Moisture-activated chlorine dioxide-releasing powder and its manufacturing method

Abstract

A method for producing a moisture-activated powder that provides for the generation and release of chlorine dioxide without detectable amounts of any toxic by-products, such as chlorine gas, chlorite, or chlorate, is provided. The powder does not need to be exposed to light before or during its exposure to moisture or relative humidity to generate gas. The powder can also be prepared under conditions that minimize or prevent the decomposition or oxidation of sodium chlorite or premature moisture activation of the powder during the manufacturing process to maximize its activity.

Description

[Technical Field]

[0001] Moisture-activated powders and methods for their manufacture are provided for use in generating and releasing chlorine dioxide. More specifically, moisture-activated controlled-release powders are provided that are capable of generating and releasing chlorine dioxide without any detectable amounts of toxic by-products, and that are prepared by methods that provide powders and maximize the activity of the controlled-release powders for use in disinfection, sanitation, sterilization, and biological or pathogenic contamination control. [Background technology]

[0002] Ethylene oxide is currently used to sterilize medical devices and other products. Ethylene oxide has been recognized by the U.S. Food and Drug Administration (FDA) as having potential adverse environmental and public health impacts. The FDA is encouraging changes to ethylene oxide sterilization processes and equipment that reduce the amount of ethylene oxide on medical devices.

[0003] Detectable amounts of toxic by-products, including chlorine gas, chlorate and / or chlorite, have been observed when chlorine dioxide is produced from some conventional chlorine dioxide products. Summary of the Invention

[0004] One option for reducing the concentration of ethylene oxide on medical devices is to completely replace it with a different gas produced by a process that has less impact on the environment and public health.

[0005] In a first aspect of the present invention, a method for making a moisture-activated powder for providing a controlled release of chlorine dioxide is provided. The method includes mixing sodium chlorite, silicate, and water to form an aqueous suspension, and spray-drying the aqueous suspension at an inlet temperature ranging from about 482 to about 537°C (900-1000°F) and an outlet temperature of 143°C (290°F) or less to form silicate particles. An inorganic acid-releasing agent, an anhydrous material, and water are mixed to form a colloidal suspension. The silicate particles are mixed with the colloidal suspension to form a slurry. The slurry is spray-dried at an inlet temperature ranging from about 482 to about 537°C (900-1000°F) and an outlet temperature of 143°C (290°F) or less to form a powder. The powder is substantially free of water and, following hydrolysis of the acid-releasing agent and reaction of the hydronium ions with chlorite, is capable of producing and releasing a disinfecting-effective amount of chlorine dioxide without releasing detectable amounts of chlorine gas, chlorate, and / or chlorite.

[0006] Powders prepared by this method are capable of producing a controlled release of chlorine dioxide from the powder without exposing the powder to light before or during exposure of the powder to moisture or relative humidity.

[0007] The aqueous suspension may contain sodium chlorite of 85-99% purity.

[0008] In a second aspect of the present invention, there is provided a moisture-activated powder prepared by the method described in the first aspect of the present invention and the Examples. The powder, upon exposure to moisture or relative humidity, can cause the controlled release of chlorine dioxide from the powder in an amount effective for disinfection, sanitation, and sterilization without the release of detectable amounts of toxic by-products, such as chlorine gas and / or chlorite and chlorate.

[0009] Other objects and features will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION OF THE INVENTION

[0010] A method for producing a moisture-activated powder has been discovered that provides for the production and release of chlorine dioxide without detectable amounts of any toxic by-products, such as chlorine gas, chlorate, and / or chlorite. The method involves an inlet spray drying temperature much higher than the 180°C decomposition temperature of sodium chlorite. Upon exposure to moisture or relative humidity, the powder can produce and release gas after an acid-releasing agent in the powder hydrolyzes to provide hydronium ions that react with sodium chlorite.

[0011] The powder can be prepared under conditions that minimize or prevent decomposition or oxidation of the sodium chlorite or premature moisture or relative humidity activation of the powder during the manufacturing process to maximize its activity.

[0012] In a first aspect of the present invention, a method for making a moisture-activated powder for providing a controlled release of chlorine dioxide is provided. The method includes mixing sodium chlorite, silicate, and water to form an aqueous suspension, and spray-drying the aqueous suspension at an inlet temperature ranging from about 482 to about 537°C (900-1000°F) and an outlet temperature of 143°C (290°F) or less to form silicate particles. An inorganic acid-releasing agent, an anhydrous material, and water are mixed to form a colloidal suspension. The silicate particles are mixed with the colloidal suspension to form a slurry. The slurry is spray-dried at an inlet temperature ranging from about 482 to about 537°C (900-1000°F) and an outlet temperature of 143°C (290°F) or less to form a powder. The powder is substantially free of water and, following hydrolysis of the acid-releasing agent and reaction of the hydronium ions with chlorite, is capable of producing and releasing a disinfecting-effective amount of chlorine dioxide without releasing detectable amounts of chlorine gas, chlorate, and / or chlorite.

[0013] The powder can have a core comprising silicate particles and a shell comprising an inorganic acid releasing agent and an anhydrous material.

[0014] The formation of chlorate and chlorite anions reduces the amount of chlorine dioxide that can be produced by powders containing silicate particles, because these anions do not efficiently produce chlorine dioxide in the presence of acid or hydronium ions. The silicate particles can be processed for a period of time at temperatures up to 537°C (1000°F) without significantly reducing the amount of gas that can be produced from powders containing the particles. While not being bound by a particular theory of the present invention, it is believed that the anions that can react with hydronium ions to form gas are dispersed within the amorphous silicate matrix, encapsulating the anions. Disproportionation of chlorite is avoided because intermolecular interactions between chlorite anions are minimized in the amorphous silicate matrix.

[0015] Preferably, each silicate particle contains about 85% to about 99% by weight of silicate and about 1% to about 15% by weight of chlorite, and more preferably, each silicate particle contains about 95% to about 99% by weight of silicate and about 1% to about 5% by weight of chlorite.

