WO1999049823A1

WO1999049823A1 - Light-activated antimicrobial polymeric materials

Info

Publication number: WO1999049823A1
Application number: PCT/US1999/006920
Authority: WO
Inventors: John E. Wilson; Deborah A. Ewaniuk; Matt Miller; Jerry Olderman
Original assignee: Fibermark, Inc.
Priority date: 1998-03-30
Filing date: 1999-03-30
Publication date: 1999-10-07
Also published as: AU3371799A

Abstract

Antimicrobial plastic materials, e.g. films and melt-blown webs for food packaging wraps, surgical drapes, face masks and the like, contain an agent such as methylene blue dispersed therein which, upon exposure to light, generates singlet oxygen having antimicrobial activity. The materials may be made by cryogenically grinding together a singlet-oxygen generating substance, ammonium stearate or other surfactant material having soap-like properties, and a polymer resin, to form a uniform concentrate as a homogeneous fine powder. The concentrate is added to large batches of polymer that are processible in conventional equipment to form plastic films, melt-blown nonwovens, fabrics, and other formed articles.

Description

IGHT-ACTΓVATED ANTIMICROBIAL POLYMERIC MATERIALS

TECHNICAL FIELD

The present invention relates to polymeric materials having broadly-active antimicrobial properties. Materials of the present invention produce singlet oxygen with antimicrobial activity when exposed to ambient light or when illuminated in a surgical or other environment. More particularly, the invention relates to plastics with light-activatable materials incorporated therein which generate singlet-oxygen upon exposure to light.

SUMMARY OF THE INVENTION

In one aspect, the invention comprises plastic materials, particularly laminar structures such as films and melt-blown webs and, in another aspect, methods of making such materials. Such materials are useful for the manufacture of plastic wraps, surgical drapes, face masks and the like, and have use in any application where there is a need for films or fabrics having broad- spectrum antimicrobial activities.

Unlike conventional available antimicrobial plastics which contain additives such as antibiotics and antimicrobial toxic substances, e.g., chlorinated aromatic molecules, no leaching of antimicrobial materials from the plastics of the present invention is required in order to kill microorganisms. Conventional antimicrobial plastics also have the disadvantage that many microbes may be resistant to the antibiotic used, and wide scale use may also select for resistance to such antibiotic. Additionally, antibiotics are without effect on viruses. Still further, antibiotics and antimicrobial toxic substances are consumed by the process of their action on microbes, and materials that incorporate such substances have a short effective life when in use. The antimicrobial action of the present invention is not consumed by the process of its action.

In accordance with the present invention novel antimicrobial plastic materials are disclosed. Such materials may be used in any manner in which conventional plastics are used and may, for example, have the laminar form of films or webs. Materials of the present invention may be used for food packaging wraps, food handling gloves, medical examination gloves, medical drapes, occlusive dressings and surgical incise drapes. The materials contain an agent dispersed therein which, upon exposure to light, generates singlet oxygen having antimicrobial activity. The materials provide antimicrobial activity while in use and continue to provide such activity while exposed to light.

The present invention also comprises methods for incorporating singlet-oxygen generating substances into materials of the present invention, so enabling protection against infections associated with bacteria and viruses by inactivating the microorganisms on surfaces and in proximity to materials of the present invention. In accordance with one embodiment of materials of the present invention, the material comprises an antimicrobial laminar structure of polymer having incorporated therein a singlet- oxygen generating amount of photosensitizer that is excited by light absorption and which generates singlet-oxygen by energy transfer from the excited photsensitizer. The laminar structure may be a film, a melt-blown web, a fabric, or a formed article.

In accordance with one method of making the materials of the present invention, a singlet- oxygen generating substance and a surfactant material having soap-like properties, and a polymer resin are cryogenically ground together, to form a uniform concentrate as a homogeneous fine powder suitable for making melt-blown nonwovens or die-extruded films. The concentrate produced by the methods of the present invention is readily added to large batches of polymer that are processible in conventional equipment to form plastic films, melt-blown nonwovens and other formed articles.

Another method of making the materials of the present invention.a singlet-oxygen generating substance and a surfactant material having soap-like properties and a polymer resin are combined or mixed togther on a compounding extruder to form a concentrate as a continuous rod or string which is cut or chopped into pellets suitable for making melt-blown nonwovens for die-extruded films. The concentrate produced by the methods of the present invention is readily added to large batches of polymer that are processible in conventional equipment to form plastic films, melt-blown nonwovens and other formed articles. Yet another method of making the materials of the present invention, a polymer resin is melted in a processing extruder. Using a second metering extruder or pump, a singlet-oxygen generating substance and a surfactant material having soap-like properties is melted and metered directly into the mixing zone of the first extruder. The extrusion rate of the first extruder and the metering rate of the second extruder are such that the level of the singlet-oxygen generating material is in the final form (plastic films, melt-blown nonwovens and other formed articles) and is in the desired concentration without further processing.

Such formed articles may be cast or formed by injection molding or other conventional techniques.

In preferred embodiments of materials of the present invention, the polymeric material is a polyolefin, e.g., polyethylene or polypropylene, or polystyrene, polyester, polyvinylidene chloride, potyvinyl chloride or another sheet-forming or film-forming polymer such as polyurethane.

