DE102007005927B4 - Process for the preparation of a hydrophobic starch derivative - Google Patents

Abstract

Process for the preparation of a hydrophobic starch derivative with the following, successive working steps:
a) dispersing starch and / or starch derivatives in an aqueous salt solution
b) Addition of carboxylic acid anhydrides
c) Setting a temperature of the reaction mixture between 0 ° C and 60 ° C.
d) stopping the reaction by adding an alcohol-water mixture, wherein the concentration of the salt solution has a molarity between 0.2 m and 7 m and the salts are inorganic salts and the cations of the inorganic salts are selected from the group consisting of Li, Mg , Al, Cu, Zn.

Description

The present invention describes a process for the preparation of a hydrophobic starch derivative by esterification of alcoholic functions with organic acid anhydrides in aqueous salt solutions. The resulting hydrophobic starch derivatives improve z. B. the water stability of papers.

In addition to cellulose, starch is already a renewable raw material used in many areas. In many plants, starch is a reserve carbohydrate and in the form of 1 to 200 .mu.m starch granules in various parts of plants, eg. In tubers or roots (potatoes, cassava, potatos), cereal seeds (wheat, maize, rye, rice, barley, millet, oats), fruits (chestnuts, acorns, peas, beans, bananas) and marrow (sago palms ) saved. Potatoes, corn and wheat are considered as suppliers of starch in Europe.

The chemical composition and the structure of starch are somewhat more complex than cellulose. Starch consists essentially of 3 different D-glucopyranose polymers: amylose, amylopectin and a so-called intermediate fraction, which is also referred to as abnormal amylopectin, and 10 to 20% water, depending on the variety and storage conditions, smaller amounts of protein, Fats and phosphoric ester groups. Depending on the variety, the contents of the listed ingredients vary.

Starch is used primarily in the paper and food industry, but also increasingly for the production of cosmetics, and as detergent raw material. Due to the hydrophilicity of the starch polysaccharide, use as a thickening and binding agent is almost adequate. The property of water binding is also adjustable as gel formation, depending on the molecular composition. After introduction of ionic substituents, the water-binding capacity can be increased to the point of use as an absorber.

However, a variety of engineering applications of starch derivatives, which must have specific solid state or surface strength properties, require stability to varying relative humidity and wettability with water. So the paper industry needs suitable water-stable products z. B. for the production of decorative and tissue paper. When in contact with water, tear resistance should be maintained for these types of paper. In the application of adhesives for paper, corrugated cardboard or packaging tubes, in addition to wet strength, mechanical stability is also required. In order to achieve the water stability of commercially available starches, various modifications are conceivable.

In many applications, water stability is achieved by adding melamine or resorcinol / formaldehyde resins, ie by crosslinking reactions. The resulting products can contain up to 12 of these resins. Recycling these products is very problematic from an environmental point of view.

The modification of the starch with hydrophobic residues, e.g. As by esterification or etherification reactions, is another way to increase the water stability of the polysaccharide. The advantage of such derivatizations is that, depending on the reagent used, the desired hydrophobic properties can already be achieved at very low degrees of substitution (DS.ltoreq.0.2), so that, from an economic point of view, the use of the relatively expensive hydrophobizing reagents is kept to an acceptable minimum can be reduced. The disadvantage is that due to the structure of starch, the introduction of long-chain residues is also possible with only small amounts. DS values in the slurry is achieved very slowly and in poor yields.

