Flame retardant characteristics of natural fibre reinforced polymer composites: A thematic review

Abstract Globally, with the advancement of industrialization and globalization, the automotive sector has drastically increased for transportation and commercial purposes. Hence, to maximize efficiency and minimize the weight of automobiles, the automotive and aerospace industries have welcomed synthetic fibre‐reinforced composites, vastly replacing conventional metals. Despite the superior performance, the usage of synthetic fibre composites has led to the massive dumping of automotive waste in landfills, making the land unfit for future purposes. Therefore, natural fibre‐reinforced composites (NFRCs) quickly replace synthetic fibres with their unique features, such as being lightweight, biodegradable, and non‐toxic, en routing a new path towards a sustainable environment. Though NFRCs are finding new applications in various industries, researchers are trying to enhance their thermal, electrical, and mechanical properties to make them synergic composites. However, with the presence of cellulose, lignin, and wax, natural fibres become highly responsive toward flammability, limiting their use in various emerging applications. As the subject of the flammability of NFRCs has a limited amount of literature, the current review article aims to address the current flammability studies and strategies adopted to improve the flame‐retardant characteristics of NFRCs exclusively. Also, this review covers the factors and influence of different types of flame‐retardant fillers adopted to improve the flame retreatant characteristic of NFRCs and their mechanism. Additionally, this review article summarises various official and laboratory flame‐testing techniques such as radial panel test (RPT), cone calorimetry, and limited oxygen index (LOI) adopted to characterize the flammable properties of NFRCs. Highlights Natural fiber biocomposites are becoming a potential candidate for structural and interior applications in the automotive and aircraft industries. Flammability becomes a major alarm as it concerns with the safety of passengers. The flammability behavior of natural fiber composites is extensively discussed. Mechanisms, factors, and selection of flame‐retardant materials are reviewed to improve the flame‐retardant characteristics. The influence of surface treatments, fiber content, and flame‐retardant nanofillers are also elaborately discussed. Advanced flame testing techniques were conversed with pictorial representation.