WO1990015826A1 - Polymere hydrocolloidal a absorption amelioree - Google Patents

Polymere hydrocolloidal a absorption amelioree Download PDF

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Publication number
WO1990015826A1
WO1990015826A1 PCT/US1990/003308 US9003308W WO9015826A1 WO 1990015826 A1 WO1990015826 A1 WO 1990015826A1 US 9003308 W US9003308 W US 9003308W WO 9015826 A1 WO9015826 A1 WO 9015826A1
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Prior art keywords
polymer
mole percent
hydrocolloid
acid
percent
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PCT/US1990/003308
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English (en)
Inventor
Gregory Hill
Eugene P. Reilly
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Weyerhaeuser Company
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Publication of WO1990015826A1 publication Critical patent/WO1990015826A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/12—Layered products comprising a layer of synthetic resin next to a fibrous or filamentary layer
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/04—Acids; Metal salts or ammonium salts thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/73—Hydrophobic

Definitions

  • the present invention relates to hydrocolloid polymers, and particularly to hydrocolloid polymers that contain
  • Water-swellable hydrocolloids are a well known class of materials that are sometimes also referred to as hydrogels or superabsorbents. Such polymers are frequently utilized in their dry or semi-dry forms (e.g. 5-15 weight percent water) in surgical dressings, disposable diapers, sanitary napkins, incontinent pads, wipes, and the like. In water-swollen form, hydrocolloids are often utilized as contact lenses, as thickeners for foods and as adhesives.
  • Exemplary totally synthetic polymers are typically prepared using about 50 to 99 or more mole percent hydrophilic monomers such as monoethylenically unsaturated carboxylic acids, amides, hydroxyalkylene amides and esters, sulfonic acids, and phosphoric acids. The remainder of the monomers typically are copolymerizable alkyl esters or amides of monoethylenically unsaturated acids or nitrile-containing monomers such as acrylonitrile or ethacrylonitrile.
  • Totally synthetic hydrocolloids supplied in dry or semi-dry form typically contain a b out 50 to 99 or more mole percent polymerized monoethylenically unsaturated monocarbozylic acid, usually acrylic acid.
  • Such polymers are also usually cross-linked by a polyethylenically unsaturated monomer that is present in an amount of about 5 to about 0.001 mole percent of the total monomer mixture.
  • exemplary cross-linking monomers have acryloyl or allylic unsaturation, or a mixture thereof as are exemplified by N,N'-methylenebisacrylamide or diethyleneglycol dimethacrylate, diallylamine, and allyl methacrylate or N,N-diallyl methacrylamide.
  • Hydrocolloid polymers are also known that are polysaccharides, e.g., modified cellulosics and starches. Such modified polymers typically contain one to a plurality of hydroxyalkylene, amine, ammonium or carboxyalkylene groups per anhydroglucose repeating unit. These modified natural polymers can also contain cross-links in addition to those that may be present in the natural polymer.
  • Still further hydrocolloid polymers are prepared by grafting a synthetic polymer on to the backbone provided by a starch or cellulosic molecule.
  • the grafted synthetic polymer portions are typically similar to those described before, but those grafted polymers typically are not cross-linked, or contain relatively more repeating units between cross-links than do the totally synthetic polymers.
  • Modified starch and cellulose derivatives are exemplified by carboxymethyl cellulose and hydroxyethyl cellulose that are commercially available from several sources.
  • a cross-linked carboxymethyl cellulose is described in U.S. Patent No. 2,639,239.
  • Grafted starch and cellulose derivatives are described in U.S. Patents No. 3,635,857; No. 3,640,826; No. 4,028, 290; No. 4,076,663; No. 4,105,033; and No. 4,340,057.
  • modified and grafted polysaccharides can provide adequate hydocolloid materials, such materials typically require several steps to prepare in addition to those required for totally synthetic hydrocolloids and are thus energy and labor intensive to prepare as compared to totally synthetic hydrocolloids.
  • the totally synthetic hydrocolloid polymers are preferred herein on a cost and energy basis.
  • hydrocolloid e.g., totally synthetic, modified polysaccharide or grafted polysachharide
  • some are soluble or dispersible in water to the extent that a viscosity can be measured, whereas other hydrocolloids are substantially not so soluble or dispersible in water.
  • solubilities or dispersibilities are frequently determined in distilled or deionized water, or sometimes in one normal sodium chloride or in synthetic urine solutions.
  • Hydrocolloids that are substantially soluble or dispersiole in aqueous solutions can provide products whose hydrocolloid polymer is extracted by contact with aqueous solutions such as urine when used in a diaper, or blood or lymph when used as a wound dressing, and thereby can provide an unpleasant feel or a contaminant, respectively.
  • U.S. Patent No. 4,654,039 theorizes that such leacning of soluble hydrocolloid from a sorbing article of manufacture such as a diaper by a body fluid such as urine can alter both the chemical and physical characteristics of the body fluid to the extent that the fluid is more slowly absorbed and more poorly held by the hydrogel-containing sorbant article. Such a situation can contribute to un ⁇ esirable leakage of body fluid from the sorbant article.
  • a similar problem as to water-extractables is noted in U.S. Patent No. 4,286,082.
  • No. 4,090,013 discloses a specific example of the use of a sulfonic acid-containing monomer in a water-sorbing polymer. That patent teaches the preparation of a water-soluble anionic polyelectrolyte that is soluble in a pH value range of from 2.0 to 8.5. The otherwise water-soluble polymer is made insoluble in water by the addition of a cation having a valence of at least three that can be added during or after polymerization. Tnat patent teaches that its polyelectrolyte must be soluble at a pH value of 2.0 to 8.5, and that its cross-linking and resulting water-insolubility are reversible depending upon the pH value.
  • the cross-linking ionic complex when polyacrylic acid is used as the polyelectrolyte, the cross-linking ionic complex is said to reverse at a pH value of about 8.5-9.0, whereas with styrene sulfonic acid, the complex is said to reverse at a pH value of about 3.5-5.0.
  • Two compositions preprared with a sulfonic acid-containing monomer (2-acrylamido-2-methyl- propanesulfonic acid) and acrylamide are described. Those polymers were cross-linked with aluminum acetate. The polymers were prepared at about ten weight percent solids, adjusted to about 5 weight percent solids, acid groups partially neutralized in water, cross-linked by the addition of a stated amount of polyvalent metal ion and then cast as films.
  • the sorbency of the cast films in 0.9 percent aqueous sodium chloride was determined after the films were dried.
  • the two copolymer films containing polymerized, partially neutralized sulfonic acid and acrylamide exhibited swell characteristics similar to those exhibited by partially neutralized homopolymers of acrylic acid.
  • hydrocolloid polymers listed above are water-insoluble, or substantially water-insoluble
  • other uses have been put forward for water-soluble polymers that contain polymerized sulfonic monomers.
  • One of those uses is in the field of tertiary oil recovery wherein thickened aqueous solutions are pumped into oil fields whose oil has been partially recovered.
