Absorbent for water and aqueous solutions

The present invention relates to absorbents for water and aqueous solutions, in particular for blood, which contain a product from the tuber of a plant from the family of the Araceae.

The present invention relates to an absorbent for water and aqueous 
solutions which contains natural products from the tubers of plants of the 
family of the Araceae. 
Swellable polymers which absorb aqueous solutions are used for the 
production of napkins, diapers, sanitary towels, tampons and other 
sanitary articles. The known polymers of this type include crosslinked 
carboxymethyl cellulose, partially crosslinked polyalkylene oxide, 
hydrolysates of starch/acrylonitrile graft copolymers and partially 
crosslinked polyacrylates. 
However, there is still a demand for novel swellable substances, in 
particular those which are distinguished by a capacity for spontaneous 
absorption and high retention capacity with regard to blood and other 
serous body fluids as well as by a high absorption capacity for aqueous 
solutions of substantial electrolyte concentrations. 
It is already known that products which belong to the polysaccharides can 
be obtained from tubers of species from the family of the Araceae. This 
applies in particular to species of the genus Amorphophallus. From the 
tubers of the species Amorphophallus Konjak, for example, which can be 
found mainly in Japan and Indonesia, the so-called Konjak flour can be 
obtained, and from this the so-called konjakumannan (U.S. Pat. No. 
3,928,322). Konjakumannan is a glucomannan which has been known for 
centuries in Japan as a foodstuff. Glucomannans are gellable products 
which can be used in particular in the food industry, but also in pharmacy 
and in other fields. 
Surprisingly, it has now been found that the products mentioned are 
outstandingly suitable as absorbents for water and aqueous solutions, in 
particular for blood. 
The present invention therefore relates to an absorbent for water and 
aqueous fluids, characterised in that it contains a product from the tuber 
of a plant from the family of the Araceae. 
Examples of suitable plants from the family of the Araceae are the Chinese 
Taro (Coiocasia esculenta var. antiquorum) and, in particular, species of 
the genus Amorphophallus, such as A. rivieri, A. aldus, A. bulbifer, A. 
campanuiatus, A. giganteus, A. variabilis, A. titanum, A. konjak and A. 
virosus. 
Products from Amorphophallus konjak, in particular Konjak flour and 
Konjakumannan, are particularly preferred. 
The claimed product can be obtained from the tubers of the plants in a 
manner known per se (see, for example, Ullmanns Encyklopadie der 
technischen Chemie, 3, [Ullmann's Encyclopedia of Industrial Chemistry], 
3rd Edition, Volume 13, page 191 (1962), but some of them are also 
commercially available. 
In a preferred embodiment, the absorbents according to the invention 
contain one or more highly-absorbent, water-swellable synthetic or natural 
polymers which are swellable in water as further absorbent component. Such 
polymers are known under the name "superabsorbent polymer" (SAP). They 
are, in particular, polymers based on (co)polymerised hydrophilic monomers 
or based on natural hydrophilic polymers. 
Particularly suitable natural hydrophilic polymers are, in particular, 
polysaccharides such as guar, carboxymethyl-hydroxypropyl guar, starch, 
cellulose, hydroxyethylcellulose as well as alginates. 
Suitable copolymerisable hydrophilic monomers are, in particular, acrylic 
acid, methacrylic acid, crotonic acid, 
2-acrylamido-2-methylpropanesulphonic acid and -phosphonic acid, 
vinylphosphonic acid, vinylphosphonic semi-esters, their salts, 
acrylamide, N-vinylamides or mixtures of these. 
Polymers of the type mentioned are described, for example, in EP-A 316 792, 
EP-A 343 427, EP-A 391 108, EP-A 400 283, EP-A 417 410, EP-A 421 264 and 
EP-A 481 370. 
Polymers which are preferably employed in the absorbents according to the 
invention are highly-absorbent, water-swellable synthetic polymers based 
on (co)polymerised acrylic acid and/or their salts and/or acrylamide. 
It is preferred for the highly-absorbent, water-swellable synthetic or 
natural polymers to have defined particle sizes. Suitable particle sizes 
are between about 0.1 to about 1 mm, the range between 0.1 and 0.85 mm 
being preferred and the range between 0.3 to 0.4 mm being particularly 
preferred. 
The ratios by weight between the natural products mentioned and the 
highly-absorbent, water-swellable synthetic polymers in the mixtures can 
vary within wide limits. The amount of polymer can vary between 1 and 99% 
by weight. 
Preferred mixtures contain 1 to 20% by weight of natural product and 80 to 
99% by weight of polymer. 
If appropriate, the absorbents according to the invention can additionally 
contain adjuvants and additives. Such adjuvants and additives are, for 
example, binders, polyglycol being particularly suitable. The absorbents 
according to the invention contain binders in amounts of, preferably, 0 to 
30% by weight, particularly preferably in amounts of 0 to 5% by weight. 
The absorbents according to the invention absorb water and aqueous 
solutions in an outstanding manner and can therefore be used in the 
production of sanitary articles, such as nappies, sanitary towels, tampons 
and other absorbent products. Their particular advantage is the capacity 
of spontaneously absorbing blood and other serous body fluids, as well as 
the retention capacity.