[0016] The silicate particles are substantially free of water to minimize the diffusion of chlorite into solution when the particles are further processed, such as when the particles are added to an aqueous slurry containing an acid-releasing agent to form a powder. For purposes of the present invention, silicate particles are substantially free of water if the amount of water in the silicate particles does not provide a pathway for the permeation of anions from the particles to the solvent. Preferably, each silicate particle contains up to about 10% by weight, preferably up to about 5% by weight, of water without providing such a pathway for diffusion from the particle to the solvent.

[0017] The aqueous suspension may contain commercially available sodium chlorite of 85-99% purity.

[0018] Upon exposure to ambient moisture, relative humidity, or otherwise contact with water, the powder can cause a controlled release of chlorine dioxide from the powder. Moisture or water diffuses into the powder and reacts with the inorganic acid-releasing agent to form an acid. The acid dissolves in water, forming hydronium ions and counterions. The hydronium ions diffuse into the silicate particles, where they react with chlorite anions to form chlorine dioxide.

[0019] The gas diffuses from the powder into the surrounding atmosphere over a period of up to about six months, affecting materials located near the powder. -6 grams of gas / cm 3 for a period of at least 1 hour, 1 day, 1 week, 1 month, or 6 months can be prepared by the process of the present invention for a variety of end uses.

[0020] Powders prepared by this method are capable of producing a controlled release of chlorine dioxide from the powder, whether or not the powder is exposed to light before or during exposure of the powder to moisture or relative humidity.

[0021] The relative humidity during the steps of the method of the present invention is preferably maintained at about 60% or less, more preferably at about 30% or less.

[0022] The silicate of the aqueous suspension used in preparing the silicate particles can include, but is not limited to, sodium silicate, sodium metasilicate, sodium sesquisilicate, sodium orthosilicate, borosilicate, aluminosilicate, or any combination thereof. Commercially available forms of such silicates suitable for use generally contain sodium and potassium cations.

[0023] The ratio of silicon measured as SiO to alkali metal cations measured as MO in the silicate particles, where M is selected from the group consisting of sodium and potassium, is from about 2.5 to about 3.5, preferably from about 3.0 to about 3.5, and most preferably about 3.2.

[0024] The silicate particles can be either solid or hollow and substantially spherical.

[0025] Inorganic acid-releasing agents such as polyphosphates form odorless powders with higher gas-releasing efficiency compared to powders containing organic acid-releasing agents. Suitable inorganic acid-releasing agents include tetraalkylammonium polyphosphate, monobasic potassium phosphate (KH2PO4), potassium polymetaphosphate (KPO3) x , where x is in the range of 3 to 50), sodium metaphosphate, borophosphate, aluminophosphate, silicophosphate, sodium polyphosphate such as sodium tripolyphosphate, potassium tripolyphosphate (KPO 10 ), sodium-potassium phosphate (NaKHPO4·7H2O), and salts containing hydrolyzable metal cations such as zinc. A preferred sodium metaphosphate is represented by the formula (NaPO3) n where n is 3 to 10 for the cyclic molecule and n is 3 to 50 for the polyphosphate chain.

[0026] The anhydrous material used in the method can bind water. The material acts as a moisture scavenger to minimize premature hydrolysis of the acid-releasing agent. Suitable anhydrous materials include sodium sulfate, calcium sulfate, calcium carbonate, magnesium sulfate, calcium chloride, moisture-depleted silica gel, alumina, zeolite, clays such as bentonite or kaolin, potassium permanganate, molecular sieves, oxygen-scavenging materials, or mixtures thereof. Anhydrous materials are commercially available from a number of sources.

[0027] In preparing the aqueous suspension in the method of the present invention, the dispersion can be mixed with silicate, sodium chlorite, and water. The dispersion can reduce agglomeration within the suspension.

[0028] In preparing the colloidal suspension or slurry in the method of the present invention, the dispersion can be mixed with an inorganic acid-releasing agent, an anhydrous material, and water, or with the colloidal suspension and silicate particles. The dispersion can reduce agglomeration within the colloidal suspension or slurry.

[0029] The dispersant can be any substance that minimizes agglomeration of silicate particles during powder preparation, controls gas release from the powder, reduces the surface reactivity of the silicate particles, controls moisture penetration through the silicate particles, and does not react with the silicate particles. Substances having hydrophilic and hydrophobic portions are preferred. The hydrophilic portion of the substance can be absorbed by the surface of the silicate particles. The hydrophobic portion of the substance minimizes agglomeration of the silicate particles when the particles are mixed. Suitable dispersants include, but are not limited to, carboxylate amides such as isostearic acid amide, polyvinyl acetate, polyvinyl alcohol, polyvinylpyrrolidone copolymers, polyglycols, polyols, polyalkylene glycols (e.g., polyethylene glycol, polypropylene glycol, polybutylene glycol), alkoxypolyalkylene glycols such as methoxypolyethylene glycol, trifunctional polyethylene glycol, alkylene oxide polymers such as poly(ethylene-propylene) glycol, metal, oligomeric or copolymeric olefin carboxylic acids and / or fatty acids, polyethers, and metal carboxylates such as zinc isostearate, as well as their derivatives (e.g., carboxylic acids such as fatty acids), blends, and copolymers, or any combination thereof. Some acid-releasing agents, such as sodium polyphosphate, also function as dispersants. Suitable polyvinylpyrrolidone copolymers include copolymers of polyvinylpyrrolidone and hexadecane, such as Ganex V-216, and copolymers of polyvinylpyrrolidone and eicosene, such as Ganex V-220, both of which are commercially available from GAF Corp.

[0030] The dispersion may contain a nonionic surfactant. Examples of nonionic surfactants include, but are not limited to, secondary alcohol ethoxylates, alkylphenol ethoxylates, alkyl ethoxylates, alkylaryl ethoxylates, polyethylene oxide-polypropylene oxide block copolymers, polyethylene glycol ethers of linear alcohols, reaction products of fatty acids with ethylene oxide and / or propylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, copolymers of polyvinyl alcohol and polyvinylpyrrolidone, copolymers of (meth)acrylic acid and (meth)acrylic acid esters, or combinations thereof.

[0031] It is also preferable to maintain the aqueous suspension at a basic pH of about 9 to about 14, preferably about 11 to about 13. The pH can be maintained by adjusting the concentration of the base added when forming the aqueous suspension.

[0032] It is also preferred to maintain the colloidal suspension at a pH of about 5 to about 7.

