WO1998029454A1

WO1998029454A1 - Biodegradable absorbing agent

Info

Publication number: WO1998029454A1
Application number: PCT/EP1997/007258
Authority: WO
Inventors: Manfred Dieter Lechner; Waldemar Lazik
Original assignee: Chp Carbohydrate Pirna Gmbh & Co. Kg
Priority date: 1996-12-30
Filing date: 1997-12-23
Publication date: 1998-07-09
Also published as: DE19654745C2; DE19654745A1; DE19654745C5

Abstract

A solid absorbing agent for water, aqueous solutions and body fluids is produced by cross-linking an ionic, carboxyl-containing polysaccharide derivative in the presence of 10-80 % by weight water (with respect to the polysaccharide derivative) at 110-180 °C. The solid absorbing material is characterised in that is consists of 100 % biodegradable renewable raw materials and in that it exhibits the qualities required of such materials in hygienic or medical articles, for example.

Description

Biodegradable absorbent

The invention relates to crosslinked polysaccharide derivatives and the production of absorption materials which are based entirely on renewable raw materials and are therefore in principle completely biodegradable. These absorbent materials can quickly absorb and bind aqueous liquids on a large scale. The benefit is based on their use in the production of water-storing agents for single use in hygiene articles, animal hygiene articles, moisture protection in packaging materials, etc.

Absorbents with high absorbency for aqueous liquids have long been known. They are not based on renewable raw materials and are fully synthetic absorbents made from petroleum products. These include, for example, crosslinked synthetic polymers and copolymers based on acrylic or methacrylic acid (US Pat. No. 4,018,951). These known synthetic absorbents are practically insoluble in water, absorb many times their weight in aqueous liquids and are hardly biodegradable.

Furthermore, mixtures of polysaccharides, polyacrylates, various auxiliaries (e.g. fibers) and additional crosslinkers (e.g. addition of borates after component mixing) are proposed according to DE-OS 42 06 856, the polyacrylate always being the main absorber. The polysaccharides are seen as building blocks for the absorber materials in order to obtain biodegradable components.

In the processes described so far according to the current state of the art, the polysaccharides have no decisive contribution as an absorber. US Pat. No. 4,959,341 describes the production of an absorber based on carboxymethyl cellulose, which consists of a mixture of carboxymethyl cellulose, cellulose fibers, a hydrophobic component and Al (OH) ₂ OOCCH ₃ ^• 1 / 3H ₃ B0 ₃ as crosslinking agent exists, the borate crosslinker causing crosslinking of the carboxymethyl starch only during the absorption of liquid. These absorbers have good absorption properties, but show disadvantageous gel blocking (ie, when they come into contact with water, the outer layers of the absorber stick together and prevent further penetration into the absorber). In addition, these absorbers are easily separated by mechanical loads, such as sieving or conveying, so that they are no longer present as a homogeneous product, which limits their possible uses.

The natural swelling agents from polysaccharides play only a minor role as absorption material for aqueous liquids, since they have a low absorption capacity. A composition of pectin (15-60%) and cellulose material (15-80%) only absorbs two to five times the amount of aqueous liquids compared to the usual cellulose material. In contrast, the biodegradability of such native swelling agents is advantageous, since the natural polymers, such as cellulose, starch, proteins, and their derivatives are degraded in biological systems in a relatively short time.

When developing absorbers (especially superabsorbers), the focus is not only on a very high free swelling capacity, also called free swelling capacity (FSC), but also on the gel strength. Absorption capacity (free swelling capacity) and gel strength, however, are opposing properties in a networked system, as described, for example, in US Pat. No. Re 32,649. This means that polymers with a particularly high absorption capacity have only a low strength of the swollen gel, with the result that the gel is deformable under an applied pressure and prevents further liquid distribution and absorption. However, a balanced relationship between absorbency and gel strength has to be striven for, so that during use such absorber the liquid absorption and liquid transport are guaranteed. It is not only important that the absorber can retain liquid under the action of a load after the absorber has been able to swell freely, but also that liquids can be taken up against a simultaneous pressure, as is the case under practical conditions

The situation with hygiene articles happens when a person sits or lies on a medical article or through it

Body movements to develop shear forces on the

Absorber gel is coming. When shear forces occur, the

Gel strength of particular importance.

There is therefore a need for absorbents with higher absorption capacities for aqueous liquids and higher gel strengths, which at the same time are said to be completely biodegradable, which do not have the deficiencies described above, in particular for use in disposable items and the consequent precautions

I. The absorbers should consist entirely of derivatives of native origin.

II. The dry absorbers should have a high mechanical strength.

III. The absorbers are said to have a comparatively high absorption rate and absorption capacity for aqueous liquids.

IV. When swollen, the absorbers should have a sufficiently high gel stability and the absorber grains should be largely separated and be present in individual particles.

V. The absorbers must not tend to gel blocking.

VI. The absorbers should be sufficiently high

Have absorption capacity under load after free swelling and under pressure during swelling for aqueous liquids.

