Water-absorbing polysaccharide and method for producing the same

Water-absorbent polysaccharide and a process for its preparation

The present invention relates generally to a method for producing a water-absorbing polysaccharide, a water-absorbing polysaccharide obtainable by this method, a water-absorbing polysaccharide, a composite, a method for producing a composite, a composite produced by this method, the use of the water-absorbing polysaccharides or the composites as well as the use of polyphosphates.

Most of the absorption materials used today, which are able to absorb large amounts of liquid (water, urine) in a short time, are primarily weakly cross-linked, synthetic polymers. These include, for example, polymers and copolymers based on acrylic acid or acrylamide that are not based on renewable raw materials and are insufficient or not biodegradable at all.

In the prior art, however, numerous water-absorbing polymers are described which are based on polysaccharides and which are at least partially biodegradable. However, the raw materials for the production of superabsorbents based on polysaccharide are frequently water-soluble and must be converted into the water-insoluble form in order to be able to use them as superabsorbents for hygiene applications.

For example, EP 0 538 904 A1 and US Pat. No. 5,247,072 describe superabsorbents based on carboxyalkylpolysaccharides. In the process, the carboxyalkylpolysaccharide is dissolved in water and isolated by drying or precipitation and then thermally crosslinked by the reaction of the hydroxyl groups of the polysaccharide chain with the acidic carboxyl groups via internal ester bridges. Since this crosslinking reaction is very sensitive to small changes in pH, temperature or reaction time, absorbers with strongly fluctuating absorption properties are obtained. The materials are characterized by a high absorption capacity under pressure, which, however, drops to a fraction of the original absorption capacity within a few weeks when the absorbers are stored.

US Pat. No. 5,550,189 describes absorbers based on carboxyalkyl polysaccharides in which the aging stability is improved by adding multifunctional crosslinking agents, such as aluminum salts or citric acid. The absorbers are produced from a common, homogeneous aqueous solution of carboxyalkyl polysaccharide and crosslinking agent, in which the components are present in low concentration, isolated together and then thermally crosslinked. The synthesis of these absorbers requires a lot of energy and time, since the aqueous solutions are only very low concentrated. In the majority of the exemplary embodiments, the improvement in the aging stability does not meet the practical requirements.

EP 855 405 A1 deals with the problem of the aging resistance of the absorbability of swellable starch maleates and suggests as a solution an addition of mercapto compounds to the double bond of the maleic acid substituent. The absorption behavior of the products, especially under pressure, is very low.

In US 4,952,550 the production of an absorber based on carboxymethyl cellulose is described, the carboxymethyl cellulose in water or org. Solvent is treated with polyvalent metal salts and a hydrophobizing component. There is no thermal crosslinking. According to the disclosure, the gel blocking in these absorbers is reduced by the hydrophobizing component.

In the processes known from the prior art for crosslinking polysaccharides, it was observed, in addition to the sometimes low resistance to aging, that the homogeneous crosslinking of the polysaccharides impedes the biodegradability of the absorber, since the accessibility to microorganisms is reduced by the restricted swelling. In addition, in the crosslinking reactions known from the prior art, the enzymatic degradation is inhibited by the additionally introduced substituents [Mehltretter et al., Journal of the American Oil Chemists Society, 47 (1970) pages 522-524].

In order to improve these disadvantageous properties, it has been proposed to limit the crosslinking of the polysaccharide to the surface area, but this usually leads to products which have a satisfactory absorption under pressure, but often only through an unsatisfactory absorption capacity under normal pressure and above all , due to the restriction¹ Cross-linking on the surface area, characterized by a low gel strength compared to homogeneously cross-linked polymers. Low gel strengths lead to the formation of fine dust particles in processing processes, such as sieving or conveying, and thus to the health of the workers responsible for producing the superabsorbers.

For example, WO 02/096953 A1 describes a process for the production of superabsorbents based on surface-modified polycarboxypolysaccharides, in which an uncrosslinked polysaccharide is swollen with water to form a hydrogel, the hydrogel is then mechanically comminuted and dried, and the polymer particles thus obtained are then mixed with a Solution of a crosslinker are coated and subjected to surface crosslinking. A disadvantage of the process described in WO 02/096953 A1, however, is that an organic solvent must be added to the water when the hydrogel is formed in order to require the swelling of the polysaccharide. However, the addition of the organic solvent means that the swollen polysaccharides are extremely "slimy", which makes their further processing significantly more difficult. In addition, the organic solvents remain at least partially in the end product, which is of concern for ecological reasons. WO 00/21581 A1 also discloses a method in which gels of crosslinked polysaccharides are brought into contact with organic solvents in order to obtain absorbent polysaccharides with improved absorption properties. The disadvantage of this method is above all the use of organic solvents.

No. 5,470,964 describes the production of an absorber crosslinked on the surface with polyvalent metal ions based on polysaccharides containing acid groups, which has an improved absorption against pressure. A disadvantage of this method is that a relatively thick layer of the surface has to be crosslinked for the improved absorption capacity of the absorber against pressure and that, according to the disclosure, this is only possible by previously swelling the polysaccharide with a large amount of solvent. When swollen, the polyvalent metal ions can penetrate deep enough into the surface. In order to achieve this, the polysaccharide is added to an excess of the aqueous metal salt solution, the excess of water in relation to the polysaccharide being 2 to 40 times the amount. Although the thick, cross-linked surface layer achieves good absorption values ​​against pressure, the free swelling capacity and the retention capacity of the absorber are thereby disadvantageously reduced. A further disadvantage of the described method is that the part of the polysaccharide last added to the crosslinker solution in the manufacturing process has less swelling time and a lower crosslinker concentration, so that an inhomogeneous distribution of the crosslinker results on the surface, which results in large fluctuations in the absorption properties .

In general, the invention was based on the object of overcoming the disadvantages arising from the prior art.

The object of the present invention was therefore to provide biodegradable, superabsorbent polymers based on renewable raw materials which do not have the deficiencies described above.

In particular, the absorbers should have a high long-term storage stability in which the absorption properties are retained as far as possible.

At the same time, it is desirable that the absorber particles have a high mechanical stability in order to avoid the formation of fine dust fractions in processing processes such as sieving or conveying.

Furthermore, the absorbers should not tend to gel blocking with regard to the absorption behavior, in particular in the case of suction layers containing a lot of superabsorber (usually more than 65% by weight based on the suction layer) and, in addition to a high absorption and retention capacity, also a high absorption capacity against pressure for water and aqueous solutions have.

In the case of suction layers or cores containing a lot of superabsorber and the diapers containing them, a soaking called leakage can often be observed. This and gel blocking are usually based on a slimy swollen hydrogel or at least on slimy components of the hydrogel. Therefore, it was an object of this invention to provide a less mucilaginous hydrogel-forming absorbent polymer which is suitable for use in hygiene articles.

For good absorption and application behavior, it is necessary for the absorbers to have a predominantly insoluble character even in an excess of aqueous solution. Furthermore, the absorbers should be characterized by particularly good biodegradability and should be as free as possible from organic solvents.

Another object of the invention is to find a manufacturing process for such superabsorbent polymers which is simple, economical and safe to carry out, provides a uniform product quality and which uses low amounts of solvent and where possible avoids organic solvents. In addition, the process should be feasible without the use of toxicologically questionable substances.

In addition, an object of the invention is to improve the biodegradability of hygiene articles such as sanitary napkins, wound dressings, incontinence articles and diapers.

A process for the production of a water-absorbing polysaccharide, comprising the process steps, contributes to solving these tasks:

- bringing an uncrosslinked polysaccharide into contact with a polyphosphate or with polyphosphoric acid as a crosslinking agent in the presence of water to form a polysaccharide gel, causing the polysaccharide to swell; Crosslinking the polysaccharide gel.

