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Surgeons and other healthcare providers often wear an over garment during operating procedures in order to enhance the sterile condition in the operating room and to protect the wearer. The over garment is typically a gown that has a main body portion to which sleeves and a tie cord are attached. The tie cord encircles the wearer at the waist to keep the gown in place. In order to prevent the spread of infection to and from the patient, the surgical gown prevents bodily fluids and other liquids present during surgical procedures from flowing through the gown.
Surgical gowns were originally made of cotton or linen, were reusable and were sterilized prior to each use in the operating room. A disadvantage of the materials used in these types of gowns is that they tend to form lint, which is capable of becoming airborne or clinging to the clothes of the wearer, thereby providing another potential source of contamination. Additionally, costly laundering and sterilization procedures were required before reuse.
Disposable surgical gowns have largely replaced the reusable linen surgical gown and many are now made in part or entirely from fluid repellent or impervious fabrics to prevent liquid penetration or “strike through”. Various materials and designs have been used in the manufacture of surgical gowns to prevent contamination in different operating room conditions. Surgical gowns are now available in a variety of different levels of imperviousness and comfort.
Gowns made from completely impervious material provide a high degree of protection, though a surgical gown constructed of this type of material is typically heavy, expensive, and uncomfortably hot to the wearer. In some surgical gowns, certain portions such as the shoulders and back panels may be of a lighter weight material in order to provide for better breathability and help reduce the overall weight of the gown. Generally, however, the higher the breathability of the material, the lower the repellency of the material.
Different types of surgical procedures expose the healthcare provider to different levels of blood and/or fluid exposure, so it is not feasible or economical to use the same type of surgical gown for every surgical procedure conducted by the healthcare provider. New guidelines have recently been created for the rating of the imperviousness of surgical gowns, gloves and the like, to provide guidance to healthcare providers. The Association for the Advancement of Medical Instrumentation (AAMI) has proposed a uniform classification system for gowns and drapes based on their liquid barrier performance. These procedures were adopted by the American National Standards Institute (ANSI) and were recently published as ANSIA/AAMI PB70: 2003 entitled Liquid Barrier Performance and Classification of Protective Apparel and Drapes Intended for Use in Health Care Facilities, which was formally recognized by the U.S. Food and Drug Administration in October, 2004. This standard established four levels of barrier protection for surgical gowns and drapes. The requirements for the design and construction of surgical gowns are based on the anticipated location and degree of liquid contact, given the expected conditions of use of the gowns. The highest level of imperviousness is AAMI level 4, used in “critical zones” where exposure to blood or other bodily fluids is most likely and voluminous. The AAMI standards define “critical zones” as the front of the gown (chest), including the tie cord attachment area, and the sleeves and sleeve seam area up to about 2 inches (5 cm) above the elbow.
The main body portion and the sleeves of a surgical gown are usually produced separately and joined together in some manner at seams in the shoulder area. The sleeves are commonly made from a flat piece of fabric that is folded upon itself and joined together at a seam that runs the length of the sleeve from the shoulder to the wrist, prior to attachment to the main body portion. A single tie cord or a pair of tie cords is also usually attached to the main body portion of the gown. A single tie cord is used to encircle the wearer at the waist and tie to itself in order to keep the gown in position during use. Two tie cords are also used to encircle the wearer at the waist and tie to each other. The seams and the tie cord attachment point are areas where many gowns have been known to fail the AAMI test procedure.
A number of surgical gowns are currently marketed which are assembled through the use of ultrasonic seam sealing. Ultrasonic seam sealing bonds the layers of material together sufficiently for strength but the bonds do not pass ASTM-1671-b; the bacteriophage penetration resistance test, a test that is now required to meet the new AAMI level 4 protection standards, nor do they pass the hydrohead test, AATCC test method 127-1998, for AAMI level 3 protection. This is particularly true for the sleeve seams and tie cord attachment point.
It is clear that there exists a need for a gown having tie cord attachments bonded in a manner that is more impervious than current methods and that meets AAMI levels 3 and 4.
FIG. 1 illustrates an exemplary gown 100 to be worn during a medical procedure as seen from the front.