  • Oil-bearing strata frequently contain brines that tend to deswell anionic polymers whose anionic groups are provided primarily by carboxylate groups. That deswelling leads to a lowered vicosity for the pumped aqueous solutions and a concomitant diminished recovery of the oil in the stratum.
  • Water-soluble polymers containing polymerized sulfonic acid-containing monomers have been found useful in combatting the brine-caused deswelling under such circumstances.
  • water-soluble polymers containing various monoethylenically unsaturated sulfonic acids and sulfonates such as
  • the present invention contemplates a hydrocolloid polymer that is substantially water-insoluble and exhibits improved liquid sorption. That polymer consists essentially of
  • the present invention also contemplates a water-insoluble fibrous matrix having thereon a coating of the before-described water-insoluble hydrocolloid polymer.
  • the polymer of the coating preferably contains about 50 to about 100 percent per acid groups, and about 50 to about zero mole percent acid groups neutralized with a monovalent cation such as an alkali metal or ammonium ion.
  • the coating is present in an amount of about 200 to about 1500 weight percent of the weight of the matrix.
  • the web prior to coating exhibits a dry bulk recovery of at least about 60 percent, an initial dry bulk of at least about 20 cc/g and a weight of less than about 2 oz/yd .
  • Figure 1 is a graph that illustrates sorption properties of hydrocolloid polymers of the invention and control polymers.
  • the left-hand ordinate (solid lines) is in units of grams of a one weight percent aqueous sodium chloride (1% NaCl) sorbed per gram (g/g) of polymer.
  • the right-hand ordinate (dashed lines) is in units of grams of deionized water sorbed per gram (g/g) of polymer.
  • the abscissa is in units of mole percent (%) of sulfonic acid monomer in an acrylic acid polymer. Open triangles represent values obtained using a control polymer prepared using only acrylic acid.
  • Open circles represent values obtained using (2-sulfo) ethyl methacrylate to replace 10 mole percent of the acrylic acid monomer.
  • Open squares represent data obtained with polymers of this invention containing 10 and 29.7 mole percents 2-acrylamido-2-methylpropanesulfonic acid (AMPS) to replace equal amounts of acrylic acid. All of the polymers contained one mole percent methylenebisacrylamide as cross-linker. Each of the polymers was prepared by free radical polymerization using potassium peroxydisulfate as the initiator as is discussed hereinafter
  • the present invention has several benefits and advantages.
  • hydrocolloid polymers having improved sorption of water and other aqueous solutions can be obtained.
  • One advantage is that the highly water-sorbing hydrocolloids can be prepared at the degree of neutralization desired for use in an ultimately made sorbent product so that subsequent steps after polymerization can be minimized.
  • hydrocolloid polymers can be polymerized in situ in a fibrous matrix to thereby form a sorbent web, thereby minimizing still further post-polymerization processing steps.
  • the present invention contemplates a substantially water-insoluble hydrocolloid polymer that exhibits enhanced sorption of aqueous solutions, as well as a water-insoluble fibrous matrix containing that polymer as a coating.
  • the polymer consists essentially of about 60 to about 90 mole percent polymerized alpha, beta-monethylenically unsaturated monocarboxy monomer containing a chain of three carbon atoms that includes the ethylenic unsaturation; (b) about 10 to about 40 mole percent polymerized 2-acrylamido-2-methylpropanesulfonic acid monomer (hereinafter sometimes referred to as AMPS) ; (c) zero to about 20 mole percent polymerized copolymerizable water-soluble monoethylenically unsaturated monomer; and (d) zero to about 3 mole percent of a copolymerizable water-soluble polyethylenically cross-linking agent.
  • AMPS 2-acrylamido-2-methylpropanesulf
  • the polymer is substantially free of polycationic metal or amine ions.
  • one gram of dry hydrocolloid polymer sorbs about 15 to about 100 percent more of an aqueous solution containing one percent sodium chloride than does a similarly prepared polymer containing identical amounts of all of said ethylenically unsaturated components except for AMPS.
  • the monoethylenically unsaturated monomers preferably contain about 50 to about 100 mole percent free acid groups and about 50 to about zero mole percent acid groups neutralized with a monovalent cation.
  • the characterization of a polymer on the basis of the monomers used in its preparation can be inaccurate because of the presence of relatively large amounts of unreacted monomers after the completion of the polymerization reaction.
  • a characterization of the polymerized hydrocolloid based upon the monomer mixture used for its preparation is accurate because substantially all of the monomeric materials originally present are converted into the polymer; i.e., these hydrocolloids contain relatively low amounts of residual monomers, as is discussed hereinafter.
  • the principal monomeric constituent of a hydrocolloid polymer of this invention is a wate -soluble alpha,beta-monoethylenically unsaturated monocarboxy monomer containing a three carbon atom chain that includes the ethylenic unsaturation.
  • the phrase "monocarboxy monomer” is utilized herein to mean a monomer that contains a single carboxy functionality. That single carboxy functionality can itself be a mixture of the free acid and monovalent cation salt forms of the free acid, as is discussed in further detail hereinafter.
  • monocarboxy monomer is thus used herein as a short-hand phrase for the free acid, salt or partially neutralized mixture of free acid and salt forms of the water-soluble alpha,beta- monoethylenically unsaturated monocarboxy monomer containing a chain of three carbon atoms that includes the ethylenic unsaturation.
  • the monocarboxy monomer and all of the other monomeric species discussed herein are referred to as being "water-soluble". That phrase is utilized herein to mean that whatever monomeric species is discussed is soluble in the aqueous mixture of monomeric species used for polymerization at the concentration utilized herein. To that end, the monocarboxy monomer and other monomers form clear, as compared to translucent or opaque, solutions in the aqueous reaction mixture used for polymerization at the concentration of use. Put differently, a water-soluble monomer forms a single phase when admixed with any other monomers and cross-linker mixture in water at the concentration at which that monomer or cross-linker is utilized herein.
  • a salt of a monocarboxy monomer with a monovalent cation is also water-soluble.
  • Exemplary monocarboxy monomers useful herein contain a chain of three carbon atoms that includes the monoethylenic unsaturation, and are exemplified by acrylic acid, methacrylic acid and cyanoacrylic acid. Mixtures of these monocarboxy monomers can also be used. Acrylic acid is particularly preferred.
  • the monocarboxy monomer constitutes about 60 to about 90 mole percent of the prepolymerized aqueous monomeric reaction mixture and polymerized monomers. More preferably, that monomer is present at about ' 65 to about 85 mole percent, and most preferably at about 70 to about 75 mole percent.
  • the monocarboxy monomer can itself be a mixture of free acid and monovalent cation salt forms.
  • the monovalent cation salt is formed from an alkali metal or monoamine. Alkali metal salts are preferred, with sodium and potassium salts being particularly preferred.
  • Ammonium salts prepared from ammonia and monoamines are also useful but such salts are preferably salts of sterically hindered, non-nucleophilic primary or secondary amines or, more preferably, tertiary amines such as tri-C,-c 4 alkyl amines such as trimethylamine, triethylamine and tributylamine, or triethanolamine.
