Pyrolysis of 3D printed polylactic acid waste: A kinetic study via TG-FTIR/GC-MS analysis

Polylactic acid (PLA) is one of the most common 3D printing materials. However, once processed, the properties of its raw material are altered. 3D printed PLA waste (3DP-PLAW) has a relatively high calorific value with low impurities, which makes waste-to-energy utilization effective through thermal conversion. In this study, the pyrolysis characteristics of 3DP-PLAW were investigated using thermogravimetric-Fourier infrared spectroscopy/gas chromatography-mass spectrometry (TG-FTIR/GC-MS). Two main pyrolysis stages were observed at 260-390 ? and 390-500 ? during 3DP-PLAW pyrolysis, which contradicts with findings from previous research. Upon reaching 390 degrees C, residual ash and char triggered a secondary reaction. It is speculated that the occurrence of a second pyrolysis stage is attributed to changes in the physicochemical properties of the PLA during the 3D printing process. It was also found that 3DP-PLAW had a higher heating value (HHV) (20.949 MJmiddotkg(-1)) than that of the raw PLA. The pyrolysis kinetics of 3DP-PLAW was analyzed using the distributed activation energy model (DAEM) as well as Flynn-Wall and Ozawa (FWO), Starink, and Friedman methods; it was found that the activation energies obtained from these methods were similar (approximately 206 kJmiddotmol(-1)). Therefore, these methods are suitable for biomass plastics. The TG-FTIR/GC-MS results showed that CO, CO2, CH4, CH3CHO, esters, carbon-based compounds, and ethene were the main gaseous products of 3DP-PLAW pyrolysis. In contrast to a previous study on raw PLA, no ketone was detected in the gaseous products during 3DP-PLAW. These findings allow for the production of energy products, instead of the usage of natural gas for recycling, which underlines the potential value of 3DP-PLAW for energy recovery and subsequent improvements on the current 3DP-PLAW disposal methods.

Automated summary

This study investigated the pyrolysis characteristics of 3D printed PLA waste (3DP-PLAW) using TG-FTIR/GC-MS and found two main pyrolysis stages, with the occurrence of the second stage attributed to changes in the physicochemical properties of PLA during 3D printing. It was also found that 3DP-PLAW had a higher heating value than raw PLA, highlighting its potential value for energy recovery.