FIG. 2 illustrates an exemplary gown 100 to be worn during a medical procedure as seen from the back.
In response to the foregoing difficulties encountered by those of skill in the art, we have successfully used a point-unbonding bond pattern with and without a reinforcement patch on medical gowns at the tie attachment point such that they will pass AAMI level 3 (AATCC 127-1998 hydrohead) 4 testing (ASTM 1670 and 1671-b).
The present invention involves the use of bonding and the placement of a reinforcement piece to meet AAMI levels 3 and 4 barrier properties in surgical gowns and similar articles formed from thermally sensitive laminate barrier materials that are composed of thermoplastic polymers.
Many surgical gowns are made from thermally sensitive laminate barrier materials composed of thermoplastic polymers. While such barrier materials may be in the form of thermoplastic polymer spunbond fabrics, thermoplastic polymer meltblown fabrics, and various combinations of such spunbond and meltblown fabrics, a particularly desirable form of these barrier materials incorporate one or more thin, breathable films that provide desirable levels of resistance to penetration by liquids and pathogens while also providing satisfactory levels of breathability and/or moisture vapor transmission.
These thin and breathable films are commonly made from thermoplastic polyolefins like polyethylene and polypropylene and copolymers thereof because of their relatively low cost and ability to be processed. Polyethylene is generally used in the film production and the film is commonly “filled” with calcium carbonate, various kinds of clay, silica, alumina, barium carbonate, soldium carbonate, magnesium carbonate, talc, barium sulfate, magnesium sulfate, aluminum sulfate, titanium dioxide, zeolites, cellulose-type powders, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, pulp powder, wood powder, cellulose derivatives, chitin and chitin derivatives, to increase breathability. Fillers produce microscopic pores in the film upon stretching to increase porosity. Unfortunately, these thin and breathable films are considered to be thermally sensitive because they have a tendency to become compromised by heat and/or or pressure. When these films are incorporated into laminate barrier materials by sandwiching them together with various combinations of other materials such as, for example, spunbond fabrics, meltblown fabrics and combinations thereof, the resulting laminate barrier materials are generally considered to be thermally sensitive as well. This characterization is particularly important for post-laminate formation processing steps. That is, manufacturing operations that convert the thermally sensitive barrier fabrics after such films are formed into the laminate barrier fabrics. For example, when thermally sensitive barrier materials are converted into gowns or other articles utilizing thermal point bonding and/or ultrasonic bonding techniques or when components such as, for example, tie cords or other features are attached to the articles, the breathable films of barrier laminate are frequently compromised such that they so longer provide desired levels of barrier to liquid penetration and pathogens.
“Spunbond” refers to fabric made from small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, and U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond fibers are generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and have average diameters (from a sample of at least 10) larger than 7 microns, more particularly, between about 10 and 20 microns.
“Meltblown” fabric is formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. The meltblown fibers are then carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting surface.
Laminates of spunbond and meltblown fabrics, e.g., spunbond/meltblown/spunbond (SMS) laminates and others are disclosed in U.S. Pat. No. 4,041,203 to Brock et al., U.S. Pat. No. 5,169,706 to Collier, et al, U.S. Pat. No. 5,145,727 to Potts et al., U.S. Pat. No. 5,178,931 to Perkins et al. and U.S. Pat. No. 5,188,885 to Timmons et al. Such a laminate may be made by sequentially depositing onto a moving forming belt first a spunbond fabric layer, then a meltblown fabric layer and last another spunbond layer and then bonding the laminate in a manner described below. Alternatively, the fabric layers may be made individually, collected in rolls, and combined in a separate bonding step. Such fabrics usually have a basis weight of from about 0.1 to 12 osy (6 to 400 gsm), or more particularly from about 0.75 to about 3 osy. Multilayer laminates may also have various numbers of meltblown (abbreviated as “M”) layers or multiple spunbond (abbreviated as “S”) layers in many different configurations and may include other materials like films (abbreviated as “F”) or coform materials (see U.S. Pat. No. 4,100,324 for descriptions of exemplary “coform” materials), e.g. SMMS, SM, SFS, etc.
