GB1583974A - Absorbent for aqueous physiological liquids and process for the production thereof - Google Patents

Abstract

Absorbent fabrics having a high liquid, absorption and retention capacity for aqueous physiological liquids are based on partially crosslinked, especially formalised, cellulose fibres. The cellulose fibres contain 5 to 20% by weight of sodium carboxymethylcellulose in the fibre. The absorbent fabrics are produced by preparing a viscous spinning solution from cellulose xanthogenate by dissolution in aqueous sodium hydroxide solution and allowing the solution to mature. This spinning solution is spun into an acid spin bath, and the filaments produced are cleaned and dried. The method is distinguished in that 5 to 20% by weight of sodium carboxymethylcellulose, based on cellulose contained in the solution, is added to the spinning solution. The filament obtained is cleaned and thereafter partially crosslinked in acid solution. The sodium salt is then reformed.

Description

(54) ABSORBENT FOR AQUEOUS PHYSIOLOGICAL LIQUIDS AND PROCESS FOR THE PRODUCTION THEREOF (71) We, VEREINIGTE PAPIERWERKE SCHICKEDANZ & CO., a body corporate organized under the laws of the German Federal Republic, of 8500 Nuremberg, 80.Schbp- pershofstrasse (Tempo-Haus), German Federal Republic, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to--be particularly described in and by the following statement: This invention relates to an absorbent with a high capacity for the absorption and retention of aqueous physiological liquids.Such absorbents are used in disposable hygienic articles, such as tampons for women's hygiene, sanitary towels, babies' napkins, sheets for sick persons and similar articles. Their purpose is to absorb as rapidly as possible the physiological liquid which occurs when they are wetted and to retain it even when pressure is exerted.

Cellulose in the form of short or long fibres is still generally used today as an absorbent for this purpose. However, it has also been proposed to use other substances for this purpose, such as for example hydrophilic polyurethane foam plastics or suitable polymers, such as polyacrylamides or poly-N-vinylpyrrolidones and the like. Furthermore it has been proposed to use as absorbent aids, that is to say as additional substances, wet cross-linked cellulose fibres, especially formalised cotton or artificial silk fibres.

The use of the last-mentioned substances either in addition to or instead of cellulose fibres only makes sense from the economic and technical point of view if these substances have a considerably increased capacity for the. absorption and retention of liquids as compared with pure cellulose. Any possible increase in these properties would technically provide a considerable gain gnd would, for the first time, make the use of the said substances possible in many cases on an economic basis. What is important in all cases, naturally, is that the said substance should be completely harmless from the physiological point of view, which according to more recent investigations is not the case with polyacrylates and polyurethanes.

In the light of this prior art there is the problem of proposing an absorbent material for aqueous physiological liquids which has a considerably increased capacity for absorption as compared with the substances named, whilst being completely unobjectionable -from the physiological point of view.

According to one aspect of the present invention there is provided an absorbent for aqueous physiological liquids, wherein the absorbent comprises partially cross-linked cellulose fibres containing in the fibre from 5 to 20 per cent by weight of sodium carboxymethylcellulose, based on the weight of cellulose contained in the fibre.

According to another aspect of the present invention there is provided a process for the production of an absorbent, comprising the steps of adding to a viscose spinning solution, produced by digesting cellulose xanthate in sodium hydroxide and ripening the splution, from 5 to 20 per cent by weight of sodium carboxymethylcellulose, based on the weight of cellulose contained in the solution, spinning the resulting solution in an acid spinning bath to produce fibres, partially cross-linking - the fibres in an acid solution, reforming the sodium salt and purifying and drying the fibres.

The partly cross-linked fibres are preferably formalised cellulose fibres, and they preferably contain in the fibre 10 per cent by weight, of sodium carboxymethylcellulose.

The expression "in the fibre" is intended to mean that it is not a question of a mixture of different fibres, but that the fibre is physically a uniform structure which only chemically consists of the two substances mentioned, namely regenerated cellulose on the one hand and sodium carboxymethylcellulose in the said quantity on the other. It has been found that fibres built up in this way possess surprisingly high absorption values, both as regards the short-term values (suction values) and also as regards the long-term values (liquid retention capacity).

The fibres used in the present absorbent preferably have a count of 1.5 to 10.0 dtex, more preferably of 1.5 to 3.5 dtex, and a length of 20 to 120 mm., more preferably 50 mm. It has been found advantageous if the fibres are activated with polyethyleneglycol with a molecular weight of 200 to 20,000, preferably 400 to 4,000.

