An absorbent polymer composition, which can be in the form of a foam, that includes a polymeric material, absorbent particles and thermally expandable (or expanded) microspheres.

SUMMARY OF THE INVENTION

In a first aspect, the present invention is directed to an absorbent polymer composition that includes a polymeric material, absorbent particles, and thermally expandable microspheres. In a second aspect, the present invention is an absorbent polymer foam composition that includes a polymeric material, absorbent particles, and thermally expanded microspheres. Herein, the absorbent particles and expandable microparticles are two distinct materials.

Preferably, the absorbent particles are provided in a matrix (e.g., a hydrocarbon oil) and form an emulsion (e.g., an inverse emulsion). Such emulsions are often referred to simply as "hydrocolloid."

In certain embodiments, the absorbent particles are superabsorbent. Herein, "absorbent" means that a material is capable of absorbing water or bodily fluids, and "superabsorbent" means that the material will absorb at least 100% of its weight.

Preferably, a polymer foam composition of the present invention that includes thermally expanded microspheres has a density less than 0.8 gram per cubic centimeter (cc), preferably less than 0.7 gram per cc.

In a particularly preferred embodiment, the present invention provides a polymer foam composition that includes: a polymeric material; a hydrocolloid comprising superabsorbent particles; and thermally expanded microspheres; wherein the polymer foam has a density of less than 0.8 gram per cubic centimeter.

In another embodiment, the present invention features an absorbent polymer foam composition that is preparable by a method that includes: combining a polymeric material, absorbent particles (preferably in the form of a hydrocolloid), and thermally expandable microspheres at a temperature below the expansion temperature of the microspheres to form a mixture; and increasing the temperature of the mixture above the expansion temperature of the thermally expandable microspheres.

In yet another embodiment, the present invention provides a method that includes: combining a polymeric material, absorbent particles (preferably in the form of a hydrocolloid), and thermally expandable microspheres to form a mixture in an extruder at a temperature below the expansion temperature of the microspheres; and increasing the temperature of the mixture above the expansion temperature of the thermally expandable microspheres during extrusion. Preferably, the resultant foamed composition has a density less than 0.8 gram per cubic centimeter (cc) (preferably less than 0.7 gram per cc) is formed.

The present invention also provides medical articles that include the polymer compositions. The medical articles can be any of a wide variety of products, but preferably are wound dressings and wound packing materials.

The present invention also provides methods of making and using the polymer compositions.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

The present invention provides polymer compositions that include a polymeric material, absorbent particles (which are preferably provided in the form of a hydrocolloid), an optional bioactive agent, and thermally expandable microspheres. The polymeric material can include a mixture of polymers. It can also include a pressure sensitive adhesive if desired. The polymer composition can be in a wide variety of forms, such as an extruded film (e.g., having a thickness of 0.5 millimeter (mm) to 10 mm), a coating, a hydrocolloid (i.e., a material that contains particles in a second phase, typically hydrophilic particles dispersed in a lipophilic phase (e.g., hydrophobic oil)), a molded article, etc.

The polymer compositions are preferably heated to expand the thermally expandable microspheres to provide a foam, such as an absorbent foam. Preferably, such a polymer foam composition with expanded microspheres therein has a density of less than 0.8 gram per cubic centimeter (cc), preferably less than 0.7 gram per cc.

Expansion of the thermally expandable microspheres can be carried out under pressure, such as that experienced in an extruder, or under ambient conditions such as that found in an air-circulating oven.

Preferably, the absorbent polymer foam composition is preparable by a method that includes combining components that include a polymeric material, absorbent particles (preferably in the form of a hydrocolloid), an optional bioactive agent, and thermally expandable microspheres at a temperature below the expansion temperature of the microspheres during extrusion such that a foamed composition having a density of less than 0.8 gram per cubic centimeter (cc) (preferably less than 0.7 gram per cc) is formed.

It has been discovered that absorbent foams of the present invention that have been formed by extruding the material and expanding the microspheres in the extruder have substantially higher initial uptake of aqueous fluids compared to: (1) un-foamed compositions (with or without unexpanded microspheres); (2) foams prepared via thermal decomposition of chemical foaming agents; and (3) foams prepared from extruded films containing thermally expandable microspheres that have been expanded after extrusion such as by thermal oven exposure.

Significantly, preferred compositions of the present invention demonstrate a surprising rate of absorbency. For example, deionized water absorbency (wet/dry weight) at 2 hours of swelling time is preferably at least 10%, and more preferably at least 20%, higher than the same polymer composition unfoamed or foamed using chemical foaming agents.

Polymeric Material

A variety of different polymers, as well as mixtures thereof, may be used for the polymeric material (i.e., polymeric matrix). Preferably, such polymers are those that are suitable for melt processing, particularly extrusion processing. As is well understood in the art, a wide range of physical properties of the polymer compositions can be obtained by selection of the types and amounts of different polymers.

Polymeric materials used to prepare the absorbent polymer compositions of the present invention are melt-processible when they are fluid or pumpable, and they do not significantly degrade or gel at the temperatures used to melt process (e.g., extruding or compounding) the composition (e.g., 50.degree. C. to 300.degree. C.). Preferably, such materials have a melt viscosity of 10 poise to 1,000,000 poise, as measured by capillary melt rheometry at the processing temperatures and shear rates employed in extrusion. Typically, suitable materials possess a melt viscosity within this range at a temperature of 125.degree. C. to 175.degree. C. and at a shear rate of approximately 100 seconds.sup.-1 (s.sup.-1).

If multiple polymer components are to be blended, preferably, each of the components has similar melt viscosity. The ability to form a finely dispersed morphology is related to a ratio of the shear viscosity of the components at melt mixing temperatures. Shear viscosity is determined using capillary rheometry at a shear rate approximating extrusion blending conditions, that is, 100 s.sup.-1 and 175.degree. C. When a higher viscosity component is present as the minor component, the viscosity ratio of minor to major components is preferably less than 20:1, more preferably less than 10:1. When a lower viscosity material is present as the minor component, the viscosity ratio of minor to major components are preferably greater than 1:20, more preferably greater than 1:10. The melt viscosities of individual components may be altered by the addition of plasticizers, tackifiers or solvents or by varying mixing temperatures.