VII. The absorbers should be largely biodegradable within a reasonable period of time.

VIII. The absorbers should have good storage stability when dry. 1

The present invention is based on the knowledge that absorber materials can be produced simply and quickly from renewable raw materials with very little solvent (water), using a starting mixture which essentially consists of the following components:

- An ionic carboxyl-containing polysaccharide derivative, or a mixture of several ionic or partially neutralized polysaccharide derivatives.

- Optionally, polyfunctional crosslinking agent, preferably ^¬ as polybasic organic acids.

- Little water (10 - 80 wt .-% based on the polysaccharide derivative) as a homogenizing agent in the starting mixture (less than the solid components polysaccharide and crosslinker) with a relatively short production time or reaction time.

Because of the native origin, the absorbers obtained do not contain any questionable residual monomers like the polyacrylate-based absorbers. The absorbers according to the invention have a comparatively high absorption capacity and absorption speed for aqueous liquids (even under pressure). They show no tendency to gel blocking (ie the outer layers of the absorber do not stick together when in contact with water and do not prevent the liquid from penetrating further into the absorber) and are mechanically stable. In the swollen state, they largely separate into individual particles, they are not aqueous and have a high gel stability. These properties can be set individually with the degree of crosslinking ^¬ properties.

The invention thus relates to a solid absorbent for water, aqueous solutions and / or body fluids, which by crosslinking an ionic carboxyl-containing polysaccharide derivative in the presence of 10-80% by weight of water (based on the polysaccharide derivative) at 110 - 180 ° C is available. Crosslinking is usually carried out over a period of 15 to 60 minutes. In the case of implementation in a microwave oven can be considerably shorter t>

Response times can be realized; for example in the seconds range. Because of the temperature used according to the invention, drying of the product will take place at the same time on a regular basis. The drying can also be carried out in a separate step, if necessary at a lower temperature, e.g. after the crosslinking reaction is about 80% complete. In principle, all ionic polysaccharide derivatives that can be covalently crosslinked are suitable. These include in particular carboxymethyl or carboxy derivatives of starch, cellulose, guar gum, locust bean gum, amylose and amylopectin, e.g. Carboxyethyl starch, carboxy starch, dicarboxy starch, tricarboxy starch, carboxymethylamylopectin, carboxymethylamylose, carboxymethylguarane or carboxymethylcarobin in partially or fully neutralized form. The polysaccharide derivatives should have an average degree of substitution of less than three, preferably in the range from 0.3 to 2.0 and particularly preferably in the range from 0.3 to 1.5. Fully neutralized polysaccharides are particularly easy to crosslink with multi-functional crosslinkers. Dicarboxylic, tricarboxylic or polycarboxylic acids and / or their anhydrides or partially neutralized salts are preferably used for this purpose, e.g. Malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, malic acid, tartaric acid, itaconic acid, sebacic acid, citric acid, mucic acid, sugar acid, furanedicarboxylic acid, butanetetracarboxylic acid, polyacrylic acid etc. In the case of partially neutralized ionic polysaccharides, it is also possible to work without a crosslinking agent. The crosslinker is usually used in a concentration of 0.001 to 0.4 mol (based on 1 mol of polysaccharide derivative), preferably 0.005 to 0.15 mol. In the case of partially neutralized polysaccharide derivatives, i.e. without crosslinker, a molar ratio of the acid groups (H form) to free hydroxyl groups (OH groups) of 0.003 to 0.2 has proven itself.

According to the invention, an absorbent or swelling agent for water, aqueous solutions and body fluids is thus obtained which can consist of 100% biodegradable, renewable raw materials. The main component this absorbent is a polymer composition consisting of the crosslinked ionic carboxyl-containing polysaccharide derivative. However, a mixture of several ionic polysaccharide derivatives can also be present. In addition to the crosslinked polysaccharide derivatives, other native polysaccharides can be used, such as xanthan, alginic acid, pectin, pectic acid, guar gum, tragacanth, karaya, carrageenans or gum arabic.

The invention also relates to a process for the preparation of the abovementioned absorbents and / or swelling agents. In the process according to the invention, fully neutralized ionic polysaccharide derivatives with a crosslinking agent and / or partially neutralized ionic polysaccharide derivatives without crosslinking agent are mixed or pasted with water (or another suitable polar solvent, such as ethanol) in a suitable mixing device. The amount of water should be about 10-80 wt .-% (based on the polysaccharide derivative). A quantity of water of 30-60% by weight is preferably used. The mixture or paste is then crosslinked at 110-180 ° C, preferably at 130-160 ° C. At the temperature specified here, a drying reaction takes place at the same time, which has proven to be advantageous for later assembly into a solid absorbent. The time for the crosslinking and drying is usually 5-60 minutes, preferably 15-30 minutes. The method according to the invention thus enables the production of a particularly advantageous product in a particularly simple and environmentally friendly manner.

It has turned out to be particularly preferred to carry out the crosslinking and drying in a microwave device. The reaction time required for crosslinking is usually only 10-200 seconds.

