Mechanical recycling emerged among other plastics recycling approaches as a profitable method. Its feasibility has enhanced by understanding of reasons of lower mechanical properties of aged materials in comparison with virgin materials, and by a proper exploitation of the knowledge of compatibilization and stabilization additives for upgrading of reused materials. This study deals with low density polyethylene (LDPE). Impact strength of recycled or pre-aged (recyclate model) LDPE / high-impact polystyrene (HIPS) blends compatibilized with styrene-butadiene copolymer / ethylene-propylene elastomer was enhanced and fineness of the phase structure of the system was improved by using N,N'-disubstituted 1,4-phenylenediamine co-additives. Mechanism of the strong synergistic compatibilization effect was explained by LDPE grafting with styrene-butadiene copolymer mediated by the bifunctional amine additive.