GB2186298A - Alkaline treatment of cellulose/polyacrylonitrile fibre blends - Google Patents

Abstract

Cellulosic/polyacrylonitrile fibre blends are subjected to an alkali treatment with a composition comprising potassium hydroxide and optionally an alkali metal silicate, a wetting agent and a cation- sequestering agent. The treated fibres have improved dimensional stability, and the cellulosic portion thereof has improved dyestuff affinity, e.g. for reactive dyes.

Description

SPECIFICATION Improvements in or relating to organic compounds The present invention provides a process for the alkaline treatment of a cellulosic/acrylic fibre blend.

Blends of cellulose and polyacrylonitrile fibres give valuable textiles combining the advantageous properties of each fibre type. It is known to submit cellulosic fibres to an alkaline pretreatment before dyeing, particularly to improve properties such as the dimensional stability, the dyestuff affinity. The hitherto known alkaline pretreatments of cellulose generally involve the use of highly concentrated sodium hydroxide solutions, tension and optionally heat treatment.

Such conditions cannot be applied to cellulose/polyacrylonitrile fibre blends as the polyacrylonitrile portion is known to be sensitive to high alkaline concentrations.

It has now been found that cellulose/polyacrylonitrile fibre blends can be submitted to an alkaline pre-treatment which improves the properties of the cellulosic portion without deleteriously affecting the polyacrylonitrile portion.

According to the invention there is provided a process for the alkaline treatment of a mixed cellulosic/polyacrylonitrile fibre substrate which comprises applying to the substrate an aqueous treatment liquor comprising potassium hydroxide.

The amount of potassium hydroxide in the treatment liquor should be enough to improve the dyeability of the cellulosic portion of the mixed fibre substrate and is preferably in the range about 120 to 400 g/l, more preferably about 200 to 330g/l, most preferably 240 to 300 g/l.

The alkaiinity of the treatment liquor desirably is in the range of about 18 to 32 Bé, especially 20 to 30 B6.

In addition to the potassium hydroxide the treatment liquor preferably contains an alkali metal silicate. More preferably, the alkali metal silicate is sodium or potassium silicate, The amount of alkali metal silicate present is generally up to about 100 g/l and is preferably in the range about 10 to 70 g/l, more preferably 15 to 35 g/l, the amount being such that the alkalinity of the treatment liquor will be as stated above.

The ratio of potassium hydroxide to alkali metal silicate may range from about 2:1 to 20:1, preferably about 4:1 to 16:1, more preferably about 6:1 to 13:1, by weight.

A further preferred constituent of the alkali treatment liquor is a wetting agent.

Preferred wetting agents are anionic, non-ionic or amphoteric surfactants which are stable to aqueous potassium hydroxide in the amounts employed. Such compounds are known and commercially available. More preferably the wetting agent is of the anionic type, optionally in the form of a mixture with one or more other anionic wetting agents or with a non-ionic or amphoteric wetting agent.Suitable anionic wetting agents include: i) sulphated C4 24 alcohols or glycols, optionally ethoxylated with 2 to 25 ethyleneoxy units; ii) alkyl C7 20 phosphoric acid esters or semi-esters; iii) alkyl C, 20 poly (1-25) glycol ether phosphoric acid esters; iv) arylsulphonates, e.g. cumenesulphonates; v) sulphated fatty acids, e.g., sulphonated aliphatic saturated or unsaturated fatty acids, preferably C16-18 fatty acids; vi) sulphated fatty acid esters, mono- or diamides; vii) sulphonated fatty acid mono- or diamides, and viii) carboxymethylated addition products of 1 to 25 moles of ethylene oxide to a C4 24 alcohol.

Preferred anionic wetting agents are those of types 1), iii), iv), vii) and viii).

Preferred non-ionic wetting agents are the addition products of 1 to 25 moles of ethylene oxide to a C4 24 alcohol, C4 12 alkyl-phenol or di (C4 12 alkyl)-phenol.

Most preferably, the wetting agent is a sulphated C4 24 alcohol.

The amount of wetting agent when present should be sufficient to promote uniform impregnation of the substrate with the treatment liquor during the application step. Preferably the amount of wetting agent is 0.1 to 10, more preferably 2 to 6 g/l.

According to a preferred embodiment there is further included, in admixture with the potassium hydroxide, alkali metal silicate and wetting agent, an alkali-resistant agent capable of sequestering or complexing with heavy metal ions. It is believed that such an agent inhibits the formation of less water-soluble metal silicates which might interfere with the removal of the alkali metal silicate during the rinsing of the substrate which follows the alkali treatment step.

