CZ20002400A3 - Absorbent polymer compositions with high sorption capacity and high fluid permeability at applied pressure - Google Patents

Abstract

This solution provides absorbent materials suitable for retaining body fluids, such as synthetic urine. The solution particularly relates to absorbent polymer blends with excellent absorbent properties in terms of absorbent capacity at applied pressures of 4.8 kPa and 9.6 kPa, as well as excellent fluid permeability. The solution further relates to an absorbent element comprising said absorbent polymer blends, and to absorbent articles comprising said absorbent element.

Description

Technical area

The invention relates to absorbent polymer compositions having a high sorption capacity and a high fluid permeability under applied pressure. These compositions are particularly useful for absorbing body fluids, such as urine and menstrual fluid. The invention also relates to absorbent elements comprising said absorbent polymers, as well as absorbent articles comprising said absorbent elements.

State of the art

There is a growing commercial interest in the development of highly absorbent products that are used as disposable diapers, such as incontinence pads, menstrual pads, sanitary napkins, etc. A highly desirable feature of such products is their thinness. Thin diapers do not wrinkle when worn, fit better under underwear, and are not even noticeable to the user when worn. They are very compact when packed, which brings advantages to the user when carrying and storing. Compactness also means reduced storage and transportation costs for the manufacturer and distributor, and much less space is needed for storage.

The ability to provide thinner absorbent articles, such as diapers, has necessitated the development of relatively thin absorbent cores or elements that can acquire and retain large quantities of body exudates, particularly urine. In this regard, the use of certain absorbent polymers, often referred to as "hydrogels", "superabsorbents", "xerogels" or "hydrocolloids", is of great importance. For example, U.S. Patent 3,699,103 (Harper et al.) issued June 13, 1972, U.S. Patent 3,770,731 (Harmon), issued June 20, 1972, disclose the use of such material (herein referred to as an absorbent polymer) in absorbent articles. The development of thinner diapers is directly dependent on the development of thinner absorbent cores that can take advantage of the ability of absorbent polymers to absorb large quantities of body exudates, especially in combination with a fibrous matrix. U.S. U.S. Patent 4,673,402 (Weisman et al.) issued June 10, 1987, U.S. Patent 4,935,022 (Lash et al.) issued June 19, 1990 discloses a two-layer core structure that includes a fibrous matrix and an absorbent polymer to provide a thin, compact, and low-volume diaper.

Absorbent polymers are often produced by the initial polymerization of unsaturated carboxylic acids or their derivatives, such as acrylic acid, an alkali metal (e.g., sodium and/or potassium), or an ammonium salt of acrylic acid, etc., in the presence of relatively small amounts of di- or polyfunctional monomers, such as N,N’ methylenebisacrylamides, trimethylpropane triacrylate, ethylene glycol di(meth)acrylate, or triallylamine. The di- or polyfunctional monomers serve to slightly crosslink the polymer chains, thereby rendering them insoluble in water while allowing them to swell in water. Such lightly crosslinked polymers contain multiple carboxyl groups attached to the polymer backbone. The carboxyl groups generate an osmotic driving force that acts to absorb body fluids through the crosslinked polymer network. Absorbent polymers can also be produced by polymerizing unsaturated amines or their derivatives in the presence of relatively small amounts of di- or polyfunctional monomers (in an analogous manner).

The degree of crosslinking of these absorbent polymers is an important factor in determining their absorbent capacity and gel strength. Absorbent polymers useful as absorbents in absorbent elements and articles, such as disposable diapers, must have a high sorption capacity, as well as a high gel strength. The sorption capacity must be sufficiently large to allow the absorbent polymer to absorb a significant amount of watery body exudates during the time the article is in use. Gel strength refers to the tendency of swollen polymer particles to deform when a certain pressure is applied, and said gel strength must be so large that the polymer particles do not deform under pressure and thereby fill the free capillary spaces in the absorbent element or article to an unacceptable extent, thereby preventing the wicking and distribution of fluid in said element or article. In general, increasing the permeability of a region or layer containing swollen absorbent polymers can be accomplished by increasing the crosslink density of the polymer gel, thereby increasing the gel strength. This is done at the expense of inadvertently reducing the absorbent capacity of the gel, see U.S. Patent 4,654,039 (Brandt et al.) issued March 31, 1987 (reissued April 19, 1988 as Patent 32,649) and U.S. Patent 4,834,735 (Alemany et al.) issued May 30, 1989.

Under certain conditions, many absorbent polymers can exhibit gel blocking. “Gel blocking” occurs when the absorbent polymer particles deform to an unacceptable extent that they fill the free capillary spaces in an absorbent element or article, thereby preventing the rate of fluid wicking or distribution within said element or article. If gel blocking occurs, further wicking and distribution is accomplished by a slow diffusion process. In practical terms, this means that gel blocking can significantly affect fluid distribution.

into relatively dry areas or zones in the absorbent core and article. Leakage from an absorbent article may occur before the absorbent polymer particles in the absorbent article are fully saturated, or before the liquid can diffuse or seep past the "blocking" particles into the remainder of the absorbent article, see U.S. Patent 4,834,735 (Alemany et al.), issued May 30, 1989.

Gel blocking necessarily requires the use of a fibrous matrix in which the absorbent polymer particles are dispersed. The fibrous matrix separates the absorbent polymer particles from each other and creates a capillary structure that allows fluid to reach the absorbent polymer located in areas remote from the initial point of fluid loading, see U.S. Patent 4,834,735 (Alemany et al.) issued May 30, 1989. Dispersing the absorbent polymer in a fibrous matrix at relatively low concentrations, in order to minimize or eliminate gel blocking, can significantly increase the volume of the absorbent article, as well as the overall retention capacity of a thinner absorbent structure.

Using a low concentration of absorbent polymers limits the real advantage of these materials, such as their ability to absorb and retain a larger amount of body fluids per given volume.

At relatively high concentrations, an important property of these polymers is their conductivity, i.e. permeability/flow. This conductivity of a material can be defined as its “Saline Flow Conductivity” (SFC). SFC is a measure of the material’s ability to transport saline fluids, for example the ability of a layer containing a swollen absorbent polymer to conduct (transport body fluids). A fabric made by laying a fibrous slurry in an air stream (e.g. with a density of 0.15 cm ³ ) will have an SFC value of around 200 x 10' ⁷ cm ³ sec/g.

Optimizing either the PUP (Performance Under Pressure) capacity or the conductivity (permeability/flow) of an absorbent polymer results in reduced fluid permeability when the polymer is in a swollen state. It would therefore be desirable to provide an absorbent polymer composition that is capable of absorbing large amounts of synthetic urine solution under pressure (4.8 kPa and greater). It would also be desirable to provide an absorbent polymer composition with high fluid permeability when the polymer is in a swollen state. It would also be desirable for a relatively high capacity (PUP) to be obtained after a period of time that is less than the period of use (overnight) of the product containing said absorbent polymer composition. The absorbent polymer should reach a high capacity after, for example, 2, 4, 8 or 16 hours.

The essence of the invention

The invention relates to absorbent materials useful as a means of containing body exudates, for example urine. The invention particularly relates to absorbent polymers having a high absorption capacity under a pressure of 4.8 kPa and/or 9.6 kPa, and further having a high fluid permeability when the polymer is in a swollen state.

In one aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 39 g/g under a pressure of 4.8 kPa after 4 hours and an SFC value of at least 50 x 10 ⁷ cm ³ sec/g. (Methods for measuring PUP capacity and SFC are described below). In another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 40 g/g under a pressure of 4.8 kPa after 8 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g. In another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 42 g/g under a pressure of 4.8 kPa after 16 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g. As used herein, the term "after" means immediately after.

In another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 35 g/g under a pressure of 9.6 kPa after 4 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g. In yet another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 36 g/g under a pressure of 9.6 kPa after 8 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g. In another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 37 g/g under a pressure of 9.6 kPa after 16 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g.

In another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 30 g/g under a pressure of 4.8 kPa after 4 and 8 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g. In yet another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 27 g/g under a pressure of 9.6 kPa after 4, 8 and 16 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g. In another aspect, the invention relates to an absorbent polymer blend having a PUP capacity of at least 27 g/g under a pressure of 9.6 kPa after 4, 8 and 16 hours and an SFC value of at least 50 x 10' ⁷ cm ³ sec/g.

In a preferred embodiment, the invention relates to a mixture comprising cation exchange absorbent polymers containing weak acid groups in an unneutralized form, and anion exchange absorbent polymers containing weak basic groups in an unneutralized form, the mixtures exhibiting high absorbency of a synthetic urine solution under PUP absorption conditions and at relatively high fluid conductivity values. Such a mixture relates to a mixed ion exchange absorbent polymer (mixed -5-

bed-ion-exchange polymer composition) This mixture will exhibit at least one of the PUP capacities that have already been described.

Overview of images on the drawing

Fig. 1 shows a schematic view of a device used to measure the PUP capacity of an absorbent polymer, Fig. 2 shows an enlarged cross-section of the piston/cylinder assembly of Fig. 1, Fig. 3 graphically describes the PUP capacity data of absorbent polymer mixtures according to the present invention and according to the prior art, where the PUP capacity is measured under a pressure of 4.8 kPa, Fig. 4 graphically describes the PUP capacity data of absorbent polymer mixtures according to the present invention and according to the prior art, where the PUP capacity is measured under a pressure of 9.6 kPa, Fig. 5 schematically shows a device for preparing samples of absorbent polymer mixtures, which are used to measure the strength by the BBS (Balí Burst Strength) ball method.

Fig. 6 schematically shows a device used for BBS measurement of mixtures of absorbent polymers.

Examples of embodiments of the invention

A. Definition

The term "bodily fluids" used includes urine, blood, menstrual and vaginal secretions.

The term “synthetic urine solution” used refers to an aqueous solution prepared by dissolving 2.0 g KCL, 2.0 g Na2 SO4, 0.85 g NH4 _H2 PO4, 0.15 g (NH4 )2 HPO4, _0.25 g CaCl2 _2H2 O, and 0.50 g _MgCl2 .6H2 _O in distilled water to make 1 liter of solution.

The term "ion exchange capacity" used refers to the theoretical or calculated ion exchange capacity of the polymer or polymers in milliequivalents/g, assuming that any unneutralized acid or base group is neutralized during ion exchange.

The term "absorbent polymer" used refers to a polymer that is capable of absorbing at least ten times its weight in deionized water and allows for adjustment of the pH of the system.

The term "absorbent core" as used herein refers to the component of an absorbent article that is responsible for the fluid handling of the article, i.e., fluid acquisition, fluid distribution, and fluid retention. The absorbent core shall not include the topsheet or backsheet of the absorbent article.

The term "absorbent element" as used herein refers to the components of an absorbent core that provide one or more handling capabilities, such as fluid acquisition, fluid distribution, fluid transport, and retention. An absorbent element may comprise the entire absorbent core or a portion of the absorbent core, meaning that the absorbent core may comprise one or more absorbent elements. The improved absorbent polymer blends described herein are particularly useful in absorbent elements whose primary function is to contain aqueous body fluids. These blends may also be used in other absorbent elements.

The term "region" or "zone" used refers to parts or sections, on a macroscopic scale, of an absorbent element.

The term "layer" as used herein refers to a portion of an absorbent article whose principal dimensions are length and width. It is understood that the term layer is not limited to a single layer or thin sheet of material. The layer may consist of a laminate or a combination of several layers of the desired material. Accordingly, the term "layer" includes both a layer and a layering.

The term "comprises" is used to mean that various components, elements, steps, etc., of the present invention may be used. Accordingly, the term "comprises" is a much more restrictive term than "consisting essentially of" and "consisting of", which restrictive terms have their standard meaning known in the art.

All percentages, ratios and proportions are by weight unless otherwise specified.

All publications and references mentioned in this application are hereby incorporated by reference, at least to the extent that they correspond to the terms and definitions of this application.

B. Absorbent polymer blends

This invention relates, at least in part, to absorbent polymer blends that exhibit high absorption capacity of a synthetic urine solution under applied load, as well as high fluid permeability when in a swollen state. The absorbent polymer blends of this invention are in the form of a mixed ion exchange base, comprising an anion exchange absorbent polymer and an absorbent polymer.

-Cation exchange polymer. These preferred mixed ion exchange base mixtures are described in more detail in the following section.

