The idea of "Nanoval technology" origins in the metal injection molding for gas atomization of metal powders and the knowledge of spunbond technologies for the creation of thermoplastic nonwovens using the benefits of both techniques. In this study, we evaluated processing limits experimentally for the spinning of different types of polypropylene, further standard polymers, and polyphenylene sulfide, marked by defect-free fiber creation. A numerical simulation study of the turbulent air flow as well as filament motion in the process visualized that the turnover from uniaxial flow (initial stretching caused by the high air velocity directed at the spinning die) to turbulent viscoelastic behavior occurs significantly earlier than in the melt-blown process. Modeling of the whole process showed that additional guide plates below the spinneret reduce the turbulent air flow significantly by regulating the inflow of secondary process air. The corresponding melt flow index of processible polymer grades varied between 35 g·10min-1 up to 1200 g·10min-1 and thus covering the range of extrusion-type, spunbond-type, yarn-type, and meltblown-type polymers. Hence, mean fiber diameters were adjustable for PP between 0.8 and 39.3 μm without changing components of the process setup. This implies that the Nanoval process enables the flexibility to produce fiber diameters in the typical range achievable by the standard meltblown process (~1-7 μm) as well as in the coarseness of spunbond nonwovens (15-30 μm) and, moreover, operates in the gap between them.
Keywords: fibers; meltblown; modeling; nonwovens; numerical simulations; polymers; processing; rheology; spinning; spunbond.