Various singlet-oxygen generating substances are known and each may be suitable for particular embodiments of the present invention. Examples of suitable singlet-oxygen generating substances are methylene blue; rose bengal; fluorescein; eosin yellowish; erythrosin B; phloxine B; thionin; azure A; azure B; azure C; riboflavin; toluidine blue O; hypericin; a phthalocyanine; and singlet-oxygen generating derivatives of the aforementioned agents such as 1,9-dimethyl methylene blue. A particular embodiment of the invention is a surgical drape comprising a film of polymeric material having incorporated therein a singlet-oxygen generating amount of a light- absorbing compound that is excited by light absorption and which generates singlet-oxygen upon decay of the excited state. Exposure of the surgical drape of the present invention to light is able to provide continued production of an antimicrobial amount of singlet-oxygen which reduces or eliminates the risk of infection to a patient and to medical personnel working on the patient and reduces the necessity to employ other antimicrobial agents such as antibiotics in the surgical arena. But it does not eliminate the necessity of the use of antibiotics given to the patient as an injection, irrigation, etc. Another embodiment of the invention is a sheet of material having the form of a film or a non-woven fabric for use where microbial contamination is to be reduced. Sheets of this embodiment of the invention produce an antiseptically active amount of singlet-oxygen when exposed to light.

Yet another embodiment of the invention is a plastic food-wrap comprising a film of polymeric material having incorporated therein a singlet-oxygen generating amount of a light- absorbing compound that is excited by light absorption and which generates singlet-oxygen upon decay of the excited state. Exposure of the food-wrap of the present invention to light facilitates continued production of antimicrobial singlet-oxygen which reduces or eliminates microbial contamination of the food to which the food-wrap is applied. Food wrap is typically sold wound around a cardboard roll and in a dispenser box.

A material of the present invention is produced by a process comprising forming a mixture of a polymeric material and a singlet-oxygen generating agent, in which mixture the singlet- oxygen generating agent is more or less uniformly dispersed in the polymeric material. The polymeric material is formed into a thin film, preferably accomplished by extrusion techniques known to those of skill in the art utilizing extrusion through heated slot dies. Another material of the present invention is produced by forming the polymeric material into a melt-blown web. The formation of the melt-blown web is preferably accomplished by extrusion techniques known to those of skill in the art utilizing extrusion through single- or multi-orifice dies into streams of heated air.

Yet another material of the present invention is produced by forming the polymeric material into the textile. The formation of the fibrous web is preferably accomplished by extrusion or spinning techniques known to those of skill in the art utilizing melt spinning through a spineret and allowed to cool in air after which it is then drawn in a separate step or in tandem with spinning to develop good tensile properties. These man-made fibers made of nylon, polyester, acrylic, etc. are then woven into fabrics.

Accordingly, it is an object of the present invention to provide an antimicrobial plastic material. Such a material is advantageously capable of reducing the level of microbial contamination and reducing the risk of infection to or by humans beings such as food handlers, consumers, physicians and patients.

It is an advantage of a method of the present invention to produce uniform distribution of component materials with minimal physical defects in products formed thereof, such as films.

It is an advantage of the present invention that the antimicrobial plastic disclosed herein may be formed to be a film or a web or any form in which conventional thermoplastics may be manufactured.

Thus, it is a feature of the present invention to provide a surgical drape capable of generating an antiseptically active amount of singlet-oxygen to a surface when the drape is exposed to light.

It is an additional feature of the present invention to produce a surgical drape wherein the drape is produced by forming a film of a polymeric material having dispersed therein a singlet- oxygen generating agent. It is a further feature of the present invention to provide a thin film material having dispersed therein a singlet-oxygen generating agent capable of reducing the level of microbial contamination of food by humans beings such as food handlers. Such reduction or elimination of microbial contamination is of particular value for packaged foods such as those distributed to airline passengers or placed in sandwich cases for later purchase. Such a food-wrap is advantageously capable of generating an antiseptically active amount of singlet-oxygen to a surface when the food-wrap is exposed to light.

Additionally, an advantage of the present invention is an antimicrobial melt-blown web material capable of reducing the level of microbial contamination and reducing the risk of infection to or by humans beings such as physicians and patients. Such a melt-blown web may be used to provide a surgical drape capable of generating an antiseptically active amount of singlet- oxygen to a surface when the drape is exposed to light.

It is an advantage of the present invention that embodiments thereof may be advantageously used in a number of items used surgical procedures, such as drapes, face masks, absorbent pads and the like. Such items comprise a melt-blown web of a polymeric material having dispersed therein a singlet-oxygen generating agent.

A particular advantage of the present invention is that the antimicrobial additives are effective at concentrations less than 300 parts per million. A further advantage of the present invention is that the additives described herein are photosensitizers that act as catalysts, not as reactants. Each singlet-oxygen-generating molecule of the additive is able to cycle through all of the various steps in generating singlet oxygen in 10 microseconds or less. Thus, one molecule is able to generate thousands of singlet oxygen molecules per minute, which can inactivate thousands of adjacent microbes. This is in contrast to a chlorinated aromatic molecule which is inactivated by interaction with a microbe.

Yet a further important advantage of the present invention is that the singlet-oxygen generating substances present in the film and melt-blown embodiments are not substantially leached out when exposed to water. These and other objects, advantages and features will be readily recognized and understood by one skilled in the art as reference is made to the following detailed description of the preferred embodiments.

DISCLOSURE OF THE INVENTION While describing the preferred embodiments, specific terminology will be utilized for the sake of clarity. It is to be understood that such terminology includes not only the recited embodiments, but all technical equivalents which perform substantially the same function in substantially the same way to obtain the same result.

A variety of substances have the properties of generating singlet oxygen upon exposure to light. Such substances are sometimes referred to herein as "singlet-oxygen generating agents" or

"SOG-additives." Various singlet-oxygen generating agents are contemplated for use in the present invention. Examples of such agents include: methylene blue; rose bengal; fluorescein; eosin yellowish; erythrosin B; phloxine B; thionin; azure A; azure B; azure C; riboflavin; toluidine blue O; hypericin; phthalocyanines; and singlet-oxygen generating derivatives of the aforementioned agents such as 1,9-dimethyl methylene blue. In a preferred embodiment of the present invention, the singlet-oxygen generating agent is methylene blue.

