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 polydispersity 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, 1, and the Rouse-mode reorientation time, 2, 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 (2×10 4 -2×10 6 1/s) using entrance pressure drop and Gibson method. Obtained plateau value of uniaxial extensional viscosity at the highest extensional strain rates, E,  , (normalized by the three times zero-shear rate viscosity, 0) and the minimum uniaxial extensional viscosity, E,min were related to Mw and T using simple equations. It has been found that the stability of fibers production captured by CV depends exclusively on the extensional properties of the polypropylene melts, namely E,U, 0 3    and E,U,min. These findings are important especially with regard to the stable production of polymeric nanofibers by melt blowing technology.

A review of processing strategies to generate melt-blown nano/microfiber mats for high-efficiency filtration applications

“…In general, decreasing molecular weight or increasing melt temperature increases (e.g., due to the decreasing reptation-mode relaxation time) the CV of fiber diameter distribution. They also found that the CV of fiber diameter distribution significantly decreases due to the extensional strain hardeningat the post die zone [90]. They stated that increased strain hardening in uniaxial extension at post die zonecould withstand inhomogeneous stretching in the post-die area, which reduces CV of fiber diameter distribution.…”

“…The decrease in elongation causes the increase in fiber diameter and fewer fiber entanglements. Tan et al 90 reported that increasing melt elasticity increased the fiber diameter and decreased the coefficient of variation (CV) (also known as normalized width of the fiber diameter distribution) while increasing viscosity did not significantly affect the CV. Drabek and Zatloukal [89] reported that polymer molecules chain branching could lower the CV of fiber diameter distribution, while they stated chain branching did not significantly influence the average fiber diameter.…”

Airflow, Fiber Dynamic Whipping, and Final Fiber Diameter in Flush Sharp-Die Melt Blowing with Different Air-Slot Widths

“…The spinning die is the core component of a melt-blown device due to the fact that the die structure has a crucial effect on the air flow field. Die types include slot die, ,, sharp die, ,− and annular die; , these dies were commonly used in the open literature. This paper focuses on the effect of flush sharp-die air-slot width on the fiber quality under the same inlet condition.…”

Overview of the Fiber Dynamics during Melt Blowing

“…SEM is another widely applied tool for measuring fiber diameter. ,,,,,− SEM images have a larger magnification and improved clarity than optical microscope images. However, SEM has several limitations.…”