Long chain branching (LCB)a well-known industrial processis shown as an innovative tool for the treatment of PP post-consumer waste. The introduction of LCB by reactive extrusion does not only compensate the degradation during product life (e.g., thermally and UV-induced chain scission), it also improves the melt properties (e.g., melt strength, strain hardening). Thus, not only a re-cycling process, even a real up-cycling can be achieved. Compared with virgin material, PP from post-consumer waste contains impurities like other polyolefines (PE-HD, PE-LD, PE-LLD, copolymers), the total removal is economically not viable. Hence, the focus of this work was the influence of PE-HD on the LCB formation of PP. Based on model mixtures with virgin PP and 10% PE-HD, it is shown that PE-HD influences the mechanical properties and gel content of the chemically modified blend but has no detrimental effect on the improved melt properties. POLYM. ENG. SCI., 57:1374-1381, 2017. (c) 2017 Society of Plastics Engineers