In addition, it has proven to be advantageous to mix the polysaccharide derivatives in the dry or in a slightly moistened to swollen state with any crosslinking agent and water in a mechanical mixer. direction, for example a trough kneader, single-shaft mixer, single-screw extruder, twin-shaft mixer with co-rotating and counter-rotating twin-screw, twin-shaft continuous kneader, continuous multi-shaft device (for example, four-screw extruder), etc.

The invention also relates to the use of the absorbent material described above for absorbing and / or retaining water and / or aqueous solutions, in particular aqueous body fluids such as urine or blood, in absorbent disposable products for hygienic, surgical and other medical purposes such as baby diapers, incontinence articles, Tampons and sanitary napkins. However, the absorption material according to the invention can also be used to absorb and / or retain water and / or aqueous solutions in technical products, for example in cable jackets, animal hygiene articles, packaging materials, plant culture vessels, for soil improvement, etc. In addition, the absorption material is suitable for subsequent controlled delivery of absorbed water and, if appropriate, of substances dissolved or bound in the aqueous polysaccharide gel (for example nutrients or active substances) to an environment, such as biological systems, seeds, plants or microorganisms. More networked products with a higher degree of substitution are also suitable as ion exchangers (biodegradable) or as agents for wastewater treatment.

As already stated above, all ionic polysaccharide derivatives which can be covalently crosslinked are suitable for the preparation of the polysaccharide derivatives according to the invention. In the case of starch, cellulose, guar gum, locust bean gum, amylose and a ylopectin derivatives, the average degree of substitution (DS) must be less than three, otherwise there would be no free crosslinking sites or the selected H form would have to be selected Diols or polyols can be used as crosslinking agents (e.g. sorbitol). The carboxymethyl derivatives and the carboxy derivatives in their fully or partially neutralized form, in particular the carboxymethyl starch and the carboxy starches, are preferably preferred a DS of 0.3-2. The native ionic polysaccharides, such as carrageenans, alginic acid, pectic acid, tragacanth, karaya, ghatti, gum arabic, xanthan, etc., are more difficult to crosslink, are not temperature-resistant and are also much more expensive. With the same amount of crosslinker, carboxymethyl starch (CMS) and amylopectin (CMAp) can be very well crosslinked, carboxymethylamylose (CMAm) can be good, carboxymethylguarane (CMG) can be crosslinked poorly, and carboxymethylcellulose (CMC) can be poorly crosslinked, which corresponds to the general reactivity of the respective polysaccharides .

Polysaccharide ethers, especially cellulose ethers, have long been known. Methods for their preparation can be found in the general manuals for carbohydrates e.g. B. by R.L. Whistler (Methods in Carbohydrate Chemistry, Academic Press, New York and London, Vol. IV, pp. 304-312, 1964).

To produce the insoluble product, covalent crosslinking of the polysaccharide derivatives with organic acids is preferably carried out. If partially neutralized carboxymethyl starches are used, the crosslinking takes place via the non-neutralized carboxyl groups of the molecules, and the additional use of polybasic acids only leads to stronger crosslinking. The crosslinking takes place via ester bonds, which are advantageous for biodegradability. The following crosslinking agents are suitable: malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, malic acid, tartaric acid, itaconic acid, sebacic acid, citric acid, mucic acid, sugar acid, furandicarboxylic acid and butanetetracarboxylic acid. These acids can mainly be produced on the basis of renewable raw materials. The dicarboxylic acids show similar crosslinking properties and are similar to sodium dihydrogen citrate (citric acid partially neutralized), which then results in analogous product properties.

Using the anhydrides of these acids directly is less advantageous because they dissolve insufficiently in water and the components are not homogenized sufficiently. 3

For good to very good gel strengths, non-partially neutralized acids should be used, preferably succinic acid, citric acid, glutaric acid and butanetetracarboxylic acid. This can be explained by the fact that during the reaction (or heating period) these acids can form anhydrides which react faster and more extensively, i.e. network. In contrast to other preparations, the acids do not have to be partially neutralized, since pH and degradation reactions are not critical during the relatively short heating.

Depending on the type of crosslinking agent and the desired degree of crosslinking (or the gel strength), 0.05 to 0.2 mol, based on one mol of polysaccharide derivative, are required for the implementation.

First, the crosslinker is dissolved in a little water and partially neutralized with sodium hydroxide solution (option). The crosslinker solution is mixed with an appropriate amount of carboxymethyl derivative to form a homogeneous dough. Kneading with a suitable apparatus (e.g. kneader, powerful mixer, etc.) is advantageous. The water content in the dough should be 20-50%, preferably 35-40% water content. The mixing or kneading time is 5-60 minutes, preferably 20 minutes, depending on the water content and mixing intensity.