Hydrophobizing reagents for modifying starch contain, in addition to a reactive group for the realization of the ester or ether group, long-chain radicals. As etherifying reagents come z. As epoxidized fatty acids or fatty acid derivatives in question. As esterification reagents, it is above all conceivable to use acid anhydrides and acid chlorides which contain long-chain groups. One possibility for representing hydrophobic starches is the reaction of starch with alkenylsuccinic anhydrides (ASA). ASA is available on an industrial scale. It is used predominantly as sizing agent and thus as a quality-improving additive in papermaking. The aim of the sizing is the hydrophobing of the natural fiber fleece, whereby the penetration of water is limited or prevented. Table 1 gives an overview of the currently commercially available alkenyl succinic anhydrides. In addition, mixtures of various anhydrides, eg. B. between C ₁₂ and C ₁₄ , C ₁₆ and C ₁₈ and anhydrides with branched alkenyl chains, eg. I-DDSA or i-ODSA. Table 1: Commercially available alkenyl succinic anhydrides (ASA) Surname contraction Number of O atoms in alkenyl radical tetrapropenylsuccinic TPSA 3 each n-octenyl succinic anhydride OSA 8th n-dodecyl DDSA 12 n-tetradecenylsuccinic anhydride TDSA 14 n-hexadecenyl HDSA 16 n-octadecenyl succinic anhydride ODSA 18 Polyisobutenyl succinic anhydride PIBSA > 4

The esterification of starch with the alkenylsuccinic anhydrides described is relatively slow and in aqueous solution only with low yields (<40%). This has steric reasons in the first place. However, considerable yield losses also lead to the hydrolysis of the anhydride as a competing reaction for ester formation ( 1 ).

On the other hand, very high yields can be achieved in the reaction of starch with ASA in organic solvents, as in the patent EP 703 243 A1 described. Here starch is reacted in a homogeneous synthesis in aprotic organic solvents such as DMF, DMSO, acetonitrile, etc. However, the processing starch industry is interested in any mass application to a heterogeneous reaction in the aqueous medium. Water promotes the hydrolysis of the anhydride, which finally leads, as already described, to limited degrees of conversion or to poorer yields.

In a typical synthesis of starch succinates in an aqueous medium, starch is first suspended in a solution of sodium carbonate or sodium hydroxide solution ( US 2,661,349 ). After addition of the anhydride is mixed well at room temperature for about 14 h. This is followed by washes and the drying of the product.

The synthesis of OSA starches in an aqueous medium is described in further patents. In the patent US 5,716,441 from 1998, before the reaction with ASA, an oxidation of the starch with potassium permanganate in an alkaline solution takes place. In this method, the combination of two previously known methods. In the first step, the starch is oxidatively degraded, described inter alia in US 4,838,944 (1989) and US 2,661,349 (1985). Then the starch is esterified, as in U.S. Patent 2,661,349 described. In addition to the already described side reactions of the reagents in an aqueous medium, it proves to be disadvantageous in this method that only degraded starch products are obtained.

In the case of Bilmers and Machkewicz ( EP 761 691 ) is carried out by intensive stirring or homogenizing (emulsifying) a mixing of starch and the acid anhydride in water. The esterification is finally initiated by the adjustment of the pH according to the invention between 7.1 and 11, wherein the pH is kept constant during the reaction in this area. A disadvantage of the conversion is that even at the initial mixing step hydrolysis of the anhydride occurs. The preparation of alkyl esters or ethers of the N-alkylamino compounds of starches and preferably their hydrolysis products is described in the EP 725 082 described. This procedure is also multi-level. First, the polysaccharide used is reductively aminated by a pressure reaction in the presence of amine donors and a Ni catalyst. The hydrophobization is then carried out after removal of the catalyst by etherification or esterification reagents. In addition to the relatively high technical complexity is to be mentioned as a disadvantage that this method only succeeds in greatly degraded starches. In addition, it is a homogeneous process, which is not desired by the starch processing industry. Advantageous, however, is the large selection of usable hydrophobing reagents, such as. As isocyanates, epoxides, methylene-β-lactones, and alkenyl succinic anhydrides.

In EP 332,027 the production of hydrophobic or hydrophobic and hydrophilic substituted esters of acid, amylolytically or thermally prehydrolyzed starch or after esterification hydrolyzed derivatives described. The esterification of the respective starch is carried out heterogeneously with OSA according to US 2,661,349 after adjustment of the degree of hydrolysis. The advantage of this method is its variety of variants, which allows the production of a functional width in the structure-activity relationships. Disadvantageous again are the occurring hydrolysis reactions of the anhydride during the heterogeneous reaction.

