Key-Words: Recycling, in-situ Transesterification, Opaque PET, Polymer blends, Reactive Extrusion Abstract: Due to better processability, mechanical properties and productivity compare to conventional low density poly(ethylene) (LDPE), the use of opaque poly(ethylene terephlate) (O-PET) in the milk bottle market continue to increase fastly. O-PET milk bottles are lighter and free of aluminum opercule. Nevertheless, the titanium dioxide nanoparticles (TiO2 NPs) used as opacifier disturb the well-establish flow of recycle transparent PET from water bottle [1]. Our project proposes to investigate new valorization solution in order to prepare the upcoming increase volume of O-PET end of life bottle. While TiO2 NPs are an issue in the current situation, they could be used advantageously as catalyst in different process like reactive extrusion [2]. In this work, PC/O-PET 50/50 w/w blends were first produced using twin-screw mini-extruder. The results show that the presence of TiO2 NPs effectively acts as catalyst in the reaction of transesterification between ester functions of PET and carbonate functions of PC during extrusion. Miscible blends exhibiting only one glass transition temperature were obtained. The influence of process parameters such as temperature, time of mixing but also type of flow (shear vs elongational) was investigated. Finally, the ability to use these PC-co-PET copolymers as compatibizing agent in industrial twin-screw extruder is also discussed. References : [1] : Maryon Pailleux. (2016). Cahier des charges: Etude de débouchés au recyclage des PET opaques [2] : Pilati, F., Marianucci, E., & Berti, C. (1985). Study of the reactions occurring during melt mixing of poly(ethylene terephthalate) and polycarbonate. Journal of Applied Polymer Science, 30(3), 1267–1275.