An exemplary method of forming a film includes a co-extrusion film apparatus that forms the film with multiple layers consisting of skin and core layers. Typically the apparatus will include two or more polymer extruders. In one method of fabrication, the film is extruded into a pair of nip or chill rollers. In another method the film is extruded onto a chilled roll which can have a smooth or matte finish. Typically, the film as initially formed will have an overall thickness of approximately 25 to 60 micrometers with, in the case of multilayer films, the total skin or bonding layer having an initial thickness that may be about 3% to 30% of the total thickness. Other film making processes known to those skilled in the art may be used as well, including cast embossing, chill and flat casting and blown film processes.
From the coextrusion film apparatus the film is directed to a film stretching unit such as a machine direction orienter (MDO), which is a commercially available device from vendors such as the Marshall and Williams Company of Providence, R.I. Such an apparatus has a plurality of paired stretch rolls that move at predetermined speeds that may rotate faster, slower or at the same speed relative to each other. Typically the stretch rolls move at a progressively faster speeds to progressively stretch and thin the film in the machine direction of the film, which is the direction of travel of the film through the process. The stretch rolls are generally heated for processing advantages.
The temperatures to which the film is heated while stretching will depend on the composition of the film as well as the breathability and other desired end properties of the laminate. In most cases the film will be heated to a temperature no higher than 5 degrees ° C. below the melting point of the core or “B” layer in the film. The purpose for heating the film is to allow it to be stretched quickly without causing film defects. The amount of stretching will depend on the polymeric composition, but, in general, the film may be stretched to about 300% or more of its original length (that is, a one cm length, for example, will be stretched to 3 cm) but less than the amount that tends to result in film defects. For most applications, for example, the stretch will be to at least 200% of the original film length and, frequently, in the range of about 250% to 500%.
The multilayer stretch-thinned film may be attached to one or more support layers to form a multilayer film/nonwoven laminate as described above. For example, a conventional fibrous nonwoven web forming apparatus, such as a pair of spunbond machines, may be used to form the support layer. The long, essentially continuous fibers are deposited onto a forming wire as an unbonded web and the unbonded web is then sent through a pair of bonding rolls to bond the fibers together and increase the tear strength of the resultant web support layer. One or both of the rolls are often heated to aid in bonding. Typically, one of the rolls is also patterned so as to impart a discrete bond pattern with a prescribed bond surface area to the web. The other roll is usually a smooth anvil roll but this roll also may be patterned if so desired.
Once the multilayer film has been sufficiently thinned and oriented and the support layer has been formed, the two layers are brought together and laminated to one another using a pair laminating rolls or other means. As with the bonding rolls, the laminating rolls may be heated. Also, at least one of the rolls may be patterned to create a discrete bond pattern with a prescribed bond surface area for the resultant laminate. Generally, the maximum bond point surface area for a given area of surface on one side of the laminate will not exceed about 50 percent of the total surface area.
The process described above may be used to create a three layer laminate. The only modification to the previously described process is to feed a supply of a second fibrous nonwoven web support layer into the laminating roll on a side of the multilayer film opposite that of the other fibrous nonwoven web support layer. Alternatively, as with the other layers, the support layer may be formed directly in-line. In either event, the second support layer is fed into the laminating rolls and is laminated to the multilayer film in the same fashion as the other support layer.
Exemplary processes and materials for forming thin films and laminates may be found in commonly assigned U.S. Pat. Nos. 5,188,885, 5,213,881, 5,271,883, 5,464,688, 5,695,868, 6,037,281, 6,309,736, 6,653,523 and 6,764,566, incorporated herein in their entirety.
FIG. 1 illustrates a typical gown 100 to be worn during a medical procedure as seen from the front. The gown 100 includes a collar 110, the cuffs 120, the primary tie cord 130 and a primary tie cord attachment area 140. The shoulder seams 150 linking the sleeves 160 to the main body 170 are also visible. FIG. 2 illustrates a typical gown 100 to be worn during a medical procedure as seen from the back. In FIG. 2 the shoulder seams 150 linking the sleeves 160 the main body 170 are visible as are the sleeve seams 180 running from the shoulder seams 150 to the cuffs 120 which are used to produce the sleeves 160. FIG. 2 also shows a secondary tie cord 180 and secondary tie attachment area 190 (not in the AAMI critical zone).
