Stringiness and Spinnability of Polymer Solutions

Spinnbarkeit is a term which describes a fluid’s tendency to form long, thin, persistent threads. Synonymous to properties like stringiness and spinnability, spinnbarkeit is an important metric in food applications such as sauces and syrups for texture and mouthfeel, health and wellness formulations such as saliva substitutes that aid in cases of xerostomia, and in this study, fiber formation for spinnable solutions. For many of these applications, polymer solutions undergo extensional flows during the manufacture and use of the products in which they are incorporated. While these solutions have been studied extensively under shear flows, a better understanding of their behavior under extension is still needed. To understand the correlation of spinnability and stringiness to extensional rheological properties, polyvinylpyrrolidone (PVP), a water-soluble, non-ionic, synthetic polymer will be incorporated. PVP is a commonly used polymer in coatings and printing techniques and has many highly sought-after properties, making it a prime candidate for many different applications, namely spinnability and stringiness studies. This contribution characterizes the extensional behavior of aqueous PVP solutions using Dripping-onto-Substrate rheometry protocols. Through the visualization and analysis of an unstable liquid bridge of aqueous PVP solutions, formed between a dispensing nozzle and a partially wettable substrate, extensional relaxation times and extensional viscosity are extracted. Extensional rheological properties are then correlated to stringiness and spinnability of polymer solutions.