; Life cycle evaluation is one of the most common approaches used to evaluate and measure the effects of goods, services, and resources over their entire lifespan on the environment. LCA is also gaining recognition as among the key factors in environmental management, most notably involving corporate and public decision making as investigated by (Saur et al., 2000). The various life cycle phases of bio fibre based polymer composites are shown in Fig. 8 (Mansor et al., 2015).

Table 2 shows the various impact categories of life cycle assessment. In decision-making, designers are only looking at technical and economic criteria when choosing the green composite materials for their intended application, but the information was given by LCA i.e., life cycle assessment complements the specifications and allows designers to achieve environmental efficiency by regulating bodies and clients. More systematic and efficient decision-making incorporates all three aspects (technical, cost and environment), allowing for the materialisation for the more sustainable product in future.

Table 2. Commonly used impact categories in life cycle assessment (LCA) research (Pelletier et al., 2007).

In the current scenario, there is a growing knowledge of environmental contamination caused by industrial waste, which has contributed to the replacement of hazardous synthetic materials with more environmentally friendly materials. Plastics are being used more frequently, especially in the home and in business. Plastic goods contribute to the accumulation of non-biodegradable waste and pose a danger to the environment. As a result, comprehensive research on the biodegradation of plastics has been conducted over the last decade. Bio fibres, in combination with synthetic biodegradable materials, can be used to develop bio fibre based polymer composites that have environmental benefits such as biodegradability, renewability of the base material, and a reduction in greenhouse gas emissions. Degradation has several benefits, including the elimination of plastic waste and the cost of waste management as investigated by (Gunti et al., 2018).

The breakdown of composite materials, as well as the loss of mechanical properties, lead to composite degradation. The deterioration of natural fibre reinforced composites in the outdoor environment is caused by ambient moisture, temperature, ultraviolet light, and the activities of microscopic organisms. The deterioration of the fibre is caused by the breakdown of hemicelluloses, lignin, and cellulose. This can cause damage to the bonding between fibres and polymer matrix. This can cause damage to the bonding between fibres and polymer matrix. Thus, leads to the lowering of the mechanical properties of the composites (de Melo et al., 2017, p. 6). The kenaf/POM composites were subjected to weathering by exposing to moisture, water spray, and UV light in an accelerated weathering chamber and the materials showed lower tensile strength and this result was attributed to the degradation of the cellulose, hemicelluloses, and lignin of kenaf fibres as investigated by (Zaki Abdullah et al., 2013). The effect of weathering on the degradation of jute/phenolic composites was investigated by (Azwa et al., 2013). The tensile strength of jute/phenolic composites was reduced by about 50% after two years of UV exposure. After weathering, the authors noticed resin cracking, bulging, fibrillation, and black spots. It is important to encourage the use of natural fibres as polymer reinforcement so that the components can be biodegradable to some degree. The proper deterioration of plastics would be a safer way to prevent adverse environmental effects which was studied by (Thiagamani et al., 2019). Therefore, one must always look for the plastics which are compostable or degradable which was put forward by (Devaraju & Harikumar, 2020). However, this cannot be implemented for every material but can be reduced with the use of biopolymers to some extent as studied by (Devaraju & Harikumar, 2020; Thiagamani et al., 2019).

5. Future market trend: bio fibre based polymer composites

The major benefits provided by bio fibre based polymer composites are lightweight and biodegradable, which are also the main reasons for their popularity among producers and consumers which was put forward by (Monteiro et al., 2009). A disturbing phenomenon plaguing most parts of the world is a plastic waste as presented by (Drzyzga and Prieto, 2019). Governments around the world are enforcing strict limits on the use of plastics and encouraging eco-friendly alternatives to resolve this issue. This is sure to help the market considerably over the forecast period. The business is likely to face such obstacles, considering different advantages. Over the next eight years, technological advances in production processes such as compression moulding, injection moulding, and extrusion are likely to have a positive impact on development. Due to low costs and enhanced sustainability, bio fibres have been replacing glass and carbon fibres in recent years as presented by (Vinod et al., 2020). In current market trends, bio fibre based polymer composites are experiencing comprehensive growth with good prospects in the automotive and construction industries. Bast fibre such as hemp, kenaf, flax, etc., are preferred for automotive applications. On the other hand, wood plastic composite is the material of choice for construction industries. Looking at the developments of the current trends to remain as the largest market for bio fibre based polymer composites due to the high acceptance level of environmentally friendly composite materials by automotive industries, government agencies, and growth in small scale environmentally friendly industries. The improvement in materials performance will drive the growth of bio fibre based polymer composites in new potential areas as directed by (Ramesh et al., 2017). Bio fibre based polymer composites are new in electrical, electronics and sporting segments, however, it has the potential to capture a good market share in the future as studied by (Das et al., 2021). The size of the global market for bio fibre based polymer composites was estimated at USD 4,46 billion in 2016. From 2016 to 2024, it is likely to record a CAGR of 11.8%. Spiralling demand from the automotive industry for lightweight products and rising recognition of green products are among the main trends in increasing market development. The moisture sensitivity of these composites, however, is likely to impede market development. The bio fibre based polymer composites made using materials such as wood, cotton, flax, kenaf, and hemp are natural fibres that are less environmentally dangerous and readily accessible which was studied by (Chaudhary and Ahmad, 2020). Raw materials used for the development of bio fibre based polymer composites are environmentally sustainable and have the ability over the coming years to replace synthetic fibres. Increasing awareness of green products, increasing consumer disposable income, a growing inclination toward environmentally friendly products, and the urge to take up recyclable products are likely to play a vital role in market growth. Bio fibre based polymer is 25.0–30.0% stronger than same-weight glass fibres. Composites made from bio fibres help to reduce the component's weight, thereby reducing the total consumption of energy. As an alternative to glass fibres, bio fibre based polymer composites used in the automotive industry are created using wood as well as non-wood fibres such as flax, hemp, and cellulose. Compared to modern materials, the resultant products are lighter. The use of these materials in the production process leads to an approximately 20.0% reduction in costs. The global market revenue for bio fibre based polymer composites in various applications is shown in Fig. 9.

