A comprehensive review of natural fiber reinforced Polymer composites as emerging materials for sustainable applications

The increasing depletion of fossil fuels and the growing demand for eco-friendly materials have driven the development of natural fiber composites. These composites possess desirable mechanical properties such as eco-friendliness, good thermal characteristics, lightweight, lower production costs, and renewability, making them preferable to synthetic composites made from glass and carbon. The use of natural fiber composites in various industries such as automotive, construction, defense, and infrastructure has grown due to their ability to reduce greenhouse gas emissions. This review examines recent advancements in natural fiber reinforced Polymer composites (NFRPCs), focusing on the diverse types of natural fibers such as flax, hemp, and ramie used as fillers and various plastics employed as Polymer matrices. It also discusses the pre-processing treatments of natural fibers, including chemical, mechanical, and thermal methods, which are crucial for optimizing NFRPC properties. Additionally, the review discusses both conventional and advanced manufacturing techniques and the key factors influencing the production quality of NFRPCs and their diverse industrial applications. However, a major challenge for NFRPCs is the hydrophilic nature of plant fibers, which limits bonding with the Polymer matrix and results in poor mechanical characteristics. Future research should focus on developing effective and affordable surface modifiers, dispersion aids, or coupling agents and on understanding the bonding mechanisms at the interface. Nanoscale interfacial characterization is crucial for exploring stress transfer, interfacial penetration, and adhesion. Incorporating nano reinforcements such as graphene and carbon nanotubes can enhance interfacial properties but preserving the intrinsic strength of modified fibers remains a challenge. Eco-friendly in-situ Polymer coatings such as polydopamine and polypyrrole offer potential solutions.