1. Absorbent polymers with mixed ion exchange base

a) Chemical composition

i) Anion exchange absorbent polymers

Absorbent anion exchange polymers containing weak basic groups include various water-insoluble polymers capable of swelling. They are primarily lightly crosslinked polymers containing a variety of basic functional groups, such as primary, secondary and/or tertiary amines or phosphines. Examples of suitable polymers include those polymers prepared from polymerizable monomers that contain basic groups or groups that can be converted to basic groups after polymerization. Such monomers include primary, secondary or tertiary amines or phosphines. Representative monomers include, but are not limited to, ethyleneimine (aziridine), allylamine, diallylamine, 4-asaminobutene, alkyl oxazoline, vinylformamide, 5-aminopentene, carbodiimide, formaldazine, mealine, and the like, and their secondary or tertiary amine derivatives. Representative functional groups that can be introduced after polymerization include alkylamine, guanidine, triazole, triazine, triamino-triazine, and the like.

In order to prepare anion exchange absorbent polymers, some monomers which do not contain basic groups may also be included, in small amounts. The absorbent polymers described may be homopolymers, copolymers (including terpolymers and higher copolymers), or mixtures of different homopolymers or copolymers. The polymers may be random, grafted or block polymers which may have a linear or branched structure. The polymers are considered to be water-insoluble but swellable substances, with a relatively low degree of crosslinking (cross-linking). This can be achieved by adding an appropriate amount of a suitable monomer which becomes a cross-linked monomer during polymerization. Examples of such crosslinking polymers include N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylpropane tri(meth)acrylate, triallylamine, diaziridine compounds, etc. Alternatively, the polymers may be crosslinked after polymerization by reaction with a suitable crosslinking agent, for example, di- or poly-halogenated compounds and/or di- or polyepoxy compounds. Examples include diiodopropane, dichloropropane, ethylene glycol diglycidyl ether, etc. The crosslinking may be homogeneously distributed throughout the gel particles, or may be concentrated at or near the surface of the particles.

-800 00 ·· 00 • · · · 0 ♦ 0 0 • 0 00 0 ♦ 0 ·

00 000 00 ·

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It is preferred that the absorbent polymers are of the same type (homogeneous), but mixtures of anion exchange polymers may also be used in the present invention. For example, mixtures of crosslinked polyethyleneimine and crosslinked polyallylamine may be used. If an anion-bound absorbent polymer is used as part of the mixed ion exchange base mixture, it starts in the form of an unneutralized base with a value of from 50% to 100%, preferably from 80% to 100%, more preferably from 90% to 100%.

In order to minimize the ion exchange capacity of the mixed ion exchange base absorbent polymer blend, it is desirable that the absorbent polymer has a high ion exchange capacity per gram of dry polymer. It is preferred that the ion exchange capacity of the anion exchange absorbent polymer be at least 10 meq/g, more preferably at least 15 meq/g, most preferably at least 20 meq/g.

ii) Cation exchange absorbent polymers

Absorbent polymers suitable for cation exchange include a variety of acidic functional groups, such as carboxylic acid groups. Examples of cation exchange polymers include polymers prepared from polymerizable, acid-containing monomers, or monomers containing functional groups that can be converted to acid groups upon polymerization. Such monomers include olefinically unsaturated carboxylic acids, anhydrides, and compounds thereof. Cation exchange polymers may also include polymers that are not prepared from olefinically unsaturated monomers. Examples of such polymers include polysaccharide-based polymers, such as carboxymethyl starch and carboxymethyl cellulose, and poly(amino acid)-based polymers, such as poly(aspartic acid). Poly(amino acid)s are described in U.S. Patent 5,247,068, issued to Donachy et al., Jan. 21, 1993. The patent is incorporated by reference.

Non-acidic monomers can also be used to prepare absorbent polymers, but usually in small amounts. Non-acidic monomers can include, for example, monomers containing the following types of functional groups: carboxylate or sulfonate esters, hydroxyl groups, amide groups, amino groups, nitrile groups, quaternary ammonium salt groups, and aryl groups (e.g., phenyl groups, such as those derived from the monomer styrene). Other optional non-acidic monomers include unsaturated hydrocarbons, such as ethylene, propylene, 1-butene, butadiene, and isoprene. Non-acidic monomers are known materials described in great detail in U.S. Patent 4,062,817 (Westerman) issued on

-913 December 1977 and in U.S. Patent 4,076,663 (Masuda et al.) issued February 28, 1978. Both patents are incorporated herein by reference.

Olefinically unsaturated carboxylic acid and anhydride monomers include acrylic acids representing acrylic acid itself, methacrylic acid, chloroacrylic acid, β-methylacrylic acid (crotonic acid), α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, β-stearyl acrylic acid, itaconic acid, citraconic acid, masaconic acid, glutaconic acid, aconitic acid, maleic acid, furmaric acid, tricarboxyethylene, maleic anhydride.

Preferred cation exchange absorbent polymers contain carboxyl groups. These polymers include hydrolyzed grafted starch-acrylonitrile copolymers, partially neutralized hydrolyzed grafted starch-acrylonitrile copolymers, hydrolyzed vinyl acetate-acrylic ester copolymers, hydrolyzed acrylonitrile or acrylamide copolymers, lightly cross-linked polymers of all of the aforementioned copolymers, polyacrylic acid, and lightly cross-linked polymers of polyacrylic acid. These polymers may be used either alone or in the form of mixtures of two or more different polymers. Examples of such polymers are disclosed in U.S. Patent 3,661,875, U.S. Patent 4,076,663, U.S. Patent 4,093,776, U.S. Patent 4,666,983, and U.S. Patent 4,666,983. patent 4,734,478.

The most preferred polymers for making cation exchange absorbent polymers are the lightly crosslinked polymers of polyacrylic acids and their starch derivatives. The crosslinking provides a substantially water-insoluble polymer and in part determines the absorbent capacity and extractable polymer content characteristics of the absorbent polymers. The process for crosslinking these polymers, as well as the crosslinking agents, are described in U.S. Patent 4,076,663.

While the cation exchange absorbent polymers are usually of one type (homogeneous), mixtures of these polymers may be used in accordance with the present invention. For example, mixtures of starch-acrylic acid graft copolymers and lightly crosslinked polyacrylic acid polymers may be used.

When used as part of a mixed ion exchange base composition, the cation exchange absorbent polymer starts at from 50% to 100%, more preferably from 80% to 100%, more preferably from 90% to 100%, in the neutralized acid form.

-1099 9 ·· ·· ·· 99

9 99 9 4 9 9 9 9 9 9 • · 9 9 · · 99·· • 9 · · 99 9·· 99 9 • 9 9999 9999

9999 «99 99 99 99 99

In order to minimize the ion exchange capacity of the mixed ion exchange base absorbent polymer blend, it is desirable that the cation exchange polymer have a high ion exchange capacity per gram of dry polymer. It is preferred that the ion exchange capacity of the cation exchange absorbent polymer be at least 4 meq/g, more preferably about 8 meq/g, more preferably about 10 meq/g, and most preferably about 13 meq/g.

iii) Mixture and common material properties

The equivalents of anion and cation exchange capacity should be equal or different in a mixture of absorbent polymers with a mixed ion exchange base. For example, it might be desirable to have more equivalents of absorbent polymers with anionic or cationic binding, i.e. to compensate for differences in pK, to compensate for differences in neutralization, to change the pH (e.g. to acidity) of ion-exchanged urine, etc.

For a polymer blend with a mixed ion exchange substrate in a high concentration absorbent core, solution flow, agitation, etc. cannot be relied upon to facilitate the movement of ions between particles and thus the rate of ion exchange. It is desirable to have morphologies suitable for enhancing the kinetics of ion exchange. Suitable morphologies include i) aggregates of mixed-base particles with high surface area (i.e., small and/or porous) and with a wide or narrow particle size distribution, ii) particles, for example of an anion-exchange absorbent polymer, which for example contain, within a smaller discontinuous (non-flowing) domain, a cation-exchange absorbent polymer, iii) particles that contain bicontinuous domains of both anion- and cation-exchange absorbent polymers, iv) mixtures in which the anion- or cation-exchange absorbent polymers are present in the form of fibers, v) fibers that contain discontinuous and/or bicontinuous domains of anion- and/or cation-exchange absorbent polymers, vi) mixtures of said particles and/or fibers. Other forms include spheres, cubes, rods, films or thin fabrics, foams, flakes, etc.

Absorbent polymers may also include mixtures with low levels of one or more additives, such as silica fume, adhesives, binders, and the like. The components in these mixtures may be physically and/or chemically combined such that the absorbent polymer components and the non-absorbent polymer in the form of an additive cannot be readily physically separated from each other. Absorbent polymers may be substantially non-porous (without internal porosity), or they may have internal porosity. In mixtures with a mixed ion exchange base, the absorbent polymer of one type may have a higher cross-link density than the absorbent polymer of another type.

-11*· » ·» »· ·· ·· • · · · ··«· ··»· * * ···· »·»· * *4 *4 *44 44 4 * * *··· *··· ***· ··· ·· ·· ·· **

The particles of absorbent polymers useful in the present invention may have a size ranging from one to 2000 μ, preferably from 20 to 1000 μ. The median particle size of the mass should be from 20 to 1500 μ, preferably from 50 to 1000 μ, and even more preferably from 100 to 800 μ.

An important property of the absorbent polymer useful in the present invention is the level of extractables present in the polymer itself, see U.S. Patent 4,654,039 (Brandt et al.), issued March 31, 1987 (reissued April 19, 1988 as Patent 32,649), both of which are incorporated herein by reference. Many absorbent polymers contain significant amounts of extractable polymeric materials that can be leached from the swollen polymer matrices by body fluids (urine) during the time the body fluids remain in contact with the absorbent polymer. Such polymeric material, extracted by body fluids in the manner described, can alter both the chemical and physical properties of the body fluid to the extent that the fluid is much more slowly absorbed by the absorbent polymer in the absorbent article and more difficult to retain. It is believed that extractable polymers are detrimental in a mixed-base ion exchange absorbent polymer system because the soluble polymer tends to migrate into the gel particles contained in the oppositely charged polymer. Both polymers will neutralize each other, thereby reducing the ion exchange capacity of the system. Since the extractable polymer includes a polyvalent ion with an opposite charge to the oppositely charged polymer, it can also form ionic cross-links, which suppresses the swelling ability of the gel.

Accordingly, it is preferred that the level of extractable polymer in the absorbent polymer be about 15% or less, more preferably 10% or less, more preferably 7% or less by weight of the total polymer.

b. Physical properties

i) Behaviour/performance under pressure

The measurement of the desired wettability, or gravimetric absorption, can provide information about the ability of highly concentrated zones or layers of absorbent polymer to absorb body fluids under applied pressure. See, for example, U.S. Patent 5,562,646 (Goldman et al.), issued October 8, 1996, U.S. Patent 5,599,335 (Goldman et al.), issued February 4, 1997, where the desired wettability or gravimetric absorption is referred to as PUP. In measuring PUP, an initial dry absorbent polymer mixture at 100% concentration is placed in a cylinder and piston device (the bottom of the cylinder is permeable to the solution but impermeable to the absorbent polymer) and is loaded with mechanical pressure and allowed to absorb synthetic urine while maintaining the desired conditions.

-12• ti ti ♦· ·· ·· ·· • ··· ti ti · ti ti » · ti • ti titititi titititi • ti titititi tititi titi • ti titititi ti··· •tititi ti·· titititi titi titi at zero hydrostatic suction and high mechanical pressure. PUP capacity is defined as the g/g absorption of a synthetic urine solution at 0.032 g/cm ² of an absorbent polymer layer, when loaded with a specific pressure for a specific time. High PUP capacity is an important critical property of an absorbent polymer when used in an absorbent element at a high concentration value.

The pressure applied to the absorbent polymers refers to both mechanical pressure (induced by the weight and movements of the user, contact forces, etc.) and capillary pressure (the pressure of capillary desorption of the obtained components in the absorbent core, which temporarily retains liquids until they are absorbed by the absorbent polymer). The total pressure of about 4.8 kPa reflects the sum of both pressures on the absorbent polymer mixture during the absorption of body fluids and under given operating conditions. Both low and high pressures can be used under normal conditions. It is preferred that the absorbent polymer according to the present invention exhibits a high PUP capacity, namely at pressures above 9.6 kPa, and at a high SFC value. It is preferred that the relatively high PUP capacity is achieved during a period that is shorter than the period of use of the products comprising the absorbent mixtures. Absorbent products demonstrate improved capacity when PUP capacity is measured after 2, 4, 8 and/or 16 hours.

