Recycled plastic content quantified through aggregation-induced emission

The linearity of the plastics economy is wasteful and polluting. To encourage recycling and decrease diversion to landfill, new legislation within the EU and UK will tax single use plastic products made with less than 30% recycled plastic. At present, quantitative determination of recycled content is elusive and existing methods inconsistent. We present a fluorescence-based analytical technique to determine recycled content in plastic and (single use) packaging. Bathochromic shifts resulting from aggregation of the fluorescent brightener 4,4’-bis(2-benzoxazolyl) stilbene (BBS) in three commodity plastics (high-density polyethylene, polypropylene and poly(ethylene terephthalate)) at loadings ≤0.5 wt% were used to systematically quantify simulated recycled contents as low as 10 wt%. Linear correlations were found between recycled content and three fluorescence-based properties: emission, lifetime, and resulting colour. We demonstrate how this multi-branched verification system is completely independent of sample dimensions and processing conditions, has a negligible effect on polymer properties, and is inexpensive and highly compatible with existing recycling infrastructure.