Theoretical Interpretation of Reduction in Melt Viscosity by Solubilized Gaseous Component

3 Theoretical Interpretation of Reduction in Melt Viscosity by Solubilized Gaseous Component 

Specifically, on the basis of free-volume theory, Doolittle (1951) has related the zero-shear viscosity (jjq) of an amorphous polymer to relative (fractional) 

Several research groups used free-volume theory, including the WLF equation and its analogues for concentration and pressure, to explain the experimentally observed reduction in viscosity of molten polymers with solubilized gaseous component. However, there is a great deal of confusion in the literature that has dealt with this problem. Because of its importance, we address this issue below. 

In analyzing the viscosity data at various temperatures and shear rates, which were obtained via slit rheometry for molten PS, PMMA, polypropylene (PP), and LDPE with solubilized CO2 at varying concentrations, Royer et al. (2000, 2001) used the following expressions, analogues of Eq. (13.13), for the concentration-dependent shift factor at temperatures below T + 100 

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