Towards recycling of challenging waste fractions: Identifying flame retardants in plastics with optical spectroscopic techniques

Abstract

The use of plastics is rapidly rising around the world causing a major challenge for recycling. Lately, a lot of emphasis has been put on recycling of packaging plastics, but, in addition, there are high volume domains with low recycling rate such as automotive, building and construction, and electric and electronic equipment. Waste plastics from these domains often contain additives that restrict their recycling due to the hazardousness and challenges they bring to chemical and mechanical recycling. As such, the first step for enabling the reuse of these fractions is the identification of these additives in the waste plastics. This study compares the ability of different optical spectroscopy technologies to detect two different plastic additives, fire retardants ammonium polyphosphate and aluminium trihydrate, inside polypropylene plastic matrix. The detection techniques near-infrared (NIR), Fourier-transform infrared (FTIR) and Raman spectroscopy as well as hyperspectral imaging (HSI) in the short-wavelength infrared (SWIR) and mid-wavelength infrared (MWIR) range were evaluated. The results indicate that Raman, NIR and SWIR HSI have the potential to detect these additives inside the plastic matrix even at relatively low concentrations. As such, utilising these methods has the possibility to facilitate sorting and recycling of as of yet unused plastic waste streams, although more research is needed in applying them in actual waste sorting facilities.

A Survey of the State of the Art in Sensor-Based Sorting Technology and Research

“…Further studies focus on the detection of additives and polymer mixtures [82]. Since additives and fillers also play a crucial role in plastic recycling, special attention is paid to the detection of heavy metals in polymers [83], [84], brominated plastics [82], [83], other flame retardants [85], and chlorinecontaining plastics [86].…”

Characterizing plastics containing brominated flame retardants with combined LIBS and Raman spectroscopy

“…The method has been applied to quantifying flame retardants in plastics, e.g. ammonium polyphosphate and aluminium trihydrate [9], as well as BFR deca-BDE [10].…”

Mid-infrared spectroscopy and machine learning for postconsumer plastics recycling

“…13 Consequently, there has been an unprecedented surge of multi-disciplinary research aimed at reducing plastic waste, limiting the production of virgin polymers, and improving pathways for PCPW to re-enter the value chain. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] The development of automated optical sorting technologies for implementation at MRFs is one of these active research thrusts in the plastics recycling community. 28,29 This is because MRFs currently rely on air jets, magnetic separators, mechanical pistons, and human intervention to sort PCPW, all of which are methods that have been deemed insufficient to meet growing recycling demands.…”