Moisture-activated chlorine dioxide-releasing powder and method of manufacture

Abstract

Methods of making moisture activated powders are provided that provide for the generation and release of chlorine dioxide without detectable amounts of any toxic by-products, such as chlorine, chlorite, or chlorate. The powder does not need to be exposed to light before or during exposure of the powder to moisture or relative humidity to generate the gas. The powder may also be prepared under conditions that minimize or prevent 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 for generating and releasing chlorine dioxide and methods for making the same are provided. More specifically, moisture-activated controlled-release powders are provided that are capable of generating and releasing chlorine dioxide without detectable amounts of any toxic byproducts and are prepared by methods of providing powders and maximizing the activity of the controlled-release powders for use in disinfection, sanitation, sterilization, and control of biological or pathogenic contamination. Background Art

[0002] Currently, ethylene oxide is used to sterilize medical devices and other products. The U.S. Food and Drug Administration recognizes that ethylene oxide has potential adverse effects on the environment and public health. The FDA is encouraging changes to ethylene oxide sterilization processes and equipment that will reduce the amount of ethylene oxide on medical devices.

[0003] When chlorine dioxide is generated from some conventional chlorine dioxide generating products, detectable amounts of toxic byproducts including chlorine gas, chlorate, and / or chlorite have been observed. Summary of the invention

[0004] One option for reducing ethylene oxide concentrations on medical devices is to replace ethylene oxide entirely 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 invention, a method for making a moisture-activated powder for providing controlled release of chlorine dioxide is provided. The method comprises mixing sodium chlorite, a silicate and water to form an aqueous suspension, and spray drying the aqueous suspension at an inlet temperature of about 482°C to about 537°C (900°F to 1000°F) and an outlet temperature of no more than 143°C (290°F) to form silicate particles. An inorganic acid release agent, 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 in the range of about 482°C to about 537°C (900°F to 1000°F) and an outlet temperature of no more than 143°C (290°F) to form a powder. The powder is substantially free of water and is capable of generating and releasing a disinfecting effective amount of chlorine dioxide after the acid release agent is hydrolyzed and the hydronium ions react with the chlorite without releasing detectable amounts of chlorine, chlorate and / or chlorite.

[0006] The powder prepared by this method is capable of generating 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 include sodium chlorite in an amount of 85% to 99% purity.

[0008] As a second aspect of the present invention, a moisture activated powder is provided. The moisture activated powder is prepared by the method described in the first aspect and examples of the present invention. When exposed to moisture or relative humidity, the powder is capable of generating a controlled release of a disinfecting, sanitizing, sterilizing effective amount of chlorine dioxide from the powder without releasing detectable amounts of toxic byproducts such as chlorine and / or chlorite, chlorate.

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

[0010] A method of making a moisture activated powder has been discovered that provides generation and release of chlorine dioxide without detectable amounts of any toxic byproducts, such as chlorine, chlorate and / or chlorite. The method includes an inlet spray drying temperature much higher than the 180°C decomposition temperature of sodium chlorite. When exposed to moisture or relative humidity, the powder is capable of generating and releasing a gas upon hydrolysis of an acid release agent in the powder that provides hydronium ions to react with sodium chlorite.

[0011] The powder may 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] As a first aspect of the present invention, a method for preparing a moisture-activated powder for providing controlled release of chlorine dioxide is provided. The method includes mixing sodium chlorite, a silicate, and water to form an aqueous suspension; and spray drying the aqueous suspension at an inlet temperature in the range of about 482°C to about 537°C (900°F to 1000°F) and an outlet temperature not exceeding 143°C (290°F) to form silicate particles. An inorganic acid release agent, 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 in the range of about 482°C to about 537°C (900°F to 1000°F) and an outlet temperature not exceeding 143°C (290°F) to form a powder. The powder is substantially free of water and is capable of generating and releasing a disinfecting effective amount of chlorine dioxide after the acid release agent is hydrolyzed and the hydronium ions react with the chlorite without releasing detectable amounts of chlorine, chlorate, and / or chlorite.

[0013] The powder may 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 generated by the powder containing silicate particles because these anions do not effectively generate chlorine dioxide in the presence of acid or hydronium ions. The silicate particles can be treated at temperatures up to 537°C (1000°F) for a period of time without significantly reducing the amount of gas that can be generated by the powder containing the particles. Without being bound by a particular theory of the invention, it is believed that the anions capable of reacting with hydronium ions to form gas are dispersed within the amorphous silicate matrix that encapsulates the anions. Because intermolecular interactions between chlorite anions are minimized in the amorphous silicate matrix, disproportionation of chlorite is avoided.

[0015] Preferably, each silicate particle comprises from about 85% to about 99% by weight silicate and from about 1% to about 15% by weight chlorite. More preferably, the silicate particles comprise from about 95% to about 99% by weight silicate and from about 1% to about 5% by weight chlorite.

[0016] The silicate particles are substantially free of water to minimize 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 the purposes of the present invention, a silicate particle is substantially free of water if the amount of water in the silicate particle does not provide a pathway for anion transfer from the particle to the solvent. Preferably, the silicate particles contain at most about 10% by weight, preferably at most about 5% by weight, of water per silicate particle without providing such a pathway for diffusion from the particle to the solvent.

