Enhancing Mechanical Properties of 3D-Printed PLA Composites Reinforced with Natural Fibers: A Comparative Study

Polylactic acid (PLA) is widely used in 3D printing for its biodegradability and ease of processing, but its brittleness and low impact strength often restrict its suitability for more demanding applications. The novelty of this work lies in its direct comparative approach: we systematically reinforce PLA with two distinct agricultural residues—rice husk and rice straw—under identical conditions to clarify how particle size (100 vs. 200 mesh) and NaOH surface treatment affect mechanical performance. Composite filaments containing 5–20 wt% of each fiber were produced and 3D-printed into standard tensile and flexural specimens. The results show that, although tensile strength declines at higher fiber loadings, tensile modulus, flexural strength, and impact resistance can improve significantly—particularly with 200-mesh and NaOH-treated fibers. Fourier transform infrared (FTIR) spectroscopy confirms partial lignin removal and enhanced cellulose exposure, improving fiber–matrix adhesion, which is corroborated by scanning electron microscopy (SEM) observations of reduced voids. This comparative study demonstrates that surface-treated, finely milled rice husk and rice straw significantly enhance PLA’s stiffness and toughness, offering a sustainable alternative to conventional polymeric additives. The insights gained here on fiber content, chemical treatment, and 3D printing parameters can guide the broader industrial adoption of these natural fiber-reinforced PLA composites, particularly in automotive and construction applications that require lightweight, durable materials.