Another aspect of the present invention is a process for producing a water-absorbing polysaccharide, comprising the process steps:

contacting a polysaccharide with a crosslinking agent in the presence of water to form a polysaccharide gel;

Drying the polysaccharide gel;

whereby at least the contacting takes place in a kneader. It is preferred that the kneader mixes the crosslinking agent with the polysaccharide as homogeneously and intimately as possible. It is preferred that the crosslinking takes place primarily in the drying step. In this embodiment of the process according to the invention, too, the crosslinking agent is preferably a polyphosphate or polyphosphoric acid.

It is further preferred in the method according to the invention that the kneader has at least two kneading shafts. The at least two kneading shafts preferably have an at least partially interlocking contour. These are preferably elements attached to the kneading shaft, such as disks, paddles, anchors or rakes, which, viewed from the central axis of the kneading shaft, form rotation radii which overlap with the rotation radii of the elements arranged on a further kneading shaft. This can be achieved, for example, in that the kneading shafts are arranged at least in sections axially parallel to one another and on the axially parallel section the distance of the central axes of the kneading shafts is chosen to be so small that the elements formed on the kneading shafts overlap at least partially during operation of the kneading shafts. It is further preferred in the method according to the invention that at least some of the elements formed on the kneading shaft are arranged and designed in such a way that they convey the material to be conveyed at least partially parallel to the central axis of the kneading shaft, the at least two kneading shafts forming at least one of the Form kneading shafts at least partially axially extending feed channel. Thus, on the one hand, the polysaccharide with the crosslinking agent can be mixed as homogeneously as possible and the homogeneous mixture containing the polysaccharide and the crosslinking agent can be fed continuously to the crosslinking or drying step carried out by temperature treatment.

In connection with the homogenization, it is preferred that in the contact step the proportion of crosslinking agent which has already reacted is not more than 30% by weight, preferably not more than 20% by weight and particularly preferably not more than 10% by weight and moreover preferably not more than 5% by weight, based in each case on the crosslinking agent. The proportion of the crosslinking agent which has already reacted can be determined by subtracting the determinable free crosslinking agent from the one originally used.

In one embodiment of the method according to the invention, the polysaccharide and crosslinking agent are brought into contact in a kneader, whereas the crosslinking or drying step following the contacting takes place in a device different from a kneader, preferably a belt dryer. Between the two steps, a comminution step such as a chopping or chopping step can also be provided in order to remove the surface of the drying or Increase networking goods. It is further preferred that there is a temperature difference between the temperature when brought into contact for homogenization and the drying or crosslinking. The two temperatures differ by at least 10 ° C, preferably by at least 20 ° C and particularly preferably by at least 40 ° C and moreover preferably by at least 80 ° C. In one embodiment of the method according to the invention, the temperature during the contacting for homogenization is in the range from 2 to 40 ° C., preferably in the range from 10 to 35 ° C. and particularly preferably in the range from 15 to 30 ° C. In order to set the suitable temperatures, it is preferred that the kneader can be tempered. Either the housing surrounding the kneading shaft (s) or the kneading shafts, possibly with the elements themselves, or both, can be temperature-controlled.

In the process according to the invention, a kneader energy in the range from 0.01 to 1 MJ / kg, preferably in the range from 0.25 to 0.75 MJ / kg and moreover preferably 0.3 to 0.7 MJ / kg can be achieved by the kneader and a specific torque of 0.1 to 70 Nm / 1, preferably in the range from 5 to 50 Nm / 1 and particularly preferably in the range from 10 to 40 MJ / kg. Suitable kneaders are described in DE 195 36 944 AI, US 5,147,135 and DE 195 33 693 AI, among others. Suitable kneaders can also be obtained commercially, for example, from List AG, Arisdorf, Switzerland.

It is generally preferred in the process according to the invention that the polysaccharide is an uncrosslinked polysaccharide. The crosslinking agent can be any suitable crosslinking agent, with polyphosphate or polyphosphoric acid or a mixture of at least two of these being particularly preferred. It is also preferred according to the invention to combine polyphosphate or polyphosphoric acid with other suitable further crosslinking agents. Suitable further crosslinking agents are, for example, aluminum chloride or citric acid, as described in WO 02/096953 AI, or polyamines, as described in US Pat. No. 6,734,298 B1.

The use of polyphosphates or polyphosphoric acid as crosslinking agents for polysaccharides in accordance with the process according to the invention makes it possible to obtain water-absorbing polysaccharides which are distinguished by excellent absorption and retention capacity for water, aqueous solutions and body fluids. In addition, the water-absorbing polysaccharide obtainable by the process according to the invention is stable in storage, essentially free of residual monomer components and organic solvents, is only slightly soluble in aqueous liquids and is highly biodegradable.

The polysaccharides used in the process according to the invention are water-soluble or water-swellable and are used in non-crosslinked form. In addition to the hydroxyl groups, they can be modified with other groups, in particular with groups which improve water solubility. Such groups include, for example, the carboxyl group, the carboxylalkyl group, particularly preferably the carboxymethyl group, the hydroxyalkyl group, in particular the hydroxymethyl group and / or the hydroxyethyl group, the hydroxymethyl group being particularly preferred, and the phosphate group.

Depending on the functional modification, the polysaccharides used in the process according to the invention can accordingly be based on electrically charged or on electrically uncharged polysaccharides. It is also conceivable to use a polysaccharide mixture based on electrically charged and electrically uncharged polysaccharides

The electrically uncharged polysaccharides preferred according to the invention include starch or starch derivatives such as, for example, hydroxypropyl starch, amylose, amylopectin, cellulose or cellulose derivatives such as, for example, ethylhydroxyethyl cellulose or hydroxypropyl cellulose or polygalactomannanane, such as, for example, guar or locust bean gum.

The electrically charged polysaccharides preferred according to the invention include in particular polycarboxypolysaccharides. The polycarboxypolysaccharides preferably used in the process according to the invention are either derived from polysaccharides which do not naturally contain carboxyl groups and are provided with carboxyl groups by subsequent modification, or they already contain carboxyl groups by nature and are optionally subsequently provided with further carboxyl groups by modification. The first group of polysaccharides includes, for example, oxidized starch, carboxylated phosphate starch, oxidized cellulose, carboxymethyl cellulose or carboxymethyl starch, of which carboxymethyl cellulose (CMC) is particularly preferred. The preferred polysaccharides which already contain carboxyl groups by nature include, for example, xanthan, alginates or gum arabic.

According to the invention, particular preference is given to using polycarboxypolysaccharides such as, for example, carboxymethyl guar, carboxylated hydroxyethyl or hydroxypropyl cellulose, carboxymethyl cellulose and carboxymethyl starch, oxidized starch, xanthan and mixtures of the individual polycarboxypolysaccharides as polysaccharides, the use of carboxymethyl cellulose being the most preferred. In principle, polycarboxypolysaccharide derivatives with low and high degrees of carboxyl substitution can be used in the process according to the invention. In a preferred embodiment, they have an average degree of carboxyl substitution in the range from 0.3 to 1.5, particularly preferably polycarboxypolysaccharide derivatives with a degree of substitution in the range from 0.4 to 1.2 are used in the process according to the invention.

In a preferred embodiment of the process according to the invention, the polycarboxypolysaccharides are used with an addition of polysaccharides free of carboxyl groups. Strongly swelling polysaccharides, such as polygalactomannans or hydroxyalkyl celluloses, are preferably used. The amounts of carboxyl-free polysaccharides to be used for modification are determined by the required property profile, 20% by weight, preferably 10% by weight, being preferred. % and particularly preferably 5% by weight, based on uncrosslinked polycarboxypolysaccharides.

