WO2000073380A1

WO2000073380A1 - Method for producing agglomerates of biodegradable starch esters which can be redispersed in water

Info

Publication number: WO2000073380A1
Application number: PCT/DE2000/001519
Authority: WO
Inventors: Rolf Kakuschke; Hartmut Stoye; Inno Rapthel
Original assignee: Buna Sow Leuna Olefinverbund Gmbh
Priority date: 1999-05-29
Filing date: 2000-05-13
Publication date: 2000-12-07
Also published as: DE19924772A1

Abstract

The invention relates to a method for producing an agglomerate on the basis of fine-particle, biodegradable starch esters which after a short period can be redispersed in water. According to said method a starch ester with a particle size of between 1 and 50 νm and a solid contents of between 5 and 16 % by mass is dehydrated to a water content of between 50 and 70 %, and the resulting moist pasty mass granulated or agglomerated and then carefully dried at between 20 and 60 °C. To improve the stability of said agglomerates a water-soluble, biodegradable polymer can be added to the moist mass.

Description

Process for the production of water-redispersible agglomerates from biodegradable starch esters

The invention relates to a process for the production of agglomerated carrier bodies from finely divided starch ester primary particles which disintegrate into redispersed primary particles within a short time when they are introduced into water.

According to EP 560 829, a process for the production of starch-containing dispersion adhesives in redispersible dry form from a mixture of aqueous dispersions of synthetic polymer compounds and water-containing starch and / or starch derivatives is known. The starch and / or the starch derivatives are used in the form of finely divided solids, these are mixed with the polymer dispersion and this multicomponent mixture is subjected to starch digestion at a temperature of at least 90 ° C. and under elevated pressure with a residence time of 0.5 to 10 min. The resulting thermoplastically processable starch is then shaped from the melting phase or subjected to further comminution.

A method for producing biodegradable granules is known from EP 444 880. In a high-speed mixer, a biodegradable resin selected from aliphatic and cycloaiiphatic polyesters and a natural substance with a high molecular weight are mixed with simultaneous heating at high speed. For example, starch or starch derivatives are selected as the natural substance. The surface of the resulting microparticles is covered with the natural substance with a high relative molecular weight in particle or fiber form. These microparticles can then be agglomerated into grains with a diameter of 0.1 to 20 mm by melt bonding. However, these grains cannot be redispersed in water.

The use of the property of biodegradability when using biodegradable or compostable materials, for example as carrier materials for pharmaceutical applications or as sustained release carrier for fertilizers, is described in a variety of ways in the literature. A use case of such materials described in the literature in this sense is the nitrification / denitrification of waste water. For example, the use of polyhydroxybutyric acid as a carrier for microorganisms in wastewater treatment is described (Sperandio, A .; Mueller, WR; Kunststoffe (1988), 78 (8), 710 - 714), EP 575695 describes spun fibers made of poly-ε- Caprolactone, polyhydroxybutyric acid, polyhydroxyvaleric acid, polyester urethanes or similar biodegradable materials are used for similar purposes. In AT 403046 a biodegradable polymer is used as a binder for calcium carbonate for the production of corresponding carrier bodies. In all cases, the bodies are compact, non-redispersible. The main reason for the use of biodegradable materials is the possibility to use the carrier as an additional source of food for the immobilized microorganisms.

In contrast, the use of such carriers in floor cleaning or in agricultural applications is not described. There is hardly any problem with the additional food source and, in contrast to the applications described above, which take place in reactors, a uniform distribution of the microorganisms, active ingredients or the like used is required for good effectiveness. The use of compact carrier bodies is therefore inexpensive for handling, but less suitable for the actual intended use. The use of carrier substances is particularly useful if this means transport and handling when using microorganisms, active substances or the like. is simplified for the corresponding applications and then uniform distribution in a simple way is required.

The object of the invention is to develop a method for producing agglomerates based on finely divided, biodegradable starch esters. It can be assumed that a starch ester is readily dispersible in water, which is suitably brought into an agglomerated form, such as, for example, granules or pellets with sufficient strength for the intended transport and handling processes. The production must be carried out in such a way that possible additives, such as microorganisms or active substances, do not suffer any damage. Upon contact with water, this agglomerate should quickly return to its well-dispersed Allow the primary particles to disintegrate and thus enable an application in the form of an aqueous dispersion for the respective application. The object is achieved by the method described in the claims. A starch ester, preferably a starch acetate, with a degree of substitution of 1.5 to 2.5, preferably 1.8 to 2.2, is used as the biodegradable carrier which is well dispersible in water. The particle size required for the procedure according to the invention is between 1 and 50 μm.

