WO2005120594A1

WO2005120594A1 - Polymers with odor control properties and method for their preparation

Info

Publication number: WO2005120594A1
Application number: PCT/US2005/019572
Authority: WO
Inventors: Young-Sam Kim; Robert M. Strom; Alan Robert Reinhardt; Marvin H. Tegen
Original assignee: Dow Global Technologies Inc.
Priority date: 2004-06-07
Filing date: 2005-06-03
Publication date: 2005-12-22
Also published as: AR058783A1

Abstract

A composition including a superabsorbent polymer and a hydrophobic porous polymer. The composition can be used in applications such as baby diapers, adult incontinence products, feminine care products, other hygiene and medical articles such as wound dressings and fabrics, and packaging, including food packaging, applications.

Description

POLYMERS WITH ODOR CONTROL PROPERTIES AND METHOD FOR THEIR PREPARATION

This invention relates to polymers with odor control properties.

Superabsorbent polymers, also referred to as aqueous fluid absorbent polymers, are primarily used in personal care products such as baby diapers, adult incontinence products and feminine hygiene products. In such applications, superabsorbent polymer particles are incorporated into absorbent structures that contain synthetic and/or natural fiber or paper based, woven and nonwoven structures, or toughened masses of fibers, such as fluff pads. The materials used in such structures can quickly absorb aqueous fluids and distribute them throughout the whole absorbent structure. The structures, in the absence of superabsorbent polymers, have limited absorption capacity, are bulky due to the large amount of material needed to provide acceptable absorption capacity, and do not retain fluid under pressure. The absorbency and fluid retention characteristics of such absorbent structures are improved by incorporating into them superabsorbent polymer particles that imbibe fluids to form a swollen hydrogel material.

Manufacturers of personal hygiene articles, such as feminine hygiene products and adult incontinence products, have long desired to have a superabsorbent polymer that would reduce unpleasant odors that can develop during use of these articles. While different methods have been employed in the prior art to reduce malodor in superabsorbent polymer- containing articles, none are entirely satisfactory.

U.S. Patent 5,552,378 discloses a complex of a cyclodextrin and an active agent, such as a perfume, which complex is suitable for use in disposable absorbent products such as diapers. However, cyclodextrins are biologically degradable, and are a good nurture for microorganisms. When contacted with microorganisms, such as the bacteria in infected urine, bacteria proliferation is increased, resulting in increased malodor. The use of perfumes and fragrances can mask malodor, but it can be difficult to match the personal odor preference of the user. Accordingly, the offensiveness of the combination of malodor and perfume can be perceived to be greater than that of the malodor alone. U.S. Patent 4,385,632 is directed to an absorbent article for urine which contains a water-soluble copper salt which impedes bacterial growth, prevents ammonia production and binds ammonia by complexation so as to prevent the occurrence of unpleasant odor. However, copper ion treatment is fairly ineffective, even at relatively high concentrations, in the case of heavy incontinence where severe urinary tract infection is present.

DE 19929106 discloses a diaper that contains an activated carbon filter layer having a high adsorption capacity for ammonia. The active carbon filter layer can be impregnated with a zinc or copper salt or phosphoric acid. Activated carbon is disfavored for use in modern personal hygiene articles due to its black color. Zeolites have been used for odor control purposes. U.S. Patent 6,096,299 discloses an absorbent article containing an odor control material that comprises a synthetic zeolite. The zeolite may optionally be mixed with a superabsorbent polymer and activated carbon. U.S. Patent 6,353,146 discloses a fibrous absorbent article comprising a natural zeolite as an odor control agent. U.S. Patent 6,277,772 discloses a superabsorbent composition containing a superabsorbent polymer and a zeolite exchanged with metal cations, such as Ag, Cu and Zn ions, having bactericidal properties. WO 00/62826 relates to an absorbent article comprising an odor controlling adsorbing material such as activated carbon and metal oxides, silicates and zeolites. However, zeolites, even when employed at micron-range sizes, can cause abrasion and/or attrition issues when used with superabsorbent polymers, since zeolites are dense and hard inorganic particles that in general are irregular shaped, sharp and/or angular.

Existing odor-control methods are incapable of sufficiently reducing malodor and/or have other drawbacks. They often require treatments with metal ions, abrasive materials, or perfumes or fragrances. Therefore, it would be desirable to have an effective, non-abrasive superabsorbent polymer composition with odor control properties.

This invention relates to a composition comprising superabsorbent polymer and a hydrophobic porous polymer.

A further aspect of the invention is a process for the preparation of a superabsorbent polymer, which comprises: (I) polymerizing a polymerization mixture comprising:

(a) one or more ethylenically unsaturated carboxyl-containing monomers,

(b) one or more crosslinking agents,

(c) optionally one or more comonomers copolymerizable with the carboxyl- containing monomer, and

(d) a polymerization medium, to form a crosslinked hydrogel,

(H) comminuting the hydrogel to particles, and (IH) drying the hydrogel, wherein a hydrophobic porous polymer is added in at least one of the following steps:

(i) to the polymerization mixture during polymerization or prior to the beginning of the polymerization, or (ii) to the crosslinked hydrogel prior to or after comminution in step (IT), or (iii) to the dried polymer particles after step (HI).

This invention also concerns an absorbent article comprising the composition of this invention.

The composition of the invention is surprisingly effective in controlling malodor that can develop from biological fluids such as urine or blood. The composition of the invention can be used in personal hygiene articles, such as baby diapers, adult incontinence products, and feminine care products, medical articles, such as wound dressings, fabrics, and packaging, including food packaging applications in which odor control is desired in addition to moisture and/or liquid absorption.

The present invention combines a hydrophobic porous polymer with a superabsorbent polymer.

For the purposes of the present invention, the term "hydrophobic porous polymer" or "HPP" means a porous material that is an organic polymer with a hydrophobicity of not more than 40 percent. For the purposes of the present invention, the term "hydrophobicity" means the value of Percent Moisture Uptake measured according to the Moisture Uptake Test specified hereinbelow. Lower Percent Moisture Uptake values indicate relatively higher hydrophobicity. The HPP suitable for use in the present invention can be any type of organic polymer having the desired characteristics. Examples of preferred HPPs include monovinyl aromatic monomer/poly vinylbenzene copolymers, such as the copolymers described in WO 00/43120 and U.S. Patents 5,504,163; 4,863,494 and 5,416,124. HPPs are commercially available and are well-known in the art. Examples of commercially available HPP's include DOWEX OPTIPORE L323, DOWEX OPTIPORE V503, and DOWEX OPTIPORE V439 brand resins, which are commercially available from The Dow Chemical Company.

The HPP can be produced by any suitable process, including, for example: heterogeneous polymerization processes, including micro-emulsion polymerization, emulsion polymerization and suspension polymerization; mechanical dispersion processes; and by mechanical size reducing processes in the presence or absence of dispersing liquid media. Preferably, the HPP is prepared by a conventional suspension polymerization process.

The preferred HPPs are prepared by copolymerizing a monomer mixture comprising a monovinyl aromatic monomer, a polyvinylbenzene monomer and, optionally, a monovinyl aliphatic monomer. Monovinyl aromatic monomers include styrenes, vinyltoluenes, ethyl vinylbenzenes, vinylnaphthalenes, and heterocyclic monomers such as vinylpyridine. Preferred monovinyl aromatic monomers include styrene and ethyl vinylbenzene, with styrene being most preferred. Mixtures of monovinyl aromatic monomers can be employed. Examples of polyvinyl aromatic crosslinking monomers include divinylbenzene and trivinyl benzene, with divinylbenzene being most preferred. Mixtures of polyvinylbenzene aromatic monomers can be employed. In a preferred embodiment, the monovinyl aromatic monomer advantageously comprises from 45 to 98 weight percent of the total monomer mixture, preferably from 65 to 95 weight percent of the total monomer mixture, with the remainder of the monomer mixture comprising a polyvinylbenzene. In a second preferred embodiment, the monovinyl aromatic monomer comprises from 10 to 60 weight percent of the total monomer mixture, preferably from 20 to 50 weight percent of the total monomer mixture, with the remainder of the monomer mixture comprising a polyvinylbenzene.

The monomer mixture can optionally include a monovinyl aliphatic monomer. The monovinyl aliphatic monomer advantageously is acrylonitrile or a derivative of acrylic acid, methacrylic acid, or acrylonitrile. Examples of preferred monovinyl aliphatic monomers include methyl methacrylate, acrylonitrile, ethyl acrylate, 2-hydroxyethyl methacrylate and mixtures thereof. The monovinyl aliphatic monomers advantageously comprise from 0 to 20 weight percent of the total monomer mixture. Since subsequent alkylene bridging occurs between aromatic rings, it is often preferable not to employ, or to minimize the use of, any monovinyl aliphatic monomer.

In a preferred embodiment of the invention, the HPP is porogen-modified, that is, prepared by suspension polymerization in the presence of a porogenic solvent or a mixture of such solvents. Porogenic solvents are solvents that are suitable for forming pores and/or displacing polymer chains during polymerization. A porogenic solvent is one that dissolves the monomer mixture being copolymerized but does not dissolve the copolymer. In addition, the porogenic solvent must be inert to the polymerization conditions, that is, neither interfere with nor enter into the polymerization. The characteristics and use of such solvents in the formation of macroreticular or macroporous resins are described in U.S. Patent 4,224,415. For crosslinked copolymers prepared from monovinyl aromatic monomers and polyvinyl aromatic crosslinking monomers, aromatic hydrocarbons such as, for example, toluene, xylene and ethylbenzene, C₆-C₁₂ saturated aliphatic hydrocarbons such as, for example, heptane and iso-octane, and C₄ - C_JO alkanols such as, for example, tert-amyl alcohol, sec-butanol and 2-ethylhexanol, are particularly effective as porogenic solvents. Aromatic hydrocarbons and C₆ -C₁₂ saturated aliphatic hydrocarbons and their mixtures are preferred, while toluene alone or in mixtures with a C₆-C₈ saturated aliphatic hydrocarbon is most preferred. A sufficient concentration of porogenic solvent is required to effect phase separation or polymer chain displacement. The porogenic solvent advantageously comprises from 35 to 70 weight percent, and preferably from 45 to 65 weight percent, of the total weight of the monomer mixture and the porogenic solvent.

