Increasing scientific interest has occurred concerning the utilization of natural fiber-enhanced hybrid composites that incorporate one or more types of natural enhancement. Annual natural fiber production is estimated to be 1,783,965 $\times {10}^3$ tons/year. Extensive studies have been conducted in the domains of natural/synthetic as well as natural/natural hybrid composites. As synthetic fibers have better rigidity and strength than natural fibers, natural/synthetic hybrid composites have superior qualities via hybridization compared to natural composites in fibers. In general, natural fiber compounds have lower characteristics, limiting the use of natural composites reinforced by fiber. Significant effort was spent in enhancing the mechanical characteristics of this group of materials to increase their strengths and applications, especially via the hybridization process, by manipulating the characteristics of fiber-reinforced composite materials. Current studies concentrate on enhancing the understanding of natural fiber-matrix adhesion, enhancing processing methods, and natural fiber compatibility. The optimal and resilient conceptions have also been addressed due to the inherently more significant variabilities. Moreover, much research has tackled natural fiber reinforced hybrid composite costs. In addition, this review article aims to offer a review of the variables that lead to the mechanical and structural failure of natural fiber reinforced polymer composites, as well as an overview of the details and costings of the composites.

Natural fibers have attracted great attention from industrial players and researchers for the exploitation of polymer composites because of their “greener” nature and contribution to sustainable practice. Various industries have shifted toward sustainable technology in order to improve the balance between the environment and social and economic concerns. This manuscript aims to provide a brief review of the development of the foremost natural fiber-reinforced polymer composite (NFRPC) product designs and their applications. The first part of the manuscript presents a summary of the background of various natural fibers and their composites in the context of engineering applications. The behaviors of NFPCs vary with fiber type, source, and structure. Several drawbacks of NFPCs, e.g., higher water absorption rate, inferior fire resistance, and lower mechanical properties, have limited their applications. This has necessitated the development of good practice in systematic engineering design in order to attain optimized NRPC products. Product design and manufacturing engineering need to move in a mutually considerate manner in order to produce successful natural fiber-based composite material products. The design process involves concept design, material selection, and finally, the manufacturing of the design. Numerous products have been commercialized using natural fibers, e.g., sports equipment, musical instruments, and electronic products. In the end, this review provides a guideline for the product design process based on natural fibers, which subsequently leads to a sustainable design.

In recent years, most boat fabrication companies use 100% synthetic fiber-reinforced composite materials, due to their high performance of mechanical properties. In the new trend of research on the fabrication of boat structure using natural fiber hybrid with kevlar/fiberglass-reinforced composite, the result of tensile, bending, and impact strength showed that glass fiber-reinforced polyester composite gave high strength with increasing glass fiber contents. At some point, realizing the cost of synthetic fiber is getting higher, researchers today have started to use natural fibers that are seen as a more cost-effective option. Natural fibers, however, have some disadvantages, such as high moisture absorption, due to repelling nature; low wettability; low thermal stability; and quality variation, which lead to the degradation of composite properties. In recent times, hybridization is recommended by most researchers as a solution to natural fiber’s weaknesses and to reduce the use of synthetic fibers that are not environmentally friendly. In addition, hybrid composite has its own special advantages, i.e., balanced strength and stiffness, reduced weight and cost, improved fatigue resistance and fracture toughness, and improved impact resistance. The synthetic–nature fiber hybrid composites are used in a variety of applications as a modern material that has attracted most manufacturing industries’ attention to shift to using the hybrid composite. Some of the previous studies stated that delamination and manufacturing had influenced the performance of the hybrid composites. In order to expand the use of natural fiber as a successful reinforcement in hybrid composite, the factor that affects the manufacturing defects needs to be investigated. In this review paper, a compilation of the reviews on the delamination and a few common manufacturing defect types illustrating the overview of the impact on the mechanical properties encountered by most of the composite manufacturing industries are presented.

Oil palm empty fruit bunches (OPEFB) fiber is a natural fiber that possesses many advantages, such as biodegradability, eco-friendly, and renewable nature. The effect of the OPEFB fiber loading reinforced fire retardant epoxy composites on flammability and tensile properties of the polymer biocomposites were investigated. The tests were carried out with four parameters, which were specimen A (constant), specimen B (20% of fiber), specimen C (35% of fiber), and specimen D (50% of fiber). The PET yarn and magnesium hydroxide were used as the reinforcement material and fire retardant agent, respectively. The results were obtained from several tests, which were the horizontal burning test, tensile test, and scanning electron microscopy (SEM). The result for the burning test showed that specimen B exhibited better flammability properties, which had the lowest average burning rate (11.47 mm/min). From the tensile strength, specimen A revealed the highest value of 10.79 N/mm². For the SEM morphological test, increasing defects on the surface ruptured were observed that resulted in decreased tensile properties of the composites. It can be summarized that the flammability and tensile properties of OPEFB fiber reinforced fire retardant epoxy composites were reduced when the fiber volume contents were increased at the optimal loading of 20%, with the values of 11.47 mm/min and 4.29 KPa, respectively.

The application of natural fibers is rapidly growing in many sectors, such as construction, automobile, and furniture. Kenaf fiber (KF) is a natural fiber that is in demand owing to its eco-friendly and renewable nature. Nowadays, there are various new applications for kenaf, such as in absorbents and building materials. It also has commercial applications, such as in the automotive industry. Magnesium hydroxide (Mg(OH)₂) is used as a fire retardant as it is low in cost and has good flame retardancy, while polyester yarn (PET) has high tensile strength. The aim of this study was to determine the horizontal burning rate, tensile strength, and surface morphology of kenaf fiber/PET yarn reinforced epoxy fire retardant composites. The composites were prepared by hybridized epoxy and Mg(OH)₂ PET with different amounts of KF content (0%, 20%, 35%, and 50%) using the cold press method. The specimen with 35% KF (epoxy/PET/KF-35) displayed better flammability properties and had the lowest average burning rate of 14.55 mm/min, while epoxy/PET/KF-50 with 50% KF had the highest tensile strength of all the samples. This was due to fewer defects being detected on the surface morphology of epoxy/PET/KF-35 compared to the other samples, which influenced the mechanical properties of the composites.

In this decade, all researchers and industry players compete to develop sustainable product design by exploring natural fibre composites in product design development. One of the essential methodologies in creating composite products is concurrent engineering (CE). Industrial design and production engineering should be involved in the development of ballistic helmets. This publication aims to provide a quick overview of the evolution of natural fibre composite ballistic helmet designs. This manuscript is still in its early stages, but it already includes a summary of the progress of ballistic helmet design from 1915 to the present. Renewable materials, such as natural fibre, should be highlighted as an alternative to synthetic composites in developing a sustainable ballistic helmet design. Furthermore, launching the design development process for a ballistic helmet demands a CE strategy that includes multi-disciplinary knowledge. Computational modelling aids in the development of ballistic helmet designs, reducing the time and cost of manufacturing ballistic helmets. The ergonomic component of ballistic helmet design is also crucial, as is the thermal comfort factor, which can be handled using natural fibre composites with thermal solid insulating characteristics. The development of natural fibre composite ballistic helmets can be used as a consideration in the future as a revolution to create a sustainable design. Finally, this review can be used as a guide for industrial designers. In conclusion, this review might be utilized as a reference for industrial designers due to a shortage of studies, especially in producing product-related natural fibre.