Enhanced mechanical and thermal performance of FDM-printed polylactic acid composites reinforced with sisal fiber powder and compatibilizers

Biodegradable polymers such as PLA are widely used in additive manufacturing, however, their inherently low toughness, limited thermal stability, and poor interfacial compatibility with natural fillers restrict their broader structural and functional applications. To address these limitations and to explore a sustainable reinforcement approach, this study investigates the mechanical, thermal, and morphological behaviour of polylactic acid (PLA) composites reinforced with sisal fibre powder and dual additives, polyethylene glycol (PEG) and Maleic anhydride-grafted polylactic acid (MAH-g-PLA), processed via fused deposition modelling (FDM). Composites with 3, 6, and 9 wt.% sisal filler were prepared, maintaining PEG at 6 wt.% and MAH-g-PLA at 2 wt.%. Tensile and flexural tests revealed that the 6 wt.% sisal-reinforced PLA exhibited optimal performance, achieving the highest tensile and flexural strength due to uniform filler dispersion, enhanced interfacial adhesion, and efficient stress transfer. Lower filler content (3 wt.%) provided insufficient reinforcement, while higher content (9 wt.%) led to filler agglomeration and void formation, causing early crack initiation and reduced mechanical performance. Scanning electron microscopy analysis confirmed well dispersed fillers and improved matrix filler adhesion at optimal loading, whereas excessive filler loading caused defects and poor interfacial bonding. Thermogravimetric analysis showed that higher filler content, particularly 9 wt.%, enhanced thermal stability and promoted residual char formation, attributed to effective filler matrix interaction and delayed degradation. PEG plasticization improved chain mobility and elongation, while MAH-g-PLA compatibilization strengthened the interface, resulting in a balanced enhancement of mechanical and thermal properties. Overall, this study demonstrates that moderate sisal filler content, combined with dual additives, provides a sustainable and efficient strategy to improve the performance of PLA based composites for additive manufacturing applications.