A Study on the Influence of Polypropylene Melt Flow Index on Nonwoven Fibers Produced Through Hot Melt Centrifugal Spinning

A hot melt centrifugal spinning process is used to manufacture polypropylene nonwoven textile such as those found in the filtering layers of medical masks. The fiber morphology and diameter distribution is influenced by the extrusion geometry and the polymer viscosity, often characterized by its melt flow index. These important geometric and physical aspects and their effects on the fiber quality are investigated in this work. The characteristics of the obtained nonwoven textile are also compared to those of the filtering layers found in a medical mask, usually made with the meltblown process. A custom-designed open-source lab-scale centrifugal spinning apparatus and the spinneret from a commercial cotton candy machine were used. This device was built at a very low cost while good quality fibers may be obtained compared to electrospinning. Its versatility allows to easily change the extrusion features. Here, a grid, nozzles, and a nozzlefree geometry, in which the polymer is extruded through a slit, were used. The behavior of five grades of polypropylene with five different melt flow indexes were compared in this process. Results show that fiber morphology improves when using the nozzle and nozzlefree geometries with a high melt flow index polymer, which were closer to the medical mask filtering layer.