This work summarizes the current state of knowledge in area of meltblown technology for production of polymeric nonwovens with specific attention to utilized polymers, die design, production of nanofibers, the effect of process variables (such as throughput rate, melt rheology, melt temperature, die temperature, air temperature/velocity/pressure and die-to-collector distance and speed) with relation to nonwoven characteristics as well as to typical flow instabilities such as whipping, die drool, fiber breakup, melt spraying, flies, generation of small isolated spherical particles, shots, jam and generation of nonuniform fiber diameters.

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In this work, linear isotactic polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) miscible blend, both having comparable weight average molecular weight, zero-shear viscosity, and polydispersity index, were used to produce nonwovens via melt blown technology in order to understand the role of long chain branching in the fiber diameter distribution. Basic morphological characteristics of produced nonwoven samples have been determined using digital image analysis of scanning electron microscope images considering different magnifications to capture nanofibers as well as microfibers. At the same air flow rate, polymer flow rate, and temperature, the average fiber diameters were the same, 1.6 μm, but the coefficient of variation, CV, was greater for the linear PP than for the blend. Material elasticity was assessed by reptation-mode relaxation time, λ, determined by fitting of deformation rate dependent shear viscosity by Cross and Carreau-Yasuda models as well as via fitting of frequency dependent loss and storage moduli master curve by a two-mode Maxwell model. It was found that λ is higher for LCB-PP in comparison with L-PP and the Cross model gives a meaningful relaxation time while the Carreau-Yasuda model does not despite giving a better numerical fit. Extensional rheology was assessed by the strain rate dependent uniaxial extensional viscosity (estimated from the entrance pressure drop using the Gibson method). The infinite shear to zero-shear shear viscosity ratio η∞/η0 (obtained directly from the shear viscosity data measured in a very wide shear rate range) was shown to be proportional to the maximum normalized extensional viscosity at very high extensional strain rates, ηE,∞/(3η0). η∞/η0 was related to temperature and basic molecular characteristics of given polymers via simple equation. It was observed that extensional viscosity for both samples first decreases with increased extensional strain rate to its minimum value at 200 000–400 000 1/s and then increases to plateau value, ηE,∞ (corresponding to the maximum chain stretch) at about 2 ⋅ 106 1/s. At low deformation rates, extensional viscosity is higher for LCB-PP in comparison with L-PP, but the trend is switched at very high deformation rates; ηE,∞ (and also ηE,∞/3η0) becomes lower for LCB-PP in comparison with L-PP. These results suggest that high stability of LCB-PP blend can be explained by its higher stretchability at very high deformation rates (occurring at the die exit where an intensive fiber attenuation takes the place) and its lower stretchability at medium and low deformation rates, at which melt/air inertia driven bending instability called whipping occurs.

Dynamics of linear polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) miscible blends, having weight average molecular weight between 64-78 kg/mol, was investigated via high shear rate rheology. Results obtained were compared with the corresponding data for L-PP. Highshear rate secondary Newtonian plateaus, , were identified at three different temperatures for well entangled L-PP/LCB-PP blends above shear rates of 2 • 10 6 1/s and their dependence on weight average molecular weight, Mw, was successfully related as  () = ∞ () • with the exponent n=1.010.

In this work, three linear isotactic polypropylenes with different weight-average molecular weights, Mw, and comparable polydispersity were used to produce nonwovens by melt blowing technology at two different temperatures, T. The air/polymer flow rate was changed to maintain the same average fiber diameter, resulting in a different broadness of fiber diameter distribution, which was quantified by the coefficient of variation, CV. The elasticity of the material was evaluated by the Reptation-mode relaxation time, 1, and the Rouse-mode reorientation time, 2, determined from the deformation rate dependent shear viscosity data. Extensional rheology was evaluated using uniaxial extensional viscosity measured over a very wide range of strain rates (2×10 4 -2×10 6 1/s) using entrance pressure drop and Gibson method. Obtained plateau value of uniaxial extensional viscosity at the highest extensional strain rates, E,  , (normalized by the three times zero-shear rate viscosity, 0) and the minimum uniaxial extensional viscosity, E,min were related to Mw and T using simple equations. It has been found that the stability of fibers production captured by CV depends exclusively on the extensional properties of the polypropylene melts, namely E,U, 0 3    and E,U,min. These findings are important especially with regard to the stable production of polymeric nanofibers by melt blowing technology.