Determination of thermomechanical properties in recycled PLA filaments for 3D printers

Abstract

In recent times, the issue of plastic recycling has become one of the leading issues of environmental protection and waste management. Polymer materials are found applied in many areas of daily life and industry. Along with their extended use, the problem of plastic waste appeared because, after withdrawal from use, they became persistent and noxious wastes. The possibility of reusing polymeric materials enables waste utilization to obtain consumable products. The 3D printing market is a well-growing sector. Printable filaments can be made from various thermoplastic materials, including those from recycling. This paper studies the thermal-mechanical properties of recycled polylactic acid (PLA) material filaments obtained from 3D-printed specimens. The analysis was first with the virgin filament (PLA N) and, subsequently, two recycling cycles (PLA 1 and PLA 2). There were thermal properties evaluations for the three processing types, as follows: differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and tensile test for both specimens and filaments. The glass transition temperatures (Tg) remained at their typical values. The same happened with the melting temperature (Tm). In the TGA, the PLA thermal stability remained constant. The FTIR presented the functional groups unaltered for the recycled samples. In the second filament recycling, the tensile strength decreased by 26%, and the maximum strain was 40%, compared to PLA N. The same occurred to PLA 2 specimens; the maximum stress and strain decreased by 45% and 31%, respectively. In terms of crystallinity, this presented a variation of 86% of the virgin material for the second recycling cycle, which correlated to tensile strength shows a weakness in the PLA recycled structure, decreasing the strain until the fracture and the tensile strength.