Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
  • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
  • A61L15/42—Use of materials characterised by their function or physical properties
  • A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
  • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
  • A61L15/22—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons containing macromolecular materials
  • A61L15/26—Macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249924—Noninterengaged fiber-containing paper-free web or sheet which is not of specified porosity
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2922—Nonlinear [e.g., crimped, coiled, etc.]

Definitions

• Disposable absorbent products are used extensively for body waste management. These disposable absorbent products include one or more absorbent structures to manage body waste effectively. The absorbent structure within the disposable absorbent product takes up and retains the body waste within the absorbent product. A variety of other components may also be present in a typical absorbent product, including liquid impermeable backing sheets, liquid permeable liners, wicking layers, and components for securing the product to the user. The particular combination and configuration of components in an absorbent product will depend on the intended use of the product.
• Absorbent structures typically include a superabsorbent material, which can absorb large amounts of water or other aqueous liquids.
• a superabsorbent material which can absorb large amounts of water or other aqueous liquids.
• One ongoing effort in the development of superabsorbent materials has been to increase the stiffness of the gel formed when the superabsorbent material has absorbed an aqueous liquid.
• Increased gel stiffness also referred to as gel strength, can increase the porosity of the absorbent structure, thereby increasing the liquid intake rate and distribution within the structure.
• thermoplastic binder fibers A common thermoplastic binder fiber for this application is a fiber having a sheath/core structure of polyethylene and polyethylene terephthalate) (PET).
• PET polyethylene terephthalate
• Polyethylene is used as the sheath polymer due to its low melting point, good rheology and low cost.
• PET is used as the core due to its higher melting point and overall stability.
• thermoplastic binder fibers tend to have low wettability due to their hydrophilic surfaces. This low wettability can reduce the overall liquid intake and distribution of the absorbent structure, despite increasing the porosity.
• the wettability of thermoplastic binder fibers can be increased by treating their surfaces with a wetting agent such as a surfactant or a fiber spin finish agent.
• these wetting agents can be dissolved in water, reducing the surface tension of the absorbed liquid and actually decreasing both the wicking of liquid into the composite and the subsequent distribution of the absorbed liquid.
• Biodegradable superabsorbent materials typically have less desirable absorbent properties relative to conventional non-biodegradable superabsorbent materials such as polyacrylates. This difference in absorbent properties is believed to be related to the lower gel stiffness of the hydrogels formed from biodegradable superabsorbent materials.
• absorbent composites made with biodegradable superabsorbents have tended to exhibit inferior intake, distribution and retention of liquids relative to absorbent composites based on polyacrylate superabsorbents.
• the gel stiffness of biodegradable superabsorbents can be increased by reinforcement with thermoplastic binder fibers.
• reinforcing a biodegradable superabsorbent material with non- biodegradable fibers would undermine the goal of constructing a compeletely biodegradable absorbent product.
• Improved absorbent structures may have improved wicking and distribution of aqueous liquids, while exhibiting other absorbent properties that are at least as good as those of conventional structures.
• the structures could be made completely of biodegradable materials to help provide biodegradable absorbent products.
• an absorbent composite comprising a biodegradable superabsorbent material, and a plurality of thennoplastic biodegradable reinforcing fibers.
• an absorbent composite comprising a superabsorbent material having a gel strength from about 500 dynes/cm 2 to about 80,000 dynes/cm 2 , and a plurality of thermoplastic biodegradable reinforcing fibers.
• thermoplastic biodegradable reinforcing fibers comprise poly(hydroxyalkanoate) fibers
• thermoplastic biodegradable reinforcing fibers comprise poly(lactic acid) fibers
• thermoplastic biodegradable reinforcing fibers are un-bonded
• thermoplastic biodegradable reinforcing fibers are wettable
• composite is free of wetting agents
• These embodiments may further include absorbent composites wherein the biodegradable superabsorbent material comprises carboxymethyl cellulose, wherein the biodegradable superabsorbent is present in a loading from about 10 wt% to about
• the absorbent composite further comprises pulp fibers, wherein the pulp fibers are present in a loading from about 25 wt% to about 85 wt%, wherein the thermoplastic biodegradable reinforcing fibers are present in a loading from about 5 wt% to about 30 wt%, and wherein the gel strength of the superabsorbent is from about 500 dynes/cm 2 to about 80,000 dynes/cm 2 .