The organic polymers suitable for the matrix of the polymer compositions of the present invention can be elastomeric, thermoplastic, or both.

Elastomeric polymers useful in the invention are typically materials that form one phase at 21.degree. C., have a glass transition temperature less than 0.degree. C., and exhibit elastomeric properties. The elastomeric polymers include, but are not limited to, polyisoprenes, styrene-diene block copolymers, natural rubber, polyurethanes, polyether-block-amides, poly-alpha-olefins, (C1 C20)acrylic esters of meth(acrylic) acid, ethylene-octene copolymers, and combinations thereof. Elastomeric materials useful in the present invention include, for example, natural rubbers such as CV-60 (a controlled viscosity grade natural rubber having Mooney viscosity of 60 +/- 5 ML, 1+4 at 100.degree. C., available as an International commodity); butyl rubbers, such as Exxon Butyl 268 available from Exxon Chemical Co., Houston, Tex.; synthetic poly-isoprenes such as CARIFLEX IR309, available from Kraton Polymers, Houston, Tex., and NATSYN 2210, available from Goodyear Tire and Rubber Co., Akron, Ohio; ethylene-propylenes; polybutadienes; polyisobutylenes such as VISTANEX MM L-80, available from ExxonMobil Chemical Co.; and styrene-butadiene random copolymer rubbers such as AMERIPOL 1011A, available from BF Goodrich of Akron, Ohio.

Thermoplastic polymers useful in the invention include, for example, polyolefins such as isotactic polypropylene; low density or linear low density polyethylene; medium density polyethylene; high density polyethylene; polybutylene; polyolefin copolymers or terpolymers, such as ethylene/propylene copolymer and blends thereof-, ethylene-vinyl acetate copolymers such as ELVAX 260, available from E. I. DuPont de Nemours & Co., Wilmington, Del.; ethylene acrylic acid copolymers; ethylene methacrylic acid copolymers such as SURLYN 1702, available from E. I. DuPont de Nemours & Co.; polymnethylmethacrylate; polystyrene; ethylene vinyl alcohol; polyester; amorphous polyester; polyamides; fluorinated thermoplastics such a polyvinylidene fluoride; polytetrafluoroethylene; fluorinated ethylene/propylene copolymers; halogenated thermnoplastics such as a chlorinated polyethylene; and combinations thereof. Other exemplary thermoplastic polymers are disclosed in International Publication No. WO 97/23577.

Thermoplastic elastomeric polymers useful in the invention are typically materials that form at least two phases at 21.degree. C., flow at a temperature greater than 50.degree. C. and exhibit elastomeric properties. Thermoplastic elastomeric materials useful in the present invention include, for example, linear, radial, star and tapered styrene-isoprene block copolymers such as KRATON D1107P, available from Kraton Polymers, and EUROPRENE SOL TE 9110, available from EniChem Elastomers Americas, Inc. Houston, Tex., linear styrene-(ethylene/butylene) block copolymers such as KRATON G1657 available from Kraton Polymers, linear styrene-(ethylene/propylene) block copolymers such as KRATON G1657X available from Kraton Polymers, styrene-isoprene-styrene block copolymers such as KRATON D1119P available from Kraton Polymers, linear, radial, and star styrene-butadiene block copolymers such as KRATON D1118X, available from Kraton Polymers, and EUROPRENE SOL TE 6205 available from EniChem Elastomers Americas, Inc., polyetheresters such as HYTR-EL G3548, available from E. I. DuPont de Nemours & Co., and poly-alpha-olefin based thermoplastic elastomeric materials such as those represented by the formula --(CH.sub.2--CHR) where R is an alkyl group containing 2 to 10 carbon atoms and poly-alpha-olefins based on metallocene catalysis such as ENGAGE EG8200, an ethylene/l-octene copolymer available from DuPont Dow Elastomers Co., Wilmington, Del. Other exemplary thermoplastic elastomers are disclosed in International Publication No. WO 96/25469.

For certain embodiments, preferably, the polymeric material includes a pressure-sensitive adhesive (PSA). It should be noted that the polymers do not need to possess pressure-sensitive properties to be useful in the invention. Different polymers may be used in combination and the particular polymer is selected based upon the desired properties of the final foam-containing article.

Pressure-sensitive adhesives useful in the present invention include, but are not limited to, natural rubbers, synthetic rubbers, styrene block copolymers, elastomers, polyurethanes, polyvinyl ethers, acrylics, poly-.alpha.-olefins, silicones, and blends thereof.

Useful natural rubber PSAs generally contain masticated natural rubber, from 25 parts to 300 parts of one or more tackifying resins to 100 parts of natural rubber, and typically from 0.5 to 2.0 parts of one or more antioxidants. Natural rubber may range in grade from a light pale crepe grade to a darker ribbed smoked sheet and includes such examples as CV-60, a controlled viscosity rubber grade, and SMR-5, a ribbed smoked sheet rubber grade. Tackifying resins used with natural rubbers generally include, but are not limited to, wood rosin and its hydrogenated derivatives; terpene resins of various softening points, and petroleum-based resins, such as, the ESCOREZ 1300 series of C5 aliphatic olefin-derived resins from Exxon Chemical Co., and PICCOLYTE S series, poly-terpenes from Hercules, Inc., Resins Division, Wilmington, Del. Antioxidants are used to retard the oxidative attack on natural rubber, which can result in loss of the cohesive strength of the natural rubber adhesive. Useful antioxidants include, but are not limited to, amines, such as N-N'di-beta-naphthyl-1,4-phenylenediamine, available as AGERITE D from R.T. Vanderbilt Co., Norwalk, Conn.; phenolics, such as 2,5-di-(t-amyl) hydroquinone, available as SANTOVAR A available from Monsanto Chemical Co., tetrakis[methylene 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propianate]methane, available as IRGANOX 1010 from Ciba Specialty Chemicals Inc., Tarrytown, N.J., and 2-2'-methylenebis(4-methyl-6-tert butyl phenol), available as Antioxidant 2246 from Cytec Industries Inc., West Patterson, N.J.; and dithiocarbamates, such as zinc dithiodibutyl carbamate. Other materials can be added to natural rubber adhesives for example, plasticizers, pigments, and curing agents to partially vulcanize the pressure-sensitive adhesive.