The method for determining the PUP capacities of these absorbent polymers is described in the section “Polymer Testing”. The method is based on the procedure described in U.S. Patent 5,562,646 (Goldman et al.) issued October 8, 1996 and is modified for longer periods of time at various pressures to more closely simulate operational conditions.

ii) Permeability of zones or layers that include the absorbent polymer

A desired property of the absorbent polymers of the present invention is their high fluid permeability. In an absorbent element or article, permeability is directly affected by the ability of the material, for example a layer comprising a swollen absorbent polymer, to transport body fluids from the receiving areas at an acceptable rate. The permeability/flux conductivity can be defined as SFC (saline fluid conductivity) which is a measure of the material's ability to transport saline fluid. A method for measuring SFC is described in U.S. Patent 5,562,646 (Goldman et al.), issued October 8, 1996. This method is modified to calculate the gel base runoff during testing of mixed ion exchange base absorbent polymers, as will be described in the "Test Methods" section. Without wishing to be bound by theory, we believe that during measurements of absorbent polymers with a mixed ion exchange base, the polymer sample will continue to exchange ions from the salt solution. The ion exchange capacity of the absorbent polymer is eventually exceeded and ··

• • 44 r » 44 4 • 4 4 4 4 4 4 • • 4 > 44 4 4 • • * 4 44« • · 44 • 4 • 4 • ♦ 44 4

The ionic strength of the solution surrounding the swollen polymer increases, resulting in the gel bed draining away. The amount of fluid that leaves the gel bed due to draining away is significantly less than the amount of fluid that passes through the gel bed during the SFC measurement. Since the final thickness of the gel bed is significantly less than the initial thickness, the final thickness value is used to calculate the SFC values. Using the final thickness value of the gel bed for the calculation provides the minimum SFC value obtained during the measurement. Using the initial or intermediate thickness value of the gel bed will yield higher SFC values.

iii) Porosity of the zone/layer comprising the absorbent polymer

Another important property of the absorbent polymers of the present invention is the openness/porosity of the zone or layer comprising the absorbent polymers when the polymers are swollen with body fluids and subjected to a certain pressure. It is believed that when the absorbent polymers used are present in absorbent elements or absorbent articles in high concentrations, they swell at a certain pressure, whereby the boundary portions of the particles come into contact and the void spaces in these high concentration regions are filled with the swollen polymer. If this happens, the openness/porosity properties of this region will be a reflection of the porosity of the zone or layer formed by the swollen polymer itself. The term "porosity" as used refers to the negligible volume that is not occupied by solid material. See J. ,M. Coulson et al., Chemical Engineering, Vol. 2, Third Edition, Pergamon Press, 1978, p. 126.

Porosity is an effective measure of the ability of a zone or layer comprising a swollen polymer to remain open and thus be able to receive and distribute body fluids when subjected to a certain pressure. It is believed that increasing the porosity of the swollen and highly concentrated areas can provide superior absorption and fluid handling capabilities of the absorbent core, thereby reducing the possibility of leakage, particularly under high fluid loads. The porosity of the zone or layer comprising a swollen absorbent polymer approaches, but exceeds, the porosity of conventional materials capable of receiving and distributing fluids, such as wood pulp wadding. See U.S. Patent 5,562,646, issued to Goldman on October 8, 1996.

iv) Integrity of the hydrogel zone or layer

Another important factor that affects fluid transport in an absorbent element is the integrity of the region or regions containing said polymer. Such region or regions,

-149 9 9 9 9 9 9 9 9 ·· · • 9 9999 999*

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9 9999 9999

9999 999 99 99 99 99 99 which has a high concentration of absorbent polymer, should have sufficient integrity in a state of Partial or complete wetting, so that the physical continuity (and thus the ability to acquire and transport fluid into and through the free space/capillaries) of the absorbent element is not seriously impaired or altered when operated under normal conditions. During normal use, the absorbent cores in absorbent articles are subjected to tensile stresses, as well as torsional forces of varying intensity and in different directions. These stresses and torsional forces cause the crotch layer to bunch and gather, stretch and experience twisting forces during wear, as well as during walking and bending. If the wet integrity is inadequate, these tensile and torsional forces can cause a substantial change and/or disruption of the physical continuity of the absorbent element, such that the ability to acquire and transport fluids into and through adjacent void spaces and capillaries is reduced. The layer containing the absorbent polymer may partially separate, completely separate, contain gaps and regions that are substantially narrowed and/or broken into a plurality of substantially smaller segments. Such a change can minimize, or completely negate, any porosity and permeation/flow conductivity properties of the absorbent polymer.

Good integrity of the zone or layer comprising the absorbent polymer can be achieved, according to the present invention, by various constructions, arrangements, compositions, etc., in an absorbent element with a high concentration of absorbent polymer, other components in the absorbent core (i.e., in the fluid acquisition elements), other components in the absorbent article (i.e., other topsheets and/or backsheets, and combinations thereof). See U.S. Patent 5,562,646, issued to Goldman et al., October 5, 1996.

In the preferred mixed ion exchange base system, the cation exchange components and the anion exchange components tend to adhere to each other. Without wishing to be bound by theory, it is believed that this is due to the opposite charge of polyions and acidic/basic species on the surfaces of the gel polymer particles, which are inherently attracted to the oppositely charged species in neighboring particles. This causes a three-dimensional network of neighboring polymer particles to form in the zone/layer containing the absorbent polymer, greatly increasing the integrity of such zone/layer.

The integrity of the region(s) comprising the polymer blends of the present invention can be measured using the Ball Burst Strength Test (BBS), which will be described later. The BBS test is the force (in grams force) required to rupture a layer of an absorbent polymer blend that is swollen in synthetic urine. The absorbent polymer blend of the present invention will likely, although not necessarily, have a value of

-15BBŠ at least 50 gf, more preferably at least 100 gf, even more preferably at least 150 gf, and most preferably at least 200 gf. Usually the BBS will have a value of from 150 to 400 gf, typically around 200 to 300 gf. c) Design of the absorbent polymer

As previously stated, the desired properties of absorbent polymers according to the present invention are their ability to absorb relatively large amounts of body fluids under pressure (defined as PUP capacity) and their ability to allow the transport of fluids from the receiving area at an acceptable rate (i.e., permeability defined as SFC values). Various embodiments of the present invention will be discussed later in terms of SFC and PUP values. PUP values at 4.8 kPa and 9.6 kPa will be described separately. It should be noted that certain absorbent materials exhibit the described absorbent properties at both 4.8 kPa and 9.6 kPa pressures.

i) SFC with a value of at least 50 x 10' cm sec/g

The present invention includes mixtures of absorbent polymers with SFC values of at least 50 x

10' ⁷ cm ³ sec/g. In these embodiments, the absorbent polymers will have an SFC of at least 70 x 10' ⁷ cm ³ sec/g, more preferably at least 70 x 10 ^{' 7} cm ³ sec/g. Typical absorbent polymers will have an SFC in the range of 50 to 100 x 10' ⁷ cm ³ sec/g, more preferably 60 to 90 x 10' ⁷ cm ³ sec/g, and more preferably 70 to 80 x 10' ⁷ cm ³ sec/g.

The absorbent polymer blends are described, in one aspect, in terms of their ability to absorb synthetic urine at a pressure of 4.8 kPa. Accordingly, the present invention relates to absorbent polymer blends having a PUP capacity in a synthetic urine solution of at least 39 g/g at a pressure of 4.8 kPa after 4 hours. It is preferred that the polymer blend have a PUP capacity in a synthetic urine solution of at least 41 g/g, more preferably at least 43 g/g, more preferably 44 g/g, after 4 hours of exposure to said pressure of 4.8 kPa. Typically, the polymer blend will have a PUP capacity of from 39 g/g to 58 g/g, more preferably from 41 g/g to 55 g/g, and more preferably from 43 g/g to 50 g/g, after 4 hours of exposure to a pressure of 4.8 kPa. In the same aspect, the absorbent polymer blend will have a PUP capacity value in a synthetic urine solution of at least 40 g/g after 8 hours of exposure to a pressure of 4.8 kPa. It is preferred that the absorbent polymer blend have a PUP capacity value of at least 42 g/g, more preferably at least 44 g/g, and most preferably at least 46 g/g after 8 hours of exposure to a pressure of 4.8 kPa. Typically, the polymer blend will have a PUP capacity value in the range of from 40 g/g to 55 g/g, more preferably from 42 g/g to 57 g/g, and most preferably from 44 g/g to 55 g/g, and most preferably from 46 g/g to 52 g/g, after 8 hours of exposure to a pressure of 4.8 kPa. In another similar aspect, the absorbent polymer blend will have a PUP capacity value of at least 42 g/g after 16 hours of exposure to a pressure of 4.8 kPa. It is preferred that the

-16provides that the absorbent polymer mixture has a PUP capacity value of at least 44 g/g, preferably at least 46 g/g, more preferably at least 48 g/g after 16 hours of exposure to a pressure of 4.8 kPa. Typically, the absorbent polymer mixture has a PUP capacity of from 42 g/g to 61 g/g, more preferably from 44 g/g to 59 g/g, more preferably from 46 g/g to 57 g/g, and most preferably from 48 g/g to 54 g/g, after 16 hours of exposure to a pressure of 4.8 kPa.

These embodiments relate to an absorbent polymer blend having a PUP capacity of at least 35 g/g after 4 hours of application of 9.6 kPa pressure. It is preferred that the absorbent polymer blend have a PUP capacity of at least 36 g/g after 4 hours of application of 9.6 kPa pressure, more preferably at least 37 g/g at 9.6 kPa pressure. Typically, the absorbent polymer blend will have a PUP capacity in the range of from 35 g/g to 50 g/g, more preferably from 36 g/g to 45 g/g, more preferably from 37 g/g to 42 g/g after 4 hours of application of 9.6 kPa pressure.

In the same aspect, the absorbent polymer mixture will have a PUP capacity of at least 36 g/g after 8 hours of application of 9.6 kPa pressure. 8 g/g, preferably 40 g/g after 8 hours of application of 9.6 kPa pressure. Typically, the absorbent polymer mixture will have a PUP capacity value in the range of 36 g/g to 54 g/g, preferably 38 g/g to 50 g/g, more preferably 40 g/g to 46 g/g, after 8 hours of application of 9.6 kPa pressure. In another aspect, the absorbent polymer mixture will have a PUP capacity value of at least 37 g/g after 16 hours of application of 9.6 kPa pressure. It is preferred that the absorbent polymer mixture has a PUP capacity value of at least 39 g/g, more preferably at least 41 g/g, after 16 hours of application of 9.6 kPa pressure. Typically, the absorbent polymer blend will have a PUP capacity value in the range of 37 g/g to 56 g/g, more preferably 39 g/g to 52 g/g, more preferably 41 g/g to 48 g/g, after 16 hours of exposure to a pressure of 9.6 kPa.

ii) SFC with a value of at least 500 x lff ⁷ cm ³ sec/g

The present invention also provides an absorbent polymer blend with an SFC value of about

500 x 10' ⁷ cm ³ sec/g. In these embodiments, it would be preferred that the absorbent polymers have an SFC of at least 700 x 10' ⁷ cm ³ sec/g, more preferably about 800 x 10' ⁷ cm ³ sec/g. Typically, the absorbent polymers have an SFC of about 500 x 1100' ⁷ cm ³ sec/g, more preferably about 600 x 1100' ⁷ cm ³ sec/g, more preferably about 700 x 1100 ⁷ cm ³ sec/g.

These absorbent polymer blends are described, in one aspect, in relation to their ability to absorb synthetic urine under a pressure of 4.8 kPa.

In view of the above, the invention relates to an absorbent polymer blend having a PUP capacity in a synthetic urine solution of at least 30 g/g after 4 hours of exposure to a pressure of 4.8 kPa. Typically, the blend will have a PUP capacity in the range of from 30 g/g to 50 g/g, more typically from 35 • ·

• · · · · · · · · · · * · · · · · g/g to 45 g/g, after 4 hours of exposure to a pressure of 4.8 kPa. According to the same aspect, the absorbent polymer mixture may have a PUP capacity in a synthetic urine solution of at least 30 g/g, after 8 hours of exposure to a pressure of 4.8 kPa. It is preferred that the polymer mixture has a PUP capacity of at least 36 g/g, more preferably at least 42 g/g, after 8 hours of exposure to a pressure of 4.8 kPa. Typically, the polymer mixture will have a PUP capacity in the range of 30 g/g to 55 g/g, more typically from 35 g/g to 50 g/g, after 8 hours of exposure to a pressure of 4.8 kPa. According to another of the same aspects, the absorbent polymer mixture will have a PUP capacity of at least 30 g/g, after 16 hours of exposure to a pressure of 4.8 kPa. It is preferred that the polymer blend has a PUP capacity of at least 37 g/g, more preferably at least 45 g/g, after 16 hours of exposure to a pressure of 4.8 kPa. Typically, the polymer blend will have a PUP capacity in the range of from 30 g/g to 58 g/g, more typically from 38 g/g to 53 g/g, after 16 hours of exposure to a pressure of 4.8 kPa.