  • the monocarboxy monomer is to be understood to be present as the free acid form, or as a mixture of free acid and monovalent cation salt forms.
  • Polyvalent cation salts of the monocarboxy monomers are not utilized and are thus substantially absent from the monomer mixture and polymerized hydrocolloid.
  • Polyvalent metal ions such as calcium, magnesium, aluminum and iron and polyvalent ammonium salts such as N,N,N' ,N'-tetramethylethylene- diamine can cross-link the monomer mixture and resulting polymerized hydrocolloid.
  • the ultimately produced hydrocolloid polymer is utilized as a sorbent coated on a fibrous web matrix of a sorbent product. When so used, it is preferred to prepare the coated web by polymerizing the monomers in the presence of the matrix; i.e., by in situ polymerization. Preferably, this is done by electron beam polymerization.
  • the free acid form of the monocarboxy monomer typically constitutes about 50 to about 100 mole percent of the monocarboxy monomer mixture, more preferably constitutes about 60 to about 80 mole percent, and most preferably constitutes about 65 to about 70 mole percent.
  • a monovalent cation salt therefore constitutes about 50 to about zero mole percent, more preferably about 40 to about 20 mole percent of the monocarboxy monomer, and most preferably about 35 to about 30 mole percent, of the monocarboxy monomer.
  • the water-soluble alpha, eta-monoethylenically unsaturated monocarboxy monomer is thus partially neutralized, with about zero to about 50 mole percent, more preferably about 15 to about 40 mole percent, and most preferably about 30 to about 35 mole percent, of the acid groups neutralized with a monovalent cation.
  • a partially neutralized water-soluble alpha,beta-monoethylenically unsaturated monocarboxy monomer saves the subsequent step of neutralization after polymerization, which step can be somewhat difficult to carry out due to the gelatinous nature of aqueous compositions of the polymerized material.
  • polymerization of a partially neutralized monocarboxy monomer whose degree of neutralization is substantially that desired in a sorbent product that is ultimately made facilitates the preparation of hydrocolloid polymer-coated sorbent webs for use in such products inasmuch as such webs are typically somewhat more difficult to manipulate than is the polymerized hydrocolloid itself.
  • a useful polymer of the invention that is free of fibrous matrix can also be prepared using the above-described percentages of free acid and salt forms of the monocarboxy monomer.
  • the second component in amount and the component primarily responsible for the enhanced aqueous solution sorptions exhibited by hydrocolloid polymers of this invention and products containing such polymers is 2-acrylamido-2-methylpropane- sulfonic acid (AMPS) .
  • AMPS can be present in an amount of about 10 to about 40 mole percent of the ethylenically unsaturated species that are present in the monomer mixture used to form a useful hydrocolloid and that hydrocolloid polymer itself.
  • AMPS is more preferably present at about 15 to about 35 mole percent, and most preferably at about 25 to 30 mole percent of the ethylencially unsaturated species that are polymerized into a hydrocolloid of this invention.
  • the enchanced sorbency of the polymer with AMPS as compared to other sulfonic acid-containing polymers is not particularly noted.
  • the dried hydrocolloids tend to be unacceptably hard and brittle when polymerized in situ on a fibrous matrix used as a sorbent web.
  • AMPS appears to be singular in its properties in a hydrocolloid of this invention and cannot be so substituted. The reason for the uniqueness of this monomer is unknown, although possible reasons are discussed hereinafter.
  • One or more additional copolymerizable, water-soluble monoethylenically unsaturated monomers can also be present in the monomer reaction mixture and polymerized hydrocolloid, so long as the novel sorption characteristics of a hydrocolloid polymer of the invention are not impaired.
  • Such monomers are familiar to those skilled in the hydrocolloid art and include methacrylamide, acrylamide, N-mono- and N,N-di-C,-C 4 alkyl acrylamides and methacrylamides such as N-methyl acrylamide, and N,N-dipropyl methacrylamide, N- and N,N-(2-hydroxy) C 2 ⁇ C 3 alk y- 1 - acrylamides and methacrylamides such as N-(2-hydroxy)propyl acrylamide and
  • the additional co-polymerizable, water-soluble monoethylenically unsaturated monomers can also include acid group-containing monomers and their water-soluble monovalent cation salts. Included among these monomers are crotonic acid, further itaconic acid, maleic acid, maleic anhydride
  • N-alkyl monoamides of maleic acid the N-(2-hydroxy)ethyl and N,N-di-(2-hydroxy)ethyl mono-amides of maleic acid, sulfonic acid monomers such as styrenesulfonic acid, 2-vinyl-4-ethylbenzene-sulfonic acid,
  • 2-sulfoethylmethacrylic acid and vinylsulfonic acid
  • phosphate-containing monomers such as methacryloxy ethyl phosphate
  • a copolymerizable monoethylenically unsaturated monomer or a mixture thereof can be present at zero to about 20 mole percent of the reaction mixture and polymerized hydrocolloid. More preferably, such monomer or monomers is present at about zero to about 10 mole percent. Most preferably, the copolymerizable monoethylenically unsaturated monomer is absent. However, when present, the mole percentage of monocarboxy monomer is typically decreased to accomodate the copolymerizable monoethylenically unsaturated monomer.
  • the water-soluble copolymerizable monoethylenically unsaturated monomer is preferably selected from the group consisting of acrylamide, methacrylamide, N-(2-hydroxy)ethyl acrylamide, N- (2-hydroxy)ethyl methacrylamide, and 2-sulfoethylmethacrylic acid.
  • the before-mentioned degree of partial acid group neutralization is to be understood to be the degree of neutralization of all of the acid groups present in the reaction mixture and resulting, polymerized hydrocolloid when acid group-containing monomers in addition to the monocarboxy monomer are present in the monomer mixture or in polymerized form.
  • the monocarboxy monomer, AMPS and the additional copolymerizable monomers that can be present are monoethylenically unsaturated
  • the degree of neutralization of all of the acid group-containing monomers can be referred to in terms of the neutralization of monoethylenically unsaturated monomers in their polymerized or unpolymerized forms.
  • the pK 3 value of a sulfonic acid is typically two or more units less than that of a carboxylic acid.
  • a neutralization percentage for a monomer mixture or hydrocolloid polymer presumes all of the sulfonic acid groups to be neutralized.
  • the monomer mixture and hydrocolloid polymer can be described in terms of neutralized monocarboxy monomer such as acrylic acid.
  • a sufficient amount of a base such as potassium hydroxide is admixed with the aqueous monomer reaction mixture to neutralize all of the AMPS present plus about 60 to about 80 mole percent of the monocarboxy monomer.
  • a base such as potassium hydroxide
  • Other means of providing a desired degree of neutralization can also be utilized, as is well known.
  • a fourth element of a reaction mixture and resulting polymer of this invention that can be present is a copolymerizable, water-soluble cross-linking agent or cross-linker.
  • a wide variety of cross-linker molecules is useful herein.
