Small angle light scattering studies of the melt blown process

Small angle light scattering, SALS, was used to study the effects of processing variables and material properties on the fiber diameter and fiber orientation near the die in the melt blown process. Several polypropylene resins of different molecular weights and molecular weight distributions were studied under different air velocities and mass flow rates. The fiber diameter experiments performed on a single hole die revealed that there is a large variation in the fiber diameter near the die, and that the attenuation process is not constant with respect to time. In the fiber orientation studies performed on a multihole die, the loss of orientation was monitored as a function of distance from the die by using the pseudo invariant to analyze the light scattering measurements. An inverse correlation was found between the loss of orientation of the fiber in motion and the formation of shot. Also, the transition from linear collimated fiber motion to random off-axis motion was documented. In addition, a quantitative scale in units of number of shot per basis weight was developed to measure the amount of shot in collected webs. These results indicated that the major mechanism for shot formation is the thermal bonding of the molten fibers near the die. Furthermore, there is potential for the development of SALS to be used as an on-line shot monitoring system for quality control and product improvement.