Characterization of poly(ethylene terephtalate) after multiple processing cycles

Poly(ethylene terephthalate) (PET) pellets used for production of soft drink bottles were reprocessed in a single-screw extruder and cut into pellets in five processing cycles. The reprocessed pellets were characterized by its rheological, mechanical, and thermal properties. Carboxylic end groups number concentration and melt flow index were also determined. After three reprocessing cycles the mechanical properties and crystallinity degree changed drastically. Moreover, after five cycles we did not observe changes in the onset temperature of mass loss; therefore, the samples were thermally stable. However, an increase in melt flow index and carboxylic end groups concentration indicated a certain degree of mechanochemical degradation.