Classifications

• • 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
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
  • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
  • A61L15/42—Use of materials characterised by their function or physical properties
  • A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents
• • 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
  • C08B11/02—Alkyl or cycloalkyl ethers
  • C08B11/04—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals
  • C08B11/14—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals with nitrogen-containing groups

Definitions

• the present invention relates to a cationic polymer more particularly a water absorbent polymer of the type commonly referred to as a "superabsorbent".
• superabsorbents are typically slightly cross-linked hydrophillic polymers.
• the polymers may differ in their chemical nature but they share the property of being capable of absorbing and retaining even under moderate pressure amounts of aqueous fluids equivalent to many times their own weight.
• superabsorbents can typically absorb up to 100 times their own weight or even more of distilled water.
• Superabsorbents have been suggested for use in many different industrial applications where advantage can be taken of their water absorbing and/or retaining properties and examples include agriculture, the building industry, the production of alkaline batteries and filters.
• the primary field of application for superabsorbents is in the production of hygienic and/or sanitary products such as disposable sanitary napkins and disposable diapers either for children or for incontinent adults.
• superabsorbents are used, generally in combination with cellulose fibres, e.g. cellulose fluff, to absorb body fluids such as menses or urine.
• the absorbent capacity of superabsorbents for body fluids is dramatically lower than for deionised water. It is generally believed that this effect results from the electrolyte content of body fluids and the effect is often referred to as "salt poisoning".
• the water absorption and water retention characteristics of superabsorbents are due to the presence in the polymer structure of ionisable functional groups.
• These groups may be carboxyl groups, a high proportion of which are in the salt form when the polymer is dry but which undergo dissociation and solvation upon contact with water.
• the polymer chain will have a series of functional groups attached to it which groups have the same electric charge and thus repel one another. This leads to expansion of the polymer structure which, in turn, permits further absorption of water molecules although this expansion is subject to the constraints provided by the cross-links in the polymer structure which must be sufficient to prevent dissolution of the polymer.
• a cationic superabsorbent based on a polysaccharide such as cellulose will have polysaccharide hydroxyl groups reacted with a reagent (a derivatising reagent) which converts these hydroxyl groups into a cationic group, e.g. a quaternary ammonium group.
• a reagent a derivatising reagent
• the product should be based on fibrous cellulose since this can be combined and processed more easily with cellulose fluff which also has a fibrous character.
• WO 92/19652 relates to a fibrous cationic polysaccharide which can be obtained by reacting fibrous polysaccharides such as cellulose with an excess of quaternary ammonium compounds containing at least one group capable of reacting with the polysaccharide hydroxyl groups. Whilst the product of WO 92/19652 shows useful properties as a superabsorbent there is a limit to the absorption properties which can be achieved.
• the absorption of water by a superabsorbent involves the functional groups attached to the polymer chain and, in principle, the absorption capacity depends on the ratio of functional groups to the remainder of the polymer, i.e. the more functional groups that are introduced the greater the repulsion between the polymer chains and the greater the potential for water absorption.
• the absorption capacity depends on the ratio of functional groups to the remainder of the polymer, i.e. the more functional groups that are introduced the greater the repulsion between the polymer chains and the greater the potential for water absorption.
• derivatisation of cellulose in particular introduction of hydrophillic groups, tends to increase solubility in water. Accordingly attempts to increase water absorption of the product of WO 92/19652 by increasing the ds would be likely to lead to a water soluble polymer rather than a superabsorbent which, by definition, must remain insoluble in water.
• the fibrous form of the material means that it is difficult for the derivatising agent to gain access to polysaccharide hydroxyl groups without destroying the structural backbone of the material.
• ds degree of substitution
• Activation can take the form, for example, of application of pressure to burst the fibres open and expose more potential reaction sites, or use of a chemical activation agent such as zinc chloride.
• Example 6 of WO 92/19652 achieves a ds of 1.10 but only by using activation with zinc chloride and the product would have been largely soluble.
• Processes are known for the cross-linking of cellulose using cross-linking agents such as formaldehyde, epichlorohydrin, diepoxides, dicarboxylic acids, dialdehydes and diisocyanates to obtain highly water insoluble products.
• cross-linking agents such as formaldehyde, epichlorohydrin, diepoxides, dicarboxylic acids, dialdehydes and diisocyanates.
• cross-linking agents such as formaldehyde, epichlorohydrin, diepoxides, dicarboxylic acids, dialdehydes and diisocyanates
• An object of the present invention is to provide a superabsorbent polymer based on a polysaccharide, preferably a fibrous polysaccharide, more preferably fibrous cellulose which has improved superabsorbent properties. It has now surprisingly been found that such a product can be produced by combining derivatisation of the polysaccharide with a appropriate degree of cross-linking to maintain water insolubility. The improvement in superabsorbent properties brought about by an increased number of functional groups (higher ds) more than outweighs any effect that the cross- linking agent has on super-absorbent properties and the product has improved superabsorbent properties, for example as compared to products of the type disclosed in WO 92/19652. Thus use of a cross-linking agent makes it possible to control the gel strength of the product and makes it easier to tailor the characteristics of the product to those which are required.
