CHAIN EXTENSION OF RECYCLED POLY(ETHYLENE-TEREPHTHALATE) WITH 2,2'-BIS(2-OXAZOLINE)

2,2'-Bis(2-oxazoline) was used as a chain extender during processing in a twin-screw extruder with the aim of counteracting degradation phenomena in recycled poly(ethylene terephthalate) (PET). The same experiments were performed on fiber-grade PET for comparison purposes. Rheological characterization showed that while the melt viscosity of fiber-grade PET at constant temperature and shear rate is quite constant with time, that of recycled PET decreases dramatically. By addition of oxazoline, an increase of melt viscosity occurs for fiber-grade PET, whereas for recycled PET, thermal and hydrolitic degradation effects are partially compensated. Characterization was performed by solution viscosity measurements, gel permeation chromatography, and COOH end-group titration on samples obtained at variable residence times at 280-degrees-C. Lower molecular weights accompanied by a higher amount of COOH were observed; the use of oxazoline resulted in higher molecular weights and lower COOH concentrations at equal residence times, while polydispersity did not vary. (C) 1993 John Wiley & Sons, Inc.