[0033] The silicate particles optionally contain a base or filler. The base controls the release of chlorine dioxide gas from the particles by reacting with hydronium ions that diffuse into the particles from the acid-releasing agent or interdiffuse into anion-rich regions of the particles to form salts. When the base is depleted, excess hydronium ions react with chlorite anions within the particles to form gas. The filler controls the release of chlorine dioxide gas by creating a barrier to the diffusion of hydronium ions. The amount of base or filler in the core can be adjusted to change the period before gas is released from the particles. For example, if a longer delay in gas release is desired, the concentration of base or filler can be increased. The base or filler can stabilize chlorite during preparation of the silicate particles or powders containing the particles. The amount of base in the particles can be adjusted to change the period of gas release and increase thermal stability. Up to about 50 wt. % of the base can be included based on the total weight of the particle.

[0034] Any base or any filler that reacts with hydronium ions can be incorporated into silicate particles or powder.Suitable bases or fillers include alkali metal bicarbonates such as lithium bicarbonate, sodium bicarbonate, or potassium bicarbonate, alkali metal carbonates such as lithium carbonate, sodium carbonate, or potassium carbonate, alkaline earth metal bicarbonates, alkaline earth metal carbonates such as magnesium carbonate or calcium carbonate, transition metal ions, protonated primary, secondary, or tertiary amines, or bicarbonates of quaternary amines such as ammonium bicarbonate, transition metal ions, protonated primary, secondary, or tertiary amines, or carbonates of quaternary amines, alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, or potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide or magnesium hydroxide, transition metal ions, protonated primary, secondary, or tertiary amines, or hydroxide salts of quaternary amines such as ammonium hydroxide, dibasic or tribasic phosphates, etc. alkali metal phosphates such as sodium sulfate or potassium sulfate, alkaline earth metal phosphates such as calcium sulfate or magnesium sulfate, phosphates of transition metal ions, protonated primary, secondary, or tertiary amines, or quaternary amines, alkali metal sulfates such as sodium sulfate or potassium sulfate, alkaline earth metal sulfates such as calcium sulfate or magnesium sulfate, sulfates of transition metal ions, protonated primary, secondary, or tertiary amines, or quaternary amines, such as ammonium sulfate, alkali metal sulfonates such as sodium sulfonate, alkaline earth metal sulfonates, or sulfonates of transition metal ions, protonated primary, secondary, or tertiary amines, or quaternary amines, alkali metal borates such as borax, alkaline earth metal borates such as magnesium orthoborate, or borates of transition metal ions, protonated primary, secondary, or tertiary amines, or quaternary amines.

[0035] Preferred bases include, but are not limited to, alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, or potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide or magnesium hydroxide, transition metal ions, protonated primary, secondary, or tertiary amines, or hydroxide salts of quaternary amines such as ammonium hydroxide. Sodium hydroxide is preferred.

[0036] In the process of the present invention, the aqueous suspension can be an azeotrope. When the aqueous suspension is an azeotrope, the spray dryer inlet temperature can be as high as 537°C (1000°F) and still avoid sodium chlorite decomposition. Azeotropes can include mixtures of solvents, including, but not limited to, acetone, acetonitrile, acrylonitrile, alcohols (e.g., ethanol, methanol, isopropanol, tert-butanol), alkenols, alkanes (e.g., hexane, 2-methylpentane), alkenals, haloalkanes (e.g., dichloromethane, trichlorotrifluoroethane), nitroalkanes (e.g., nitromethane), aniline, cycloalkanes (e.g., cyclopentane, cyclohexane), benzene, alkylbenzenes, halobenzenes, carbon disulfide, carbon tetrachloride, chloroform, epichlorohydrin, alkylamines, dialkylamines, alkyl halides (e.g., methyl iodide, ethyl iodide), alkyl ethers (e.g., isopropyl ether), alkyl acetates (e.g., methyl acetate), haloalkenes, alkenyl chlorides, trifluoroacetic acid, toluene, xylene, or any combination thereof.

[0037] For example, the aqueous suspension may comprise an azeotrope comprising acetone and one or more solvents including ethanol, methanol, isopropanol, tert-butanol, hexane, 2-methylpentane, dichloromethane, trichlorotrifluoroethane, nitromethane, cyclopentane, cyclohexane, carbon disulfide, carbon tetrachloride, chloroform, methyl iodide, ethyl iodide, isopropyl ether, methyl acetate, or trifluoroacetic acid.

[0038] The silicate particles are preferably formed from an aqueous suspension containing sodium silicate and sodium chlorite. The anhydrous material is preferably magnesium sulfate. The inorganic acid-releasing agent is preferably a polyphosphate such as sodium hexametaphosphate.

[0039] The sodium silicate and other ingredients used in the method of the present invention can be manufactured by conventional processes and packaged in dry, sealed containers, or can be purchased from a variety of sources. The ingredients are stored in a dry atmosphere before being used in the powder preparation process.

[0040] An inert atmosphere, such as a nitrogen blanket, can be used during the process. The inert atmosphere can be present during the entire process, or during the mixing step, the spray-drying step, when collecting the spray-dried product, and / or when storing the spray-dried product.

[0041] Aqueous suspension can be prepared by mixing its components in any order of addition.For example, sodium chlorite can be mixed with water and silicate to form an aqueous suspension, and optionally a solvent can be added to the suspension to form an azeotrope.Alternatively, silicate and sodium chlorite can be mixed before being mixed with water to form an aqueous suspension.When preparing suspension, ultrasonic mixing, high shear mixing, or any conventional homogenization method can be used.

[0042] Once the aqueous suspension is formed, it can be spray-dried to form silicate particles by any method known in the art, including any known atomization method, such as a nozzle or rotating disk. Typically, the inlet and outlet temperatures are maintained in the ranges of about 482 to about 537°C (900 to 1000°F) and about 121 to about 143°C (250 to 290°F), respectively. The spray-drying process is generally rapid (e.g., within up to about 60 seconds). If desired, the silicate particles may then be further dried by any conventional method. The silicate particles are stored in a dry atmosphere.

