Absorbent material for aqueous physiological fluids and process for its production

An absorbent material is provided having exceptional fluid suction and holding power for aqueous physiological fluids, and which is thus especially adaptable for use as tampons, sanitary napkins, baby diapers, hospital pads and the like. The material consists essentially of cellulose fibers containing from 5 to 20% by weight of sodium carboxymethyl cellulose. The material is formed by a process in which a viscose spinning solution is produced from cellulose xantogenate by dissolving in aqueous caustic soda solution and permitting the solution to ripen, spinning the latter in an acid spinning bath, and then cleaning and drying the resultant threads, the spinning solution containing 5 to 20% by weight of sodium carboxymethyl cellulose.

The invention concerns an absorbent material with great fluid suction and 
holding power, for aqueous physiological fluids. Such absorbent materials 
are used in hygienic one-use articles, such as tampons for feminine 
hygiene, sanitary napkins, baby diapers, hospital pads and similar 
articles. They have the property of absorbing as quickly as possible, on 
wetting, the physiological fluids occurring, and holding them fast, even 
under the effect of pressure. 
As absorbent material for these purposes, cellulose is still used today, as 
a rule, in the form of short or long fibers. The use of other materials 
for this purpose is also known, such as hydrophil polyurethane foams (Ger. 
Disclosure No. 1,198,060), for example, or suitable polymers, such as 
polyacrylamide or Poly-N-vinyl pyrrolidone and others (Ger. Disclosure No. 
1,617,998). The use is also known, as aids to absorption, and thus as 
additives, of netted cellulose fibers, especially formalized that is, 
crosslinking with formaldehyde cotton or rayon fibers (Ger. Disclosure No. 
1,492,365). 
The use of the last-named materials, in addition to or instead of cellulose 
fibers is only reasonable, economically and technically, if these 
materials have a considerably heightened fluid absorption and holding 
power, as compared with pure cellulose. Any possible increase of these 
properties means technically a considerable gain, and makes the use of the 
said material possible, economically, for the first time, in many cases. 
But it is important, naturally, in all cases, that the said materials are 
fully unobjectionable physiologically, which, for example, is not the case 
with polyacrylates, according to recent research. 
With this State of the Art, the problem exists of proposing an absorbent 
material for aqueous physiological fluids, which, compared with the known 
materials, with fuller physiological unobjectionability, has a 
considerably heightened suction power. 
This problem is solved by the fact that, starting with an absorptive 
material based on partly netted (reticulated), especially formalized 
cellulose fibers, which is distinguished, according to the invention, by 
the fact that the partly netted, especially formalized cellulose fibers 
contain in their fibers 5-20% by weight, preferably 10% by weight, sodium 
carboxymethyl cellulose. The expression "in the fibers" is intended to 
mean that it is not a matter of a mixture of different fibers, but rather 
that the fiber is physically a unified structure, which only consists 
chemically of the said two materials, namely, regenerated cellulose, on 
the one hand, and sodium carboxymethyl cellulose in the said amount, on 
the other. It has been found that fibers so made up have an unexpected 
absorption value, and namely, both as to short-time values (suction 
values) and also long-term values (power to hold the fluid fast). 
The fibers proposed, according to the invention, have, to advantage, a 
titer of 1.5 to 10.0, preferably 1.5 to 3.5 dtex, and a length of 20 to 
120 mm, preferably 50 mm. It has proved favorable when the fibers are 
revived with polyethylene glycol of a molecular weight 200 to 20,000, 
preferably 400 to 4,000. 
For the production of the proposed fibers, we start with the viscose 
process, known per se. Cellulose xanthogenate is processed by dissolving 
in aqueous caustic soda solution and allowing the solution to ripen to a 
viscous spinning solution. This spinning solution is then spun in an acid 
spinning bath and then the resultant threads are cleaned and dried. For 
production of the proposed fibers, there is added to the spinning solution 
5 to 20% by weight, preferably 10% by weight, of sodium carboxymethyl 
cellulose, based on the cellulose contained in the solution, and the 
threads obtained in the spinning, after their cleaning in the manner known 
per se, in acid solution are partly netted (reticulated), especially 
formalized, and then the sodium salt is formed again by washing the fiber 
with sodium hydrogen carbonate solution, or similarly. 
By this process it is possible to incorporate the said amounts of sodium 
carboxymethyl cellulose into the fiber and by the said partial 
reticulation, especially formalizing, to bind it with the rest of the 
cellulose molecules so that, in all, a chemically unified structure 
results, from which the sodium carboxymethyl cellulose molecule can no 
longer be removed by washing. There results in this way a fiber material 
with greatly increased suction values, these values being almost doubled 
as compared with most other physiologically unobjectionable absorbent 
materials to be considered. To demonstrate the advantageous properties of 
the absorbent material proposed, the examples of comparison listed below 
were carried out.

