Interrelationships of Pressure-Dependent Hole Fraction and Elongational Viscosity in Polymer Melts

The elongational flow behavior of polyethylene, polypropylene, polystyrene, poly(methyl methacrylate), and polycarbonate, temperatures from 70 to 290 °C and pressures up to 70 MPa, is examined with the Yahsi-Dinc-Tav (YDT) model and its particular case known as the Cross model. The viscosity data employed in the range of 3-405 s-1 elongational rates were acquired from the literature at ambient and elevated pressures. The predictions and the fitting results of the proposed YDT model with the same measurement data are compared with the Cross model. The average absolute deviations of the viscosities predicted by the YDT model range from 0.54% to 9.44% at ambient and 1.95% to 6.28% at high pressures. Additionally, the linear formulations derived from the YDT model are employed to relate the viscosity with temperature and hole fraction (“thermooccupancy” function) at zero level of elongational rate and constant elongational rate along with constant elongational stress. The effects of the four viscosity parameters (such as transmission and activation energy coefficients in these equations) on the elongational viscosity are analyzed in detail and some conclusions on the structural differences for the polymers are discussed.

Hole Fraction Dependence on Linear Viscosity of PS, PP and ABS

A linear dependency of zero shear, constant shear-rate and constant shear-stress viscosities with temperature and hole fraction (“thermo-occupancy” function) was derived for polyacrylonitrile-butadiene-styrene (ABS), polypropylene (PP) and polystyrene (PS). The relation of viscosity parameters, such as transmission coefficient and a measure of activation energy coefficient, with shear-rate and shear-stress was also investigated and some conclusions on the differences for the studied polymers were discussed. In particular, it was found that, for all materials, the derivative of logarithm of viscosities at zero shear, constant shear-rate and constant shear-stress decreases with decreasing rate with the hole fraction.

Free Volume from Pressure and Temperature Dependent Viscosity and from PVT Measurements for Homo- and Copolymers

Pressure and temperature dependency of shear and elongation viscosity and the thermal expansivity and the compressibility determined from PVT data were investigated for propylene homo- and propylene-1-pentene, -1-hexene, 1-heptene and -nonene copolymers and ethylene homopolymer and ethylene-1-butene, 1-pentene and 1-hexene copolymers. The short branching degree dependence of thermal sensitivity and pressure coefficient and the thermal expansivity and the compressibility has been determined. The fractional free volumes were calculated from the viscosity and PVT curves and the thermal expansion coefficient and compressibility factor of fractional free volume were determined. The temperature, pressure and stress dependence of fractional free volume was investigated. The fractional free volume calculated from viscosity data were compared from values comes from PVT measurement. A conversion equation was suggested.