Layer-to-layer additive manufacturing of high-strength PLA/PALF green composites using a custom 3D printing system

The limited capability of existing fiber 3D-printing techniques to process natural fibers—due to restricted material compatibility, complex fiber feeding mechanisms, fiber damage, and inadequate interlayer bonding—remains a major challenge in the additive manufacturing of high-performance green composites. To address these limitations, this study develops a custom-engineered 3D printing system and a novel deposition strategy for fabricating natural fiber–reinforced green composites with enhanced mechanical performance and sustainability. Layer-to-layer printing has emerged as a critical technique for reducing matrix degradation in additively manufactured green composites. Accordingly, a dedicated 3D printing system is introduced for fabricating pineapple leaf fiber (PALF)–reinforced composites using polylactic acid (PLA) as the matrix. The system employs an alternating deposition strategy, in which molten PLA pellets and PALF sheets are sequentially deposited to form an integrated composite architecture with controlled fiber placement and improved interfacial bonding. Mechanical performance was evaluated through tensile and flexural testing standards. Optimization of the printing process was performed through a systematic parametric investigation, in which key printing parameters—including extrusion rate, PLA layer thickness, center-to-center deposition line spacing, and the number of PALF sheet layers—were independently varied to identify processing conditions that maximized mechanical performance while ensuring stable extrusion and consistent interlayer bonding. Under optimized printing conditions (5.0 mm3/s extrusion rate, 0.3 mm PLA layer thickness, and 0.8 mm line spacing) with three PALF sheet layers, the PLA/PALF composites achieved a modulus of elasticity of 235 MPa and a tangent modulus of 1130 MPa. Tensile and flexural strengths increased by 37.6% and 15.86%, respectively, compared with additively manufactured pure PLA. These results demonstrate the capability of the proposed system to produce high-strength, sustainable PLA/natural fiber composites for scalable additive manufacturing.