Impact and Interaction of Additives on the Formation of Nonintentionally Added Substances and Polystyrene Rheology

Recycling polystyrene on an industrial scale remains challenging. One of the key challenges lies in the formation of nonintentionally added substances (NIAS) arising from polymer manufacturing, polymer or additive degradation, and contaminants. This study aims at investigating the interactions between the polystyrene matrix and five common additives (antioxidants, UV stabilizer, brominated flame retardant, inorganic flame retardant). The main objective is to evaluate the impact of these interactions on NIAS formation and polymer rheological behavior. Our previously developed simple and efficient extraction was used to recover additives, and NIAS and was adapted for the low solubility additive decabromodiphenyl ether, to reach combined extraction efficiency (considering additives and their degradation products) between 81.3 and 100 wt %. Extracts were identified by ¹H, ³¹P nuclear magnetic resonance (NMR), and LC-MS and quantified by LC-MS with limits of quantification (LOQ) as low as 0.21 ng/L. Extended investigation of the rheological behavior showed the impact of processing parameters and presence of additives. Chemical interaction between additives also highly impacted NIAS production, leading to either a decrease (up to 8.5-fold) or an increase (up to 3.5-fold) formation of NIAS. The present work contributes to the better understanding of interactions present during PS processing or recycling, highlighting the challenges linked to polystyrene mechanical recycling and the production of potentially toxic species.