When a suspension polymerization process is employed, the preferred suspending medium is water, and the preferred suspending agent is a suspension stabilizer, for example, gelatin, polyvinyl alcohol or a cellulosic such as hydroxyethyl cellulose, methyl cellulose or carboxymethyl methyl cellulose. The polymerization preferably is conducted in the presence of a free radical initiator. Free radical polymerization and free radical initiators are well known to those skilled in the art. Many free radical initiators are commercially available. In a preferred embodiment, when the HPP is a porogen-modified crosslinked copolymer, it comprises the polymerized residue of from 65 to 98 weight percent of at least one monovinyl aromatic monomer, from 0 to 20 weight percent of a monovinyl aliphatic monomer and from 2 to 15 weight percent of a polyvinyl aromatic crosslinking monomer, the copolymer being further crosslinked by methylene bridging. In a second preferred embodiment, when the porogen-modified crosslinked copolymer will not be further crosslinked by methylene bridging, the copolymer comprises the polymerized residue of from 10 to 60 weight percent of at least one monovinyl aromatic monomer, from 0 to 20 weight percent of a monovinyl aliphatic monomer and from 20 to 90 weight percent of a polyvinyl aromatic crosslinking monomer.

The monovinyl aromatic monomer/polyvinlybenzene copolymer optionally can be subjected to chloromethylation and subsequent post-crosslinking by methylene bridging, as is known to those skilled in the art. For the purposes of the present invention, the term "methylene- bridged aromatic polymer" refers to porous copolymers of a monovinyl aromatic monomer and a polyvinyl aromatic crosslinking monomer that have been chloromethylated and then post-crosslinked in a swollen state, preferably in the presence of a Friedel-Crafts catalyst. Such resins have been referred to as "hypercrosslinked' or 'post-crosslinked' resins and their preparations and uses have been described, for example, in U.S. Patents 4,191,813; 4,263,407; 4,950,332; 5,079,274; 5,288,307; 5,773,384; and in U.S. Patent Application Publications 2003/0027879 and 2004/0092899.

Chloromethyl groups can be incorporated into the HPP using a chlormethylation agent such as, for example, chloromethyl methyl ether, or by use of vinylbenzyl chloride as a portion of the monovinyl aromatic monomer. Chloromethylation is preferably carried out by treatment of the copolymer with chloromethyl methyl ether in the presence of a Friedel-Crafts catalyst. Post-crosslinking, that is, methylene bridging, is optional and preferably is accomplished by treatment with ethylene dichloride to first swell the chloromethylated aromatic copolymer followed by treatment with a Friedel-Crafts catalyst. Chloromethylated aromatic copolymers typically contain from 0.1 to 0.9, preferably from 0.6 to 0.8, chloromethyl groups per aromatic ring. Chloromethylations are described, for example, in U.S. Patents: 2,597,492; 2,629,710; 2,642,417; and 2,960,480; and in WO 00/43120. In preparation for methylene bridging, the chloromethylated copolymer is contacted with a swelling agent to expand the copolymer structure. Suitable swelling agents are solvents that are substantially inert during post-crosslinking of the copolymer and include chlorinated hydrocarbons, such as 1,2 dichloroethane, methylene chloride, and propylene dichloride. The preferred swelling agent is 1 ,2-dichloroethane. Advantageously, the copolymer is contacted with the swelling agent for a time sufficient to substantially attain equilibrium with respect to swelling by the particular swelling agent employed. Preferably, the copolymer is allowed to swell in an excess amount of the swelling agent for at least 30 minutes. It is also generally convenient to dissolve within the swelling agent the Friedel-Crafts catalyst employed in the subsequent post-crosslinking reaction.

Once swollen, the chloromethylated copolymer is maintained under reaction conditions in the presence of a Friedel-Crafts catalyst such that bridging moieties (-CH₂-) are formed by reaction of the chloromethyl groups with a neighboring aromatic ring. Any Friedel- Crafts-type catalyst can be utilized to catalyze the post-crosslinking reaction. Examples of suitable catalysts include the acidic metal halides such as aluminum chloride, stannic chloride, aluminum bromide, boron trifluoride, zinc chloride, ferric chloride, and mixtures thereof. The catalyst is typically effective in amounts ranging from 0.001 to 50 and preferably from 5 to 30 percent by weight, based on weight of polymeric material. The optimum amount depends upon the reactants and conditions selected for carrying out the reaction, as is known by those skilled in the art. The mixture of copolymer and catalyst is heated to a temperature ranging from 20°C to 180°C for a period sufficient to post-crosslink the resin, preferably from 0.5 to 30 hours. More preferably, the temperature ranges from 60°C up to the reflux temperature of the organic swelling liquid and the reaction period ranges from 0.5 to 8 hours. Most preferably, the temperature ranges from 60°C to 85°C. The reaction temperature and time may vary depending on the reactive species and catalyst in the reaction mixture.

When chloromethylated aromatic copolymers are post-crosslinked to form methylene bridges between neighboring aromatic rings, it is typical that not all chloromethyl groups can react because of spatial considerations. Usually, from 2 to 10 percent of the chloromethyl groups remain unreacted depending on the overall extent of chloromethylation. In general, the greater the extent of chloromethylation, the greater the ratio of unreacted chloromethyl groups to aromatic rings. Methylene-bridged monovinyl aromatic monomer/divinylbenzene polymers can further be subjected to a subsequent hydrophobic treatment by capping the unreacted chloromethyl groups with a hydrophobic capping compound, as is known to those skilled in the art. By capping the residual chloromethyl groups with hydrophobic aromatic compounds prior to their opportunity to hydrolyze or oxidize, the hydrophobicity of a methylene-bridged aromatic polymer is increased.

Any unreacted chloromethyl groups in the copolymer preferably are capped with hydrophobic aromatic compounds according to known methods, such as the method of U.S. 5,504,163. In the capping process, the residual chloromethyl groups alkylate a hydrophobic aromatic compound in a Friedel-Crafts alkylation which is not subject to the spatial or geometric constraints imposed on further methylene bridging with aromatic rings confined to the rigid hypercrosslinked polymer backbone. Examples of hydrophobic aromatic compounds include benzene and its derivatives that are from weakly deactivated to weakly to moderately activated towards electrophilic aromatic substitution as defined in "Organic Chemistry" by R. T. Morrison and R. N. Boyd, 6th Edition, Prentice Hall, Inc., Englewood Cliffs, N J., p. 22 (1992). The preferred hydrophobic aromatic compounds are substituted benzene or naphthalene, with toluene and ethyl benzene being most preferred.

The HPP can be employed in any form. Preferably, the HPP is employed in bead form, ground form, or as a mixture thereof. The HPP can be employed wet or dry, including as a paste, and can be employed with or without an aqueous and/or a nonaqueous organic liquid. The dry powder form is more preferred. In order to prepare a ground HPP, any known particle size reduction means can be employed, including crushing, grinding, chopping and milling, such as ball milling and ultracentrifugal milling. The HPP size reducing process can be done on dry HPP or wet, including slurry form, HPP. The original physical properties of a crosslinked monovinyl aromatic HPP in bead form, for example, BET surface area, porosity and average pore size, are not expected to be altered substantially by the size reducing process due to the high inner surface areas of the numerous pores present in the initial HPP beads. The terminology used to describe various adsorbent properties is not always consistent. With respect to the characterization of pores, a definitive line of demarcation between the sizes of the various pore types does not really exist. The molecular and capillary sized pores in copolymers and adsorbents are irregularly shaped as are the probe molecules that are used in the measurements for determining their pore structures. Most classical techniques used to measure the geometric properties of copolymers and adsorbents assume the pores to be either cylindrical or slit shaped and the pore structure is defined by the corresponding geometric relationships. Consequently, the pore structure depends a great deal on the model used to interpret the characteristic adsorption/desorption isotherm.

As used herein, the various pore types have the following definitions. Micropores are defined as pores of less than 2 nm in diameter. Mesopores are defined as pores ranging from 2 to 20 nm in diameter. Macropores are defined as pores of greater than 20 nm in diameter. The terms microporosity, mesoporosity and macroporosity refer to the pore volume per gram of sample for each type of pore respectively and are reported in units of cc/g. These porosities, as well as surface area and average pore size, are determined by the nitrogen adsorption method in which dried and degassed samples are analyzed on an automatic volumetric sorption analyzer. The instrument works on the principle of measuring the volume of gaseous nitrogen adsorbed by a sample at a given nitrogen partial pressure. The volumes of gas adsorbed at various pressures are used in the BET model for the calculation of the surface area of the sample. The average pore radius is calculated from the relationship between the surface area and the pore volume of the sample, assuming cylindrical pore geometry.

Preferred average pore diameters of the HPP range from 0.5 nm to 15 nm, more preferably from 1 nm to 8 nm, and most preferably from 1.5 nm to 5 nm.

In a preferred embodiment of the invention, the HPP has a microporosity of from 0.2 to 0.4 cc/g, a mesoporosity of at least 0.3 cc/g, more preferably at least 0.5 cc/g, and a total porosity of at least 0.8 cc/g, more preferably at least 1.5 cc/g, and the microporosity comprises less than 40 percent, more preferably less than 20 percent, of the total porosity.

The BET surface area of the HPP advantageously ranges from 200 to 1800 m²/g, preferably is from 400 to 1600 m²/g, and most preferably is from 600 to 1400 m²/g. The average particle diameter of the HPP beads from suspension polymerization advantageously ranges from 25 to 2500 μm, and an average particle diameter of from 30 to 1500 μm is preferred. The particle size distribution is not critical and can vary from monodisperse, to Gaussian, to random. In applications where the HPP is used as whole beads, monodisperse particle sized beads can offer advantages in kinetics and capacity. If the HPP is employed as a ground powder, the majority of the final HPP particles advantageously will have a particle size in the range of from 0.001 μm to 1000 μm, preferably from 0.05 μm to 500 μm, more preferably from 0.1 μm to 300 μm, and most preferably from 0.5 μm to 150 μm. Particle size analysis methods and instruments are well known to the skilled person in the art.