[0043] Without limitation, spray drying of the aqueous suspension is believed to form solid or hollow spheres composed of a solid solution, such as a substantially amorphous silicate matrix, in which the anions are uniformly dispersed and encapsulated. Such uniform dispersion and encapsulation enhances the thermal stability of the silicate particles and powders containing silicate particles. Powders containing silicate particles are believed to release significantly more gas than powders containing crystalline cores. Gas release efficiencies of 75-100% are typical for powders of the present invention.

[0044] The encapsulation of the powder in the amorphous silicate shell can be determined by energy dispersive spectroscopy.

[0045] The wall thickness of the hollow particles can be altered by changing process conditions such as the feed rate, residence time, air flow rate, air temperature, flow direction in the dryer, or the type of nozzle or atomizer used in the spray drying process, or by changing the composition of the feed material, such as particle size, solids concentration, viscosity, surface tension, or temperature of the feed solution.

[0046] The crystallinity of the silicate particles is altered by varying the silicate used in preparing the particles.

[0047] When preparing a colloidal suspension, the components can be mixed in any order of addition. Ultrasonic mixing, high shear mixing, or any conventional homogenization method can be used.

[0048] Once the colloidal suspension containing the inorganic acid-releasing agent, anhydrous material, and water is formed, it can be spray-dried to form a powder by any method known in the art, including any known atomization method, such as a nozzle or rotating disk. Typically, the inlet and outlet temperatures are maintained in the ranges of about 482 to about 537°C (900 to 1000°F) and about 121 to about 143°C (250 to 290°F), respectively. The spray-drying process is generally rapid (e.g., within up to about 60 seconds). If desired, the powder may then be further dried by any conventional method. The powder is stored in a dry atmosphere.

[0049] After spray drying to form a powder, the powder can be mixed with a desiccant to further protect the powder from moisture activation. The desiccant can include, but is not limited to, silica, silicates such as sodium silicate, sodium metasilicate, sodium sesquisilicate, sodium orthosilicate, borosilicate, aluminosilicate, zeolites, sodium sulfide, or combinations thereof.

[0050] The powder can then be packaged in a container that is impermeable to moisture or relative humidity.

[0051] The powder produced by the method of the present invention can comprise about 30% to about 80% by weight of anhydrous material, about 10% to about 50% by weight of an inorganic acid-releasing agent, about 5% to about 40% by weight of silicate, and about 0.01% to about 50% by weight of sodium chlorite, or about 35% to about 70% by weight of anhydrous material, about 15% to about 45% by weight of an inorganic acid-releasing agent, about 10% to about 35% by weight of silicate, and about 1% to about 30% by weight of sodium chlorite, or about 40% to about 60% by weight of anhydrous material, about 20% to about 40% by weight of an inorganic acid-releasing agent, about 15% to about 30% by weight of silicate, and about 0.5% to about 5% by weight of sodium chlorite.

[0052] Chlorine dioxide release rates that are effective for disinfection can range, for example, from about 0.08 ppm / min to about 50 ppm / min over a period of about 2 to about 72 hours. The release rate can be increased by increasing the amount of chlorite in the powder, achieving, for example, release rates of 100 ppm / min, 200 ppm / min, or greater, over a period of about 2 to about 72 hours or longer.

[0053] Powders formed by spray-drying a slurry containing silicate particles and a colloidal suspension are substantially water-free to minimize chlorite diffusion before chlorine dioxide release from the powder begins when the particles are stored prior to use. For purposes of the present invention, a powder is substantially water-free if the amount of water in the powder does not provide a pathway for premature release of chlorine dioxide from the powder. Preferably, each powder particle contains up to 0.3 wt.%, preferably up to 0.2 wt.%, up to 0.1 wt.%, up to 0.05 wt.%, or up to 0.03 wt.%, or 0.001-0.3 wt.%, 0.001-0.2 wt.%, 0.001-0.1 wt.%, 0.001-0.05 wt.%, or 0.001-0.03 wt.%, without providing such a pathway for premature release. The moisture content can be determined by differential scanning calorimetry.

[0054] Without wishing to be bound by any particular theory, it is believed that the water in the powder is free water (ie, water that is not bound to any component of the powder).

[0055] In a second aspect of the present invention, there is provided a moisture-activated powder prepared by the method described in the first aspect of the present invention and the Examples. The powder, upon exposure to moisture or relative humidity, can cause a controlled release of chlorine dioxide from the powder in a disinfecting-effective amount without releasing detectable amounts of chlorine gas and / or chlorite or chlorate.

[0056] The applications of powders are numerous. They can be used in almost any environment where exposure to moisture or relative humidity can occur. Powders can be formed into solids by molding or sintering. Powders can also be impregnated, melt processed, sintered, blended with other powders, or otherwise incorporated into various materials to provide films, fibers, coatings, tablets, resins, polymers, plastics, tubing, membranes, industrial materials, paints, coatings, and adhesives for a wide range of end uses. Powders are particularly useful for preparing any injection-molded, compression-molded, thermo-formed, or extrusion-molded product, such as cast or blown film. The thermal stability of powders allows for their use in injection molding processes.

[0057] The powders of the present invention are preferably incorporated into injection-molded, compression-molded, thermoformed, or extruded plastic products by compounding and pelletizing the powders via conventional means and mixing the pellets with materials prior to conventional forming or molding processes. Suitable materials for forming these products include any polymer, e.g., multicomponent polymers such as copolymers, terpolymers, or oligomers, and polymer alloys or blends thereof, or any wax. Representative polymers include polyolefins such as polyethylene and polypropylene, polyethylene terephthalate, polyvinyl chloride, polyurethane, metallocene polymers, polyesters, polyacrylates, acrylics, polystyrene, polycarbonates, polyamides, polyesteramides, ethylene-vinyl acetate copolymers, ethylene-methacrylate copolymers, and polyacetals. Suitable waxes include microcrystalline wax, paraffin wax, and synthetic waxes such as chlorinated waxes, polyethylene waxes, polyethylene glycols, and polypropylene glycols. Preferably, the polymer is biodegradable.

[0058] The formed or molded product preferably contains about 0.1 to about 70% by weight of the powder of the present invention and about 30 to about 99.9% by weight of the material, more preferably about 1 to about 50% by weight of the powder of the present invention and about 50 to about 99% by weight of the material, and most preferably about 2 to about 50% by weight of the powder of the present invention and about 50 to about 98% by weight of the material.

