Kinetic Analysis of PMDA-Induced Chain Extension in Polyester Blends: Differential Reactivity of rPET and PBT during Reactive Extrusion

This study aimed to enhance understanding of the reactions occurring during the extrusion of polyester blends. Initial investigations revealed that pyromellitic dianhydride (PMDA) can effectively elongate recycled polyethylene terephthalate (rPET) chains, as indicated by an increase in force during reactive processing with a microcompounder, even at low contents of chain extender. In contrast, no significant change in force was observed for polybutylene terephthalate (PBT), suggesting that the reaction between PMDA and rPET is more favorable than that between PMDA and PBT. Differentiated evaluations of the reaction-related rate constant further supported these findings, as the reaction’s activation energies was 34% lower for rPET compared to PBT-dominant blend. Detailed rheological analyses of the microcompounder materials also allowed to assess the characteristics for foaming. As the PBT content increased, a significant rise in viscosity and a decrease in the loss factor were observed. Additionally, the proportion of branched chains systematically increased from rPET to PBT-dominant blend.