US2202334A - Treatment of textiles - Google Patents

Description

e-lsa FIPFiSB? IVII vv ea g gozezse Patented May 28, 1940 OFFICE TREATMENT OF TEXTILES Ernest Butterworth, Ballymena, Northern Ireland, and Bertram Pusey Ridge, Grappenhall, England, assignors to Imperial Chemical 1ndustries Limited, a corporation of Great Britain No Drawing. Application June 10, 1938, Serial 5 Claims.

This invention relates to "the treatment of textiles; and it comprises an improvement in the bleaching of bast fibers such as linen, jute, hemp and the like with p eutral hyp ochlo 'te followed by alkaline hydrogen peroxidefthe 'iniprsvemene being that the unbleached bast fibers are submitted to a preliminary treatment with a reducing material, usually a sulphite, prior to treating with hypochlorite and alkaline peroxide; all as more fully hereinafter set forth and as claimed.

In another and copending prior application Serial No. 183,396, filed January 4, 1938, of which this is a continuation-in-part, there is described and claimed a method of bleaching bast fibers and particularly linen fibers to obtain better whiteness with less loss of strength; the bast fibers being treated with a neutral hypochlorite and then with alkaline peroxide. We have discovered that a preliminary treatment of bast fiber with a reducing agent prior to the treatment with hypochlorite and hydrogen peroxide gives better results; a greater whiteness is secured without degradation of the cellulose. In securing the greater whiteness the solubility number, hereinafter defined, is not impaired.

The usual methods for the bleaching of cellulose in its various forms differ considerably; the methods being in each case adapted to the particular material. But whether the material is a short fiber like paper pulp or a long textile fiber, the methods are based on combinations of treatments with alkaline solutions and hypochlorite solutions, sours, antichlors and washes being used at the various stages when they are considered to be necessary. Treatments with solutions containing peroxides and persalts have also been used in conjunction with combinations of treatments of the above type. These various methods have resulted very largely from an empirical development over a long period, and while they can be operated to give very good results as regards whiteness, they are somewhat lengthy and frequently give rise to considerable chemical degradation of the cellulose. This is particularly true in the bleaching of linen and other bast fibres, and for this reason the description hereinafter will be directed more especially to the bleaching of linen in which the object is to obtain a maximum whiteness by an attack on the non-cellulose while minimizing as much as possible an attack on the cellulose. This is effected in using the process of the acknowledged copending application by a method in which, as more particularly appears in the examples found post, the un- In Great Britain June 16, 1937 bleached bast fiber is preliminarily treated with a reducing agent, usually a sulphite.

The chemical degradation of cellulose has an important influence in reducing the effective life of the bleached material, and therefore it is obviously desirable to avoid this type of attack on the goods being bleached. As a convenient means of expressing the degree of chemical degradation of line-n we use the term solubility number. This number furnishes a measure of the amount of the material soluble in caustic soda solutions under closely specified conditions, and since it is mainly the chemically degraded cellulose that dissolves under these conditions, high solubility numbers are associated with severe degradation and low numbers with but slight attack. The conditions and method of determining solubility numbers are set out in a paper by C. R. Nodder in The Journal of the Textile Institute 1931, 22, T. 416.

In our copending application Serial No. 183,396 we have described methods whereby bast fibres such as linen, can be bleached without undue attack on the cellulose as evidenced by the solubility number. These methods are essentially processes comprising at least two stages in one of which the materials are treated with a hypochlorite solution maintained within a substantially neutral pH range, by means of a buffer compound and in a subsequent stage or stages with an alkaline solution containing hydrogen peroxide.

This invention has as an object to devise an improved process of bleaching bast fiber material. A still further object is to devise a method whereby an optimum white can be obtained for any given solubility number. A still further object is to provide bast fiber material having a better white in relation to solubility number than has hitherto been possible. Further objects will appear hereinafter. These objects are accomplished by the following invention.

We have now found that in the treatment of bast fiber materials according to the above process an improved bleaching effect can be obtained without adversely affecting the tensile strength or increasing the chemical degradation of the material by giving the material a treatment with reducing agents prior to a treatment with neutral hypochlorite. Reducing agents, including sulphites, are often used as anti-chlors after a hypochlorite bleach; they are used to remove residual chlorine. We have found, however, that a treatment of bast fibers with one of these reducing agents in an alkaline solution prior to submitting to the action of a neutral hypochlorite gives us a better bleaching action with less attack on the fiber. The reducing agent may be an alkaline sulphite; that is, a solution of S02 with somewhat more alkali than is necessary to form a neutral sulphite. Other reducing agents such as hyposulphite, zinc formaldehyde sulphoxylate, etc., may be used.

