Selective dispersion of SEBS copolymer in the compatibilization of PS/PP recycled copolymer blend: towards the circular economy

The effect of four mixing protocols was investigated in blends of polystyrene (PS) with recycled copolymer polypropylene (PPr), using 10% by weight of styrene-(ethylene-butylene)-styrene (SEBS) as a compatibilizing agent. The polymeric blends were processed in a co-rotational twin-screw extruder and injection molded. The melt flow index (MFI), Izod impact strength, tensile strength, Shore D hardness, differential scanning calorimetry (DSC), thermogravimetry (TG) properties, and scanning electron microscopy (SEM) were evaluated. The MFI indicated that when incorporating SEBS into the PS/PPr system, the fluidity was reduced, suggesting that the level of molecular entanglement increased, confirming the expressive results of impact strength and elongation at break. When PS and SEBS were blended in a first extrusion, before the incorporation of PPr in a second extrusion, there were gains of 541% and 814.3% in impact strength and elongation at break compared to pure PS, respectively. On the other hand, pre-mixing PPr and SEBS, before adding PS in the second extrusion step, reduced the toughening effectiveness. Simultaneous mixing of all PS/PPr/SEBS components, in a single extrusion, showed the best balance of mechanical properties and increased thermal stability. The selective dispersion of SEBS in the PS/PPr blend affected the degree of refinement as verified in the morphology obtained by SEM directly reflecting on the mechanical properties. The results showed that using SEBS as a compatibilizer, PPr can be used as an impact modifier of the brittle PS matrix, generating a tough material.