The dough is placed in a preheated reaction apparatus. In principle, all apparatuses are suitable for this that enable rapid heat transfer to the dough and thus rapid evaporation of the water. Roller dryers, high-performance forced-air drying ovens, microwave ovens, waffle irons, drum dryers, jacket-heated high-performance mixers etc. can be used.When drum dryers and mixers are used, very fine-grained products are sometimes obtained (grain fractions are smaller than 150 μm), so that grinding is eliminated, but the product application options are severely restricted . The temperature should be 110-170 ° C during production. At higher temperatures, however, the yellow-brown discoloration was too strong and worse Properties observed. The residence time in the reaction apparatus is too long at low temperatures. A temperature of 130-160 ° C should preferably be selected. This was also confirmed by thermogravimetric studies.

In order to allow the dough water to evaporate quickly, the dough surface should be made as large as possible (e.g. by rolling it out). Depending on the initial water content, the specified temperature and the dough surface used, the product is ready after 10 - 50 minutes. With a dough surface of approx. 250 cm ² (approx. 30 g) and a temperature of 150 ° C, the product is ready after 20 - 30 minutes. Guaran derivatives are completed in about 40 minutes.

The use of microwave ovens makes production much shorter, but requires sufficient experience in handling and implementation. For example, the product is finished after about 100 seconds and after about 120 seconds of treatment time it can be unusable; when using an RF output power of 500 W and a frequency of 2450 MHz.

After the product is dry (end of the reaction), further heating has no special advantages (e.g. better product properties). The rapid evaporation of the water causes the product to swell, making it very porous (which explains the rapid absorption rate due to the capillary forces in the pores; this can be derived from SEM images). The more water is used, the greater the bloating.

The finished product in solid form is crushed, ground and sieved. The grain fraction 200 - 500 μm is used for the absorption tests.

In the described embodiments, the method according to the invention leads to products which still contain a certain water-soluble fraction; with most products this at 10-15%, sometimes over 30%. This portion does not interfere with many uses, so that removal of the water-soluble portions is usually unnecessary. In some cases of further use of these absorbent products, the water-soluble portion is even advantageous since it increases its adhesive strength, for example on polysaccharide substrates or surfaces (cellulose, cellulose fiber or film, or starch film). If the water-soluble part interferes, it can be removed with various washing methods. In most cases, the removal of the water-soluble components also leads to better absorption properties. This behavior is understandable since the absorption results are based on one gram of product and the total weight is taken into account for technical products with soluble components, although the soluble components do not contribute to the absorption capacity. Water or aqueous-organic solvents have been found to be advantageous for washing out the soluble fractions. When using fully demineralized water for washing out, however, a considerable excess of water compared to the absorber must be expected. Usually about 50 - 100 liters of water must be used for one kilogram of product. The washing process is carried out by stirring the swollen product in the washing liquid with subsequent filtration. A drum filter is preferably suitable for this purpose, the washing water being most easily separated off by centrifugation.

The washing water can be cleaned again of the soluble components and reused by common separation processes (e.g. reverse osmosis). The separated soluble fractions can be reused as starting material. In order to reduce the considerable amounts of wash water, the use of organic-aqueous mixtures, preferably methanol / water, ethanol / water or acetone / water, is recommended. This considerably reduces the swelling of the product and only about 5 to 10 liters of washing mixture are used per kilogram of product, the mixing ratio preferably being 50%. Test methods

FSC (Free Swellinq Capacitv):

Weigh 0.2-0.25 g of product into a commercially available tea bag. The open end of the tea bag is sealed and the tea bag is placed in a photo bowl with a 0.9% NaCl solution. The tea bag is pressed briefly so that the liquid wets it from all sides. The test time is one hour. The tea bag is then left to drain for 5 minutes, hanging on a clothespin. The tea bag is then weighed (in grams, g) and the absorption value is determined:

g (NaCl solution) Weighing out (tea bag) - tea bag blank FSC in ^~ g (product) weight

CRC (Centrifuqe Retention Capacity): The tea bag from the FSC determination is spun for 3 minutes at 2800 rpm in a commercial spin dryer (with an interior diameter of 24 cm), which corresponds to 26.6 times the acceleration due to gravity. The centrifuged product is then weighed. The calculation is carried out analogously to the formula given above.

Absorption Under Load (AUL): This test procedure uses round plastic pots (d = 2.985cm), which are open at one end and closed at the other end with a mesh (mesh size 100 - 150 μm). The product is weighed into these pots and evenly distributed on the net. The weight of the product in two tests is 0.05 g and 0.4 g, since it was found that the AUL value worsens with increasing weight. The usual weight is 0.15 g. This phenomenon is not due to errors, but to the behavior of the Gel particles under pressure: With higher weights, there are several layers of particles that lie on top of each other. Due to the external pressure during absorption, there is close contact between the layers and thus also good liquid transport. However, the gel-like particles penetrate one another, so that there is not always an isolated swelling of the individual grain. At low weights, the granules can distribute themselves isolated on the net surface and swell freely, so that a higher AUL value is obtained. This phenomenon is more or less pronounced in all absorbers (including synthetic ones). This effect can also be observed at high gel strengths, since apparently the intrusion is inevitable. This is not gel blocking because all layers or grains are swollen after the test.