Another useful class of PSAs comprises synthetic rubber. Such adhesives are generally rubbery elastomers, which are either self-tacky or non-tacky which are made tacky with tackifiers. Self-tacky synthetic rubber PSAs include, for example, butyl rubber, a copolymer of isobutylene with less than 3 percent isoprene, poly-isobutylene, a homo-polymer of isoprene, poly-butadiene, such as TAKTENE 220 available from Bayer Corp., Pittsburgh, Pa., and styrene/butadiene rubber. Butyl rubber PSAs often contain an antioxidant such as zinc dibutyl dithiocarbamate. Poly-isobutylene pressure-sensitive adhesives do not usually contain antioxidants. Synthetic rubber pressure-sensitive adhesives are also generally easier to melt process. They typically comprise poly-butadiene or styrene/butadiene rubber, from 10 parts to 200 parts of a tackifier, and generally from 0.5 to 2.0 parts per 100 parts rubber of an antioxidant such as IRGANOX 1010 from Ciba Specialty Chemicals. An example of a synthetic rubber is AMERIPOL 1011A, a styreneibutadiene rubber available from BF Goodrich. Tackifiers useful for synthetic rubber include derivatives of rosins such as FORAL 85 stabilized rosin ester from Hercules, Inc.; and synthetic hydrocarbon resins such as the PICCOLYTE A series polyterpenes from Hercules, Inc., the ESCOREZ 1300 series and the ESCOREZ 2000 Series of C9 aromatic/aliphatic olefin-derived resins both from Exxon Chemical Co, and poly-aromatic C9 resins, such as the PICCO 5000 series of aromatic hydrocarbon resins, from Hercules, Inc. Other materials can be added for special purposes, including hydrogenated butyl rubber, pigments, plasticizers, liquid rubbers, such as VISTANEX LMMH poly-isobutylene liquid rubber available from ExxonMobil Chemical Co., and curing agents to partially vulcanize the adhesive.

Styrene block copolymer PSAs generally comprise elastomers of the A-B or A-B-A type, where A represents a thermoplastic polystyrene block and B represents a rubbery block of poly-isoprene, poly-butadiene, poly(ethylene/propylene), or poly(ethylene/butylene), and resins. Examples of block copolymers useful in block copolymer PSAs include linear, radial, star and tapered styrene-isoprene block copolymers such as KRATON D1107P, available from Kraton Polymers Co., and EUROPRENE SOL TE 9110, available from EniChem Elastomers Americas, Inc.; linear styrene-(ethylene/butylene) block copolymers such as KRATON G1657, available from Kraton Polymers Co.; linear styrene-(ethylene/propylene) block copolymers such as KRATON G1750X, available from Kraton Polymers Co.; and linear, radial, and star styrene-butadiene block copolymers such as KRATON D1118X, available from Kraton Polymers Co., and EUROPRENE SOL TE 6205, available from EniChem Elastomers Americas, Inc. The polystyrene blocks tend to form domains that cause the block copolymer PSAs to have two-phase structures. Resins that associate with the rubber phase generally develop tack in the pressure-sensitive adhesive. Examples of rubber phase associating resins include aliphatic olefin-derived resins, such as the ESCOREZ 1300 series available from Exxon Chemical Co., and the WINGTACK series, available from Goodyear Tire & Rubber Co.; rosin esters, such as the FORAL series and the STAYBELITE Ester 10, both available from Hercules, Inc.; hydrogenated hydrocarbons, such as the ESCOREZ 5000 series, available from Exxon Chemical Co.; poly-terpenes, such as the PICCOLYTE A series; and terpene phenolic resins derived from petroleum or terpentine sources, such as PICCOFYN A100, available from Hercules, Inc. Resins that associate with the thermoplastic phase tend to stiffen the pressure-sensitive adhesive. Thermoplastic phase associating resins include poly-aromatics, such as the PICCO 6000 series of aromatic hydrocarbon resins, available from Hercules, Inc.; coumarone-indene resins, such as the CUMAR series, available from Neville Chemical Company, Pittsburgh, Pa.; and other high-solubility parameter resins derived from coal tar or petroleum and having softening points above 85.degree. C., such as the AMOCO 18 series of alphamethyl styrene resins, available from Amoco Chemicals, Warrensville Heights, Ohio, PICCOVAR 130 alkyl aromatic poly-indene resin, available from Hercules, Inc., and the PICCOTEX series of alphamethyl styrene/vinyl toluene resins, available from Hercules, Inc. Other materials can be added to styrene block copolymers for special purposes, including rubber phase plasticizing hydrocarbon oils, such as Polybutene-8 from Chevron Phillips Chemical Co. LP, Houston, Tex., KAYDOL available from Witco Corp., Greenwich, Conn., and SHELLFLEX 371 available from Kraton Polymers Co.; pigments; antioxidants, such as IRGANOX 1010 and IRGANOX 1076, both available from Ciba Specialty Chemical Inc., BUTAZATE, available from Uniroyal Chemical Co., Middlebury, Conn., CYANOX LDTP, available from Cytec Industries, Inc., West Paterson, N.J., and BUTASAN, available from Monsanto Co.; anti-ozonants, such as NBC, a nickel dibutyldithiocarbamate, available from E. I. DuPont de Nemours & Co.; liquid rubbers such as VISTANEX LMMH poly-isobutylene rubber available from ExxonMobil Chemical Co., Houston, Tex.; and ultraviolet light inhibitors, such as IRGANOX 1010 and TINUVIN P, available from Ciba Specialty Chemical Inc.