The carboxyl group-free polysaccharides can be mixed with the uncrosslinked polycarboxypolysaccharide before being brought into contact with the polyphosphate or the polyphosphoric acid or only after the contacting of the uncrosslinked polycarboxypolysaccharide with the polyphosphate or the polyphosphoric acid with the polycarboxypolysaccharide. It is also conceivable that the carboxyl-free polysaccharides are first brought into contact with the polyphosphate or the polyphosphoric acid or with an aqueous solution containing the polyphosphate or the polyphosphoric acid and the mixture thus obtained is then mixed with the polycarboxypolysaccharide.

The carboxyl groups of the uncrosslinked polycarboxypolysaccharides preferably used in the process according to the invention are at least 50%, preferably at least 80%, particularly preferably at least 90% and very particularly preferably 100% neutralized. Alkali metal hydroxides such as sodium and potassium hydroxide, sodium and potassium carbonates or hydrogen carbonates and ammonium hydroxide and amines have proven themselves as neutralizing agents.

The preferred water-soluble polysaccharides used in the process according to the invention have a high average molecular weight and therefore also a high solution viscosity in dilute aqueous solution, such as carboxymethyl cellulose produced from cotton linters, within the framework of the molecular weight distribution prescribed by the natural polymer structure. Polysaccharides with a solution viscosity in 1% aqueous solution of more than 2,000 mPas are preferred. If a polycarboxypolysaccharide is used in the process according to the invention, it should have a solution viscosity in 1% strength aqueous solution of more than 5,000 mPas and particularly preferably of more than 7,000 mPas.

Due to the manufacturing process, polysaccharides can contain different amounts of salt as a minor component. Typical salt contents of carboxymethyl celluloses in food qualities preferred as polysaccharides according to the invention are about 0.5% by weight, for technical qualities in the range from about 2% by weight to 25 to 50% by weight for products used as protective colloids. Although the water-absorbing polysaccharides obtained by the process according to the invention have a high tolerance towards a salt load, the uncrosslinked polysaccharides to be used should have a salt content of not more than 20% by weight, preferably not more than 15% by weight, particularly preferably not more than 5 wt. % and more preferably not more than 2% by weight of salt, in each case based on the weight of the uncrosslinked polysaccharide used in the process according to the invention. The physical form of the polysaccharides used in the process according to the invention is of no importance for the properties of the water-absorbing polysaccharides obtainable by the process according to the invention. Therefore, the polysaccharides, for example in the form of powders, very fine powders, granules, fibers, flakes, pearls or compacts, the use of powdery materials with a grain size in the range from 1 to 2,000 μm being preferred due to the ease of metering and conveying.

Chain-shaped polyphosphates (cαtewα-phosphates) or the ring-shaped polyphosphates (cyclophosphates, also referred to as “metaphosphates”) are preferably used as polyphosphate or polyphosphoric acid, the polyphosphates being the salts and esters of polyphosphoric acids.

Particularly preferred polyphosphates are compounds of the composition

M^I._{n + 2}[P_nO_{3n +}ι] or M^I._n[HP_nO_{3n +}ι], connections of the structure M^I._n[H₂P_nO_{3n + 1}] are particularly preferred. Among these, compounds of the composition Na are particularly preferred_nH₂PnO_3n+ ι, such as the "Graham salt", the "taddrell salt", the "Jurrol salt" or the "Calgon" used in detergents.

Preferred metaphosphates are compounds of composition M.¹_n[PO₃]_n.

In the above formulas, M¹ for monovalent metal, preferably for sodium or potassium, n preferably has a value of at least 2, preferably at least 10 and furthermore preferably a value of at least 50, a value of 5,000, preferably 1,000 and particularly preferably 100 not being exceeded . In a particular embodiment of the process according to the invention, polyphosphates are used which have been prepared by condensation of dihydrogen monophosphates and in which the H atoms of the acidic OH group bound as a chain end group have not been replaced by metal. The particularly preferred polyphosphates have the composition M^I._n[HP_nO_{3n +}ι], where M 'and n have the meaning explained above.

Preferred polyphosphoric acids are polyphosphoric acids, which are added to P by the controlled addition of water₄O]₀ or by condensation when heating H₃PO₄ be preserved. The preferred polyphosphoric acids according to the invention have the composition

H_n+ 2PnO_{3n +}ι or (HPO₃) ", Where polyphosphoric acids of the composition (HPO₃)_n are also referred to as metaphosphoric acids, where n preferably has a value of at least 2, particularly preferably at least 10, more preferably at least 20 and furthermore particularly preferably at least 50, preferably a value of 10,000, particularly preferably 1,000 and more preferably of 100 is not exceeded.

With increasing value for n, the above composition approaches H_{n +}2PnO_3n+ ι the composition (HPO₃)_n of metaphosphoric acids.

It is further preferred according to the invention that the polyphosphate or the polyphosphoric acid with the uncrosslinked polysaccharide in an amount in a range from 0.001 to 20% by weight, preferably in an amount in a range from 0.01 to 10% by weight. and particularly preferably in an amount in a range from 0.05 to 5% by weight, based in each case on the weight of the uncrosslinked polysaccharide, is brought into contact with the uncrosslinked polysaccharide. It is also preferred that the polyphosphate or the polyphosphoric acid with the uncrosslinked polysaccharide in the presence of water at a temperature in a range from 15 to 60 ° C, particularly preferably in a range from 18 to 40 ° C and more preferably in a range from 20 to 30 ° C in contact. Most preferably, the polyphosphate or polyphosphoric acid is brought into contact with the polysaccharide at room temperature.

The above-mentioned polyphosphates or polyphosphoric acid can be used alone or in combination with other crosslinkers not based on polyphosphates or polyphosphoric acids for crosslinking the polysaccharide. As additional crosslinking agents not based on polyphosphates or polyphosphoric acids, preference is given to those crosslinking agents which are mentioned in WO 02/096953 AI as covalent or ionic postcrosslinking agents, and those crosslinking agents which are described in WO 00/21581 AI on page 6 in the first Paragraph. The weight ratio between these other crosslinkers not based on polyphosphates or polyphosphoric acids and the polyphosphates or polyphosphoric acids is preferably in a range from 1: 0.01 to 1:50, particularly preferably in a range from 1: 0.1 to 1: 20 and more preferably in a range from 1: 1 to 1:10.

The swelling time depends on the temperature at which the polyphosphate or the polyphosphoric acid is brought into contact with the uncrosslinked polysaccharide and on the starting compounds used and can easily be determined by simple preliminary tests. The first process step of the process according to the invention is preferably ended when a further increase in volume of the polysaccharide due to the swelling can no longer be observed. The contacting of the polyphosphate or the polyphosphoric acid with the uncrosslinked polysaccharide is preferably carried out for a period of from 1 minute to 48 hours, particularly preferably from 1 hour to 24 hours and moreover preferably from 12 to 20 hours.

The uncrosslinked polysaccharide is preferably brought into contact with the polyphosphate or with the polyphosphoric acid at a pH in a range from 7 to 13, particularly preferably in a range from 7.5 to 12.5 and furthermore preferably in a range from 8 to 12. This applies in particular when a polycarboxypolysaccharide is used as the polysaccharide. By adjusting the pH within the pH ranges specified above, the carboxyl groups present in the polysaccharide are at least partially neutralized. In addition, the polyphosphoric acid is also at least partially neutralized.

In a particularly preferred embodiment of the process according to the invention, the uncrosslinked polysaccharide is brought into contact with the polyphosphate or the polyphosphoric acid in such a way that the polyphosphate or the polyphosphoric acid is first dissolved or dispersed in water, in the aqueous solution or the aqueous dispersion of the polyphosphate or the Polyphosphoric acid has a pH in a range from 7 to 13, is preferably set from 7.5 to 12.5 and particularly preferably from 8 to 12 and then the aqueous solution or the aqueous dispersion of the polyphosphate or the polyphosphoric acid is brought into contact with an uncrosslinked polysaccharide.