These embodiments also relate to a polymer blend having a PUP capacity of at least 25 g/g after 2 hours of exposure to 9.6 kPa pressure. The absorbent polymer blend will further have a PUP capacity of at least 27 g/g after 4 hours of exposure to 9.6 kPa pressure. It is preferred that the polymer blend have a PUP capacity of 33 g/g, more preferably 37 g/g, after 4 hours of exposure to 9.6 kPa pressure. Typically, the polymer blend will have a PUP capacity in the range of 27 g/g to 47 g/g, more typically 33 g/g to 42 g/g, after 4 hours of exposure to 9.6 kPa pressure. According to the same aspect, the absorbent polymer blend will have a PUP capacity of at least 27 g/g after 8 hours of exposure to 9.6 kPa pressure. It is preferred that the polymer blend has a PUP capacity of at least 33 g/g, more preferably 39 g/g, after 8 hours of exposure to a pressure of 9.6 kPa. Typically, the polymer blend will have a PUP capacity in the range of 27 g/g to 52 g/g, more typically 33 g/g to 47 g/g, after 8 hours of exposure to a pressure of 9.6 kPa. In another related aspect, the absorbent polymer blend will have a PUP capacity of at least 27 g/g, after 16 hours of exposure to a pressure of 9.6 kPa. It is preferred that the polymer blend has a PUP capacity of at least 34 g/g, more preferably at least 42 g/g, after 16 hours of exposure to a pressure of 9.6 kPa. Typically, the polymer blend will have a PUP capacity in the range of 27 g/g to 55 g/g, more typically 35 g/g to 50 g/g, after 16 hours of exposure to 9.6 kPa pressure.

d. Methods of producing absorbent polymer

The absorbent polymer useful in the present invention may be formed by polymerization and/or crosslinking techniques. Typical processes for making these polymers are described in U.S. Reissue Patent 32,649 (Brandt et al.), issued April 19, 1988, U.S. Patent 4,666,983 (Tsubakimoto et al.), issued May 19, 1987, and U.S. Patent 4,666,983 (Tsubakimoto et al.), issued May 19, 1987.

- 18 (Tsubakimoto et al.), published on November 25, 1986, all of which are incorporated herein by reference.

Polymerization methods for preparing ion exchange polymers suitable for the present invention include free radical, closed chain opening, condensation, anionic, cationic, or irradiation techniques. The polymers may be prepared in neutralized, non-neutralized, or partially neutralized forms, even if the desired product is in the non-neutralized form. The absorbent polymer may be prepared by a homogeneous solution polymerization process, or by multiphase polymerization techniques, such as inverse emulsion or suspension polymerization procedures.

Crosslinking of the polymer can be achieved during polymerization by including suitable monomers with crosslinking capabilities. Alternatively, the polymers can be crosslinked after polymerization by reaction with a suitable crosslinking reagent. Surface crosslinking of the initially formed polymers is a preferred process which provides an absorbent polymer with relatively high PUP capacity, porosity and permeability. Without wishing to be bound by theory, it is believed that surface crosslinking of the polymer increases the resistance to deformation of the surface of the swollen absorbent polymer particles, thereby reducing the degree of contact between adjacent polymer particles when the swollen particles are deformed by external pressure. Surface crosslinked absorbent polymers have a higher level of crosslinking near the surface than inside. The term "surface" as used describes the exterior of the inverted boundary/interface of the particles. For porous absorbent polymers (porous particles, etc.), internal exposed boundaries/interfaces may also be included. By high level of crosslinking near the surface is meant that the level of functional crosslinking of the absorbent polymer near the surface is generally higher than the level of functional crosslinking within the polymer. The gradation of crosslinking from the surface to the interior of the polymer varies, both in depth and in profile.

A number of methods for implementing crosslinking are described in the prior art.

Suitable methods of surface crosslinking include those in which i) di- or polyfunctional agents capable of reacting with existing functional groups in the absorbent polymers are applied to the surface of the absorbent polymer; ii) di- or polyfunctional agents capable of reacting with other added agents and possible functional groups in the absorbent polymer, for example to increase the level of crosslinking at the surface, are applied to the surface (i.e. adding monomer plus crosslinking agent and initiating a second polymerization reaction; iii) no further polyfunctional agents are added, but an additional reaction is induced between existing components of the absorbent polymer, either during or after the primary polymerization process, to generate a higher level of crosslinking at or near the surface (the process

-19• · · * · · · · · · · • · · · · · · · · · · · · · · · 9 9999 999«

9 ·· · · 999 99 9 • « ···· 9999

9999 999 99 99 · · «9 interrupted polymerization, in which the crosslinking agent is inherently present, at a high level near the surface); iv) other materials are added to the surface to induce a higher level of crosslinking, or otherwise reduce the deformability of the surface of the resulting hydrogel. Suitable general methods for carrying out crosslinking of an absorbent polymer, according to the present invention, are disclosed in U.S. Patent 4,541,871 (Obayashi), issued September 17, 1985, in PCT Application WO92/16565 (Stanley) published October 1, 1992, in Patent Application WO90/08789 (Tai) published August 9, 1990, in Patent Application WO93/05080 (Stanley), published March 18, 1993, in U.S. U.S. Patent 4,824,901 (Alexander), issued April 25, 1989, U.S. Patent 4,789,861 (Johnson), issued January 17, 1989, U.S. Patent 4,587,308 (Makita), issued May 6, 1986, U.S. Patent 4,734,478 (Tsubakimoto), issued March 29, 198 Patent 5,164,459 (Kimura et al.) issued November 17, 1992, in German Patent Application 4,020,780 (Dahmen) published August 29, 1991, in European Patent Application 509,708 (Gartner, published October 21, 1992, all of which are incorporated herein by reference. For cationic absorbent polymers, suitable di- or polyfunctional crosslinking agents include di/poly-haloalkanes, di/poly epoxides, di/poly acid chlorides, di/poly-tosyl alkanes, di/poly-aldehydes, di/poly acids, and the like.

C. Testing methods

1. PUP capacity

This test is based on the method described in U.S. Patent 5,599,335 (Goldman et al.) issued February 4, 1997. The test determines the amount of synthetic urine solution absorbed by absorbent polymers (including blends of absorbent polymers with mixed ion exchange bases) that are transversely mounted in a piston/cylinder assembly under a pressure of 4.8 kPa or under a pressure of 9.6 kPa. The objective of this test is to determine the ability of the absorbent polymer to absorb body fluids after a period of time comparable to the period of use (overnight) of products comprising the absorbent polymer blend (i.e., 1, 2, 4, 8, 16 hours), wherein the polymers are present in the absorbent element in high concentration and are subjected to operating pressure. The operating pressure against which absorbent polymers are forced to absorb fluids includes mechanical pressures resulting from the weight and/or movement of the wearer, mechanical pressures from the elastic and fastening system, and hydrostatic desorption pressures from adjacent layers and/or elements.

The test fluid for the PUP capacity test is a synthetic urine solution. The fluid is absorbed by the absorbent polymer under the desired absorption conditions and under the influence of almost zero hydrostatic pressure.

-20• · · · · · « • · · · · ·* · · ·· · «

A suitable apparatus for this test is shown in Fig. 1. At one end of this apparatus is a tank 712 (like a petri dish) with a lid 714. The tank 712 rests on an analytical balance 716. At the other end of the apparatus 710 is a fritted funnel 718, a piston/cylinder assembly 720 that fits into the funnel, and a cylindrical fritted funnel lid 722 that tightly covers the funnel 718, which is open at the bottom and closed at the top, where a small hole is formed in the upper part. The apparatus 710 includes an omnidirectional fluid delivery system consisting of a section of glass tubing 724 and 731a, a flexible plastic tubing 731b (1/4 inch and 3/8 inch Tygon brand tubing), a stopcock assembly 726 and 738, and Teflon® connectors 748, 750, and 752 that connect the glass tubing 724, 731 and the stopcock assembly 726, 738. The stopcock assembly 726 consists of a three-way valve 728, a glass capillary tube 730, 734 located in the main fluid system, and a section of glass capillary tube 732 used to drain the tank 712 and to forward rinse the fritted disc in the fritted funnel 718. The stopcock assembly 738 similarly It includes a three-way valve 740, glass capillary tubes 742 and 746 in the main fluid line, and a section of glass capillary tubes 744, which serve to drain fluids from the system.

The assembly 720 shown in Fig. 1 consists of a cylinder 754, a cup-shaped piston 756, and a weight 758 located inside the piston 756. A mesh 759 of 400 stainless steel is attached to the bottom of the cylinder 754 and is stretched in the collection of two axes before being attached.

A mixture of absorbent polymer 760 is placed on the mesh 759. The cylinder 754 is formed by boring a rod of transparent Lexan® (or equivalent) to an inner diameter of 6.0 cm (area of 28.27 cm ² ), with a wall thickness of approximately 5 mm and a height of approximately 5 cm. The piston 756 is a Teflon® or Kel-F® cup shaped and machined to fit snugly within the cylinder 754, with a gap between the cylinder and the piston ranging from 0.114 to 0.191 mm. The cylindrical stainless steel weight 758 is formed to fit snugly within the piston 756 and is provided with a handle on the top for easy removal from the piston. To achieve a pressure of 4.8 kPa, the combined mass of piston 756 and weight 758 is 1390 g, which corresponds to a pressure of 9.6 kPa over an area of 28.27 cm ² . To achieve a pressure of 9.6 kPa, the combined mass is 2780 g.

The components of the device 710 are sized such that the flow rate of synthetic urine through the fritted disc components of the fritted funnel 718, at a hydrostatic head of 10 cm, is 36 g/hr/cm ² . Factors that significantly affect the flow rate include the permeability of the fritted disc in the fritted funnel 718, as well as the inner diameters of the glass tubes 724, 730, 734, 742, and 731a, and the valves of the stopcocks 728 and 740.

« 4

• · 4 4 4 9 9 9 • 494 ·»«· • · ·· · · · ·

The tank 712 is placed on an analytical balance 716 (with an accuracy of 0.01 g and a drift of less than 0.1 g/hr). The balance is connected to a computer that has software that can: i) monitor changes in weight at predetermined intervals, starting from the beginning of the PUP test; ii) set the automatic initialization of data collection at changes of 0.01 - 0.05 g, depending on the sensitivity of the balance. The tube 724 entering the tank 712 should not touch the bottom of the tank or the lid 714. The volume of liquid in the tank 712 should be large enough to prevent air from entering the tube 724 during the measurement. The liquid level in the reservoir 712 should be 2 mm below the top surface of the fritted disk of the fritted funnel 718 at the start of the measurement. This can be accomplished by placing a small amount of drops on the fritted disk and gravimetrically monitoring the flow of this amount of liquid back into the reservoir 712. The level should not change significantly when the piston/cylinder assembly 720 is positioned within the funnel 718. The reservoir 712 should be of a sufficiently large diameter (about 14 cm) that removing about 40 ml of liquid will result in a change in level of less than 3 mm.

