In recent days, natural fiber reinforced polymer composite is more popular due to its extensive properties suitable for various potential applications. The attention towards natural fibers is because of low cost, biodegradable, recyclability, nonabrasive, combustible, lightweight, and nontoxic properties. However, there is a need for furthermore fundamental knowledge for the raw materials processing and fabrication of composite structures, which is still challenging in current days. Natural fiber sources exist all over the world, which is obtained from animals, plants and minerals. The quality of the natural fibers depends on the extraction methods and different processing techniques. These natural fibers surface characteristics could be enhanced by selecting suitable surface treatment and chemical treatment. These fiber treatments reduce the water intake percentage, improve the adhesive nature, and enhance the overall performance of resulting polymer composites. Among all the chemical treatments, alkaline treatment (NaOH) is the most preferred chemical treatment because of its effectiveness and its low cost. This review article proposes the natural fibers detailed classification, composition, structure, properties, and extraction methods, chemical and surface treatments. We also summarize the previous research work findings on the fibers treatment, properties of natural/natural hybrid polymer composites and natural/synthetic hybrid polymer composites with applications.

The continuous delivery of E-waste from petroleum-based products creates ecological and environmental problems due to non-biodegradable polymers, which release harmful chemicals and toxic gases. This results in biodegradable polymers/fibers appearance, which are biocompatible and degrade in the surrounding environments without causing any environmental pollution and these relieve environmental burden. However, the bio-based materials are unable to meet certain properties in the way of flexibility, dielectric properties, electrical properties, water and gas vapor barrier properties. The current day's research focus is towards the implementation of biodegradable composites properties by introducing different nanostructures. The biopolymers/biofibers

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The continuous demands for reducing environmental impact and energy consumption are the major driving factors for the development of natural fiber (NF)-reinforced composites (NFRCs). The huge demand for sustainable materials in industries leads to the usage of NFs in product developments. These NFs are more attractive due to their lightweight, cost-effectiveness, ease of availability, and environmentally friendly aspects. Green composites are the best alternatives in place of petroleum-based composites which meet the current industrial requirements. In recent years, researchers are more focused on the development of NF composites as a potential candidate in real-life applications due to economic advantages. This review gives a brief overview of NFs introduction, types, economic aspects, and the recent developments in NFRCs with an analysis of mechanical, thermal, and dielectric properties. Moreover, the water absorption behavior, applications, and challenges in using NFs are also studied in this review. Additionally, this review will motivate the researchers for further developments and exist as foundation literature for upcoming researchers.

The main challenging things in railway vehicles are to reduce the consumption of energy for transportation and to decrease the emission of harmful gasses by limiting the consumption of fuel sources. These drawbacks can be overcome by lightweight structures designed for the vehicle bodies and frameworks. The composite materials with fiber reinforcements are the preferred choice for manufacturing lightweight structures to reduce the overall weight of the rail vehicle. The fiber reinforced polymer (FRP) materials possess light‐weightiness, high strength, high stiffness value and are more durable in nature. The researchers are continuously putting their efforts into new innovations in concern towards the replacement of existing conventional materials by FRP composites in railway applications. This review focuses on the overview of FRP composites, the role of composites in past rail vehicles, the rail vehicle component selection and methodology and FRP composites used for various railway components manufacturing with their challenges. Also, this review included the data of FRP composites used in various countries for different railway components applications. Hence, this review is beneficial for the upcoming researchers as a foundation literature to work on railway vehicle applications using variety of FRP materials. Moreover, the challenges are quoted in this review through the comprehensive analysis of literature and hence it provides the information in the form of research gap, so that it would be helpful for the researchers to overcome all the challenges in their upcoming research works.