Abstract:

The effects of hydrostatic pressure on the rheological behavior of PET with different intrinsic viscosities were studied using a capillary rheometer and its matched counterpressure chamber to control the pressure of capillary outlet in an average pressure of 5–50 MPa. The results indicated that the shear viscosity of PET exponentially increased with increasing average pressure, conforming to the Barus equation. The pressure coefficient decreased with increasing intrinsic viscosity, , when the intrinsic viscosity increased from 0.48 to 0.67 dl/g, the press coefficient decreased significantly, and this change with the increase in the shear rate was attenuated. When intrinsic viscosity ≥0.67 dl/g, the press coefficient changed slightly with intrinsic viscosity. The press coefficient decreased with increasing the shear rate. When the intrinsic viscosity was 0.48 dl/g, the change was significant; however, intrinsic viscosity ≥ 0.67 dl/g, the press coefficient changed slightly. The press coefficient decreased with increasing temperature and the change rate decreased significantly with the increase of temperature. The changes in Press coefficient of PET in different intrinsic viscosity indicated that when the intrinsic viscosity and the glass transition temperature was low, the affect of pressure on press coefficient was significantly. When the intrinsic viscosity were 0.67 and 1.00 dl/g, the decrease of the free volume were no longer obvious, therefore the affect of pressure on press coefficient were insignificant.

Key words: PET, pressure coefficient, intrinsic viscosity, rheological behavior