EXAMPLES 
Example 1 
a) Preparation of a synthetic, absorbent polymer 
3650 g of demineralised water are introduced under adiabatic conditions 
into a 5 l cylindrical wide-mouth reaction flask, 500 g of a freshly 
boiled starch solution of 50 g maize starch and 450 g of demineralised 
water, 15 g of a reaction product of 1.98 mol of maleic anhydride and 1.0 
mol of polyglycol 300, which also acts as grafting substrate, 1250 g of 
acrylic acid and 0.625 g of tetraallyloxyethane are dissolved therein, and 
the mixture is brought to 20.degree. C. Nitrogen is passed into the 
monomer solution (approx. 2 1/minute) so as to lower the oxygen content. 
At a content of approx. 0.8 ppm O.sub.2, 34 g of a 4% aqueous solution of 
2,2'-azobis(amidinopropane) dihydrochloride are added, more N.sub.2 is 
passed in, 17 g of an 0.75% H.sub.2 O.sub.2 solution are added when the 
O.sub.2 content is approx. 0.08 ppm, and, finally, 4.5 g of an 0.15% 
ascorbic acid solution are added at an O.sub.2 content of approx. 0.01 
ppm. Incipient polymerisation, during the course of which the temperature 
rises to approx. 90.degree. C., results in the formation of a solid gel 
which is subsequently mechanically comminuted. 1000 g of the comminuted 
gel are treated with 346 g of 27% sodium hydroxide solution (degree of 
neutralisation of the acrylic acid =70 mol%), the mixture is kneaded 3 
times, and the product is subsequently dried in a thin layer at 
temperatures above 100.degree. C., ground and, if appropriate, screened. 
b) Preparation of an absorbent according to the invention 
In a kneader, 1000 g of the neutralised gel of Example 1 are treated with 
20 g of commercially available "Amorphophallus konjak radix" powder, and 
the mixture is kneaded until completely homogeneous and subsequently dried 
in vacuo at 80.degree. C. in a thin layer, ground and, if appropriate, 
screened. 
Example 2 
2.5 kg of screened polymer powder with a particle size of 0.1-0.85 mm, 
prepared as described in Example 1a, are introduced into a 10 l PETERSON & 
KELLY mixer. 76.5 g of polyethylene glycol 300, which acts as binder, are 
sprayed in the course of 5 minutes, and mixing is continued for 1 minute. 
After 2.5 kg of commercially available "Amorphophallus konjak radix" 
powder have been added, mixing is continued until the mixture is 
completely homogenised. 
Example 3 
In a 500 ml screw-top flask, 50 g of screened polymer powder with a 
particle size of 0.1-0.85 mm, prepared as described in Example 1a, and 1.8 
g of commercially available "Amorphophallus konjak radix" powder are mixed 
on a roller frame until the mixture is completely homogeneous. 
The absorbents according to the invention of the following examples can 
also be prepared as described in Examples 1b, 2 and 3: 
Example 4 
Absorbent of 20% by weight of commercially available "Amorphophallus konjak 
radix" powder and 80% by weight of the polymer as described in Example 1a 
with a particle size of 0.1-0.85 mm. 
Example 5 
Absorbent of 98.5% by weight of commercially available "Amorphophallus 
konjak radix" and 1.5% by weight of polyglycol 300. 
Example 6 
Absorbent of 3.5% by weight of commercially available "Amorphophallus 
konjak radix" powder and 96.5% by weight of the polymer as described in 
Example 1a with a particle size of 0.1-0.4 mm. 
Example 7 
Absorbent of 1% by weight of commercially available "Amorphophallus konjak 
radix" powder and 99% by weight of the polymer as described in Example 1a 
with a particle size of 0.1-0.4mm. 
Example 8 
Absorbent of 10% by weight of commercially available "Amorphophallus konjak 
radix" powder, 88.5% by weight of the polymer as described in Example 1a 
with a particle size of 0.1-0.4 m and 1.5% by weight of polyglycol 300. 
Example 9 
Absorbent of 20% by weight of commercially available "Amorphophallus konjak 
radix" powder, 78.5% by weight of the polymer as described in Example 
1with a particle size of 0.1-0.4 mm and 1.5% by weight of polyglycol 300. 
Example 10 
Absorbent of 90% by weight of commercially available "Amorphophallus konjak 
radix" powder, 8.5% by weight of the polymer as described in Example 1with 
a particle size of 0.1-0.4 mm and 1.5% by weight of polyglycol 300. 
Example 11 
Absorbent of 1.5% by weight of commercially available "Amorphophallus 
konjak radix" powder and 98.9% by weight of the polymer as described in 
Example 1 of Offenlegungsschrift DE 3,738,602 with a particle size of 
0.1-0.85 mm. 
Example 12 
Absorbent of 5% by weight of commercially available "Amorphophallus konjak 
radix" powder, 93.5% by weight of the polymer as described in Example 1 of 
Offenlegungsschrift DE 3,738,602 with a particle size of 0.1-0.4 mm and 
1.5% by weight of polyglycol 300. 
