Tarrytown, New York-based Ampacet Corp. and Pellenc ST, Pertuis, France, are partnering to develop methods to assess the detectability of dark polyethylene terephthalate (PET) packaging in optical sorting.
Plastics separated into mono
-material streams at material recovery facilities (MRFs) are scanned by near-infrared technology (NIR) to recognize the resin type used in plastic articles but are limited by NIR’s inability to separate plastics that contain carbon black, the most commonly used black pigment. Carbon black absorbs the most part of the infrared spectrum, preventing the backscattering of infrared light to the NIR spectrometer and consequently blocking the recognition of the resin’s fingerprint.
Such mixed plastic packaging ends in a residual fraction, which is disposed of mainly through incineration rather than recycled. Ampacet says it has developed alternative black masterbatch coloring under its Rec-NIR-Black brand that can be sorted using conventional NIR technologies and be effectively recycled.
PET recyclers are equipped with visible optical sensors that sort PET streams by colors, but identifying transparent and dark plastic can be troublesome. Due to the use of black conveyor belts, the visible domain spectrometers positioned above can struggle to distinguish dark containers from transparent ones, directing the dark packaging to the transparent stream.
PellencST says sorting tests conducted on PET containers colored with Ampacet’s REC-NIR-BLACK allowed it to establish the optimal conditions and adjust the computer algorithm to differentiate transparent packaging from dark and send them to the correct streams. Tests were conducted under a protocol developed by Cotrep, a French technical committee for plastics recycling, using a previous version of Pellenc ST’s sorting machine along with the new optical sorter Mistral+ Connect.