Characterisation and manufacturing methods of material extrusion 3D printing composites filaments based on polylactide and nanohydroxyapatite

As the pace of scientific research and technological advancement accelerates, there is an increasing demand for rapid on-site prototyping with specific materials. Additive manufacturing through material extrusion 3D printing has emerged as an economically viable solution to this need. The production of custom filaments for this process frequently depends on low-volume filament manufacturing lines. A significant challenge in such production processes is maintaining the quality of the filament throughout its entire length, as this has a considerable impact on the quality of the final printed object. To ensure consistent quality, it is essential to monitor and manage a range of essential properties, including diameter consistency, volume variation, ovality, material homogeneity, compound ratio and the absence of internal and external defects such as air bubbles. This study presents the implementation of a real-time filament quality monitor (R-FQM), which provides detailed insights into the characteristics of the filament during the manufacturing process. In conjunction with a proof-of-concept drawing process for reducing filament diameter by solid-state extrusion, this approach addresses the challenge of maintaining the quality of filaments. The innovative techniques are illustrated in the fabrication of polylactide-based composite filaments with nanohydroxyapatite filler using a multi-stage drawing die solid-state extrusion process. Throughout the manufacturing process, the filaments were characterised using structural and thermal property analyses as well as a proposed tensile test, thereby confirming the effectiveness of the described approach.