Before measurement, the assembly is filled with synthetic urine solution and the fritted disc of the fritted funnel is rinsed by filling it with fresh synthetic urine solution. If possible, bubbles are removed from the bottom surface of the fritted disc and from the system connecting the funnel to the tank. The following procedures are performed using sequential operations of the three-way stopcock:

1. Remove excess liquid on the top surface of the fried disc from the fried funnel 718.

2. The height/weight of the solution in tank 712 is set to the correct level/value.

3. The 718 frit funnel is placed at the correct height relative to the tank.

4. The fryer hopper 718 is covered with the fryer hopper lid 722.

5. Tank 712 and frit hopper 718 are balanced by valves 728 and 740 of tap assembly 726 and 738 in the open state.

6. Valves 728 and 740 close.

7. Valve 740 is rotated so that the funnel opens towards the drain pipe 744.

8. The system is allowed to balance in this position after 5 minutes.

9. Valve 740 returns to the closed position.

Steps 7-9 temporarily dry the surface of the fritted funnel 718 by applying a small hydrostatic suction of -5 cm. This suction is achieved when the open end of the tube 744 is brought 5 cm below the level of the fritted disc in the fritted funnel 718 while it is filled with synthetic urine. Typically, 0.2 g of fluid is removed from the system during this procedure. This procedure will prevent premature absorption of the synthetic urine if the assembly is

9

·· ·· • · · · • · · ·

9 9 9

99 piston/cylinder 720 located inside the fritted funnel 718. The amount of fluid that drains from the fritted funnel during the procedure (called the fritted funnel correction weight) is measured in the PUP test (see below) for 15 minutes without the piston/cylinder assembly 720. Any fluid drained from the fritted funnel during the procedure is very quickly reabsorbed by the frit at the start of the test. Therefore, it is necessary to subtract this correction weight from the weight of fluid removed from the tank during the PUP test (see below).

The absorbent polymer mixture 760 is dried by suitable methods, such as high vacuum drying, at a temperature and for a sufficient time to reduce the amount of moisture as determined by appropriate techniques, such as Karl Fischer titration or thermogravimetric analysis, to less than 5%, preferably less than 3%. Approximately 0.9 g (W _ap ) of the dried absorbent polymer mixture 760 (corresponding to a basis weight of 0.032 g/cm ² ) is added to the cylinder 754 and evenly distributed over the said mesh 759. Care is taken to prevent the absorbent polymer 760 from adhering to the inner walls of the cylinder 754. The piston 756 is inserted into the cylinder 754 and placed on the surface of the absorbent polymer 760, taking care to allow the piston to slide freely within the cylinder. The piston can be rotated slightly to help distribute the absorbent polymer. The piston/cylinder assembly 720 is placed on top of the fritted portion of the funnel 718, the weight 758 is inserted into the piston 756, and the top of the funnel 718 is covered with the fritted funnel lid 722. Once the equilibrium condition is established, the test is started by opening valves 728 and 740, thereby connecting the funnel 718 to the reservoir 712. When automatic start is selected, the data appears immediately as the funnel begins to absorb fluid again.

The weight of the fluid remaining in the tank 712 is recorded at certain time intervals throughout the duration of the test. The PUP capacity is calculated at any time t according to the following equation:

PUP capacity(g/g, t) = [W _r (t=0) - Wf _c ] / W _ap , where W _r (t=0) is the weight in grams of the tank 712 before its installation, W _r (t) is the weight of the tank in grams after the passage of time t (1,2, 4, 8,16 hours), Wf _c is the correction weight of the fritted funnel in grams (measured separately), and W _ap is the initial dry weight in grams of the absorbent polymer.

2. BBS test

This test determines the ball burst strength of an absorbent polymer blend. BBS represents the force (peak load in gram force) required to rupture a layer of absorbent polymer blend that has been swollen in a synthetic urine solution according to the procedures

-23• ** ·· ·· ·· ♦ ·· * * · ♦ ♦ ♦ » · 9 9 9 99 9 9 9 9 specified in the test method chapter. BBS is a measure of the integrity of the absorbent polymer blend layer in the swollen state.

A suitable apparatus for performing BBS measurements is shown in Fig. 5. This apparatus includes an inner cylinder 270, which is used to accommodate the absorbent polymer layer 260, an outer cylinder 230, a Teflon flat bottom pan 240, an inner cylinder cover plate 220, and a stainless steel weight 210. The inner cylinder is made by drilling a rod of transparent Lexan® and has an inner diameter of 6.0 cm (area 28.27 cm ² ) and a wall thickness of about 0.5 cm and a height of about 1.5 cm. The outer cylinder 230 is also made by drilling a rod of Lexan® and has an inner diameter that is slightly larger than the outer diameter of the inner cylinder 270, so that the inner cylinder fits into the outer cylinder 230, where it can slide freely. The outer cylinder 230 has a wall thickness of about 0.5 cm and a height of about 1.0 cm. The bottom of the outer cylinder 230 is covered with a 400 stainless steel mesh 250, which is stretched in the direction of two axes before being attached to the bottom of the cylinder. The cover plate of the inner cylinder 220 is made of a 0.8 cm thick glass plate, which has a weight of 500 g. The stainless steel weight has a weight of 1700 g.

This type of test uses a tensile testing machine with a test load cell (available as the Intelect-II-Std Tensile Tester manufactured by Thwing-Albert Instrument Co., Pennsylvania). As shown in FIG. 6, the apparatus includes a load cell sensitive to applied force 330. which is equipped with a polished ball-shaped probe 290, a movable crosshead 320, a stationary crosshead 310, a circular lower pressure plate 280, and an upper clamping pressure plate 300, which is used to pneumatically clamp a sample 260. The lower clamping pressure plate 280 is mounted on the stationary crosshead 310. Both pressure plates 280, 300 have a diameter of 115 mm. a thickness of 2.9 mm and a circular hole of 18.65 mm. The stainless steel ball-shaped probe 290 has a diameter of 15.84 mm. During the BBS test procedure, the movable crosshead 320 moves upward, resulting in the probe 290 contacting the sample 260 and then the sample When the probe penetrates the sample, the test is considered complete and the relevant data is recorded.

The sampling device shown in Fig. 5 shows that the inner cylinder 270 is inserted into the outer cylinder 230. A 1.0 g sample of the absorbent polymer mixture is placed into the inner cylinder 270 where it is uniformly dispersed on the 400 mesh stainless steel screen 250. The assembled absorbent polymer cylinders are transferred to a flat Teflon bottom pan 240, and the inner cylindrical bottom plate is placed on the inner cylinder 270. 30.0 ml of synthetic urine solution is poured into the flat Teflon pan 240. The synthetic urine solution passes through the stainless steel screen and is absorbed by the absorbent polymer mixture 260. A stainless steel weight 210 is placed on the cover plate of the inner cylinder 220 five minutes after the addition of the liquid. After

-24After another 25 minutes, the weight 210 and the cover plate of the inner cylinder 220 are removed. For the entire procedure to be valid, the entire amount of synthetic urine solution must be absorbed by the absorbent polymer mixture after the aforementioned time. The inner cylinder 270 with the layer of swollen absorbent polymer 260 is immediately transferred to the test device to perform the BBS measurement.

In the test apparatus shown in Fig. 6, an inner cylinder 270 with a swollen layer of absorbent polymer 260 is centrally located on a lower clamping pressure plate 280 and is pneumatically connected to an upper clamping pressure plate 300. The measurement is made at a tear sensitivity of 10.00 g and a test speed of 12.7 cm/min. The measurement is started by moving the crosshead 320 upward until the polished stainless steel spherical probe 290 penetrates the gel layer of absorbent material 260. Once the sample rupture is registered, the moving crosshead 320 returns to its starting position. BBS is expressed as the peak load in grams force. The average of the three measurements is given as the BBS for a given absorbent polymer blend.

3. Saline Conductivity (SFC)

Permeability measurements and porosity indications are made by means of the conductivity of a saline solution of the gel base, as described in U.S. Patent 5,562,646 (Goldman et al.) issued October 8, 1996. This method is modified for mixed ion exchange base absorbent polymer systems, as will be described later.

It is assumed that the absorbent polymer sample, with a mixed ion exchange base, continues to ion exchange from the saline solution during the SFC measurement. Eventually, the ion exchange capacity of the absorbent polymer is exceeded and the ionic strength of the solution surrounding the swollen polymer increases, resulting in some reduction in the swelling of the gel base. The amount of fluid expelled from the gel due to the reduction in swelling is small compared to the amount of fluid flowing through the gel base during the SFC measurement. Since the final thickness of the gel base is significantly less than the initial thickness, the final thickness of the gel base is used to calculate the SFC values. Using the final thickness of the gel base in the calculation provides the minimum SFC values achieved during the measurement.

Although SFC is not a direct measure of porosity, high fluid permeability in a particulate absorbent polymer system also requires a high degree of porosity. Thus, a relatively high SFC value for a mixed ion exchange-based absorbent polymer blend also indicates a relatively high level of porosity.

-259 99 9

• 9 9 99

99 • 9 9 9

9 9 9

9 9 9 • 9 9 9

99

D. Absorbent elements

The absorbent elements of the present invention include the previously described blends of absorbent polymers, with or without other optional components, such as fibers, thermoplastic materials, and the like. Preferred materials are described in detail in paragraph 23, line 13 to paragraph 29, line 16, of U.S. Patent 5,562,646 (Goldman et al.). These absorbent elements comprising these absorbent polymers can function as fluid storage elements in an absorbent core. The primary function of such fluid storage elements is to absorb liquid body exudates, either directly or from other absorbent elements (elements that receive and distribute the fluid), and to contain them even when subjected to pressures caused by the wearer's movements. It is to be understood that absorbent elements comprising such an absorbent polymer can have functions other than fluid retention.

In a preferred embodiment, the absorbent elements of the present invention comprise one or more regions with a relatively high concentration of these absorbent polymers. In order to provide relatively thin absorbent articles capable of absorbing and retaining large amounts of body fluids, it is desirable to maximize the level of these absorbent polymers and minimize the level of other components, particularly fibrous components.

To maintain these absorbent polymers at a high concentration, it is important that these polymers have a relatively high required absorbent capacity under relatively high pressure (PUP capacity) and a high pressure-to-fluidity (SFC). This is so that the polymer, when swollen in the presence of fluid, provides adequate capacity to receive body fluids, transport them through zones or layers with a relatively high gel concentration to other areas of the absorbent element and/or absorbent core, and/or retain these fluids.

When measuring the concentration of the absorbent polymer blend in a given area of the absorbent element, the weight percentage of the absorbent polymer relative to the combined weight of the absorbent polymer and other components (fibers, thermoplastic material, etc.) present in a given area of the absorbent element. The concentration of the absorbent polymer blend in a given area of the absorbent element, according to the present invention, has a value in the range of from 40 to 100%, or from 90 to 100%. In general, the higher the concentration of the absorbent polymer, the thinner and less bulky the absorbent element.

E. Absorbent cores and absorbent products

The absorbent polymer blends of the present invention can be used as a conventional absorbent polymer in any absorbent core and/or absorbent article that

Or · · · * ·♦ «a ^w ZO · ·«···«♦** • * ·····« ···· ··♦ ·· ·· ·* used to absorb body fluids, as described in U.S. Patent 5,562,646 to Goldman et al. This patent describes absorbent cores in detail in paragraph 52. line 24, as well as absorbent articles in paragraph 52, line 25 to paragraph 54, line 9. Such articles include diapers, menstrual products and/or adult incontinence products. By substituting conventional absorbent polymers with mixed ion exchange base absorbent polymers of the same weight, articles with increased absorbent capacity can be obtained. Alternatively, a low weight absorbent polymer can be substituted without increasing the absorbent capacity of the article, but a lighter, thinner and less bulky article can be obtained.

The incorporation of the absorbent polymer of the present invention into any of the products already described will be apparent to one skilled in the art. Such products are characterized by features such as breathability of the backsheet, hook/loop fasteners (Velcro), a bicomponent fibrous matrix, and the like.

Absorbent articles may include absorbent polymer blends described and disclosed, for example, in U.S. Patent 3,224,926 (Bemardin), issued December 21, 1965, in U.S. Patent 3,440,135 (Chung), issued April 22, 1969, in U.S. Patent 3,932,209 (Chatteijee), issued January 13, 1976, in U.S. Patent 4,035,147 (Sangenis et al.), issued July 12, 1977. More preferred reinforced fibers are disclosed in U.S. Patent 4,822,453 (Dean et al.), issued April 18, 1989, U.S. Patent 4,888,093 (Dean et al.), issued December 19, 1989; U.S. Patent 5,137,537 (Herrow et al.), issued April 11, 1992; U.S. Patent 4,818,598 (Wong), issued April 4, 1989; U.S. Patent 5,562,646 (Goldman et al.), issued October 8, 1996; U.S. Patent 5,217,445 (Young et al.), issued June 8, 1993; U.S. Patent 5,360,420 (Lash et al.), U.S. Patent Application Serial No. 08/153,739 (Dragoo et al.), filed November 16, 1996. 1993, in the U.S. in U.S. Patent Application Serial No. 08/164,049 (Dragoo et al.), filed December 8, 1993, in U.S. Patent 4,260,443 (Lindsay et al.), in U.S. Patent 4,467,012 (Pedersen et al.), issued August 21, 1984, in U.S. Patent 4,715,918 (Lang), issued December 29, 1987, in U.S. Patent 4,851,069 (Packard et al.), issued July 25, 1989, in U.S. Patent 4,950,264 (Osborn), issued August 21, 1990, in U.S. Patent 4,994,037 (Bernardin, issued February 19, 1991 1991, in U.S. Patent 5,009,650 (Bernardin), issued April 23, 1991, in U.S. Patent (Osborn), issued April 23, 1991, in U.S. Patent 5,128,082 (Makoui), issued July 7, 1992, in U.S. Patent 5,149,335 (Kellenberger et al.), issued September 22, 1992, in U.S. Patent 5,176,668 (Bernardin), issued January 5, 1993, in U.S. Patent Application 141,156 (Richards et al.), filed October 21, 1993, in U.S. Patent 4,429,001 (Kolpin et al.), issued January 31, 1984, in U.S. patent application 07/794,745

99

9

-279 «·«

9 99 • 9 9

9 9

9 Φ

9 9 9 9

99 (Aziz et al.), filed on November 19, 1991, all of which are included for comparison.

