Post-industrial plastic waste streams can be re-used as secondary material streams for polymer processing by extrusion or injection moulding. One of the major commercially available waste stream contains polypropylene (PP) contaminated with polyester (PET). An important practical hurdle for the direct implementation of this waste stream is the immiscibility of PP and PET in the melt, which leads to segregation within the polymer structure and adversely affects the reproducibility and mechanical properties of the manufactured parts. It has been indicated in literature that the creation of PET microfibrils in the PP matrix could undo these drawbacks and upcycle the PP/PET combination. Within the current research, a commercially available post-industrial PP/PET waste stream was compared to virgin PP/PET as precursor for the microfibrillar preparation. The mechanical properties (tensile and impact), physicochemical properties (DSC and TGA) and morphology (SEM) of the composites were characterized at different stages of the microfibrillar preparation.