Compounds useful for tying up heavy metal ions in aqueous media are known. The preferred such compounds for use in the process of the present invention are alkali metal salts of hydroxycarboxylic acids, particularly pentonic, hexonic and heptonic acids, and more particularly giuconic acid, especially sodium gluconate. Other compounds known to be useful as cation sequestering agents include alkali metal glucoheptonates and alkali metal salts of nitrilocarboxylic acids and of ethylenediaminetetraacetic acid.

The sequestering or complexing agent is conveniently added to the treatment liquor in an amount which may range up to about 40 girl, depending, for instance on the hardness of the water. Preferably the amount of this component is in the range about 0.2 to 20, more preferably about 0.5 to 10, most preferably 2.5 to 5 g/l.

The metal-sequestering or complexing agent is conveniently added to the treatment liquor in admixture with a dispersing agent, preferably an anionic dispersant, such as a sulphonated fatty acid amide. A particularly preferred mixture is an aqueous composition comprising by weight, 15% sodium gluconate and 5% sulphonated fatty acid amide.

It is also advantageous to include in the alkali treatment liquor a compound having textile lubricating as well as dispersing properties, and particularly such compounds which have the further property of acting as retarding levelling agents for reactive dyes. Anionic compounds are preferred, especially sulphonated or sulphated castor oil. The amount of such a compound is preferably 0.1 to 15, more preferably 1 to 15 grams per liter of alkali treatment bath.

The aqueous treatment liquor is applied to the substrate at a temperature in the range 10-100"C, preferably 20-80"C, most preferably 20-40"C.

The liquor can be applied to the substrate by various methods, such as padding, spraying or immersion of the substrate in the liquor, preferably by padding. By controlling the rate of initial application or by removing excess liquor, as by squeezing, a pick-up of 70 to 180%, preferably 100 to 130% is achieved.

Following the application of the treatment liquor, the substrate is allowed to dwell for a period of time sufficient to permit the components of the liquor to act on the celluloisic portion of the substrate. This dwell time is preferably about 0.1 to 10 hours, more preferably 1 to 4 hours.

The temperature is preferably 20 to 60"C more preferably 25 to 40"C. In order to accelerate the action of the treatment liquor components on the substrate, the impregnated substrate may be heat treated at a temperature from 60 to 105"C, e.g. with moist heat such as steam, or dry heat.

Following the dwelling, the substrate can be washed and dried in conventional fashion. Washing is generally effected with water, which may advantageously be softened or demineralized at room temperature to boiling, preferably at about 60 to 95"C. The washing step may include a neutralizing step with an acid either at the beginning or to the end of the washing.

The substrate treated according to the present invention can be a blend of cellulosic fibres with polyacrylonitrile fibres in any commercially available ratio, e.g. from 75:25 to 25:75; preferably the substrate is a mixed substrate containing at least 50% by weight cellulosic fibres, e.g. natural or regenerated cellulosic fibres, preferably cotton, more preferably 50 to 75% by weight cellulosic fibres. Furthermore, the substrate can be in a variety of forms, e.g., yarn, woven, knitted, plush or carpets. It is a particular advantage of the process of the invention that it can be used for the alkali treatment of knitted goods, more particularly tubular knitted goods of mixed cellulosiclacrylic fibres.

Mixed textiles treated with a process according to the invention have a smooth appearance with increased gloss, tensile strength, and elongation strength and dimensional stability. The cellulosic portion is particularly characterized by its improved dyeability, e.g., with reactive dyes.

It has also been observed that the treated goods undergo substantially less shrinkage than is usually experienced in alkali treatments of cellulosic materials.

Because of the aforementioned reduced shrinkage, it is a further advantage of this invention that the process can be effected without the need for having the goods under tension (except the normal lengthwise tension exerted when the material is drawn between rollers during a continuous treatment). Thus, the need for a stenter frame to keep the material under tension is avoided and the process can be employed for the treatment of tubular knitted goods. The polyacrylonitrile portion is not damaged by the alkaline conditions.

In the following Examples, all parts and percentages are by weigth and all temperatures are in degrees celsius, unless otherwise indicated.

EXAMPLES Preparation of Treatment Baths Alkaline treatment baths are made up as follows: Half of the final bath volume of soft water at a temperature of 35-40"C is poured into the bath and the required amount of potassium hydroxide is added and stirred. The silicate is then stirred in, followed by a commercially available sequestering agent as described above and the wetting agent, sodium-2-ethylhexyl sulphate. Finally, the bath volume is made up to the required amount by the addition of cold soft water.

The composition of each bath is given in the Table below.

