FILAMENT EXTRUSION USING RECYCLED MATERIALS : Experimental investigations on recycled Polylactic Acid (PLA) materials

University essay from Högskolan i Halmstad/Rydberglaboratoriet för tillämpad naturvetenskap (RLAS)

Abstract: 3D printing or additive manufacturing is a process of building threedimensional solid object from a digital file. In additive processes, an object is formed by laying down successive layers of material until the object is created. The most commonly used materials for 3D printing are PLA (Polylactic Acid) and Acrylonitrile Butadiene Styrene (ABS). Appreciable feature of the materials that are used in 3D printing is their ability to re-melt and extrude without a noticeable loss of material. It enables to make our own filament, which reduces wastage and filament cost.  In Fused Deposition Modelling (FDM), an additive manufacturing process, preparation of qualified filaments is critical requirement. At first step, PLA failed parts should be separated from other materials as different materials have different melting characteristics and properties. Segregated PLA failed parts are shred into small pieces. Then shredded pieces are filtered to achieve a homogenous size distribution. These shredded and filtered materials undergo dehumidifying process by the help of a dehumidifier to reduce the moisture content. Finally, the materials are melted and extruded into filaments.  In the filament extrusion process, the most important parameters to consider are the diameter of the filament and uniformity over its length. The acceptable filament diameter for 3D printing is 1.75mm with tolerance of ±50µm. Variation of the diameter of the filament above ±50µm makes the filament not useful for 3D printing. In this thesis, optimal process parameters for the fabrication of qualified filaments are determined. This thesis includes investigations on factors affecting the quality of the filament such as material properties, material size, flow of the material from hopper to the spool, lack of pushing force of the materials in the feed screw, speed of the feed screw and extrusion temperature of different heaters in the extruder. From the investigations, the flow was improved by insertion of a stopper at the feeding zone. Further, investigations on identifying the ideal conditions for extruding other recycled thermoplastic materials will enhance the materials choice for manufacturing and stimulates circular economy.

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