Abstract
The growing emphasis on sustainable material design has intensified interest in bio-based additives as environmentally friendly alternatives to conventional synthetic modifiers. This study evaluates the effects of four natural compounds-cetyl alcohol, thymol, lanolin, and lecithin-on the thermal, rheological, mechanical, surface, and aging properties of regranulated low-density polyethylene (RLDPE). Post-consumer polyethylene waste was used as the polymer matrix, while biochar served as a sustainable reinforcing filler replacing carbon black. Differential scanning calorimetry, melt flow index measurements, rheological behavior, surface energy analysis, mechanical testing and thermo-oxidative aging assessments were conducted to assess structure-property relationships. Biochar increased stiffness, hardness, and impact resistance but reduced ductility and melt flow due to restricted chain mobility. The addition of natural compounds partially compensated for these effects by improving melt flow, modifying crystallization behavior, and enhancing resistance to thermo-oxidative degradation without severely diminishing mechanical performance. Cetyl alcohol promoted the highest crystallinity and flexural properties, lanolin exhibited the strongest plasticizing effect and improved post-aging ductility, while lecithin and thymol produced intermediate changes, with lecithin significantly increasing surface energy. These results indicate that selected natural additives can act as effective ecological plasticizers or processing aids in biochar-filled recycled polyethylene composites.