Manufacturing of a PET Filament from Recycled Material for Material Extrusion (MEX)

Abstract

Due to its low cost and easy use, the use of material extrusion (MEX) as an additive manufacturing (AM) technology has increased rapidly in recent years. However, this process mainly involves the processing of new plastics. Combining the MEX process with polyethylene terephthalate (PET), which offers a high potential for mechanical and chemical recyclability, opens up a broad spectrum of reutilization possibilities. Turning used PET bottles into printable filament for MEX is not only a recycling option, but also an attractive upcycling scenario that can lead to the production of complex, functional parts. This work analyzes the process of extruding recycled PET bottle flakes into a filament, taking different extrusion screws and extrusion parameters into account. The filament is subsequently processed with MEX into tensile tests. An accompanying thermal, rheological and mechanical characterization of the recycled resin is performed to offer a comparison to the virgin material and a commercially available glycol modified polyethylene terephthalate (PETG) filament. The results show the importance of adequate drying parameters prior to the extrusion and the sensitivity of the material to moisture, leading to degradation. The recycled material is more prone to degradation and presents lower viscosities. Mechanical tests display a higher tensile strength of the recycled and virgin resin in comparison to the PETG. The extrusion of the used PET into a filament and the subsequent printing with the MEX process offers a viable recycling process for the discarded material.

Multi‐material distributed recycling via material extrusion: recycled high density polyethylene and poly (ethylene terephthalate) mixture

“…The MFI tests were performed three times and the results for the rPET90//rHDPE10 blend showed medium MFI of 39.4 ± 2.4 g/10 min. This value is consistent with similar values reported in the literature for rPET 66–68 . This result suggests that the addition of low percentage of HDPE does not significantly impact the MFI value of rPET.…”

“…This value is consistent with similar values reported in the literature for rPET. [66][67][68] This result suggests that the addition of low percentage of HDPE does not significantly impact the MFI value of rPET. As the material flowed at a temperature of 255 C in the MFI test, this temperature was used as the input temperature for optimizing the parameters of the 3D printer.…”

“…Another visible issue present in the close angles of the printed object was the shrinkage (Figure 10D), which occurs during solidification and particularly upon polymer crystallization. Moreover, PET easily absorbs moisture, which makes it difficult to extrude 66 . PET can depolymerize in the presence of water, lowering the quality of the print.…”

“…Moreover, PET easily absorbs moisture, which makes it difficult to extrude. 66 PET can depolymerize in the presence of water, lowering the quality of the print. Prior to printing the chair, some samples exhibited brittle behavior and void formation; therefore, the material was dried and the hopper was kept closed to prevent moisture from entering the environment.…”

Using numerical-experimental analysis to evaluate rPET mechanical behavior under compressive stresses and MEX additive manufacturing for new sustainable designs

“…Approaching the design of a new component safely implies validating its behavior using FEM numerical simulations (Mercado-Colmenero and Martin-Doñate, 2020; Bustos Seibert et al , 2022; Negoro et al , 2016). However, it is a fundamental requirement to previously know the mechanical properties of the material with which the component will be manufactured (Marciniak et al , 2018; Bączkowski et al , 2021).…”