In another particular embodiment of the process according to the invention, the uncrosslinked polysaccharide is brought into contact with the polyphosphate or the polyphosphoric acid in such a way that the uncrosslinked polysaccharide is first mixed with the polyphosphate or the polyphosphoric acid under dry conditions and the mixture thus obtained is then mixed with water is brought into contact. It is preferably ensured by adding acids or bases to the water or to the mixture of the polycarboxypolysaccharide and the polyphosphate or the polyphosphoric acid that contacting the uncrosslinked polysaccharide with the polyphosphate or the polyphosphoric acid at a pH in a range from 7 to 13, preferably from 7.5 to 12.5 and particularly preferably from 8 to 12.

In a further special embodiment of the method according to the invention, the uncrosslinked polysaccharide is brought into contact with the polyphosphate or the polyphosphoric acid in such a way that first the uncrosslinked polysaccharide is brought into contact with water and then the swollen polysaccharide is brought into contact with the polyphosphate or the polyphosphoric acid is brought. Here, too, it is preferably ensured by adding acids or bases to the water or to the polysaccharide brought into contact with the water or to the polyphosphate or to the polyphosphoric acid that the uncrosslinked polysaccharide is brought into contact with the polyphosphate or the polyphosphoric acid at a pH in in a range from 7 to 13, preferably from 7.5 to 12.5 and particularly preferably from 8 to 12.

It is further preferred according to the invention that the uncrosslinked polysaccharide is brought into contact with the polyphosphate or the polyphosphoric acid in the presence of an auxiliary, the auxiliary being able to be mixed beforehand with the uncrosslinked polysaccharide or with the polyphosphate or the polyphosphoric acid or already with the polyphosphate or the uncrosslinked polysaccharide brought into contact with the polyphosphoric acid can be added. If the uncrosslinked polysaccharide is brought into contact with the polyphosphate or the polyphosphoric acid in such a way that an aqueous solution or an aqueous dispersion of the polyphosphate or the polyphosphoric acid is first prepared, to which the polysaccharide is then added, the aid can also be added to the aqueous solution or added to the aqueous dispersion of the polyphosphate or polyphosphoric acid.

The auxiliaries can be present in an amount in a range from 0.01 to 20% by weight, preferably in an amount in a range from 0.1 to 10% by weight and particularly preferably in an amount in a range from 1 to 5 wt .-%, each based on the weight of the uncrosslinked polysaccharide, are added.

Preferred auxiliaries are antiblocking additives which improve the processability of the hydrogel formed and which remain at least partially in the product after drying. Preferred antiblocking additives are native or synthetic fiber materials or other materials with a large surface area, for example from the group of the silica gels and synthetic silicas and the water-insoluble mineral salts.

Further preferred auxiliaries are water-soluble auxiliaries from the group of bases, salts and blowing agents. Inorganic or organic compounds which release gas under the influence of catalysts or heat, for example azo and diazo compounds, carbonate salts, ammonium salts or urea, are chosen as blowing agents.

Other auxiliaries are pH regulators such as alkali metal hydroxides, ammonia, basic salts such as alkali metal carbonates or acetates. Other auxiliaries are neutral salts, such as, for example, alkali metal or alkaline earth metal sulfates or chlorides for regulating the ionic strength of the solution or the salt content of the powdered absorber resin. Furthermore, water-miscible, organic solvents, preferably boiling below 100 ° C., can be used as auxiliaries in the aqueous hydrogel. During the subsequent drying process, these volatile organic solvents largely escape from the hydrogel. In the subsequent surface post-crosslinking, these solvents are finally evaporated.

The contacting of the uncrosslinked polysaccharide with the polyphosphate or the polyphosphoric acid in the presence of water can be carried out continuously or batchwise, preferably continuously. Suitable mixing devices are, for example, discontinuous kneaders such as trough kneaders, internal mixers or continuous kneaders such as single, twin or multi-shaft mixers.

When the polysaccharide gel is produced in the first process stage of the process according to the invention, the content of polysaccharide in the mixture of polysaccharide, water and polyphosphate or polyphosphoric acid can vary within wide limits; in a preferred embodiment of the process it is in the range from 5 to 65% by weight, particularly preferably 10 to 50% by weight and moreover preferably 15 to 30% by weight.

In a preferred embodiment, the water or the aqueous solution or aqueous dispersion of the polyphosphate or polyphosphoric acid is fed continuously to the dry raw material polysaccharide, for example in an extruder, the process being carried out in such a way that the water is in deficit.

According to the invention, the mixture of polysaccharide, polyphosphate or polyphosphoric acid and water can additionally contain up to 30% by weight, preferably up to 20% by weight, of one or more organic solvents which are miscible with water and immiscible with the polysaccharide. Preferably, the uncrosslinked polysaccharide is brought into contact with the polyphosphate or with the polyphosphoric acid, however, in the absence of an organic solvent.

It has proven to be particularly advantageous if the swollen gel is crushed before crosslinking. Gel comminution primarily increases the ratio of gel surface area to gel volume, which means that the subsequent drying step requires significantly less energy input. The method of gel comminution is not restricted. In a particularly preferred embodiment, the gel is comminuted by compressing the gel through a perforated disk to form gel strands, which can optionally be cut into shorter gel strands by a cutting tool.

The gel consistency can be specifically adjusted via the type and amount of addition of polyphosphates or polyphosphoric acid. The use of organic solvents in this regard, as described in WO 02/096953 AI, is surprisingly not necessary for this.

In the second stage of the process according to the invention, the polysaccharide gel or the comminuted polysaccharide gel is crosslinked to form a crosslinked polysaccharide and preferably dried simultaneously to a low residual water content. It is also conceivable to first crosslink the polysaccharide gel under conditions which do not lead to the polysaccharide gel drying and only then to dry the crosslinked polysaccharide gel.

The crosslinking step can immediately follow the pre-swelling, but it is also possible to store the polysaccharide gels or the comminuted polysaccharide gels for a longer period, for example several weeks, before further processing, without the properties interfering change the resulting superabsorbent according to the invention.

The polysaccharide gel is preferably crosslinked at a temperature above 70.degree. C., preferably above 100.degree. C. and particularly preferably above 115.degree. C. and is preferably dried at the same time, preferably a crosslinking or drying temperature of 300.degree preferably not exceeding 250 ° C. and more preferably not exceeding 200 ° C. It is also conceivable to first dry the polysaccharide gel at temperatures lower than 70 ° C., preferably under reduced pressure, and only then to increase the temperature of the dried polysaccharide to a temperature which enables the polysaccharide to crosslink. In principle, the crosslinking step can be carried out at any conceivable temperature, provided the temperature is high enough to enable at least partial crosslinking of the polysaccharide gel by the polyphosphate or the polyphosphoric acid and does not exceed a temperature which leads to decomposition of the polysaccharide .

With the crosslinking or drying temperatures, it should be noted that the parameters such as the polymer content of the gel, the pH of the mixture, the mixing process, the crosslinking or drying temperature and the drying time influence one another and are preferably coordinated so that no internal crosslinking of the hydrogel takes place during the crosslinking of the polysaccharide with the polyphosphate or polyphosphoric acid. For example If an aqueous solution with a pH value below 7 is used in the preparation of the polysaccharide gel, when polycarboxypolysaccharides are used, some of the carboxylate groups present in the polysaccharide derivative are converted into the free acid form, which in particular towards the end of drying can esterify as an internal crosslinker by esterification with the hydroxyl groups. In order to avoid or largely suppress this, in principle undesirable, internal crosslinking, the crosslinking or drying in these cases is preferably carried out at temperatures in the range from 70-100 ° C. The pH is usually adjusted to 6 or higher. In a preferred embodiment of the invention, an aqueous solution with a pH of> 7 is selected for the preparation of the polysaccharide gel and the crosslinking or Drying carried out at temperatures from 110 ° C, preferably from 115 to 120 ° C.