After weighing, a small plastic disc (d = 2.985 cm; m =

7.59 g ± 0.01 g) and with a cylindrical piece of metal

(m = 316g ± 0.24 g) weighted. The tare weight (potty with disc, without metal piece) and sample weight are weighed. A glass frit is placed in a photo bowl. The frit is covered with filter paper (of the same size). Sufficient 0.9% NaCl solution is poured into the photo bowl so that the liquid surface is flush with the surface of the frit.

Then the pots are placed on the prepared fries. The test time is one hour at a test pressure of 4550 Pa (or 0.66 psi or 46.3 g / cm ² or 300 g / in ² ). Then the metal piece is removed and the potty (potty + plastic disc + swollen product) weighed:

g (NaCl solution) balance - (tare + weight)

AUL in - - - r- = - g (product) weight

Gel strength (storage module G ') The gel strength G 'of the swollen absorbers was determined on the basis of US Pat. No. Re 32,649 (or EP 02 05 674).

- Device: Rheometer CSL 100, TA Instruments Ltd. (Leatherhead, Surrey, KT22 7UQ, England)

- Measuring conditions: cone and plate system, cone diameter 2 cm, angle 2 °, temperature 25 ° C, frequency 1 Hz, specified

Deformation = 2%.

This test is an oscillation test with a predetermined deformation of the gel. Compliance with the deformation specification is very important, since this is a linear viscoelastic area. If larger deformations (e.g. more than 10%) were used, the gel would be irreversibly destroyed and the values would not be reproducible (since the linear viscoelastic range would change into the non-linear range; see also explanations in W.-M. Kulicke Flow behavior of substances and mixtures of substances, p.90, Sect. 2.2.1, Hüthig & Wepf Verlag Basel, Heidelberg, New York 1986).

The required oscillating shear stress σ, the gel strength (or storage modulus) G 'and the loss modulus G' 'or the tan (δ) value are determined at the same time. The

Shear stress σ indicates how much force is required to deform the gel for the given factor. The gel strength is obtained via the memory module. With the help of the tan (δ) value (= G '' / G ') it is determined whether the gel has elastic properties or viscous flowing properties (with a tan () <1 the gel is elastic and a tan (<5 )> 1 it is viscous flowing). The gel is "slippery" if the resulting shear stress σ <10 Pa and the G '<100 Pa. On the other hand, the gel is (very) firm when σ> 100 Pa and G '> 5000 Pa. Insoluble shares (UA):

The insoluble parts give a direct indication of the cross-linked part of the polysaccharide. A glass filter bowl (size 2) is used to check the UA.

Weigh exactly 1 g into a beaker and add 300 ml of double-distilled water. The solution is stirred for 30 minutes. The solution is then left to stand for 5 minutes, the gel settling out and a supernatant solution being formed. The supernatant solution is decanted off over the glass filter plate and the remaining gel is filled up with 300 ml of fresh, double-distilled water. The mixture is stirred for a further 30 minutes. This process is repeated two more times.

Finally, the entire solution is filtered. The beaker is distilled with 100 ml. Washed out water and this washing liquid is also filtered through the same glass filter pot. The glass filter plate with swollen sample is dried for 6 hours in a forced air drying cabinet at 120 ° C. The glass filter plate is then cooled to room temperature and weighed:

Scales - crucibles

UA - - - • 100%

Weight

Effects of the washing frequency on the insoluble parts UA (in%) of two samples:

Frequency: lx 2x 3x

Sample 1: 82.1 80.4 80.2

(98.2) (96.2) (95.9)

Sample 2: 78.3 75.8 75.7

(95.0) (92.0) (91.9)

The information in brackets (UA ¹ ) refer to the insoluble portion of the starch derivative used, because the cross-linking only takes place on the starch derivative. Example of UA and UA ': In sample 1, citric acid and carboxymethyl starch (CMSOl) were used as the starting material for crosslinking. The share of citric acid in the dry matter was 12.3%, the CMSOl share was 83.6% and the rest of 4.1% was NaCl (as an impurity of CMSOl). Since the degree of crosslinking is normally low (or should be; approx. 1 - 5%) and NaCl is irrelevant, only the CMSOl can make up the insoluble components. This means that 16.4% (12.3% + 4.1%) soluble components are present in this cross-linked sample. Only the remaining 83.6% of the sample is examined for insolubility. When 82.1% of the insoluble parts UA of the entire sample were determined, 98.2% (= UA ') of the CMSOl became insoluble (98.2% = 82.1 / 83.6 * 100%). This approach is more of a theoretical nature, since this information gives a direct indication of the degree of networking of the CMS.

Determination of the crosslinker content:

The proportion of the bound crosslinker in the purum product was determined, the proportion being in milligrams of crosslinker per gram of product. This titrimetric determination with copper sulfate is carried out according to the instructions in: H.Klaushofer, E. Berghofer, R.Pieber, Starch / Starch, Vol.31, pp.259-261, 1979.