• an absorbent composite comprising from about 10 wt% to about 70 wt% of a biodegradable superabsorbent material, from about 25 wt% to about 85 wt% of pulp fibers, and from about 5 wt% to about 30 wt% of poly(lactic acid) reinforcing fibers.
• These embodiments may further include absorbent composites wherein the poly(lactic acid) reinforcing fibers are un-bonded, wherein the poly(lactic acid) reinforcing fibers have a length from about 2 mm to about 60 mm, wherein the poly(lactic acid) reinforcing fibers have a diameter from about 1.5 denier to about 6 denier, wherein the poly(lactic acid) reinforcing fibers have from about 0 crimps per inch to about 12 crimps per inch, wherein the composite has a permeability of at least 10 darcies, wherein the composite has a density from about 0.09 grams per cubic centimeter to about 0.3 grams per centimeter, wherein the composite is free of wetting agents, wherein the weight ratio of pulp fibers to poly(lactic acid) reinforcing fibers is from about 1 : 1 to about 5:1, and wherein the weight ratio of biodegradable superabsorbent material to poly(lactic acid) reinforcing fibers is from about 1 : 1 to about 4:1
• a method of forming an absorbent composite comprising combining a superabsorbent material and a plurality of biodegradable reinforcing fibers into a mixture, and compressing the mixture in a dry state into a composite having a density from about 0.09 grams per cubic centimeter to about 0.3 grams per centimeter, wherein the biodegradable reinforcing fibers remain un-bonded.
• these embodiments may further include a method wherein the biodegradable reinforcing fibers comprise poly(hydroxyalkanoate) fibers, wherein the biodegradable reinforcing fibers comprise poly(lactic acid) fibers, wherein the composite is free of wetting agents, wherein the combining comprises air-forming the superabsorbent material with the biodegradable reinforcing fibers, wherein the combining further comprises combining pulp fibers with the superabsorbent material, and the biodegradable reinforcing fibers, and wherein the combining comprises air- forming the superabsorbent material with the biodegradable reinforcing fibers and the pulp fibers.
• the biodegradable reinforcing fibers comprise poly(hydroxyalkanoate) fibers
• the biodegradable reinforcing fibers comprise poly(lactic acid) fibers
• the composite is free of wetting agents
• the combining comprises air-forming the superabsorbent material with the biodegradable reinforcing fibers
• the combining
• Figure 1 is a graph of permeability of absorbent composites containing a variety of superabsorbent materials, both with and without biodegradable reinforcing fibers;
• Figure 2 is a graph of the mass of liquid absorbed over time by absorbent composites containing a biodegradable superabsorbent material
• Figure 3 is a graph of the mass of liquid absorbed over time by absorbent composites containing a high gel stiffness superabsorbent material
• Figure 4 is a graph of liquid distribution within an absorbent composite containing a high gel stiffness superabsorbent material with and without biodegradable reinforcing fibers;
• Figure 5 is a graph of liquid distribution within an absorbent composite containing a biodegradable superabsorbent material with and without biodegradable reinforcing fibers.
• An absorbent structure includes a superabsorbent material and a plurality of biodegradable reinforcing fibers together as an absorbent composite.
• the presence of reinforcing fibers can increase the stiffness and improve the resiliency of the composite structure.
• Biodegradable reinforcing fibers may be used in conjunction with biodegradable superabsorbent materials to produce a composite that is biodegradable.
• Reinforcing fibers that are inherently wettable may allow for a reduction or elimination in the amount of surfactant used in the composite.
• fibers made of aliphatic polyesters can be incorporated readily into an absorbent structure, can provide desirable absorbent properties, and also can be biodegradable.
• Aliphatic polyesters that can be used as reinforcing fibers include biodegradable poly(hydroxyalkanoates) such as poly(lactic acid).
• Absorbent composites include a superabsorbent material and a plurality of reinforcing fibers.
