Concentrated solution and melt rheology of poly(vinylidene fluoride)

Abstract

The concentrated solution and melt rheology of poly(vinylidene fluoride) [PVDF] were studied by using a falling needle solution viscometer, a Brookfield viscometer, and a Kayeness capillary rheometer. It was found that the concentrated solution (15 wt% in N‐dimethyl acetamide) rheology exhibited a different behavior for various grades of PVDF produced by different types of polymerization. While Newtonian behavior was found in one type of PVDF, shear thinning was found in another type. The power law model was used to describe the general solution behavior of these materials. Zero shear rate viscosity correlated well with the molecular weight (Mw) of the material. Melt viscosity of PVDF exhibited continuous shear thinning behavior throughout the whole range of shear rates. The data were best fitted by a second‐degree polynomial curve. Correlations were established between the molecular weight, molecular weight distribution, and the parameters of the polynomial curve. These correlations are useful for the prediction of various grades of PVDF designated for specific engineering applications. The correlations obtained from solution provided better and more accurate correlations to Mw parameters than those of melt rheology.

Rheological characterization of ethylene vinyl acetate copolymers

“…This value could be due to broadness of the molecular weight distribution10, 11 but it is also known that for low density polyethylenes, high exponent have been reported 12. Kraus and Gruver13 have also noted that high slope is obtained when the branch length is above the critical length for entanglement in polybutadienes.…”