On the non‐newtonian viscous behavior of polymer melts in terms of temperature and pressure‐dependent hole fraction

Abstract

A new theoretical non‐Newtonian viscosity model is developed by taking the fractional series expansion of Eyring's shearing strain rate. A broad range of experimental rheological data of various polymer melts including polyethylenes, polypropylene, polystyrene, poly (methyl methacrylate), and polycarbonate are fitted well using the proposed model. From the model; zero shear, constant shear‐stress and constant shear‐rate viscosities are derived as a linear function of viscosity related quantity, Yh, called “thermo‐occupancy function” and their coefficients are discussed in detail. The thermo‐occupancy function is expressed in terms of temperature and structural vacancies such as hole fraction computed from the Simha‐Somcynsky Hole Theory (SS). In addition, the derivative of the logarithm of viscosities with respect to the hole fraction, named as viscoholibility, is observed decreases with the increasing hole fraction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40540.

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

“…We have shown previously that the Yahsi-Dinc-Tav (YDT) non-Newtonian viscosity model fitted well the shear viscosity data particularly at high pressure [6]. For the bulk structured polymers like PMMA, PC, and PS of which the viscosity values are high comparing the remaining polymers, the outcomes were found reasonable as well.…”

“…The characteristic scaling parameters, * , * , * as well as temperature-and pressure-dependent hole fraction h(P,T) parameter can be determined by superimposing experimental PVT data on the theoretical̃-̃-̃surface with the use of (3) and (4). The model is advantageous in that it provides the complementary hole fraction, h, which has been correlated with transport properties and explains the mechanical behavior of polymers such as viscosity [6,10], ionic conductivity [20], etc.…”

“…In his study, while the XPP model accurately describes the elongational viscosity up to elongational rate about 10 s -1 , at higher elongational rates, poor estimation is accomplished. In a similar manner, the elongational flow, in this paper, has been represented by the YDT (Yahsi-Dinc-Tav) model which has been successfully employed for the shear viscosity previously [6]. The model works successfully on both temperature-and pressure-dependent zero level of viscosities and critical stress parameter with a single fitting parameter.…”

“…In recent years there has been a considerable interest in free volume concept as a means to describe the mechanical behavior of polymer materials, particularly viscosity [6][7][8][9][10][11][12][13][14]. The term "free volume", which is expressed as an additional space needed for the thermal motion, is first introduced in Van der Waals' thesis [15].…”

“…Sedlacek et al [11] applied their modified Utracki's hole fraction model to linearize the zero shear and constant shearstress viscosities data. In recent articles, the YDT model by Dinc et al [6,13,14] offered a linear relation between shear-rate/shear-stress viscosities and temperature-and hole fraction-dependent thermooccupancy function for various polymers. Although to date several derived models have been developed to account for the relation of shear viscosity to the free volume [6][7][8][9][10][11][12][13][14], almost no studies have been carried out for the elongational viscosity.…”