Dynamics of formation of poly(vinyl alcohol) filaments with an energetically efficient micro-mixing mechanism

Abstract

We present a pneumatic approach for massive production of poly(vinyl alcohol) (PVA) filaments based on a mixing mechanism at the micrometer scale using so-called Flow Blurring (FB) atomizers. This micro-mixing is triggered by a turbulent, bubbly motion generated by implosion of a gas current into a liquid feeding tube. The energy of the gas, the liquid viscosity, and the geometry of the atomizer play an active role in the size and shape of the ejecta. The shear viscosity of aqueous solutions of PVA of various molecular weights was investigated to assess their rheological nature using a dimensionless parameter based on the solutions’ concentration and the polymer’s molecular weight and its entanglement molecular weight. The solutions exhibited a shear thinning behavior at low shear rates and a Newtonian behavior at moderate rates. PVA solution with viscosity above the threshold value is prone to forming filaments during atomization with FB devices. Analyses of the dynamics of the atomization revealed two main types of ejections depending on the liquid flow rate and viscosity: either a bundle of filaments formed from within the atomizer or a more continuous single structure developed in the vicinity of the atomizer exit. Furthermore, based on Kolmogorov’s energy cascade, we propose a scaling law for the mean filament diameter as a function of liquid properties, atomizer geometry, and imposed pressure. The present work may have significant implications in the large-scale processing of liquids leading to useful materials.