Raw materials

There are the usual short names with a

Code used for the corresponding degree of substitution, e.g .:

CMSOl = carboxymethyl starch with DS = 0.1

CMS07 = carboxymethyl starch with DS = 0.7

CMC12 = carboxymethyl cellulose with DS = 1.2

CMG15 = carboxymethylguaran with DS = 1.5

CMApl2 = carboxymethyamylopectin with DS = 1.2

Sources of supply:

- CMSOl - Emsize CMS 60, Emsland -force GmbH (49820 Emiichheim)

- Other CMS - Manufactured using the method of: J.W. Sloan, C.L. Mehltretter, F.R. Senti, Journal of Chemical and Engineering Data, Vol.7, pp.156-158, 1962.

CMC12 (M _w = 250,000 g / mol) - Aldrich Chemical Company, Inc., (Milwaukee, WI 53233 USA)

- CMG15 - Meyhall Chemical AG (CH-8280 crossings)

- Gum Guar, Gum Ghatti, Gum Tragacanth (tragacanth), Gu Karaya

Sigma Chemical Co., (St. Louis, MO 63178 USA)

- Other polysaccharides in BioChemika quality and organic acids in p.a. Quality - Fluka Chemie AG (CH-9470 Buchs)

- Comparative sample 1 (VI): FAVOR® SXM (cross-linked polyacrylate, manufactured by the Chemische Fabrik Stockhausen, Krefeld)

- Comparative sample 2 (V2): ι-carrageenan (BioChemika, Art. No. 22045, Fluka) Manufacturing examples

All of the following samples in the examples were produced according to the same principle: dissolving the crosslinking agent in an appropriate amount of water, adding the derivative and then mixing or kneading (10 minutes), heating for 20 minutes at 150 ° C. and a dough area of 250 cm ² in one Waffle iron (or in a forced-air drying oven with the same results), grinding and sieving to 200 - 500 μm; this product is referred to below as a technical product. The rest of the sieving is washed twice with an excess of water (100 ml of water are used on 1 g), filtered and dried at 120 ° C. for 4 hours (depending on the water content) in a circulating air drying cabinet. If the gel is very swollen, centrifuging or pressure filtration of the gel is recommended. This product is called the Purum product.

Example 1:

Product made from 30 g CMSOl, 1.118 g citric acid and

16.2 g water.

Example 2:

Product made from 30 g CMSOl, 1.677 g citric acid and

16.2 g water.

Example 3:

Product made from 30 g CMSOl, 1.957 g citric acid and

16.2 g water.

Example 4:

Product made from 30 g CMSOl, 1.246 g

Natriu dihydrogen citrate and 16.2 g water.

Example 5:

Product made from 30 g CMSOl, 1.87 g

Sodium dihydrogen citrate and 16.2 g water. Example 6:

Product made from 30 g CMSOl, 2.181 g

Sodium dihydrogen citrate and 16.2 g water.

Example 7:

Product made from 30 g CMSOl, 4.269g

Disodium hydrogen citrate hydrate and 16.2 g water.

Example 8:

Product made from 30 g CMSOl, 5.337 g

Disodium hydrogen citrate hydrate and 16.2 g water.

Example 9:

Product made from 30 g CMSOl, 6.404 g

Disodium hydrogen citrate hydrate and 16.2 g water.

Example 10:

Product made from 30 g CMSOl, 1.118 g citric acid and 16.2 g water. The finished dough was left closed for 18 hours.

Example 11:

Product made from 30 g CMSOl, 1.677 g citric acid and 16.2 g water. The finished dough was left closed for 18 hours.

Example 12:

Product made from 30 g CMSOl, 1.246 g sodium dihydrogen citrate and 16.2 g water. The finished dough was left closed for 18 hours.

Example 13:

Product made from 30 g CMSOl, 1.87 g

Sodium dihydrogen citrate and 16.2 g water. The finished dough was left closed for 18 hours. Example 14:

Product made from 30 g CMSOl, 4.269 g

Disodium hydrogen citrate hydrate and 16.2 g water. The finished dough was left closed for 18 hours.

Example 15:

Product made from 30 g CMSOl, 6.404 g

Example 16:

Product made from 20 g CMS07, 0.615 g citric acid and

10.8 g water.

Example 17:

Product made from 20 g CMS07, 0.923 g citric acid and

10.8 g water.

Example 18:

Product made from 20 g CMSOl, 0.686 g

Sodium dihydrogen citrate and 10.8 g water.

Example 19:

Product made from 20 g CMSOl, 1.028 g

Sodium dihydrogen citrate and 10.8 g water.

Example 20:

Product made from 20 g CMSOl, 2.348 g

Disodium hydrogen citrate hydrate and 10.8 g water.

Example 21:

Product made from 20 g CMSOl, 3.522 g

Disodium hydrogen citrate hydrate and 10.8 g water.

Example 22:

Product prepared as in Example 18, however, the ground product was again mixed with 10.8 g of water and processed again according to the same procedure to determine whether rewetting and heating is worthwhile.

Example 23:

Product prepared as in Example 20, but the ground product was again mixed with 10.8 g of water and processed again according to the same procedure in order to determine whether rewetting and heating is worthwhile.