Various methods are known for drying the polysaccharide gels. Possible processes are, for example, evaporation drying, evaporation drying, radiation drying (example: infrared drying), high-frequency drying (example: microwave drying), vacuum drying, freeze drying or spray drying. For example, drying can be carried out using the thin-film drying process, e.g. with the help of a two-axis drum dryer, after the plate drying process, according to which the hydrogel polymer particles are loaded onto plates in several layers in a drying chamber, in which hot air is circulated, after the rotating drum process with the help of drum dryers or after the conveyor belt process, also in the following referred to as belt drying. Belt drying, in which perforated hordes of a circular conveyor are loaded with drying material in a tunnel and the drying material is dried during the conveyance by blowing hot air through the tray holes, is the most economical drying method for water-swellable hydrophilic hydrogels and is therefore preferred.

The moisture of the polymer formed by drying the polysaccharide gel is advantageously not more than 30% by weight, preferably not more than 15% by weight and particularly preferably not more than 10% by weight. If the polysaccharide gel is produced in a continuous mixer, for example in an extruder, the preliminary products which have not yet been post-crosslinked on the surface can have high retentions of greater than or equal to 40 g / g from pH values ​​of 7 onwards, which increase during annealing 60 minutes and 120 ° C have proven to be stable and differ only slightly from products manufactured with higher pH values. If, on the other hand, the hydrogels are produced in a batch process, the stability to tempering increases with increasing pH of the gel. A preferred pH setting for hydrogel formation in the batch process is therefore pH 10 or higher.

In a further embodiment of the process according to the invention, the crosslinked polycarboxypolysaccharide obtained after drying the polycarboxypolysaccharide gel or the comminuted polysaccharide gel is ground in a further process step. By comminuting the polysaccharide gel and grinding the dried, crosslinked polycarboxypolysaccharide, particulate, crosslinked polysaccharides are obtained.

For the subsequent grinding of the dried polysaccharide gels or the dried and previously comminuted polysaccharide gels, it is advantageous to dry the dry material in the last section of the preferred belt drying to temperatures <70 ° C., preferably <60 ° C. and particularly preferably <50 ° C. cool down. The dried, cooled polysaccharide gels or comminuted polysaccharide gels are first broken up, for example with the aid of a finger breaker. The dried gel particles pre-comminuted in this way are then ground, the grinding preferably being carried out with the aid of a roller mill in order to keep the accumulation of fine particles as low as possible. In a particularly preferred embodiment, the grinding takes place in two stages, first over a coarse roller mill, then over a fine roller mill, the latter again being able to be one or two stages. In the subsequent sieving, the particle size distribution is set, which is generally between 10 and 3000 μm, preferably between 100 and 2000 μm and particularly preferably between 150 and 850 μm. Particles that are too coarse can be subjected to grinding again, particles that are too fine can be returned to the production process.

In a special embodiment of the method according to the invention, the drying step or the grinding step is followed by a further process step in which the particulate, crosslinked polysaccharide is postcrosslinked in the outer region of the particles with a postcrosslinking agent.

The outer region of the particles is preferably understood to mean any volume element of the particle whose distance from the center of the particles is at least 75%, preferably at least 85% and particularly preferably at least 95% of the outer radius of the polymer particles.

The surface crosslinking of the dried, particulate, crosslinked polycarboxypolysaccharide is preferably carried out with 0.001 to 25% by weight, particularly preferably with 0.1 to 20% by weight, of the postcrosslinking agent, in each case based on the weight of the crosslinked polysaccharide. The post-crosslinking agent is preferably used in the form of a 0.01 to 80% by weight, preferably a 0.1 to 60% by weight solution. The post-crosslinking agent is supplied in suitable mixing units. These are, for example, Paterson-Kelly mixers, DRAIS turbulence mixers, Lödige mixers, Ruberg mixers, screw mixers, plate mixers, fluidized bed mixers or Schugi mixers. After the solution of the postcrosslinking agent has been sprayed on, a temperature treatment step can follow, preferably in a downstream dryer, at a temperature between 40 and 250 ° C., preferably 60-200 ° C. and particularly preferably 80-160 ° C., over a period of 5 minutes to 6 Hours, preferably 10 minutes to 2 hours and particularly preferably 10 minutes to 1 hour, solvent components being removed. The optimal duration of the reheating can easily be determined for the individual types of crosslinkers with just a few attempts. It is limited if the desired property profile of the super absorber is destroyed again as a result of heat damage. The thermal treatment can be carried out in conventional dryers or ovens; examples include rotary kilns, fluid bed dryers, plate dryers, paddle dryers or infrared dryers.

It has proven to be advantageous in some cases for the aqueous solution of the surface postcrosslinker to be set to a temperature of 15 ° C. to 100 ° C., preferably to 20 ° C. to 60 ° C., before it is used.

The covalent post-crosslinking can optionally be accelerated by catalysts. Compounds which catalyze the esterification reaction between a carboxyl group and a hydroxyl group, such as, for example, hypophosphites, acetylacetonates, mineral acids, such as, for example, sulfuric acid and Lewis acids, are preferably used as catalysts. Sulfuric acid and hypophosphite are preferably used. The weight ratio of surface postcrosslinker to crosslinking catalyst is 1: 0.001-1: 1, preferably 1: 0.1-2: 1

In a preferred embodiment, the crosslinking catalysts are mixed into the solution of the surface postcrosslinker.

The postcrosslinking solution can optionally contain up to 70% by weight of one or more auxiliaries. Aids are above all water-soluble compounds which promote the homogeneous distribution of the crosslinking solution on the surface of the absorber by slowing down the penetration of the solvent into the interior of the superabsorbent particles and reducing the solubility of the particle surface and thus the tendency of the moist superabsorbent particles to stick together. In addition to water-miscible organic solvents such as ethanol, propanol, 2-propanol, acetone, glycerin, tetrahydrofuran and dioxane, preferred auxiliaries are also water-soluble hydrophilic organic solids, in particular polymers such as polyalkylene glycols, polyvinyl alcohols, preferably polyethylene glycols.

The post-crosslinking of the outer region can be accomplished by ionic or covalent post-crosslinking agents which react with the functional molecular groups near the surface, preferably carboxyl, carboxylate or hydroxyl groups, preferably with heating.

Crosslinkers which react with the functional groups of the polysaccharides to form covalent bonds are used as covalent postcrosslinking agents, which can also be used in combination with ionic crosslinkers. In a preferred embodiment, crosslinking agents are used which can react with the hydroxyl groups or, when polycarboxypolysaccharides are used, with the carboxyl groups of the crosslinked polysaccharide, for example substances containing acid groups. In particular, low molecular weight polycarboxylic acids and their derivatives such as malonic acid, maleic acid, maleic anhydride, tartaric acid and polymeric polycarboxylic acids, for example based on (meth) acrylic acid and / or maleic acid. Citric acid, butanetetracarboxylic acid and polyacrylic acid are preferred, and citric acid is particularly preferably used. The polycarboxylic acids can also be used in partially neutralized form, for example by partial neutralization with alkali metal hydroxides or amine bases. In addition to these postcrosslinking agents, polyphosphates and polyphosphoric acids are particularly preferred as postcrosslinking agents, preference being given to using those polyphosphates and polyphosphoric acid which have already been mentioned in connection with the first process stage of the process according to the invention.