The singlet-oxygen generating antimicrobial agent is preferably present in a laminar embodiment of the invention in an amount of about 5 ppm to about 1000 ppm by weight of polymeric material. More preferably the agent is present at between about 50 ppm and about 500 ppm by weight.

An optimal concentration of SOG-additive in the polymer is desirably determined empirically, as by the techiques described in the Examples below, or equivalents thereof. It has been found that too much of the additive can be less effective than a lower but optimal concentration, apparently due to self-quenching. Experimentally, the present inventors have determined that conventional approaches do not permit the preparation of a uniform mixture of the SOG-additives and polyethylene pellets. For example, the present inventors found that the such materials were essentially impossible to grind in a mortar and pestle and that films incorporating SOG-additives formed by conventional technology had a non-uniform distribution of component materials, had numerous physical defects and did not yield films with satisfactory and uniform antimicrobial activity.

The inventors of the present invention have discovered that a surfactant such as ammonium stearate can be caused to interact with a hydrophilic singlet-oxygen-generating substance such as methylene blue to form blends, referred to herein as "SOG-blends," that are dispersible in a hydrophobic plastic such as polyethylene. Such methods are part of the present invention. Such surfactants include, for example: the potassium salt, or the ammonium salt or another salt or a mixed salt of the following - undecylenic acid, stearic acid, dodecylbenzene sulfonic acid, polystyrene sulfonic acid, polyvinylsulfonic acid, poly(butadiene-maleic acid), 2,5- furandione polymer with methoxyethene, Epolene C-16P (Eastman Chemical) a graft polymer of polyethylene and maleic anhydride, C(30) polyanhydride resin (Chevron), copolymers of octadecene-1 and maleic anhydride, 3,3',4,4'- benzophenone tetracarboxylic anhydride, 1,2,4,5- Benzenetetracarboxylic acid, Pomareze X8039 (Baker Petrolite Corp.) olefin/maleic anhydride copolymer, Pomarez X8040 olefin/maleic anhydride copolymer, Baker Petrolite X-5005 copolymer of ethylene with isopropyl maleic anhydride, Baker Petrolite X5388 carboxy functional linear olefin and similar materials known to those familiar with compounding plastic materials. In accordance with the invention, other plastic additives can be added to provide conventional benefits including slip additives, antioxidants, antiblocking additives, additional surfactants and other known plastic additives, provided they do not significantly interfere with the generation of singlet oxygen.

In one embodiment of the present invention, an SOG-blend and a polymer resin are cryogenically ground together, to form a uniform SOG-additive concentrate as a homogeneous powder. To produce a material that exemplifies the present invention, an SOG-blend comprising an ammonium stearate/methylene blue mixture was combined with polyethylene pellets and reduced to a fine powder suitable for making melt-blown nonwovens or die-extruded films.

An SOG-additive concentrate so produced is readily added to a large batch of polymer that is processible in conventional equipment to form a plastic film, a melt-blown nonwoven or other formed articles. We have found that plastic films and melt-blown nonwovens formed from plastic resins to which SOG-additive concentrates have been added, have light-activatable antimicrobial properties. Examples of polymers useful in the present invention are Dow Polyethylene 640i, Exxon PP3546G Polypropylene and Exxon PP3505G Polypropylene. Other suitable polymers are commercially available. PREPARATION OF SOG BLEND Five-hundred grams of ammonium stearate (33% in an aqueous base) and 4.65 grams of methylene blue powder (USP/NF) were added to a one quart plastic bottle. The mixture was mixed on a laboratory mixer for two hours and then poured out and dried on a Teflon coated cookie baking sheet for four hours at 200 °F until substantially free of moisture. The dried ammonium stearate/methylene blue mixture was recovered from the cooled cookie sheet in flakes and sealed in an airtight jar. The dried ammonium stearate/methylene blue mixture was ground by hand to form a granular SOG-blend powder with particles ranging in size from dust to pea size particles. CRYOGENIC GRINDING TO PREPARE SOG-ADDITIVE CONCENTRATE

Five grams of the ground ammonium stearate/methylene blue mixture were weighed into a plastic bag together with 495 grams of Dow 640i polyethylene pellets. The contents were mixed by squeezing and rotating the closed plastic bag end-over-end. Cryogenic grinding was achieved by immersing the ammonium stearate/methylene blue/Dow 640i polyethylene pellets mixture in liquid nitrogen at minus 320 °F for 15 to 20 minutes to allow temperature equilibration. The materials formed an easily-pourable slurry which was poured into a laboratory sized grinder capable of processing 200 to 400 pounds of material per hour. Material initially emerged from the grinder at minus 124 °F, and by the end of the run the material was at minus 50 °F. The ground material passed through a 60 mesh exit screen on the grinder and was of a uniform texture and color. The ground material is referred to herein as a "SOG-additive concentrate." COMMERCIAL SCALE PRODUCTION

It is envisaged that the process of preparing an SOG-blend could be performed on a large scale by reacting stearic acid with anhydrous ammonia in the presence of a singlet-oxygen generating substance in a reactor to form an SOG-blend. The SOG-blend would be fed from the reactor into a hopper which also receives the polymeric substrate. In turn the hopper would feed a metering extruder which would combine the SOG-blend and the polymeric substrate to form the SOG-additive concentrate. The metering extruder would feed the SOG-additive concentrate into melted polymer in the hot-zone of either a film extruder or a melt-blown extruder to form the antimicrobial substrate of the present invention. Alternatively, the SOG-blend from a reactor would feed into melted polymer in the hot-zone of a metering extruder which would, in turn, feed the directly into the hot zone of a film extruder. ANTIMICROBIAL FILMS

The present invention includes film materials generally formed with SOG-additive concentrate. Such film materials are particularly suited to surgical drapes and food-wraps which employ polymeric substrates.

