Recyclability of Polystyrene Bead Foams : Degradation Behavior over 10 Extrusion Cycles

This study investigates the recyclability of expandable polystyrene (EPS) bead foams under conditions aligned with the EU Packaging and Packaging Waste Regulation (PPWR) by simulating 10 consecutive extrusion cycles with a consistent 35 wt% recycled fraction. Although molar mass distribution and MFI remained nearly constant across all cycles, mechanical properties deteriorated during the first four cycles. Compression modulus decreased by 24%, flexural modulus by 14% and flexural strength by 21% in these initial cycles. Faster pentane diffusion, reflected in shorter steaming times, indicates that changes in diffusion behavior, rather than chain scission, govern the loss in mechanical performance. After Cycle 4, both processing behavior and mechanical properties reached a plateau, demonstrating that the required 35 wt% recycled content leads to a stable material condition for future industrial practice. A complete post-use recycling loop (C + 1), including prefoaming, welding, compression, shredding, and pelletizing, revealed the strongest degradation, with a 15% drop in molar mass and an increase in MFI, which was caused primarily by the pelletizing step. Overall, the results show that EPS bead foams can withstand multiple recycling cycles when blended with virgin material, while highlighting that pelletizing and blowing agent diffusion must be monitored closely in circular EPS production.