Impact of filament preparation on the performance of fdm 3D printed composites

Filament preparation is a prerequisite procedure in composites 3D printing based on fused deposition modelling (FDM). However, the impact of filament preparation on the properties of resultant FDM products has not been reported. In this work, the short glass fibre/polylactide (GF/PLA) composites were made into filaments via two different workflows: a 3-step workflow of melt compounding - granulation - extrusion, or a 2-step workflow of material blending and extrusion. The filaments were then used for FDM. For the 3-step workflow, fibres were apparently shortened after melt compounding, especially for the ~ 4 mm fibre bundles that were shortened by > 90%. The 2-step workflow worked smoothly to prepare filaments containing ~ 0.1 mm fibres. However, the ~ 4 mm fibre bundles led to jammed extrusion and the 2-step workflow was frequently interrupted. In contrast to 3-step workflow, the 2-step workflow only led to <10% length reduction of fibres. FDM products made with different filaments were examined for the fibre length/orientation as well as their flexural properties. More than 55% of short fibres aligned with the FDM extrusion paths, and over 80% fibres were parallel with the horizontally deposited layers. The FDM products made with 2-step filaments showed superior strength and stiffness, as higher degree of fibre alignment and greater fibre length led to improved flexural properties. Greater fibre length was beneficial for higher strength and stiffness of the additive-manufactured polymer composites, and the fibre length was more influenced by the filament preparation than the final additive manufacturing process.