6. Application of bio fibre based polymer composites

Due to the promising properties of bio fibre based polymer composites, they are used in various application which was presented by (Das and Chaudhary, 2021a). Some of the few applications are discussed below and also presented in Fig. 10 as follows-

6.1. Automotive applications

For various automotive components, bio fibres have proven to be a viable reinforcement agent. For door covering, seatback linings and floor panels, for example, flax, sisal, and hemp are added as presented by (Thilagavathi et al., 2010). For seat bases, back coats, and head ties, coconut fibres are used, while cotton fibres are used in vehicle parts requiring successful soundproofing. In the seatback covers and body panels, wood fibres and fabrics also are used.

6.2. Packing application

Millions of tonnes, because the energy resources are not recyclable, are used to manufacture plastic bags to be recycled for future needs. Banana fibres are used for the preparation of cosmetic boxes and food packaging tiffin boxes. These composites are also a popular choice for packaging and, due to improved mechanical and thermal efficiency, nanoparticles are used for packaging fruit, vegetables, and liquid as studied by (Lucera et al., 2012).

6.3. Energy sector

The construction of rooftop wind turbines is one of the key areas for natural composites, such as Biotex Flax and sisal, to play a significant role in the energy sector. Bamboo fibres can also be potential material in energy applications, given the estimated rise in wind power blade demand for 20% over the coming years as mentioned by (Bajwa and Bhattacharjee, 2016).

6.4. Musical instruments

Green composites are also important for musical instruments, provided the good sound output of plant fibres. They are also lightweight, some of the examples being neck stiffeners, bows and top plates. Their advantage is their production material. The other explanation for these products is their short processing time and their strong environmental tolerance (e.g., dirt, water, bumps, and bleach). At Present, high-quality flax fibres are used in the manufacture of speakers as studied by (Yıldızhan et al., 2018).

In recent years, the automotive and aircraft industries have successfully processed various forms of bio fibre components for their interior components as presented by (Puttegowda et al., 2018). Insulation parts are also manufactured from natural fibres for various application areas, such as blowing insulation, pouring insulation, impact sound insulation materials and thermal insulation ceiling panels, and acoustic sound insulation which was presented by (Akin, 2010). With a wide range of construction materials, forms, and even the development of widely used materials today, natural fibres exhibit a sustainable architectural future which was presented by (Sanjay et al., 2016). The use of synthetic fibres in the field of architecture could be substituted with natural fibres. It is also used as a material for sunscreens, cladding, walling, and flooring which was presented by (Li et al., 2020).

7. Conclusion

The present article majorly focuses on the various recycling and degradation mechanism that have employed to bio fibre based polymer composite. As synthetic fibre-based materials are creating environmental pollution, due to which bio fibre-based materials are emerging as a suitable replacement for synthetic materials and find a wide spectrum of applications. Few important findings from this study are as follows:

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As the green economy plays an important role in maintaining an eco-friendly environment, so industries are also inclining towards the area of bio fibre based polymer composites as a replacement of synthetic fibre based composites.
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Recycling is the keyway to waste reduction to reduce environmental pollution.
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A various method such as mechanical, chemical, thermal recycling along with various degradation method is used profoundly for recycling purpose.
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The reviewed publications provide strong support for claims that textile reuse and recycling, in general, reduce environmental impact compared to incineration and landfilling, and that reuse is more beneficial than recycling.
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In the thermal recycling method, especially, the pyrolysis process leads to the formation of gases, which can be used as a fuel and it also reduces the greenhouse effect.
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Biodegradation of green composites leads to the complete degradation of the composite while in the case of synthetic fibre polymer composites, the fibres are reused, and their properties are not greatly affected.
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Due to lightweight, low cost, recyclable, and biodegradable, bio fibre based polymer composites are also used in various application ranging from automobile, aerospace, military and various biomedical applications.
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The size of the global market for bio fibre based polymer composites was estimated at USD 4,46 billion in 2016. From 2016 to 2024, it is likely to record a CAGR of 11.8%. Spiralling demand from the automotive industry for lightweight products and rising recognition of green products are among the main trends in increasing market development.
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LCA (Life cycle assessment) is also recognised as key environmental management factors, particularly for the decision-making of business and in the public sector.
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More research, more inventory data, and processes such as processing, sorting, monomer recycling and polymer recycling, in particular, are needed.
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There is a need for more studies of the environmental potential of cascade systems designed to get the most out of a given virgin or recycled material.
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In the near future, bio fibres will become one of the sustainable and renewable resources in the composite field which can replace synthetic fibres in many applications.

Declaration of competing interest

The authors declare that they have no known competing financial interests or persona