F. Specific examples

A slightly crosslinked, partially neutralized absorbent polymer poly (acrylic acid) with a relatively high PUP capacity (33 g/g at 4.8 kPa, 60 minutes) is available from Chemdal Corporation of Palantine, Illinois (ASAP-2300 Stock No. 426.152). (Similar samples to AS/PA-2300 are available from The Procter & Gamble CO., Paper Technology Division, Cincinnati, OH.) This material serves as a control and is referred to herein as the "Control Sample".

A sample of absorbent polymer that provides enhanced integrity over conventional polyacrylate absorbent polymers is available from Nippon Shokubai (stock # TN37408). It is a polyacrylate surface-treated with polyethyleneimine. The polymer is described in detail in U.S. Patent 5,382,610 filed January 17, 1995. This material is referred to herein as "sample ST".

Example 1

Preparation of ion-exchanged absorbent polymers

i) Cation exchange absorbent polymer

In the preparation of cation exchange absorbent polymer, a portion of the control sample is sieved through a U.S.A. standard 50 sieve to remove particles larger than 300 μ in diameter. About 50 g of the sieved absorbent polymer with particles smaller than 300 μ is converted to the acid form by dissolving the polymer in a dilute hydrochloric acid solution prepared by adding about 46.5 g of concentrated HCl (Baker, 36.5-38% HCl) to 900 ml of distilled deionized water. The suspension is stirred gently for about 1.5 hours, after which time the absorbent polymer is allowed to settle and the liquid is removed by decanting. The removed liquid is replaced with an equal volume of distilled deionized water, the suspension is stirred gently for about an hour, the absorbent polymer is allowed to settle and the liquid is removed again. The exchange process is repeated (about eight times) with the same volume of distilled and deionized water until the pH of the removed water reaches a value of 5-6. The exchange process is then repeated three times with isopropanol (VWR reagent grade, West Chester, PA), three times with acetone (VWR reagent grade), and once with anhydrous ether (EM Science reagent grade, Gibbstown, NJ). The product is gently spread onto a polytetrafluoroethylene sheet and allowed to dry overnight. After being gently disturbed with a spatula, the product is dried under high vacuum for 96 hours at room temperature to remove any residual solvents. The sample is sieved

-28 through a U. S. A. 20 sieve, thereby removing any larger particles or agglomerates. Approximately 30 g of crosslinked ion-exchanged poly(acrylic acid) absorbent polymer is obtained, which is stored in a dry atmosphere (sample PAA).

ii) Anion exchange absorbent polymer

A colorless polyethyleneimine with an average molecular weight of 750,000 g/mol was obtained as a 50% aqueous solution from Aldrich Chemical Co., Milwaukee, Wisconsin (catalog number 18,917-8, part number 12922PQ). 20 grams of this solution was further diluted with 37 grams of distilled water and stirred for 30 minutes in a 250-ml beaker to achieve complete dissolution. Ethylene glycol diglycidyl ether (50% solution) in an amount of 2.14 g was added to the polyethyleneimine solution, the resulting mixture was stirred at room temperature for approximately two minutes and then placed in a ventilated oven at 65°C for about three hours. The resulting gel was allowed to cool and then crushed into smaller pieces about 1 to 5 mm in diameter. The mixture is transferred to a 4000 ml beaker containing two litres of distilled water and stirred overnight. The excess water is removed and the remaining sample is dried under high vacuum for approximately 96 hours to obtain a lightly crosslinked polyethylenimine absorbent polymer with a mixed ion exchange base which is stored in a dry atmosphere (sample ΒΡΕΙ).

iii) Absorbent polymer with mixed ion exchange base

The crosslinked anion exchange absorbent polymer (sample ΒΡΕΙ) is cooled to low temperature and sieved in dry nitrogen. The individual particles of the size fraction are collected and sieved through a U.S. A standard 25 sieve, but not through a U.S. A standard 70 sieve (i.e., the fraction with particles with a diameter in the range of 200 to 700 μ).

Approximately equal weights of a crosslinked cation exchange poly(acrylic acid) absorbent polymer (sample PAA) are mixed with a crosslinked anion exchange polyethyleneimine absorbent polymer (sample ΒΡΕΙ) to ensure uniform particle distribution of both polymer types in the mixture. The resulting mixture comprises a mixed ion exchange base absorbent polymer blend (sample MB-1) according to the present invention.

iv) PUP capacity measurement

Approximately 0.9 g of mixed ion exchange base absorbent polymer (sample MB-1) is transferred to a PUP cylinder (described in the “Test Method” section) and gently

-299· ♦ 9 4 9· * 9 99 9 9 9 9

9 9 9 99

9 9 9 9 9 9 • · 9 9 9 9

9*99 999 9» 99 spread over the entire surface of the sieve including the base of the cylinder. PUP capacities are determined on individual samples at pressures of 4.8 and 9.6 kPa, with the amount of fluid absorbed measured at regular intervals over a period of 16 hours. The measured PUP capacities at pressures of 4.8 and 9.6 kPa are shown as a function of time in Figs. 3 and 4. Selected data values after 2, 4, 8 and 16 hours are given in Table 1.

Table 1

PUP capacities of absorbent polymer blends

4.8 kPa 4 hours 4.8 kPa 4 hours 4.8 kPa 4 hours 9.6 kPa 2 hours 9.6 kPa 8 hours 9.6 kPa 16 hours Sample MB-1 44/g 48 g/g 50 g/g 32 g/g 40 g/g 42 g/g Control sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g 20 g/g

Comparison of PUP capacities indicates that the blends of the absorbent polymer with the mixed ion exchange base (sample MB-1) show approximately 100% increase in PUP capacity at a pressure of 9.6 kPa and approximately 40% increase in PUP capacity at a pressure of 4.8 kPa after 8 hours, relative to the capacities of partially neutralized polyacrylate absorbent polymers under analogous test conditions (control sample).

v) Permeability measurement

The permeability measurement and porosity indication are provided by the SFC of the gel base, as described in U.S. Patent 5,562,646 (Goldman et al.) issued October 8, 1996. This method is modified for mixed ion exchange absorbent polymer systems, as previously described in the section, "Test Methods". Approximately 0.9 g of the mixed ion exchange absorbent polymer blend (Sample MB-1) is transferred to a cylinder designed for measuring saline conductivity (SFC) and spread gently over the entire surface of the screen comprising the cylinder base. The SFC values are given in Table 2.

-30• tititi

Table 2

SFC values of absorbent polymer blends

SFC values Sample MB-1 ~ 68 x 10 ^z cm ³ sec/g Control sample ~ 10 x 10' ⁷ cm ³ sec/g

Comparison of SFC values shows that the porosity and permeability of the mixture of absorbent polymer with mixed ion exchange base (sample MB-1) is significantly greater than that of partially neutralized absorbent polyacrylate polymer (control sample), under analogous testing conditions vi) Integrity of gel base

The measurement of the integrity of the absorbent polymer mixture layer in the swollen state is performed using the BBS test, as already mentioned. The values of this BBS test for sample MB-1, sample ST and the control sample are given in Table 3.

Table 3

BBS values of the absorbent polymer blend with mixed ion exchange base

BBS Sample MB-1 225 gf ST sample 133 gf Control sample 17 gf

A comparison of the BBS test values in Table 3 shows that the mixture of the absorbent polymer with the mixed ion exchange base (sample MB-1) exhibits a significantly increased gel layer integrity value when compared to the values of the partially neutralized absorbent polymer acrylate (control sample) and sample ST, under analogous test conditions.

φφφ

-31• ΦΦΦ φ ♦ » ·< ·· φ» φφφφ φφφφ • φ ·· φφφφ ···· φφφφ φφ φφ φφ φφ

Example 2 i) Cation exchange absorbent polymers

The cation exchange absorbent polymer is prepared as described in Example 1, section i), (sample PAA).

ii) Anion exchange absorbent polymer

a) Preparation of crosslinked polyallylamine

Polyallylamine hydrochloride with a nominal average molecular weight of 60,000 g/mol is available from Polysciences, Inc. Warrington, Pennsylvania (catalog number 18378, part number 455913). A solution of polyallylamine hydrochloride is prepared by dissolving 16.4 g of the polymer in 165 ml of distilled water. 15.6 g of 50% aqueous sodium hydroxide solution is added dropwise with constant stirring. Ethylene glycol diglycidyl ether (50% solution), 2.0 g (Aldrich Chemical Co., cat. no. E2,720-3, part number 07405DN) is then added to the polyallylamine solution with constant stirring for two minutes at room temperature, and the resulting solution is placed in a ventilation oven at a temperature of approximately 65°C and left there for about three hours. The resulting gel is crushed into smaller pieces of 5 mm diameter and transferred to a 4000 ml beaker containing 1 litre of distilled water. The mixture is gently mixed and the excess liquid is poured off. The remaining sample is dried under high vacuum at room temperature for approximately 96 hours to obtain a lightly crosslinked polyallylamine anion exchange absorbent polymer, which is stored in a dry atmosphere.

b) Methylation of the PAAM sample

To 800 g of distilled water, add formic acid (96% solution), 21.02 g (Aldrich Chemical Co., catalog number 25.136-4), formaldehyde (37% solution), 36.56 g (Aldrich Chemical Co., catalog number 25.254-9, part number 04717TZ). 10 g of cross-linked polyallylamine (sample PAAM) is added to the solution and the new mixture is placed in an oven at 70°C for 24 hours. The gel is drained and stirred overnight in 1000 ml of water to remove the extractants. The slurry is drained and replaced with one liter of 1.7% aqueous sodium hydroxide solution to remove excess formic acid from the gel. The mixture is left to stand for about 24 hours and the polymer is decanted. The process is repeated (usually three times) with one liter of 1.7% aqueous sodium hydroxide solution until a pH of 13 is reached. The gel is treated by vacuum filtration and

-32» « * · · · « • · · · · · · · · · « « φ • · · · · · · · · 9 • · * · · · ··· ··*· ··* ♦« «· ·♦ ·· is soaked in 3000 ml of water overnight. The excess water is removed and the sample is dried under high vacuum at room temperature for approximately 96 hours to yield a lightly crosslinked tertiary polyallylamine anion exchange absorbent polymer, which is stored in a dry atmosphere. NMR spectroscopic analysis indicates that approximately 90% of the amine groups in the polymer are methylated groups, which form tertiary amine moieties (sample tPAAM).

iii) Absorbent polymer with mixed ion exchange base

The cross-linked tertiary polyallylamine anion exchange absorbent polymer (sample t-PAAM) is frozen and sieved under a dry nitrogen atmosphere. The fraction with a certain particle size that passes through a U.S.A. Series Standard 25 sieve but does not pass through a U.S.A. Series Standard 70 sieve (i.e., the fraction with particles with a diameter ranging from 200 to 700 μ) is collected.

Approximately 0.29 grams of a screened blend of a crosslinked cation-exchange poly(acrylic acid) absorbent polymer (sample PAA) and 0.71 grams of a screened crosslinked tertiary-polyallylamine anion-exchange absorbent polymer (sample t-PAAM) are mixed and the resulting mixture is spread so that both types of polymer particles are evenly distributed throughout the mixture. The mixture contains a mixed ion-exchange base absorbent polymer (sample MB-2 of the present invention).

iv) PUP capacity measurement

Approximately 0.9 grams of the mixed ion exchange base absorbent polymer blend (sample MB-2) is transferred to the PUP cylinder (as described in the "Test Methods" section) and gently spread over the entire surface of the screen comprising the cylinder base. The PUP capacities are determined for individual samples at pressures of 4.8 and 9.6 kPa, with the amount of fluid absorbed being measured at regular intervals over a period of 16 hours. The measured PUP capacities at pressures of 4.8 and 9.6 kPa are shown as a function of time in Figures 3 and 4.