[0059] Formed or shaped products can be made by any conventional polymer processing method. For example, the powder or powder pellets of the present invention and material can be mixed together in a mixer, such as a Henschel mixer, and fed to an extruder or molding device operated at a temperature not exceeding about 200°C to form a melt. The melt can be cast extruded as a film, formed into pellets using dry air cooling on a vibrating conveyor, or formed into the desired shape by conventional injection molding, thermoforming, or compression molding methods.

[0060] The melt can be applied to a surface as a film by using well-known hot melt, dip coating, spray coating, curtain coating, dry wax, wet wax, and lamination processes. When the powder is in small particle form (e.g., 5-20 microns in diameter), a transparent film can be formed.

[0061] Conventional film-forming additives can be added to the material as needed, including crosslinkers, UV stabilizers, flame retardants, emulsifiers, compatibilizers, lubricants, antioxidants, colorants, and dyes.

[0062] A multilayer composite can be formed to generate gas within an enclosure formed from the composite. Such a composite includes a gas-generating layer and a barrier layer. The gas-generating layer includes a powder. The barrier layer is adjacent to a surface of the gas-generating layer. The barrier layer is permeable to moisture so as to transmit moisture to the gas-generating layer. However, the barrier layer is impermeable or only semi-permeable to the gas generated and released by the gas-generating layer. The gas-generating layer can generate and release chlorine dioxide after activation when exposed to moisture or relative humidity.

[0063] The gas-releasing powders, films, or other compositions of the present invention can be used to slow, kill, prevent, or control microbiological contamination or biochemical degradation on the surface of, within, or in the atmosphere surrounding a material by placing the material adjacent to the composition of the present invention and exposing the composition to moisture or relative humidity, thereby releasing chlorine dioxide from the composition into the atmosphere surrounding the material. Microbiological contaminants can include bacteria, viruses, mold, and fungi.

[0064] The compositions can also be used to retard, prevent or control biological contamination of the atmosphere by exposing the composition to moisture or relative humidity to generate chlorine dioxide from the composition and release it into the atmosphere surrounding the composition.

[0065] As used herein, the slowing, prevention, or control of biological contamination is also referred to as “sanitization,” “disinfection,” or “sterilization.” Biological contamination can include bacteria, viruses, such as coronaviruses (e.g., SARS-COV-2 and its variants, e.g., Delta or Omicron variants), molds, and fungi.

[0066] The compositions can also be used to delay, prevent, or control biological contamination of a material by placing the material adjacent to the composition and exposing the composition to moisture or relative humidity to generate chlorine dioxide from the composition and release it into the atmosphere surrounding the material. For example, chlorine dioxide is used after biological warfare to inactivate biological contaminants (e.g., anthrax) or for other military decontamination.

[0067] As an example, the powder or any composition containing the powder, such as a film, can be placed in a sealable bag or other container used in sterilizing medical devices, or in a "red bag" used in decontaminating or disinfecting medical waste or personal protective equipment such as masks, gowns, and pants. Alternatively, the bag or container can be made from a film containing the powder of the present invention. The chlorine dioxide released by the powder or composition is effective against SARS-COV-2 and its variants, such as the Delta or Omicron variants.

[0068] The composition can also be used to deodorize the surface of a material or the atmosphere surrounding a material, or to enhance the freshness of a material, by placing the material adjacent to the composition and exposing the composition to moisture or relative humidity, causing the composition to generate chlorine dioxide, which is released into the atmosphere surrounding the material.

[0069] The compositions can also be used to delay, prevent, inhibit, or control the chemotactic attraction of organisms to a material by placing the material adjacent to the composition and exposing the composition to moisture or relative humidity, causing the composition to generate chlorine dioxide and release it into the atmosphere surrounding the material.

[0070] In the above methods, the surface of the material or the entire material can be impregnated with the powder of the present invention or coated with the composition, the composition can be mixed with the material, the composition can be enclosed in a gas-permeable container, or the material and composition can be enclosed in a container. If the composition is enclosed in a container, the container can be hermetically sealed or partially sealed to allow some gas to escape from the container.

[0071] Chlorine dioxide-releasing powders can be impregnated into, for example, containers used to store food, soap, laundry detergent, documents, clothing, paint, seeds, medical instruments, devices and supplies such as catheters and sutures, personal care products, medical or biological waste, athletic shoes, ostomy bags, footwear, and garbage. Such powders can also be impregnated into covers for medical, hospital, household, or commercial equipment, or covers used in storage. Powder packets, sachets, "tea bags," or other gas-permeable containers can be included in storage containers to provide a chlorine dioxide microatmosphere upon activation. Chlorine dioxide-releasing powders can also be impregnated into paper or polymeric materials (e.g., shower mats, shoe inserts or insoles, bandage material, meat cutting boards, food packaging, food packaging trays, seed packets, or air filters); incorporated into wax or polymer coatings applied to paperboard containers or other surfaces; incorporated into films such as packaging films or covers for storage or medical, hospital, household, or commercial equipment; formed into porous parts to sterilize water; mixed with materials to create a chlorine dioxide microatmosphere around the material (e.g., soil) or mixed with other powders to kill microorganisms, enhance freshness, or deodorize (e.g., powders for treating soft surfaces such as foot powder, bath powder, carpet powder, desiccant for moisture removal).

[0072] The powder can also be used to neutralize malodors, delay, prevent, inhibit or control chemotaxis (i.e., the attraction of living tissue to chemicals), or reduce or eliminate bacteria in animal feed, potentially reducing the bacterial load in the intestines of animals consuming the feed.

[0073] The compositions of the present invention effectively release gas at temperatures commonly encountered in the above uses, including refrigeration temperatures. Chlorine dioxide-releasing compositions can be used, for example, in packaging medical supplies, food, or other materials that require refrigeration to sterilize or deodorize the materials. Multilayer films containing barrier layers can also be used to form packaging such as those used for medical supplies or food. The barrier layer retains the generated gas within the package to, for example, extend shelf life, prevent mold growth in food, or enhance sterilization of medical supplies.

[0074] Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention as defined in the appended claims. [Example]

[0075] The following non-limiting examples are provided to illustrate the present invention.

