| Title | Direct Injection Molding of Recycled Thermoplastics using a Two-stage Process including Melt Filtration and Degassing |
|---|---|
| ID_Doc | 13724 |
| Authors | Köpplmayr, T; Fellner, K; Fehringer, S; Klammer, G; Traxler, I; Czaker, S; Fischer, J |
| Title | Direct Injection Molding of Recycled Thermoplastics using a Two-stage Process including Melt Filtration and Degassing |
| Year | 2024 |
| Published | |
| Abstract | Mechanical recycling is an essential tool in transitioning the plastics industry to a circular economy. The traditional route requires pelletizing after extrusion with melt filtration and degassing of the material. These (re)granulated materials can be later processed via injection molding. We present a study of a machine concept, which can be used to directly convert grinded or agglomerated thermoplastic materials to injection-molded products using a two-stage process. The machine concept consists of an extruder, a melt filter and an injection unit. To reduce odor and volatile organic contaminations, which are often present in post-consumer and sometimes also in post-industrial waste, a degassing system is introduced for the injection unit. Our study covers (i) virgin polypropylene with a humidity carrier and varying amount of water, (ii) grinded polyethylene from post-consumer caps, (iii) polypropylene agglomerate from post-consumer sheets, (iv) pre-sorted polypropylene flakes from post-consumer waste and (v) commercially available pellets from post-consumer PE/PP mixtures. Process stability and plasticizing performance is investigated under different boundary conditions. Effective degassing is achieved by increasing the free surface of the melt in the first section of the injection screw. Voids and closed pores are further reduced if vacuum is used. Mechanical testing shows an increasing tensile modulus of the injection-molded parts due to the reduction of volatile contaminations. The comparison to a state-of-the-art compounding process shows similar results. The machine concept represents an advanced opportunity to increase the content of recycled thermoplastics in injection molding including melt filtration and degassing, which would be very limited in a standard injection molding process. |
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