Rheological properties of poly (vinylpiyrrolidone) as a function of average molecular weight and its applications

Polyvinylpyrrolidone (PVP) is an attractive material due to its solubility in aqueous and organic solvents, excellent film forming capability, and its ability to act as a dispersant in colloidal suspensions and slurries. These characteristics of PVP have led to its use in a large variety of formulations for pharmaceutics, food, personal care, or coatings, paintings, and printing applications. It is also widely used as organic additive, i.e. dispersant for ceramics. Regardless of the application, the control over the polymer behavior in solution is required for an efficient optimization of the formulation. Specifically, understanding the rheological properties is of paramount interest. Among the different factors that influence the rheological behavior, viscosity average molecular weight of the polymer is the most relevant. In this work, PVP polymers with various molecular weights have been characterized regarding their viscosimetric properties in ethanol. Average molecular weights (Mw, Mn, and Mz) have been determined by gel permeation chromatography (GPC), and then used in a numerical method to evaluate the viscosity average molecular weight (Mv) via the Mark-Houwink-Sakurada (MHS) equation. The MHS equation relates the intrinsic viscosity [η] of a polymer in a given solvent at fixed temperature to the molecular weight. The adopted method also enables for the evaluation of the two MHS equation parameters (a and K), and of the polydispersity correction factor (qMHS). The intrinsic viscosity, which is the inherent ability of a solute to increase the viscosity of a solvent, used in the MHS equation, has been evaluated via the dilution method. The knowledge obtained from this fundamental study on PVP behavior, has been successfully applied to different case studies.