Regenerated cellulose fibres are produced by the viscose process in which cellulose xanthate is processed by digesting in aqueous caustic soda solution and ripening the solution, to form a viscose spinning solution. This spinning solution is then spun into an acid spinning bath and then the resultant fibres are purified and dried. For the production of the fibres used in the present absorbent, there is added to the viscose spinning solution from 5 to 20 per cent by weight, preferably 10 per cent by weight, of sodium carboxymethylcellulose, based on the cellulose contained in the solution, and the fibres obtained during the spinning, after being purified, are partially cross-linked in a known manner in an acid solution, preferably formalised, and then the sodium salt is re-formed by washing the fibres with sodium bicarbonate solution or in a similar manner.

By this process it is possible to incorporate into the fibre the stated quantity of sodium carboxymethylcellulose and by the stated partial cross-linking, especially formalising, to combine it with the usual cellulose molecules in such a way that the result is a chemically uniform structure from which the sodium carboxymethylcellulose molecule can no longer be removed by washing. Thus the result is a fibrous material with highly increased absorption values, these values being almost double those of most of the other physiologically unobjectionable absorbents under consideration.

The invention will now be illustrated by the following Examples Example I Production of absorbent A mixed staple fibre consisting of 90% cellulose and 10% sodium carboxymethylcellulose having a count of 1.7 dtex and a cut length of 50 mm. was formalised in a bath of the following composition: 1125 ml. water 1875 ml. concentrated hydrochloric acid (37%) 750 ml. formaldehyde solution (37%) 3750 ml.

Into this bath 100 g. of the abovementioned staple fibre were fed at a temperature of 20"C.

After a residence time of 20 minutes, the fibre was taken out and washed neutral with water.

The fibre was then placed in 2 litres of a 10% sodium bicarbonate solution in order to re-form the sodium salt of the carboxymethylcellulose, the reaction time being 10 minutes.

After the re-formation of the salt form, the fibre was once again washed neutral, the last washing water containing 0.5% of polyethyleneglycol with a molecular weight of 400, and finally dried at 115"C..

Example 2 Production of trial tampons The fibre prepared according to Example 1 was carded in the usual manner, formed into strips 50 mm. wide and tampon units were produced from the strips by winding and pressing.

In the same way tampdns were produced from various comparative fibres, the gross weight of the tampons in each case being about 3.0 g.

The following comparative fibres were used: . 100% cellulose count 3.6 dtex, cut length 30 mm; 2. Non-formalised mixed fibre of cellulose and 10% carboxymethylcellulose. This is the same fibre that was used as the starting material in Example 1 before the formalising.

Count: 1.7 dtex, cut length 50 mm.

3. Cellulose count 5.2 dtex, 40 mm. staple length; formalised.

On all the trial tampons the expansion after 1 minutes, after 3 minutes and after 15 minutes was measured against a pressure of 170 mm. water column and the volume expansion depending upon the time was determined by collecting the quantity of water displaced and weighing it, using a blood replacement liquid of the following compositions: 70 g. "Tylose" H 20 ("Tylose" is a registered Trade Mark) 50 g. NaCl 20 g. NaHCO3 5 g. red dyestuff 500 g. glycerol Water to make up to 5000 ml.

The values for the liquid absorption after 15 minutes were determined by re-weighing. The figures obtained can be seen from the Table below: Tampons Wkight. Ejrpansioliiml).: Liquid absorption (g) 1 min: 3 min..- 15 min. after 15 min. (ml) 100% cellulose 3.02- 3.4 6.8 ' 10.8 13.8 3.6 dtex 30 mm.

10% Carboxymethyl cellulose 2.93 3.6 7.2 12.2 16.4 Cellulose + 1.7 dtex 50 mm.

Formalised Cellu lose 2.89 5.8 12.0 17.8 22.6 5.2 dtex 40 mm.

Formalised mixed cellulose and 10% Carboxymethylcellulose 3.00 9.1 20.4 22.3 26.9 1.7 dtex 50 mm.

The tests show that all the values were greatly increased as compared with those previously known and in some cases show an increase of over 100%. It is interesting to note that the tampon made of formalised mixed fibres also had greatly increased absorption values as compared with the unformalised mixed fibres.

WHAT WE CLAIM IS: 1. An absorbent for aqueous physiological liquids, wherein the absorbent comprises partially cross-linked cellulose fibres containing in the fibre from 5 to 20 per cent by weight of sodium carboxymethylcellulose based on the weight of cellulose contained in the fibre.