Polyvinyl ether PSAs are generally blends of homo-polymers of vinyl methyl ether, vinyl ethyl ether or vinyl iso-butyl ether, or blends of homo-polymers of vinyl ethers and copolymers of vinyl ethers and acrylates to achieve desired pressure-sensitive properties. Depending on the degree of polymerization, homo-polymers may be viscous oils, tacky soft resins or rubber-like substances. Polyvinyl ethers used in polyvinyl ether adhesives include polymers based on: vinyl methyl ether such as LUTANOL M 40, available from BASF Corp., Mount Olive, N.J., and GANTREZ M 574 and GANTREZ 555, available from International Specialty Products, Inc. Wayne, N.J.; vinyl ethyl ether such as LUTANOL A 25, LUTANOL A 50 and LUTANOL A 100; vinyl isobutyl ether such as LUTANOL 130, LUTANOL 160, LUTANOL IC, LUTANOL 160D and LUTANOL 165D; methacrylate/vinyl isobutyl ether/acrylic acid such as ACRONAL 550 D, all available from BASF Corp. Antioxidants useful to stabilize the poly-vinylether pressure-sensitive adhesive include, for example, IRGANOX 1010 available from Ciba Specialty Chemical Inc., and Antioxidant ZKF all available from Bayer Corp. Other materials can be added for special purposes as described in BASF Corp. literature including tackifier, plasticizer, pigment, and combinations thereof.

Acrylic pressure-sensitive adhesive polymers can be formed by polymerizing one or more (meth)acrylic esters of non-tertiary alkyl alcohols, with the alkyl groups typically having form 1 to 20 carbon atoms (e.g., from 3 to 18 carbon atoms). Suitable acrylate monomers include methyl acrylate, ethyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, iso-octyl acrylate, octadecyl acrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, and combinations thereof. The corresponding methacrylates are useful as well. Also useful are aromatic acrylates and methacrylates, e.g., benzyl acrylate, cyclobenzyl acrylate, and combinations thereof.

Optionally, one or more mono-ethylenically unsaturated co-monomers may be polymerized with the (meth)acrylate monomers; the particular amount of co-monomer is selected based upon the desired properties of the polymer. One group of useful co-monomers includes those having a homo-polymer glass transition temperature greater than the glass transition temperature of the acrylate homo-polymer. Examples of suitable co-monomers in this group include acrylic acid, acrylamide, methacrylamide, substituted acrylamides such as N,N-dimethyl acrylamide, itaconic acid, methacrylic acid, acrylonitrile, methacrylonitrile, vinyl acetate, N-vinyl pyrrolidone, isobornyl acrylate, cyano ethyl acrylate, N-vinylcaprolactam, maleic anhydride, hydroxyalkylacrylates, N,N-dimethyl aminoethyl (meth)acrylate, N,N-diethylacrylamide, beta-carboxyethyl acrylate, vinyl esters of neodecanoic, neononanoic, neopentanoic, 2-ethylhexanoic, or propionic acids (e.g., available from Union Carbide Corp. of Danbury, Conn. under the trade designation VYNATES), vinylidene chloride, styrene, vinyl toluene, alkyl vinyl ethers, and combinations thereof. A second group of monoethylenically unsaturated co-monomers which may be polymerized with the acrylate or methacrylate monomers includes those having a homo-polymer glass transition temperature less than the glass transition temperature of the acrylate homo-polymer. Examples of suitable co-monomers falling within this class include ethyloxyethoxy ethyl acrylate (Tg=-71.degree. C.), a methoxypolyethylene glycol 400 acrylate (Tg=-65.degree. C.; available from Shin Nakamura Chemical Co., Ltd., Tokyo, JP, under the designation "NK Ester AM-90G"), and combinations thereof.

Poly-.alpha.-olefin PSAs, also called a poly(1-alkene) pressure-sensitive adhesives, generally comprise either a substantially uncrosslinked polymer or a uncrosslinked polymer that may have radiation activatable functional groups grafted thereon as described in U.S. Pat. No. 5,209,971 (Babu et. al.). The poly-alpha-olefin polymer may be self-tacky and/or include one or more tackifying materials. If uncrosslinked, the inherent viscosity of the polymer is generally between 0.7 and 5.0 deciliters per gram as measured by ASTM D 2857-93, "Standard Practice for Dilute Solution Viscosity of Polymers". In addition, the polymer generally is predominantly amorphous. Useful poly-alpha-olefin polymers include, for example, three to eighteen carbon (C3 C18) poly(1-alkene) polymers, preferably C5 C12 alpha-olefins and copolymers of those with C3 and more preferably C6 C8 and copolymers of those with C3. Tackifying materials are typically resins that are miscible in the poly-alpha-olefin polymer. The total amount of tackifying resin in the poly-alpha-olefin polymer ranges from 0 to 150 parts by weight per 100 parts of the poly-alpha-olefin polymer depending on the specific application. Useful tackifying reins include resins derived by polymerization of C5 to C9 unsaturated hydrocarbon monomers, polyterpenes, synthetic polyterpenes and the like and combinations thereof. Examples of such commercially available resins based on a C5 olefin fraction of this type are WINGTACK 95 and WINGTACK 15 tackifying resins from Goodyear Tire & Rubber Co. Other hydrocarbon resins include REGALREZ 1078 and REGALREZ 1126 available from Hercules, Inc., and ARKON P115 available from Arakawa Chemical USA, Inc., Chicago, Ill. Other materials can be added, including antioxidants, fillers, pigments, radiation activated crosslinking agents, and combinations thereof.

