Abstract
A hot melt centrifugal spinning process is used to manufacture polypropylene nonwoven textile such as those found in the filtering layers of medical masks. This process is based on a rotating heated and punctured emitter, a “spinneret”, containing the molten polypropylene polymer. As the emitter rotates at high speed, the centrifugal force expels the polymer melt through the emitter's orifices. As it is extruded, the polymer melt elongates and solidifies into fibres that are collected at some distance from the emitter, similar to a cotton candy machine. The fibre 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 fibre 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. Three spinneret extrusion features are used, namely, a grid, nozzles and a nozzlefree geometry in which the polymer is extruded through a slit. Five grades of polypropylene with five different melt flow indexes were used in the process. Results show that fibre 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.