In use, a surgical drape is applied to a patient at the portion of the body where a surgical incision is to be made. The surgical drape of the present invention is characterized by having incorporated in its substrate singlet-oxygen generating material in an antiseptically effective amount. Thus, when the drape is used in light, singlet oxygen is generated and migrates to the outer surface of the substrate where it inactivates microbes on the patient. As the singlet oxygen is removed by reaction, it is replenished from the drape.

The thin sheet substrate used as the surgical drape may be selected from a number of materials. The substrate may be a woven, knitted fabric or an extruded sheet comprised of plastic material such as polyvinyl chloride, polypropylene, polyethylene or polyurethane. The polymeric films are continuous in that they have no voids but may be moisture vapor permeable.

The melt index of Dow Polyethylene 640i (2.0) is suitable for the formation of films of the present invention, which can be up to 75 microns in thickness. More preferably films are less than 40 microns and usually about 20 to 30 microns in thickness.

Incorporated into and throughout the structure of the polymeric materials of the present invention is an oxygen-generating substance capable of producing antiseptically active amounts of singlet oxygen upon exposure to light. The singlet oxygen functions to prevent bacterial growth at the site of application of the sheet and further functions to provide protection to personnel working in the surgical arena.

Plastic films of the present invention may be produced as follows: The polymeric material and the singlet-oxygen generating agent are mixed together to uniformly and stably disperse the singlet-oxygen generating agent in the polymeric material. A sheet is mechanically formed from the mixture by procedures known in the art. Examples of such procedures include film extrusion, injection molding, film blowing and extrusion molding. Another method for producing plastic films is solvent casting. In the preferred embodiment, an extrusion technique is used.

For example, when producing a polyethylene surgical drape having a singlet oxygen- generating agent dispersed therein by an extrusion technique, a film-type extruder having a slot die is used to produce a sheet having a thickness of less than 400 microns. In operation, this technique involves extrusion of polyethylene feed through the die, followed by passage of the film through guiding devices after which it is wound up into a roll.. The film can then be used in the assembly of surgical drapes and gowns or used separately to cover Mayo stands and other equipment. Alternatively, the technique involves extrusion of polyethylene feed through the die onto a continuous belt moving faster than the polymer film exiting the die. This causes that film to thin-out. By changing the speed of the continuous belt, the thickness of the resulting film can be changed. The mixture produced as described in the section "CRYOGENIC GRINDING" above, when mixed with more polymer, extruded into a clear, transparent film of very light-violet color substantially free of voids and imperfections except for cross web caliper variation. The caliper of the film was measured to be from 3.1 to 5.9 mils. The width of the film was 2% inches.

The methylene blue content of a film produced as aforesaid was determined to be 274 ppm. The film, when tested for antibacterial properties, killed greater than 99.94% of applied bacteria when the system was exposed to a light intensity of 6000 foot candles for 60 minutes. In other embodiments of the process for producing the plastic films of the present invention, a blown film extruder may be used as disclosed in U.S. Patent RE 28,600, the disclosure of which is incorporated herein by reference.

In an embodiment wherein a fabric is produced, the singlet-oxygen generating agent is directly added to the material from which the fabric is formed. This material may be, for example the fiber from which the film and threads forming the fabric are formed. The resultant material is then formed into a fabric by knitting, in the case of a knitted drape, or by utilizing process techniques known in the art to produce a nonwoven fabric such as melt-blowing, as described

8 below.

A surgical drape of the present invention may also include additional materials to conform to the desired use, such as commercially available antistatic materials. An example of such an antistatic material is Electrosol S-l-X, manufactured by Alframine.

MELT-BLOWN WEBS

The melt-blowing apparatus can be thought of as being composed of three major pieces of equipment. These pieces are: a screw extruder, a die section, and an air supply system.

Screw Extruder: The primary function of the extruder is to supply a constant flow of molten polymer to the die section. The extruder used for the work described herein was an instrumented Killion Single Screw Extruder. The extruder accomplishes melting of the polymer by heating the polymer in five consecutive stages using band heaters. A motor driven single screw establishes the desired polymer flow rate, or throughput, entering the die section. In order to ensure constant polymer flow rate, a Dynisco pressure sensor is located between the 4th and 5th heater zones to monitor the pressure being exerted by the polymer on the extruder walls. To replenish the polymer extruded through the die section, raw polymer is fed into a hopper at regular intervals. The extruder's zone heaters and motor speed were controlled by a control panel.

