Sustainable Additive Manufacturing: Mechanical Response of High-Density Polyethylene over Multiple Recycling Processes

Abstract

Polymer recycling is nowadays in high-demand due to an increase in polymers demand and production. Recycling of such materials is mostly a thermomechanical process that modifies their overall mechanical behavior. The present research work focuses on the recyclability of high-density polyethylene (HDPE), one of the most recycled materials globally, for use in additive manufacturing (AM). A thorough investigation was carried out to determine the effect of the continuous recycling on mechanical, structural, and thermal responses of HDPE polymer via a process that isolates the thermomechanical treatment from other parameters such as aging, contamination, etc. Fused filament fabrication (FFF) specimens were produced from virgin and recycled materials and were experimentally tested and evaluated in tension, flexion, impact, and micro-hardness. A thorough thermal and morphological analysis was also performed. The overall results of this study show that the mechanical properties of the recycled HDPE polymer were generally improved over the recycling repetitions for a certain number of recycling steps, making the HDPE recycling a viable option for circular use. Repetitions two to five had the optimum overall mechanical behavior, indicating a significant positive impact of the HDPE polymer recycling aside from the environmental one.

MEX 3D Printed HDPE/TiO2 Nanocomposites Physical and Mechanical Properties Investigation

“…The literature reports developments in sustainable additive manufacturing by studying the mechanical and thermal behavior of Acrylonitrile Butadiene Styrene (ABS) in FFF and after repeated heating cycles and extruded material reprocessing [4,5]. The literature also reports similar studies with Polypropylene (PP) [6], and Polyethylene (PE) (with the brand name Kritilen, procured from its manufacturer Plastika Kritis S.A., Heraklion, Greece) [7]. Moreover, studies on FFF and the mechanical properties of 3D printed parts report that 3D printing parameters can directly affect the mechanical properties of the final part [8][9][10][11][12][13].…”

Additive Manufacturing of Polyolefins

“…HDPE is a linear polymer that can be processed by many common melt-processing means, for instance, through injection molding or extrusion [ 101 ]. HDPE is the second-most recycled plastic, and the ability to recycle HDPE in additive manufacturing, through FFF, has been demonstrated [ 102 , 103 ].…”

Measurement of material degradation in dependence of shear rate, temperature, and residence time

“…In many cases, material degradation after multiple extrusion has also been considered for both single-screw extrusion and twin-screw extrusion. [8,11,[23][24][25][26][27][28][29][30][31][32][33] Here, among other factors, different screw speeds or screw configurations were investigated. Greater degradation was found with higher shear rates in the single-screw extruder [23] and with the increased use of kneading blocks on the twin-screw extruder.…”