Previous tie cord sealing methods tended to damage the layers of the gown and to impair the liquid resistance of the bond to a point that the gown failed the AAMI level 3 or 4 test at the bond, or to be prohibitively expensive. These methods included ultrasonic or thermal point bonding and adhesive bonding. The inventors believe, though do not wish to bound by that belief, that the former methods tend to bond materials through their entire thickness, thus disrupting the structure to a relatively high degree. Since many surgical gowns include a film layer in order to increase the penetration resistance of the gown and because film layers tend to be relatively weak, the robust bonding used previously tended to damage this layer and increase liquid penetration. In the case of adhesive bonding the manufacturing challenges and expense are relatively great since adhesives tend to be expensive and time consuming to apply and can have detrimental effects on manufacturing facility cleanliness.
As noted above, the process conditions will vary depending on the materials of construction. For example, the current thermoplastic polymeric materials commonly used in disposable gowns and for components such as, for example, tie cords that are presently attached to such disposable gowns, are typically nonwoven fabrics formed from polypropylene and/or polyethylene and have a basis weight typically ranging from about 0.5 (17 gsm) to about 1.5 osy (51 gsm).
Desirably, the tie cord material may be a folded 1.0 osy (34 gsm) SMS material made as described above. Fabric for the fabrication of gowns may be, for example, made of random copolymer spunbond, a three layer (Catalloy®/polyethylene/Catalloy®) or “ABA” calcium carbonate filled film, and a spunbond/meltblown/spunbond (SMS) layer. This “SFSMS” may bonded together to form the gown with the SMS against the skin. The spunbond layer and film may have a basis weight of between 0.2 and 1.0 osy (7 and 34 gsm) or more particularly about 0.6 osy (20.3 gsm). The SMS layer may have a basis weight of between 0.5 and 1.5 osy (17 and 51 gsm) or more particularly about 0.75 osy (25.4 gsm).
The inventors have found that the attachment of a reinforcement piece on the side opposite the tie cord attachment side can provide sufficient assistance to the barrier properties such that the attachment point passes the hydrohead test. The reinforcement piece may be formed from various materials including films, papers, meltblown fabrics, etc. provided, however that the material from which the piece is made has a hydrohead above the AAMI level 3 standard. The piece may also have an adhesive for ease of application. The reinforcement piece may be, for example, a wax-treated paper available under the tradename “Fastape” from the Avery-Dennison Specialty Tape Division, 250 Chester St., Painesville, Ohio 44077. Fastape® paper also has an adhesive.
The reinforcement piece must be sufficiently large to cover the area of attachment of the tie cord. Generally a piece from about 1.5 inches to 2.5 inches (38 to 64 mm) in width to about 2.5 to 4 inches (64 to 102 mm) in length should suffice, giving an area of at most 10 square inches (645 square centimeters).
In addition to the reinforcement piece described above for AAMI level 3 testing, the inventors have found that a change in the bonding pattern is required in order to successfully reach AAMI level 4 requirements. Previous thermal bonding patterns have used “male” patterns. The inventors have found that “female” or point-unbonded (PUB) patterns provide greatly improved bonding for the purposes of the AAMI level 4. The method of attaching the reinforcement piece is desirably by bonding it ultrasonically with the new PUB bonding pattern.
Traditional “male” thermal point bonding generally involves passing a fabric to be bonded between a heated calender roll and an anvil roll. The calender roll is usually, though not always, patterned in some way so that the entire fabric is not bonded across its entire surface, and the anvil roll is usually flat. As a result, various patterns for calender rolls have been developed for functional as well as aesthetic reasons. One example of a pattern has points and is the Hansen Pennings or “H&P” pattern with about a 30% bond area with about 200 bonds/square inch as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. The H&P pattern has square point or pin bonding areas wherein each pin has a side dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches (1.778 mm) between pins, and a depth of bonding of 0.023 inches (0.584 mm). The resulting pattern has a bonded area of about 29.5%. Another typical point bonding pattern is the expanded Hansen Pennings or “EHP” bond pattern which produces a 15% bond area with a square pin having a side dimension of 0.037 inches (0.94 mm), a pin spacing of 0.097 inches (2.464 mm) and a depth of 0.039 inches (0.991 mm). Another typical point bonding pattern designated “714” has square pin bonding areas wherein each pin has a side dimension of 0.023 inches, a spacing of 0.062 inches (1.575 mm) between pins, and a depth of bonding of 0.033 inches (0.838 mm).
