NEAR-INFRARED IDENTIFICATION AND SORTING OF POLYLACTIC ACID

Abstract

Biobased plastics are often seen to be an environmentally friendly alternative to conventional plastics, with their share, though being less now, is gradually increasing. This necessitates that the waste management of these possibly eco-friendly materials is also at par with their growth. Near-infrared (NIR) sorting is an effective waste sorting technology and is already widely used for conventional plastics. Thus, it would be imperative to analyse whether this effective existing infrastructure could also be successfully used to sort bioplastic. In the present study, the lab-scale NIR sensor-based sorting system in Montanuniversität Leoben was used to analyse polylactic acid (PLA) in three sets of experiments. First, the spectra of 7 conventional plastics were compared to that of virgin PLA and it was found that PLA has a distinct spectrum and should ideally be detected from a mixed plastic fraction. Second, it was assessed whether different grades and thicknesses of virgin PLA samples produced different spectra and it was found that there is a slight difference in the intensities without any wavelength shift of the recognizable peaks. Lastly, the detection of 10 PLA product samples was tested using the NIR recipe of a virgin PLA. It was observed that the samples were successfully detected and blown out as PLA for all the conducted trials. Additionally, it was also seen that an appropriate backlight setting is important to be able to correctly sort the transparent PLA products in the used chute-type sorter.