Suitable ionic postcrosslinking agents, which can be used alone or in combination with the covalent postcrosslinking agents, are salts of at least divalent metal cations, for example alkaline earth metal ions such as Mg²⁺, Approx²⁺, as well as Al³⁺, Ti⁴⁺, Fe²⁺/ Fe³⁺, Zn²⁺ or Zr⁴⁺, with Al³⁺, Ti⁴⁺ and Zr⁴⁺ are preferred and AI is particularly preferred. Aluminum salts are preferably used in an amount of 0.2-1.0% by weight, preferably 0.25-0.85% by weight, based on the crosslinked polysaccharide.

The salts of the metal cations can be used either alone or in a mixture with one another. The metal cations in the form of their salts have a sufficient solubility in the solvent used; the metal salts with weakly complexing anions such as chloride, nitrate, sulfate and acetate are particularly preferably used.

Further suitable post-crosslinking agents are those which can form both covalent and ionic crosslinking bonds, for example di- and polyamines which can act both as covalent crosslinkers, via amide groups, and as ionic crosslinkers, via ammonium salt complexes.

In a particularly preferred embodiment of the process according to the invention, polyphosphates or polyphosphoric acids are used as postcrosslinking agents, in another, particularly preferred embodiment there is a mixture of polyphosphates or polyphosphoric acids and at least one of the above-mentioned postcrosslinking agents which are not based on polyphosphates or polyphosphoric acids, in particular mixtures of polyphosphates or polyphosphoric acids and ionic postcrosslinking agents, for use, mixtures of polyphosphates or polyphosphoric acids and aluminum salts being very particularly preferred.

When polyphosphates or polyphosphoric acids are used as postcrosslinking agents, they are preferably used in the form of an aqueous solution with a pH in a range from 7 to 13, particularly preferably in a range from 8 to 12. When using polyphosphates or polyphosphoric acids as post-crosslinking agent, it is further preferred that the polyphosphates or the polyphosphoric acids in an amount in a range from 0.01 to 10 wt .-%, particularly preferably in an amount in a range from 0.1 to 5 wt .-% and particularly preferably in an amount in a range from 0.3 to 1.5 wt .-%, each based on the weight of the crosslinked polysaccharides.

In connection with the post-crosslinking of the crosslinked polysaccharides, it is preferred in a particular embodiment of the method according to the invention that the crosslinked polysaccharide is brought into contact with an inorganic material.

As inorganic material, any particulate inorganic material known to the person skilled in the art can be brought into contact with the crosslinked polysaccharides, which is suitable for modifying the properties of water-absorbing polymers. The preferred inorganic materials include silicates, in particular framework silicates such as zeolites or silicates, which have been obtained by drying aqueous silica solutions or silica sols, for example the commercially available products such as precipitated silicas and pyrogenic silicas, for example aerosils, aluminates, titanium dioxides, zinc oxides, clay materials and others minerals familiar to the expert as well as carbon-containing inorganic materials.

Preferred silicates are all natural or synthetic silicates which are described in “Holleman and Wiberg, Textbook of Inorganic Chemistry, Walter de Gruyter-Verlag, 91.-100. Edition, 1985 "on pages 750-783, as silicates. The above section of this textbook is hereby incorporated by reference and is considered part of the disclosure of the present invention.

Zeolites are particularly preferred silicates. All synthetic or natural zeolites known to the person skilled in the art can be used as zeolites. Preferred natural zeolites are zeolites from the natrolite group, the harmoton group, the mordenite group, the chabasite group, the faujasite group (sodalite group) or the analcite group. Examples of natural zeolites are analcim, leucite, pollucite, wairakite, bellbergite, bikitaite, boggsite, brewsterite, chabazit, willerson sonite, cowlesite, dachiardite, edingtonite, epistilbit, erionite, faujasite, ferrierite, amicite, garronite, gismondite, gismondite , Gmelinite, gonnardite, goosecreekite, harmotome, phillipsite, wellsite, clinoptilolite, heulandite, laumontite, levyne, mazzite, merlinoite, montesommaite, mordenite, mesolite, natrolite, scolecite, offretite, paranatrolite, Paulingite, Perlialite, Barrerite, Stilbit, Stellerit, Thomsonite, Chemichite or Yugawaralite. Preferred synthetic zeolites are zeolite A, zeolite X, zeolite Y, zeolite P or the product ABSCENTS.

Zeolites of the so-called "medium" type, in which the SiO₂/ AlO₂- Ratio is less than 10, the SiO is particularly preferably₂/ AlO₂- Ratio of these zeolites in a range from 2 to 10. In addition to these “medium” zeolites, it is also possible to use zeolites of the “high” type, which include, for example, the known “molecular sieve” zeolites of the ZSM type and β-zeolite. high "zeolites are preferably by an SiO₂/ AlO₂- Ratio of at least 35, particularly preferably of an SiO₂/ AlO₂- Ratio marked in a range from 200 to 500.

The naturally occurring spinels, in particular ordinary spinel, zinc spinel, iron spinel or chromium spinel, are preferably used as aluminates.

Preferred titanium dioxides are titanium dioxide in the crystal forms rutile, anatase and brookite, and iron-containing titanium dioxides such as, for example, ilmenite, calcium-containing titanium dioxide such as titaniumite or perovskite.

Preferred clay materials are those described in “Holleman and Wiberg, Textbook of Inorganic Chemistry, Walter de Gruyter Verlag, 91.-100. Edition, 1985 "on pages 783-785 as clay materials. The above section of this textbook is hereby incorporated by reference and is considered part of the disclosure of the present invention. Particularly preferred clay materials are kaolinite, illite, halloysite, montmorillonite and talc .

Preferred carbon-containing, but not organic materials are those carbons which are described in “Holleman and Wiberg, Textbook of Inorganic Chemistry, Walter de Gruyter-Verlag, 91.-100. Edition, 1985 "on pages 705-708 as graphite. The above section of this textbook is hereby incorporated by reference and is considered part of the disclosure of the present invention. Particularly preferred graphites are artificial graphites such as coke, pyrographite, activated carbon or soot. When using the above-mentioned inorganic materials or their mixtures, it is particularly preferred that these materials in an amount in a range from 0.1 to 1 wt .-%, more preferably in an amount in a range from 0.25 to 0.75% by weight and, moreover, more preferably in a range from 0.4 to 0.6% by weight, based on the total weight of the crosslinked polysaccharides, are brought into contact with the crosslinked polysaccharides.

It is further preferred according to the invention that the inorganic materials have a specific surface area determined according to the BET method in a range from 30 to 850 m Ig, preferably in a range from 40 to 500 m / g, particularly preferably in a range from 100 to 300 m²/ g and more preferably in a range from 150 to 250 m²/ g. In general, and in the event that the inorganic materials are sipemates or aerosils, the surface is in a range from 30 to 850 m²/ g, preferably in a range from 40 to 500 m Ig, particularly preferably in a range from 100 to 300 m²/ g and is determined with nitrogen in an aromatic meter according to ISO 5794, Annex D.

When using inorganic materials in the form of particles, it is further preferred that at least 90% by weight, preferably at least 95% by weight and moreover preferably at least 99% by weight of the inorganic material have a particle size of less than 200 μm, particularly preferably less than 100 μm and furthermore preferably less than 1 μm and furthermore preferably less than 500 nm and furthermore even more preferably less than 100 nm. The sipemates have a particle size in the range from 10 to 180 μm, preferably in the range from 20 to 150 μm and particularly preferably in the range from 30 to 110 μm. In another embodiment of the present invention, the sipemates have a particle size in the range from 1 to 40 μm, preferably in the range from 2 to 30 μm and particularly preferably in the range from 3 to 20 μm. This is the mean particle size determined according to the multisizer capillary method according to ASTM C690-1992. Aerosils are characterized by a particle size in the range from 5 to 50 nm, preferably in the range from 8 to 20 nm (such as "Aerosil 200" from Degussa AG). The particle size can be determined according to ASTM C 690- 1992 using a multisizer.