Example 24:

The product was produced as in Example 4, but the ground product was again mixed with 16.2 g of water and processed again using the same method to determine whether it was worth re-wetting and heating.

Example 25:

Product produced as in Example 24 to determine whether the repeat procedure can be made reproducible and whether the properties are similar.

Example 26:

Product made from 20 g CMApl2, 0.578 g

Sodium dihydrogen citrate and 10.8 g water.

Example 27:

Product made from 20 g CMApl2, 1.98 g

Disodium hydrogen citrate hydrate and 10.8 g water.

Example 28:

Product made from 20 g CMApl2, 1.164 g

Sodium dihydrogen citrate and 10.8 g water.

Example 29:

Product made from 15 g CMAp04, 1.8 g

Disodium hydrogen citrate hydrate and 10g water. Example 30:

Product made from 15 g CMAp04, 3.7 g

Disodium hydrogen citrate hydrate and 10g water.

Example 31:

Product made from 15 g CMC12, 0.402 g citric acid and

16.2 g water.

Example 32:

Product made from 15 g CMC12, 0.448 g

Sodium dihydrogen citrate and 16.2 g water.

Example 33:

Product made from a mixture with 15 g CMSOl and 1.5 g

Xanthan, 2.3 g disodium hydrogen citrate hydrate and 10 g water.

Example 34:

Product made from a mixture of 15 g CMSOl and 3.5 g

Xanthan, 2.6 g disodium hydrogen citrate hydrate and 10 g water.

Example 35:

Product made from a mixture with 15 g CMSOl and 1.5 g alginic acid (Na salt), 2.3 g disodium hydrogen citrate hydrate and 10 g water.

Example 36:

Product made from a mixture with 15 g CMSOl and 3.5 g alginic acid (Na salt), 2.6 g disodium hydrogen citrate hydrate and 10 g water.

Example 37:

Product made from a mixture of 20 g CMSOl and 4.6 g

Guar gum, 1.2 g sodium dihydrogen citrate and 33.1 g water.

Example 38:

Product made from a mixture of 20 g CMSOl and 4.6 g

Guaran, 3.6 g disodium hydrogen citrate hydrate and 36.9 g water. Example 39:

Product made from a mixture of 20 g CMSOl and 4.6 g

Tragacanth, 1.2 g sodium dihydrogen citrate and 36.9 g water.

Example 40:

Product made from a mixture of 20 g CMSOl and 4.6 g

Tragacanth, 3.7 g disodium hydrogen citrate hydrate and 37 g water.

Example 41:

Product made from a mixture of 20 g CMSOl and 4.6 g

Karaya, 1.2 g sodium dihydrogen citrate and 36.9 g water.

Example 42:

Product made from a mixture of 20 g CMSOl and 4.6 g

Karaya, 3.7 g disodium hydrogen citrate hydrate and 37 g water.

The following samples in the examples were produced according to the same scheme: dissolving the crosslinking agent in an appropriate amount of water, adding the derivative and then mixing or kneading (10 minutes). The rolled-up dough (diameter: approx. 4-5 cm) was treated in a commercially available microwave oven, with a side radiation source and turntable, for 90-100 seconds, with an RF output power of 500 W and a frequency of 2450 MHz. The dough expanded to twice its volume and a dry product was obtained after the treatment period, which was worked up as in the examples above.

Example 43:

Product made from 20 g CMS07, 0.615 g citric acid and

10.8 g water.

Example 44:

Product made from 20 g CMS07, 0.615 g citric acid and

10.8 g water (repetition of example 43). Example 45:

Product made from 20 g CMS07, 0.923 g citric acid and

10.8 g water.

Explanations

Tables 1 and 2: Column 1: Example number

Column 2: Carboxymethyl derivative used Column 3: Crosslinker used (CiS = citric acid; NaCiS = sodium dihydrogen citrate; Na ₂ CiS = disodium hydrogen citrate) Column 4: Molar ratio F of crosslinker and polysaccharide derivative

Column 5: FSC of the technical product Column 6: CRC of the technical product

Column 7: AUL of the technical product. Numerical values with double information refer to a weight of 0.6 g (without brackets) and 0.05 g (with brackets). Numerical values with simple information refer to a weight of 0.15 g. Column 8: Insoluble fractions in% of the technical product Column 9: Insoluble fractions in% based on the polysaccharide derivative

Column 10: shear stress for 2% deformation of the swollen technical sample

Column 11: Storage module G 'in Pa of the swollen technical sample

Column 12: Loss angle δ or tan (<5) of the swollen technical sample

Column 13: FSC of the purum product

Column 14: CRC of the purum product

Column 15: AUL of the purum product. Numerical values with double

Figures refer to a weight of 0.6 g (without bracket) and 0.05 g (with bracket). Numerical values with simple information refer to a weight of 0.15g.