TABLE Bath 1 Bath 2 Bath 3 KOH (dry wt.) 200 g/l 200 g/l 250 g/l Potassium Silicate (2056) 75 gjl Sodium Silicate (30%) 75 g/l 100 g/l Wetting Agent (17%) 30 g/l 30 g/l 30 g/l Sodium gluconate- 20 g/l 20 g/l 20 g/l Sulphonated Fatty Amide Example 1 a) A flattened length of a mixed 75:25 cotton/polyacrylonitrile tubular knit grey (unbleached) is continuously drawn from a basket through Bath 1 above which is at approximately room temperature. The immersion time in the bath is about 1 to 5 seconds. The wetted substrate is then squeezed between a pair of rollers to a wet pick-up of about 100%.During this sequence the only tension on the substrate is that caused by the lengthwise pulling of said substrate from its initial slack position in the basket through the nip of the squeezing rollers. The wetted substrate is then fed into a second basket where it is allowed to dwell in a tension-free condition for a period of about two hours at room temperature.

b) The above-treated substrate is then washed continuously for about 5 to 10 minutes with water at about 70 to 85"C, treated with sufficient aqueous acetic acid to neutralize any residual alkali and washed again briefly with water to remove any excess acetic acid.

A substrate having a homogeneous smooth appearance is obtained.

Example 2 A flattened length of a 50:50 mixed cotton/polyacrylonitrile fabric is treated as described in paragraghs a) and b) of Example 1 except that it is padded with Bath 2 instead of Bath 1.

Example 3 A flattened length of a 75:25 mixed cotton/polyacrylonitrile fabric is treated as described in paragraphs a) and b) of Example 1, except that it is padded with Bath 3 instead of Bath 1.

Claims (22)

1. A process for the alkali treatment of a mixed cellulosic/polyacrylonitrile fibre substrate comprising applying to the substrate an aqueous alkali liquor comprising potassium hydroxide.

2. A process according to Claim 1, in which the aqueous alkali liquor contains an alkali metal silicate.

3. A process according to Claim 2, wherein the alkali metal silicate is sodium silicate.

4. A process according to any one of the preceding claims, wherein the aqueous alkali liquor has a strength within 18 and 32 Bé.

5. A process according to Claim 4, wherein the aqueous alkali liquor has a strength within 20 to 30 Bé.

6. A process according to Claim 4 or 5, wherein the aqueous alkali liquor contains from 200 to 330 g/l potassium hydroxide.

7. A process according to any one of the Claims 4 to 6, wherein the aqueous alkali liquor contains up to 100 g/l alkali metal silicate.

8. A process according to Claim 7, wherein the aqueous alkali liquor contains from 10 to 70 g/l alkali metal silicate.

9. A process according to any one of Claims 4 to 8, wherein the ratio of potassium hydroxide to alkali metal silicate is from 4:1 to 16:1.

10. A process according to any one of the preceding claims, wherein the aqueous alkali liquor contains a wetting agent.

11. A process according to Claim 10 wherein the wetting agent is an anionic, non-ionic or amphoteric surfactant.

12. A process according to Claim 11, wherein the wetting agent comprises at least one wetting agent of the anionic type.

13. A process according to Claim 12, wherein the anionic wetting agent is selected from i) sulphated C4 24 alcohols or glycols and sulphated C4 24 alcohols or glycols ethoxylated with 2 to 25 ethyleneoxy units; ii) alkyl C7 20 phosphoric acid esters or semi-esters; iii) alkyl C, 20 poly (1-25) glycol ether phosphoric acid esters; iv) arylsuiphonates; v) sulphated fatty acids; vi) sulphonated fatty acid esters, mono- or diamides; vii) sulphonated fatty acid mono- or diamides, and viii) carboxymethylated addition products of 1 to 25 moles of ethylene oxide to a C4 24 alcohol.

14. A process according to any one of Claims 10 to 13 wherein the wetting agent is used in an amount from 0.1 to 10 g/l.

15. A process according to any one of the preceding claims, wherein the aqueous alkali liquor contains a cation-sequestering or -complexing agent.

16. A process according to Claim 15, wherein the aqueous alkali liquor contains up to 40 g/l of a cation-sequestering or -complexing agent.

17. A process according to any one of the preceding claims wherein the substrate contains at least 50% by weight cotton.

18. A process according to any one of the preceding claims, wherein the substrate is knitted goods.

19. A process according to any one of the preceding claims wherein, following application of the composition, the substrate is dwelled for a period of time sufficient for the treatment liquor components to act on the substrate and is then washed to remove the potassium hydroxide.

20. A method according to any one of the preceding claims wherein, during the application, dwelling and washing steps, the substrate is free from tension across its width.

21. A process substantially as hereinbefore described with reference to any one of Examples 1 to 3.

22. A mixed polyacrylonitrile/cellulosic fibre substrate whenever obtained by a process according to any one of the preceding claims.