Surface area, pore size and porosity are determined on a Quantachrome Model Autosorb-1 nitrogen adsorption analyzer by measuring the volume of gaseous nitrogen adsorbed by a sample at a given nitrogen partial pressure and by conducting the appropriate calculations according to the BET model.

In an optional embodiment of the invention, the HPP is subjected to bleaching in order to render it whiter in color. Any bleaching agent can be employed for this purpose. Examples of bleaching agents include sodium hypochlorite and hydrogen peroxide.

Preferred Percent Moisture Uptake, or hydrophobicity, values of the HPP advantageously range from 0.01 percent to 40 percent, more preferably from 0.1 percent to 20 percent, and most preferably from 0.5 percent to 10 percent. Thus, for the purposes of the present invention, a polymer is hydrophobic if it has a Percent Moisture Uptake of not more than 40 percent, preferably not more than 30 percent, more preferably not more than 20 percent and most preferably not more than 10 percent.

Optionally, physical and/or chemical means to increase the hydrophobicity of a given HPP can be employed. Examples of such means include the following: a hydrophobic treatment with surfactants; lyophobization using organic solvents or mineral oils; a plasma treatment resulting in a hydrophobic polymeric surface; a treatment with hydrophobic polymeric materials with or without functional groups that can undergo a covalent and/or a Coulombic electrocharge interaction reaction; a treatment with a fluorine-containing polymer; a treatment with fluorine-containing small organic molecules with and without reactive functional groups; a treatment with a silicon-containing polymers with or without reactive functional groups; and a treatment with silicon-containing small organic molecules with or without reactive functional groups.

Superabsorbent polymers are widely commercially available and are well-known in the art. Such polymers advantageously are derived from one or more ethylenically unsaturated carboxylic acids, ethylenically unsaturated carboxylic acid anhydrides or salts thereof. Additionally, such polymers may include comonomers known in the art for use in superabsorbent polymers or for grafting onto the superabsorbent polymers including comonomers such as an acrylamide, an acrylonitrile, a vinyl pyrrolidone, a vinyl sulphonic acid or a salt thereof, a cellulosic monomer, a modified cellulosic monomer, a polyvinyl alcohol or a starch hydrolyzate. If used, the comonomer comprises up to 25 percent by weight of the monomer mixture.

Preferred unsaturated carboxylic acid and carboxylic acid anhydride monomers include the acrylic acids typified by acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α -cyano acrylic acid, β-methyl acrylic acid (crotonic acid), α -phenyl acrylic acid, β-acryloyloxy propionic acid, sorbic acid, α-chloro sorbic acid, angelic acid, cinnamic acid, p-chloro cinnamic acid, beta-styrenic acrylic acid (l-carboxy-4-phenyl butadiene- 1,3), itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, maleic acid, fumaric acid and maleic acid anhydride. More preferably the starting monomer is acrylic acid, methacrylic acid, or a salt thereof with acrylic acid or a salt thereof being most preferred. The use herein of the prefix "(meth)" with generic terms, such as, for example, "acrylic acid" or "acrylate," is meant to broaden the terms to include both acrylate and methacrylate species. Thus, the term "(meth)acrylic acid monomer" includes acrylic acid and methacrylic acid.

Preferably, 25 mole percent or greater of the carboxylic acid units of the superabsorbent polymer are neutralized with base, even more preferably 50 percent or greater and most preferably 65 percent or greater. This neutralization may be performed after completion of the polymerization. In a preferred embodiment the starting monomer mix has carboxylic acid moieties that are neutralized to the desired level prior to polymerization. The final polymer or the starting monomers may be neutralized by contacting them with a salt- forming cation. Such salt-forming cations include alkaline metal, ammonium, substituted ammonium and amine based cations. Preferably, the polymer is neutralized with an alkali metal hydroxide such as, for example, sodium hydroxide or potassium hydroxide, or an alkali metal carbonate such as, for example, sodium carbonate or potassium carbonate.

The superabsorbent polymers are lightly crosslinked to make them water-insoluble. Vinyl, non-vinyl, or dimodal crosslinkers can be employed, either alone, as mixtures, or in various combinations. Polyvinyl crosslinkers commonly known in the art for use in superabsorbent polymers advantageously are employed. Preferred compounds having at least two polymerizable double bonds include: di- or polyvinyl compounds such as divinyl benzene, divinyl toluene, divinyl xylene, divinyl ether, divinyl ketone and trivinyl benzene; di- or polyesters of unsaturated mono- or polycarboxylic acids with polyols, such as di- or tri-(meth)acrylic acid esters of polyols such as ethylene glycol, diethylene glycol, triethylene glycol, tetra ethylene glycol, propylene glycol, dipropylene glycol, tri propylene glycol, tetra propylene glycol, trimethylol propane, glycerin, polyoxyethylene glycols and polyoxypropylene glycols; unsaturated polyesters that can be obtained by reacting any of the above-mentioned polyols with an unsaturated acid such as maleic acid; di- or polyesters of unsaturated mono- or polycarboxylic acids with polyols derived from reaction of C₂-C₁₀ polyhydric alcohols with 2 to 8 C₂-C alkylene oxide units per hydroxyl group, such as trimethylol propane hexaethoxyl triacrylate; di- or tri-(meth)acrylic acid esters that can be obtained by reacting polyepoxide with (meth)acrylic acid; bis(meth) acrylamides such as N,N-methylene-bisacrylamide; carbamyl esters that can be obtained by reacting polyisocyanates such as tolylene diisocyanate, hexamethylene diisocyanate,

4,4'-diphenyl methane diisocyanate and NCO-containing prepolymers obtained by reacting such diisocyanates with active hydrogen atom-containing compounds with hydroxyl group-containing monomers, such as di-(meth)acrylic acid carbamyl esters obtainable by reacting the above-mentioned diisocyanates with hydroxyethyl(meth)acrylate; di- or poly(meth)allyl ethers of polyols such as alkylene glycols, glycerol, polyalkylene glycols, polyoxyalkylene polyols and carbohydrates such as polyethylene glycol diallyl ether, allylated starch, and allylated cellulose; di- or poly-allyl esters of polycarboxylic acids, such as diallyl phthalate and diallyl adipate; and esters of unsaturated mono- or polycarboxylic acids with mono(meth)allyl ester of polyols, such as allyl methacrylate or (meth)acrylic acid ester of polyethylene glycol monoallyl ether. The preferred classes of crosslinkers for superabsorbent polymers include, for example, bis(meth)acrylamides; allyl(meth)acrylates; di- or poly-esters of (meth)acrylic acid with polyols such as diethylene glycol diacrylate, trimethylol propane triacrylate, and polyethylene glycol diacrylate; and di- or polyesters of unsaturated mono- or poly-carboxylic acids with polyols derived from the reaction of Cι-C₁₀ polyhydric alcohols with 2 to 8 C₂-C alkylene oxide units per hydroxyl group, such as ethoxylated trimethylol propane triacrylate. More preferably the crosslinking agents correspond to Formula 1 :

R¹ <(R² O)_n— C(O)R³)_x Formula 1 wherein:

R¹ is a straight- or branched-chain polyalkoxy radical with 1 to 10 carbon atoms, optionally substituted with one or more oxygen atoms in the backbone, having x valences; R² is independently in each occurrence an alkylene group of 2 to 4 carbon atoms; R is independently in each occurrence a straight- or branched-chain alkenyl moiety with 2 to 10 carbon atoms; n is a number from 1 to 20; and x is a number from 2 to 8.

In the most preferred embodiment the polyvinyl crosslinker corresponds to Formula 1 wherein R¹ is derived from trimethylolpropane, R² is ethylene -(CH₂CH₂)-, R³ is vinyl - (CH=CH₂), the average value of n is from 2 to 6, and x is 3. The most preferred polyvinyl crosslinker is ethoxylated trimethylolpropane triacrylate, containing an average of 15 to 16 ethoxyl groups per molecule of trimethylolpropane. Crosslinkers corresponding to Formula 1 are available from Craynor under the trademark Craynor and from Sartomer under the trademark Sartomer. Generally, the crosslinkers described by Formula 1 are found as a mixture of materials described by the formula and by-products resulting from the preparation process. Mixtures of polyvinyl crosslinkers can be employed.

The non-vinyl crosslinkers that can be employed in making superabsorbent polymers are agents having at least two functional groups capable of reacting with the carboxyl groups of the polymer, and include materials such as glycerin, polyglycols, ethylene glycol digylcidyl ether, and diamines. Many examples of these agents are given in U.S. Patents 4,666,983 and 4,734,478 which teach the application of such agents to the surface of absorbent polymer powder followed by heating to crosslink surface chains and improve absorption capacity and absorption rate. Additional examples are given in U.S. Patent 5,145,906, which teaches post-crosslinking with such agents. The non-vinyl crosslinkers advantageously can be added homogeneously to the polymerization mixture at the start of the process. Preferred non-vinyl crosslinkers include hexane diamine, glycerin, ethylene glycol diglycidyl ether, ethylene glycol diacetate, polyethylene glycol 400, polyethylene glycol 600, and polyethylene glycol 1000. Examples of more preferred non-vinyl crosslinkers include polyethylene glycol 400 and polyethylene glycol 600. Mixtures of non-vinyl crosslinkers can be employed.