“Point unbonded” or “PUB” bonding means a fabric pattern having continuous bonded areas defining a plurality of discrete unbonded areas. The fibers or filaments within the discrete unbonded areas are dimensionally stabilized by the continuous bonded areas that encircle or surround each unbonded area and the unbonded areas are specifically designed to afford spaces between fibers or filaments within the unbonded areas. A suitable process for forming the pattern-unbonded nonwoven material of this invention includes providing a nonwoven fabric or web, providing opposedly positioned first and second calender rolls and defining a nip therebetween, with at least one of said rolls being heated and having a bonding pattern on its outermost surface comprising a continuous pattern of land areas defining a plurality of discrete openings, apertures or holes, and passing the nonwoven fabric or web within the nip formed by said rolls. Each of the openings in said roll or rolls defined by the continuous land areas forms a discrete unbonded area in at least one surface of the nonwoven fabric or web in which the fibers or filaments of the web are substantially or completely unbonded. Stated alternatively, the continuous pattern of land areas in said roll or rolls forms a continuous pattern of bonded areas that define a plurality of discrete unbonded areas on at least one surface of said nonwoven fabric or web. Examples of point unbonded patterns are illustrated in U.S. Pat. No. 5,858,515 to Stokes et al.
The amount of bonding for use herein is between about 20 and 30 percent, preferably about 25 percent. An exemplary PUB pattern for use in reaching the AAMI level 4 criteria is characterized by multiple unbonded areas of 0.030″ (0.762 mm) open space and a 0.010″ (0.254 mm) seal line per every 0.040″ (1.016 mm), producing a bond area of 25%.
The bonding “window” or conditions under which bonding takes place, is between the point at which holes will form in the fabric or where it will fail the AAMI levels 3 and 4 testing, and the point at which ties will be easily pulled off of the gown after bonding. The examples below were bonded using a Branson 900 series ultrasonic welding machine by Branson Ultrasonics Corporation, of Danbury Conn. The Branson 900 is controlled by setting the pressure and weld or contact time between the bonding points and the material. The pressure and contact time for use herein are between 50 and 90 psi and between 0.05 and 0.25 seconds, respectively, more particularly between 60 and 75 psi and 0.1 and 0.2 seconds, still more particularly about 65 psi and about 0.18 seconds.
The examples below show that the addition of a reinforcing piece allows gowns to pass the AAMI level 3 test and that adding PUB bonding allows the gown to pass AAMI level 4 testing.
AATCC test Method 127-1998: This test uses a Hydrostatic Pressure Tester, apparatus available from Alfred Suter Co., PO Box 350, Ramsey N.J. 07445-0350. An alternative but similar tester, the Textest Hydrostatic head Tester, is available from Schmid Corp., 140-B Venture Blvd, Spartanburg, S.C. 29301.
The Suter apparatus is an inverted conical well equipped with a coaxial ring clamp to fasten the cloth specimen under the well bottom. The apparatus introduces water from above the specimen over an area 114 mm in diameter at a rate of 10.0±0.5 mm of hydrostatic head per second. A mirror is affixed below the specimen to enable the operator to ascertain penetration of the specimen by drops of water. A valve is provided for venting the air in the well.
A minimum of three fabric specimens should be taken diagonally across the width of the fabric to be tested. Cut specimens at least 200 by 200 mm to allow proper clamping. The specimen should be conditioned at 21° C. and 65 percent relative humidity for at least 4 hours before testing. The specimen is clamped in the apparatus with the surface to be tested facing the water, which is at 21° C. The apparatus is turned on and water is introduced at the stated rate. Droplets appearing within 3 mm of the edge of the specimen should be disregarded and the pressure at which droplets penetrate the fabric in three different places is recorded. The pressure is reported as the height (in millimeters) of water above the fabric. An average should be calculated for each sample. The AAMI level 3 standard of 50 cm must be reached in order to pass the test.