Selected capacity values at times 2,4, 8,16 hours are shown in Table 4.

-33·· « • · ·· »· ·· »* ·» ···* · · · · • · ·· » · · f ·>** » ·· · · ·· · ♦ * ·· ·· ♦ »

Table 4

PUP capacities of absorbent polymer blends

4.8 kPa 4 hours 4.8 kPa 8 hours 4.8 kPa 16 hours 9.6 kPa 2 hours 9.6 kPa 8 hours 9.6 kPa 16 hours Sample MB-2 41 g/g 43 g/g 44 g/g 33 g/g 40 g/g 42 g/g Control sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g 20 g/g

A comparison of PUP capacities shows that blends of the absorbent polymer with a mixed ion exchange base (sample MB-2) absorb significantly more synthetic urine solution than the partially neutralized polyacrylate absorbent polymer (control sample), under the test conditions already described.

Example 3

i) Cation exchange absorbent polymer

The cation exchange absorbent polymer is prepared as described in Example 1, section i), (sample PAA) ii) Anion exchange absorbent polymer a) Preparation of linear polyethylenimine

Poly(2-ethyl-2-oxazoline) with a nominal average molecular weight of 500,000 g/mol can be obtained from Aldrich Chemical Co., Milwaukee, Wisconsin (cat. no. 37,397-4, part no.

17223HB). 100 grams of the sample of poly(2-ethyl-2-oxazoline) are dissolved in a hydrochloric acid solution prepared by mixing 1000 ml of water and 200 ml of concentrated hydrochloric acid. The solution is dewatered at 100°C for 72 hours and then cooled to room temperature. The product is obtained by settling the solution by adding 256 ml of 50% sodium hydroxide solution dropwise with constant stirring. The white solid precipitate is vacuum filtered and washed with 5000 ml of water. The product is freeze-dried for 48 hours to obtain linear polyethyleneimine.

-34«· • φ

9999

• 99 99 ΦΦ 99 ♦ · Φ Φ * 9 9 9 9 9 • 9 Φ 99 • · 9 Φ 9 999 Φ • · • Φ * »· 9 » 99 9 Φ • Φ

b) Preparation of cross-linked linear polyethyleneimine

5.0 grams of linear polyethyleneimine prepared as previously described was dissolved in 50 ml of methanol. Ethylene glycol diglycidyl ether (50 solution), 0.5 g (Aldrich Chemical Co., Cat. No. E2,720-3, Part No. 07405DN) was added to the linear polyethyleneimine solution, the mixture was stirred at room temperature for approximately two minutes, and then placed in a ventilated oven at approximately 65°C for three hours. The resulting gel was crushed into particles of about 5 mm diameter and gently stirred in 500 ml of methanol overnight. The sample was de-liquidated, dried under high vacuum for approximately 48 hours to yield a lightly crosslinked polyethyleneimine anion exchange absorbent polymer, which was stored in a dry atmosphere (sample LPRI-1).

c) Partial methylation of cross-linked polyethyleneimine

5.37 grams of linear polyethyleneimine are dissolved in 45 g of methanol. Ethylene glycol diglycidyl ether (50% solution), 1.07 grams (Aldrich Chemical Co., cat. no. E2.7820-3, part no. 07405 DN) is added to the linear polyethyleneimine solution, the resulting mixture is stirred at room temperature for approximately two minutes, then placed in a ventilated oven at a temperature of about 65°C for three hours. The resulting gel is crushed into particles with a diameter of about 5 mm, and then stirred in 500 ml of methanol overnight. The sample is drained and dried under high vacuum for 48 hours, thereby obtaining a lightly crosslinked polyethyleneimine anion exchange absorbent polymer, which is stored in a dry atmosphere (sample LPEI-2).

Formic acid (96% solution), 48.44 grams ((Aldrich Chemical Co., cat. no. 25,136-4), formaldehyde (37% solution), 81.17 grams (Aldrich Chemical Co., cat. no. 25,254-9) were added to 370.39 grams of distilled water to give 500 grams of complete solution. 46.98 grams of this solution was added to 5.37 grams of crosslinked linear polyethyleneimine (sample LPEI-2). This mixture was diluted with 450 ml of distilled water and placed in an oven at 70°C for 24 hours. The gel was drained and stirred in 2500 ml of water overnight to remove the extractants. The supernatant was removed and replaced with 20 ml of 50% aqueous sodium hydroxide solution to remove excess acid from the gel. formic. The mixture is allowed to settle for about three hours, the polymer is removed from the supernatant. The process is repeated (approximately three times) with 20 ml of 50% aqueous sodium hydroxide solution until a pH of 13 is reached. The gel is treated by vacuum filtration and allowed to soak in 1000 ml of water overnight. The supernatant liquid is removed and replaced with 500 ml of tetrahydrofuran. After 24 hours, the tetrahydrofuran is removed and replaced with 500 ml of anhydrous ether. After 24 hours, the ether

99 9 • 9 99 99 99 • 9 ·· • 9 9 O 9 9 9 «1 • • • • 99 « 9 9 9 9 9 • • 9 • 9 9 9 9 9 9 ···· ··· 9« 99 49 99

removed and the gel dried under high vacuum at room temperature for 48 hours.

NMR spectroscopic analysis of the product indicated that approximately 65% of the amine groups in the polymer were methylated, thereby forming tertiary amine moieties (sample NMEI-65).

iii) Absorbent polymers with mixed ion exchange base

Cross-linked linear polyethyleneimine and poly(N-methylethyleneimine) anion exchange absorbent polymers (samples LPEI-1 and NMEI-65) are separately frozen and sieved under dry nitrogen. The size fractions of individual materials that pass through a U.S.A. Senes Standard 25 sieve but do not pass through a U.S.A. Series Standard 70 sieve (i.e., the fractions with particle diameters between 200 and 700 μ) are collected.

Approximately one gram of each of the screened crosslinked absorbent polymers (samples LPEI-1 and NMEI-65) are separately blended with one gram of the screened crosslinked cation exchange poly(acrylic acid) absorbent polymer (sample PAA) such that the particles of each polymer type are evenly distributed throughout the blend. Each blend comprises a mixed ion exchange base absorbent polymer blend (samples MB-3a and MB-3b) according to the present invention.

iv) PUP capacity measurement

Approximately 0.9 grams of the mixed ion exchange base absorbent polymer blend (samples MB-3a and MB-3b) is transferred to separate PUP cylinders (as described in the “Testing Methods” section) and gently spread over the entire surface of the screen including the cylinder base. PUP capacities are determined for individual samples by applying pressures of 4.8 kPa and 9.6 kPa and measuring the absorbed fluid at given intervals for a period of 16 hours. The measured PUP capacities at pressures of 4.8 and 9.6 kPa are shown as a function of time in Figs. 3 and 4. Selected PUP capacity values at times 4, 8 and 16 hours are given in Table 5.

Table 5

PUP capacities of ion-exchange absorbent polymer

4.8 kPa 4.8 kPa 4.8 kPa 9.6 kPa 9.6 kPa Sample MB-3a - - - 32 37 Sample MB-3b 39 g/g 42 g/g 43 g/g - - Control pattern. 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g

Comparison of PUP capacity values indicates that the mixed ion exchange base absorbent polymer blends (samples MB-3a and MB-3b) absorb significantly more synthetic urine solution than the partially neutralized polyacrylate absorbent polymer (control sample) under the test conditions described previously.

Example 4

Preparation of ion-exchanged absorbent polymers

i) Cation exchange absorbent polymers

Homogeneously crosslinked poly(acrylic acid) is synthesized by placing 24.03 grams of acrylic acid monomer (Aldrich Chemical Co., Cat. No. 14.723-0, Part No. 10115JC) in a clean 250 mL resin kettle. Ν,Ν’-Methylenebisacrylamide (Aldrich Chemical CO., Cat. No. 14.607-2, Part No. 0762EQ), 0.77 grams, and 2,2’-Azobis(2-amidinopropane) dihydrochloride (Wako, Part No. P2197), 0.093 grams, are dissolved in 96 grams of water and added to the acrylic acid monomer in the resin kettle. The kettle is sealed and purged with nitrogen for 15 minutes, then placed in an oven at 65°C for 16 hours.

The resulting gel is cooled and crushed into pieces with a diameter of 1 to 5 mm and dried under vacuum at 70°C for 16 hours. The sample is ground in a Wiley mill and passed through a U.S. A. 20 mesh sieve to obtain homogeneously crosslinked poly(acrylic acid) particles. The sample is then passed through a U.S. A Series Standard 25 mesh sieve but not through a U.S. A Series Standard 70 mesh sieve (fraction with particles with a diameter ranging from approximately 212 to 710 μ) (sample PAA-2).

ii) Anion exchange absorbent polymer

0.15 grams of Span 40 (Ruger Chemical Co., part no. W4250C12) was added to 200 ml of cyclohexane (Aldrich, part no. LR00246KR) in a 500 ml resin kettle. The mixture was stirred for 30 minutes at 60°C to achieve complete dissolution of the mixture. A branched polyethyleneimine with a nominal average molecular weight of 750,000 g/mol is available as a 50% aqueous solution from Aldrich Chemical Co., Milwaukee, Wisconsin (cat. no. 18,917-8, part no. 12922PQ). 20 grams of this sample was further diluted with 30 grams of distilled water and further stirred for 30 minutes in a 250 ml beaker to ensure complete dissolution. Ethylene glycol diglycidyl ether (50% solution), 2.4 g (Aldrich Chemical Co., cat. no. E2,720-3, part. no. 07405DN) was added to the polyethyleneimine solution and the mixture was stirred at room temperature for approximately one minute, and then the cyclohexane solution was slowly added with constant stirring. The mixture was stirred for two hours at 60°C. The excess cyclohexane was filtered off and the remaining beads were rinsed with 200 ml of hot fresh cyclohexane. The beads were soaked overnight in • ·

300 ml of distilled water. The excess water is then filtered off and the remaining beads are washed in 1000 ml of distilled water. The cross-linked polyethyleneimine beads are transferred to a 100 ml wide-necked container, 0.005 grams of hydrophobic silica (Sipemat D17, CAS No. 68611-44-9) is added and the mixture is shaken gently to evenly distribute the silica throughout the mixture. The material is dried under high vacuum for approximately 96 hours to obtain lightly cross-linked polyethyleneimine absorbent polymer beads, which are stored in a dry atmosphere. The material is screened to obtain particles that would pass through a U.S.A. Series Standard 25 sieve but would not pass through a U.S.A. Series Standard 50 sieve (fractions with particles in the approximate 300 to 700 μ diameter range) (Sample BPEI-2).

iii) Absorbent polymer with mixed ion exchange base

Approximately equal amounts by weight of screened and crosslinked cation-exchange poly(acrylic acid) absorbent polymer particles (sample PAA-2) and screened crosslinked spherical polyethyleneimine anion-exchange absorbent polymer particles (sample BPEI-2) are mixed together, thereby uniformly dispersing the particles of both types of polymer throughout the mixture. The resulting mixture is a mixed-base ion-exchange absorbent polymer blend (sample MB-4) of the present invention.

iv) PUP capacity measurement

Approximately 0.9 grams of the mixed ion exchange base absorbent polymer blend (sample MB-4) is transferred to the PUP cylinder (described in the Test Methods section) and gently spread over the entire surface of the screen comprising the cylinder base. The PUP capacities are determined for each sample at pressures of 4.8 kPa and 9.6 kPa by measuring the absorbed fluid at regular intervals over a period of 16 hours. The measured PUP values at the aforementioned pressures are shown as a function of time in Figs. xx and yy . Selected PUP capacity values at times 2, 4, 8 and 16 are shown in Table 6

Table 6

PUP capacities of absorbent polymer blends

4.8 kPa 4 hours 4.8 kPa 8 hours 4.8 kPa 16 hours 9.6 kPa 2 hours 9.6 kPa 8 hours 9.6 kPa 16 hours Sample MB-4 30 g/g 33 g/g 36 g/g 25 g/g 30 g/g 32 g/g Control sample 33 g/g 33 g/g 33 g/g 20 g/g 20 g/g 20 g/g

A comparison of PUP capacities shows that the blend of absorbent polymer with mixed ion exchange base (sample MB-4) exhibits approximately 60% increase in PUP capacity values at a pressure of 9.6 kPa and approximately 9% at a pressure of 4.8 kPa after 16 hours, compared to the partially neutralized polyacrylate absorbent polymer (control sample), under analogous testing conditions.

v) Permeability measurement

Permeability measurements and porosity indications are made using a gel base SFC as described in U.S. Patent 5,562,646 (Goldman et al.), issued October 8, 1996. This method is modified for mixed ion exchange base absorbent polymer systems as described in the Test Methods section. Approximately 0.9 grams of the mixed ion exchange base absorbent polymer blend (Sample MB-4) is transferred to the SFC cylinder and spread gently over the entire surface of the screen including the base of the cylinder. SFC values are given in Table 7.

