Influence of extrusion process on the physical and mechanical properties of short natural fibre reinforced PLA filaments

The aim of the study is to understand and evaluate the consequences of the extrusion process on the physical and mechanical properties of natural short fibre reinforced filament for 3D printing. A reliable experimental protocol was built to evaluate the monotonic and dynamic mechanical behaviour of the coil filament with a diameter of 1.75 mm, regardless of other printing parameters, while comparing it to the extruded filament, with a diameter of 0.4 mm. The physical behaviours were investigated with micro-tomography, TGA and DSC. The mechanical tests were carried out with DMA. In order to consider reinforcement nature and geometry, the tests were carried out on neat and reinforced PLA, with hemp, flax and wood fibres, all reinforced with 20%wt. The study showed that extrusion led to a modification of glass transition temperature of all grades and decreased the Young modulus from about 14% for the neat PLA, up to nearly 50% for PLA reinforced with hemp.