The dimodal crosslinkers that can be employed in the preparation of superabsorbent polymers are agents that have at least one polymerizable vinyl group and at least one functional group capable of reacting with carboxyl groups. They are called "dimodal crosslinkers" to distinguish them from normal vinyl crosslinkers, because they use two different modes of reaction to form a crosslink. Examples of dimodal crosslinkers include hydroxyethyl methacrylate, polyethylene glycol monomethacrylate, glycidyl methacrylate, and allyl glycidyl ether. Many examples of these type of crosslinkers are given in U.S. Patents 4,962,172 and 5,147,956 which teach the manufacture of absorbent films and fibers by (1) the preparation of linear copolymers of acrylic acid and hydroxyl containing monomers, (2) forming solutions of these copolymers into the desired shapes, and (3) fixing the shape by heating the polymer to form ester crosslinks between the pendant hydroxyl and carboxyl groups. The dimodal crosslinker advantageously is added homogeneously to the polymerization mixture at the start of the process. Preferred dimodal crosslinkers include hydroxyethyl (meth)acrylate, polyethylene glycol 400 monomethacrylate, glycidyl methacrylate. Hydroxyethyl (meth)acrylate is an example of a more preferred dimodal crosslinker. Mixtures of dimodal crosslinkers can be employed.

Combinations of crosslinkers can be employed. The total amount of all crosslinkers present is sufficient to provide a polymer with good absoφtive capacity, good absoφtion under load, and a low percent of extractable materials. Preferably the crosslinkers are present in an amount of 1 ,000 parts per million or more by weight based on the amount of the polymerizable monomer present, more preferably 2,000 ppm or more and most preferably 4000 ppm or greater. Preferably, the crosslinkers are present in an amount of 50,000 parts per million or less by weight based upon the amount of the polymerizable monomer present, more preferably in amounts of 20,000 ppm or less and most preferably 15,000 ppm or less. In superabsorbent polymers that utilize a blend of polyvinyl crosslinkers with non-vinyl and/or dimodal crosslinkers, the effect on heat-treated capacity of all three types of crosslinkers is additive in nature. That is, if the amount of one crosslinker is increased the amount of another must be decreased to maintain the same overall heat-treated capacity. In addition, the proportion of the crosslinker components within the blend may be varied to achieve different polymer properties and processing characteristics. In particular, polyvinyl crosslinkers are typically more expensive than non-vinyl or dimodal crosslinkers. Therefore, the overall cost of the polymer is reduced if a greater proportion of the crosslinker blend is composed of less expensive non-vinyl and or dimodal crosslinkers. However, the non-vinyl and dimodal crosslinkers function essentially as latent crosslinkers. That is, the crosslinking imparted to the polymer by these agents is essentially not developed or seen until after a heat-treatment step. Little if any toughness is added to the hydrogel immediately after polymerization by use of such latent crosslinkers. This is an important concern for those processes for which a "tough" gel is desirable.

If too little of the total crosslinker blend is composed of polyvinyl crosslinker the polymerized hydrogel may not have sufficient toughness to be easily ground, processed, and dried. For this reason the proportion of polyvinyl crosslinker in the total crosslinker blend is preferably at least sufficient to produce a hydrogel that has enough toughness to be readily ground, processed, and dried. This toughness is inversely proportional to the centrifuged capacity of the polymer after drying but before heat-treatment. The exact amount of polyvinyl crosslinker required in the blend to achieve this level of toughness will vary, but is enough to provide a centrifuged absoφtion capacity of the polymer after drying but before heat-treatment of at least 10 g/g and preferably 45 g/g or less, more preferably 40 g/g or less, and most preferably 35 g/g or less.

Conventional additives that are well known in the art, such as surfactants, can be incoφorated into the polymerization mixture. HPP can also be incoφorated into the polymerization mixture. Polymerization can be accomplished under polymerization conditions in an aqueous or nonaqueous polymerization medium or in a mixed aqueous/nonaqueous polymerization medium. Polymerization accomplished by processes which employ nonaqueous polymerization media may use various inert hydrophobic liquids which are not miscible with water, such as hydrocarbons and substituted hydrocarbons including halogenated hydrocarbons as well as liquid hydrocarbons having from 4 to 20 carbon atoms per molecule including aromatic and aliphatic hydrocarbons, as well as mixtures of any of the aforementioned media.

In one embodiment, superabsorbent polymer particles are prepared by contacting the appropriate monomers and crosslinkers in an aqueous medium in the presence of a free radical or oxidation reduction (redox) catalyst system and optionally a chlorine- or bromine- containing oxidizing agent under conditions such that a crosslinked hydrophilic polymer is prepared. As used herein, the term "aqueous medium" means water, or water in admixture with a water-miscible solvent. Examples of such water-miscible solvents include lower alcohols and alkylene glycols. Preferably the aqueous medium is water.

The monomers and crosslinkers are preferably dissolved, dispersed or suspended in a suitable polymerization medium, such as, for example, the aqueous medium, at a concentration level of 15 percent by weight or greater, more preferably 25 percent or greater, and most preferably 29 percent or greater. The monomers and crosslinkers are preferably dissolved, dispersed or suspended in the aqueous medium.

Another component of the aqueous medium used to prepare the superabsorbent polymers comprises a free radical initiator, which may be any conventional water-soluble polymerization initiator including, for example, peroxygen compounds such as sodium, potassium and ammonium peroxodisulfates, caprylyl peroxide, benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tertiary butyl dipeφhthalate, tertiary butyl perbenzoate, sodium peracetate and sodium percarbonate. Conventional redox initiator systems can also be utilized, which are formed by combining the foregoing peroxygen compounds with reducing agents, such as, for example, sodium bisulfite, sodium thiosulphate, L- or iso- ascorbic acid or a salt thereof or ferrous salts. The initiator can comprise up to 5 mole percent based on the total moles of polymerizable monomer present. More preferably the initiator comprises from 0.001 to 0.5 mole percent based on the total moles of polymerizable monomer in the aqueous medium. Mixtures of initiators can be employed.

In one embodiment of the invention, at least one chlorine- or bromine-containing oxidizing agent is added to the monomer mixture or to the wet hydrogel in order to reduce the amount of residual monomers in the final polymer. It is preferably added to the monomer mixture. Preferred oxidizing agents are bromates, chlorates and chlorites. Preferably, a chlorate or bromate salt is added. The counterion of the bromate or chlorate salt can be any counterion which does not significantly interfere in the preparation of the superabsorbent polymers or their performance. Preferably, the counterions are alkaline earth metals ions or alkali metal ions. More preferred counterions are the alkali metals, with potassium and sodium being even more preferred. Chlorine-containing oxidizing agents are preferred. The oxidizing agent is present in sufficient amount such that after heat-treatment the residual monomer level is reduced and the desired balance of centrifuged absoφtion capacity and absoφtion under load (AUL) is achieved.

Preferably, 10 ppm by weight or greater of a chlorine- or bromine-containing oxidizing agent based on the total weight of monomers (a), (b) and (c) is added, more preferably 50 ppm or greater and even more preferably 100 ppm or greater and most preferably 200 ppm or greater. Desirably, the amount of a chlorine- or bromine-containing oxidizing agent added is 2000 ppm or less by weight based on the monomers, more desirably 1000 ppm or less, preferably 800 ppm or less and most preferably 500 ppm or less.

The superabsorbent polymer can be prepared in a batch or continuous manner. The polymerization can be performed in a batch manner wherein all of the reaction materials are contacted and the reaction proceeds, or it may take place with the continuous addition of one or more of the components during the reaction period. See WO 03/022896 for a description of a continuous process for the preparation of superabsorbent polymer. The polymerization mixture in the polymerization medium is subjected to polymerization conditions that are sufficient to produce the water-absorbent polymers. Preferably, the reaction is performed under an inert gas atmosphere, for example, under nitrogen or argon. The reaction may be performed at any temperature at which polymerization occurs, preferably 0°C or greater, more preferably 25°C or greater and most preferably 50°C or greater. The reaction is conducted for a time sufficient to result in the desired conversion of monomer to crosslinked hydrophilic polymer. Preferably, the conversion is 85 percent or greater, more preferably 95 percent or greater and most preferably 98 percent or greater. Advantageously, initiation of the reaction occurs at a temperature of at least 0°C.

It is also possible to prepare the superabsorbent polymer with the addition of recycled "fines" to the polymerization mixture. See U.S. Patent 5,342,899. The amount of fines added to the polymerization mixture is preferably less than 12 weight percent based on the amount of monomer in the polymerization mixture, more preferably less than 10 weight percent, and most preferably less than 8 weight percent.

It is also possible to carry out the polymerization process using multiphase polymerization processing techniques such as inverse emulsion polymerization or inverse suspension polymerization procedures. In the inverse emulsion polymerization or inverse suspension polymerization procedures, the aqueous reaction mixture as hereinbefore described is suspended in the form of tiny droplets in a matrix of a water-immiscible, inert organic solvent such as cyclohexane. Polymerization occurs in the aqueous phase, and suspensions or emulsions of this aqueous phase in an organic solvent permit better control of the exothermic heat of polymerization and further provide the flexibility of adding one or more of the aqueous reaction mixture components in a controlled manner to the organic phase.

Inverse suspension polymerization procedures are described in greater detail in U.S. Patents 4,340,706; 4,506,052; and 5,744,564. When inverse suspension polymerization or inverse emulsion polymerization techniques are employed, additional ingredients such as surfactants, emulsifiers and polymerization stabilizers can be added to the overall polymerization mixture. When any process employing organic solvent is utilized, it is preferred that the hydrogel-forming polymer material recovered from such processes be treated to remove substantially all of the excess organic solvent. Preferably, the hydrogel- forming polymers contain no more than 0.5 percent by weight of residual organic solvent.

During polymerization, the superabsorbent polymer generally absorbs all of the aqueous reaction medium to form a hydrogel. The polymer is removed from the reactor in the form of an aqueous hydrogel. The term "hydrogel" as used herein refers to water swollen superabsorbent polymer, and can be in the form of polymer particles. In preferred embodiments, hydrogels coming out of the reactor comprise 15 to 50 percent by weight polymer, with the remainder comprising water. In a more preferred embodiment the hydrogel comprises 25 to 45 percent polymer. The hydrogel is preferably processed into a particulate shape during the polymerization reaction process in the reactor by the agitator or other means in order to facilitate the removal of the hydrogel from the reactor. Preferred particle sizes of the hydrogel range from 0.001 to 25 cm, more preferably from 0.05 to

10 cm. In multiphase polymerization, the superabsorbent polymer hydrogel particles may be recovered from the reaction medium by azeotropic distillation and/or filtration followed by drying. If recovered by filtration, then some means of removing the solvents present in the hydrogel must be used. Such means are commonly known in the art.

