Electrostatic application of carpet yarn spin finishes as a strategy for reducing environmental water pollution: theoretical basis

High-speed processing of yarns into carpet and textile consumer products generally requires application of friction-reducing coatings onto the fibers. Such coatings, often totaling up to 1 1/2 - 2 wt% as applied both by the original fiber manufacturer and additionally by the final product manufacturer, facilitate trouble-free movement of the fibers across surfaces and through guides associated with weaving and other manufacturing operations. These yarn spin finishes unfortunately present significant air- and water-pollution concerns in the final stages of production. Their volatilization during heat-setting of yarns generates appreciable emission of VOC air pollutants in both the ambient and the workplace atmospheres. Their removal by product-washing operations results in spin finishes typically contributing up to 60-70% of the COD pollution load of wastewater effluents from carpet manufacturing plants. Due primarily to lack of uniformity of the fiber coating achieved by conventional application methods, excess spin finish is routinely dispensed at the time of "spinning" polymeric fibers to ensure satisfactory performance. Furthermore, it is topically applied to the peripheral surface of the coalesced fiber bundle and not more effectively onto the individual filaments, which comprise the bundle as they issue from the spinnerets; typically 60-120 such filaments are brought together to comprise one fiber threadline. This paper reports the theoretical basis of an electrostatics-based 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 such coated fibers. Prototype evaluations on-line at a full-scale 15 m/s polymeric-fiber production unit will subsequently be presented.