Starch succinates with DS values up to 1.5 can be achieved by the method of Shogren. In this case, dried in vacuo starch is reacted in glacial acetic acid with the anhydride at temperatures between 120 and 180 ° C. The reactions give mixed esters with good yields. The high temperatures and the high pressures prevailing during the synthesis make this method of hydrophobing starch but relatively expensive.

The most significant disadvantages of the prior art for the synthesis of ASA starches are that they either take place in organic solvents or result in only very moderate yields as a result of the hydrolysis of the anhydride in competition with the esterification and / or the synthesis only with great technical effort, how high temperatures and pressures, multi-step synthesis routes or limited choice of output strengths is possible. The traditional starch processing industry carries out all modifications of the starting starch in the slurry system, i. H. in an aqueous medium and in a temperature range between 10 and 60 ° C. The realization of the synthesis of ASA starches with the known methods would thus entail costly investments. For environmental reasons, the replacement of water as a reaction medium by organic solvents in the present time would be incomprehensible.

The US 3,839,320 relates to a process for the preparation of starch esters from mono- and dibasic organic acid anhydrides, wherein magnesium oxide or magnesium hydroxide is used to control the formation of excess acid.

The DE 199 51 734 A1 relates to regioselectively substituted oligo- and polysaccharide esters, a process for their preparation and their use.

In the GB 1 585 200 describes a process for the preparation of carbohydrate esters and other organic compounds containing hydroxyl groups.

The JP 06192995 A concerns, inter alia, the production of coated paper.

In the DE 699 13 064 T2 Thixotropic paints with hydrophobic starch derivatives are described.

Starting from the prior art, it was thus an object of the present invention to provide a process for the preparation of hydrophobic starches, with the highest possible degree of substitution can be achieved with the most efficient use of reagents and thus the most economical process flow is guaranteed. The process should be simple and applicable to a variety of strengths.

This object is achieved by the method having the features of claim 1.

• a) Dispergieren von Stärke und/oder Stärkederivaten in einer wässrigen Salzlösung,
• b) Zugabe von Carbonsäurearihydriden,
• c) Einstellung einer Temperatur des Reaktionsgemisches zwischen 0°C und 60°C,
• d) Abbrechen der Reaktion durch Zugabe eines Alkohl-Wasser-Gemisches, wobei die Konzentration der Salzlösung eine Molalität zwischen 0.2 m und 7 m aufweist und die Salze anorganische Salze sind und die Kationen der anorganischen Salze ausgewählt sind aus der Gruppe bestehend aus Li, Mg, Al, Cu, Zn.

According to the invention, a process for the preparation of a hydrophobic starch derivative with the following, successive working steps is proposed:

• a) dispersing starch and / or starch derivatives in an aqueous salt solution,
• b) addition of carboxylic acid anhydrides,
• c) setting a temperature of the reaction mixture between 0 ° C and 60 ° C,
• d) stopping the reaction by adding an alcohol-water mixture, wherein the concentration of the salt solution has a molarity between 0.2 m and 7 m and the salts are inorganic salts and the cations of the inorganic salts are selected from the group consisting of Li, Mg , Al, Cu, Zn.

Surprisingly, it has been found that the synthesis of starch esters in aqueous salt solutions succeeds with very high yields. It was particularly surprising that the concurrent hydrolysis of the carboxylic anhydride used can be suppressed by the addition of salts to the aqueous reaction medium, which finally leads to higher yields and thus to a cost reduction compared to the known from the prior art. Another advantage of this is that one Recycling of the salt solution is readily possible if the resulting filtrates are collected in the washing processes.

The optimum concentration is determined by a dependence of the solubility of the salt used in water.

According to the invention, the anions of the inorganic salts are not particularly limited, but it is advantageous if the anions are selected from chloride, sulfate and / or nitrate.

