Reaction Kinetics of Recycled Polyethylene Terephthalate with PMDA Chain Extender Analyzed by a Microcompounder

With the simultaneous growth of plastic demand and the need for a circular economy, processes for recycling discarded and worn-out consumer goods are also becoming increasingly important. In this context, reactive processing of recycled poly(ethylene terephthalate) (rPET) with pyromellitic dianhydride (PMDA) offers a frequently studied modification approach to optimize the viscous and elastic material properties of degraded PET through mechanical recycling. However, the kinetics of the underlying chain extension reaction have not been investigated yet. In this study, the parametric parameters for reaction kinetics are investigated as a function of material and process parameters. For this purpose, three series of experiments were carried out with rPET and PMDA on a microcompounder. The screw force was recorded, and the data was analyzed using an Avrami and Arrhenius approach. In order to follow the rheological and chemical changes during reactive extrusion, the samples were examined using SEC, FT-IR, and small amplitude oscillatory shear (SAOS) rheological analysis. An activation energy of 70 kJ/mol was determined for the process studied. Furthermore, a linear increase in polydispersity was observed over the processing time. An analogous behavior could be determined by FT-IR spectroscopy.