GB489496A - Improvements in or relating to the treatment of textiles - Google Patents

Abstract

Cellulosic materials, especially bast fibres such as linen, jute or hemp, are bleached with a minimum of chemical degradation of the cellulose in a process comprising at least two stages, viz. a treatment with a hypochlorite solution maintained within a substantially neutral pH range, approximately 6 to 8, by means of a buffer salt and a subsequent treatment with an alkaline solution of an oxidizing bleaching agent, the alkalinity, when a hypochlorite is used, being such that pH is >8. The materials are preferably subjected to a preliminary treatment with a wetting-out agent and/or with an alkaline scouring liquor and are preferably subjected to an acid sour between the above two stages of the treatment. Specified buffer salts are alkali metal bicarbonates, phosphates and borates. The treatment with the buffered hypochlorite solution is advantageously effected in the absence of actinic rays. In examples: (1) hanks of linen yarn are scoured for 3 hours with a soda ash solution at 65 DEG C., washed, treated in subdued light for 1/2 hour on a reeling machine with a solution at 14 DEG C. of bleaching powder buffered with sodium bicarbonate to pH = 6.5, rinsed, treated for 1/2 hour with a cold dilute hydrochloric acid solution, washed, treated for 3 hours with an alkaline solution at 65 DEG C., made up with sodium peroxide, sulphuric acid and sodium silicate, washed and dried to obtain a good half-white bleach; (2) linen yarn is scoured for 2 1/2 hours with a soda ash solution at 65 DEG C., washed, reeled for 1/2 hour in a solution at 15 DEG C. of bleaching powder buffered with disodium phosphate to pH = 6.8, rinsed, soured, washed and treated for 2 1/2 hours with an alkaline peroxide solution as in (1) to obtain a better than half-white bleach; (3) linen yarn, treated as in (1) except for the final drying, is immersed for 1/2 hour in a hypochlorite solution at 15 DEG C. buffered with sodium bicarbonate, washed and treated for 3 hours with an alkaline peroxide solution at 65 DEG C. made up as in (1) using half the quantities of peroxide and acid, washed, subjected to a repetition of the hypochlorite treatment using a solution containing less available chlorine, washed, treated with a dilute sodium thiosulphate solution, washed and dried to obtain a full white bleach; (4) hemp yarns is scoured for 3 hours with dilute caustic soda solution at 70 DEG C., washed, reeled for 1/2 hour in a buffered hypochlorite solution at 15 DEG C. as in (1), rinsed, soured, washed, treated for 3 hours with an alkaline solution at 65 DEG C. made up with hydrogen peroxide, sodium silicate and caustic soda, washed and dried to obtain a three-quarter white bleach; (5) a flax-jute mixture yarn is scoured for 3 hours in dilute caustic soda at 60 DEG C., washed, reeled for 1/2 hour in a solution at room temperature of bleaching powder buffered with sodium bicarbonate, washed, treated with an alkaline peroxide solution as in (4), washed and dried; (6) cloth is scoured for 5 hours in first a stronger and then a weaker soda ash solution at 75 DEG C., washed, treated for 4 hours with a buffered hypochlorite solution at room temperature, rinsed, soured, washed, treated for 5 hours in an alkaline peroxide liquor at 75-80 DEG C., rinsed, soured, washed, treated for 3 hours with a weaker buffered hypochlorite solution, washed, soured, washed, treated with a still weaker buffered hypochlorite solution, washed and antichlored. Specifications 339,550, [Class 15 (i)], and 401,199 are referred to.