To produce the agglomerate according to the invention, water is added to the starch ester until a pasty, plastifiable mass is formed. The moisture content of this mass after the addition of water is 50-70%, preferably 55-65%. The same effects can be achieved if the starch ester is precipitated in water from the acetic acid solution obtained from the production process and the precipitated product is dried to the stated moisture content under gentle conditions at 20 - 40 ° C.

After the mass has been homogenized and the microorganisms or active ingredients have been introduced, it is processed into an agglomerate in a manner known per se and dried gently. Drying is carried out, for example, by circulating air at temperatures of 20 to 60 ° C.

This procedure leads to the result according to the invention if the degree of substitution (DS) is between 1.5 and 2.5. When using starch acetate, the DS should be closer to the top. If longer ester groups such as propionate and butyrate are used, a DS closer to the lower value of the specified range is recommended.

Maintaining the drying temperatures is of essential importance for the procedure according to the invention, since at higher temperatures starch esters begin to sinter with the degrees of substitution mentioned and the moisture contents indicated. The redispersibility would be lost. To produce the agglomerates from the water-moist mass, this can be pressed, for example, through a perforated plate with a hole diameter of 2-5 mm and then laid out on a plate for drying. It must also be ensured that gentle drying takes place at temperatures below 60 ° C. Another way of making an agglomerated form of redis Pearable, biodegradable starch ester is a granulation or pelleting of the water-moist mass according to known methods. A biodegradable water-soluble polymer can be added to the water to increase the strength of the agglomerates. The content of these polymers is 0 to 20%, preferably 2 to 10% by mass of the total mass of the agglomerates.

Examples of water-soluble polymers that can be used are polyethylene glycols with molecular weights from 5,000 to 20,000, polypropylene glycols with molecular weights up to 1,000, propoxylated or ethoxylated starches with degrees of substitution> 2, starch acetates with degrees of substitution <1, 2 and polyvinyl alcohol. The addition of active ingredients or microorganisms can take place in the stage of the preparation of the pasty, water-moist mass. Subsequent application is also possible if no large amounts of water are required that would impair the pasty state of the mass. If the agglomerate produced according to the invention is added to water and stirred, it breaks down again into its primary particles in a few seconds. These can be dispersed in water by simple stirring, so that, for example, uniform application to agricultural areas is possible.

The invention is illustrated by the following examples, examples 1 to 3 relating to the synthesis of the starch acetate.

Example 1 :

1380 g wheat starch (12.3% moisture) 300 g glacial acetic acid 950 g acetic anhydride

are heated in a 30 l stirred reactor with reflux condenser to about 120 ° C. and kept at this temperature for 30 min. After that, over 15 minutes more 1,900 g of acetic anhydride and 2,000 g of glacial acetic acid were added. The reaction mixture is refluxed for 6 hours with vigorous stirring. After cooling to 90 ° C., 17 liters of water are metered into the clear starch acetate solution with vigorous stirring over 5 minutes, and the reaction mixture, which is clearly cloudy, is then precipitated into 8 liters of water with vigorous stirring. The decay suspension pre-concentrated by sedimentation and decanting to 6% starch acetate is filtered through a pressure filter at 3.5 bar, the filter cake is stirred five times with 2 l of distilled water each time and filtered again at 3.5 bar.

The starch acetate thus represented has a degree of substitution of DS = 2.3. The filter cake containing about 40% starch acetate is resuspended with the addition of water by stirring with an Ultra-Turrax at about 10,000 rpm, the solids content of the suspension being adjusted to 12%, followed by drying with circulating air at 30 ° C. or pressure filtration up to a moisture content of 60 wt .-% according to the required for ^'the examples 4 to 12 water content. The material pre-dried in this way can, for example, be put in granular form through a perforated plate or a screw granulator and then dried gently at a maximum of 60 ° C.

Example 2:

1380 g corn starch (13% moisture) 500 g glacial acetic acid 1020 g acetic anhydride

are heated in a 10 l stirred reactor with reflux condenser to about 120 ° C. and kept at this temperature for 30 min. Then 1360 g of acetic anhydride are metered in over 15 minutes. The reaction mixture is refluxed for 6 hours with vigorous stirring, after which it is diluted with 2000 g of glacial acetic acid. After cooling to 90 ° C., the clear starch acetate solution is mixed with five times the amount of water via a mixing nozzle, and the reaction mixture, which is then very cloudy, is precipitated in 50 l of water with gentle stirring. The precipitation suspension is filtered through an inverting filter centrifuge, the filter cake is washed five times with 2 l of distilled water and filtered again. The starch acetate thus represented has a degree of substitution of DS = 1.80. The viscous suspension containing about 10% starch acetate is homogenized by stirring with an Ultra-Turrax at about 10,000 rpm and pre-dried to a water content of 55%.

