Effect of Nozzle Geometry on the Rheological Properties of Natural Fiber-Reinforced Thermoplastic Composites in Fused Deposition Modeling: A Review

Fused Deposition Modeling (FDM) has emerged as one of the most widely adopted additive manufacturing (AM) technologies, valued for its simplicity, cost-effectiveness, and versatility in fabricating complex geometries. The geometry of the extrusion nozzle plays a critical role in determining melt flow behavior, extrusion stability, and final print quality of thermoplastic materials. When utilizing natural fiber-reinforced thermoplastic composites (NFRCs), understanding and optimizing nozzle geometry becomes increasingly important due to the complex rheological behavior of fiber-filled melts, including challenges such as increased viscosity, shear-thinning effects, and susceptibility to nozzle clogging. The reviewed literature shows that optimized nozzle geometry, supported by computational and statistical tools, can improve the printability and mechanical performance of natural fiber composites, although further advancements are needed to address material variability and complex fiber–matrix interactions. This review paper presents a comprehensive overview of the effects of nozzle geometry on melt flow behavior in FDM, covering computational modeling approaches, experimental characterization studies, and optimization methodologies for enhancing the performance of natural fiber-reinforced composites in additive manufacturing applications. The integration of sustainable materials into FDM processes represents a significant advancement toward environmentally responsible manufacturing while maintaining mechanical performance requirements.