DE102005004586B4 - Starch phosphates, process for their preparation and their use - Google Patents

Abstract

Process for the preparation of highly substituted starch phosphates, in which
a) in a pretreatment step, the starch is dissolved in a mixture of phosphating agent, water and, in the event that the phosphating agent is free of urea, urea is dissolved,
b) the water is removed from the mixture in step a) and
c) followed by a thermal conversion to the starch phosphate.

Description

The The invention relates to a process for the preparation of starch phosphates low in carbamate, which has a high degree of substitution with regard to the phosphate groups. Likewise, the concerns Invention prepared starch phosphates, and their use.

A typical process for the preparation of starch monophosphates is the conversion of the starch according to the so-called Neukom process (US Pat. US 2,884,412 ). The starch is first suspended in an aqueous solution of alkali metal phosphate. The thus impregnated starch is filtered, pre-dried in air or in a drying oven at temperatures below the gelatinization temperature and then tempered at temperatures around 140 ° C (± 30 ° C). The resulting products have DS values <0.1 and usually have a brownish discoloration. This discoloration can, as in DE 2 114 305 be suppressed by intensive mixing at 40 to 70 ° C during the pretreatment. This pretreatment requires a low temperature and a shorter reaction time for the esterification. In addition, urea is added to the mixture as an esterification aid. To obtain starch phosphates with increased viscosities is one as in DE 12 12 010 required fractionation required. While the products made by the modified Neukom process have DS values down to -0.2, in DE 19 859 123 Starch phosphates with degrees of substitution up to 1.0 claimed. Thereafter, the starch is tempered with the phosphating agent and urea at 90 to 140 ° C in a vacuum (≤ 100 Torr) without further mixing. There are products with degrees of substitution of the carbamate groups and the phosphate ester groups in each case in the range of 0.1 to 1.

In Towle and Whistler, Methods Carbohydr. Chem. 6, (1972), 408-410 Starch phosphates with DS up to 1.75. The strength is in a homogeneous process in DMF as a solvent with tetrapolyphosphoric acid reacted in the presence of tri-butylamine. Also high degrees of substitution (to DS = 1) are described in Tomasik et al., (Starch / (starch) 43/2 (1991) 66-69 achieved by a heterogeneous reaction in the slurry process. The starch is added in a mixture of benzene and phosphoric anhydride 80 ° C implemented. It but preferably arise crosslinked products.

For the production of highly substituted starch phosphates with a DS between 0.5 and 1.5 with polyelectrolyte properties it is desirable Products with as possible to obtain a low proportion of crosslinks. Under economic and ecological Ge point of view is the production of such derivatives according to the Towle and Whistler described method not effective.

Previous methods for preparing highly substituted starch phosphates with DS <1.0 are coupled to the use of solvents. Solvent-free methods achieve DS values up to 1.0, with a high proportion of carbamate groups attached (DS _Carb 0.1 to 1.0).

From the DE 198 59 123 is a process for the preparation of starch phosphates, in which first a mixture of starch (eg corn starch), water, phosphoric acid and urea is produced.

The DE 197 22 340 relates to water-swellable, hydrophilic polymer compositions preparable by radical (co) polymerization of one or more hydrophilic monomers in the presence of starch and / or chemically modified starch, wherein a radical initiator is used, which forms three or more radical sites per molecule.

From the DE 14 43 509 is a method for producing reaction products of carbohydrates with phosphorus compounds with and without the addition of nitrogen compounds known.

Furthermore, the describes DE 851 180 a process for producing a potato starch starch product using phosphoric acid in the presence of small amounts of water.

The EP 14 31 393 relates to a genetically modified plant cell, wherein such plant cells and plants synthesize a modified starch having an amylose content of at least 30% and a phosphate content increased compared to starch.

In addition, the describes EP 0 897 964 polymeric protective films for the removal of soils and methods for the preparation of the protective films, wherein the protective film of polymers, such as polysaccharide derivatives, is formed, which may be phosphated.

outgoing It was the object of the present invention to provide a process for the preparation of highly substituted starch phosphates with a low carbamate group content to provide, with the measure an easy-to-use and therefore economical process provide.

