Electrostatic Application of Carpet Yarn Spin Finishes as a Strategy for Reducing Environmental Water Pollution: Theoretical Basis

High-speed processing of synthetic yarns into carpet and textile consumer products generally requires application of friction-reducing coatings onto the fibers. Due primarily to lack of uniformity of the fiber coating achieved by conventional application methods, excess spin finish up to 1.5-2 wt.% is routinely topically applied to the peripheral surface of the coalesced fiber bundle at the time of "spinning" polymeric fibers to ensure satisfactory performance. These yarn spin finishes unfortunately present significant air and water pollution concerns in the final stages of production, contributing up to 60%-70% of the chemical oxygen demand (COD) pollution load of wastewater effluents from carpet manufacturing plants. This paper reports the theoretical basis for an electrostatic process and engineering prototype for the precharging of high-speed dielectric filament arrays, the electrohydrodynamic spray application of charged spin finish thereon, and the net charge balance/neutralization of fibers comprised of such coated filaments. Consistent with practically attainable surface charge limits (e.g., 25 muC/m²) and spray charge limits (e.g., 10 mC/kg), attractive forces typically 60- to 120-fold greater than gravity are theoretically predicted for charged-finish droplets at 20 and 10 droplet-diameter spacings, respectively, from an oppositely charged filament. Prototype evaluations online at a full-scale 15-m/s polymeric fiber production unit will subsequently be reported