If inorganic materials are used, it is further preferred that the crosslinked polysaccharide is brought into contact with the inorganic material preferably in the presence of a “binder”. This is preferably provided as a solution for contacting. This solution is preferably a An aqueous solution: All organic polymers which appear suitable to the person skilled in the art are suitable as binders. Particularly preferred polymers have a melting point according to ISO 11357 in the range from -15 to 150 ° C, preferably in the range from -12 to 100 ° C and particularly preferably in the range from -9 to 90 ° C. Polyethylene glycols are preferred as binders.

The binders are preferably in the form of a film. This film is preferably located on the surface of the water-absorbing polysaccharide according to the invention. This film preferably has a thickness in the range from 0.001 to 20 nm, preferably in the range from 0.01 to 15 nm and particularly preferably in the range from 0.1 to 10 nm. The thickness can be measured using suitable microscopes, for example. It is advisable to make an average of at least 10 cuts. It is entirely possible that the film only covers parts of the surface of the water-absorbing polysaccharide according to the invention. Suitable binders are generally polymeric materials with a molecular weight of more than about 290 g / mol, which have a corresponding melting temperature and, at a corresponding application temperature, show no decomposition or any other change in the molecular structure which is disadvantageous for the adhesive effect.

The number average molecular weight determined by gel permeation chromatography (GPC) (M_n) The polymers which can be used as binders are preferably in the range from 290 to 1,000,000, particularly preferably in the range from 1,000 to 100,000 and moreover preferably in the range from 5,000 to 20,000 g / mol.

The molecular weight distribution of the polymers mentioned, as can also be determined by gel permeation chromatography (GPC), can be monomodal. If appropriate, a polymer which can be used as a binder can also have a bimodal or higher-modal distribution.

Furthermore, when using binders, it is preferred that they are present in an amount in a range from 0.001 to 10% by weight, preferably 0.01 to 5% by weight and more preferably 0.05 to 2.5% by weight. -%, based on the total weight of the crosslinked polysaccharide, are used.

If inorganic materials are used, optionally in combination with binders, these additional components can be brought into contact with the polysaccharides before the post-crosslinking, during the post-crosslinking or also after the post-crosslinking, the addition of these components after the post-crosslinking being particularly preferred is. If the inorganic material and the binder are added before the crosslinking of the crosslinked polysaccharides, then by heating the polysaccharide to a temperature in the range from 100 to 160 ° C. and preferably from 120 to 140 ° C., the crosslinking and the binding of the inorganic material.

The invention also relates to a water-absorbing, at least partially neutralized polysaccharide which can be obtained by the process described above.

The water-absorbing polysaccharide obtainable by the process according to the invention is distinguished by an excellent absorption and retention capacity for water, aqueous solutions and body fluids. At the same time, due to the targeted cross-linking of the surface, it has a significantly improved absorption capacity for aqueous solutions against external pressure. In addition, the water-absorbing polysaccharide obtainable by the process according to the invention is stable in storage, essentially free of residual monomer fractions and organic solvents which often occur in the production of polyacrylates, is only slightly soluble in aqueous liquids and highly biodegradable.

Furthermore, the present invention relates to a particulate, water-absorbing polysaccharide, the polysaccharide with a polyphosphate or with polyphosphoric acid in an amount in a range from 0.001 to 20% by weight, preferably in an amount in a range from 0.01 to 10% by weight. -% and particularly preferably in an amount in a range from 0.05 to 5 wt .-%, each based on the weight of the polysaccharide, is crosslinked.

In a further embodiment, the invention also relates to a particulate water-absorbing polysaccharide, preferably with at least 5% by weight and particularly preferably at least 90% by weight, in each case based on the water-absorbing polysaccharide, a branched polysaccharide, preferably cellulose and / or their Derivatives, the water-absorbing polysaccharide having a surface area coated with an inorganic particle. In addition, it may be preferred that the water-absorbing polysaccharide according to the invention also has a binder, at least in the surface area. The water-absorbing polysaccharide according to the invention preferably has inorganic particles in an amount in the range from 0.001 to 20 and particularly preferably in the range from 0.01 to 10% by weight, in each case based on the water-absorbing polysaccharide according to the invention. Irrespective of this, the water-absorbing polysaccharide according to the invention preferably has an amount in the range from 0.001 to 20 and particularly preferably in the range from 0.01 to 10% by weight, in each case based on the water-absorbing polysaccharide according to the invention.

Preferred polysaccharides are those polysaccharides which have already been mentioned in connection with the process according to the invention for producing a water-absorbing polysaccharide, the same also being true for inorganic particles and for binders.

In a preferred embodiment, the water-absorbing polysaccharide according to the invention has an average particle diameter determined according to ERT 420.1-99 in a range from 1 to 2,000 μm, preferably in a range from 100 to 1,000 μm and particularly preferably in a range from 150 to 850 μm in front. It is further preferred that at least 50% by weight, preferably at least 75% by weight and particularly preferably at least 100% by weight of the water-absorbing polysaccharide according to the invention has a particle size in the range from 300 to 600 μm determined by sieve analysis. It is further preferred that the particulate, water-absorbing polysaccharide according to the invention has at least one, preferably each, of the following properties: (α 1) an A UL value determined according to the test method described herein at a pressure of 0.9 psi in a range from 10 to 22 g / g, particularly preferably in a range from 12 to 19 g / g and beyond in a range from 14 to 17 g / g with a CRC value determined in accordance with the test method described herein in a range from> 15 to <20 g / g; (α2) an AUL value determined according to the test method described herein at a pressure of 0.9 psi in a range from 6 to 20 g / g, particularly preferably in a range from 8 to 17 g / g and moreover preferably in one Range from 10 to 14 g / g with a CRC determined in accordance with the test method described herein in a range from> 20 to <25 g / g; (α3) an A UL value determined according to the test method described herein at a pressure of 0.9 psi in a range from 6 to 15 g / g, particularly preferably in a range from 7 to 12 g / g and moreover preferably in a range of 8 to 10 g / g with a CRC determined in accordance with the test method described herein in a range of> 25 to <30 g / g; (α4) an A UL value determined according to the test method described herein at a pressure of 0.9 psi in a range from 5 to 12 g / g, particularly preferably in a range from 6 to 10 g / g and more preferably in a range of 7 to 9 g / g with a CRC value of> 30 g / g determined according to the test method described herein;

In principle, each of the preceding digits or a combination thereof represents a preferred embodiment of the present invention. Preferred particulate, water-absorbing polysaccharides according to the invention are those which are characterized by the following properties or combinations of properties: α1, α2, α3, α4, α5, α6, αlα2, αlα3, αlα4, α2α3, α2α4, α3α4, αlα2α3, αlα3α4, α2α3α4, αlα2α3α4.

It is further preferred that the particulate, water-absorbing polysaccharides according to the invention have at least one, preferably each, of the following properties:

(β1) a biodegradability determined according to the test method described herein of at least 40% in 90 days, preferably of at least 50% in 90 days and more preferably of at least 65% in 90 days and more preferably of at least 75% in 90 days ;

(β2) an extractable fraction determined according to ERT 470.2-99 in a range from 5 to 60%, preferably in a range from 8 to 30% and moreover preferably in a range from 10 to 20%; (β3) a value for the gel bed permeability determined in accordance with the test method described herein in a range from 1 to 500, preferably in a range from 5 to 300 and more preferably in a range from 20 to 200 x 10-9 cm².

