An experimental investigation on the production of microfibers and the web defect known as shot for the melt blowing process

An extensive experimental investigation was performed to determine the effect that processing parameters, fiber flight dynamics, and polymer Melt Flow Rate (MFR) had on the production of microfibers and the web defect known as shot, using the melt blowing process. Both single and multi- hole die configurations, utilizing polypropylene resins ranging between 400 and 1385 MFR, were used during this investigation. Among the processing parameters that were examined were the polymer temperature, air jet temperature, and air jet exit velocity. Using the typical melt blowing configuration, the average fiber diameter and shot intensity values decreased with increasing air jet exit velocity for the various MFR polymers investigated. Also, an increase in polymer temperature led to a decrease in average fiber diameter values and an increase in shot intensity values. As the air jet exit velocity was increased to supersonic speeds using a converging - diverging nozzle configuration, the average fiber diameter approached an asymptotic value between 1.8 and 4.5 microns. At low die stagnation pressures (subsonic flow conditions), fibers produced using a "downstream" converging - diverging nozzle were smaller than those produced using the classical melt blowing configuration. Stop motion photography and high speed video analysis indicated that the primary mechanism causing the production of shot was not a "snapping" back phenomenon, but rather, the "touching" or colliding of molten fibers close to the die exit plane. Two types of shot were identified; these were: (1) a shot particle within the web which resembled a film spot and showed signs of melting the adjacent fibers and (2) a shot particle within the web which showed no signs of web melting.