• the present invention provides a cationic polysaccharide, preferably a fibrous cationic polysaccharide, having superabsorbent characteristics, the polysaccharide being substituted by quaternary ammonium groups and having a ds of at least 0.5, preferably 0.5 to 2.5, and the polysaccharide being cross-linked to a sufficient extent that it remains insoluble in water.
• the polysaccharide according to the present invention is preferably based on cellulose, more preferably fibrous cellulose, although the invention can also be applied to other polysaccharides such as starch and natural products based on saccharide units.
• the present invention can be applied to fibrous cellulose derived by any chemical and/or mechanical treatment, for example cellulose fibres obtained from wood pulp purified by the sulphate process or the bisulphite process, cellulose fibres obtained from wood pulp by thermomechanical or mechanical treatment, beet cellulose, regenerated cellulose or cotton linters.
• the cellulose fibres are obtained from wood pulp purified by the sulphate process or as cellulose "fluff" derived from mechanical treatment or wood pulp and are of the type generally used for the preparation of absorbent pads in disposable products, for example sanitary napkins and towels and diapers.
• the invention may also be applied to cellulose powders.
• the polysaccharide according to the invention can be prepared by a process which involves derivatising a polysaccharide, preferably a fibrous polysaccharide, with quaternary ammonium groups and cross-linking with a suitable cross-linking agent.
• the derivatising and cross-linking can generally be carried out under similar conditions so that it is possible to carry out both reactions in a single stage. However, the reactions may become competitive so that it is preferred to carry out the derivatising reaction as a first stage, followed by cross-linking as a separate second stage. This two stage approach allows greater control of the reaction in terms of ds, degree of cross-linking, freedom from undesired secondary products, etc.
• the present invention provides a process for the production of a cationic polysaccharide, preferably a fibrous cationic polysaccharide, having superabsorption characteristics which comprises:
• the polysaccharide is in fibrous form.
• step (ii) is carried out subsequently to step (i) with or without intermediate isolation of the product of step (i) .
• Use of the cross-linking agent in the process according to the invention improves the yield cf the process by reducing the amount of soluble product which is obtained.
• the reaction with the quaternary ammonium compound is generally carried out in the presence of base and preferably in aqueous medium.
• bases include alkali and alkaline earth metal hydroxides and alkoxides, for example the hydroxide, methoxide, ethoxide, propoxide, isopropoxide, n-butoxide or t-butoxide of an alkali metal such as potassium or preferably sodium.
• the most preferred base is generally sodium hydroxide .
• Suitable quaternary ammonium compounds can be represented by one of the following general formulae (I) and (II) :
• n is an integer from 1 to 16;
• X is halogen, in particular fluorine, chlcrine. fcro . ⁇ ne or iodine, preferably chlorine;
• Z ⁇ is an anion which may be inorganic, f ⁇ r exa-ple r.alide (fluoride, chloride, bromide or iodide, preferably r.lcride) , nitrate, nitrite; phosphate or hydroxide, cr organic, for example carboxylate such as acetate or propionate;
• R, R 1 , R 2 and R 3 which may be the same or different, are each an organic radical, preferably containing up to 10 carbon atoms, or preferably hydrogen; or additionally R 2 may represent a group of formula (III) or (IV) :
• n, R, R ] R- X and Z are as defined above.
• each of R, R 1 , R 2 and R 3 is hydrogen.
• one of these groups is an organic radical this should not contain any substituent having an unacceptable adverse effect on the derivatisation reaction or the subsequent cross-linking reaction or on the properties of the material produced, for example superabsorbent properties.
• Suitable organic groups include alkyl, hydroxyalkyl, alkenyl and aryl. Large organic groups increase the molecular weight of the product so that smaller groups are preferred. The most preferred organic group is methyl or hydroxymethyl.
• quaternary ammonium compounds include: glycidyltrimethylammoniu chloride;
• 3-epoxypropyl-N,N,N-trimethylammonium chloride (commercially available from Degussa A.G. as a 70% aqueous solution under the name QUAB 151 or as the pure compound in solid form from Fluka under product code 50045) ; 3-chloro-2-hydroxypropyl-N,N, N-trimethylammonium chloride (commercially available from Degussa A.G. as a 65% aqueous solution under the name of QUAB 188) ; 3-chloro-2-hydroxypropyl-N,N,N-dimethylethanolammonium chloride (commercially available from Degussa A.G. as a 65% aqueous solution under the name of QUAB 218) ;
• a particularly preferred quaternary ammonium compound is glycidyltrimethylammonium chloride.