Basically, each of the preceding numbers or a combination thereof represents a preferred embodiment of the present invention. Preferred particulate, water-absorbent polysaccharides according to the invention are those which are characterized by the following properties or combinations of properties: ßl, ß2, ß3, ßlß2, ßlß3, ß2ß3, ßlß2ß3.

In another embodiment of the water-absorbing polysaccharide according to the invention, a biodegradability determined according to the test method described here is in a range from 25 to 50% in 45 days and in a range from more than 50 to 90% in 90 days, preferably of at least 28% in 45 days and at least 51% in 90 days before. In connection with the particulate, water-absorbing, at least partially neutralized polysaccharides according to the invention, it is further preferred that, in the swollen state, they have a "sliminess" determined according to the test method described herein in a range from 1 to 3, preferably in a range from 1 to 2 and moreover preferably have from 1.

It is further preferred that the particulate water-absorbing polysaccharides according to the invention have an inner region and an outer region surrounding the inner region, the outer region having a higher degree of crosslinking than the inner region, so that a core-shell structure is preferably formed. The increased crosslinking in the outer region of the crosslinked polysaccharides is preferably achieved by crosslinking reactive groups close to the surface. Polyphosphates and polyphosphoric acid are preferred as postcrosslinkers for postcrosslinking, those polyphosphates and polyphosphoric acids which have already been mentioned in connection with the first process step of the process according to the invention for the preparation of water-absorbing polysaccharides being particularly preferred.

The outer region of the particles is preferably understood to mean any volume element of the particle whose distance from the center of the particles is at least 75%, preferably at least 85% and particularly preferably at least 95% of the outer radius of the polymer particles.

The invention further relates to a composite comprising a previously defined water-absorbing polysaccharide and a substrate. The water-absorbing polysaccharide according to the invention and the substrate are preferably firmly connected to one another. Films made of polymers, such as polyethylene, polypropylene or polyamide, metals, nonwovens, fluff, tissues, fabrics, natural or synthetic fibers, or other foams, are preferred as substrates.

According to the invention, sealing materials, cables, absorbent cores, and diapers and hygiene articles containing them are preferred as the composite.

The invention further relates to a method for producing a composite, wherein a water-absorbing polysaccharide according to the invention and a substrate and, if appropriate, a suitable auxiliary are brought into contact with one another. The contacting is preferably carried out by wetlaid and airlaid processes, compacting, extruding and mixing.

In addition, the invention relates to a composite that can be obtained by the above method.

The invention further relates to chemical products, in particular foams, moldings, fibers, foils, films, cables, sealing materials, liquid-absorbing hygiene articles, carriers for plant or fungal growth regulating agents or crop protection agents, additives for building materials, packaging materials or soil additives which comprise the water-absorbing polysaccharide according to the invention or include the composite described above. These chemical products are particularly characterized by their particularly good biodegradability.

In addition, the invention relates to the use of the water-absorbing polysaccharide according to the invention or the composite described above in hygiene products, for flood control, for insulation against water, for regulating the water balance in soils or for treating food. Finally, the invention also relates to the use of polyphosphate or polyphosphoric acid for crosslinking an uncrosslinked polysaccharide, preference being given to those polyphosphates, polyphosphoric acids and polysaccharides which have already been mentioned in connection with the first process step of the process according to the invention for the production of water-absorbing polysaccharides.

The invention will now be explained in more detail on the basis of test methods and non-limiting examples.

TEST METHODS DETERMINATION OF GEL BED PERMEABILITY (GBP)

This property is determined according to the test method disclosed in US Pat. No. 6,387,495 B1. DETERMINATION OF CENTRIFUGATION RETENTION CAP ACITY (CRC)

This property is determined according to the test method disclosed in EP 0 601 529 B1. DETERMINATION OF ABSORPTION UNDER LOAD (AUL)

This property is determined according to the test method disclosed in EP 0 339 461 B1, the pressure loads mentioned in the tables below being used. DETERMINATION OF SLIMICITY

For this purpose, the swollen gel obtained in the course of determining the CRC is assessed by daylight by daylight and the following notes are given according to the visual impression. For clarification, reference is also made to the pictures assigned to the individual notes.

<img file="WO2005123781A2_D0001.tif" />

DETERMINATION OF BIODEGRADABILITY

The biodegradability (mineralization) is determined by the controlled posting test (according to ISO 14855, ASTM D5338-92, DIN V54900-2). EXAMPLES

EXAMPLE 1

1 A) STAGE OF THE PROCEDURE OF THE INVENTION

Polyphosphoric acid (84% from Clariant, Germany) is dissolved in an amount of 0.09% by weight, based on the amount of sodium carboxymethyl cellulose used, in distilled water and brought to a pH of 11.5 with an alkali metal hydroxide solution set. The sodium carboxymethyl cellulose (Cekol^® 100,000 from Noviant, the Netherlands, with an active substance content of 15% by weight) is kneaded homogeneously into the solution and then bulged. The curved gel is then dried at temperatures of 120 ° C. for 150 minutes and then ground to a grain size in a range from 850 μm to 150 μm.

An AI powder is obtained.

1 B) STAGE OF THE PROCEDURE OF THE INVENTION

An aqueous solution with a pH of 11.0 containing 6% by weight, based on the total weight of the aqueous solution, polyphosphoric acid as postcrosslinker, is mixed with the powder AI in an amount of 10% by weight, based on the total weight of powder AI, brought into contact. The coated intermediate product is heated at temperatures of 130 ° C for 50 minutes.

A powder B1 is obtained. The powders AI and Bl were characterized by the following properties:

Table 1

<img file="WO2005123781A2_D0002.tif" />

EXAMPLE 2

2A) STAGE OF THE PROCEDURE OF THE INVENTION

Example 1A was repeated, using instead of 0.09% by weight, based on the amount of sodium carboxymethylcellulose used, 0.1% by weight of polyphosphoric acid (84% strength from Clariant, Germany).

A powder A2 is obtained.

2B) STAGE OF THE PROCEDURE OF THE INVENTION

Example 1B was repeated, the aqueous solution with a pH of 11.0 additionally comprising 0.3% by weight, based on the amount of powder A2, Aerosil 200 from Degussa AG, Germany and 5% by weight of polyphosphoric acid , based on the total weight of the aqueous solution, was used and heated at 125 ° C. for 65 minutes.

A powder B2 is obtained. The powders A2 and B2 were characterized by the following properties:

Table 2

<img file="WO2005123781A2_D0003.tif" />

EXAMPLE 3

3A) STAGE OF THE PROCEDURE OF THE INVENTION

Example 1A was repeated using instead of Cecol^® 100,000 now Cecol⁴ 50,000 was used.

A powder A3 is obtained.

3B) STAGE OF THE PROCEDURE OF THE INVENTION

Example IB was repeated, the aqueous solution having a pH of 11.0 additionally comprising 0.3% by weight, based on the amount of powder A3, Aerosil 200 from Degussa AG, Germany. It was also dried at 130 ° C for 110 minutes.

A powder B3 is obtained. Powders A3 and B3 were characterized by the following properties:

Table 3

<img file="WO2005123781A2_D0004.tif" />

EXAMPLE 4

4A) STAGE OF THE PROCEDURE OF THE INVENTION

Example 1A was repeated, using instead of 0.09% by weight, based on the amount of sodium carboxymethyl cellulose used, 0.1% by weight of polyphosphoric acid (84% from Clariant, Germany).

A powder A4 is obtained.

4B) STAGE OF THE PROCEDURE OF THE INVENTION

Example IB was repeated, the aqueous solution with a pH of 11.0 additionally containing 0.5% by weight, based on the amount of powder A4, sipernate 22S from Degussa AG, Germany, and at 125 ° C. was heated over 65 minutes.

A powder B4 is obtained. Powders A4 and B4 were characterized by the following properties:

Table 4

<img file="WO2005123781A2_D0005.tif" />