Recycling of Bottle Grade PET: Influence of HDPE Contamination on the Microstructure and Mechanical Performance of 3D Printed Parts

Abstract

As part of a project that aims to provide people with disabilities with simple assistive devices in Colombia, the possibility of creating a PET filament that can be printed by Fused Deposition Modelling (FDM) from beverage bottle waste was investigated, with the aim to remain as simple as possible in terms of plastic collection, sorting, processing, and printing. Recycled PET filaments were thus produced by extrusion from collected PET bottles, with the potential addition of HDPE, which comes from caps and rings. The microstructure, mechanical performance, and printing quality of parts produced with these filaments were investigated in comparison to commercial PET virgin and recycled filaments. HDPE presence as an immiscible blend did not affect the ease of extrusion or the quality of the printing, which were all satisfactory. In some conditions, the addition of 5%wt of HDPE to recycled PET had a toughening effect on otherwise brittle samples. This behavior was attributed to the presence of elongated HDPE inclusions resulting from shear forces induced by the layer-by-layer printing, provided that the interface temperature remained high between layer depositions. This confirms that the mechanical performance of recycled PET is very sensitive to the processing conditions, especially in the case of 3D printing. Nonetheless, this low-cost process that did not require sophisticated compatibilization schemes allowed for the printing of parts with mechanical properties comparable to those obtained with high purity, commercially recycled filaments, opening interesting perspectives for a low-cost PET recycling process.

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

“…The melting points of rHDPE and rPET are 131.7 and 249.9 C, respectively, which align with previous findings in the literature. 30,64,65 Melting and crystallization temperature of rPET increased, while that of rHDPE slightly decreased. The rHDPE appears to act as a nucleating agent for the rPET given the larger melting peak, which corresponds to a 3.5% increase in the degree of crystallization in the blend as well as the increase in crystallization temperature (Table 2).…”

“…7 Efforts are being made to identify sustainable feedstocks for 3D printing. 23,24 Several studies have expanded the range of recycled filament materials including PLA, 25,26 ABS, 27,28 PET, 29,30 HDPE, 9,27,31 and PC. 32 In fact, Ref.…”

“…The addition of rHDPE at higher levels, however, helped to meet the brittle-ductile transition in 15% despite the low interfacial tension of both polymers, allowing the printing of quality parts. 30 While former studies have proven successful in FFF, a new approach to DRAM is fused granular fabrication (FGF) or fused particle fabrication (FPF), where the material-extrusion AM systems print directly from pellets, granules, flakes, shreds, or grinder material. 11,48 In the context of recycling, this could reduce the number of melt/extrusion cycles that degrade the material needed in the filament fabrication process.…”

“…Likewise, Ref. 30 studied the evaluation of the microstructure, mechanical performance, and printing quality of filaments made from rPET and rHDPE varying the wt% of HDPE material from 0% to 10%. They confirmed the increase in Young's modulus from 1.7 GPa of the pure PET to 2.1 GPa for all the HDPE concentrations.…”

Colombian Sustainability Perspective on Fused Deposition Modeling Technology: Opportunity to Develop Recycled and Biobased 3D Printing Filaments

“…Results demonstrated that recycled PET filaments could replace commercial filaments. Vaucher et al [ 128 ] evaluate the possibility to develop PET filaments form beverage bottle waste and the potential addition of HDPE from bottle caps and rings. Results showed that the HDPE presence does not affect the extrusion process or the 3D printing quality of the filaments.…”