High density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS) are among the most used polymers around the world. Statistics show that in Brazil they together represent more than 50% of virgin resins used to produce plastic artefacts. One alternative to reuse them could be the production of polymer blend; However, they are immiscible and incompatible. The objective of this work is to achieve compatibility of the ternary blend by Friedel-Crafts alkylations. Two sets were prepared varying the ratio of HDPE, PP, and, respectively: 50/30/20 and 40/40/20. For each composition, it was added 0.6% styrene (w / w), the co-catalyst, and varying concentrations of AlCl 3, the catalyst: 0.3, 0.5, and 0.7% (w / w). Mix was prepared in an internal mixer, at 200 ºC and 100 rpm. Polymers were added first and after 3 minutes, enough to melt them, the catalyst / co-catalyst (cat/co-cat) system was added and the reaction took place from up to 5 minutes more. Morphological characterization was carried out by cryogenic fracture followed by styrene extraction in chloroform solution, gold sputtering and examination in a scanning electron microscope Mira3 (Tescan) equiped with field emission gun (FEG). It was observed an emulsification effect when cat/ co-cat system was added. Thin films were produced for mechanical test following ASTM D-882 standard. It was observed to increase in elastic modulus and ultimate tensile strength for the compatibilized blends, mainly for 0.3% AlCl 3.