• absorbent composites can include pulp fibers.
• An absorbent composite can be a simple mixture of these components, or the reinforcing fibers can be bonded to the other components of the composite, for example by heating the mixture at an elevated temperature or by treating the mixture with a bonding agent.
• the term "superabsorbent material” refers to a water- swellable, water-insoluble organic or inorganic material having an absorbent capacity for a 0.9 percent by weight (0.9 wt%) aqueous sodium chloride solution of at least 10 grams of solution per gram of polymer. That is, a superabsorbent material is capable of absorbing at least about 10 times its own weight in a 0.9 wt% aqueous sodium chloride solution.
• a superabsorbent material is capable of absorbing at least about 20 times its weight, more preferably at least about 30 times its weight, even more preferably at least about 40 times its weight, even more preferably at least about 50 times its weight, even more preferably at least about 60 times its weight in a 0.9 wt% aqueous sodium chloride solution.
• the term "hydrogel” refers specifically to superabsorbent material in the water-swollen state.
• organic superabsorbent materials include natural materials such as agar, pectin, guar gum and the like, as well as synthetic materials such as synthetic superabsorbent polymers.
• Superabsorbent polymers include, for example, polyacrylamides, polyvinyl alcohol, ethylene maleic anhydride copolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinylmorpholinone, alkali metal salts of polyacrylic acids, and polymers and copolymers of vinyl sulfonic acid, polyacrylates, polyacrylamides, polyvinyl pyridines, and the like.
• exemplary superabsorbant polymers include hydrolyzed acrylonitrile grafted starch, acrylic acid grafted starch, and isobutylene maleic anhydride copolymers and mixtures thereof.
• polyacrylate superabsorbent materials include SANWET ASAP 2300 polymer (Chemdal, Portsmouth, VA), DOW DRYTECH 2035LD polymer (Dow Chemical Co., Midland, MI), FAVOR SAB 870M and FAVOR SAB 880 polymers (Stockhausen, Inc., Greensboro, NC), and the high gel stiffness polymer SXM 9543 (Stockhausen).
• biodegradable superabsorbent materials include carboxymethyl cellulose materials, such as biodegradable superabsorbents available from Stochkausen.
• Carboxymethyl cellulose based biodegradable superabsorbent materials are described, for example, in U.S. Patent Application Publication No. 2004/0157734 Al, which is incorporated by reference herein.
• a partially neutralized, uncrosslinked, carboxyl-containing polysaccharide can be preswelled and subsequently dried, and the dried polycarboxypolysaccharide can be surface-post crosslinked by means of a surface crosslinker.
• Polycarboxypolysaccharides may inherently contain carboxyl groups, or they may be derived from polysaccharides without carboxyl groups but that are provided with carboxyl groups by subsequent modification. Polycarboxypolysaccharides may be modified to contain other groups, particularly groups that improve the solubility in water, such as hydroxyalkyl and especially hydroxyethyl groups and also phosphate groups. Specific examples of polycarboxypolysaccharides include carboxymethylguar, carboxylated hydroxyethyl or hydroxypropylcellulose, carboxymethylcellulose and carboxymethylstarch, oxidized starch, carboxylated phosphatestarch, xanthan and mixtures thereof.
• Polycarboxy-polysaccharide superabsorbent polymers may be modified by addition of carboxyl-free polysaccharides, such as polygalactomannans or hydroxyalkylcelluloses, and/or by addition of other additives.
• the polycarboxypolysaccharide may be preswollen in an aqueous phase to form a hydrogel, and the aqueous phase may also include additive substances.
• the surface of the polycarboxypolysaccharide powder can be crosslinked with covalent and/or ionic crosslinkers which react with surface moieties, preferably carboxyl, carboxylate or hydroxyl groups, preferably by heating.
• the resulting particulate superabsorbent polymers can exhibit very good retention and absorption ability, significantly improved absorbency for water and aqueous fluids against an external pressure, and excellent ageing stability.
• the superabsorbent materials may be in any form suitable for use in absorbent composites including particles, fibers, flakes, films, foams, or spheres.