The test uses a penetration test cell available from Wilson Road Machine Shop, Rising Sun, Md. The cell has a capacity of about 60 ml. In the test cell, the specimen acts as a partition separating the challenge fluid from the viewing side of the penetration cell. An annular flange cover with an open area to allow visual observations of the specimen, and a transparent cover are included. The cell body has top port for filling and a drain valve for draining the penetration test cell. The penetration cell is further specified in Test Method F903.
The fabric specimen is placed in the penetration cell with the layer that is normally outermost facing the back (solid flange) part of the cell where the challenge fluid is placed. The cell is filled through the top port with the challenge fluid and observed for 5 minutes. Air is then supplied to the top port and the sample held at 13.8 kPa (2 psig) for 1 minute and the pressure released. If liquid penetration is not yet seen, the sample is allowed to stand for 54 minutes and observed. If bacteriophage is the test fluid, the sample is subsequently assayed using a 0.5 ml sample size onto agar for 6 to 18 hours at 35 to 37° C. to test for passage of fluid that is not observable to the unaided eye.
The Kimberly-Clark Ultra® Impervious gown is made from 1.5 osy (51 gsm) polypropylene SMS and has a reinforcing section in the sleeves and chest (the AAMI “critical area”). The reinforcing material is a 1 mil polyethylene film. The sleeve is bonded film to film and turned inside out so the SMS is nearest the skin.
Kimberly-Clark MicroCool® surgical gowns are made of random copolymer spunbond, a three layer (Catalloy®/polyethylene/Catalloy®) calcium carbonate filled film, and a polypropylene spunbond/meltblown/spunbond (SMS) layer. This “SFSMS” is bonded together to form the gown with the SMS against the skin. The random copolymer of which the outermost layer of spunbond material is made is a 2.5 weight percent ethylene-propylene copolymer known as R532-35R, from the Dow Chemical Company of Midland, Mich. No treatments are applied to the fabric. The spunbond layer and film each had a basis weight of 0.6 osy (20.3 gsm). The SMS layer had a basis weight of 0.75 osy (25.4 gsm).
The tie cord to be bonded to the gown was a folded 1.0 osy (34 gsm) SMS material. The material was folded either once for a double layer of fabric, or twice for a triple layer of fabric. The outer layer (spunbond) was made from a 2.5 weight percent ethylene-propylene copolymer known as R532-35R, from the Dow Chemical Company and the outer layer is treated with an antistat and a fluorochemical to reduce surface tension. Prior to bonding to the gown, a additional piece of tie cord material was bonded to the tie cord near an end to produce a “Y” shaped end for bonding to the gown on both upper end of the Y. The Y was flattened out onto the gown for bonding at two points on the branches of the Y but near the stem of the Y.
A double folded SMS tie cord was bonded to an Ultra® surgical gown at a weld time of 0.175 seconds and a pressure of 65 psi using a point bond pattern. The bonded area was tested according to AATCC 127-1998. Twelve out of 12 samples failed.
A double folded SMS tie cord was bonded to an Ultral® surgical gown at a weld time of 0.175 seconds and a pressure of 65 psi using a PUB bond pattern with 25 percent bond area as described above. A 2.5 inch by 4 inch piece of Fastape® adhesive tape was placed below the tie cord bond site prior to bonding. The bonded area was tested according to AATCC 127-1998. Twelve out of 12 samples passed.
As will be appreciated by those skilled in the art, changes and variations to the invention are considered to be within the ability of those skilled in the art. Examples of such changes are contained in the patents identified above, each of which is incorporated herein by reference in its entirety to the extent it is consistent with this specification. Such changes and variations are intended by the inventors to be within the scope of the invention. It is also to be understood that the scope of the present invention is not to be interpreted as limited to the specific embodiments disclosed herein, but only in accordance with the appended claims when read in light of the foregoing disclosure.