Die Section: The die section of the melt-blowing apparatus comprises a spacer block, a screen pack, a 30 degree nosepiece, two cartridge heaters, air thermocouples, a polymer thermocouple, a pressure gauge, and upper and lower adjustable face plates. Polymer from the extruder flows through the spacer block, through the screen pack, and into the 30 degree nosepiece where it then exits through small die orifice holes into converging streams of heated air. Dies may have single or multiple orifices, e.g., 30 orifices. The spacer block was used as an adjustment piece for the nosepiece. This block has a series of through-holes that allow equalization and mixing of the air between the upper and lower regions of the die section. The screen pack was used to exclude foreign particles capable of clogging the die orifices. The nosepiece of the die contained two cartridge heaters rated at 280 watts each to maintain the desired polymer temperature at the die tip. A Type K thermocouple was used to measure the polymer temperature, and the die had 30 orifices per inch, each with a diameter of 356 microns. Converging air streams were created by adjustable face plates mounted adjacent to the end of the nosepiece. These plates could be adjusted either vertically or horizontally depending on the desired test configuration. A pressure gauge and a Type K thermocouple were used to measure the stagnation pressure and temperature of the heated air before leaving the die section. Air Supply System: The air supply system comprises a compressor, an air-water separator, a pressure regulator, a measuring orifice to permit determination of the mass flow rate of the air, manual throttling valve and two air heaters. Upon leaving the air heaters, the air passed through two 2-inch insulated steel pipes to the upper and lower regions of the die section. Experimental Procedures: In contrast to the sheet extrusion process described above, the melt indices of Exxon PP3546G Polypropylene and Exxon PP3505G Polypropylene (1163 and 421, respectively) are suitable for the formation of melt-blown webs of the present invention. Conventional procedures for forming polypropylene melt-blown webs were performed as follows, using materials of the present invention as described herein. The steady-state run conditions that were needed for the given test were first established. This was done by turning on the air supply, using a manual throttling valve, to a "home" position of h = 2 inches of water on the orifice pressure gauge. Then air heaters and all five zone heaters of the extruder were set to a pre- specified temperature. Once all the heaters had reached the set temperatures, the screw motor was turned on and adjusted to obtain a desired polymer flow rate (throughput). Once the desired polymer throughput was obtained, the throttling valve was then adjusted to increase or decrease the amount of air flow to the die section so causing an increase or decrease in the desired air velocity at the die exit. Once the air velocity was set, and enough time was allowed for the system to reach steady state conditions at the new air velocity, a web sample was collected. The collection of samples from the multi-hole die was achieved using a variable speed cylindrical collector placed a certain distance from the die exit plane. This distance is called the die to collection distance or "DCD" and is typically 16 inches. By using a variable speed collector, the thickness of the web is controlled.

Each time a web sample was collected, the test parameters were recorded. Therefore, for each sample, the polymer and air temperatures measured by the Type K thermocouples, the air temperature in the research lab, the air pressure measured by the die test section pressure gauge, the pressure across the measuring orifice, the melt pressure, and the screw RPM were recorded onto a data collection sheet.

In a "static kill" experiment, where a bacterial suspension was applied to the surface of an exemplary web of the present invention, greater than 99% of applied bacteria were killed in 60 minutes at a light intensity of 6000 foot candles.

Example 1

This example describes how to make an embodiment of the SOG-blend for light-activated antimicrobial polymeric materials.

To a round quart bottle add 500g of 33% ammonium stearate (CAS# 1002-89-7 Original Bradford Soap Works, Inc.), 4.65g methylene blue (CAS# 7220-79-3 Spectrum Quality Products, Inc.), and about 12 ceramic stones. Place lid tightly on bottle. Place bottle on lab mechanical roller and roll bottle. After two hours remove bottle and pour contents onto a fluorocarbon- polymer-coated baking pan. Remove stones from the pan. Place pan in a 200 °F drying oven for seven hours. Remove and allow cooling to room temperature. Scrape dried mixture into a storage container and seal with a lid. Alternatively, the ammonium stearate and methylene blue are

10 mixed together (without the addition of ceramic stones) with an electric-motor-driven or air- driven lab mixer for two hours. The mixture is then dried as before.

Example 2 This example describes how to make plastic film using the SOG-blend from Example 1.

Grind by hand (or other suitable technique) in a mortar and pestle the dried ammonium stearate/methylene blue mixture from Example 1 (the SOG-blend) until the dried mixture ranges in size from a dust to pea size granules. Weigh out 495 grams of Dow low density polyethylene resin 6401 into a plastic bag. Weigh out 5 grams of the ground ammonium stearate/methylene blue into the plastic bag containing the LDPE resin. Mix the contents of the closed bag by squeezing and rotating the bag end-over-end. A sample of the mixture prepared as stated above was then extruded using a Brabender Plasti-corder into a clear, very light violet film substantially free of voids and imperfections except for cross-web caliper variation. The extrusion conditions were as follows: Extruder barrel Zone 1 - 300°F, Zone 2 - 330°F, Zone 3 - 340°F, slot die temperature Zone 4 - 345°F; the extruder screw was at 60 rpm and the torque was approximately

50 meter grams. Caliper: 3.1 to 5.9 mils. Width: 2.625 inches. Methylene Blue: 274 ppm.

Antimicrobial testing was conducted according to the following procedure on 1.5 by 1.5- inch square samples cut from the above extruded film. The results listed in Table 1 show the unique light-activated antimicrobial properties of the film with both gram positive and gram negative bacteria using the additive from Example 1.

Light Activated Antimicrobial Test Protocol Overview

All microbial strains were obtained from the AmericanType Culture Collection (ATCC). In general, a seed culture was grown up overnight, adjusted spectrophotometrically, diluted appropriately, and used to inoculate six swatches of each material to be tested. Two of the swatches were immediately run through the recovery procedures to serve as zero time controls. Two more swatches were kept in the dark while the last two were illuminated for the specified time, usually one hour, following which all four were run through the recovery procedure. After a suitable incubation (24-48 hours), bacterial colonies were counted, and log reduction and % kill calculated. Inoculum Preparation

The test organism was transferred into 10 ml of sterile tryptic soy broth or brain heart infusion broth in a 10 ml test tube and incubated at 37°C for 18 hours. This culture was then adjusted spectrophotometrically to a density of about 10⁸ colony forming units/ml. The 10⁸ culture was then diluted 1:100 to achieve 10⁶ CFU's/ml (10⁶ CFU's/O.lml). Each test swatch was inoculated with 100 μl of the 10⁵ suspension in phosphate buffered saline. The inoculum was also

1 1 serially diluted and plated. Swatches

Test swatches were cut aseptically into 1.5 inch squares with rounded edges and placed into sterile 60 mm Petri dishes. If the swatch is absorbent, the inoculum is applied directly to each swatch. If the swatch is not abosrbent but has a porous structure, the swatch is pre-wet with

