Modifying Mechanical Performance of an LLDPE/PP Waste Blend During a Single Recycling Cycle Using Organometallic Complexes

In this study, organometallic complexes were introduced at 0.05 wt% to modify the performance of a 70/30 LLDPE/PP waste blend during a single recycling cycle under high shear. Four complexes (C₈-Ti, C₈-Zr, C₁₈-Ti, and C₁₈-Zr), based on Titanium (Ti) or Zirconium (Zr) with phosphate esters of different alkyl chain lengths (P_C8 or P_C18), were incorporated under high-shear mixing, and their effects on structural, thermal, morphological, and mechanical properties were investigated. Sequential processing of the unmodified waste increased PP crystallinity from 16.1% to 42.7% and reduced total crystallinity from 30.4% to 24.5%, indicating progressive phase separation. Upon additive incorporation, total crystallinity further decreased to 27.9% for C₁₈-Ti and 29.3% for C₈-Ti, while C₁₈-Zr showed a slight increase to 35.2%, indicating structure-dependent effects on phase packing. T_{_onset} values ranged from 409°C to 444°C across all formulations, indicating essentially unchanged thermal stability. Mechanical testing showed that Charpy impact strength increased by up to 50%, rising from 11.3 to approximately 16.7 kJ/m² (ISO 179-1), without detrimental effects on tensile properties, as confirmed by statistical analysis (ANOVA). Fracture analysis indicated that Ti-containing samples exhibited more fibrillation, whereas Zr-containing systems showed finer, small-void fracture surfaces. Overall, the findings demonstrate that these organometallic complexes represent a potentially scalable additive strategy for improving mechanical performance in mixed-waste polyolefin streams within a single high-shear recycling cycle.