  • cross-linkers are compounds that contain two or three moieties that contain acrylic-type unsaturation as well as those that contain two moieties of allylic-type unsaturation.
  • Such cross-linking agents can be referred to as bis-acryloyl or bis-methacryloyl and bis-allyl compounds, respectively.
  • a first, bis- or tris-acryloyl or bis- or tris-methacryloyl cross-linker has a structure that corresponds to the formula:
  • R is hydrogen or C. -c . alkyl, n is 2 or 3; and A is a divalent or trivalent radical that contains a chain of 3 to about 30 atoms free from copolymerizable unsaturation that is terminated by oxygen or nitrogen atoms; i.e., A is bonded to
  • a radical is preferably divalent; i.e., n is preferably 2.
  • a second, bis-allyl, cross-linker compound and has a structure that corresponds to the formula:
  • Divalent and trivalent radicals A and B above while generally being different in structure, share the properties of "containing a chain of 3 (or 4) to about 30 (or 10) atoms” being “free from copolymerizable unsaturation” and being “terminated by oxygen or nitrogen atoms.” These phrases are utilized herein as follows.
  • the phrase "free from copolymerizable unsaturation” is used to mean that although some unsaturation can be present in either radical, that unsaturation does not take part in a polymerization reaction contemplated herein. Exemplary of such unsaturation is that found in a benzene ring.
  • the phrase "contains a chain of 3 (or 4) to about 30 (or 10) atoms” is meant to indicate a lower limit of chain length of 3 or 4 atoms in a straight or branched chain radical whose longest axis contains at least 3 or 4 atoms, respectively, and is the axis that joins the two or three acryloyl or allylic portions of the molecule, and which axis can be as long as 30 or 10 atoms, respectively.
  • the enumerated number of atoms in the phrase is also meant to encompass the presence of one or more rings whose axial length between the two or three acryloyl or allylic portions of the molecule cannot be defined in terms of whole numbers of atoms.
  • the enumerated number of atoms in the phrase is still further intended to encompass the terminal oxygen or nitrogen atoms, that are discussed below.
  • terminal by oxygen or nitrogen atoms is meant to indicate that the two or three acryloyl portions of the first cross-linker are present as esters or amides, respectively, whereas the two allyl portions can be present as ethers (oxygen atom-terminated) , or amides, or amines (nitrogen atom-terminated) , respectively.
  • the phrase is also meant to indicate that the terminal atoms of the divalent radicals are the same atom, which can be either oxygen or nitrogen.
  • a or B is cyclic and may therefore not strictly speaking contain termini, such cyclic radicals are considered herein to have termini that are defined by the atoms that bond the A or B radicals to the acryloyl or allylic portions.
  • the phrase is also meant to indicate that the terminal atoms of the divalent or trivalent radicals are the same atom, which can be either oxygen or nitrogen.
  • the first cross-linker is, for example, a tris- or bis-acrylate, a tris- or bis-methacrylate, a tris- or bis-acrylamide or a tris- or bis-methacrylamide.
  • the water-soluble allyl derivatives that constitute the second cross-linker are bis-compounds, except for triallyl amine as is discussed hereinafter.
  • Exemplary useful water-soluble cross-linkers that contain the A divalent radical include methylenebisacrylamide, methylenebismethacrylamide , polyethylene glycol (PEG) diacrylates and methacrylates that contain an average of one to about 9 PEG units per molecule such as ethyleneglycol dimethacrylate, tetraethyleneglycol diacrylate [that can also be named polyoxyethylene (4) diacrylate or PEG-4 diacrylate] , and polyoxyethylene (9) diacrylate [that can also be named nonaethylenegylcol diacrylate or PEG-9 diacrylate] , meta-xylylenyl bisacrylamide (the bisamide formed between two moles of acrylic acid and one mole of meta-xylylenediamine) , 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, 1,3-butanediol diacrylate, trimethylenebisacrylamide (TMBA) , and the like.
  • PEG polyethylene
  • tris-acrylates and methacrylates include trimethylolpropane triacyrlate (TMPTA) and trimethacrylate, respectively, as well as pentaerythritol triacrylate or trimethacrylate.
  • TMPTA trimethylolpropane triacyrlate
  • trimethacrylate trimethacrylate
  • pentaerythritol triacrylate or trimethacrylate methylenebisacrylamide (MBA) and PEG diacrylates containing an average of 1 to 9 PEG units per molecule are preferred, with MBA being particularly preferred.
  • Exemplary useful cross-linkers that contain the B divalent radical include water-soluble di- or bisamides of allylamine and dicarboxylic acids such as those formed from carbonic acid, oxalic acid, malonic acid, succinic acid, malic acid and tartaric acid, which can be named diallyl urea, dially urea, oxalamide, diallyl urea, diallyl malonamide, diallyl succinamioe, diallyl malamide and diallyl tartaramide.
  • Exemplary diamine derivatives include N,N'-diallylypiperazine, N,N'-diallylethylenediamine and the like.
  • Exemplary diethers include the polyethylene glycol (PEG) derivatives that include an average of 1 to 3 PEG repeating units such as ethyleneglycol diallyl ether, diethyleneglycol diallyl ether and triethyleneglycol diallyl ether.
  • PEG polyethylene glycol
  • diallyl ethers include those compounds formed from 1,3-butanediol, 1,2,3-trihydroxybutane, 2,3,4-trihydroxy butyric acid, the aldo- and ketotetroses such as erythrose and erythrulose, respectively, the aldo- and ketopentoses such as ribose and xyloketose, respectively, the aldo- and keto-hexoses such as glucose and fructose, respectively, as well as from a saccharide such as sucrose or maltose.
  • diallyl ethers are referred to as reaction products of allyl alcohol and a polyhydric alcohol, those ethers are most frequently prepared by a
  • a further useful allyl-containing cross-linker is triallylamine. It is well known that diallyl group-containing compounds wherein the allyl groups are separated by three atoms such as in diallylamine and diallyl ether form cyclic compounds when polymerized. As a consequence, such compounds do not contribute well to cross-linking, but rather tend to homopolymerize. A particular example of this phenomenon is diallylamine, which when protonated during polymerization as would be the case here, forms six- and/or seven-membered ring, straight chain homopolymers. Triallylamine is useful herein because it can form cross-links in addition to cyclizing.
  • the minimum chain length of the before-mentioned bis- or di-allyl-containing cross-linkers is at least three atoms as to avoid the cyclopolymerization route.
  • a before-described cross-linking agent can be present at zero to about 3 mole percent of the total copolymerizable ethylenically unsaturated species present in the reaction mixture, and can therefore be absent as where electron beam or other ionizing radiation radiation utilized to polymerize the monomers is used in addition to cross-link the hydrocolloid. More preferably, however, an externally-provided cross-linker as described hereinabove is utilized.
  • That cross-linker is present in an amount of up to about 3 mole percent, more preferably in an amount of about 0.03 to about 1 mole percent, and most preferably in an amount of about 0.05 to about 0.1 mole percent. Mixtures of one or more of the before-recited cross-linking agents can also be utilized. Again, the amount of monocarboxy monomer is typically reduced to ccomodate the cross-linker.