0.1% Triton X-100 in deionized water and rinsed thoroughly in deionized water before the inoculum is applied to each swatch. If the swatch is a film, the inoculum is applied to the center of the film swatch; then an identical film swatch is placed on top of the inoculum to prevent evaporation of water during the one hour contact time. Procedure

Four swatches of each material were inoculated, half being placed under the light source and the other plate being wrapped in aluminum foil to keep them dark. The light source was a 500 watt photoflood lamp with reflector (photoflood lamp ECT, 3200K with 10 - 12" reflector) set 15 inches above a bench top (equivalent to 2000 foot candles unless another light level is specified; 6000 foot candles is equal to the light bulb surface 9.25 inches from samples) at room temperature. A 9" square Pyrex baking dish containing 1" to 1 Vz" water at 4°C (40°F) from a circulating temperature controller (or filled with an inch of ice water if specified) was placed between the light source and the samples to absorb heat and any ultraviolet irradiation. Samples were illuminated for a defined period of time, generally one hour unless noted otherwise. While the samples were being illuminated, the last two swatches were inoculated and immediately started through the recovery procedure in order to find the bacterial count at zero time. Recovery Procedure

Samples and Petri dish (in case the inoculum penetrated through the sample) were aseptically transferred into a sterilized jar containing 100 ml of Letheen Broth to stop any antimicrobial activity. The cap was sealed and the jar shaken vigorously. Serial tenfold dilutions were prepared from the recovery fluid, and each dilution was plated in duplicate with tempered tryptic soy agar in 100 mm plastic Petri plates. Appropriate dilutions of the recovery fluid were also plated directly (in duplicate) in a 100 mm Petri plate. Plates were incubated at 37°C for one to two days until countable.

Calculations

The zero time counts recovered from the swatches were compared with the inoculum count. Recovery was generally between 90 and 100%. All the zero time counts were combined by averaging their base 10 logarithms to obtain the average log zero time reading. The four counts for each test condition (duplicate platings for each of the pair of samples) were also combined by averaging the base 10 logarithms of the bacterial counts. A logarithmic scale of killing efficiency, log reduction, was calculated as the difference between the sample and average zero time

12 logarithms. Percent kill was calculated as ioo*(l-10^{0ogredu,:tion)}). Example 3

This example shows that the light-activated antimicrobial property is dependent on the quantity of the additive present in the polymer. Too much agent may be undesirable. Weighed out 480 grams of Dow low density polyethylene resin 6401 into a plastic bag.

Weighed out 20 grams of the ground ammonium stearate/methylene blue SOG-blend into the plastic bag containing the LDPE resin. Mixed the contents of the closed bag by squeezing and rotating the bag end-over-end. The mixture was then extruded under the same conditions as Example 2 into a hazy, violet film substantially free of voids and imperfections except for cross- web caliper variation. Caliper: 3.1 to 5.9 mils. Width: 2.438 inches. Methylene Blue: 1096 ppm.

Antimicrobial testing was conducted according to the previous procedure on 1.5 by 1.5-inch square samples cut from the extruded film. The result listed in Table 1 shows that at higher levels of the plastic additive there is no antimicrobial activity. When the methylene blue is too concentrated, self quenching of the sensitizer (methylene blue) occurs before the energy can be transferred to oxygen to generate singlet oxygen.

Example 4

This example describes an experiment seeking to make an alternative SOG-blend with stearic acid. Compare to Example 1. To a pint jar add 33.14g of pure stearic acid (CAS# 57-11-4 Spectrum Quality Products,

Inc.), 0.99g methylene blue (CAS# 7220-79-3 Spectrum Quality Products, Inc.), and about 10 ceramic stones. Place lid tightly on jar. Place bottle on lab mechanical roller and roll bottle. After two hours remove the jar from the rollers, scrape mixture into a storage container and seal with a lid.

Example 5

This example shows that the light-activated antimicrobial properties of the present invention are enabled by choosing the right surfactant to carry the singlet-oxygen generating agent into the plastic. Stearic acid was found not to be effective with methylene blue and the low density polyethylene resin tested.

Weighed out 495 grams of Dow low density polyethylene resin 6401 into a plastic bag. Weighed out 5 grams of the stearic acid/methylene blue mixture into the plastic bag containing the LDPE resin. Mixed the contents of the closed bag by squeezing and rotating the bag end-over- end. The mixture was then extruded under the same conditions as Example 2 into a clear, light violet film substantially free of voids and imperfections except for cross-web caliper variation.

Caliper: 3.9 to 6.3 mils. Width: 2.5 inches. Methylene Blue: 290 ppm. Antimicrobial testing was conducted according to the previous procedure on 1.5 by 1.5-inch square samples cut from the

13 above extruded film. The result listed in Table 1 shows that when stearic acid was used instead of ammonium stearate in the plastic additive, there was very little antimicrobial activity.

Example 6

Dow low density polyethylene resin 6401 (480 g) was weighed out into a plastic bag. Weighed out 20 grams of the stearic acid/methylene blue mixture into the plastic bag containing the LDPE resin. Mixed the contents of the closed bag by squeezing and rotating the bag end-over- end. The mixture was then extruded under the same conditions as Example 2 into a hazy, violet film substantially free of voids and imperfections except for cross-web caliper variation. Caliper: 3.1 to 8.3 mils. Width: 2.438 inches. Methylene Blue: 1160 ppm. Antimicrobial testing was conducted according to the previous procedure on 1.5 by 1.5-inch square samples cut from the above extruded film. The result listed in Table 1 shows that at higher levels of the stearic acid/methylene blue plastic additive there was no antimicrobial activity.

Example 7

This example compares pure polyethyene to the performance of the previous examples. Dow 6401, low density polyethylene was extruded under the same conditions as Example 2 into a clear, colorless film substantially free of voids and imperfections except for cross-web caliper variation. Caliper: 1.6 to 3.1 mils. Width: 2.813 inches. Methylene Blue: None. Antimicrobial testing was conducted according to the previous procedure on 1.5 by 1.5-inch square samples cut from the above extruded film. The result listed in Table 1 shows that pure polyethylene film does not have any antimicrobial activity whether in the dark or in the light.

