Influence of multiple mechanical recycling on short fiber reinforced thermoplastic for additive manufacturing

Material Extrusion (MEX) is an additive manufacturing method in which material is selectively dispensed through a nozzle or other type of orifice. The main material for this is thermoplastic filament. In recent years, a new technology evolved using granulate, which is plastified in a screw extruder as feedstock, called Fused Granulate Fabrication (FGF): reducing material prices and increasing deposition rates. In order to decrease thermal expansion, increase viscosity during deposition, and increase mechanical performance, short fiber reinforced thermoplastics are widely used. These composite materials are fully mechanically recyclable. However, if recycling is performed, it is done by shredding and re-compounding the printed material, which uses additional resources, damages the material, and is uneconomical for smaller amounts of material. Thus, this study investigates the material damage induced by multiple mechanical recycling and reprinting of three commonly used printing materials and their influence on the material viscosity. The study finds a correlation between viscosity at different shear rates and fiber and matrix damage, thereby providing an effective means to assess the quality of recycled and virgin materials in additive manufacturing applications.