  • reaction mixture and polymer can also be substantially free of the water-soluble copolymerizable monoethylenically unsaturated monomer, substantially free of the water-soluble polyethylenically unsaturated cross-linking agent, as well as being substantially free of both that copolymerizable monomer and that cross-linking agent in monomeric and polymerized forms.
  • the minimum mole percentages of monocarboxy monomer ana AMPS are defined as are the maximum mole percentages of those monomers, when either or both of the copolymerizable monomer and cross-linking agent are present, the maximum mole percentage of one or both of the monocarboxy monomer and AMPS must be reduced accordingly, while maintaining the minimum percentages.
  • the monocarboxy monomer is present in the greatest mole percentage, and as a consequence, a reduction in the mole percentage of that monomer provides a relatively smaller change in relative mole percentage and effect as compared to a change in the AMPS concentration.
  • the maximum monocarboxy monomer that can be present is 89.97 mole percent rather than the 90 mole percent stated previously.
  • the maximum is 84.97 mole percent for a preferred reaction mixture and polymer, and 74.97 mole percent for a most preferred reaction mixture and polymer.
  • a recited minimum mole percentage of AMPS, plus minimum mole percentages of a copolymerizable monomer and/or cross-linking agent, when present, define the maximum mole percentage of the monocarboxy monomer, when specific recitations of mole percentages adding up to 100 mole percent are not made.
  • the monoethylenically unsaturated monomers and polyethylenically unsaturated cross-linking agent (solids) constitute a total of about 10 to about 70 weignt percent of the aqueous monomer reaction mixture, with the remaining about 90 to about 30 weight percent being substantially only distilled or deionized water.
  • the acidic monomers be at about the degree of neutralization that is ultimately desired for use, and that about 55 to about 65 weight percent, and more preferably about 60 to about 65 weight percent, of the aqueous composition be solids.
  • the monocarboxy monomer is preferably in its acid form, and the solids level be about 10 to about 30 weight percent, and more preferably about 10 to about 20 weight percent.
  • the aqueous reaction mixture has a pH value that is dictated by the degree of neutralization of the acid groups present.
  • the aqueous reaction mixture and resulting hydrocolloid polymer can contain a complex mixture of free acid and acid salt, although most are carboxylic acids and their salts, with a significant amount of sulfonate salt and little free sulfonic acid.
  • the aqueous reaction mixture behaves as a buffer over the range of acid group neutralization levels contemplated, with most of the buffering capacity present being due to the carboxyl groups since the sulfonic acid c pKa value is about 3 to 4 pKa units lower than that of the carboxylic acids present.
  • the pH value of the reaction mixture is typically about 4 to about 8. It is noted that the pH value observed after polymerization can be different from that of the reaction mixture if only because the pK values of polymerized ethylenically unsaturated acids typically broaden and differ from those monomeric species that contain ethylenic unsaturation, and also oecause of proximity effects of the polymeric polyanionic material formed.
  • the reaction mixture is polymerized using standard polymerization techniques such as redox-initiated or other free radical methods, actinic radiation preferably in the presence of a sensitizer, or the particularly preferred electron beam polymerization techniques that are described in detail hereinafter.
  • Polymerization is carried out in a manner such that substantially all of the mono- and polyethylenically unsaturated components of the reaction mixture are polymerized, regardless of the method used. Thus, conversion is substantially 100 mole percent.
  • the quantity of residual monomer (measured after drying) is typically below about 500 parts per million (ppm) of polymer, and is usually in the range of about 100 to about 200 ppm.
  • a hydrocolloid polymer of the present invention is substantially water-insoluble, as noted previously.
  • a dried hydrocolloid of the invention about 10 to about 40 weight percent can be extracted. More usually, about 20 to about 30 weight percent of tne dry weight of such a hydrocolloid can be extracted using a method discussed hereinafter.
  • the resulting hydrocolloid polymer is dried by any of a number of well known techniques. Exemplary drying procedures are described hereinafter.
  • That drying can be to what can be called "bone" dryness at which substantially no water is left in the hydrocolloid as determined by a Karl-Fisher titrator.
  • Bone dryness is the degree of dryness utilized when comparing sorption of a hydrocolloid polymer of this invention with other hydrocolloid polymers. More preferably, however, the hydrocolloid polymer is dried sufficiently to contain about zero to about 15, and most preferably about 5 to about 10 weight percent water by the above test.
  • one gram of a dry polymer prepared from 69.3 mole percent acrylic acid, 29.7 mole ' percent AMPS and 1 mole percent methylenebisacrylamide sorbs about 15 to about 100 percent more of a one percent aqueous sodium chloride solution than does one gram of a dry polymer prepared from 99.0 mole percent acrylic acid (69.3 plus 29.7 mole percents) and 1 mole percent of methylenebisacrylamide, as aoove.
  • a dry (bone dry) hydrocolloid polymer of the invention sorbs about 250 to about 65u percent, or more, more of deionized water than does a similarly prepared polymer containing identical amounts of all of the ethylenically unsaturated components except for AMPS, and includes acrylic acid in place of AMPS on a mole for mole basis.
  • the range of about 15 to about 100 percent, or more, improvement in saline sorption and of about 250 to about 650 percent, or more, for deionized water sorption between the two types of polymer is stated for the acid form of the polymer.
  • Saline and deionized water sorptions are also a function of the percentage neutralization of the polymer, with more highly neutralized polymers typically providing higher differences in sorption, within the range of neutralizations discussed previously.
  • the increase in sorption generally increases with increasing amounts of AMPS, at least between about 10 and 40 mole percent AMPS.
  • AMPS and also contains acryloyl unsaturation, but only marginally improved sorption of a one percent aqueous sodium chloride solution at about 10 mole percent as compared to about a 25 percent improvement with the same concentration of AMPS in a similarly prepared polymer.
  • Another contributing feature may be the relative bulk of AMPS as compared to acrylic acid or (2-sulfo) ethyl methacrylate. As compared to acrylic acid, it is readily seen that both AMPS and (2-sulfo) ethyl methacrylate are longer than is acrylic acid, and both thereby may not pack as tightly and sorb less in a relatively high ionic strength medium as does polyacrylic acid.
  • AMPS also contains an alpha-methyl group rather than a hydrogen present in the (2-sulfo) ethyl methacrylate.
  • the presence of that added methyl group may further inhibit close packing at relatively high ionic strengths and may be an underlying cause for the relative improvement in brine sorption shown by the present polymers as compared to other sulfonic acid-containing mostly acrylic acid polymers. That increased bulk should not, however, account for the observed increase in sorption of deionized water where the ionic strength is due only to the hydrocolloid polymer.
