The mechanical and morphological behavior of polypropylene (PP) and high-density polyethylene (HDPE), recycled and non-recycled,by the addition of an ethylene-propylene block copolymer, was studied. In the non-recycled samples, the effect of the copolymer on the mechanical and morphological properties is negligible. In the recycled samples, it was shown that with 5% copolymer, both particle size in the dispersed phase and interface thickness decreased, and that 5% copolymer composition is optimal in improving the adhesion and flexibility of the blend.