The superabsorbent polymer may be in the form of particles or other forms, such as fibers. Preferably, the superabsorbent polymer is in the form of particles and is derived from one or more ethylenically unsaturated carboxyl-containing monomers and optionally one or more comonomers copolymerizable with the carboxyl-containing monomer.

After removal from the reactor, the hydrogel polymer is subjected to comminution, such as, for example, by a convenient mechanical means of particle size reduction, such as grinding, chopping, cutting or extrusion. The size of the gel particles after particle size reduction should be such that homogeneous drying of the particles can occur. Preferred particle sizes of the hydrogel range from 0.5 to 3 mm. This particle size reduction can be performed by any means known in the art that gives the desired result. Preferably, the particle size reduction is performed by extruding the hydrogel.

The comminuted hydrogel polymer particles are subjected to drying conditions to remove the remaining polymerization medium and any dispersing liquid including the optional solvent and substantially all of the water. Desirably, the moisture content of the superabsorbent polymer after drying is between zero and 20 weight percent, preferably between 5 and 10 weight percent.

The temperature at which the drying takes place is a temperature high enough such that the polymerization medium and liquid including water and optional solvent is removed in a reasonable time period, yet not so high so as to cause degradation of the superabsorbent polymer particles, such as by breaking of the crosslink bonds in the polymer. Preferably, the drying temperature is 180°C or less. Desirably, the temperature during drying is 100°C or above, preferably 120°C or above and more preferably 150°C or above. The drying time should be sufficient to remove substantially all of the water and optional solvent. Preferably, a minimum time for drying is 10 minutes or greater, with 15 minutes or greater being preferred. Preferably, the drying time is 60 minutes or less, with 25 minutes or less being more preferred. In a preferred embodiment, drying is performed under conditions such that water, and optional solvent, volatilizing away from the absorbent polymer particles is removed. This can be achieved by the use of vacuum techniques or by passing inert gases or air over or through the layers of polymer particles. In a preferred embodiment, the drying occurs in dryers in which heated air is blown through or over layers of the polymer particles. Preferred dryers are fluidized beds or belt dryers. Alternatively a drum dryer may be used. Alternatively the water may be removed by azeotropic distillation. Such techniques are well known in the art.

During drying, the superabsorbent polymer particles may form agglomerates and may then be subjected to comminution, such as, for example, by mechanical means for breaking up the agglomerates. In a preferred embodiment, the superabsorbent polymer particles are subjected to mechanical particle reduction means. Such means can include chopping, cutting and/or grinding. The object is to reduce the particle size of the polymer particles to a particle size acceptable in the ultimate end use. In a preferred embodiment, the polymer particles are chopped and then ground. The final particle size is preferably 2 mm or less, more preferably 0.8 mm or less. Preferably the particles have a size of 0.01 mm or greater, more preferably 0.05 mm or greater. Dried superabsorbent polymer particles can be used as the basis polymer for further surface crosslinking treatment, for example, using polyvalent cations like aluminum ions and/or using one of the crosslinkers mentioned above by coating and subsequent heating at elevated temperatures.

In one embodiment of the invention, the superabsorbent polymer particles are subjected to a heat-treatment step after drying and optional particle size reduction. Heat-treatment of the superabsorbent polymer provides a beneficial increase in the absoφtion under load (AUL) of the superabsorbent polymer, particularly the AUL under higher pressures. Suitable devices for heat-treatment include, but are not limited to, rotating disc dryers, fluid bed dryers, infrared dryers, agitated trough dryers, paddle dryers, vortex dryers, and disc dryers. One of ordinary skill in the art would vary the time and temperature of heat-treatment as appropriate for the heat transfer properties of the particular equipment used.

The time period and temperature of the heat-treatment step are chosen such that the absoφtion properties of the polymer are improved as desired. The polymers are desirably heat-treated at a temperature of 170°C or above, more desirably 180°C or above, preferably at 200°C or above and most preferably at 220°C or above. Below 170°C no improvement in the absoφtion properties is seen. The temperature should not be so high as to cause the polymers to degrade. Preferably, the temperature is 250°C or below and more preferably 235°C or below. The polymers are heated to the desired heat-treatment temperature and preferably maintained at such temperature for 1 minute or more and more preferably 5 minutes or more and most preferably 10 minutes or more. Below 1 minute no improvement in properties is generally seen. If the heating time is too long it becomes uneconomical and there is a risk that the polymer may be damaged. Preferably, polymer particles are maintained at the desired temperature for 60 minutes or less, preferably 40 minutes or less. Above 60 minutes no significant improvement in properties is noticed. The properties of the polymer particles can be adjusted and tailored by adjustment of the temperature and the time of the heating step.

After heat-treatment the superabsorbent polymer particles may be difficult to handle due to static electricity. It may be desirable to rehumidify the particles to reduce or eliminate the effect of the static electricity. Methods of humidification of dry polymers are well known in the art. In a preferred mode, the dry particles are contacted with water vapor. The dry particles are contacted with a sufficient amount of water to reduce or eliminate the effects of the static electricity, yet not so much so as to cause the particles to agglomerate. Preferably, the dry particles are humidified with 0.3 percent or more by weight of water and more preferably 5 percent or more by weight of water. Preferably, the dry particles are humidified with 10 percent or less by weight of water and more preferably 6 percent or less by weight of water. Optionally, agglomeration prevention or rehydration additives may be added to the crosslinked hydrophilic polymer. Such additives are well known in the art and include surfactants and inert inorganic particles such as silica; see, for example, DE 2706135 and U.S. Patents 4,286,082 and 4,734,478. Remoisturization can also be accomplished using certain salt solutions as taught in EP 0 979 250.

According to a preferred process for the preparation of compositions with odor control properties, the HPP can be added to the superabsorbent polymer manufacturing process at any time. For example, the HPP can be added to the reaction mixture, to a feed stream to the reactor, to the hydrogel, or to the dried polymer before or after heat treatment. However, it is preferred that the HPP be added at some stage after the hydrogel leaves the superabsorbent polymer reactor. The HPP may be added to the superabsorbent polymer polymerization mixture (i) during polymerization or prior to the beginning of the polymerization, or (ii) to the crosslinked hydrogel prior to or after comminution, or (iii) to the dried superabsorbent polymer particles prior to or after heat-treatment, if a heat-treatment is performed. It is also within the scope of the present invention to add the HPP several times at various stages of the superabsorbent polymer preparation process. It is preferred to add the HPP to the dried superabsorbent polymer particles, which are optionally heat-treated. It is also possible to add superabsorbent polymer to the HPP manufacturing process. Blending two commercially available products is also a method of preparing the composition of the invention.

The HPP preferably is distributed on and adsorbed or adhered to the surface of the superabsorbent polymer. Additional mixing means, such as agitating and stirring, may be applied to improve the distribution of the HPP on the surface of the superabsorbent polymer. In a preferred embodiment of the invention, the HPP is essentially homogeneously distributed on the surface of superabsorbent polymer particles. In a preferred embodiment, a binder is employed to bind the HPP and superabsorbent polymer together.

If the HPP is added to the dried and optionally heat-treated superabsorbent polymer, the HPP can be applied in connection with a dust control agent such as, for example, a polyether polyol as described in U.S. Patents 6,323,252 and 5,994,440. The polyether polyols are particularly suitable to bind the fine dust of the final superabsorbent polymer particles without causing agglomeration, and to bind the fine particles of powdery HPP particles on the surface. The addition of the polyether polyol further results in a more homogeneous distribution of the HPP or other additives on the surface of the superabsorbent polymer particles in the absence of organic solvent. Exemplary polyether polyols are available from The Dow Chemical Company under the brand name VORANOL. The polyether polyol is advantageously used in an amount of from 500 to 2,500 ppm, based on the weight of dry superabsorbent polymer. The concentration of the polyether polyol in water preferably ranges from 1 to 10 weight percent and more preferably from 3 to 6 weight percent.

Preferred binders include water-soluble polymers, more preferably cationically charged water-soluble polymers. Suitable water-soluble polymers are those that can be substantially dissolved in water to form a stable solution. Examples of preferred water-soluble polymers that can be employed as a binder in the present invention include polycationic water-soluble polymers that are a linear polyelectrolyte with a cationic charge density. Preferred water- soluble polymers include poly(diallyldimethylammonium chloride), cationic hydroxyethyl cellulose, for example, UCARE JR-09, JR-400, LR-400 and JR-30M (Amerchol Coφoration, USA), and a chiosonium pyrrolidone carboxylate available commercially as KYTAMER PC from Amerchol Coφoration.

The solubility of preferred water-soluble polymers advantageously is such that at least 0.5 gram, preferably at least 1 gram, and more preferably at least 2 grams, of water-soluble polymer is soluble in 100 grams of de-ionized water at room temperature and one atmosphere.

Water-soluble polymeric binders having a wide range of molecular weights are suitable for use in the present invention. Advantageously, the water-soluble polymer has a weight average molecular weight ranging from 500 to 10,000,000 grams per mole, more preferably from 2,000 to 2,000,000 grams per mole, and most preferably from 50,000 to 500,000 grams per mole. Methods for determining the weight average molecular weight of water-soluble polymers are well known in the art. For the puφoses of the present invention, weight average molecular weight is determined using gel permeation chromatography.

The water-soluble polymer binder advantageously is employed as a solution. The Brookfield viscosity (25°C) of the binder solution suitably is from 1 mPa-s (1 centipoise) to 5,000 mPa-s, more preferably from 5 mPa-s to 2,500 mPa-s, and most preferably from 10 mPa-s to 500 mPa-s.