Table 1

Amount

Example Methylene Light Level Time Organism Dark Light Leaching

Comments Blue ppm footcandles minutes % Kιll % Kιll % in Sampl e

K bnella Dow 640_/A__timonium

2 274 6000 60 None 99 95 3 6 pnnwumtae Stearate Methylene Blue

Enteroeoocus Dow 640ι/Ammonιum

2 274 6000 60 None 9995 3 6 faecalta Stearate Methylene Blue

S—ph loeoec a Dow 640ι/Ammomum

2 274 6000 60 None 99 77 3 6 αureus Stearate Methylene Blue

Dow 640ι/Ammomum

2 274 6000 60 Eadurtehtα coli None 99 2 3 6 Stearate/Methylene Blue

Klebatellα Dow 640ι/Ammoraum

3 1096 6000 60 None None 0 69 pneumontα Stearate Methylene Blue

KUbnella Dow 640ι/Steaπc

5 290 6000 60 None 4998 0 4 prummoniαe Aci Methylene Blue

14 K baietla Dow 640i/Stearic

6 1160 6000 60 pneumonia. None None None Acid/Methylene Blue

KlΛeieUa

7 - 6000 60 pneumoniae None None - Dow 640i Polymer Film

Enteroaoccus

7 - 6000 60 fάecali. None None - Dow 640i Polymer Film

Staphylococcus

7 - 6000 60 aureue None None - Dow 640i Polymer Film

Dow 640i Polymer

7 - 6000 60 Ee heriehi coll None None -

Film 1

Example 8

This example shows one way of obtaining a uniform mixture of the additive for light- activated antimicrobial polymeric materials with the polymer in pellet or powder form before processing through an extruder.

One of the problems overcome by the present invention was how to obtain a polymeric material (film or fiber) containing a uniform distribution of the light-activated antimicrobial agent. This can be accomplished as stated earlier by making a pelletized concentrate using the polymer of interest. The concentrate containing the light-activated antimicrobial agent at a much higher concentration than is desired in a finished material is then added to more polymer and extruded into a material containing the light-activated antimicrobial agent at the desired concentration. One way to avoid the two extrusion process is to obtain uniform mixing of the light-activated antimicrobial agent and the polymer before the final extrusion.

To a one gallon plastic bag, there were weighed out 1500 grams of Exxon polypropylene grade Escorene™ PP3546G (a fiber grade granular resin for melt blown fibers) and 13.68 grams of dried ammonium stearate/methylene blue SOG-blend mixture from Example 1. This mixture of polymer and SOG-blend was placed in a two gallon Styrofoam™ (Dow Chemical Co.) bucket. Enough liquid nitrogen at minus 320 °F was added to cover the material in the bucket and make an easily pourable slurry. After soaking for 15 to 20 minutes, the contents of the bucket were slowly poured into a lab size (200 to 400 pounds per hour) cryogenic grinder (hammer mill). During the grinding the temperature of the material exiting the grinder was monitored. It varied from minus 124°F in the beginning to minus 50°F near the end of the grinding. All of the material exited the grinder through a 60 mesh screen. The ground material was a finely ground powder uniform in texture and color.

Example 9

This example describes how to make melt blown polypropylene nonwoven material containing the light-activated antimicrobial agent/polymeric mixture from Example 8.

The objective of this example is to make a melt blown nonwoven material employing the

15 light-activated antimicrobial technology. With such a material, the high surface area to volume ratio of the fibers will expose more light-activated antimicrobial agent on the surface of the fiber to bacteria or viruses that might come in contact with the fiber surface than would be exposed on the surface of a comparable two-dimensional film. In order to obtain quick melting and uniform composition in the melt, powdered polymers with a high melt index were used. The Exxon polypropylene resin PP3546G has a melt index value of 1163 grams per ten minutes. The one inch wide melt blowing extruder was set up to run under the following conditions: extruder screw speed - 14J rpm, temperature settings - extruder Zone 1 - 300°F, Zone 2 -350°F, Zone 3 - 375°F, melt temperature - 392°F, Zone 4 - 400°F, polymer temperature in the die - 430°F, air blowing temperature at the die - 438°F, air pressure at the die - 1.1 psig for blowing the polymer into fibers. The temperature settings were adjusted to obtain polymer temperatures in the die of 400°F. Polymer flow rate was 0.733 grams per minute per hole (diameter - 0.079 inches). For a one inch wide die there were 30 holes. About 10 lineal yards (2" to 2 V." wide) of the melt blown nonwoven web were collected by winding up a roll of the web by hand off of the round collector screen located 16" from the melt blown extruder die. Nonwoven web caliper: 9 to 18 mils. Width:

2 to 2.5 inches. Methylene Blue: 264 ppm. Antimicrobial testing was conducted according to the previous procedure on 1.5 by 1.5-inch square samples cut from the nonwoven web. The results listed in Table 2 show the unique light-activated antimicrobial properties of the melt blown nonwoven using the plastic additive from Example 1.

Example 10

This example compares the melt blown nonwoven made from the pure polypropylene resin to the performance of the previous examples.

The Exxon polypropylene resin PP3546G was used to make a melt blown nonwoven material without any Light-Activated Antimicrobial. The conditions used to make the nonwoven were the same as in Example 9. No cryogenic grinding was necessary since the polypropylene resin was already in a powder form. Caliper: 12 to 21 mils. Width: 2 to2.5 inches. Methylene Blue: None. Antimicrobial testing was conducted according to the previous procedure on 1.5 by 1.5-inch square samples cut from the nonwoven web. The results listed in Table 2 show that the melt blown nonwoven using just polypropylene with any light-activated antimicrobial agent has no antimicrobial activity in the light or in the dark.

