Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/20—Post-etherification treatments of chemical or physical type, e.g. mixed etherification in two steps, including purification
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/005—Crosslinking of cellulose derivatives

Definitions

• the present invention relates to glyoxal-crosslinked polysaccharide derivatives, for example cellulose ethers, of reduced unbound glyoxal content, and to a method for decreasing the unbound glyoxal in these polysaccharide derivatives.
• untreated polysaccharide derivatives can only be dissolved, dispersed or emulsified with great effort in many instances, because when the polymer particles are introduced into an aqueous or water-containing solution of the polysaccharide derivatives, a gel layer forms on the surface of these particles. Since water can only penetrate slowly to reach the interior of the polymer, the dissolution, dispersion or emulsification is achieved with great effort. In addition, the resulting swollen particles which are covered with a gel layer have a tendency to agglomerate, and as such lumps are form thereby and the homogeneous distribution of the remaining components is made possible only by means of time- and energy-consuming mixing operations.
• U.S. Pat. No. 3,356,519 teaches that weak bases, for example, sodium tetraborate are added as additive to glyoxal-crosslinked cellulose ethers to increase the pH of the polymers and thus reduce the time up to complete dissolution of these substances.
• weak bases for example, sodium tetraborate
• the prior art process of accelerating the time for the dissolution, dispersion or emulsion is undesirable and can be suppressed by adding acids.
• U.S. Pat. No. 3,356,519 teaches that solely cellulose ether powders or cellulose ether granules, are surface-treated with 0.1-0.2% by weight of glyoxal.
• the inventive process relates to water-soluble polymers which are brought to reaction with more than 0.2% by weight of glyoxal.
• the inventively treated polysaccharide derivatives may also be brought into solution in a lump-free manner at the preferred pH in the vicinity of the neutral point.
• the sodium tetraborate is not added in solid form after grinding the cellulose ether. Instead a water-soluble borate in dissolved form is added, preferably before grinding, so that intimate mixing of the methyl cellulose with the water-soluble borate takes place.
• U.S. Pat. No. 4,400,502 describes contacting anionic water-soluble cellulose ethers with a solution of water, glyoxal and sodium tetraborate in a slurry medium.
• U.S. Pat. No. 4,400,502 requires the presence of a non-solvent for the polysaccharide derivative, and a flammable and environmentally harmful organic liquid, which must be removed from the product and reprocessed in a complex manner.
• relatively large amounts of sodium tetraborate are required, that is to say at least 50 parts by weight per 100 parts by weight of glyoxal used. It is also of note that this patent does not teach how the procedure is to be followed with alkyl-group-containing polysaccharide derivatives, to reduce the content of unbound glyoxal.
• DE-A-2 535 311 describes a process for improving the dispersibility of a cellulose ether in aqueous liquids having a pH greater than 10, by adding boric acid or a water-soluble borate; in addition a dialdehyde, for example glyoxal.
• a delayed solubility can also optionally be achieved solely using sodium tetraborate, whereas this is impossible using solely a water-soluble borate or boric acid in the case of the polysaccharide derivatives used according to the present invention.
• the patent describes treating the cellulose ether with boric acid or sodium tetraborate in a non-acidic, preferably alkaline medium, by setting a pH using one or more additional components.
• the content of unbound glyoxal can be decreased by the addition of additives, for example water-soluble borates, so that in the products thus produced, compared with the prior art, significantly less unbound glyoxal is present.
• additives consist essentially of water-soluble compounds containing elements of Main Group 3 of the Periodic Table of the Elements. Of this group, water-soluble borates and aluminium salts have proved to be particularly effective.
• the content of unbound glyoxal can be markedly lowered compared with the processes obtained according to the prior art. A product which is more environmentally friendly and thus more readily handleable and marketable is thus obtained.
• the invention therefore, relates to glyoxal-treated polysaccharide derivatives, characterized in that, to decrease the unbound glyoxal, they are treated with an aqueous solution of one or more water-soluble aluminium salts, or one or more water-soluble borates, or a combination of one or more water-soluble aluminium salts and one or more water-soluble borates, and, if appropriate, with suitable buffer substances to set the pH, and are dried.
• water-soluble borates for the purposes of this invention means alkali metal salts and ammonium salts of polyboric acids which are characterized by the general formula H n ⁇ 2 B n O 2n ⁇ 1 . Preference is given to the use of Na 2 B 4 O 7 , K 2 B 4 O 7 and (NH 4 ) 2 B 4 O 7 , which may contain water of crystallization. Salts and esters of orthoboric acid and metaboric acid are less suitable.
• a high content of alkyl-derivatized hydroxyl groups of the polysaccharide derivative generally increases the content of unbound extractable glyoxal.
• the alkylated hydroxyl groups can no longer react with the dialdehyde used for the reversible crosslinking and therefore contribute to increasing the content of unbound extractable glyoxal. Therefore, in the case of alkylated polysaccharide derivatives, there is a particularly great need to decrease the content of unbound glyoxal.
