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Poly (ethylene terephthalate) (PET) recycling process is well established nowadays for PET bottles. On the other hand, recycling of PET from food trays (tPET) is still challenging because of its lower molecular weight and the possible presence of other polymers as a consequence of the use of multi-layered trays. In this work, end-of-life PET trays have been chemically modified through the melt reactive processing into a covalent associative network, in order to enhance its performance. In particular, upcycling of tPET was obtained by the reaction of diglycidyl ether of bisphenol A (DGEBA) in the presence of zinc acetylacetonate as a transesterification catalyst, to obtain a reversibly cross-linked material, i.e. a vitrimeric material, which retains recyclability while significantly enhancing mechanical properties of tPET. Indeed, rheological test demonstrated clear crosslinking of tPET vitrimers, with a high temperature relaxation explained by the exchange of covalent bonds. Dynamic mechanical analysis showed high thermomechanical resistance, while tensile test at room temperature demonstrated strong enhancement in tensile strength and elongation at break compared to tPET. The results reported in this paper opens to the upcycling of other low grades of PET, including textiles and other goods produced with previously recycled polymer, thus contributing to the establishment of a circular economy for PET, beyond bottles. [Display omitted] • Upcycling of low-quality PET from recycled trays validated via vitrimers chemistry. • Crosslinked fraction up to 75%, still re-processable by compression moulding. • TPET vitrimers exhibit a two-fold increase in mechanical strength compared to tPET. [ABSTRACT FROM AUTHOR]