[0076] Example 1 The moisture-activated powder was manufactured by a two-stage spray drying process to create multi-layered particles with a size distribution of D10 0.79 microns, D50 13.24 microns, D90 30.99 microns.

[0077] Preparation of Core Powder: A liquid slurry was prepared in a blending tank and spray dried to form the core powder. The blending tank had an agitator that was running during the addition of all ingredients.

[0078] First, a blending tank was filled with deionized water in an amount that provided a 27.3% liquid slurry before spray drying. Sodium chlorite powder (2.7% by weight) was added to the water, followed by sodium silicate (70% by weight) to form a pale yellow, transparent slurry. The amounts listed are based on the total weight of the liquid slurry before spray drying. The slurry was then transferred to a feed tank, again equipped with an agitator, that led to the spray dryer.

[0079] Approximately 22.8 kg (50 lbs) of liquid slurry containing dissolved sodium chlorite and suspended sodium silicate was pumped into a spray dryer using a positive displacement pump. The absolute viscosity of the slurry, containing 35.2% solids, was 1.4 centipoise at 29°C (85°F) and the pH was 12.8. The spray dryer inlet temperature ranged from 510°C (950°F) to 527°C (980°F) over the course of the run. The outlet temperature ranged from 121°C (250°F) to 124°C (255°F). A powder was produced by spray drying the slurry.

[0080] The resulting fine, white, hygroscopic powder was sieved through a 50 micron mesh into a poly-barrel lined with two opaque plastic bags. To facilitate cooling, a perforated hose connected to a nitrogen gas cylinder was inserted into the barrel. Once the temperature had dropped to 32°C (90°F), the bag and drum were sealed.

[0081] Preparation of Finished Core-Shell Powder. A liquid slurry was prepared in a blending tank containing deionized water maintained at a temperature of 45°F (7.2°C). Sodium polyphosphate was added to the cold water and stirred until dissolved. Magnesium sulfate was then added, resulting in a colloidal suspension that periodically accumulated on the sidewalls of the blending tank and was periodically removed from the sidewalls and redeposited into a mixture having a pH of 6.

[0082] The core powder was then added and mixed with the colloidal suspension in the blend tank. This final slurry had a pH of 7 and contained the following components by weight: 77.3% distilled water, 6.4% sodium polyphosphate, 11% magnesium sulfate, and 5.2% core powder. The final slurry was then transferred to a pump-off feed tank for pumping to the spray dryer. The absolute viscosity of the slurry, containing 24.1% solids, was 58.72 centipoise and the pH was 7.0. The inlet temperature of the spray dryer ranged from 510°C (950°F) to 527°C (980°F) over the course of the run. The outlet temperature ranged from 121°C (250°F) to 124°C (255°F). Powder was produced by spray drying the slurry.

[0083] The resulting fine white powder, with an average moisture content of 4.6%, was sieved through a 50 micron mesh into a poly barrel lined with two opaque plastic bags. To facilitate cooling, a perforated hose connected to a nitrogen gas cylinder was inserted into the barrel. Once the temperature had dropped to 32°C (90°F), the bag and drum (subject to a nitrogen inert atmosphere) containing the final powder were sealed.

[0084] Four samples of the finished powder were collected throughout the experiment and tested for chlorine dioxide production when exposed to a moist sponge. Chlorine dioxide production of over 250 ppm was consistently observed after 60 seconds of exposure of 5 grams of powder to moisture. Prolonged exposure to moisture produced levels of chlorine dioxide greater than 1,000 ppm from 5 grams of powder. All four samples produced the same results: over 250 ppm of chlorine dioxide after 60 seconds of exposure of 5 grams of powder to moisture, and greater than 1,000 ppm of chlorine dioxide within 20 minutes of exposure.

[0085] Example 2 Pellet Formation: The spray-dried powder of Example 1 is compounded into pellets using a range of polymers, such as 2-20 melt index linear low-density polyethylene (LLDPE) resins, at a concentration of 20% powder and 80% resin. The pellets are packaged under nitrogen and stored in a dry atmosphere.

[0086] Film formation: The pellets are blown into a film using a range of resins such as 2-20 melt index LLDPE resin (50% letdown). The resulting film contains approximately 10% powder by weight. The film is stored in a dry atmosphere.

[0087] Moisture activation of film: A film sample is placed in a jar (containing a desiccant to create 0% relative humidity) with a 0-10 ppm chlorine dioxide electrochemical detector attached to the lid. During this time, no chlorine dioxide is produced. Introduction of moisture, relative humidity, or water will cause chlorine dioxide production.

[0088] Example 3 The moisture content of the powder product of Example 1 was believed to be an inaccurate measurement. Therefore, the moisture content of the powder produced in Example 1 was retested. The powder was stored in a polybag inside an aluminum flexible foil bag and sealed for over a year.

[0089] Three samples were taken from the bag and analyzed for moisture content by placing the samples in a 215°F (101.67°C) oven. After weighing, the samples were placed in the oven for 1 hour and then reweighed. The samples were then placed in the oven for an additional 2 hours and reweighed at the end of that period. The post-oven weight was subtracted from the original weight. The difference was then divided by the original weight to calculate the moisture content. The results were as follows ("na" means not applicable due to some powder being lost during the test):

[0090] [Table 1]

[0091] The data obtained showed high reproducibility. The average moisture content of the powder of Example 1 at both drying times was 0.027% by weight. The data also showed that the drying times were of sufficient duration. From these results, the average moisture content of the powder of Example 1 was 0.027% by weight both when the powder was made and after at least one year of storage.

[0092] definition The term "suitable substituent" as used herein is intended to mean a chemically acceptable functional group, preferably a moiety that does not negate the activity of the compound of the present invention.Such suitable substituents include, but are not limited to, halo group, perfluoroalkyl group, perfluoroalkoxy group, alkyl group, alkenyl group, alkynyl group, hydroxy group, oxo group, mercapto group, alkylthio group, alkoxy group, aryl or heteroaryl group, aryloxy or heteroaryloxy group, aralkyl or heteroaralkyl group, aralkoxy or heteroaralkoxy group, HO-(C=O)- group, heterocyclic group, cycloalkyl group, amino group, alkylamino group and dialkylamino group, carbamoyl group, alkylcarbonyl group, alkoxycarbonyl group, alkylaminocarbonyl group, dialkylaminocarbonyl group, arylcarbonyl group, aryloxycarbonyl group, alkylsulfonyl group and arylsulfonyl group.Those skilled in the art will understand that many substituents can be substituted with additional substituents.