This object is achieved by the method having the features of claim 1 and the starch phosphates having the features of claim 10. The further dependent claims show Partial training on. Claims 12 to 16 mention preferred uses of the starch phosphates according to the invention.

• a) in einem Vorbehandlungsschritt wird die Stärke in einem Gemisch aus Phosphatierungsmittel, Wasser und für den Fall, dass das Phosphatierungsmittel frei von Harnstoff ist, Harnstoff aufgelöst
• b) das Wasser wird aus dem Gemisch in Schritt a) entfernt und
• c) anschließend erfolgt eine thermische Umsetzung zum Stärkephosphat.

According to the invention there is provided a process for the preparation of highly substituted starch phosphates based on the following steps:

• a) in a pretreatment step, the starch is dissolved in a mixture of phosphating agent, water and in the event that the phosphating agent is free of urea, urea is dissolved
• b) the water is removed from the mixture in step a) and
• c) followed by a thermal conversion to the starch phosphate.

The Use of highly substituted starch phosphates under basic Conditions requires that the products be as low as possible with carbamate groups are substituted, otherwise they split off with the release of ammonia become. Surprisingly could be shown that evenly substituted with the process of the invention starch phosphates with degrees of substitution of phosphate groups of 0.01 to 2, preferably from 0.5 to 1.55, and at the same time minimal degrees of substitution Carbamate groups of less than 0.1 can be provided.

The Presence of urea is not mandatory in case that urea phosphate is used as the phosphating agent.

Preferably If the mixture consists of phosphating agent, water and optionally urea to 0 to 50 wt .-%, preferably from 1 to 50 wt .-% and especially preferably from 20 to 40% by weight of urea.

The Mixture is preferably from 3 to 40 wt .-%, in particular of 10 to 20 wt .-% phosphating agent, these statements on the use of urea phosphate as a phosphating agent Respectively.

The performed in step b) Removal of the water may be through any of the prior art known procedures are carried out. Preferred here is an azeotropic Distillation with an alcohol, e.g. 2-propanol.

The thermal reaction in step c) is preferably carried out in a drying oven, an oven or a fluidized bed reactor. The preferred Temperature in the thermal reaction 100 to 150 ° C, especially preferably 120 ° C.

When Phosphating agents are preferably used phosphate salts. In this case, in particular phosphoric acid and / or urea phosphate prefers.

According to the invention as well a starch phosphate with a degree of substitution of phosphate groups from 0.01 to 2.0, and a content of carbamate groups of less than 0.1. Preferred is the degree of substitution of phosphate groups from 0.5 to 1.5.

Surprisingly, it has been found that the starch phosphates according to the invention have a high degree of substitution of bound phosphate groups, the phosphorus contents of these groups being 16%. The bound phosphate groups are composed of mono-, di- and triphosphate esters, the majority being monophosphate. Furthermore, the products have a low content of carbamate groups DS _Carb less than 0.1.

By the pretreatment becomes the accessibility for the Reagent improves and results in products with a more uniform Distribution of the substituents along the chain.

The Products are white to slightly yellowish, show in 2% aqueous solution thickening properties and polyelectrolyte complex formation with correspondingly positively charged Polymers, such as poly (diallyldimethylammonium) chloride. Starch phosphates according to the invention show additionally a high water retention capacity.

use find the starch phosphates according to the invention et al in the building materials sector, for example as an additive in mineral or dispersion-bound building material systems, where they are used for adjustment the rheology and / or water retention are used can. Another use is as an additive in pharmacy and the cosmetics. Further fields of application concern the use as anionic component for Polyelectrolyte complexes. Likewise the starch phosphates according to the invention as a carrier material, especially in agriculture.