  • Exemplary means of polymerization include the particularly preferred electron beam method described in detail hereinafter as well as other radiative processes such as by the use of gamma radiation and actinic light, preferably in the presence of a photosensitizer. Additional means include use of a free radical initiator and heat such as azobisisobutyronitrile or sodium or potassium peroxydisulfate, organic peroxide initiators such as ⁇ -butyl hydoperoxide or benzoyl peroxide; and oxidation-reduction (redox) polymerization utilizing a redox couple such as hydrogen peroxide and ascorbic acid.
  • the polymerizations can be carried out in water, as is preferred, or an appropriate mixed solvent such as a water-methanol mixture.
  • the polymerization reaction can also be carried out using so-called inverse phase polymerization techniques that utilize an organic solvent such as hexane as the continuous phase, an appropriate water-in-oil surfactant and an aqueous solution of all of
  • a hydrocolloid polymer of the invention is typically utilized as a sorbent in an article of manufacture such as a sanitary napkin, a surgical or wound dressing, a diaper, a wipe or the like.
  • the hydrocolloid polymer is contained in and on a supporting fibrous web matrix and constitutes a portion of what is commonly referred to as an absorbent layer (or sorbent layer since both absorption and adsorption can occur) because most such products contain a plurality of layers that each serve a particular function.
  • the hydrocolloid polymer is often utilized in a sorting article in the form of a powder that is typically prepared by drying and then pulverizing the polymerized material, or the hydrocolloid polymer is prepared _in situ on a supporting web that is thereafter dried as a unit.
  • the sorbent layer comprising a supporting fibrous web matrix and hydrocolloid polymer, however applied, can be referred to as a "polymer-containing web", a “nydrocolloid-containing web” or a "polymer-coated web”.
  • the hydrocolloid polymer is distributed within a water-insoluble fibrous matrix web that comprises a substantially high loft, resilient fibrous web layer, and is present in an amount of about 200 to about 1500 percent by weight add-on to the matrix based upon the weight of fibrous matrix. Most preferably, the hydrocolloid polymer is present at about 500 to about 1000 percent weight aod-on.
  • the matrix plus hydrocolloid polymer constitute a hydrocolloid polymer-containing web or sorbing layer.
  • one or more additional webs are placed adjacent to or disposed on one or both surfaces defined by the hydrocolloid polymer-containing web to form a sorbent laminate.
  • Such additional webs can constitute a so-called "wicking layer” that functions to transport the liquid to be sorbed to the hydrocolloid polymer.
  • An additional web can also constitute a water-impermeable membrane that provides an outside surface to the article such as a diaper, or a water-permeable layer that constitutes an inner layer of the article. Where a powdered form of the hydrocolloid polymer is utilized, it can be sprinkled onto and into the interstices of a fibrous web matrix, and thereby form a coating on the web matrix.
  • the hydrocolloid is prepared _in_ situ on the resilient fibers of the fibrous web matrix.
  • the web is sprayed or submerged or otherwise coated with an aqueous solution of the appropriate, partially neutralized monomer and cross-linkers, and the polymer thereafter formed.
  • the polymer is formed by use of irradiation such as electron beam irradiation.
  • the hydrocolloid polymer coating is present arrayed around, between and on the resilient fibers of the fibrous web matrix of the sorbing layer in an intermittently dispersed form.
  • the hydrocolloid polymer is in the form of particles that can be in the shape of fibers, spheres, bits of film when added as a pre-formed dry powder.
  • the hydrocolloid polymer provides globules and bits of film-like particles that are adhered to and around the fibers of the fibrous web.
  • a polymer-containing web made by _in situ polymerization can be distinguished from a similar web made by adding the pre-formed dry powder.
  • Sorbent layers comprising a web matrix coated with hydrocolloid polymer are most preferably prepared by electron beam irradiation.
  • a web matrix is submerged in an aqueous solution of monomers and cross-linkers as described before, placed into a polyethylene bag so that tne plane of the web is parallel to the major plane defined by the sides of the bag, and the bag is sealed.
  • the bag and its contents are then irradiated.
  • the bag is thereafter turned over and irradiated again.
  • Powder samples are similarly prepared except that the bags are free of the matrix, and are not turned over.
  • Add-on of hydrocolloid to a fibrous web matrix to form a sorbent layer is determined by weighing a known area of dried sorbent layer subtracting the weight of a similar area of starting web matrix and dividing the resulting number by the weight of that area of starting web matrix. Add-on is thus expressed as a ratio of the hydrocolloid polymer weight relative to the weight of the starting weo matrix.
  • the sorbing layer formed by the resilient fibrous web matrix and hydrocolloid polymer It is of some import to the function of the sorbing layer formed by the resilient fibrous web matrix and hydrocolloid polymer to have that polymer present in a quantity that is sufficient to sorb a desired amount of liquid, and spaced on and within the web in a manner such that gel blocking does not substantially occur.
  • Gel blocking occurs when hydrocolloid polymer is present in a sufficient quantity and spaced so closely together that as the particles imbibe liquid and swell, a layer of gel is formed that blocks further penetration of liquid into the layer.
  • the _in situ polymerization technique described herein when used to provide about 200 to about 1500 percent add-on of hydrocolloid polymer, provides a sufficient amount of liquid sorbency while exhibiting a relatively minimal amount of gel blocking, if any.
  • a sorbent laminate comprised of the supporting fibrous web matrix that contains the hydrocolloid polymer (sorbing layer) , and one or more adjacent webs such as wicking layers are compressed as a composite after polymerization and before drying, with the fibrous web layer being maintained in the compressed state by the dried hydrocolloid polymer.
  • the sorbent laminate is compressed to substantially reduce its thickness.
  • such a structure is compressed sufficiently to reduce the thickness of the laminate structure by at least 50 percent and the pressure utilized in conjunction with drying is sufficient to cause the composite to remain compact after the pressure is released.
  • the compression utilized should not be so high as to substantially crimp or crease the resilient fibers of the fibrous layer.
  • the hydrocolloid Upon wetting tne fibrous matrix, the hydrocolloid becomes wet so that the fibrous layer expands from its compressed state due to the inherent resilience of the fibers of that layer, and thereby facilitates swelling of the hyrocolloid polymer.
  • the starting fibrous web matrix (prior to the addition of hydrocolloid polymer) has an initial dry bulk recovery of at least about 30 percent, and more preferably at least about 60 percent, an initial dry bulk of at least about 20 cubic centimeters per gram (cc/g) , and a weight of less than about 2 oz/yd - (about 68 gm/m ) .
  • the initial dry bulk is the area times thickness of the layer under the load of 0.01 pounds per square incn calculated in cubic centimeters. This value is divided by the weight in grams to provide the measurement in cubic centimeters per gram.
  • the dry bulk recovery is obtained by subjecting the web to a load of 1.75 pounds per square inch (psi) for five minutes, removing the load and allowing the web to rest for one minute, subjecting the web to a load of 0.01 psi for one minute and then measuring the final dry bulk under the 0.01 psi load.
  • the dry bulk recovery is the final bulk divided by the initial bulk expressed in percent.
  • fibrous web can provide this dry bulk recovery and has an initial dry bulk of at least 20
  • the fibrous web meets the requirements of the sorbing layer.