2. An absorbent as claimed in claim 1 , wherein the fibres contain 10% by weight of sodium carboxymethylcellulose.

3. An absorbent as claimed in claim 1 or 2, wherein the fibres have been partially cross-linked by formalisation.

4. An absorbent as claimed in any preceding claim, wherein the fibres have a count-of 1.5 to 10 dtex and a length of 20 to 120 m..

5. An absorbent as claimed in any preceding claim, wherein the fibres have a count of 1.5 to 3.5 dtex, and a length of 50 mm..

6. An absorbent as claimed in any preceding claim, wherein the fibres have been treated with a polyethyleneglycol having a molecular weight of 200 to 20,000.

7. An absorbent as claimed in any preceding claim, wherein the fibres have been treated with a polyethyleneglycol having a molecular weight of 400 to 4,000.

8. An absorbent substantially as hereinbefore described in Example 1 of the foregoing Examples 9. A tampon, pad or like article for absorbing aqueous physiological liquids comprising the absorbent claimed in any preceding claim.

10. A process for the production of an absorbent, comprising the steps of adding to a viscose spinning solution, produced by digesting cellulose xanthate in sodium hydroxide and ripening the solution, from 5 to 20 per cent by weight of sodium carboxymethylcellulose, based on the weight of cellulose contained in the solution, spinning the resulting solution in an acid spinning bath to produce fibres, partially cross-linking the fibres in an acid solution, reforming the sodium salt and purifying and dryipg the fibres.

11. A process as claimed in claim 10, wherein 10 per cent by weight of sodium carboxymethylcellulose is added to the viscose spinning solution.

12. A process as claimed in claim 10 or 11, wherein the cross-linking is effected by formalisation.

13. A process for the production of an absorbent substantially as hereinbefore described in Example 1 of the foregoing Examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. Tampons Wkight. Ejrpansioliiml).: Liquid absorption (g) 1 min: 3 min..- 15 min. after 15 min. (ml) 100% cellulose 3.02- 3.4 6.8 ' 10.8 13.8 3.6 dtex 30 mm. 10% Carboxymethyl cellulose 2.93 3.6 7.2 12.2 16.4 Cellulose + 1.7 dtex 50 mm. Formalised Cellu lose 2.89 5.8 12.0 17.8 22.6 5.2 dtex 40 mm. Formalised mixed cellulose and 10% Carboxymethylcellulose 3.00 9.1 20.4 22.3 26.9 1.7 dtex 50 mm. The tests show that all the values were greatly increased as compared with those previously known and in some cases show an increase of over 100%. It is interesting to note that the tampon made of formalised mixed fibres also had greatly increased absorption values as compared with the unformalised mixed fibres. WHAT WE CLAIM IS:

1. An absorbent for aqueous physiological liquids, wherein the absorbent comprises partially cross-linked cellulose fibres containing in the fibre from 5 to 20 per cent by weight of sodium carboxymethylcellulose based on the weight of cellulose contained in the fibre.

2. An absorbent as claimed in claim 1 , wherein the fibres contain 10% by weight of sodium carboxymethylcellulose.

3. An absorbent as claimed in claim 1 or 2, wherein the fibres have been partially cross-linked by formalisation.

4. An absorbent as claimed in any preceding claim, wherein the fibres have a count-of 1.5 to 10 dtex and a length of 20 to 120 m..

5. An absorbent as claimed in any preceding claim, wherein the fibres have a count of 1.5 to 3.5 dtex, and a length of 50 mm..

6. An absorbent as claimed in any preceding claim, wherein the fibres have been treated with a polyethyleneglycol having a molecular weight of 200 to 20,000.

7. An absorbent as claimed in any preceding claim, wherein the fibres have been treated with a polyethyleneglycol having a molecular weight of 400 to 4,000.

8. An absorbent substantially as hereinbefore described in Example 1 of the foregoing Examples

9. A tampon, pad or like article for absorbing aqueous physiological liquids comprising the absorbent claimed in any preceding claim.

10. A process for the production of an absorbent, comprising the steps of adding to a viscose spinning solution, produced by digesting cellulose xanthate in sodium hydroxide and ripening the solution, from 5 to 20 per cent by weight of sodium carboxymethylcellulose, based on the weight of cellulose contained in the solution, spinning the resulting solution in an acid spinning bath to produce fibres, partially cross-linking the fibres in an acid solution, reforming the sodium salt and purifying and dryipg the fibres.

11. A process as claimed in claim 10, wherein 10 per cent by weight of sodium carboxymethylcellulose is added to the viscose spinning solution.

12. A process as claimed in claim 10 or 11, wherein the cross-linking is effected by formalisation.

13. A process for the production of an absorbent substantially as hereinbefore described in Example 1 of the foregoing Examples.