Influence of molecular weight, temperature, and extensional rheology on melt blowing process stability for linear isotactic polypropylene

Abstract

In this work, three linear isotactic polypropylenes with different weight-average molecular weights, Mw, and comparable polydispersities were used to produce nonwovens by melt blowing technology at two different temperatures, T. The air/polymer flow rate was changed to maintain the same average fiber diameter, resulting in a different broadness of fiber diameter distribution, which was quantified by the coefficient of variation, CV. The elasticity of the material was evaluated by the reptation-mode relaxation time, λ1, and the Rouse-mode reorientation time, λ2, determined from the deformation rate dependent shear viscosity data. Extensional rheology was evaluated using uniaxial extensional viscosity measured over a very wide range of strain rates (2 × 104 s−1–2 × 106 s−1) using entrance pressure drop and Gibson methods. An obtained plateau value of uniaxial extensional viscosity at the highest extensional strain rates, ηE,∞ (normalized by the three times zero-shear rate viscosity, η0), and the minimum uniaxial extensional viscosity, ηE,min, were related to Mw and T using simple equations. It has been found that the stability of fiber production captured by CV depends exclusively on the extensional properties of the polypropylene melts, namely, ηE,U,∞3η0 and ηE,U,min. These findings are important especially with regard to the stable production of polymeric nanofibers by melt blowing technology.