  • the fibrous web matrix has these requirements, it can retain hydrocolloid polymer up to at least 1,500 percent of the dry basis weight of the web. It is preferable that the web contain 200 percent to 1,500 percent by weight dry basis hydrocolloid, relative to the dry basis weight of the web. More preferred is a range from about 400 percent to about 1,200 percent, and most preferably about 500 to 1000 percent weight add-on. These weight add-ons can also be expressed as a ratio of hydrocolloid polymer weight to starting fibrous web matrix weight.
  • a suitable fibrous web for a sorbing layer has a substantially high loft, and on compression followed by release, has a tendency to return substantially to its original thickness.
  • the resulting resiliency of the fibrous web typically permits a sorbing layer containing a hydrocolloid polymer to regain at least about 75 percent of its original thickness when it is released from its compressed state as liquid penetrates the sorbent product.
  • Such webs are typically formed from synthetic staple fibers such as polyethylene, polypropylene, polyester, nylon, bicomponent fibers and the like are particularly desirable. Cellulosic fibers such as rayon can also be used.
  • the fibrous web can be formed by carding, dry laying or wet laying fibers so as to provide a low density structure, as is well known in the art.
  • staple polyester fibers are air laid with a minor portion of fusible fibers to form a web whose fibers are lightly bonded by passing hot air through the web fibers making the fusible fibers tacky so as to stick to each other and the staple fibers to provide furter integrity to the web structure.
  • the wicking layer is comprised of substantially uniformly disposed, frictionally engaged particles of hydrophilic fibers, such as rayon fibers, cellulosic fibers, or peat moss, or mixtures thereof.
  • the cellulosic fibers include wood pulp fibers, cotton linters, and the like.
  • the wood pulp fibers generally are those that are used to form the fluff or fibrous batt layer in conventional sorbent products such as disposable diapers, sanitary napkins, etc.
  • Other cellulosic fibers that can also be used are rayon fibers, flax, hemp, jute, ramie, cotton and the like.
  • the particles of fibers or peat moss or mixtures thereof are placed in such a way as to form a layer in which the particles are spaced sufficiently close to one another so as to promote rapid movement of liquid (wicking) in the plane of the layer.
  • tne sorbent web and wicking layer that comprises portions of the engaged wicking layer particles that extend into the hydrocolloid polymer and become integral therewith so that those particles are in intimate contact with the hydrocolloid polymer.
  • An exemplary compressed, composite useful in a diaper can be prepared as follows.
  • the sorbent composite is made by four steps. First, a fibrous web structure is made by blending polyester fiber T-375W manufactured by DuPont and fusible BICO 1040 fiber, made by BASF, in a ratio of 67/33 percent by weight. This blend is carded into a high bulk non-woven web structure of approximately 1.20 oz/yd 2 (about 40.7 g/m2) weight and passed through an air bonder at a temperature of 325° F (about 163°C) for a duration of 5.6 seconds and at a pressure differential of 0.25 incnes (0.64 cm) of water. This heat process bonds the web by partially melting the BICO fiber.
  • the second step consists of applying to that web a coating of an aqueous acrylic acid/potassium acrylate, AMPS and cross-linker (when present) concentration solution at a consistency of about 65 percent solids and about 60 percent neutralized monocarboxy monomer.
  • the monomer is added by suction o coating to a desired level of 12.0 oz/yd (about 40
  • the thus applied coating is polymerized and cross-linked into a hydrocolloid polymer by multiple electron beam irradiations of 2 Mrads and 2 Mrads with an ESI 300 KV electron accelerator.
  • Pulp wicking layers are attached as the third step.
  • the polymer Prior to this, the polymer is adjusted to a 25 percent moisture content. It is passed through the suction zone of a Hammermill where pulp is defiberized and deposited at a weight of 4.8 oz/yd 2 (about 162.75 g/m 2 ). The use of vacuum causes at least some of the deposited fibers to migrate into the polymer-containing web and become integral therewith. Pulp is applied to the other side similarly.
  • a useful sorbent layer can also be prepared in compressed form having a single wicking layer or no wicking layer.
  • the pulp Upon release of pressure, the pulp has formed into a high density layer with a capillary size suitable for liquid wicking and the resilient fioer layer remains compressed.
  • the hydrocolloid polymer Upon use of the resulting dry structure, when a significant amount of liquid contacts the surface and migration of liquid into the sorbent layer takes place, the hydrocolloid polymer becomes soft and releases the resilient fibers so that the thickness of the structure increases markedly. This increase in thickness provides an area for storage of liquid.
  • a hydrocolloid polymer of the invention when employed as a portion of a sorbent layer of a sorbing article and polymerized in situ by an electron beam as described before, the liquid sorbing properties of the polymer are often reduced as compared to the same properties of a similar polymer prepared separately.
  • the reason for the difference in properties is thought to reside in the fact that the dose of radiation utilized for an in situ polymerization process is generally greater than that required for formation of a hydrocolloid prepared free in an aqueous medium.
  • the liquid sorption 'properties of webs so produced are however improved over the same properties obtained utilizing a single cross-linker or obtaining cross-linking solely via the electron beam.
  • a dry hydrocolloid polymer _ir situ- polymerized on the matrix fibers of a fibrous web typically exhibits sorptions of a 1 weight percent saline solution of about 25 to about 45 g/g (about 250 to about 450 percent) , and more preferably about 30 to about 40 g/g. Extractables levels of an in situ web-polymerized hydrocolloid polymer are typically between about 10 to about 20 percent.
  • Residual monomer levels are determined by high-performance liquid cnromatography (HPLC) .
  • the monomers assayed are acrylic acid and its ester dimer.
  • Glacial acrylic acid in an amount of about 500 milligrams (mg) is weighed to the nearest 0.1 mg into a 100 milliliter (ml) volumetric flask and is diluted to volume with 0.01 N sulfuric acid to form Solution A.
  • Acrylic acid ester dimer (at least 95 percent pure) in an amount of about 100 mg is weighed to the nearest 0.1 mg into a second 100 ml flask, and is diluted to volume with 0.01 N sulfuric acid to form Solution B.
  • Solutions A and B is mixed tnoroughly.
  • Solution A (10 ml) and Solution B (10 ml) are pipetted into a third 100 ml volumetric flask and diluted to volume with 0.01 N sulfuric acid to form Working Standard I (WS I) .
  • Working Standard II (WS II) is prepared similarly using 1 ml of each of
  • Duplicates of each WS I and WS II are prepared. Portions of each of the four standards are placed into autosampler vials and capped.
  • a generally similar procedure is utilized for sorbent layers comprised of a web matrix coated with hydrocolloid polymer except that approximately 1.0 gram (g) of the coated web, weighed to the nearest 0.1 mg, is weighed into a 30 ml serum vial. The above amount of sulfuric acid is added and the vial is capped and sealed. Where sorbency is too great to permit ready extraction, 30 ml of 0.1 N sulfuric acid are used with a larger serum vial.