• the derivatisation reaction with the quaternary ammonium compound can be carried out in a single step or as two or more steps with or without intermediate separation and purification of the product.
• the reaction is carried out by contacting the polysaccharide with the base, preferably in aqueous medium.
• the quaternary ammonium compound is used in excess, for example in a molar ratio based on saccharide units in the polysaccharide of 5:1 to 40:1, more particularly 20:1 to 40:1.
• a molar ratio of 10:1 to 20:1 preferably applies in each step.
• the base preferably sodium hydroxide
• the base is used in the or each step in a molar ratio of 1:3 to 3:1 based on hydroxyl groups in the monosaccharide units and in a molar ratio of 5:100 to 300:100, preferably 100:100 to 300:100, based on the quaternary ammonium compound where this is a compound of formula (I) or 10:100 to 50:100 where this is a compound of formula (II) .
• the reaction temperature for the or each step may be from 15 to 120oc, preferably 70 to lOOoC, and the reaction time overall may be for example 1 to 20 hours. Where the derivatisation reaction is carried our in two or more stages, the reaction time for each stage will generally be 0.25 to 5 hours, preferably 0.25 to 2 hours.
• the derivatised product may be isolated and purified by removing excess alkc. i by washing to neutrality, for example with dilute, e.g. 4%, aqueous sodium chloride.
• the product may then be converted to salt form by treatment with a strong excess of acid, e.g. 4% aqueous hydrochloric acid, and washed to neutral.
• the product is then dehydrated, for example with acetone and recovered by filtration and/or centrifugation.
• Derivatised polysaccharides prepared as described above in which one or more of R 1 , R 2 and R 3 is hydrogen can subsequently be converted into the corresponding compounds in which one or more of R 1 , R 2 and R 3 is a hydrocarbon group by an N-alkylation reaction, for example with a compound of formula R 5 Hal where R 5 is an optionally substituted hydrocarbon group, for example alkyl, hydroxyalkyl or alkenyl and Hal is halogen, more particularly fluorine, chlorine, bromine or iodine, to effect guaternisation of some of all of the ammonium groups.
• the polysaccharide is cross-linked either in the same reaction as the derivatisation reaction or preferably subsequently thereto.
• Suitable cross-linking agents for polysaccharides such as cellulose include: formaldehyde; methylolated nitrogen compounds such as dimethylolurea dimethylolethyleneurea and dimethylolimidazolidone; diacarboxylic acids such a maleic acid; dialdehydes such as glyoxal; diepoxides such a l,2:3,4-diepoxybutane and 1,2:5,6- diepoxyhexane; diisocyanates; divinyl compounds such as divinylsulphone; dihalogen compounds such as dichloroacetone, dichloroacetic acid, 1,3-dichloropropan-2-ol,dichloroethane, 2, 3-dibromo-l-propanol, 2,3-dichloro-l-propanol and 2,2- dichloroethyl ether; halohydrins such as epichlorohydrine; bis (epoxypropyl)ether; vinyleyelohe
• N,N' -dimethylol methylenebis (acrylamide)
• triacrylolhexahydrotriazine acrylamidomethylene chloroacetamide
• Preferred cross-linking agents include di-epoxy compounds and haloepoxy compounds such as 1,3-bis (glycidyldimethylammonium) propanedichloride and epichlorohydrin.
• the conditions are as described above for the derivatisation reaction.
• the reaction conditions are also generally as described above for the derivatisation reaction.
• the amount of cross-linking agent which is necessary will depend on the nature of the agent, the starting material and the conditions of the cross-linking reaction. In all cases the reaction should be such as to provide a degree of cross- linking which imparts the desired water insolubility to the polymer but does not interfere with the water absorption properties of the polymer (superabsorbent properties) imparted by the quaternary ammonium group.
• the cross-linking reaction is carried out at a temperature of 15 to HOoC, more preferably 35 to 85°C for a time of 1 to 20 hours, preferably 2 to 10 hours.
• the degree of substitution and the degree of cross- linking can both be controlled by appropriate variation in the amounts of starting materials and the reaction conditions, in particular the concentration of the derivatising and/or cross-linking reagent, reaction time, amount of base, reaction temperature, and the nature of the substrate.
• concentration of the derivatising and/or cross-linking reagent concentration of the derivatising and/or cross-linking reagent
• reaction time amount of base
• reaction temperature a polysaccharide
• the nature of the substrate e.g., cellulose
• appropriate modifications will need to be made to the reaction conditions and, for example, it is known that starch is generally more reactive than cellulose.