• the superabsorbent material includes particles of hydrocolloids, preferably an ionic hydrocolloid.
• the superabsorbent polymers preferably are lightly crosslinked to render the material substantially water insoluble. Crosslinking may be accomplished, for example, by irradiation and/or by covalent, ionic, van der Waals, or hydrogen bonding.
• Superabsorbent materials may be shell crosslinked so that the outer surface or shell of the superabsorbent particle, fiber, flake, film, foam, or sphere possesses a higher crosslink density than the inner portion of the superabsorbent.
• fiber refers to a particulate material wherein the ratio of the length of the particulate material to the diameter of the particulate material is greater than about 10.
• a nonfiber or nonfibrous material refers to a particulate material wherein the length to diameter ratio is about 10 or less.
• Both the reinforcing fibers and the pulp fibers are fibrous materials.
• a wide variety of fibers can be used as, or in the preparation of, the fibrous pulp. Examples of pulp fibers include, but are not limited to, cellulosic fibers such as wood and wood products, e.g., wood pulp fibers.
• pulp fibers include non-woody paper-making fibers from cotton; from straws and grasses, such as rice and esparto; from canes and reeds, such as bagasse; from bamboos; from stalks with bast fibers, such as jute, flax, kenaf, cannabis, linen and ramie; and from leaf fibers, such as abaca and sisal.
• pulp fibers include man-made fibers obtained from regenerated cellulose or cellulose derivatives, such as cellulose acetate.
• the fibrous pulp also can use mixtures of such materials, e.g., mixtures of one or more cellulosic fibers.
• Fibers from which the fibrous pulp may be made include non-cellulosic fibers such as wool and glass, and synthetic fibers, such as polyethylene, polypropylene and polyester.
• Pulp fibers generally may have lengths from about 0.5 mm to about 20 mm.
• pulp fibers may have lengths from about 1 mm to about 10 mm, and may have lengths from about 2 mm to about 5 mm.
• Biodegradable reinforcing fibers can be any thermoplastic fiber made of a biodegradable material.
• thermoplastic refers to a polymeric material that can be processed by melting, forming, and shaping.
• ASTM American Society for Testing and Materials
• D 5338 Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions
• Biodegradable reinforcing fibers may be continuous in length, that is, individual fibers may extend the length or width of the absorbent composite. Spunbond fibers are an example of continuous fibers. Biodegradable reinforcing fibers may also be non-continuous. Non-continuous fibers include staple fibers, linters, and melt blown fibers, and may range from 2 mm to 60 mm in length. In certain embodiments of the invention, the non-continuous reinforcing fibers may range from 5 mm to 40 mm in length. Other embodiments include biodegradable reinforcing fibers which are between 7 mm and 25 mm long. Biodegradable reinforcing fibers may have diameters from about 1.5 denier to about 6 denier and may have from zero to 12 crimps per inch.
• the biodegradable reinforcing fibers are wettable.
• wettable refers to a material such as a fiber that, without any separate substance on its surface, exhibits a water-in-air contact angle of less than 90° (i.e., 0° to 90°).
• the biodegradable reinforcing fibers exhibit a water-in-air contact angle from about 0° to about 85°, and more preferably from about 0° to about 80°.
• wettable biodegradable fibers exhibit a water-in-air contact angle of less than 90°, at a temperature from about 0 0 C to about 100 0 C, and preferably at typical use conditions, such as from about 2O 0 C to about 4O 0 C.
• the addition of wetting agents to the absorbent composite reduces the absorbent properties of the composites.
• the biodegradable reinforcing fibers do not contain any separate substance on the fiber surface other than the fiber material.
• biodegradable reinforcing fibers include biodegradable aliphatic polyesters.
• Aliphatic polyesters are polyesters that contain alkyl groups, including alkanes, alkenes and alkynes, but do not contain aromatic groups. The alkyl groups may be linear, branched and/or cyclic.
• a preferred class of aliphatic polyesters is the poly(hydroxyalkanoate) family (PHAs). PHAs have the general structural formula (I):
• R is hydrogen or an alkyl group
• x is an integer from 0 to 10
• n is the number of repeating units.
