Effect of molecular weight and extensional rheology on melt blown process stability for linear isotactic polypropylenes

Abstract

Two linear isotactic polypropylenes with different molecular weight have been used to produce nonwovens via melt blown technology in order to understand role of molecular weight and extensional rheology on fiber diameter distribution. Extensional rheology was assessed by the strain rate dependent uniaxial extensional viscosity (estimated from the entrance pressure drop using the Gibson method) as well as through infinite shear to zero-shear viscosity ratio η∞/η0 (obtained directly from the shear viscosity data measured in a very wide shear rate range), which was shown to be related with temperature and basic molecular characteristics of given polymers via a simple equation. This allowed us to determine η∞/η0 ratio for additional nine polypropylene melt blown nonwovens with known weight average molecular weight and coefficient of fiber diameter variation, taken from the open literature. Obtained results indicates that firstly, an increase in the molecular weight decreases η∞/η0 as well as maximum attainable normalized extensional viscosity ηE,∞/3η0 and secondly, there exists optimum η∞/η0 ratio, at which the coefficient of fiber diameter variation is minimal. © 2019 Author(s).