  • a Waters Associates HPLC equipped with a model M-590 pump, a model M-481 ultraviolet detector (set at 214 nm) and an autosampler is used.
  • the HPLC uses an Aminex ⁇ HPX-87H ion exchange (Bio-Rad) column and a guard column. Sulfuric acid (0.01 N) is used as the mobile phase.
  • Injection volume 20 microliters (ul)
  • the HPLC is run for about 30 minutes prior to use or until a stable baseline is obtained.
  • Samples of WS I and WS II are injected.
  • Duplicate samples of WS I and WS II are injected and the areas/mg of both runs for each sample determined. The values of area/mg should agree within _+2% of their averages or the runs are repeated.
  • Response factors for each sample are also calculated.
  • An aliquot of each sample extract to be assayed is injected once.
  • the results for each pair of duplicate samples should agree within +3 percent or the duplicate samples are reassayed.
  • the amounts of acrylic acid and its ester dimer present in the sample are thereafter calculated from the areas of the HPLC chart, the response factor, the dilution factor and sample weight using a standard equation, and are expressed in parts per million of the original sample.
  • Percentage extractables are determined in a manner generally similar to the manner of determining residual monomer. In this case, however, a standard of polyacrylic acid (PAA) of a molecular weight of about 80,000 is utilized.
  • PAA polyacrylic acid
  • the powder sample of hydrocolloid polymer (150 mg) weighed as before is placed into a 50 ml centrifugee tube to which 25 ml of 0.2 M Na personallyS0 4 are added.
  • the tube is capped and shaken on a mechanical wrist shaker for 25 minutes, filtered as before into an autosampler vial, and the vial is capped. If the filtrate is not clear, the cloudy filtrate is returned to the centrifuge tube, the tube is centrifuged and the supernatant filtered as above.
  • the sorbent layer samples are prepared as discussed previously, and assayed as discussed above.
  • the standards and samples are prepared as in duplicate.
  • HPLC HPLC is run as described before.
  • Typical instrument settings are:
  • a size exclusion stationary phase (3000 PW) is used with a Toyo Soda TSK guard column.
  • the working standards of PAA and GAA are injected separately and their retention times are determined. Duplicates of each standard are run. The areas/mg for each of the two injections should agree within +5 percent of their average for each standard, or the standarization procedure is repeated. The response factors are calculated for the standards.
  • Both high and low molecular weight polymers are extractable.
  • the high molecular weight percentage extractables is related to the 80,000 molecular weight standard using the response factor for that polymer, whereas the low molecular weight percentage extractables is related to the monomer standard using the response factor for the monomer.
  • the percentage extractables for high and low molecular weight polymers are calculated separately, each using the appropriate peak areas and response factors, as well as the dilution factor, and sample weight. The individual extractables percentages are then summed to provide the extractables percentage.
  • Fluid sorption by a hydrocolloid polymer is determined as follows. A powder sample in acid form is dried in a vacuum oven for about 18 hours at a temperature of 40° C. An aliquot of about 100 mg, weighed to the nearest 0.1 mg, is added to 200 ml of deionized water, and permitted to sorb the water for a time period of 2 hours.
  • a filter paper is soaked with deionized water and allowed to drain until no further drops of water appear.
  • the wet filter is thereafter weighed.
  • the mixture of hydrocolloid polymer and water is thereafter filtered through the wet filter paper.
  • the combined wet filter paper and swollen hydrocolloid are weighed to provide a total weight. Subtraction of the weight of dried hydrocolloid polymer powder and wet filter paper from the total weight provides the weight of sorbed deionized water, which is expressed as a percentage of the original weight of the dried hydrocolloid polymer weight, or in milliliters of deionized water sorbed per gram of dry hydrocolloid polymer.
  • hydrocolloid polymer of the invention that is prepared using a thermally initiated reaction based on the free radical initiator potassium thiosulfate.
  • This polymer contains 10 mole percent AMPS and 1 mole percent MBA as cross-linker, with the remaining monomer being acrylic acid.
  • the gelatinous mass is cut into cubes and freeze dried.
  • the resulting powder is ground in a Wiley mill until all of it passes through a 20 mesh sieve screen (U.S. Standard Sieve series) .
  • the powder is thereafter dried in a vacuum oven at a temperature of 40 degrees for a period of 16 hours.
  • Swelling studies are carried out using such a powoered polymer by weighing out about 0.100 g, weighed to the nearest 0.01 g, of the powder and adding an amount of aqueous sodium hydroxide sufficient to neutralize 60 mole percent of the total acid functionality present, followed by dilution to 500 ml of deionized water. The resulting gel is weighed two hours thereafter and its sorbency calculated. For saline (1 percent NaCl) sorbency, a 1 weight percent solution of sodium chloride was used in place of the deionized water.

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Abstract

Polymère à sorption améliorée d'eau désionisée et de solutions aqueuses de chlorure de sodium à 1 % en poids, ainsi que produits absorbants comprenant ce polymère. Le polymère hydrocolloïdal comprend essentiellement (a) entre 60 et 90 % molaires environ d'un monomère monocarboxyle alpha et bêta monoéthyléniquement insaturé polymérisé contenant une chaîne de trois atomes de carbone, (b) entre 10 et 40% molaires environ d'acide 2-acrylamido-2-méthylpropanesulfonique polymérisé, (c) entre 0 et 20 % molaires environ d'un monomère monoéthyléniquement insaturé co-polymérisable polymérisé, soluble dans l'eau, et (d) entre 0 et 3% molaires environ d'un agent de réticulation croisée polyéthyléniquement insaturé, soluble dans l'eau et copolymérisable. Un gramme du polymère hydrocolloïdal sec, sous forme d'acide libre, sorbe une quantité d'une solution aqueuse de chlorure de sodium à 1 % en poids, supérieure de 15 à environ 100 % à celle que sorbe un polymère préparé de manière similaire contenant des quantités identiques de tous les composants éthyléniquement insaturés, sauf le monomère d'acide sulfonique, et de l'acide acrylique au lieu dudit monomère d'acide sulfonique.
PCT/US1990/003308 1989-06-12 1990-06-11 Polymere hydrocolloidal a absorption amelioree WO1990015826A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120202959A1 (en) * 2011-02-07 2012-08-09 Basf Se Process for Producing Water-Absorbing Polymer Particles
WO2012107344A1 (fr) * 2011-02-07 2012-08-16 Basf Se Procédé de préparation de particules polymères hygroscopiques

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4192727A (en) * 1976-08-24 1980-03-11 Union Carbide Corporation Polyelectrolyte hydrogels and methods of their preparation

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4192727A (en) * 1976-08-24 1980-03-11 Union Carbide Corporation Polyelectrolyte hydrogels and methods of their preparation

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120202959A1 (en) * 2011-02-07 2012-08-09 Basf Se Process for Producing Water-Absorbing Polymer Particles
WO2012107344A1 (fr) * 2011-02-07 2012-08-16 Basf Se Procédé de préparation de particules polymères hygroscopiques

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