• the reaction between the dialdehyde glyoxal and the hydroxyl groups of a polysaccharide or polysaccharide derivative is known to those skilled in the art as hemiacetal or acetal formation (F. H.
• Alkyl substituents are linear, branched or cyclic substituents consisting of the elements carbon and hydrogen. These substituents are bound to an oxygen atom of the polysaccharide either directly or via a number of further atoms or molecular groups. Preferably these substituents contain from one to eighteen carbons. Particularly preferred alkyl substituents are methyl and ethyl.
• the total degree of substitution of all alkyl substituents is generally greater than 1, preferably between 1 and 2, and particularly preferably between 1.3 and 1.7. If appropriate, other substances can be present, such as carboxymethyl, hydroxyethyl and hydroxypropyl.
• the polysaccharide derivatives are cellulose ethers.
• cellulose ethers examples include methyl cellulose, methyl hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl ethyl cellulose, methyl ethyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, methyl hydroxyethyl hydroxypropyl cellulose, ethyl hydroxyethyl hydroxypropyl cellulose, methyl carboxymethyl cellulose, ethyl carboxymethyl cellulose, propyl cellulose, isopropyl cellulose and cyclohexyl cellulose.
• those polysaccharide derivatives are used which are insoluble in boiling water, independently of the type of substituents.
• a polysaccharide derivative is hydroxypropyl cellulose.
• the amount of unbound glyoxal can be determined by extracting the cellulose ether with a solvent. Suitable solvents dissolve the unbound glyoxal, but not the cellulose ether under test, that is to say for example, toluene, chloroform, dichloromethane, tetrahydrofuran. In the extract, the gyloxal is detected photometrically after a derivatization.
• Photometric analytical methods are known to those skilled in the art and are described in the literature, for example: Lange and Vejdelek, Photometrische Analyse [Photometric Analysis], Verlag Chemie, Weinheim 1980.
• one or more buffer substances are added to the polysaccharide derivative, which buffer substances desirably affect the pH.
• This can avoid too high a pH being set due to a high amount of a basic glyoxal-binding additive.
• Such a pH leads to an accelerated dissolution of the polysaccharide derivative which is undesirable in many applications. It is likewise possible to avoid molecular weight breakdown and thus viscosity breakdown occurring due to too low a pH.
• the buffer substances used are citric acid or salts thereof in combination with water-soluble aluminium salts.
• at least one mole of trisodium citrate is used per mole of the water-soluble aluminium salt, so that the aluminium cation is completely complexed in solution and does not interact undesirably with further constituents, for example present in a preparation.
• the buffer substances used are phosphoric acid or salts thereof in combination with water-soluble borates, to set the desired pH.
• suitable compounds are able to elevate or, depending on requirements, decrease the pH of an aqueous solution for the purpose of setting the desired pH.
• a further object of the invention is a process for decreasing the unbound glyoxal in glyoxal-treated polysaccharide derivatives.
• the polysaccharide derivative is mixed, preferably at a temperature between 20 and 70° C., with an aqueous solution of one or more water-soluble aluminium salts, or one or more water-soluble borates, or a combination of one or more aluminium salts and one or more water-soluble borates, the solution containing further buffer substances to set the pH, and then
• the inventive process therefore consists essentially of adding to the polysaccharide derivative an aqueous solution of glyoxal and an additive consisting essentially of a water-soluble aluminium salt or a water-soluble borate, preferably sodium tetraborate, and also optionally a further component for setting a desired pH.
• the additive markedly decreases the content of unbound glyoxal that can be extracted.
• the third component which can consist of a mixture of various substances, the pH can be set according to the requirements of the application. In most applications a pH of 8 or more is undesirable, since the retardation of dissolution is then too low to bring the polymer into solution in a lump-free manner.
• the inventive process can avoid this disadvantage.
• the glyoxal is used in the form of a 40% strength by weight aqueous solution.
• one or more water-soluble borates and one or more substances for setting the pH are dissolved in water and then added to the polysaccharide derivative.
• a water-moist filter cake obtained after hot water washing preferably has a dry matter content of 40-60% is used.
• This filter cake is preferably sprayed with a solution of glyoxal, water-soluble borate and buffer substance and, if appropriate, water, while it is maintained in motion and then dried and ground or subjected to a grinder-drying.
• the filter cake is sprayed with a solution of glyoxal, water-soluble aluminium salt and buffer substance and also, if appropriate, water.
• the amount of glyoxal added to the filter cake is preferably at least 0.4 percent by weight, based on the mass of the dried and ground polysaccharide derivative, particularly preferably between 0.4 and 1 percent by weight.
• the amount of water-soluble tetraborate or water-soluble aluminium salt, based on the dry substances, is preferably less than 0.5 part by weight per part by weight of glyoxal, particularly preferably between 0.1 and 0.3 part by weight per part by weight of glyoxal.