Silicone PSAs comprise two major components, a polymer or gum, and a tackifying resin. The polymer is typically a high molecular weight polydimethylsiloxane or polydimethyldiphenylsiloxane, that contains residual silanol functionality (SiOH) on the ends of the polymer chain, or a block copolymer comprising polydiorganosiloxane soft segments and urea terminated hard segments. The tackifying resin is generally a three-dimensional silicate structure that is endcapped with trimethylsiloxy groups (OSiMe.sub.3) and also contains some residual silanol functionality. Examples of tackifying resins useful with silicones include SR 545, from General Electric Co., Silicone Resins Division, Waterford, N.Y., and MQD-32-2 from Shin-Etsu Silicones of America, Inc., Torrance, Calif. Manufacture of typical silicone pressure-sensitive adhesives is described in U.S. Pat. No. 2,736,721 (Dexter). Manufacture of silicone urea block copolymer pressure-sensitive adhesive is described in U.S. Pat. No. 5,214,119 (Leir et al). Other materials that can be added to silicones, include pigments, plasticizers, and fillers. Fillers are typically used in amounts from 0 parts to 10 parts per 100 parts of silicone pressure-sensitive adhesive. Examples of fillers that can be used with silicones include zinc oxide, silica, carbon black, pigments, metal powders, calcium carbonate and combinations thereof.

Solid elastomeric gels produced by the process described in International Publication No. 97/00163 are also useful polymers in the present invention. Generally, the method described in WO 97/00163 is for making solid elastomeric gel from styrene block copolymer (e.g., styrene-isoprene-styrene, styrene-ethylenebutylene-styrene) and plasticizers. The method includes the steps of: (1) providing an extruder having multiple in-feed sections with each followed by a mixing section along a barrel of the extruder; (2) introducing the copolymer into one of the in-feed sections of the operating extruder; (3) heating and shearing the copolymer in a subsequent mixing section; (4) introducing the plasticizer to the copolymer through at least one of the feeding sections in a pattern and at a rate that produces solid elastomeric gel at room temperature that will retain its shape after repeated compression and decompression of the gel; and (5) ejecting the gel from the extruder. The ejecting step may include ejecting the gel through a die to form a length of the gel having a predetermined cross-section, and the method may further include (6) cutting the extruded gel into lengths to form pieces of the gel with uniform cross sections that can be used in pads. Alternatively, the method can further include the step of (6) injecting the ejected gel into a mold having a pre-determined shape.

Various combinations of the foregoing polymers can be used for desired effects.

The polymer may be crosslinked by adding a crosslinking compound or through electron beam or gamma radiation. A crosslinking compound can be a multi-ethylenically unsaturated compound wherein the ethylenic groups are vinyl groups, allyl groups, and/or methallyl groups bonded to nitrogen, oxygen, or carbon atoms. Exemplary compounds for crosslinking vinyl-containing polymers include, but are not limited to, divinyl, diallyl or dimethallyl esters (e.g., divinyl succinate, divinyl adipate, divinyl maleate, divinyl oxalate, divinyl malonate, divinyl glutarate, diallyl itaconate, diallyl maleate, diallyl fumarate, diallyl diglycolate, diallyl oxalate, diallyl adipate, diallyl succinate, diallyl azelate, diallyl malonate, diallyl glutarate, dimethallyl maleate, dimethallyl oxalate, dimethallyl malonate, dimethallyl succinate, dimethallyl glutarate, and dimethallyl adipate), divinyl, diallyl or dimethallyl ethers (e.g., diethyleneglycol divinyl ether, butanediol divinyl ether, ethylene glycol divinyl ether, ethylene glycol diallyl ether, diethylene glycol diallyl ether, butane diol diallyl ether, ethylene glycol dimethallyl ether, diethylene glycol dimethallyl ether, and butane diol dimethallyl ether), divinyl, diallyl or dimethallyl amides including bis(N-vinyl lactams), (e.g., 3,3'-ethylidene bis(N-vinyl-2-pyrrolidone)), and divinyl, diallyl or dimethallyl ureas. Various combinations of such crosslinking agents can be used if desired.

Absorbant Particles

The addition of absorbent particles, preferably in the form of a hydrocolloid, to the polymer imparts hydrophilic character to the composition. The particles used in the present invention may be any synthetically prepared or naturally occurring polymer capable of absorbing aqueous fluids including human sera. Varieties of particles within the scope of the present invention include synthetic polymers prepared from single or multiple monomers, naturally occurring hydrophilic polymers or chemically modified naturally occurring hydrophilic polymers.

Non-limiting examples of such particles include polyhydroxyalkyl acrylates and methacrylates, polyvinyl lactams, polyvinyl alcohols, polyoxyalkylenes, polyacrylamides, polyacrylic acid, polystyrene sulfonates, natural or synthetically modified polysaccarides, alginates, xanthan gums, guar gums, cellulosics, and combinations thereof.

When used in medical applications, the particles are preferably dermatologically acceptable and non-reactive with the skin of the patient or other components of the foamed absorbent composition including any antimicrobial agents that may be present in the composition.

Desirably, the particles include a synthetic polymer that may be either linear or crosslinked. Non-limiting examples of synthetic hydrocolloids include polymers prepared from N-vinyl lactams, e.g. N-vinyl-2-pyrrolidone, 5-methyl-N-vinyl-2-pyrrolidone, 5-ethyl-N-vinyl-2-pyrrolidone, 3,3-dimethyl-N-vinyl-2-pyrrolidone, 3-methyl-N-vinyl-2-pyrrolidone, 3-ethyl-N-vinyl-2-pyrrolidone, 4-methyl-N-vinyl-2-pyrrolidone, 4-ethyl-N-vinyl-2-pyrrolidone, N-vinyl-2-valerolactam, N-vinyl-2-caprolactam, and combinations thereof.

Other monomers useful to prepare absorbent particles include hydroxyalkyl acrylates and methacrylates (such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2,3-dihydroxypropyl methacrylate), acrylic acid, methacrylic acid and a tertiary amino-methacrylimide (e.g., trimethylamino-methacrylimide), crotonic acid, pyridine, and combinations thereof.