Example 3:

1600 g wheat starch (12.3% moisture) 500 g glacial acetic acid 1500 g butyric anhydride

are heated in a 30 l stirred reactor with reflux condenser to about 120 ° C. and kept at this temperature for 30 min. Then over 15 min. another 2380 g of butyric anhydride and 2,000 g of glacial acetic acid were metered in. The reaction mixture is refluxed for 8 hours with vigorous stirring.

After cooling to 90 ° C over 5 min. 17 l of water are metered into the clear starch butyrate solution with very vigorous stirring, the reaction mixture, which is then clearly cloudy, is precipitated into 8 l of water with vigorous stirring. The precipitate suspension, which was preconcentrated by sedimentation and decanting to 6% starch butyrate content, is filtered through a pressure filter at 3.5 bar, the filter cake is stirred five times with 2 l of distilled water each time and filtered again at 3.5 bar.

The starch butyrate thus represented has a degree of substitution of DS = 1.5. The filter cake containing about 45% starch butyrate is resuspended with the addition of water by stirring with an Ultra-Turrax at about 10,000 rpm, the solids content of the suspension being adjusted to 12%, followed by drying with circulating air at 30 ° C. or pressure filtration up to a moisture of 60% by mass corresponding to the water content required for Examples 4 to 12. The moist pasty mass from Examples 1 to 3 is homogenized (Examples 4 and 10 according to the invention) or mixed with a water-soluble polymer before the homogenization (Examples 5-9 and 11-12 according to the invention) and pressed through a perforated plate with holes with a diameter of 4 mm .

Table 1: Composition in Examples 4 to 12 according to the invention

¹ Information based on dry matter

² hydroxypropoxy starch DS 3

In accordance with the objective, the following determinations were carried out on the agglomerates thus produced: I. Bulk density: according to DIN

2. Abrasion resistance: 100 g of the 3 - 5 mm sieve fraction were rotated in a container for 5 min at a speed of 60 min ^-1 . The abrasion was then recorded as a sieve fraction <1 mm.

3. Time to re-50 g of the sieve fraction 3 - 5 mm were placed in a beaker with dispersion: 500 ml of water. The time was recorded until a uniformly fine dispersion had formed optically. Table 2: Results of the test

Processing the starch ester according to the invention (examples 4 and 10 according to the invention) thus already provides an agglomerate which corresponds to the objective of the invention. The proposed additional addition of a water-soluble biodegradable polymer improves the strength and the redispersibility of the agglomerate. Example 12 according to the invention shows that longer-chain fatty acid esters can also be used if the required degree of substitution can ensure the required hydrophilicity of the starch ester.

Claims

claims

1. A process for the preparation of water-redispersible agglomerates from biodegradable starch esters, preferably starch acetate, with degrees of substitution from 1.5 to 2.5, characterized in that the starch ester with a grain size of 1 to 50 microns in an aqueous dispersion with a solids content generated from 5 to 16% by mass, then predried at temperatures below 30 ° C. to a water content of 50 to 70% by mass, preferably 55 to 65% by mass and, if appropriate, a water-soluble, biodegradable polymer is added, and then the pasty, moist water mass is homogenized and agglomerated and dried in the temperature range between 20 ° C and 60 ° C.

2. The method according to claim 1, characterized in that the adjustment of the grain size of 1 to 50 microns in aqueous dispersion of the starch ester with solids concentrations of 5 to 15% by mass is carried out by means of Ultraturax.

3. The method according to claim 1, characterized in that the adjustment of the grain size of 1 to 50 microns of the starch ester is carried out by precipitation of an acetic acid reaction solution from starch.

4. The method according to claim 1, characterized in that 0 to 20 mass%, preferably 2 to 10 mass% of the water-soluble, biodegradable polymer are added to the starch ester.

5. The method according to claims 1 and 4, characterized in that as a water-soluble, biodegradable polymer polyethylene glycol with molecular weights from 2000 to 20,000, polypropylene glycol with molecular weights up to 1000, alkoxylated starch with degrees of substitution> 1, starch acetate with a degree of substitution <

1, 2 or polyvinyl alcohol or mixtures thereof can be used.