A Corona Discharge Method of Producing Shrink-Resistant Wool and Mohair

Abstract

Wool fibers were exposed to corona discharge under a variety of voltages, fre quencies, temperatures, and gaseous environments. Optimum temperatures to give shrink resistance were between 100 and 140°C. Substantial shrink resistance was obtained with an exposure time as short as 2 sec. Oxygen slightly improved the results obtained in air. but nitrogen markedly reduced the effectiveness of the treatment. Fibers had to be thinly spread in the corona cell for uniform effect. Reaction rate increased with voltage and frequency and with center-tap grounding of the transformer. Small holes were burned in the samples at 400-800 cps. but burning could he prevented by using a corona cell with dielectric material at both electrodes. Corona discharge treatment increased the cohesive force of top and the tensile strength of yarn, perhaps because of increased single-fiber surface friction. Unchanged dyeing rates, unchanged solubility in acids and bases, and unchanged single-fiber tensile properties indicate that the reaction is limited to the cuticle. Application of cationic softeners at low pII eliminated shrink resistance; removal of the cationic compounds restored the shrink resistance. The corona treatments cause fibers to acquire a positive electrostatic charge. Fabric could not be made shrink resistant because the gaseous reactants did not penetrate adequately. However, shrink-resistant fabric was produced from 'continuously treated card webbing. Difficulty was encountered in pin drafting the sliver. Fiber and fabric hand was usually somewhat harsh, depending on degree of treatment, but softening agents at neutral or higher pH restored hand without significant loss of shrink resistance, No chemicals are required for the process, only electrical power. At one treatment level, electrical cost is estimated to be 0.05¢ or less per pound of wool treated. Low processing cost should make the method commercially attractive. The treatment can also make mohair shrink resistant.