The binder, when employed, is employed in an amount sufficient to improve the degree of binding between the HPP and the superabsorbent polymer. The binder preferably is added as an aqueous solution simultaneously with, prior to, or after the addition of the HPP to the superabsorbent polymer. The binder is preferably used in an amount of from 0.01 to 2 weight percent, more preferably from 0.025 to 1.0 weight percent, and most preferably from 0.075 to 0.25 weight percent, based on the weight of dry superabsorbent polymer, and its concentration in water is desirably from 0.1 to 25 weight percent. Mixtures of binders can be employed. The use of an aqueous binder solution comprising a polyether polyol and a cationically charged water-soluble polymer is especially preferred. In one embodiment, the dried and optionally heat-treated superabsorbent polymer particles are surface treated with aluminum sulfate. The aluminum sulfate may be added as an aqueous solution simultaneously with, prior to or after the addition of the HPP. The aluminum sulfate is preferably used in an amount of from 0.1 to 10 weight percent, based on dry superabsorbent polymer and its concentration in water is desirably from 5 to 49 weight percent. The use of an aqueous solution comprising a polyether polyol, a cationically charged water-soluble polymer, and aluminum sulfate is especially preferred.

Additives to which some odor control function is attributed can be used in addition to the HPP. These additives can be added to the dried and optionally heat-treated superabsorbent polymer prior to, simultaneously with or after the addition of HPP. Exemplary additives include, for example: activated carbon; chlorophyllin; chelating agents; sodium bicarbonate; various metals and metal compounds, including copper sulfate, copper acetate, zinc sulfate and zinc chloride; silicates; natural and synthetic zeolites, clay; perfumes; metallic or ionic silver in various forms, such as colloidal silver, silver acetate, silver nitrate and silver thiosulfate complexes; cyclodextrin; citric acid; biocides, such as Bronopol; plant extracts, such as extract and/or dry powder of green tea leaves, olive leaves, yucca, aloe, and quillaja; and combinations thereof. It is also possible to employ additive having no odor control function. Mixtures of additives can be employed.

To increase the flowability of the dried and optionally heat-treated superabsorbent polymer particles silicon dioxide, preferably fumed silica, or other fine inorganic or organic powders may be mixed with the polymer particles. Powdery additives are desirably added to and mixed with the polymer particles together with the fumed silica. The fumed silica is preferably used in amounts of from 0.01 to 5 weight percent, and more preferably from 0.05 to 3 weight percent, all based on dry polymer. An exemplary fumed silica is Aerosil R972, available from Degussa AG, Germany. The additives may be added dry or in dispersed form, such as in the form of an aqueous dispersion.

In yet another embodiment, dried and optionally heat-treated HPP-free superabsorbent polymers are combined with HPP-treated superabsorbent polymer. The HPP-treated superabsorbent polymer can be normally-sized material or can be "fines" or mixture of these. "Fines" are superabsorbent polymer particles that are created from drying, grinding, and natural attrition during transport and heat-treating process of the typical gel process. The fine particle size fraction is in general undesirably small and therefore generally not suitable for incoφoration by itself in personal care article such as diapers. However, fines can be recycled, as described in U.S. Patent 5,342,899, or blended with larger particle size fractions of superabsorbent polymer. This fine particle size fraction is often small enough to create dusting problems in production and can be a source of performance deterioration due to the well-known gel blocking tendency upon initial wetting. In a preferred embodiment, 'fines' are superabsorbent polymer particles which preferably pass through a 45 mesh (350 μm) screen and have been optionally heated to a temperature of from 170 to 250°C for from 1 to 60 minutes.

The relative proportions of the HPP and the superabsorbent polymer can vary widely depending on the intended use of the composition. The composition of the invention preferably comprises HPP in an amount of from 0.0001 to 100, more preferably from 0.0005 to 25, even more preferably from 0.001 to 1 and most preferably from 0.0025 to 0.05, all based on one part by dry weight of the superabsorbent polymer. Advantageously, the amount of HPP employed is at least 0.0005, preferably at least 0.0001 , more preferably at least 0.0005, and most preferably at least 0.0025 weight part per weight part of dry superabsorbent polymer. The amount of HPP employed advantageously is at most 100 parts, preferably at most 25 parts, more preferably at most 1 part, and most preferably at most 0.05 part per part of dry superabsorbent polymer.

The composition of the present invention can be used to control malodors comprising malodorous volatile organic compounds including, for example: indoles; mercaptans; sulfides, such as dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide; ammonia; amines, such as, trimethyl amine; alcohols; ketones, aldehydes; and volatile fatty acids.

These volatile organic molecules represent many of the typical malodors generated by feces, urine, sweat odor, body odor, pet odors, trash and waste, tobacco smoke, and cooking odors, such as the odors of garlic, onions, fish and grease.

The improved odor control properties of the composition of the invention are confirmed by subjecting the composition to swelling with a human urine solution using the sample preparation method and test protocol described hereinbelow, in which a sample is subjected to a sensory evaluation ('sniff test') using an ASTM E544-99 "Standard Practice for Referencing Suprathreshold Odor Intensity", wherein the assessors rate the malodor intensity of the sample. The sniff test is used to quantity malodor intensity, wnicn is expressed as an n-butanol equivalent malodor intensity in parts per million of n-butanol.

The n-butanol equivalent malodor intensity is improved by employing the composition of the invention rather than pure superabsorbent polymer. Advantageously, the n-butanol concentration is not more than 60 ppm, preferably below 50 ppm and most preferably below 40 ppm at time zero when subjected to the sniff test method. The n-butanol concentration is preferably below 70 ppm, more preferably below 60 ppm and most preferably below 50 ppm at 1 hour. The n-butanol concentration is preferably below 90 ppm, more preferably below 70 ppm and most preferably below 50 ppm at 3 hours. The n-butanol concentration is preferably below 125 ppm, more preferably below 90 ppm and most preferably below 70 ppm at 6 hours.

Suφrisingly, some physical properties, such as permeability and attrition resistance, of the superabsorbent polymer are improved by incoφorating HPP into the superabsorbent polymer.

The polymer composition of this invention preferably is non-abrasive and can be used in any application where absoφtion and binding of aqueous fluids is desired, and is especially suitable for such applications where it would be desirable to inhibit the development of malodor or control malodor. In a preferred embodiment, the composition of this invention is mixed into or attached to a structure of absorbent material such as synthetic or natural fibers or paper- based woven or nonwoven fibers to form an article. In such an article, the woven or nonwoven structure functions as a mechanism for wicking and transporting fluid via capillary action to the superabsorbent polymer particles which bind and retain such fluids. Examples of such articles include sanitary napkins, diapers, and adult incontinence articles. In addition, there are various applications of the odor control compositions of the invention in non-personal care applications, for example in: medical care; agriculture; livestock odor containment; horticulture; gardening; pet litter; fertilizer; clothing; perspiration pads; diaper pails; control of household and office odors; laundry bags; trash bags and containers; caφet deodorizers; caφet backing; furniture deodorizers; fabric deodorizers; footwear; foam fabrication; film fabrication; fiber fabrication, including bi- component fibers; wateφroofing; landfills; pulp and paper manufacturing; water-absorbing structures, cable wrap; and packaging, including food packaging. The absorbent structures according to the present invention comprise means to contain the polymer having odor control property. Any means capable of containing the described polymer, which means is further capable of being positioned in a device such as an absorbent garment, is suitable for use in the present invention. Many such containment means are known to those skilled in the art. For example, the containment means may comprise a fibrous matrix such as an airlaid or wetlaid web of cellulosic fibers, a meltblown web of synthetic polymeric fibers, a spunbonded web of synthetic polymeric fibers, a coformed matrix comprising cellulosic fibers and fibers formed from a synthetic polymeric material, airlaid heat-fused webs of synthetic polymeric material or open-celled foams. In one embodiment, it is preferred that the fibrous matrix comprise less than 10, preferably less than 5, weight percent of cellulosic fibers. Further, the containment means may comprise a support structure, such as a polymeric film, on which the superabsorbent polymer particles is affixed. The superabsorbent polymer particles may be affixed to one or both sides of the support structure which may be water-pervious or water-impervious.

The absorbent structures according to the present invention are suited to absorb many fluids including body fluids such as, for example, urine, menses, and blood and are suited for use in absorbent garments such as diapers, adult incontinent products and bed pads; in catamenial devices such as sanitary napkins and tampons; and in other absorbent products such as, for example, wipes, bibs and wound dressings. Accordingly, in another aspect, the present invention relates to an absorbent garment comprising an absorbent structure as described above.

In yet another aspect, the present invention relates to an absorbent article described above containing HPP but optionally without superabsorbent polymer particles. For example, such an absorbent article can comprise HPP and at least one of a woven or nonwoven structure of paper, synthetic fibers, synthetic films, synthetic foams, natural fibers, or a combination of these. Such articles also can be used in the end use applications described hereinabove.

Specific Embodiments of the Invention

The following examples are included to illustrate the invention, and do not limit the scope of the claims. All parts and percentages are by weight unless otherwise stated. The following materials are employed in the experiments.

The superabsorbent polymer (hereinafter SAP) is DRYTECH ST 10 brand superabsorbent polymer, which is commercially available from The Dow Chemical Company.

DOWEX OPTIPORE L323, DOWEX OPTIPORE V503, and DOWEX OPTIPORE V439 brand resins, which are commercially available from The Dow Chemical Company, are used as the HPP. These HPPs contain residual moisture. A 10.0 gram sample of each HPP, in duplicate, is placed in an air-circulated oven at 105°C for 3 hours. Each sample is then cooled to room temperature over copper sulfate in a desiccator. Each sample is weighed and the moisture content is calculated. The moisture content for V503 is 0.5 percent, for L323 is 57.0 percent, and for V493 is 2.2 percent.

Cationic water-soluble polymers employed in the examples include UCARE JR-09 brand hydroxyethyl cellulose and KYTAMER PC brand chiosonium pyrrolidone carboxylate, both available from Amerchol Coφoration, USA.

VORANOL CP 755 brand polyether polyol is commercially available from The Dow Chemical Company.