To achieve good results of the process, it is furthermore advantageous if the concentration of the starch and / or starch derivative dispersion is 1 to 50% (w / w), preferably 5 to 30% (w / w), particularly preferably 10 to 25% ( w / w).

The process according to the invention can be carried out with any desired starches and / or starch derivatives. For example, potatoes, corn, peas or cereals can serve as a source of starch.

It is also irrelevant whether the starch and / or starch derivatives used are untreated, partially substituted, partially oxidized and / or partially degraded. According to the invention, it is likewise possible to use mixtures of the abovementioned starches and / or starch derivatives.

In the process, it is advantageous if the pH of the reaction medium to a value between 3 and 9, preferably between 4 and 8.5, is set.

In an advantageous development of the process, in step b) the carboxylic acid anhydrides are added in a molar ratio with respect to the starch, depending on the desired DS value, between 0.01 and 1.0, preferably between 0.05 and 0.5. Here again, the advantage of the method according to the invention over the prior art is clear, since in the prior art ever greater amounts of carboxylic acid anhydrides with respect to the strength had to be added to soften a corresponding degree of substitution (DS).

Alkenylsuccinic acid anhydrides can preferably be used according to the invention as carboxylic anhydrides. Very particular preference is given to those given in Table 1.

In a further advantageous embodiment of the method, a temperature between 10 and 60 ° C, more preferably between 15 and 40 ° C is maintained in step c).

The reaction time to be maintained in step c) can advantageously be from 2 hours to 200 hours, preferably from 2 to 96 hours, more preferably from 2 to 48 hours.

To terminate the reaction, a mixture of alcohols and water is added according to the invention. In principle, all alcohols which are miscible with water can be used. Examples are: ethanol, 2-propanol, methanol, tert. Butanol.

Depending on the process, the degree of substitution of the hydrophobic starch derivatives can be adjusted to between 0.01 and 1 according to the invention. The adjustment of the degree of substitution can be done by the appropriate amount of acid anhydride, but also by stopping the reaction at the given time.

Preferably, the method finds use in the manufacture of paper products.

The invention is explained in more detail by the following examples, without being limited thereto:

Example 1:

First, 12.5 g (0.077 mol / AGU) of native potato starch in 50 ml of a 2 M ZnCl ₂ solution and stirred min intensively. Subsequently, 1.6 g (0.008 mol) of octenylsuccinic anhydride (OSA) are added and stirred for 16 hours at room temperature. For work-up, a mixture of 250 ml of ethanol / water (50/50, v / v) is added. After filtration through a G2 frit, wash with ethanol / water (50/50, v / v) until free of chloride. Finally, the sample is washed with ethanol and the OSA Starch dried in a drying oven at 80 ° C. The procedure described gives an OSA strength with DS = 0.1. The associated ¹³ C-CP / MAS spectrum is in 2 shown.

Example 2:

20 g (0.123 mol / AGU) of native potato starch are added to 40 ml of a 1 M ZnCl ₂ solution and thoroughly mixed for 10 min. Subsequently, 1.3 g (0.0062 mol) of OSA are added and stirred for 16 hours at room temperature. After washing and drying according to Example 1, an OSA starch with a DS = 0.04 is obtained.

Example 3:

200 g (1.23 mol / AGU) of a cationic starch (DS = 0.03) are placed in 600 ml of a 2 M ZnCl ₂ solution and thoroughly mixed for 10 min. After addition of 20.8 g (0.1 mol) of OSA is stirred while keeping the pH to 4 for 72 h. After washing and drying according to Example 1, an OSA starch with a DS = 0.08 is obtained.

Example 4:

10 g (0.054 mol / AGU) of carboxymethyl starch (DS = 0.56) are added to 100 ml of a 2 M ZnCl ₂ solution and stirred vigorously for 10 min. The pH is adjusted to 4. Subsequently, 1.14 g (0.005 mol) of octenylsuccinic anhydride (OSA) are added and stirred for 18 hours at room temperature. The pH is kept constant at 4 during the synthesis. After washing and drying according to Example 1, 10.34 g of the starch derivative were obtained with a DS (OSA) = 0.08.