Accordingly the present invention consists in the improvement or modification of the process of application Serial No. 183,396 in which the bast fiber materials are treated with a solution of a reducing agent prior to the treatment with the neutral hypochlorite solution. The introduction of this treatment does not preclude other treatments such as the usual preliminary steep or boil in an alkaline liquor, e. g. soda ash solution.

As reducing agents capable of being used in the process are alkali metal and alkaline earth metal sulphites, bisulphites, and hyposulphites and the corresponding acids. More particularly we have found that the sodium salts of sulphurous acid, sodium sulphite and sodium bisulphite are cheap and convenient reducing agents for use in the process and consequently we shall describe the process in greater detail with reference to these salts as applied to linen. When a bisulphite is added to an alkaline material it is of course con verted into a sulphite and if the goods are alkaline from the use of an alkaline liquor, the alkali present may sufiice for converting a bisulphite into a sulphite.

We have found that it is advantageous to carry out the treatment with sodium bisulphite at a somewhat elevated temperature, e. g. at 60 C. up to boiling point. As there appear to be no great differences in the quality of the material resulting from the differences of temperature we prefer for reasons of economy to use the lower portion of the above range, that is to treat the goods at about 70 C. For a similar reason we prefer to limit the concentration of the sodium bisulphite in the liquor to about 0.5% and to use a treatment time of about an hour. With regard to the concentration, lower figures, e. g. 0.1%, have been found to give results satisfactory for many purposes, but the final white obtained was not so good as with 0.5% concentration. Increasing the concentration above 0.5% up to 2.0% was not productive of appreciably improved results. Still higher concentrations were likewise of no advantage. A treatment time of about half an hour appears to be the minimum which is required for uniformity and for the improved bleaching effect on the final material, although in some cases We have found twenty minutes to be satisfactory. Increasing the time up to two hours did not adversely affect the properties of the bleached material, but at the same time did not improve the white.

Following the treatment with the alkaline solutions and/or reducing agent, the goods should be Well washed before being treated with the hypochlorite solution.

As has been described in the prior application Serial No. 183,396, the preparation and maintenance of the hypochlorite solution within the controlled pH range are conveniently effected by the addition to a suitable hypochlorite solution, e. g. sodium or calcium hypochlorite, of a salt having the required buffer characteristics, more particularly sodium bicarbonate. The conditions of the use of such a hypochlorite solution are also described in detail and it is stated that in order to obtain satisfactory bleaching while avoiding damage to the cellulose the available chlorine concentration should be within the limits 1.5 and 5.0 grams per litre. The amount of buffer salt added may be varied to some extent in accordance with the concentration of available chlorine, but in general a liquor containing before use between 2.5 and 3.5 grams of available chlorine, and 8 grams of sodium bicarbonate per litre, will be found applicable for most purposes. The source of the hypochlorite is to a large extent immaterial and in most cases it will be found that a solution prepared by the usual methods from bleaching powder is applicable. To avoid undue attack on the cellulose the hypochlorite solution should be applied with the substantial exclusion of actinic rays. The temperature should not be higher than 20 C. and preferably not higher than 15 C. The time of treatment may be varied considerably, but for the solutions containing about 3.0 or more grams of available chlorine per litre mentioned above, we find that half an hour should preferably not be exceeded.

in preparing the neutral hypochlorite solution we have referred only to the use of sodium bicarbonate as the buffer salt having the required characteristics. We have done this as we prefer to use this salt on account of its cheapness and general convenience. We may, however, use other substances for the adjustment of the liquor to the required stabilised condition of substantial neutrality, for example, alkali metal phosphates and borates. It is also to be noted that when we refer to substantial neutrality we do not restrict ourselves to the precise neutral point but to a region within approximately one unit above and below 7 on the pH scale. More particularly have we obtained excellent results in the region of pH 6.5.