Based The following examples are intended to illustrate the subject matter of the invention be explained in more detail, without this on the specific embodiments shown here restrict to want.

example 1

17.1 g potato starch with a solids content of 82.5% are stirred in a solution of 57.0 g urea and 20.7 g urea phosphate in 60.0 wt .-% water for 1 h at 25 ° C. Subsequently, a total of 910 ml of 2-propanol are added, which together with water at 60 ° C / 200 mbar Azeotropically distilled off. The intermediate product is dried to a solids content of 95 to 99% at 60 ° C / 45 mbar and reacted in a drying oven at 120 ° C for 2 h. After purification, a product is obtained with a total phosphorus content of 9.8% and an inorganic phosphate content of 0.26%. This results in a phosphate group substitution degree DS _phosphate = 0.80 bound to the starch. A 2% aqueous solution gives a cloudy solid gel. The content of carbamate groups is DS _carbamate = 0.05

Example 2

45.2 g of potato starch with a solids content of 82.5% are stirred in a solution of 150.7 g of urea and 54.5 g of urea phosphate in 158.3 g of water for 1 h at 25 ° C. Subsequently, a total of 2.5 / 2-propanol are added, which are distilled off together with water at 60 ° C / 200 mbar as an azeotrope. The intermediate product is dried to a solids content of 95 to 99% at 60 ° C / 45 mbar and reacted in a kneader at 120 ° C for 2 h. After purification, a product is obtained with a phosphorus content of 8.5%, which corresponds to a degree of substitution DS _phosphate = 0.65. The content of carbamate groups is DS _carbamate = 0.07. A 2% aqueous solution is slightly cloudy and shows thickening properties.

Example 3

42.3 g of potato starch with a solids content of 82.5% are stirred in a solution of 141.3 g of urea and 51.1 g of urea phosphate in 178.1 g of water for 1 h at 25 ° C. Subsequently, 2.5 / 2-propanol are added, which are distilled off together with water at 60 ° C / 200 mbar as an azeotrope. The intermediate product is dried to a solids content of 95 to 99% at 60 ° C / 45 mbar and reacted in a kneader at 120 ° C. After 2 h, the crude product is dissolved in water and purified. The result is a product with a phosphorus content of 8.9% bound to the starch. This results in a degree of substitution DS _phosphate = 0.69. The content of _{carbamate groups} is DS _carbamate = 0.09. The water retention is WRV = 9750%. The WRV was determined according to the regulation Zellchiming IV / 33/57. A 2% aqueous solution is a slightly turbid solid gel and shows a significant precipitate with poly (dadmac).

Claims (16)

Process for the preparation of highly substituted starch phosphates, in which a) in a pretreatment step, the starch in one Mixture of phosphating agent, water and, in the event that the phosphating agent is free of urea, urea is dissolved, b) the water is removed from the mixture in step a) and c) subsequently a thermal conversion to starch phosphate he follows. Method according to claim 1, characterized in that that the mixture of urea, phosphating agent and water from 0 to 50 wt .-% urea. Method according to one of claims 1 or 2, characterized that the mixture of urea, phosphating agent and water contains from 20 to 40 wt .-% urea. Method according to one of the preceding claims, characterized characterized in that the mixture of urea, phosphating agent and water from 3 to 40% by weight, in particular from 10 to 20% by weight Contains phosphating agent. Method according to one of the preceding claims, characterized characterized in that the water in step b) by azeotropic distillation is separated. Method according to one of the preceding claims, characterized characterized in that in step c) the thermal reaction in a Drying oven, an oven or a fluidized bed reactor takes place. Method according to one of the preceding claims, characterized characterized in that in step c) the thermal reaction at a temperature in the range of 100 to 150 ° C. Method according to one of the preceding claims, characterized in that phosphate salts are used as the phosphating agent become. Method according to the preceding claim, characterized in that as phosphating agent phosphoric acid and / or Urea phosphate is used. starch phosphate with a degree of substitution of phosphate groups of 0.01 to 2 and a content of carbamate groups of less than 0.1 and hersgetellt according to the method of any one of claims 1 to 9. starch phosphate according to claim 10, characterized in that the degree of substitution to phosphate groups from 0.5 to 1.55. Use of starch phosphates according to one of claims 10 or 11 as an additive in mineral and dispersion bound Building material systems. Use of starch phosphates according to one of claims 10 or 11 as an additive in pharmacy or cosmetics. Use of starch phosphates according to one of claims 10 or 11 as anionic component for polyelectrolyte complexes. Use of starch phosphates according to one of claims 10 or 11 as a carrier material, in particular in agriculture. Use of starch phosphates according to one of claims 10 or 11 for binding water.