Other monomers useful to prepare absorbent particles include water soluble amides (such as N-(hydroxymethyl)acrylamide and -methacrylamide, N-(3-hydroxpropyl)acrylamide, N-(2-hydroxyethyl) methacrylamide, N-(1,1-dimethyl-3-oxabutyl)acrylamide N-[2-(dimethylamine)ethyl]acrylamide and -methacrylamide, N-[3-(dimethylamino)-2-hydroxylpropyl]methacrylamide, and N-[1,1-dimethyl-2-(hydroxymethyl)-3-oxabutyl]acrylamide); water-soluble hydrazine derivatives (such as trialkylamine methacrylimide, and dimethyl-(2-hydroxypropyl)amine methacrylimide); mono-olefinic sulfonic acids and their salts (such as sodium ethylene sulfonate, sodium styrene sulfonate and 2-acrylamideo-2-methylpropanesulfonic acid); and the following monomers containing nitrogen in the non-cyclic or cyclic backbone of the monomer: 1 -vinyl-imidazole, 1-vinyl-indole, 2-vinyl imidazole, 4-vinyl-imidazole, 2-vinyl-1-methyl-imidazole, 5-vinyl-pyrazoline, 3-methyl-5-isopropenyl-pyrazole, 5-methylene-hydantoin, 3-vinyl-2-oxazolidone, 3-methacrylyl-2-oxazolidone, 3-methacrylyl-5-methyl-2-oxazolidone, 3-vinyl-5-methyl-2-oxazolidone, 2- and 4-vinyl-pyridine, 5-vinyl-2-methyl-pyridine, 2-vinyl-pyridine-1-oxide, 3-isopropenyl-pyridine, 2- and 4-vinyl-piperidine, 2- and 4-vinyl-quinoline, 2,4-dimethyl-6-vinyl-s-triazine, 4-acrylyl-morpholine, and combinations thereof.

Other absorbent particles include polymers that are either naturally occurring or synthetically prepared. These materials include polyvinyl alcohol, polyoxyalkylenes, and such naturally occurring or synthetically modified materials as polysaccharides, gums, modified cellulosics, and combinations thereof.

Representative polysaccarides include starch, glycogen, hemicelluloses, pentosans, gelatin, celluloses, pectin, chitosan, and chitin. Representative gums include Arabic, Locust Bean, Guar, Agar, Carrageenan, Xanthan, Karaya, alginates, tragacanth, Ghatti, and Furcelleran gums. Representative modified celluloses include methyl cellulose, hydroxypropyl methyl cellulose, carboxymethylcellulose, and hydroxypropyl cellulose.

Useful absorbent particles of the present invention are preferably prepared by reverse-phase polymerization methods described in European Patent Specifications 0 172 724 B1 and 0 126 528 A2, which form inverse-emulsions having 0.2 to 10 micron diameter crosslinked hydrophilic polymer microparticles dispersed in hydrophobic oils (preferably the polymer is chosen to be miscible with the hydrophobic oil). These emulsions are commercially available under the trade designation of SALCARE from Ciba Specialty Chemicals. The hydrophilic polymers can be either anionic (e.g., 50 weight percentage solids sodium polyacrylate in mineral oil, available as SALCARE SC91) or cationic (e.g., 50 weight percentage solids methylene chloride quaternary ammonium salt of dimethylaminoethylmethacrylate in mineral oil, available as SALCARE SC95). Other absorbent particles can be prepared using a volatile solvent as described in European Patent Application 0 489 967 A1.

Crosslinking of the linear polymer chains of the absorbent particles may be desired to improve cohesive properties upon absorption of aqueous fluids. When such crosslinking is desired for polymers made from vinyl monomers discussed above, a multi-ethylenically unsaturated compound with the ethylenic groups being vinyl, allyl, or methallyl groups bonded to nitrogen, oxygen or carbon atoms can be used.

Non-limiting examples of crosslinking agents for vinyl containing polymers include divinyl, diallyl, or dimethallyl esters (e.g. ethylene glycol dimethacrylate, divinyl succinate, divinyl adipate, divinyl maleate, divinyl oxalate, divinyl malonate, divinyl glutarate, diallyl itaconate, diallyl maleate, diallyl fumarate, diallyl diglycolate, diallyl oxalate, diallyl adipate, diallyl succinate, diallyl azelate, diallyl malonate, diallyl glutarate, dimethallyl maleate, dimethallyl oxalate, dimethallyl malonate, dimethallyl succinate, dimethallyl glutarate, and dimethallyl adipate); divinyl, diallyl or dimethallyl ethers (e.g. diethyleneglycol divinyl ether, butane diol divinyl ether, ethylene glycol divinyl ether, ethylene glycol diallyl ether, diethylene glycol diallyl ether, butane diol diallyl ether, ethylene glycol dimethallyl ether, diethylene glycol dimethallyl ether, and butane diol dimethallyl ether); divinyl, diallyl or dimethallyl amides including bis(N-vinyl lactams), (e.g., 3,3'-ethylene bis(N-vinyl-2-pyrrolidone) and methylene-bis-acrylamide); and divinyl, diallyl and dimethallyl ureas. Various combinations of crosslinking agents can be used.

For n-vinyl lactams, the preferred crosslinking agents are diallyl maleate and 3,3'-ethylidene bis (N-vinyl-2-pyrrolidone). For acrylates and methacrylates, the preferred crosslinking agents are ethylene glycol dimethacrylate and methylene-bis-acrylamide. For polyvinyl lactams (e.g., poly-N-vinylpyrrolidone), the preferred crosslinking agents are diallyl maleate or 3,3'-ethylidene bis (N-vinyl-2-pyrrolidone).

Expandable Microspheres

The expandable microspheres useful in the invention feature a flexible, thermoplastic, polymeric shell and a core that includes a liquid and/or gas that expands upon heating above the expansion temperature of the microsphere. This expansion typically involves softening of the polymeric shell and expansion of the liquid or gas core. Preferably, the core material is an organic substance that has a lower boiling point than the softening temperature of the polymeric shell. Examples of suitable core materials include propane, butane, pentane, iso-butane, neo-pentane, and combinations thereof.