Example 13 
Absorbent of 5% by weight of commercially available "Amorphophallus konjak 
radix" powder and 1.5% by weight of usual commercial starch and 93.5% by 
weight of the polymer as described in Example 1a with a particle size of 
0.1-0.4 mm. 
Example 14 
Absorbent of 15% by weight of commercially available "Amorphophallus konjak 
radix" powder and 98.5% by weight of a graft copolymer based on acrylic 
acid with a degree of neutralisation of 75 mol%. 
Example 15 
Absorbent of 3% by weight of commercially available "Amorphophallus konjak 
radix" powder, 1.5% by weight of alginate and 95.5% by weight of the 
polymer as described in Example 1a with a particle size of 0.1-0.4 mm. 
Example 16 
Absorbent of 1.5% by weight of commercially available "Amorphophallus 
konjak radix" powder, 1% by weight of guar flour and 97.5% by weight of 
the polymer as described in Example 1a with a particle size of 0.1-0.4 mm. 
To characterise the absorbents according to the invention, the free 
absorbency (ATB) and the centrifugal retention (CRET) of the examples of 
Table 1 below were measured in electrolyte solution. Detailed measurements 
of the demand absorbency (DA) in blood and electrolyte solution, the 
penetration of blood, as well as rheological measurements of the products 
which had been preswollen in blood were furthermore carried out. 
The free absorbency and the centrifugal retention are determined with the 
aid of the teabag method and indicated as the mean of two measurements: 
approx. 0.2 g of absorbent are sealed in a teabag and immersed for 20 
minutes in an electrolyte solution. To determine the absorption, the 
teabag is now suspended diagonally for 10 minutes and then weighed. To 
determine the retention, the teabag is first immersed (swelling for 10 
minutes) and then centrifuged for 3 minutes in a centrifuge (23 cm 
diameter, 1400 rpm) and weighed. The blank value is determined with the 
aid of a teabag without polymer: 
##EQU1## 
Demand absorbency: 0.1 g of absorbent are weighed into a Plexiglas cylinder 
(internal diameter: 25 mm, height: 33 mm, bottom: wire mesh with mesh size 
140 .mu.m) and exposed to absorption for 5 minutes. The amount of liquid 
absorbed is determined via the weight less of the storage container. 
In the penetration test, the penetration capacity of sheep's blood into the 
test substance is assessed visually. A value of 1 means a very good 
penetration, a value of 6 a poor penetration. 
The modulus of elasticity is measured using a controlled-stress rheometer 
with a plate-plate configuration, manufactured by Carri-Med. To determine 
the modulus of elasticity, 1 g of absorbent is allowed to swell for 12 
hours in 40 g of sheep's blood and the storage modulus of this swollen gel 
is subsequently measured as a function of the strain at a frequency of 1 
Hz. The plateau value is recorded as the modulus of elasticity G'. 
The swelling viscosity was determined using a high-shear rotary viscometer. 
During the measurement, absorbent is sprinkled into stirred sheep's blood 
at a defined point in time, and the swelling time and the swelling 
capacity (as a function of time) are recorded. 
The readings are compiled in Table 1 below. The abbreviations denote: 
ATB--free absorbency 
CRET--centrifugal retention 
DA--demand absorbency 
P--penetration 
G'--modulus of elasticity 
Q--swelling viscosity 
EL 1--0.9% strength sodium chloride solution 
EL 2--electrolyte solution composed of 0.9% NaCl, 0.25% (NH.sub.4).sub.2 
HPO.sub.4, 0.4% K.sub.2 SO.sub.4, 0.1% MgCl.sub.2. 6H.sub.2 O, 0.08% 
CaCl.sub.2. 2H.sub.2 O. 
TABLE 1 
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Sheep's blood 
Q EL 1 EL 2 
G' 5'/10'/15' 
DA DA ATB 
CRET 
ATB 
P [Pa] 
[mPas] 
[g/g] 
[g/g] 
[g/g] 
[g/g] 
[g/g] 
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Ex. 
2 2-3 989 45/51/50 
9.4 
32 38 28 28 
3 3-4 930 10/50/145 
10 52.5 
54 38 45 
4 3 1035 
43/55/48 
9.5 
38 50 36 35 
5 2 100 20/20/20 
8.8 
15 20 15 18 
6 3-4 940 36/123/150 
10.2 
53 54 38 45.5 
7 4 835 81/179/125 
10.7 
53.5 
54 37 46 
8 2 855 64/88/93 
10.2 
41 47 33 40.5 
9 2 1080 
77/126/130 
9 35 44 31 36 
10 2 315 46/58/57 
9 20 25 20 22 
11 4 1060 
79/170/125 
10.2 
52 53 37 45 
12 2 825 58/90/93 
10 43 45 31 40 
13 3 860 42/55/48 
9.7 
38 51 37 35 
14 4 1080 
81/180/127 
10.3 
53 54 37 43 
15 3 920 45/51/50 
9.4 
39 50 35 34 
16 3 970 44/55/49 
9.7 
38 52 34 36 
Comparison: 
Example 
1a 4-5 920 8/45/145 
7.5 
50 53 38 44 
Particle size: 
0.1-0.85 mm 
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