Test Methods

"Percent Moisture Uptake" Test Method

This method is used to determine the hydrophobicity of a sample of polymer. The sample is air dried overnight in a fume hood and then vacuum dried at 60°C for 3 hours. Approximately 5.0 grams of the dried polymer is placed on a moisture balance and dried to constant weight at 90°C. The dried polymer is transferred to a small glass column, and then 85 percent relative humidity air is passed through the column for two hours. The humidified adsorbent is transferred to a moisture balance and dried to determine the weight percent water uptake from the humid air. Percent Moisture Uptake is calculated as (g water/ (g water + g dry polymer)) x 100.

Particle Size Analysis

A Becker Coulter RapidVue (Beckman Coulter Particle Characterization, Miami, FL 33116-

9105 ) is suitable for HPP beads that have mean particle sizes between 70 and 1560 microns. Another analyzer, RapidVue 5X, is used for the fine powdery HPP particle analysis. This method is applicable to HPP materials that have mean particle sizes between 15 and 500 microns. In both particle size analysis methods, a sample of HPP is analyzed by pumping it, in a dilute aqueous slurry form, through a cell, which is illuminated by a strobe lamp. The image is recorded by a charge-coupled device (CCD) camera. The system analyzes each image or frame, determines the number of valid counts per frame, the diameter of each valid particle and subsequently accumulates the data over several frames. As a mean diameter, the volume median diameter (VMD) is the diameter that lies at 50 vol. percent when the cumulative vol. percent is plotted as a function of particle size in μm. The coefficient of variation (CV), expressed as a percentage, is defined as: diameter at 84 cum. vol. % - diameter at 16 cum. vol. % ϊ ^{x l0}°

In order to prepare a fine powder of HPP, the following grinding procedures are employed.

Wet Grinding Procedure

Approximately 3 grams of HPP are placed in a mortar, and then 2-3 grams of deionized water are added. The wetted polymer is then crushed thoroughly by hand using a pestle to form a crushed polymer paste. The paste is dried over copper sulfate in a desiccator that is placed in an air-circulated oven at 50°C overnight resulting in a dried cake. After cooling, the cake is broken down to a fine powder of HPP using the mortar and pestle. This material is used "as is," without screening or segregation of particle sizes.

Dry Grinding Procedure

The desired amount of HPP is introduced into an Ultracentrifugal Mill (Retsch GmbH, Germany), which has an inner screen with openings of 80 micrometers, at a speed of 10,000 φra. The resulting powder is collected for later use without further treatment.

A RapidVue 5X was used for the fine powdery HPP particle analysis, and the volume median diameter (VMD), coefficient of variation (CV), and volume percent in different size ranges are given in Table 1. Table 1: Particle Size Analysis of HPP Powders

Preparation of Water-Soluble Polymer Solution The desired quantity of water is measured into a small beaker containing a magnetic stir bar. The speed of the magnetic stirrer is adjusted so that a small vortex is present. The desired amount of water-soluble polymer is slowly added until fully dissolved. If any VORANOL CP 755 brand polyether polyol is to be added, it can be added at any point during the mixing process.

BLENDING METHODS Mini-Blender Procedure This method uses small homemade lab blender, referred to hereinafter as the 'mini-blender,' which comprises a mixing chamber of a volume of approximately 200mL, a shaft with rotor blades, and a nozzle. The mixing chamber dimensions are as follows; the length is 125mm and 67mm in diameter. The shaft is 13mm in diameter and runs the full length of the mixing chamber including penetration of both ends of this unit. Eight paddles are fixed to the shaft via welds. Starting from one end, the paddles are opposed to each other down the length to get optimum blending and are offset 90° to each other in a clockwise rotation. The paddles measure 24mm in height, 20mm wide at the point of attachment to the shaft, and 29mm wide at the farthest point from the shaft. The outer most edge is curved to match the inside diameter of the mixing chamber. The spray nozzle is from the Spraying Systems Company, Wheaton, IL. 60189-7900, USA. This is a single flat fan pattern with an approximately 75° spray pattern. This nozzle is based on a venturi type nozzle where air (5psi) comes in one side and causes a vacuum to propel the liquid into the mixing chamber. A 75.0 g sample of SAP is placed into the mini -blender at room temperature. The desired amount of HPP powder is then added to the SAP powder and the mixture is agitated at 200 rpm for 5 minutes. If a binder is added, it is added using an aqueous solution comprising VORANOL CP 755 brand polyether polyol or polycationic water-soluble polymers. The mixture is then agitated at 200 rpm for another 5 minutes.

Forberg Blender Procedure This blending method uses a Forberg blender having a mixing volume of approximately

2,500 mL, a shaft with rotor blades and a nozzle. A 2.0 kg sample of SAP and is placed into the Forberg blender at room temperature. The desired amount of HPP is added to the blender and the mixture is agitated at 126 rpm for 2 minutes. An aqueous solution (4 percentr b.o. dry SAP) having 950 ppm of VORANOL CP 755 polyether polyol and 1250ppm of UCARE JR09 water-soluble polycationic polymer is prepared in a small beaker and stirred with a magnetic stirrer until the resulting solution is homogeneous. The solution is sprayed onto the dry polymer with agitation (126 φm). The mixture then is agitated (126 φm) for another 5 minutes. The resulting product is sieved to remove agglomerates using a No. 16 ASTM El l specification shaking sieve.

The sample preparation procedures described above are employed for all experiments except as otherwise noted.

Two different methods are used for evaluating odor control efficacy; gas chromatography using a solid phase micro extraction (SPME), or a sniff test according to ASTM E544-99.

GAS CHROMATOGRAPHY (GC) EXPERIMENTS USING SOLID PHASE MICRO EXTRACTION (SPME)

This method is used to measure the efficiency of HPP as a means of controlling malodor. Dimethyl disulfide (DMDS) and trimethyl amine (TMA) are used as model malodor molecules. The determination of TMA and DMDS in the headspace above SAP samples by gas chromatography (GC) /mass spectrometry (MS) using solid phase microextraction (SPME) is conducted as follows. Equipment Gas Chromatograph: Agilent 6890 gas chromatograph, 395 Page Mill Rd. Palo Alto, CA 94306, USA. Mass Selective Detector: Agilent 5973 MSD. SPME Fiber: Supelco Fiber Assembly, 57348-U, 2 cm-50/30 μm DVB/Carboxen/PDMS Stableflex Fiber 100 mL Serum Vials: Available from Wheaton, 1501 N 10^th St, Millville, NJ 08332

Teflon lined septum: Available from VWR, 6801 Gray Road, Suite D, Indianapolis, IN 46237 Standards and Reagents

Sodium Chloride: 99+percent Reagent ACS grade, Catalog # 42429-5000 from ACROS Organics, Fisher Scientific, 2000 Park Lane Dr. Pittsburg, PA 15275

Trimethylamine: 40 percent in water, Catalog # 43,326-8, available from Aldrich Chemicals, P.O. Box 355, Milwaukee, WI 53201

Dimethyldisulfide: 99+percent, Catalog # 24,131-8, available from Aldrich Chemicals, P.O. Box 355, Milwaukee, WI 53201

High Purity Water: Milli-Q water system (in house)

Methanol: HPLC grade available from VWR, 6801 Gray Road, Suite D, Indianapolis, IN 46237

Malodor Solution Preparation

Stock solutions of TMA and DMDS are prepared by diluting the standards in water and methanol, respectively. The working solutions are prepared by adding known amounts of NaCl and the stock TMA and DMDS solutions to water in order obtain a solution containing 400-800 ppm TMA and 5 ppm DMDS.

Sample Preparation

1 gram of each sample of HPP/SAP is loaded into 100 mL serum vials. In addition to the samples, a vial containing just the TMA/DMDS solution, and a vial containing a control SAP sample are analyzed. At approximately 35 minute intervals, 30 mL of the TMA/DMDS solution is added to each of the vials. The vials are sealed immediately after the solution is added to them. The blank solution sample contained only solution without SAP. SAP without treatment with the solution is used as a control. The vials are placed in an oven at 38°C for known amount of time. Each sample/control is prepared such that they have the same heating time in the oven prior to volatiles collection using the SPME fiber. Sample Analysis The two control samples (30 mL of the TMA/DMDS solution and 1 gram of the base SAP plus 30 mL of the TMA/DMDS solution) were analyzed before any samples of the modified polymer. Following a known constant amount of time, the samples are sequentially removed from the oven and the SPME fiber is inserted through the septum of the serum vial. The volatiles in the headspace are collected on the fiber for 5 minutes. The fiber is withdrawn from the sample and inserted into the inlet of the Agilent 6890 gas chromatograph connected to the Agilent MSD (mass selective detector), and data acquisition is initiated. The fiber is desorbed in the inlet for 5 minutes. Following data acquisition, the 58 mass ion of TMA and the 94 mass ion of DMDS are extracted from the total ion chromatogram (TIC). The areas of these two ions are measured and are used to compare the relative amount of the TMA and DMDS in the headspace above the samples. The conditions for gas chromatography / mass spectrometry experiments with solid phase microex traction are shown in Table 2.

Table 2: Gas Chromatography/Mass Spectrometry Conditions

Gas Chromatograph Agilent 6890

Mass Selective Detector Agilent 5973

Column HP 5 percent Phenyl Methyl Siloxane 30 M x 0.25 mm x 0.25 μm film thickness

Inlet Temperature 260°C

Mode Splitless

Pressure 13 psi

Purge flow 23.8 mL/min

Purge Time 0.75 min

Total Flow 27.6 mL/min

Gas Helium

MSD Transfer Line 290°C

Solvent Delay O min

Low Mass 15

High Mass 450

MS Quad 150°C

MS Source 230°C Oven Initial Temperature 35°C Initial Time 2 min Ramp 1 15°C/min to 250°C Hold 0 minutes SNIFF TEST: ODOR EVALUATION PROCEDURE ACCORDING TO ASTM E544 - 99

Odor evaluation of various samples of the present invention is conducted by St. Croix Sensory Inc, (Lake Elmo, MN, USA). The odor evaluation testing involves analyzing the odor of test samples that are contacted with a 120 mL composite urine sample collected from 10 healthy adults. The composite urine samples for each test are tested for in-vitro urinalysis diagnostic parameters using a clinical dipstick test method. Table 3 below summarizes the number of adult urine donors, the number of male and female donors, and the results of the diagnostic test on the composite urine sample. Table 3: Superabsorbent Polymer Odor Testing with Adult Urine: Adult Composite Urine Sample Summary

All odor testing is conducted by ten (10) assessors trained and experienced at odor evaluation of products and materials. The assessors rate the odor intensity of each sample following the procedure of ASTM E544-99, "Standard Practice for Referencing Suprathreshold Odor Intensity."