The choice of thermoplastic resin for the polymeric shell influences the mechanical properties of the foam. Accordingly, the properties of the foam may be adjusted through appropriate choice of microsphere, or by using mixtures of different types of microspheres. For example, acrylonitrile-containing resins are useful where high tensile and cohesive strength are desired, particularly where the acrylonitrile content is at least 50% by weight of the resin, more preferably at least 60% by weight, and even more preferably at least 70% by weight. In general, both tensile and cohesive strength increase with increasing acrylonitrile content. In some cases, it is possible to prepare foams having higher tensile and cohesive strength than the polymer matrix alone, even though the foam has a lower density than the matrix. This provides the capability of preparing high strength, low density foams.

Examples of suitable thermoplastic resins that may be used as the polymeric shell include (meth)acrylic acid esters such as poly-acrylate; acrylate-acrylonitrile copolymer; and methacrylate-acrylic acid copolymer. Vinylidene chloride-containing polymers such as vinylidene chloride-methacrylate copolymer, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-vinylidene chloride-methacrylonitrile-methyl acrylate copolymer, and acrylonitrile-vinylidene chloride-methacrylonitrile-methyl methacrylate copolymer may also be used, but are not preferred where high strength is desired. In general, where high strength is desired, the microsphere shell preferably has no more than 20% by weight vinylidene chloride, more preferably no more than 15% by weight vinylidene chloride. Even more preferred for high strength applications microspheres have essentially no vinylidene chloride units.

Examples of suitable commercially available expandable polymeric microspheres include those available from Pierce Stevens, Buffalo, N.Y., under the trade designations MICROPEARL F30D, F80SD, and F100D. Also suitable are expandable polymeric microspheres available from Expancel, Inc., Duluth, Ga., under the designations EXPANCEL 551, EXPANCEL 461, and EXPANCEL 091. Each of these microspheres features an acrylonitrile-containing shell. In addition, the MICROPEARL F80SD and F100D, and EXPANCEL 091 microspheres have essentially no vinylidene chloride units in the shell.

Various combinations of expandable microspheres can be used. The amount of expandable microspheres is selected based upon the desired properties of the foam product. In general, the higher the microsphere concentration, the lower the density of the foam. In general, the amount of microspheres is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight, based on 100 parts of polymer. The amount of microspheres is preferably at most 50 parts by weight, and more preferably at most 20 parts by weight, based on 100 parts of polymer.

Bioactive Agent

The polymer compositions of the present invention can include a bioactive agent. Examples include, but are not limited to, antimicrobial agents such as silver chloride, silver oxide, silver nitrate, silver acetate, silver lactate, silver sulfate, copper chloride, copper nitrate, copper acetate, copper lactate, copper sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc lactate, and zinc sulfate. Other antimicrobial agents that can be used include parachlorometaxylenol, chlorhexidine and salts thereof, iodine, and iodophores, and antibiotics such as neomycin, bacitracin, and polymyxin B. Preferred compositions have more than one bioactive agent.

The bioactive agent can be present in the polymer composition in an amount to produce a desired effect (e.g., antimicrobial effect). Preferably, the bioactive agent is present in an amount such that the polymer composition is stable. In this context, "stable" means the composition does not turn black over a typical exposure time in the presence of at least one of the following types of radiation: visible light, ultraviolet light, electron beam, and gamma ray sterilization.

Optional Additives

The polymer compositions of the present invention can include a wide variety of optional additives (in addition to the additives discussed above in reference to PSAs). Examples include secondary bioactive agents, secondary absorbent particles, chemical foaming agents, physical foaming agents, swelling agents, fillers, pigments, dyes, plasticizers, tackifiers, crosslinking agents, ultraviolet and thermal stabilizers, antioxidants, colorants, extruding aids, chain transfer agents, and combinations thereof.

In certain embodiments, polymer compositions of the present invention can include fillers, which can be inorganic or organic. Examples of inorganic fillers include barytes, chalk, gypsum, kieserite, sodium carbonate, titanium dioxide, cerium oxide, silica dioxide, kaolin, carbon black, and hollow glass micro-beads. Examples of organic fillers include powders based on polystyrene, polyvinyl chloride, urea-formaldehyde and polyethylene. The fillers may be in the form of fibers, such as chopped fibers. Examples of suitable chopped fibers include glass fibers (typically 0.1 millimeter (mm) to 1 mm long) or fibers of organic origin such as, for example, polyester or polyamide fibers.

In order to confer color to the polymer compositions it is possible to use dyes or colored pigments of an organic or inorganic basis such as, for example, iron oxide or chromium oxide pigments or phthalocyanine- or monoazo-based pigments.

Method of Preparation

The following exemplary extrusion process can be used for preparing absorbent polymer foam compositions featuring a polymer matrix, absorbent particles (typically provided in the form of a hydrocolloid), an optional bioactive agent, and expandable polymer microspheres. In the process, polymer(s) is initially fed into a first extruder (typically a single-screw extruder) that softens and grinds the resin into small particles suitable for extrusion. The polymer will eventually form the polymer matrix of the foam. The polymer may be added to the first extruder in any convenient form, including pellets, billets, packages, strands, and ropes.

Next, the polymer, absorbent particles, and all other additives except the expandable microspheres are fed to a second extruder (e.g., a single or twin-screw extruder) at a point immediately prior to the kneading section of the extruder. Once combined, the polymer and additives are fed to the kneading zone of the second extruder where they are mixed well. The mixing conditions (e.g., screw speed, screw length, and temperature) are selected to achieve optimum mixing. Preferably, mixing is carried out at a temperature insufficient to cause microsphere expansion. It is also possible to use temperatures in excess of the microsphere expansion temperature, in which case, the temperature is decreased following mixing and prior to adding the microspheres.