Following the hypochlorite treatment we have found it desirable to rinse the goods with cold water and then to sour. This latter step is of importance in the treatment of linen goods, and is of effect for dealing with the woody fragments of the plant remaining in the yarn after spinning, and commonly known as sprit. The sour should advantageously be applied cold and may be of any strength normally applied to cellulosic fibres. We have found satisfactory a liquor containing about 0.5% H61 applied for half an hour. Sulphuric acidv may be used but it is preferable to use a hydrochloric acid sour when the hypochlorite bath has been made up from bleaching powder. The risk of calcium sulphate remaining on the fibre due to its relatively low solubility is thereby avoided.

After the sour the goods are thoroughly washed in cold water and then treated in an alkaline solution and with an oxidising bleaching agent. This treatment may comprise two stages such as a plain treatment at an elevated temperature With an alkaline solution, followed by a hydrogen peroxide solution. Advantageously, however, we combine the alkali and oxidising bleaching treatment by using an alkaline solution containing hydrogen peroxide.

Various methods have been described in application Serial No. 183,396 for the preparation of the hydrogen peroxide bath. For example, sodium peroxide may be dissolved in water, or in an amount of dilute acid which is sufficient to give complete or partial neutralisation, depending on the degree of alkalinity desired in the peroxide bath. In the event of the peroxide being completely neutralised, a suitable alkaline material is then added to put the liquor into bleaching DLLrsuHewu TEE LCHEWCAE. ocean condition. We may also make further additions to the peroxide solution, as, for example, to stabilise the peroxide or maintain a desirable condition of alkalinity. Such additions include, for example, silicates and calcium and magnesium salts.

Alternatively, the peroxide bath may be prepared by diluting a strong hydrogen peroxide solution with water and adding a suitable alkali. Other additions as have been mentioned in connection with the bath made from sodium peroxide may also be made. I

The concentrations of the alkali and peroxide in the liquor are capable of being varied within very wide limits, while still enabling very good whites to be attained and avoiding undue attack on the material.

As a general guide we have found that alkali concentrations equivalent to 0.15% to 0.4% NazO and peroxide concentrations between 0.05% and 0.2% H202 can be utilised for good bleaching without danger to the fibre.

In applying the peroxide bath to the goods we have found it desirable to observe a temperature maximum of 85 C. in order to avoid attack on the cellulose, and in general find that We can obtain good whites by treatments at between 65 and C. for three hours with liquors of the limits of compositions set out above.

Treated in the above manner all normal qualities of linen yarn will be bleached to a degree which is better than the half white stage and in many cases may be what is known as three-quarter white. If the desired white has been attained the material will now be washed, finished as desired, and dried. If, however, higher shades of white are desired it is only necessary to apply one or more treatments with hypochlorite liquors and alkaline liquors alternately as required. These treatments may be carried out with neutral hypochlorite solutions and alkaline peroxide solutions in which case they will be on the same general principles as already set out but with reduced severity.

In the foregoing we have described in considerable detail the special characteristics of the combination of steps comprising the invention. We have not thought it necessary to describe methods whereby the particular liquors can be applied to textile materials as these will be apparcut to those having a knowledge of the processing of textile materials. Neither have We thought it necessary to draw attention to those elementary precautions which are well known to bleachers and others dealing with cellulosic fibres, and which are necessary to prevent damage when treating such fibres with acids and alkalies.

The following examples illustrate but do not limit the invention.

Example 1 A batch of linen yarn was treated for one hour at 70 C. in fifteen times its weight of liquor containing 0.65% soda ash and 0.35% sodium sulphite (NazSOs) and washed well first in warm and then in cold water. The hanks were transferred to a reeling machine and treated for thirty minutes in a neutral hypochlorite liquor prepared by diluting a strong solution of bleaching powder and adding sodium bicarbonate. The initial available chlorine content of the liquor was 3.0 grams per litre and the sodium bicarbonate used was 5 grams per litre. Reeling was done between 15 and 16 C. in the dark. After reeling the yarn was rinsed in cold water, soured in 0.5% hydrochloric acid and well washed. The yarn was then bleached for two hours at 65 C. in a liquor containing 0.2% sodium peroxide, 0.24% concentrated sulphuric acid (168 Tw.) and 0.3% sodium silicate solution (100 Tw.), washed and dried. The yarn was a good half white, in fact, approaching three-quarters white, and had a solubility number 3.9.