• R is hydrogen or an alkyl group containing from 1 to 15 carbon atoms.
• the physical properties of PHAs can be controlled by altering the R group and/or by altering the number (x) of -CH 2 - groups between the ester groups.
• Different repeating units may also be combined into a single polymer, and the nature and distribution of the repeating units can also affect the final properties.
• PHAs include poly(3-hydroxybutyrate), poly(4- hydroxybutyrate), poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)], poly(glycolic acid), poly(lactic acid), and poly(caprolactone).
• biodegradable reinforcing fibers that are wettable are fibers made of poly(lactic acid) (PLA).
• PLA is a biodegradable PHA having the general formula (I) where R is methyl (-CH 3 ) and x is zero.
• Fibers of PLA can be made to have a tensile modulus of at least 2 gigaPascals (GPa), providing for good resiliency of the fibers and of absorbent composites containing the fibers. Since PLA is thermoplastic, exposure of a composite containing PLA to elevated temperatures can provide for softening or melting of the outer surface of the fibers and subsequent bonding of the fibers to the other components of the composite.
• PLA fibers can be used as reinforcing fibers in absorbent composites to yield composites having increased absorbent capacity, improved liquid wicking, better liquid intake, higher resiliency of the absorbent structure, and improved permeability of the structure.
• biodegradable PLA fibers that may be used as reinforcing fibers include the PLA fibers disclosed in U.S. Patent Nos. 6,506,873 and 6,177,193, and the PLA/PLA bicomponent fibers disclosed in U.S. Patent No. 5,698,322.
• the high modulus of PLA fibers can impart increased resiliency to stabilized composites.
• an increase in gel stiffness in a superabsorbent material can result in a decrease in the absorbent capacity of the superabsorbent in conventional systems.
• Absorbent capacity is the amount of liquid absorbed per unit mass of superabsorbant material.
• Gel stiffness may be defined as the ratio of the absorbency under a load of 0.9 pounds per square inch (psi) to the centrifuge retention capacity. The measurement of gel stiffness is described in U.S. Patent No. 5,415,643, which is incorporated herein by reference. Alternatively, direct measurements of the response of a swollen gel to shear forces may be used to determine gel strength; Onwumere et al. (US Patent 5,047,456, granted 10 September 1991, assigned to Kimberly-Clark Corporation), incorporated herein by reference, provides such a test method.
• gel strength may be represented by the shear or storage modulus G' of a swollen gel at a strain of 1% and frequency of 1 rad/sec measured using a RDS-II Rheometer (Rheometrics, Inc. Buffalo Grove , IL) and expressed in units of dynes/cm 2 .
• PLA fibers can be used in a composite with high gel stiffness superabsorbent materials to improve the absorbent capacity of the composite.
• PLA fibers can also be used in a composite with superabsorbent materials having lower gel stiffness to increase the resiliency of the composite.
• Absorbent composites comprising superabsorbents with a gel strength in the range of 500 - 80,000 dynes/cm 2 can advantageously benefit from the inclusion of PLA fibers.
• absorbent composites comprising superabsorbents with a gel strength in the range of 1000 - 40,000 dynes/cm 2 or in the range of 2000 - 20,000 dynes/cm 2 can benefit from the inclusion of PLA fibers.
• Resiliency in absorbent composites is useful in keeping the absorbent structure open and in preventing collapse of the capillary structure in the composite upon absorption of liquid. This open structure is believed to allow better penetration of liquid into the composite, thereby improving permeability. Improving the permeability of a composite is beneficial in improving the overall performance of an absorbent product and can result in better liquid intake, more efficient utilization of the absorbent capacity, and increased skin dryness for the user.
• the resilient nature of PLA helps to reinforce the composite structure and provides for greater void volume under an applied external load. This can lead to a higher absorbent capacity of the composite compared to composites containing only superabsorbent material and pulp fibers.
• PLA fibers to reinforce the absorbent composite enables superabsorbents with low gel stiffness to function effectively in structures stabilized with PLA. This is particularly beneficial for obtaining satisfactory performance using biodegradable superabsorbents, which typically have lower gel stiffness compared to conventional polyacrylate superabsorbents .
