Granule-based material extrusion is comparable to filament-based material extrusion in terms of mechanical performances of printed PLA parts: a comprehensive investigation

Abstract

To implement a circular economic life for thermoplastic waste, such as polylactic acid (PLA) waste from filament-based material extrusion (FME) printing and reduce the costs associated with producing filaments for the FME process, a granule-based material extrusion (GME) printer was developed by modifying a filament-based extrusion head with a granule-based extrusion head. However, concerns have been raised about the mechanical performance of parts printed using the GME method. Previous studies have reported mixed results, with some finding inferior mechanical performance of GME printed parts compared to FME counterparts, while others reported comparable or slightly better performance. Moreover, these studies were limited to tensile or flexural performance evaluations, lacked a clear explanation to support them. Therefore, to address this uncertainty and research gaps, a comprehensive mechanical performance comparison and analysis study was conducted among the specimens printed by these two types of material extrusion printers. Characterization tests were conducted, including tensile tests, impact tests, 3-point bending tests, and hardness tests, to reveal the comprehensive mechanical properties of the printed parts. Furthermore, scanning electron microscope (SEM) tests, differential scanning calorimetry (DSC) tests, thermal imaging, rheological tests, and gel permeation chromatography (GPC) tests were carried out to analyze and explain the results. The results indicated no significant differences (P > 0.05) in the mechanical properties of FME and GME printed parts in terms of tensile properties, flexural strength and modulus, and impact strength. However, there was a significant difference in shore D hardness and bending strain at break between the two methods, and the complex viscosity of GME printed samples was greater than that of FME counterparts. Remarkably, the average molecular weights of GME printed samples were higher than those of FME ones, which can be attributed to lower actual temperature of the GME extrusion chamber due to its different location among the heater, thermistor and melting chamber compared to the FME extrusion head.