[0093] The term "alkyl," as used herein, refers to a straight-chain, branched-chain, or cyclic hydrocarbon radical preferably having 1 to 32 carbon atoms (i.e., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 39, 30, 31, or 32 carbons), and more preferably having 1 to 18 carbon atoms. Alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, and tert-butyl. An alkyl group can be unsubstituted or substituted with one or more suitable substituents.

[0094] The term "alkenyl," as used herein, refers to a straight-chain, branched-chain, or cyclic hydrocarbon radical, preferably having 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 39, 30, 31, or 32 carbons, more preferably having 1 to 18 carbon atoms, and having one or more carbon-carbon double bonds. Alkenyl groups include, but are not limited to, ethenyl, 1-propenyl, 2-propenyl (allyl), iso-propenyl, 2-methyl-1-propenyl, 1-butenyl, and 2-butenyl. Alkenyl groups can be unsubstituted or substituted with one or more suitable substituents, as defined above.

[0095] The term "alkynyl," as used herein, refers to a straight-chain, branched-chain, or cyclic hydrocarbon radical, preferably having 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 39, 30, 31, or 32 carbons, more preferably having 1 to 18 carbon atoms, and having one or more carbon-carbon triple bonds. Alkynyl groups include, but are not limited to, ethynyl, propynyl, and butynyl. Alkynyl groups can be unsubstituted or substituted with one or more suitable substituents, as defined above.

[0096] The terms "aryl" or "ar" as used herein alone or as part of another group (e.g., aralkyl) refer to a monocyclic, bicyclic, or tricyclic aromatic radical, such as phenyl, naphthyl, tetrahydronaphthyl, indanyl, and the like, optionally substituted with one or more suitable substituents, preferably 1 to 5 suitable substituents, as defined above. The term "aryl" also includes heteroaryl.

[0097] "Arylalkyl" or "aralkyl" refers to an aryl group connected to a parent molecule via an alkylene group. The number of carbon atoms in the aryl and alkylene groups is selected so that there are a total of about 6 to about 18 carbon atoms in the arylalkyl group. A preferred arylalkyl group is benzyl.

[0098] The term "cycloalkyl," as used herein, refers to a monocyclic, bicyclic, or tricyclic carbocyclic radical (e.g., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclopentenyl, cyclohexenyl, bicyclo[2.2.1]heptanyl, bicyclo[3.2.1]octanyl, bicyclo[5.2.0]nonanyl, and the like), optionally containing one or two double bonds. A cycloalkyl group can be unsubstituted or substituted with one or more suitable substituents, preferably 1 to 5 suitable substituents, as defined above.

[0099] The term "-ene" used as a suffix as part of another group denotes a divalent radical in which a hydrogen atom has been removed from each of the two terminal carbons of the group, or, if the group is cyclic, from each of two different carbon atoms in the ring. For example, alkylene denotes a divalent alkyl group such as ethylene (-CHCH-) or isopropylene (-CH(CH)CH-). For clarity, the addition of the -ene suffix is not intended to alter the definition of the head word other than to indicate a divalent radical. Thus, continuing with the above example, alkylene denotes an optionally substituted straight-chain saturated divalent hydrocarbon radical.

[0100] The term "ether," as used herein, refers to a divalent (ie, difunctional) group containing at least one ether linkage (ie, --O--).

[0101] The term "heteroaryl," as used herein, refers to a monocyclic, bicyclic, or tricyclic aromatic heterocyclic group containing in one or more rings one or more heteroatoms (e.g., 1 to 3 heteroatoms) selected from O, S, and N. Heteroaryl groups include, but are not limited to, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, thienyl, furyl, imidazolyl, pyrrolyl, oxazolyl (e.g., 1,3-oxazolyl, 1,2-oxazolyl), thiazolyl (e.g., 1,2-thiazolyl, 1,3-thiazolyl), pyrazolyl, tetrazolyl, triazolyl (e.g., 1,2,3-triazolyl, 1,2,4-triazolyl), oxadiazolyl (e.g., 1,2,3-oxadiazolyl), thiadiazolyl (e.g., 1,3,4-thiadiazolyl), quinolyl, isoquinolyl, benzothienyl, benzofuryl, and indolyl. A heteroaryl group can be unsubstituted or optionally substituted with one or more suitable substituents, preferably 1 to 5 suitable substituents, as defined above.

[0102] The term "hydrocarbon" as used herein describes compounds or radicals consisting solely of the elements carbon and hydrogen.

[0103] The term "substantially amorphous" is defined as having no more than 20%, preferably no more than 10%, and more preferably no more than 2% crystalline content.

[0104] The term "substituted" means that in the group in question, at least one hydrogen atom bonded to a carbon atom is replaced with one or more substituents, such as hydroxy (-OH), alkylthio, phosphino, amido (-CON(RA)(RB), where RA and RB are independently hydrogen, alkyl, or aryl), amino (-N(RA)(RB), where RA and RB are independently hydrogen, alkyl, or aryl), halo (fluoro, chloro, bromo, or iodo), silyl, nitro (-NO), ether (-ORA, where RA is alkyl or aryl), ester (-OC(O)RA, where RA is alkyl or aryl), keto (-C(O)RA, where RA is alkyl or aryl), heterocyclo, etc. When the term "substituted" introduces or follows a list of possible substituted groups, it is intended that the term apply to all members of that group. That is, the phrase "optionally substituted alkyl or aryl" should be interpreted as "optionally substituted alkyl or optionally substituted aryl." Similarly, the phrase "optionally substituted with fluorine" should be interpreted as "optionally substituted with fluorine alkyl or optionally substituted with fluorine aryl."