Example 5:

25 g (0.154 mol / AGU) of native potato starch are added to 50 ml of a 5.5 m MgCl ₂ solution and thoroughly mixed for 10 min. Subsequently, 3.3 g (0.016 mol) OSA are added and stirred for 16 hours at room temperature. After washing and drying according to Example 1, an OSA starch with a DS = 0.01 is obtained.

Example 6:

25 g (0.154 mol / AGU) native potato starch in 100 ml of a 1.0 M Al (NO _{3) 3} solution and mixed for 10 minutes intensively. Subsequently, 3.2 g (0.015 mol) of OSA are added and stirred for 16 hours at room temperature. After washing and drying according to Example 1, an OSA starch with a DS = 0.02 is obtained.

Example 7:

In about 70 ml of a 0.44 m ZnCl ₂ solution (4.21 g ZnCl ₂ to 70 g H ₂ O), the pH is adjusted to 4 by addition of 0.1 N HCl. Subsequently, 25 g (0.1 54 mol / AGU) of native potato starch are added to the salt solution and stirred vigorously for 10 min. Finally, 4.1 g (0.02 mol) of OSA are added, the mixture is stirred for a total of 24 h and the pH is kept constant at 4 with 1N NaOH throughout. After washing and drying according to Example 1, 30.15 g of OSA starch (dry content: 92.94) and with a DS (OSA) = 0.13 were obtained.

Example 8:

200 g (1.23 mol / AGU) of a cationic starch (DS = 0.03) are placed in about 600 ml of a 2 M ZnCl ₂ solution (163.6 g ZnCl ₂ in 600 ml H ₂ O) and 10 intensively stirred. Within 5 minutes, 31.1 g of LA-SAR (succinic anhydride with C16 to C18 side chains) are added dropwise. The pH is kept constant at 4 for the reaction time. After 45 h, the reaction is terminated by adding 1.2 l of ethanol / water mixture (50/50, v / v). Washing and drying are carried out analogously to Example 1. The DS of the hydrophobic LASAR starch is 0.04.

Example 9 (size press and Cobb values):

The papers (inkjet base paper without surface sizing with a weight per unit area of 80 g / m ² ) are treated in a laboratory size press from Mathis at a liquor temperature of 50 ° C. with 8% strength starch solution. The leaves are then dried by means of rapid drying. The applied amount of starch is in each case about 1.5 g / m ² / side.

The determination of the water absorption of the thus coated papers was carried out according to the method according to Cobb 60 (regulation DIN 53 132). The results are shown in Tab. Table 2: Determination of Cobb ₆₀ values paper DS of OSA strength Water absorption in [g / m ² ] (method according to Cobb ₆₀ ) Raw paper (without starch coating) - 50 Cationized, oxidized potato starch (reference) - 38 with hydrophobicized starch 0.04 26 with hydrophobicized starch 0.05 24 with hydrophobicized starch 0.07 17

Example 10 (determination of the contact angle):

The contact angle or angle forms at the phase boundary of three mutually immiscible phases, z. B. in the limited wetting of a solid by a liquid. The contact angle characterizes the degree of wetting and gives z. B. Information on the printability of paper.

The contact angle of the papers coated according to Example 9 with a hydrophobicized starch prepared according to Example 3 with DS (OSA) = 0.05 is determined. As a reference, a cationized, oxidized starch ( 3 ). The values are shown in Tab.

The recording and the measurement of the contact angle was carried out with an optical contact angle measuring instrument from the company DataPhysics Instruments according to the Sessile Drop method. The test liquid was distilled water. Table 3: Determination of the contact angles of different strengths sample contact angle Cationized, oxidized potato starch 62 ° Hydrophobized starch with DS = 0.05 105 °

1 shows a synthesis scheme for the preparation of a starch derivative of the invention. In this case, the reaction step according to the invention, in which the hydrolysis of the acid anhydride used is largely avoided, is contrasted with the undesired secondary reaction.

