Aggregation-Induced Enhanced Emission for Quantification of Recycled Content in Automotive Plastics

The use of plastics in the automotive industry is increasing due to their versatility, light weight, and affordability. To improve their sustainability credentials, incorporation of recycled content is desired, driven by recent European Union mandates for 25 % recycled content for automotive plastics. Current methods to quantify recycled content, however, are imprecise and could promote fraud. This paper extends a method to quantify recycled content in packaging plastics using a fluorescent brightener 4,4′-bis(2-benzoxazolyl) stilbene (BBS) to automotive grade polymers. BBS aggregates above threshold concentrations to exhibit Aggregation Induced Enhanced Emission (AIEE). This study investigates whether fluorescence emission, lifetime, and colour analyses can be used to quantify recycled content in four automotive plastics with different chemical structures, matrices or fillers. Quantification using BBS AIEE was most successful for semi-crystalline polymers with minimal additives (polyamide-6 and polyamide-6,6), with high confidence correlations between fluorescence emission and lifetime measurements and recycled content. Detection was suppressed in amorphous polycarbonates and filled polypropylenes, suggesting this quantification technique may be application limited. These new insights into quantifying recycled content in automotive plastics point to both opportunities and limitations for fluorescence-based techniques in assuring a more circular world.