• the retardation of dissolution can be determined using a rheometer which is able to measure the shear stress as a function of time.
• the measurement starts with sprinkling the cellulose ether into the water which has been charged.
• the measured values thus obtained are entered onto a diagram, so that an S-shaped curve is produced which reproduces the shear stress as a function of time.
• a tangent is drawn to the point of inflection of the curve, the intersection of which tangent with the time axis (x axis) gives the retardation of dissolution.
• the viscosities were determined at a temperature of 20° C. on a 2% by weight solution of the treated air-dried polysaccharide derivative in distilled water.
• the measuring instrument used was a Rotovisko VT 550, manufacturer: Haake, equipped with an MVII rotor and a MV measuring cup from the same manufacturer.
• the shear gradient was 2.55 s ⁇ 1 .
• the pH reported was determined electrometrically using a single-rod electrode on a 2% by weight solution of the treated air-dried polysaccharide derivative in distilled water.
• Glyoxal was used in the form of a 40% strength aqueous solution.
• DS (M) gives the average degree of substitution of an anhydroglucose unit by methyl substituents. Substitution by reagents which form a further hydroxyl group is characterized by the molar degree of substitution (MS). MS(HE) gives the average number of hydroxyethyl groups per anhydroglucose unit and can be greater than three, since more than three hydroxyethyl groups can be bound to each anhydroglucose unit.
• DS and MS are determined by the Zeisel method known to those skilled in the art described, for example, in P. W. Morgan, Ind. Eng. Chem. Anal. Ed. 18 (1946) 500-504 and R. U. Lemieux, C. B. Purves, Can. J Res. Sect. B 25 (1947) 485-489.
• MHEC water-moist methyl hydroxyethyl cellulose
• MHEC water-moist methyl hydroxyethyl cellulose
• Mg(SO 4 ).7.H 2 O aluminium sulphate hexadecahydrate
• citric acid monohydrate sodium tetraborate decahydrate
• Na 2 B 4 O 7 .10H 2 O citric acid monohydrate
• disodium hydrogenphosphate dihydrate Na 2 HPO 4 .2H 2 O
• sodium dihydrogenphosphate dihydrate NaH 2 PO 4 .2H 2 O
• Glyoxal was used as aqueous solution with a glyoxal content of 40 percent by weight
• Water-moist methyl hydroxyethyl cellulose (2 500 g of dry matter), characterized by an average degree of substitution DS (M) of 1.76 (average number of methyl groups per anhydroglucose unit), and a molar degree of substitution MS (HE) of 0.32 (average number of hydroxyethyl groups per anhydroglucose unit), viscosity 39 000 mPa.s (2% strength solution in water) is placed in a mixer and mixed there with an aqueous solution of glyoxal, water and aluminium sulphate. The solution additionally contains a citrate buffer prepared from citric acid and sodium hydroxide solution. After adding the reagents, the mixture is mixed over the course of 90 min at an internal temperature of 55° C.
• M average degree of substitution DS
• HE molar degree of substitution MS
• Methyl hydroxyethyl cellulose (2 500 g of dry matter), characterized by DS (methyl) of 1.57 and MS (HE) of 0.27, viscosity 30 000 mpa.s (2% strength solution in water) is placed in a mixer and mixed there with water, a buffer mixture consisting of sodium dihydrogenphosphate and disodium hydrogenphosphate and also I) glyoxal, II) glyoxal and sodium tetraborate or III) sodium tetraborate. After the reagents are added the mixture is mixed over the course of 90 min at an internal temperature of 55° C.
• a further sample without glyoxal that is to say only with boric acid and a buffer mixture consisting of sodium dihydrogenphosphate and disodium hydrogenphosphate was sprayed and dried.

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• 2003
  • 2003-02-26 DE DE10308109A patent/DE10308109A1/de not_active Withdrawn
• 2004
  • 2004-02-13 EP EP04003373A patent/EP1452544B1/de not_active Expired - Lifetime
  • 2004-02-13 DE DE502004003920T patent/DE502004003920D1/de not_active Expired - Lifetime
  • 2004-02-13 AT AT04003373T patent/ATE363492T1/de not_active IP Right Cessation
  • 2004-02-13 ES ES04003373T patent/ES2285287T3/es not_active Expired - Lifetime
  • 2004-02-17 BR BR0400556-2A patent/BRPI0400556A/pt not_active IP Right Cessation
  • 2004-02-19 US US10/781,230 patent/US20040167326A1/en not_active Abandoned
  • 2004-02-23 CA CA002458334A patent/CA2458334A1/en not_active Abandoned
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  • 2004-02-25 JP JP2004049949A patent/JP4800583B2/ja not_active Expired - Lifetime
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  • 2004-02-25 KR KR1020040012574A patent/KR101075293B1/ko active IP Right Grant
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• 2006
  • 2006-11-01 US US11/591,654 patent/US8138331B2/en not_active Expired - Lifetime
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