• the wettability of PLA can reduce or eliminate the need for surfactant treatments.
• the contact angle of the reinforcing fibers ideally is low enough to be wetted by the liquid insult, so that the liquid can be taken up efficiently into the composite.
• the advancing contact angle of PLA is about 82 degrees, and the receding contact angle is about 68 degrees.
• PLA fibers are sufficiently wettable in the absence of wetting agents, surfactants, spin finish agents, or other surface treatments.
• the wettability of PLA also enables larger quantities of PLA reinforcing fibers to be incorporated into an absorbent composite without impairing the wicking behavior of the composite.
• conventional polyethylene/PET bi-component binder fibers typically cannot be incorporated into an absorbent composite at levels greater than 5 wt%, as higher loadings reduce the rate of liquid absorption of the composite.
• PLA reinforcing fibers can be added at levels as high as 25 wt% of the absorbent composite without reducing the wicking of liquids.
• the biodegradability of PLA fibers can allow for the development of biodegradable absorbent composites.
• the absorbent properties of biodegradable superabsorbent materials typically are not as good as those of non-biodegradable superabsorbents, such as the conventional polyacrylate systems.
• Biodegradable superabsorbents tend to have lower gel stiffness than the non-biodegradable materials, which can limit the rate of absorption as well as the overall absorbent capacity.
• PLA fibers can be used successfully as reinforcing fibers in biodegradable superabsorbent materials, and the entire absorbent composite can thus be disposed of as biodegradable waste.
• the use of PLA fibers as reinforcing fibers in biodegradable absorbent composites surprisingly can improve the absorbent properties of biodegradable systems to levels comparable to those of polyacrylate superabsorbents .
• Biodegradable reinforcing fibers also include fibers containing PLA together with other polymers, which may or may not be biodegradable. It is noted that a fiber may contain a significant amount of non-biodegradable material, yet still fall within the definition of "biodegradable” as set forth above when the entire fiber is considered.
• biodegradable reinforcing fiber materials containing PLA together with other polymers include blends of PLA with non-biodegradable polymers such as polyethylene, polypropylene, polystyrene, and poly (ethylene terephthalate). Examples also include composite fibers of PLA and other polymers. Preferably the biodegradable reinforcing fibers contain less than 10 wt% of non-biodegradable material.
• biodegradable reinforcing fibers contain less than 7 wt% of non-biodegradable material, still more preferably contain less than 5 wt% of non-biodegradable material, and still more preferably contain less than 1 wt% of nonbiodegradable material.
• the individual components of the absorbent composite can be present in varying amounts. However, it has been found that the following percentages work well in forming an absorbent composite for use in an absorbent structure.
• the pulp fibers can range from about 25 wt% to about 85 wt% of the absorbent composite.
• the reinforcing fibers can range from about 5 wt% to about 30 wt% of the absorbent composite.
• the superabsorbent can range from about 10 wt% to about 70 wt% of the absorbent composite.
• an absorbent composite for absorbing and retaining urine contains about 58 wt% pulp fibers, about 10 wt% of reinforcing fibers, and about 32 wt% of superabsorbent.
• an absorbent composite for absorbing and retaining a variety of aqueous body wastes, including urine contains from about 35 wt% to about 60 wt% of pulp fibers, from 5 wt% to about 25 wt% of reinforcing fibers, and from about 15 wt% to about 40 wt% of superabsorbent.
• the pulp fibers preferably are present in the absorbent composite in a greater weight percentage than the reinforcing fibers. Desirably the weight ratio of pulp fibers to reinforcing fibers is in the range of 1 : 1 to 5: 1. Alternatively the weight ratio of pulp fibers to reinforcing fibers is in the range of 1.5 : 1 to 3 : 1.
• the reinforcing fibers are present in a loading of at least 5 wt% of the absorbent composite to ensure that the absorbent composite has sufficient mechanical properties.
• the weight ratio of superabsorbent to reinforcing fibers be in the range of 1 : 1 to 1 :4.
• absorbent composites with the weight ratio of reinforcing fibers to superabsorbent be in the range of 0.33:1 to 0.75:1 may be used. In these ranges there are sufficient reinforcing fibers to enhance absorbent performance without adding excessive cost.