Column 16: Bound crosslinker in milligrams per gram of purum

product

Column 17: shear stress in Pa for 2% deformation of the swollen purum sample

Column 18: Storage module G 'in Pa of the swollen purum sample

Column 19: Loss angle δ or tan (<5) of the swollen purum sample Abbreviations: = not applicable (determination not applicable) nb = not determined (determination not carried out) not possible = not possible (determination not possible)

∞ = infinite (value is infinite and cannot be determined)

Table 3: IT

Column 1: Example number

Column 2: Carboxymethyl derivative used Column 3: Proportion of the carboxymethyl derivative in the polysaccharide mixture

Column 4: additionally mixed polysaccharide Column 5: proportion of the additional polysaccharide in the polysaccharide mixture

Column 6: Crosslinker used (CiS = citric acid; NaCiS = sodium dihydrogen citrate; Na ₂ CiS = disodium hydrogen citrate) Column 7: Molar ratio F of crosslinker and polysaccharide derivative

Column 8: FSC of the technical product Column 9: CRC of the technical product

Column 10: AUL of the technical product. Numerical values with double information refer to a weight of 0.6 g (without brackets) and 0.05 g (with brackets). Numerical values with simple information refer to a weight of 0.15 g. Column 11: Insoluble parts in% of the technical product Column 12: Insoluble parts in% based on the polysaccharide derivative

Column 13: shear stress for 2% deformation of the swollen technical sample

Column 14: Storage module G 'in Pa of the swollen technical sample

Column 15: Loss angle δ or tan (<?) Of the swollen technical sample

Column 16: FSC of the purum product

Column 17: CRC of the purum product

Column 18: AUL of the purum product. Numerical values with double

Figures refer to a weight of 0.6 g (without bracket) and 0.05 g (with bracket). Numerical values with simple information refer to a weight of 0.15 g.

Column 19: shear stress in Pa for 2% deformation of the swollen purum sample

Column 20: Storage module G 'in Pa of the swollen purum sample

Column 21: Loss angle δ or tan (δ) of the swollen purum sample Abbreviations: = not applicable (determination not applicable) nb = not determined (determination not carried out) not possible = not possible (determination not possible) oo = infinite (value is infinite and cannot be determined)

Table

Table 2

03

5β n

H l H-H o H W CΛ

03 tr ►

H H

O

t- ¹

Table 3

03 ms n

HH

M co 03 r>

H H

3

Claims

Patent claims

1. Biodegradable, solid absorbent for water, aqueous solutions and body fluids, with high absorption capacity and high gel strength, which shows no sticking of the outer layers of the absorbent particles on contact with water, with the result that further penetration of the liquid into the absorbent particles is prevented , obtainable by crosslinking an ionic carboxymethyl or carboxy polysaccharide derivative in the presence of 10 to 80% by weight (based on the polysaccharide derivative) of water at 110-180 ° C., in the event that crosslinking agents are used, the crosslinking agents are dicarboxylic, tricarboxylic or polycarboxylic acids.

2. Absorbent according to claim 1, wherein the polysaccharide derivatives used have an average degree of substitution less than 3, preferably in the range from 0.3 to 2.0.

3. Absorbent according to claim 1 or 2, wherein dicarboxylic, tricarboxylic or polycarboxylic acids have been used as crosslinking agents.

4. Absorbent according to one of the preceding claims, wherein the crosslinking agents were used in a concentration of 0.001 to 0.4 mol (based on 1 mol of polysaccharide derivative), preferably 0.005 to 0.2 mol.

5. Absorbent according to one of the preceding claims, wherein neutralized or partially neutralized carboxymethyl or carboxy derivatives are used as polysaccharide derivatives.

6. Absorbent according to claim 5, wherein the polysaccharide derivative is derived from starch, cellulose, guar gum, locust bean gum, amylose or amylopectin.

7. Absorbent according to claim 5, wherein in the absence of a crosslinker partially neutralized polysaccharide derivatives with a molar ratio of the acid groups (H form) to free hydroxyl groups (OH groups) of 0.003 to 0.2 were used.

8. A method for producing an absorbent according to any one of the preceding claims, characterized in that a fully neutralized ionic carboxymethyl or carboxy polysaccharide derivative with a crosslinking agent or an ionic partially neutralized polysaccharide derivative without crosslinking agent in the presence of an amount of water from 10 to 80 wt. -% (based on the polysaccharide derivative) are mixed and then a crosslinking is carried out for 10 - 50 min at 110 to 180 ° C.

9. Use of the absorption material according to one of claims 1 to 7 for the absorption and / or retention of water and / or aqueous solutions, in particular of aqueous body fluids, such as urine or blood, in absorbent products for hygienic and medical purposes.

10. Use of an absorption material according to one of claims 1 to 7 for the absorption and / or retention of water and / or aqueous solutions and / or aqueous dispersions in packaging materials, plant culture vessels or cable jackets.

11. Use of an absorption material according to one of claims 1 to 7 for the absorption and / or retention of water and / or aqueous solutions and for the subsequent controlled release of the absorbed water and, if appropriate, the substances dissolved or bound in aqueous polysaccharide gel as nutrients or Active ingredients in an environment.