Sandra Beckamp, managing director at Institut cyclos-HTP, discusses how a unique and in-depth near-infrared study with CEFLEX showed how different designs of flexible packaging affect recognition and sortability

This was the first NIR study of its kind and the aim was to better understand the technology’s characteristics, behaviour and capability for detecting and classifying flexible packaging waste. The research examined numerous flexible packaging structures in a series of tests focused on detecting and classifying materials through the automated and manual examination of their NIR spectra and signal intensities.

While the study anonymised the source of all the samples, CEFLEX had obtained detailed specifications about them, which supported a thorough and systematic evaluation of each sample. This enabled our collaboration with the fellow testing centres to better coordinate measurement procedures, calibration and summarisation of results. When this was combined with our industrial NIR sorting machine, which gives access to the ‘inner workings’ of the electronic data programme, we could manually review and generate raw data that provided very interesting insights, including visualisations of the materials’ spectrums (profiles).

NIR sorting technology has been used in practise by the waste management and recycling industry for almost three decades, but we still lacked some fundamental understanding of how it ‘sees’ more complex structures and different types of materials, depending on layer thickness and sequence in flexible packaging. Our investigations with CEFLEX and its stakeholders not only clarified how a modern NIR camera sees the packaging, but also shows which specific design measures can be used to influence the actual sorting results of this technology in a targeted manner. In other words, our findings can be utilised in design for recycling guidelines.

Our understanding of how NIR technology works has increased in several ways as a result of the CEFLEX testing programme.

It was astonishing that almost all multi-material combinations could be specifically identified as such. In certain cases, even the concentration of the components can be determined.

Furthermore, the study showed, contrary to our previous assumptions about limited penetration depth, that NIR can penetrate significantly beyond the outer layer of most flexible packaging structures. This explains why measurement of asymmetrical structures can provide identical results from both sides.

Indeed. We already know that carbon-based black masterbatches are problematic for NIR based sorting, but we learned this also applies to using black inks which contain carbon black, when used on large parts of the surface, such as a background colour. At the same time, testing of black print in finer patterns, such as typical for text, barcodes and line graphics could clearly be shown to not cause sorting issues.