• the absorbent composite can be formed by mixing the superabsorbent, biodegradable reinforcing fibers, and optional fibrous pulp. This mixture, in a substantially dry condition, can then be compressed to a density ranging from about 0.09 grams per cubic centimeter (g/cm 3 ) to about 0.3 g/cm 3 . Preferably, the absorbent composite is compressed to a density ranging from about 0.15 g/cm 3 to about 0.22 g/cm 3 . More preferably, the absorbent composite is compressed to a density of about 0.2 g/cm 3 . This compression of the absorbent composite will assist in forming the absorbent article.
• Absorbent composites can be made by a variety of methods, including airlaid, carding, wetlaid and coform processes. Exemplary embodiments of airlaid processes are described in U.S. Patent Nos. 4,666,647; 5,028,224; 6,207,099; 6,479,061.
• the carding process uses a "card” which is a machine consisting of a series of rolls, the surfaces of which are covered with many projecting wires or metal teeth. See, for example, the "Dictionary of Fiber & Textile Technology", Hoechst Celanese Corp., Charlotte, NC, 1990. Carding separates, aligns, and delivers fibers as a nonwoven web.
• the wetlaid process consists of dispersing fibers in an aqueous suspension and then filtering the fibers onto a screen belt or perforated drum.
• Wetlaid nonwovens generally utilize shorter fibers than carding.
• the wetlaid process results in a more random orientation of the fibers and more isotropic properties than carding. Exemplary embodiments of coform processes are described in U.S. Patent Nos. 4,100,324 and 5,952,251.
• the mixture can be heat cured prior to compression, during the compression, or after the composite has been compressed.
• heat curing can be carried out by heating the mixture to a temperature of about 165°C for a time from about 8 seconds to about 10 seconds.
• microwave radiation may be used to heat the absorbent composite, using methods such as those disclosed in U.S. Patent No. 5,916,203.
• the thermoplastic nature of PLA allows PLA reinforcing fibers to be thermally bonded to one or more other components of the absorbent composite.
• PLA fibers can be fabricated to have a wide range of melting points, allowing for optimization of the time and temperature of the bonding process.
• PLA reinforcing fibers provide better absorbent properties when they are not thermally bonded.
• absorbent composites containing un-bonded PLA fibers may provide more rapid vertical wicking than composites containing no reinforcing fibers or containing PLA fibers that have been thermally bonded into the composite. This is in contrast to conventional binder fibers, which provide their optimum performance only when the binder fibers have been thermally bonded.
• the elimination of thermal bonding from the manufacturing process may reduce production time and cost and may reduce the variability of properties of absorbent composites within a particular system.
• stabilized absorbent composites containing biodegradable reinforcing fibers have minimal tensile strength.
• Composites of this type can be incorporated into a disposable absorbent product by, for example, depositing a portion of the composite onto a substrate and depositing a layer over the composite to secure the composite within the product.
• stabilized absorbent composites containing biodegradable reinforcing fibers can have sufficient tensile strength in the machine direction to allow the composite to be wound into rolls. Rolls of this type can be unwound later, and the unwound composite can be processed on conventional converting equipment.
• the tensile strength of the composite can be adjusted by changing parameters including the concentration of the reinforcing fibers, the conditions used for the optional thermal bonding, the specific density to which the composite is compacted, and other parameters known to those skilled in the art.
• Tensile strengths of absorbent composites can be tested using a model MTS/Sintech 1/S which is commercially sold by MTS Systems Corporation (Research Triangle Park, N.C.). The tensile strength at peak load is measured by securing a 50 mm strip of stabilized material between two movable jaws of a tensile tester.
• the tensile strength is recorded as peak load.
• Absorbent composites that have been thermally bonded may have a tensile strength of at least 12 Newtons per 50 mm (N/50 mm).
• Absorbent composites that have not been thermally bonded typically will have a tensile strength of less than 12 N/50 mm.
• Examples 1-12 - Formation of Absorbent Composites Individual mixtures were prepared containing 40 wt% superabsorbent and 60 wt% fibrous component, which included fibrous pulp and biodegradable reinforcing fibers.
