Development and Feasibility of In Situ Coconut Fibre-Reinforced PLA via MEX-TRB/P

This study aims to evaluate the feasibility of embedding coconut fibre (CF) as reinforcement into polylactic acid (PLA) for the fabrication of bio-composites using material extrusion-thermal reaction bonding of polymer (MEX-TRB/P) 3D printing. Traditional natural fibre-reinforced composites rely on premixed filaments or other additive manufacturing (AM) techniques, which limit control over fibre placement and distribution. As sustainability becomes an increasingly important focus in materials engineering, natural fibres and biodegradable polymers like PLA present a promising path toward eco-friendly manufacturing. However, no standardised method exists to manually integrate fibres onto polymer during MEX-TRB/P 3D printing. In this project, CFs were chemically treated using sodium hydroxide (NaOH) to remove surface impurities to improve fibre-matrix adhesion. The treated fibres were then oven-dried and embedded into the PLA matrix during the MEX-TRB/P 3D printing process via a new fabrication approach, where the print was paused at specific layers to insert fibre strands between layers of molten PLA. Each strand has four fibres, and the strands were placed perpendicular to the direction of the impact force. Five composite types were fabricated, which are neat PLA, 1-layer untreated, 3-layer untreated, 1-layer treated and 3-layer treated bio-composites. Impact strengths of the composites were determined using the Izod impact test. The results showed a significant increase in impact resistance with the inclusion of fibres. Compared to neat PLA (9.75 J/m), untreated 1-layer and 3-layer composites recorded 12.34 and 14.72 J/m, which showed a 26.6% and 51.0% increase compared to neat samples, respectively. Meanwhile, treated 1-layer and 3-layer composites reached 13.66 and 14.99 J/m, showing a 40.1% and 53.7% increase compared to neat samples, respectively. Fracture analysis confirmed ductile failure with strong fibre-matrix adhesion, especially in treated samples. This study introduces the first reported method of embedding CFs directly into an MEX-TRB/P 3D-printed PLA composite. The results demonstrate the potential of this newly proposed method to produce strong and sustainable composites.