The results of this example can be compared with the results of Example I of application Serial No. 183,396. In both cases the solubility number has been kept at almost the same figure but in the present application a distinctly whiter bleach was obtained.

Example 2 A small lot of linen yarn was thoroughly Wet out, treated at C. for one hour in a liquor containing 0.5% sodium bisulphite and washed thoroughly. The yarn was then treated in a neutral hypochlorite liquor, rinsed, soured, washed, bleached in peroxide liquor, washed off and dried precisely as in Example 1.

Again a noticeable improvement in white was obtained while the solubility number was raised no higher than when bleaching to a half-white by the process of Serial No. 183,396.

The times and the temperatures which are stated in the above description and examples to be suitable for the treatments may however be taken to apply equally to cases where other fibres are treated and a reducing agent other than sodium bisulphite is used. Where a concentration of sodium bisulphite is specified, a chemically equivalent concentration of another reducing agent is equally applicable.

As we have previously indicated, the reducing agent treatment can be used with or without an alkaline steep or boil. When such an alkali treatment is not used it is preferable that the linen to be bleached is thoroughly wetted out prior to the treatment with the solution of the reducing agent. This may quite easily be done by means of water containing a small amount of a known wetting out agent such as Turkey red oil.

When the solution of reducing agent is used in conjunction with an alkali treatment, it may precede or follow it, or the two treatments may be combined. Except in the case of a combined reducing agent-alkali treatment the conditions of concentration, temperature and time, which have been outlined above apply. When the reducing agent is used in conjunction with the alkali in a single bath we find it is better to allow a longer treatment time, say at least one hour, but in respect of concentration of reducing agent and temperature the conditions are the same.

The conditions to be used in an alkali scour in which there is no reducing agent, are similar to those which have been described in our prior specification. In most cases we have found satisfactory results to be obtained on linen yarn by the complete process when using scours containing 5% to 10% of sodium carbonate on the Weight of the goods applied for 2 to- 3 hours at 65 to C. With woven goods it is usually preferable to scour more severely because of the physical condition of the material.

Instead of the sodium sulphite and bisulphite used in the above examples we could have used any of the soluble sulphites, bisulphites or hyposulphites of the following metals: sodium, potassium, lithium, calcium, barium, strontium, zinc, magnesium or beryllium, sulphurous acid or any other sulphur containing acid which is a reducing HUUUU agent. Compounds of the type of zinc formaldehyde sulp-hoxylate may also be used.

This invention is a valuable advance in the art as by its use we can again improve the process that we disclosed in Serial No. 183,396. As is shown by the examples we can get finer bleaching and at the same time preserve the fibre to the same extent.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof, except as defined in the appended claims.

We claim:

1. As an improvement in bleaching linen and like relatively long bast fibers to a whiteness of one-half to full white, said bleached bast material having a solubility number less than 5.0, the improved process which comprises first contacting the unbleached material with alkaline aqueous solution of a sulphite containing between 0.1 per cent to 0.5 per cent of sulphite and maintaining said solution at a temperature between and C. during said contact, to facilitate the subsequent bleaching of said material, and then bleaching the so-treated material, in two stages, by next contacting it with a substantially neutral hypochlorite solution, having a pH value between 6 and 8 and containing between 1.5 and 5 grams per liter of available chlorine and sufiicient buffer compound to maintain the pH value within said range during said contact, at a temperature not exceeding 20 C. and for a time sufiicient to substantially attack and remove most of the coloring thereafter treated with a solution of an alkali an dhydrog enper e, the improvement in proc'dure consisting" rating the unbleached fiber with an alkaline solution of a reducing agent prior to the treat rnent with the neutral hypochlorite solution, whereby a final bleached product is obtained with a minimum loss of strength.

3. A process as claimed in claim 2 in which the reducing agent is chosen from the soluble members of the class which consists of the sulphites, bisulphites and hyposulphites of sodium, potassium, lithium, calcium, barium, strontium, zinc, magnesium, beryllium and sulphurous acid.

4. A process as claimed in claim 2 in which the reducing agent is present in the solution of reducing agent in a quantity equivalent to at least 0.1 per cent of sodium bisulphite.

5. A process as claimed in claim 2 in which the treatment with a reducing agent is carried out at a temperature of between 60 and 100 C.

ERNEST BUTTERWORTH. BERTRAM PUSEY RIDGE.