Once the polymer, absorbent particles, and other additives (except the expandable microspheres) have been adequately mixed, expandable polymeric microspheres are added to the resulting mixture, at a downstream entrance to the second extruder, and melt-mixed to form an expandable extrudable composition. The purpose of the melt-mixing step is to prepare an expandable extrudable composition in which the expandable polymeric microspheres and other additives are distributed substantially homogeneously throughout the molten polymer. Typically, the melt-mixing operation uses one kneading block to obtain adequate mixing, although simple conveying elements may be used as well. The temperature, pressure, shear rate, and mixing time employed during melt-mixing are selected to prepare this expandable extrudable composition without causing the microspheres to expand or break; once broken, the microspheres are unable to expand to create a foam. Specific temperatures, pressures, shear rates, and mixing times are selected based upon the particular composition being processed.

Following melt-mixing, the absorbent expandable polymer composition is metered into an extrusion die (for example, a contact or drop die) through a length of transfer tubing using a gear pump that acts as a valve to control die pressure and thereby prevent premature expansion of the microspheres. The temperature within the die is preferably maintained at substantially the same temperature as the temperature within transfer tubing, and selected such that it is at or above the temperature required to cause expansion of the expandable microspheres. However, even though the temperature within transfer tubing is sufficiently high to cause microsphere expansion, the relatively high pressure within the transfer tubing prevents them from expanding. Once the composition enters the extrusion die, however, the pressure drops because the volume of the die is greater than the volume of the tubing. The pressure drop, coupled with heat transfer from the die, causes the microspheres to expand within the die, leading to foaming. The pressure within the die continues to drop further as the composition approaches the exit, further contributing to microsphere expansion within the die. The flow rate of polymer through the extruder and the die exit opening are maintained such that as the polymer composition is processed through the die, the pressure in the die cavity remains sufficiently low to allow expansion of the expandable microspheres before the polymer composition reaches the exit opening of the die.

The shape of the absorbent polymer foam is a result of the shape of the exit of the extrusion die. Although a variety of shapes may be produced, the foam is typically produced in the form of a continuous or discontinuous sheet.

Another continuous forming method involves directly contacting the extruded absorbent polymer foam to a rapidly moving plastic web or other suitable substrate. In this method, the extruded absorbent polymer foam can be applied to the moving web using a die having flexible die lips such as a reverse orifice coating die and other contact dies using rotating rods.

After extrusion, the absorbent polymer foam is preferably solidified by quenching using either a direct method, such as chill rolls or water baths, or an indirect method, such as air or gas impingement. This step arrests the continued expansion of the microspheres as they exit the die.

The foam may optionally be combined with a liner dispensed from a feed roll. Suitable materials for liners include silicone release liners, polyester films (e.g., polyethylene terephthalate films), and polyolefin films (e.g., polyethylene films). The liner and the foam are then laminated together between a pair of nip rollers. Following lamination, the foam is optionally exposed to radiation from an electron beam source to crosslink the foam; other sources of radiation (e.g., ion beam, gamma, and ultraviolet radiation) may be used as well. Crosslinking improves the cohesive strength of the foam. Following exposure, the laminate can be rolled up onto a take-up roll. Optionally, the rolled up laminate can be exposed to gamma radiation to crosslink the foam.

If desired, the smoothness of one or both of the foam surfaces can be increased by using a nip roll to press the foam against a chill roll after the foam exits die. It is also possible to emboss a pattern on one or both surfaces of the foam by contacting the foam with a patterned roll after it exits the die.

The foam may also be combined with one or more additional polymer compositions, e.g., in the form of layers, stripes, rods, etc., preferably by co-extruding additional extrudable polymer compositions with the microsphere-containing extrudable compositions. It is also possible to use a co-extrusion process such that a two-layer article is produced, or such that articles having more than three layers (e.g., 10 100 layers or more) are produced. This is accomplished by equipping the extrusion die with an appropriate feed block, or by using a multi-vaned or multi-manifold die as in U.S. Pat. No. 6,379,791 (Cernohous et al.). Multi-layer foam articles can also be prepared by laminating additional layers to the foam core, or to any of the co-extruded layers after the absorbent polymer foam exits the extrusion die.

Medical Articles

The polymer compositions of the present invention can be used in a wide variety of products, although they are preferably used in medical articles. Such medical articles can be in the form of a wound dressing, wound packing material, or other materials that are applied directly to or contact a wound.

Such articles may or may not include a backing. If a backing is desired, it may or may not be porous. Suitable materials are preferably flexible, and may be fabric, non-woven or woven polymeric films, metallic foils, paper, and/or combinations thereof. More specifically, film backings are useful with the polymer compositions of the present invention and include, for example, ethylene-propylene-diene rubbers, polyesters, poly-isobutylenes, polyolefins, polyolefin-based non-wovens, polyurethanes, vinyls including polyvinylchloride and ethylene-vinyl acetate, and/or combinations thereof. For particular purposes, the backing may be coated on one or both major surfaces, with a primer or a release agent, which may be a low-adhesion backsize (LAB) material. For example, when using a plasticized polyvinylchioride (PVC) backing, an embodiment of the present invention comprising a butadiene- or isoprene-containing polymer along with a polyisoprene-polyvinylpyridine (PI-PVP) compatibilizer has a particular advantage in that the composite PSA has an affinity for acidic PVC.

The backing can also be provided with stretch-release properties. Stretch-release refers to the property of an adhesive article characterized in that, when the article is pulled from a surface, the article detaches from the surface without leaving significant visible residue. For example, a film backing can be formed from a highly extensible and highly elastic composition comprising elastomeric and thermoplastic A-B-A block copolymers, having a low rubber modulus, a lengthwise elongation to break of at least 200%, and a 50% rubber modulus of not above 2,000 pounds/square inch (13.8 megapascals (MPa)). Such backings are described in U.S. Pat. No. 4,024,312 (Korpman). Alternatively, the backing can be highly extensible and substantially non-recoverable such as those described in U.S. Pat. No. 5,516,581 (Kreckel et al).
 

Claim 1 of 34 Claims

1. An absorbent polymer composition comprising: a polymeric material; absorbent particles; and thermally cxpandable microspheres, wherein a thermally expandable microsphere comprises a thermoplastic polymeric shell and a core that includes a liquid and/or gas.

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