Flow Blurring-Enabled Production of Polymer Filaments from Poly(ethylene oxide) Solutions

Abstract

Flow blurring (FB) atomizers are relatively simple yet robust devices used for the generation of sprays from solutions of a wide range of viscosities. In this work, we have demonstrated that FB devices may also be applied for massive production of liquid filaments from polymeric solutions. They can later be transformed into solid filaments and fibers, leading to the production of so-called fiber mats. The liquid precursors consisted of poly(ethylene oxide) (PEO) solutions of varying molecular weights (10 5 [100k] to 4 × 10 6 g/mol [4M]) and concentrations. The FB device was operated in the gas pressure range of 3–6 bar. Except for solutions of PEO 100k, all solutions exhibited a shear thinning behavior. For massive filament production, a threshold polymer concentration ( c t ) was identified for each molecular weight. Below such concentration, the atomization resulted in droplets (the classical FB functioning mode). Such a threshold value decreased as the PEO molecular weight increased, and it coincides with the polymer coil overlap concentration, c *. The viscoelastic nature of the solutions was also observed to increase with the molecular weight. A 3.2 dependency of the zero-shear rate viscosity on a so-called Bueche parameter was found for filament production, whereas a nearly linear dependency was found for droplet production. In general, the mean diameter of the filaments decreased as they traveled downstream from the atomization point. Furthermore, at a given distance from the atomizer outlet and gas pressure, the mean filament diameter slightly shifted toward larger sizes with increasing PEO molecular weight. The tendency agrees well with the calculated filaments’ Deborah number, which increases with PEO molecular weight. The approach presented herein describes a high-throughput and efficient method for the massive production of viscous filaments. These may be transformed into fibers by an on-line drying step.

On the Ejection of Filaments of Polymer Solutions Triggered by a Micrometer-Scale Mixing Mechanism

“…The solutions’ properties at concentrations used herein are summarized in Table 1 . These concentration values were selected because they are either incipient concentrations for semi-dilute solutions [ 24 , 25 ], just were polymer chains’ interactions become relevant, or concentrations were chains are known to strongly interact.…”

“…Overlapping of polymer coils is key in filament formation with FB, since if , droplets will be ejected from the atomizer as reported by Hermosín-Reyes et al [ 25 ]. Conversely, filaments will be ejected if is at least of order 1 [ 23 , 24 ]. In the present work, the concentration regime where is analyzed and thus filament generation is expected.…”

“…Another parameter to take into account is the so-called entanglement concentration, , the critical concentration above which the polymer coils begin to form entanglements, which has been calculated for all solutions with . is the number of monomers between entanglements and is obtained as the ratio of the molecular weight of entanglement ( to the molecular weight of the monomer ( ), that is [ 24 ]. For PEO in water, the exponent is and (in mL mol/g 2 ) [ 27 ].…”

“…The typical setup used for atomization experiments is shown in Figure 3 and is similar to that in our previous publications [ 23 , 24 , 25 ]. In this case, the atomizer was mounted on an optical table using high-precision components, which allowed its vertical displacement, up and down.…”

“…Solutions with concentrations, , of 0.5 wt.%, 0.8 wt.%, 1.5 wt.%, and 1.6 wt.% were prepared. For atomization experiments a commercial FB atomizer (Ingeniatrics Tecnologías, Seville, Spain) with was used as in our previous studies [ 23 , 24 , 25 ].…”