Further Aspects of Bisulphite Setting of Wool Carpet Yarns in a Tape Scouring Machine

The benefit of using a hot sodium perborate solution, as well as hot-water rinsing, as a stabilizing treatment in the reductive setting of wool carpet yarn is minimal. Using a tape scouring machine, yarn should be treated with a solution prepared from sodium metabisulphite and adjusted to pH7, followed by thorough rinsing with hot water, to set the twist. A bisulphite solution of pH6 has poor pH stability at 85 ºC, but at pH 7 the pH is stable for at least 5 h. The bisulphite concentration decreases with time at both pH values at this temperature. The use of alternatives to sodium metabisulphite, e.g. moboethanolamine sulphite, needs careful consideration on a cost-benefit basis. On a basis of equal SO2 vontent, the degree of set is similar with various compounds