The main objective is to develop a thought out model-driven mechanical recycling strategy for polyesters with varying feedstock, to enhance processing efficiency and product quality, while minimizing resources and ameliorating environmental impacts. A systematical experimental approach will be considered which will provide knowledge on the interplay between processing conditions (screw intensity and temperature profile) and material behaviour (strength). This will act as a foundation for informed decision making in industrial applications such as (food) packaging, by far the most important polyester application, with a current PET market size larger than 20 billion dollars of which plastic bottles take a share of more than 80%. It will be established what the boundaries are for acceptable mechanical recycling applications and what the nature of the PET-rich feedstock must ideally be to perform extrusion, reactive extrusion, solid-state polymerization or a combination. Taking advantage of the knowledge of CPMT (promotor: Prof. Mariya Edeleva) on (reactive) extrusion, recycling and material characterization, and the expertise of LCT (promotor: Prof. Dagmar R. D'hooge) in multi-scale and diffusion modelling, a synergetic effect in merging several engineering fields is obtained. Moreover, the research stay abroad at UMons and ULeoben will facilitate validation under melt and solid state conditions with different mechanical forces.