A compatibilizer is a well-known additive to improve amongst others the mechanical properties by increasing the interfacial adhesion during the mechanical recycling of mixed waste streams. As this waste is reused in new products and collected again for a new lifetime, will the compatibilizer continuously improve the mechanical properties? Polypropylene (PP)/poly(ethylene terephthalate) (PET) blend is a common polymer waste stream for foils in tray packaging. In this research a PP/PET (75/25 wt%) blend is extruded in a single screw for five times. Another PP/PET blend is processed in the same manner as the binary blend but mixed with the addition of 5 wt% compatibiliser block copolymer poly(styrene-co-(ethylene-butylene)-styrene) grafted with maleic anhydride (SEBSgMAH). This as comparison to evaluate the degradation effects and the morphology stabilisation by adding the compatibiliser. Scanning Electron Microscopy (SEM) showed the destabilisation of the morphology of the PP-PET blends after the third extrusion step whereas the demixing for the compatibilized mix is lower. Differential Scanning Calorimetry (DSC) highlighted the fine dispersion of the compatibilized blend. However, there is an increase in crystallisation enthalpy for multiple extruded PET in every set. The increase was less prominent for the compatibilised blend compared to the binary blend. What concerns the mechanical properties, the Young’s Modulus and stress at yield (zero slope) where almost unaffected by multiple extrusions for both types of blend as these parameters are strongly dependent on composition. However, the strain at break and strain at yield were significantly altered by demixing and degradation. The decrease of these parameters was strongly noticeable for the binary blend and remained mostly the same for the compatibilised blend over the five extrusions confirming the stabilising effect of the compatibilizer in the ternary blend.