Intensity Calculation Example

This example outlines the calculations from a laboratory test used to determine odor intensity using the trained panel of assessors as described above. This example illustrates the Dynamic-Scale Method, which utilizes an eight (8) level intensity scale presented with the UTRI Dynamic Dilution Binary Olfactometer (n-butanol Wheel). The eight levels of the intensity scale are:

Table 4: Intensity (n-butanol) Scale

The assessor sniffs the product sample and then compares the observed intensity of the sample to a specific concentration level of the standard odorant (n-butanol) from the olfactometer device. The assessor reports which level on the butanol scale matches the intensity of the odorous sample, for example "Level 3." The Table 5 below is an example data sheet containing the results of five assessors determining the odor intensity of a hypothetical sample A.

Table 5: Example of Intensity Calculation of Sample A

The butanol scale is a geometric progression (each level is approximately twice the previous); therefore, logarithmic transformation must be performed on each value in order to use normal statistics. Once the average logarithmic value is obtained, the final result can be calculated by taking the anti-log of the average. For this referencing method of quantifying odor intensity, the result is expressed in parts per million (PPM) of n-butanol. For Sample A, the odor intensity is reported as 42-ppm n-butanol equivalent.

Adult Urine: Urine is received from healthy adult contributors. In a timely manner (within 1 hour) each contributor delivers urine into a 500 mL wide mouth, amber-glass bottle. A uniform volume (150 mL) from each contribution is added to a container to form a composite urine sample.

SAP Samples: Four grams of each SAP sample are placed in the bottom of a 250 mL wide mouth, amber-glass jar at room temperature. Then, 120 grams (120-mL) of the composite urine is added to each SAP sample. The jar is then capped and shaken gently for 15 seconds. The SAP begins to swell in the jar. The bottles are then placed in an oven at 38°C for 15 minutes. After 15 minutes in the oven, the samples are removed and the sensory evaluation is started (time zero). All sensory evaluations take place at room temperature. After all sensory evaluations are complete at time zero, the samples are returned to the oven at 38°C. This process is repeated at times 1 hour, 3 hours, and 6 hours after time zero. Adult Urine Presentation: The odor evaluations are conducted in "double-blind" test protocol wherein the assessors (judges) and the presenter (panel administrator) are not aware of the sample type nor sample properties. The samples are presented in a "Latin Square" random design with each sample being evaluated in each sequence position and never preceding and following the same samples. Each assessor observes (sniffs) the sample container headspace with the nose approximately 1-inch above the jar rim.

Example 1

A blend of 2.0 weight percent HPP (DOWEX OPTIPORE V493 or V503 from the Wet Grinding Procedure) based on the dry weight of SAP is prepared via the Mini-Blender Procedure. The blend is subjected to GC/MS SPME evaluation. The DMDS and TMA concentrations in the malodor solution control are 4.7 ppm and 409 ppm, respectively. The results are shown in Table 6. Numbers in parentheses are the relative percent TMA and percent DMDS reduction relative to the SAP control.

Table 6: Peak Areas and Odor Control Efficacy of SAP/HPP Compositions on Trimethyl Amine (TMA) and Dimethyl Disulfide (DMDS)

The head space concentration of the solution control (blank malodor solution) shows an essentially constant concentration of DMDS and TMA over the time period of 390 minutes. The head space TMA concentration of the solution control is reduced by the presence of SAP by 97.4 percent, 97.5 percent and 98.5 percent for 0, 180 and 390 minutes, respectively. Both the SAP/HPPs compositions further significantly reduced the TMA concentration in the head space. The efficacy of the V503 HPP in this experiment is much greater than that of the V493 HPP.

The head space DMDS concentration of the solution control is not reduced by the presence of SAP alone, regardless of the time. Suφrisingly, both the SAP/HPP compositions significantly reduced the DMDS concentration. Example 2

Example 1 is repeated except that the HPP is L323, an aqueous (2 wt. percent b.o. dry SAP) solution of 950 ppm (b.o. dry SAP) VORANOL CP 755 brand polyether polyol is employed in the blending procedure, and the DMDS and TMA concentrations in the malodor solution control are 5 ppm and 430 ppm, respectively. The results are shown in Table 7.

The TMA concentration of the solution control is reduced remarkably by the mere presence of SAP by 97.8 percent, 98.7 percent and 99.0 percent for 0, 180 and 390 minutes, respectively. The SAP/HPP composition reduced the TMA concentration in the head space significantly compared to the control SAP. The efficacy of the SAP/HPP composition versus TMA is found to increase with time. The SAP/HPP composition also strongly reduces the DMDS concentration.

Table 7: Peak Areas and Odor Control Efficacy of L323 Polymeric Adsorbent Resins on Trimethyl Amine (TMA) and Dimethyl Disulfide (DMDS)

Example 3

A blend of 1.8 weight percent V503 based on the dry weight of SAP is prepared via Mini- Blender Procedure using a water-soluble polymer as shown in Table 8. HPP from the wet grinding procedure is used. The blend is subjected to GC/MS SPME evaluation. The DMDS and TMA concentrations in the malodor solution control are 5 ppm and 478 ppm, respectively. The results are shown in Table 9. Numbers in parentheses are the relative percent TMA and percent DMDS reduction relative to the SAP control. Table 8: Experiments with Water-soluble Polymers

Table 9: Peak Areas and Odor Control Efficacy of Water-Soluble Polymers

In Table 9 it is seen that the SAP/HPP together with a binder shows a significant improvement both for TMA and DMDS reduction compared to the control.

Example 4

Table 10 below summarizes the results from the sniff tests from samples treated with V503 or L323 HPP. Commercially available HPP beads are ground using the ultracentrifuge mill without further treatment. The samples are prepared using the Forberg lab blender and contain 1250 ppm JR-09 cationic water-soluble polymer and 950 ppm VORANOL CP 755. The amount of the HPP is varied from 0.25 percent to 1.8 percent. The odor intensity for samples treated with varying concentration of the polymeric adsorbent is expressed in ppm (n-butanol) as a function of time. Table 10: Sniff Test and Odor Intensity Expressed in PPM (n-butanol) as a Function of Time for samples Treated with V503 or L323 HPP

The malodor of the SAP control steadily increased with time. All samples demonstrate improved efficacy of odor reduction versus the SAP control regardless of the type of HPP employed.

Physical Characteristics of HPP

Some of the physical characteristics of the different HPPs are given in Table 11. The V503 and V493 material have the same pore size and have similar BET surface areas, but the moisture uptake differs greatly. Moisture uptake is a measure for hydrophobicity for a given polymer adsorbent, and is a material specific property. The pore size and BET surface area are inversely proportional, as can be seen in Table 11. Table 1 1 : HPP Properties

The overall results from the Tables above suφrisingly show that SAP/HPP compositions are highly effective in odor control. The best odor control efficacy is found with V503 and L323. Both had much lower moisture uptake (percent), and therefore, are much more hydrophobic, than V493. At a comparable hydrophobicity (as in the case of V503 and L323), V503, having a higher surface area and smaller pore size, generally performs better than L323.

Claims

WHAT IS CLAIMED IS:

1. A composition comprising a superabsorbent polymer and a hydrophobic porous polymer.

2. The composition of Claim 1 wherein the amount of hydrophobic porous polymer is from 0.0001 to 100 weight parts per weight part of superabsorbent polymer.

3. The composition of any of the preceding claims further comprising a binding amount of a material that binds at least part of the hydrophobic porous polymer to the superabsorbent polymer.

4. The composition of any of the preceding claims wherein the hydrophobic porous polymer is a methylene bridged aromatic polymer.

5. The composition of any of the preceding claims wherein the hydrophobic porous polymer is a methylene-bridged styrene/divinylbenzene copolymer having a hydrophobicity of not more than 40 weight percent.

6. The composition of any of the preceding claims wherein the hydrophobic porous polymer has a hydrophobicity of not more than 30 weight percent.

7. An absorbent article comprising the composition of any of the preceding claims.

8. A process for the preparation of superabsorbent polymer particles, the process comprising:

(I) polymerizing a polymerization mixture comprising: (a) one or more ethylenically unsaturated carboxyl-containing monomers, (b) one or more crosslinking agents, (c) optionally one or more comonomers copolymerizable with the carboxyl- containing monomer, and (d) a polymerization medium, to form a crosslinked hydrogel,

(IT) comminuting the hydrogel to particles, and (HI) drying the hydrogel, wherein a HPP is added in at least one of the following steps: (i) to the monomer mixture prior to the beginning of the polymerization or to the polymerization mixture during polymerization, or (ii) to the crosslinked hydrogel prior to or after comminution in step (U), or (iii) to the dried polymer particles after step (HI).

9. A composition comprising:

(a) from 0.01 to 99.99 weight percent of a superabsorbent polymer; and

(b) from 0.01 to 99.99 weight percent of a material having the following characteristics: (i) microporosity of from 0.2 to 0.4 cc/g, a mesoporosity of at least 0.3 cc/g, and a total porosity of at least 0.8 cc/g wherein the microporosity comprises less than 40 percent of the total porosity;

(ii) a BET surface area of from 200 to 1800 m²/g; (iii) an average pore diameter of from 0.5 nm to 15 nm; and (i v) a hydrophobicity of from 0.01 percent to 40 percent, with the proviso that the sum of the percentages of (a) and (b) equals 100 percent.

10. An absorbent article comprising a hydrophobic porous polymer.