• the superabsorbent was one of three superabsorbent materials - biodegradable superabsorbent, high gel stiffness SXM 9543, or FAVOR SAB 880 - all obtained from Stockhausen, Inc. (Greensboro, NC).
• the fibrous pulp was CR 1654, a southern softwood kraft pulp made by Alliance Corporation (a unit of The Aaron Group of Companies, Plymouth Meeting, PA).
• the PLA fibers were mono-component staple PLA fibers produced by Fiber Innovations Technology (FIT, Johnson City, TN). These fibers had a melting point of about 162 0 C, a fiber length of 1.5 inch (3.8 cm), 3 denier fiber diameter, and about 9 crimps/inch. Two types of PLA fibers were used. Referring to Table 1, the fibers indicated as "neat” were fibers of pure PLA without any separate substance on the fiber surface. The fibers indicated as having a spin finish contained residual surfactant on the fiber surface, since these fibers were treated with a spin finish containing 0.03% surfactant.
• Permeability is a measure of the ease with which liquid can pass through a material. Absorbent composites through which liquid can pass more easily should have a higher measured value of permeability, and are said to be more "open.”
• the permeability test uses Darcy's Law to calculate the permeability by measuring the flow of liquid through a fully swollen composite. This test was carried out as described in U.S. Pat. No. 6,437,214, which is substantially equivalent to Federal Test Method Standard FTMS 191 Method 5514, dated Dec. 31, 1968. In measuring permeability, absorbent samples were cut into 2 V 8 inch (6.0 cm) diameter circles and placed in a cup with a mesh screen at the bottom.
• Vertical wicking is a measure of the ease with which a liquid is absorbed into a material.
• the ability of a composite to wick liquid vertically and to distribute the absorbed liquid is related to its capillary tension, which in turn is a function of the surface tension between the composite and the liquid and of the pore size within the composite.
• 12.5 x 3 inch (31.8 x 7.6 cm) absorbent composite samples were placed vertically into a pool of saline for 30 minutes. The mass of liquid absorbed by the sample in a given amount of time was recorded.
• the effect of PLA staple fibers on vertical wicking is illustrated in the graphs of Figures 2 and 3, each of which plot the mass of liquid absorbed as a function of time.
• FIG. 2 shows the results for Example Nos. 1-5, containing biodegradable superabsorbent.
• the composite containing 15 wt% PLA without surfactant treatment (“neat PLA") had more rapid liquid absorption compared to the composite containing 15 wt% PLA with surfactant treatment. Also, liquid absorption was higher at 15 wt% PLA fiber content than at 25 wt% PLA fiber content.
• Figure 3 shows the results for Example Nos. 6-10, containing the high gel stiffness superabsorbent. Here also PLA without surfactant treatment provided for more rapid liquid absorption. In both the biodegradable superabsorbent system and the high gel stiffness system, thermal bonding of the PLA reinforcing fibers resulted in the lowest measurements of vertical wicking. [0068] X-ray Densitometry Measurements
• liquid distribution within the sample can be determined using x-ray densitometry.
• the sample containing the absorbed liquid is placed flat in an x-ray unit and exposed.
• the x-ray image is captured and analyzed for liquid distribution using software from
• FIGS 4 and 5 are shown in Figures 4 and 5, respectively.
• Figure 4 illustrates that the liquid distribution profile for composites containing a high gel stiffness superabsorbent with 15 wt% PLA fibers is a more even distribution than for the same composite without PLA reinforcing fibers. This is observed in that more liquid is present at greater heights above the saline pool for the PLA-containing composite than for the control.
• Figure 5 A similar improvement in the liquid distribution with incorporation of 15 wt% PLA fibers is also illustrated in Figure 5 for the lower gel stiffness biodegradable superabsorbent system.
• liquid wicking and distribution results illustrated in Figures 2-5 all indicate a surprising and unexpected benefit in using PLA fibers to improve liquid distribution. This is in addition to the surprising and unexpected benefit in using PLA fibers to increase the overall permeability of absorbent composites.

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