Table 2

Amount

Example Methylene Light Level Time Organism Dark Light Leaching

Comments Blue

PPm footcan les minutes % Kιll % KiIl % in Sample

16 Klebtiella Exxon

9 264 6000 60 16.7 >99.95 N.D pneumoniae PP3546G/Ammomum

KUbnella

10 - 6000 60 None 1.6 3546G pneumomae - Exxon PP

N.D. stands for "Non Detected"

LEACHING TEST

A two-and-one-half gram sample to be tested is placed in a bottle containing twenty-five grams of deionized water. With the lid placed tightly on the bottle, the bottle is shaken for fifteen minutes on a laboratory wrist shaker. The sample is removed from the bottle. The sample is gently squeezed. Any water from the sample is collected in the original sample bottle. About two milliliters of the extracted water is placed in a microcentrifuge tube and centrifuged for fifteen minutes to remove any fibers that might be in the extract. One milliliter of extract is carefully removed from the upper part of the centrifuge tube and placed in a microcuvette to determine the amount of the photosensitizer extracted from the sample based on the calibration curves for the photosensitizer of interest. CONCLUSION

Having described the invention in detail and by reference to the preferred embodiments thereof, it will be apparent to those of skill in the art that modifications and variation are possible without the departing from the spirit of the disclosed invention, as claimed in the appended claims.

17

Claims

CLAIMSWe claim:

1. An antimicrobial laminar structure of polymer having incorporated therein a singlet-oxygen generating amount of a photosensitizer that is excited by light absorption and which generates singlet-oxygen by energy transfer from the excited photosensitizer.

2. The antimicrobial laminar structure of claim 1, wherein said structure is an extruded film.

3. The antimicrobial laminar structure of claim 1, wherein said structure is a melt-blown web.

4. The antimicrobial laminar structure of claim 1, wherein said structure is a fabric.

5. The antimicrobial laminar structure of claim 1, wherein said photosensitizer is uniformly dispersed therethrough.

6. The antimicrobial laminar structure of claim 1, wherein said polymer is a polymer or copolymer of an olefin, a urethane, an ester, styrene, vinyl chloride, vinylidene chloride, an amide, or an acrylate.

7. The antimicrobial laminar structure of claim 1, wherein said photosensitizer is methylene blue; rose bengal; fluorescein; eosin yellowish; erythrosin B; phloxine B; thionin; azure A; azure B; azure C; riboflavin; toluidine blue O; hypericin; a phthalocyanine; or a singlet-oxygen generating derivative thereof.

8. The antimicrobial laminar structure of claim 1, wherein said photosensitizer is methylene blue.

9. The antimicrobial laminar structure of claim 1, wherein said photosensitizer is uniformly dispersed throughout said polymer.

10. The antimicrobial laminar structure of claim 9, wherein said photosensitizer is present in an amount of about 5 ppm to about 1000 ppm by weight of polymer.

11. The antimicrobial laminar structure of claim 9, wherein said structure is an extruded film, further comprising a roll around which said film is wrapped and a box from which said film is dispensed.

12. A method of making an antimicrobial laminar structure of polymer, comprising the steps of:

18 combining a singlet-oxygen generating substance, a surfactant material having soap-like properties, and a polymer resin to form a uniform concentrate; dispersing said concentrate in a batch of polymer to form a polymeric mixture; and forming said polymeric mixture into a formed shape selected from a film, a melt-blown nonwoven, a woven fabric and a formed article; the concentration of singlet-oxygen generating substance in said polymeric mixture being selected such that antimicrobial amounts of singlet-oxygen are generated when said formed shape is exposed to light.

13. The method of claim 12, wherein said combining is performed by cryogenic grinding to form a homogeneous fine powder.

14. The method of claim 12, wherein said combining is performed by a compounding extruder to form a concentrate as a continuous rod or string which is cut or chopped into pellets.

15. The method of claim 12, wherein said surfactant material is selected from the group consisting of ammonium salts of the following : undecylenic acid, stearic acid, dodecylbenzene sulfonic acid, polystyrene sulfonic acid, polyvinylsulfonic acid, poly(butadiene-maleic acid), 2,5- furandione polymer with methoxyethene, a graft polymer of polyethylene and maleic anhydride, copolymers of octadecene-1 and maleic anhydride, 3,3',4,4'- benzophenone tetracarboxylic anhydride, 1,2,4,5-benzenetetracarboxylic acid, olefin/maleic anhydride copolymers, copolymers of ethylene with isopropyl maleic anhydride, and carboxy functional linear olefin.

16. The method of claim 15, wherein said surfactant material is ammonium stearate.

17. The method of claim 12, wherein said singlet-oxygen generating substance is methylene blue; rose bengal; fluorescein; eosin yellowish; erythrosin B; phloxine B; thionin; azure A; azure B; azure C; riboflavin; toluidine blue O; hypericin; a phthalocyanine; or a singlet-oxygen generating derivative thereof.

18. The method of claim 17, wherein said singlet-oxygen generating substance is methylene blue.

19. The method of claim 12, wherein said singlet-oxygen generating substance is first mixed with said surfactant material to form an SOG-blend, and said SOG-blend is then combined with said polymer resin.

20. The method of claim 19, wherein said SOG-blend is combined with said polymer resin using a metering extruder.

19

21. The method of claim 19, wherein said SOG-blend is combined with said polymer resin by cryogenic grinding.

22. The method of claim 12, wherein said polymeric mixture is formed into a film by extrusion.

23. The method of claim 12, wherein said polymeric mixture is formed into a melt-blown nonwoven.

20