EXAMPLE 1 
Production of the proposed absorbent material 
We started with a mixed fiber of 90% cellulose and 10% sodium carboxymethyl 
cellulose. The fiber had a titer of 1.7 dtex and a section length of 50 
mm. 
For the formalizing, the following bath was prepared: 
1125 ml water 
1875 ml conc. hydrochloric acid (37%) 
750 ml formaldehyde solution 
3750 ml 
Into this bath were put, at a temperature of 20.degree. C. 100 grams of the 
staple fiber described above. After 20 minutes stay time, the fiber was 
removed and washed neutral with water. Then the fiber was put into 2 
liters of a 10% solution of sodium-hydrogen carbonate, to form back the 
sodium salt of the carboxymethyl cellulose. The action time was 10 
minutes. 
After reforming the salt form, the fibers were washed neutral again, the 
last wash water containing 0.5% polyethylene glycol of molecular weight 
400. Then it was dried at 115.degree. C. 
EXAMPLE 2 
Production of experimental tampons 
The fiber prepared according to Example 1, was carded in the usual way, 
formed to strips 50 mm. wide and by winding and pressing, tampon bodies 
were produced. 
In the same way, tampons were produced from various comparison fibers, in 
which the tampon raw weight in each case was about 3.0 grams. As 
comparison fibers, the following were used: 
1. 100% cellulose, 3.6 dtex, 30 mm. 
2. Non-formalized mixed fiber of cellulose and 10% carboxymethyl cellulose. 
This was the same fiber as that taken above as initial product for 
formalization. Titer: 1.7 dtex; 50 mm. fiber length. 
3. Cellulose, Titer 5.2 dtex, 40 mm. staple length; formalized. 
In all the experimental tampons, the expansion after 1 minute, after 3 
minutes and after 15 minutes was measured against a pressure of 170 mm. 
water column, and the volume expansion, dependent on time, determined by 
collecting and weighing the amount of water driven out. The synthetic 
blood fluid had the following composition: 
70 grams Tylose H 20 (Hoechst) 
50 grams NaCl 
20 grams NaHCO.sub.3 
5 grams red coloring 
500 grams glycerine 
Water to make up 5000 ml. 
The values for fluid absorption after 15 minutes were determined by 
weighing back. The values obtained appear from the following table: 
______________________________________ 
Fluid 
absorption 
Expansion (ml) 
after 15 
Tampon Weight 1 min 3 min 15 min 
min (ml) 
______________________________________ 
Cellulose, 100% 
3,02 3,4 6,8 10,8 13,8 
3,6 dtex/30 mm 
Cellulose 2.93 3,6 7,2 12,2 16,4 
1,7/50 + 10% CMC 
Cellulose, 5,2/40 
2,89 5,8 12,0 17,8 22,6 
formalized 
Cellulose 1,7/50, 
3,00 9,1 20,4 22,3 26,9 
+ 10% CMC mixed 
fiber, formalized 
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The experiments show that all values are greatly increased as compared with 
those known before, and in part, an increase of over 100% is shown. It is 
interesting that the formalized mixed fiber proposed also has greatly 
increased absorptive value over the non-formalized mixed fiber.