Many plastic waste recycle streams are blends of various types of polypropylene (PP) and polyethylene (PE). When reprocessing these blends into products it is difficult to obtain good mechanical and optical properties due to the immiscibility of the components. Blend morphology is one of the governing factors for these properties. Therefore morphology control is a key challenge when turning plastic waste into valuable materials. In this work, the effect of a novel polymeric compatibilizer on the morphology of PP–PE blends was investigated via rheological and scanning electron microscopy experiments. Homopolymer PP was combined with PE of varying comonomer level. In addition to the effect of including compatibilizer, the effect of blend ratio and viscosity ratio is discussed. It was found that very fine dispersions could be obtained when including the compatibilizing polymer for all studied systems. The blend rheology was compared with predictions from empirical and physics-inspired mixing rules. The difference between measured and predicted rheology is expected to provide insight into the structure of the various blend systems. POLYM. ENG. SCI., 58:460–465, 2018.