2 shows a section of a ¹³ C NMR

Spectrum of a starch derivative prepared according to the invention, which was synthesized starting from potato starch by reaction with octenyl succinic anhydride (OSA). The degree of substitution in this example is 0.1. In the spectrum all C-atoms are designated. Between 60 and 100 ppm, the 6 C atoms of the starch anhydoglucose unit (AGU) can be found. At 130 ppm, the double bond of the octenyl radical can be seen.

At 181 ppm, the carboxyl function is observed. The alkyl groups such as CH ₃ , CH ₂ , and CH are found between 10 and 50 ppm. The DS value is determined by integration of the NMR signals and comparison of the resulting areas and the peaks. The ratio of the integrals of the alkyl groups of the octenyl radical, z. As the methyl group, to the C ₁ signal of the starch AGU determines the DS value.

3 shows the influence of the hydrophobization of a starch derivative prepared according to the invention (potato starch rendered hydrophobic with OSA, DS = 0.05) versus cationized, oxidized potato starch on the basis of the contact angle formed on wetting with a water drop. It can be clearly seen that in the starch derivative prepared according to the invention the contact angle is significantly greater than in the case of the untreated starch.

Claims (13)

Process for the preparation of a hydrophobic starch derivative with the following, successive working steps: a) dispersing starch and / or starch derivatives in an aqueous salt solution b) Addition of carboxylic acid anhydrides c) Setting a temperature of the reaction mixture between 0 ° C and 60 ° C. d) stopping the reaction by adding an alcohol-water mixture, wherein the concentration of the salt solution has a molarity between 0.2 m and 7 m and the salts are inorganic salts and the cations of the inorganic salts are selected from the group consisting of Li, Mg , Al, Cu, Zn. A method according to claim 1, characterized in that the anions of the inorganic salts are selected from the group consisting of chloride, sulfate and / or nitrate. Method according to one of the preceding claims, characterized in that the concentration of the starch and / or starch derivative dispersion 1 to 50% (w / w), preferably 5 to 30% (w / w), particularly preferably 10 to 25% (w / w). w) is. Method according to one of the preceding claims, characterized in that the starch and / or starch derivatives of potatoes, rice, corn, peas and / or cereals originate. Method according to one of the preceding claims, characterized in that untreated, partially substituted, partially oxidized and / or partially degraded starch and / or starch derivatives or mixtures thereof are used in step a). Method according to one of the preceding claims, characterized in that the pH of the starch and / or starch derivative dispersion in step a) is adjusted to a value between 3 and 9, preferably between 4 and 8.5. Method according to one of the preceding claims, characterized in that in step b) the carboxylic anhydrides are added with respect to the starch in a molar ratio of between 0.01 and 1.0, preferably between 0.05 and 0.5. Method according to one of the preceding claims, characterized in that the carboxylic anhydrides are selected from the group of alkenyl succinic anhydrides (ASA). A method according to the preceding claim, characterized in that the alkenyl succinic anhydrides (ASA) are selected from the group consisting of tetrapropenylsuccinic anhydride (TPSA), n-octenylsuccinic anhydride (OSA), n-dodecylsuccinic anhydride (DDSA), n-tetradecenylsuccinic anhydride (TDSA), n-hexadecylsuccinic anhydride (HDSA), n-octadecyl succinic anhydride (ODSA), polyisobutenyl succinic anhydride (PIBSA) and / or mixtures thereof. Method according to one of the preceding claims, characterized in that in step c) a temperature between 10 and 60 ° C, preferably between 15 and 40 ° C is set. Method according to one of the preceding claims, characterized in that a reaction time in step c) of 2 hours to 200 hours, preferably from 2 to 96 hours, most preferably from 2 to 48 hours, is maintained. Method according to one of the preceding claims, characterized in that the alcohols (step d) are selected from water-miscible alcohols. Method according to one of the preceding claims, that a degree of substitution (DS) of the synthesized hydrophobic starch derivative is adjustable between 0.01 and 1.

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