Natural Fiber Reinforced Polymer Composites for Aerospace Applications: A Critical Review on Performance, Flammability, and Environmental Durability

Abstract The aerospace industry is under increasing pressure to reduce carbon footprints while maintaining stringent safety and performance standards. Natural fiber reinforced polymer composites (NFRPCs) have emerged as a potential sustainable alternative to synthetic composites for secondary structural and interior applications. This review critically evaluates the current state of research on natural fibers (flax, hemp, jute, basalt—though basalt is mineral, often grouped—and sisal) for aerospace applications. We focus on the critical bottlenecks that have historically precluded widespread adoption: high moisture absorption, poor interfacial adhesion, inherent flammability, and variability in mechanical properties. Recent advances in fiber surface modification, hybridisation with synthetic fibres, and the development of bio-derived thermoset and thermoplastic matrices are examined. Furthermore, this review assesses the lifecycle assessment (LCA) claims against the reality of aviation certification standards (FAR 25.853). We conclude by identifying key research trajectories, including nano-reinforcement of the interphase, predictive modelling of long-term creep behaviour, and the development of multifunctional composites that combine structural integrity with embedded sensing for structural health monitoring (SHM). Keywords: Natural fibres; aerospace composites; flax fibre; flammability; moisture absorption; biocomposites; sustainable aviation; secondary structures.