[0105] When introducing elements of the present invention or preferred embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0106] In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

[0107] Because various changes can be made in the products and methods described above without departing from the scope of the invention, it is intended that all matter contained in the above specification and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. 1. A method of making a moisture-activated powder for providing a controlled release of chlorine dioxide, comprising: mixing sodium chlorite, silicate, and water to form an aqueous suspension, the aqueous suspension comprising 85-99% pure sodium chlorite; spray drying the aqueous suspension at an inlet temperature in the range of about 482 to about 537°C (900 to 1000°F) and an outlet temperature of not more than 143°C (290°F) to form silicate particles; mixing an inorganic acid releasing agent, an anhydrous material, and water to form a colloidal suspension; mixing the silicate particles with the colloidal suspension to form a slurry; spray drying the slurry at an inlet temperature in the range of about 482 to about 537°C (900 to 1000°F) and an outlet temperature of not more than 143°C (290°F) to form the powder; wherein the powder is substantially free of water and is capable of producing and releasing a disinfecting-effective amount of chlorine dioxide after hydrolysis of the acid-releasing agent and reaction of the hydronium ions with chlorite without releasing detectable amounts of chlorine gas, chlorate, and / or chlorite.

2. 10. The method of claim 1, further comprising mixing the dispersion with the sodium chlorite, the silicate, and the water to form the aqueous suspension.

3. The method of claim 2 , wherein the dispersion comprises a non-ionic surfactant.

4. 4. The method of claim 3, wherein the nonionic surfactant comprises a secondary alcohol ethoxylate, an alkylphenol ethoxylate, an alkyl ethoxylate, an alkylaryl ethoxylate, a polyethylene oxide-polypropylene oxide block copolymer, a polyethylene glycol ether of a linear alcohol, a reaction product of a fatty acid with ethylene oxide and / or propylene oxide, a polyvinyl alcohol, a polyvinyl pyrrolidone, a copolymer of polyvinyl alcohol and polyvinyl pyrrolidone, a copolymer of (meth)acrylic acid and a (meth)acrylic acid ester, or any combination thereof.

5. 5. The method of claim 1, wherein the aqueous suspension has a pH of from about 9 to about 14.

6. 5. The method of claim 1, wherein the pH of the colloidal suspension is from about 5 to about 7.

7. 7. The method of any one of claims 1 to 6, wherein the silicate comprises sodium silicate, sodium metasilicate, sodium sesquisilicate, sodium orthosilicate, borosilicate, aluminosilicate, magnesium silicate, calcium metasilicate, aluminum silicate, zinc silicate, or any combination thereof.

8. 8. The method of any one of claims 1 to 7, wherein the inorganic acid-releasing agent comprises tetraalkylammonium polyphosphate, monobasic potassium phosphate, potassium polymetaphosphate, sodium metaphosphate, borophosphate, aluminophosphate, silicophosphate, sodium polyphosphate, potassium tripolyphosphate, sodium-potassium phosphate, or any combination thereof.

9. 9. The method of any one of claims 1 to 8, wherein the anhydrous material comprises sodium sulfate, calcium sulfate, calcium carbonate, magnesium sulfate, calcium chloride, moisture-depleted silica gel, alumina, zeolite, clay, potassium permanganate, molecular sieves, or any combination thereof.

10. 10. The method of any one of claims 1 to 9, wherein the powder comprises about 30% to about 80% by weight of the anhydrous material, about 10% to about 50% by weight of the inorganic acid-releasing agent, about 5% to about 40% by weight of the silicate, and about 0.01% to about 50% by weight of sodium chlorite.

11. 10. The method of any one of claims 1 to 9, wherein the powder comprises about 35% to about 70% by weight of the anhydrous material, about 15% to about 45% by weight of the inorganic acid-releasing agent, about 10% to about 35% by weight of the silicate, and about 1% to about 30% by weight of sodium chlorite.

12. 10. The method of any one of claims 1 to 9, wherein the powder comprises about 40% to about 60% by weight of the anhydrous material, about 20% to about 40% by weight of the inorganic acid-releasing agent, about 15% to about 30% by weight of the silicate, and about 0.5% to about 5% by weight of sodium chlorite.

13. A method according to any one of claims 1 to 12, wherein the aqueous suspension is an azeotrope.

14. 14. The method of claim 13, wherein the azeotrope in the aqueous suspension comprises acetone, acetonitrile, acrylonitrile, an alcohol, an alkenol, an alkane, an alkenal, a haloalkane, aniline, a cycloalkane, benzene, an alkylbenzene, a halobenzene, carbon disulfide, carbon tetrachloride, chloroform, epichlorohydrin, an alkylamine, a dialkylamine, an alkyl halide, an alkyl ether, an alkyl acetate, a haloalkene, an alkenyl chloride, toluene, or xylene.

15. 14. The method of claim 13, wherein the azeotrope comprises acetone and one or more solvents comprising ethanol, methanol, isopropanol, tert-butanol, hexane, 2-methylpentane, dichloromethane, trichlorotrifluoroethane, nitromethane, cyclopentane, cyclohexane, carbon disulfide, carbon tetrachloride, chloroform, methyl iodide, ethyl iodide, isopropyl ether, methyl acetate, or trifluoroacetic acid.

16. 16. The method of any one of claims 1 to 15, wherein the disinfecting effective amount ranges from about 0.08 ppm / min to about 50 ppm / min for a period of about 2 to about 72 hours.

17. 17. The method of any one of claims 1 to 16, further comprising cooling the powder and / or packaging the powder under an inert atmosphere.

18. 18. The method according to any one of claims 1 to 17, wherein the silicate particles are amorphous.

19. 20. The method of claim 19, wherein the powder is encapsulated in an amorphous silicate shell.

20. 20. The method of any one of claims 1 to 19, wherein the powder comprises 0.001 to 0.3% by weight of water.

21. 21. The method of claim 20, wherein the powder comprises 0.001 to 0.2% by weight of water.

22. 21. The method of claim 20, wherein the powder comprises 0.001 to 0.1% by weight of water.

23. 23. A moisture-activated powder, wherein exposure to moisture can cause the controlled release of chlorine dioxide from the powder in a disinfecting-effective amount without releasing detectable amounts of chlorine gas, chlorate and / or chlorite, wherein the powder has been prepared by the method of any one of claims 1 to 22.

24. 24. The powder of claim 23, wherein the powder has a particle size distribution in which 90% of the powder particles are smaller than 31 microns and the median particle size is from about 10 to about 15 microns.

25. 25. A film comprising the moisture-activated powder of claim 23 or 24 and a biodegradable polymer.

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