• the process as described above leads to the polysaccharide derivative in base form as a result of the use of base (e.g. sodium hydroxide) as catalyst in the derivatisation and cross-linking reactions.
• base e.g. sodium hydroxide
• the polysaccharide is required in salt form and this can be prepared by treatment with strong acid (e.g. HCl) followed by washing with water to neutral pH. If necessary, the polysaccharide in salt form can be converted to base form by treatment with strong base (e.g. NaOH) followed by washing with water.
• cellulose for example in the form of cellulose Kraft pulp
• glycidyltrimethylammonium chloride for example to a ds of about 0.65
• 1, 3-bis(glycidyldimethylammonium)propane dichloride in the presence of sodium hydroxide.
• the reaction scheme can be represented as follows: l Derivatisation
• the cationic cross-linked cellulose according to the present invention can be prepared without a limitation on ds imposed by increasing water solubility.
• the material can be used as an absorbent for water or saline in either salt of basic form.
• the polysaccharide according to the invention in basic form.
• the polymer also has a desalting effect on the liquid by virtue of the fact that on being placed in salt solution the quaternary ammonium groups in basic form act as a strong anion exchanger and convert spontaneously to salt form.
• the absorbent according to the present invention is particularly suitable for use in applications where it is desired to absorb salt containing aqueous liquids.
• liquids include in particular menses and urine and particularly when in fibrous form the absorbent material can be used as the filling in catamenials and diapers, generally in admixture with a fibrous absorbent such a cellulose fluff.
• the absorbent according to the present invention, in base form can also be used in conjunction with an anionic superabsorbent in free acid form or a cation exchanger in acid form as described in our co-pending patent applications Nos ... (internal reference DR 24) and ... (internal reference DR 26) respectively.
• the present invention provides the use of a cationic polysaccharide, preferably a fibrous cationic polysaccharide, as defined above as an absorbent, more particularly as an absorbent in hygienic and/or sanitary articles.
• the sample had an absorbency (tea-bag test as described below) of 54 (after draining) and 29 (after centrifugation at 60 g) .
• the sample had an absorbency (tea-bag test) of 21 (after draining) and 18 (after centrifugation at 60 g) .
• the tea-bag test was performed by weighing about 0.3 g of the product into a tea-bag envelope which was itself then weighed and immersed in 150 ml of liquid (1% NaCl Solution or distilled water) in a 250 ml beaker for 1 hour. The envelope was then removed from the liquid and allowed to drain for 10 minutes, weighed, and then centrifuged at 60 g for 10 minutes and weighed again. Absorbency is calculated as follows:
• A absorbency (after draining or centrifugation) ;
• w wet weight of envelope containing sample after draining or centrifugation (grams) ;
• W d weight of envelope containing sample before immersion (grams) ;
• G weight of sample used for the test (grams) .
• the product had an absorbency (tea-bag test in accordance with Example 1) of 50 (after draining) and 39 (after centrifugation) .
• Example 2(a) The procedure of Example 2(a) was repeated to produce a different sample of essentially the same product but with a ds of 0.50.
• the product had an absorbency (tea-bag test in accordance with Example 1) of 34 (after draining) and 29 (after centrifugation) .
• ds of the intermediates is measured as described in WO 92/19652. The ds of the final product was not measured but would not be expected to differ significantly from the intermediate.
• Example 2 of WO 92/19652 had a ds 0.64, and an absorbency (tea-bag test in accordance with Example 1) of 42.9 (after draining) and 23.2 (after centrifugation) .
• 0.25 g of the same product in a tea-bag type envelope is placed in 1 litre of 0.1 N NaOH (aqueous solution) for 10 hours with mechanical stirring and is then washed with water to neutrality and dried with acetone to produce the product in unsalified form which had an absorbency of 42.9 (after draining) and 23.2 (after centrifugation) .
• Examples 1 (a) and 1 (b) show improved gel strength and are obtained in improved yield relative to WO 92/19652.
• the products of Examples 2(b) and 3(b) were obtained from intermediates which were soluble.

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• 1994
  • 1994-11-10 IT IT94TO000891A patent/IT1267496B1/it active IP Right Grant
• 1995
  • 1995-11-13 KR KR1019970703136A patent/KR970707165A/ko not_active Application Discontinuation
  • 1995-11-13 CA CA002205026A patent/CA2205026C/en not_active Expired - Fee Related
  • 1995-11-13 EP EP95941377A patent/EP0791015A4/en not_active Withdrawn
  • 1995-11-13 WO PCT/US1995/014679 patent/WO1996015154A1/en not_active Application Discontinuation
  • 1995-11-13 JP JP8516232A patent/JPH10509753A/ja active Pending
  • 1995-11-13 AU AU42819/96A patent/AU4281996A/en not_active Abandoned

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