Table 7

SFC values of the absorbent polymer blend

SFC values Sample MB4 ~ 800 x 10' ⁷ cm ³ sec/g Control sample ~ 10 x 10' ⁷ cm ³ sec/g

-39A comparison of SFC values indicates that the porosity and permeability values of the mixed ion exchange base absorbent polymer blend (sample MB-4) are significantly higher than those of the partially neutralized polyacrylate absorbent polymer (control sample) under analogous test conditions.

Claims (56)

PATENT CLAIMS An absorbent polymer composition having a PUP capacity (pressure behavior), a synthetic urine solution at a pressure of 4.8 kPa, at least 39 g / g after 4 hours and an SFC (saline conductivity) of at least 50 x 10 ⁷ cm ³ sec / g. The absorbent polymer composition of claim 1, wherein the composition has an SFC of at least 50 to 100 x 10 ^-7 cm ³ sec / g. An absorbent polymer composition according to claims 1 to 2 having a PUP capacity in the synthetic urine solution, at an applied pressure of 4.8 kPa and after 4 hours, of at least 41 g / g. An absorbent polymer composition according to any one of claims 1 to 3 having a PUP value in a synthetic urine solution at an applied pressure. 4.8 kPa and after 4 hours, at least 43 g / g. An absorbent polymer composition according to any one of claims 1 to 4 having a PUP value in the synthetic urine solution at the applied pressure. 4.8 kPa and after 4 hours in the range of 39 to 58 g / g. An absorbent polymer composition according to any one of claims 1 to 5 having a PUP value in the synthetic urine solution at the applied pressure. 4.8 kPa and after 4 hours in the range of 41 to 55 g / g. An absorbent polymer composition according to any one of claims 1 to 6 having a PUP capacity in the synthetic urine solution at a pressure of 4.8 kPa and after 4 hours in the range of 43 to 50 g / g. 8. The absorbent polymer composition has (i) a PUP value in the synthetic urine solution at an applied pressure of 4.8 kPa and at least 30 g / g after 4 hours; and (ii) a value of SFC of at least 500 x 10 ⁷ cm ³ sec / g. -41 · ···································· The absorbent polymer composition of claim 8, wherein the composition has an SFC of at least 500 x 10 ⁷ cm ³ sec / g. The absorbent polymer composition of claims 8 to 9, wherein the PUP capacity in the synthetic urine solution, at an applied pressure of 4.8 kPa, has a value of at least 35 g / g after 4 hours. The absorbent polymer composition of claims 8 to 10, wherein the PUP capacity in the synthetic urine solution, at an applied pressure of 4.8 kPa, has a value of at least 40 g / g after 4 hours. The absorbent polymer composition of claims 8 to 11, wherein the PUP capacity in the synthetic urine solution, at an applied pressure of 4.8 kPa, has a value in the range of 30 to 50 g / g after 4 hours. The absorbent polymer composition of claims 8 to 12, wherein the PUP capacity in the synthetic urine solution, at an applied pressure of 4.8 kPa, has a value in the range of 30 to 50 g / g after 4 hours. 14. The absorbent polymer composition has i) a PUP capacity in a synthetic urine solution, at an applied pressure of 4.8 kPa, has a value of at least 40 g / g and an SFC value of at least 50 x 10 ^-7 cm ³ sec / g after 8 hours. 15. The absorbent polymer composition of claim 14 wherein the composition has an SFC of at least about 50 to about 100 * 10 &lt; ⁷ & gt ^; cm &lt; ³ &gt; sec / g. The absorbent polymer composition of claims 14 to 15, wherein the PUP capacity in the synthetic urine solution has a value of at least 42 g / g after 8 hours and at a pressure of 4.8 kPa. The absorbent polymer composition of claims 14 to 16, wherein the PUP capacity in the synthetic urine solution has a value of at least 44 g / g after 8 hours and at a pressure of 4.8 kPa. • • • -4218. Absorbent polymer composition according to claims 14 to 17, characterized in that the PUP capacity in the synthetic urine solution has a value in the range from 40 to 59 g / g after 8 hours and at a pressure of 4.8 kPa. 19. An absorbent polymer composition according to claim 14, wherein the PUP capacity in the synthetic urine solution has a value in the range of 42 to 57 g / g after 8 hours and at a pressure of 4.8 kPa. The absorbent polymer composition of claims 14 to 19, wherein the PUP capacity in the synthetic urine solution has a value in the range of 44 to 55 g / g after 8 hours and at a pressure of 4.8 kPa. 21. The absorbent polymer composition has i) a PUP capacity in a synthetic urine solution, at a pressure of 4.8 kPa, at least 42 g / g after 16 hours, and ii) an SFC value of at least 50 x 10 ^-7 cm ³ sec / g . 22. An absorbent polymer composition according to claim 21 wherein the composition has an SFC in the range of from about 50 to about 100 * 10 &lt; ⁷ & gt ^; cm &lt; ³ &gt; sec / g. 23. The absorbent polymer composition of claims 21 to 22 having a PUP capacity of at least 44 g / g in a synthetic urine solution at a pressure of 4.8 kPa after 16 hours. 24. The absorbent polymer composition of claims 21 to 23 having a PUP capacity in the synthetic urine solution at a pressure of 4.8 kPa (16 psi) of at least 46 g / g after 16 hours. 25. An absorbent polymer composition according to claim 21 to 24 having a PUP capacity in a synthetic urine solution at a pressure of 4.8 kPa (16 to 50 psi) in the range of 42 to 61 g / g after 16 hours. 26. The absorbent polymer composition of claims 21 to 25 having a PUP capacity in a synthetic urine solution at an applied pressure of 4.8 kPa (16 psi) in the range of 44 to 59 g / g after 16 hours. 27. An absorbent polymer composition according to claim 21 to 26 having a PUP capacity in a synthetic urine solution at a pressure of 4.8 kPa at 16 to 57 g / g after 16 hours. An absorbent polymer composition according to claims 21 to 27 having a PUP capacity in a synthetic urine solution at a pressure of 4.8 kPa at a pressure of 48 to 54 g / g after 16 hours. 29. The absorbent polymer blend has a PUP value in the synthetic urine solution at a pressure of 9.6 kPa, at least 35 g / g after 4 hours, and ii) an SFC value of at least 50 x 10 ^-7 cm ³ sec / g. The absorbent polymer composition of claim 29, wherein the composition has an SFC of at least 50 x 10 ^-7 cm ³ sec / g. An absorbent polymer composition according to claims 29 to 30 having a PUP value after 4 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, at least 36 g / g. An absorbent polymer composition according to claims 29 to 31 having a PUP capacity after 4 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, at least 37 g / g. An absorbent polymer composition according to claims 29 to 32 having a PUP value after 4 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, ranging from 35 to 50 g / g. 34. An absorbent polymer composition according to claim 29 to 33 having a PUP value after 4 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, ranging from 36 to 45 g / g. -44 • 4 9 9 ·· ··· · 4 · * 4 · 4 44 4 4 4 4 4 · 4 4 4 4 4 9 9 4 4 4 9 9 4 9 9 4 4444 494 ·· ·· · «·· 35. An absorbent polymer composition according to any one of claims 29 to 34 having a PUP capacity in a synthetic urine solution after 4 hours at the applied pressure. 9.6 kPa, in the range of 37 to 42 g / g. 36. The absorbent polymer composition has (i) at 4 hours a PUP value in the synthetic urine solution at an applied pressure of 9.6 kPa of at least 27 g / g and (ii) an SFC value of at least 500 χ 10 ' ⁷ cm ³ sec / g. 37. The mixture of absorbent polymer according to claim 36, wherein the composition has an SFC value of at least between 500-1100 χ 10 ^"7 cm ³ sec / g. 38. An absorbent polymer composition according to claim 36 to 37 having a PUP capacity in a synthetic urine solution after 4 hours at the applied pressure. 9.6 kPa, at least 33 g / g. 39. An absorbent polymer composition according to claim 36 to 38 having a PUP value after 4 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, at least 47 g / g. 40. An absorbent polymer composition according to claim 36 to 39 having a PUP capacity after 4 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, ranging from 27 to 47 g / g. 41. An absorbent polymer composition according to claim 36 to 40 having a PUP capacity in a synthetic urine solution after 4 hours at the applied pressure. 9.6 kPa, ranging from 33 to 42 g / g. 42. The absorbent polymer blend has (i) a PUP capacity in a synthetic urine solution of at least 36 g / g at an applied pressure of 9.6 kPa after 8 hours; and (ii) an SFC of at least 50 χ 10 ' ⁷ cm ³ sec / g. 43. The absorbent polymer composition of claim 42, wherein the composition has an SFC in the range of from about 50 to about 100 cm &lt; ⁷ & gt ^; cm ³ sec / g. -459 * 999 · 99999 9 · 9 9 9 9 9 9999 9 9 9999 99 * 9 9 9 9 9999 9999 999 99 99 99 99 44. An absorbent polymer composition as claimed in claim 42 to 43 having a PUP value after 8 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, at least 38 g / g. 45. An absorbent polymer composition according to claim 42 to 44 having a PUP value after 8 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, at least 40 g / g. 46. An absorbent polymer composition according to any one of claims 42 to 45 having a PUP value after 8 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, ranging from 36 to 54 g / g. 47. An absorbent polymer composition according to claim 42 to 46 having a PUP value after 4 hours in a synthetic urine solution at an applied pressure. 9.6 kPa, in the range of 38 to 50 g / g. 48. An absorbent polymer composition according to any one of claims 42 to 47 having a PUP capacity in a synthetic urine solution after 4 hours at the applied pressure. 9.6 kPa, in the range of 40 to 46 g / g. 49. The absorbent polymer composition has (i) at least 37 g / g after 16 hours of PUP capacity in the synthetic urine solution at an applied pressure of 9.6 kPa and (ii) an SFC of at least 50 x 10 &lt; ⁷ & gt ^; cm ³ sec / g. 50. The absorbent polymer composition of claim 49, wherein the composition has an SFC in the range of 50 to 100 * 10 &lt; ⁷ & gt ^; cm &lt; ³ &gt; sec / g. 51. The absorbent polymer composition of claims 49 to 50 having a PUP capacity in the synthetic urine solution at a pressure of 9.6 kPa (16 psi) of at least 39 g / g after 16 hours. 52. The absorbent polymer composition of claim 49-51 having a PUP capacity in the synthetic urine solution at a pressure of 9.6 kPa (16 psi) of at least 41 g / g after 16 hours. -46 ♦ · 0 00 00 00 00 0 000 0 00 0 0 0 0 0 0 0 00 00 0000 0 0 00 00 000 000 0 0 0 0000 0000 000 000 00 00 00 00 00 53. The absorbent polymer blend of claims 49-52, having a PUP capacity in a synthetic urine solution at a pressure of 9.6 kPa (16 psi) in the range of from about 37 to about 16 hours. 56 g / g. 54. The absorbent polymer composition of claims 49-53 having a PUP capacity in a synthetic urine solution at a pressure of 9.6 kPa at 16-5 g / g after 16 hours. 55. An absorbent polymer composition according to claim 49-54 having a PUP capacity in a synthetic urine solution at a pressure of 9.6 kPa (16 psi) in the range of 41 to 48 g / g after 16 hours. The absorbent element for retaining aqueous body exudates comprises at least one absorbent polymer region according to any one of claims 1-55. An absorbent article comprising a liquid pervious topsheet, a backsheet, and an absorbent core positioned between the topsheet and the backsheet is characterized in that the absorbent core comprises an absorbent element according to any one of claims 1-56.