Rheological characterization of unmodified and chemically modified poly (ethylene terephthalate) resins

Intrinsic viscosity (IV) has often been misused for estimating both melt viscosity and elasticity of poly(ethylene terephthalate) (PET). A rheological study was conducted to determine the variations between a virgin unmodified PET and a recycled and chemically modified PET, both having a reported nominal IV of 0.95. The modified material had a larger melt viscosity (capillary and dynamic) than the virgin material (by an average of 61%). The extrudate swell, a better indicator of melt elasticity, of the modified was more than 110% greater than that of the unmodified material. Activation energies for melt viscosity and extrudate swell were found to be approximately 20 KJ/mol and 3 kJ/mol respectively, for the unmodified material at high shear rates. The melt viscosity for both materials was found to be best fitted by the Cross Model using a least-squares fit