[0017] The aqueous suspension may include 85% to 99% pure sodium chlorite, which is commercially available.

[0018] The powder is capable of generating a controlled release of chlorine dioxide from the powder when exposed to ambient moisture, relative humidity, or otherwise in contact with water. Moisture or water diffuses into the powder and reacts with the inorganic acid release agent to form an acid. The acid dissolves in the water, thereby 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 for a period of up to about six months to affect materials located in the vicinity of the powder. The release of at least about 1.0×10 -6 Gram gas / cm 3 Powders for a period of at least one hour, one day, one week, one month, or six months can be formulated 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 regardless of whether 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 present method is preferably maintained at or below about 60%, and more preferably at or below about 30%.

[0022] The silicate used to prepare the aqueous suspension of silicate particles may 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 typically include sodium and potassium cations.

[0023] SiO in silicate particles 2 Measured silicon and M 2 The ratio of alkali metal cations measured by O is between about 2.5 and about 3.5, preferably between about 3.0 and about 3.5, most preferably about 3.2, wherein M is selected from the group consisting of sodium and potassium.

[0024] The silicate particles may be solid or hollow, and may be substantially spherical.

[0025] Inorganic acid releasers such as polyphosphates form odorless powders with higher gas release efficiency compared to powders containing organic acid releasers. Suitable inorganic acid releasers include tetraalkylammonium polyphosphates, potassium dihydrogen phosphate (KH 2 PO 4 )、Potassium polymetaphosphate (KPO 3 ) x , wherein x is in the range of 3 to 50), sodium metaphosphate, borophosphate, aluminum phosphate, silicophosphate, sodium polyphosphate such as sodium tripolyphosphate, potassium tripolyphosphate (K 5 P 3 O 10 ), sodium-potassium phosphate (NaKHPO 4 7H 2 O), and salts containing hydrolyzable metal cations such as zinc. Preferred sodium metaphosphates have the formula (NaPO 3 ) n , wherein n is from 3 to 10 for the cyclic molecules and from 3 to 50 for the polyphosphate chains.

[0026] The anhydrous material used in the method can be combined with water. The material acts as a dehumidifier to minimize the premature hydrolysis of the acid release agent. Suitable anhydrous materials include sodium sulfate, calcium sulfate, calcium carbonate, magnesium sulfate, calcium chloride, poor moisture silica gel, aluminum oxide, zeolite, clay (such as bentonite or kaolin), potassium permanganate, molecular sieves, deoxygenation materials or their mixtures. Anhydrous materials are commercially available from many sources.

[0027] When preparing the aqueous suspension in the method of the present invention, a dispersant may be mixed with the silicate, sodium chlorite and water. The dispersant may reduce agglomeration within the suspension.

[0028] When preparing the colloidal suspension or slurry in the method of the present invention, the dispersant can be mixed with the inorganic acid release agent, the anhydrous material and water, or with the colloidal suspension and silicate particles. The dispersant can reduce agglomeration in the colloidal suspension or slurry.

[0029] Dispersant can be any material that minimizes the agglomeration of silicate particles during powder preparation, controls the release of gas from powder, reduces the surface reactivity of silicate particles, controls the moisture penetration through silicate particles and does not react with silicate particles. Material with hydrophilic and hydrophobic parts is preferred. The hydrophilic part of the material can be absorbed by the surface of silicate particles. When particles are mixed, the hydrophobic part of the material minimizes the agglomeration of silicate particles. Suitable dispersants include but are not limited to amides of carboxylates such as isostearic acid amide, polyvinyl acetate, polyvinyl alcohol, polyvinyl pyrrolidone copolymers, polymers of alkylene oxides such as polyglycols, polyols, polyalkylene glycols (for example, polyethylene glycol, polypropylene glycol, polybutylene glycol), alkoxy polyalkylene glycols such as methoxy polyethylene glycol, trifunctional polyethylene glycol, poly (ethylene-propylene) glycol, metal, oligomeric or copolymerized olefinic carboxylic acids and / or fatty acids, polyethers and metal carboxylates such as zinc isostearate and derivatives (for example, carboxylic acids such as fatty acids), their blends and copolymers, or their any combination. Some acid release agents, such as sodium polyphosphate, also act 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, which are commercially available from GAF Corp.

[0030] The dispersant may include 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, polyvinyl pyrrolidone, copolymers of polyvinyl alcohol and polyvinyl pyrrolidone, copolymers of (meth) acrylic acid and (meth) acrylic esters, or combinations thereof.

[0031] The aqueous suspension is also preferably maintained at an alkaline 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] The colloidal suspension is also preferably maintained at a pH of about 5 to about 7.

[0033] The silicate particles optionally contain an alkali or filler. The alkali controls the release of chlorine dioxide gas from the particles by reacting with hydronium ions, which diffuse from the acid releaser into the particles or diffuse into the anion-rich regions of the particles to form salts. When the alkali is exhausted, the excess hydronium ions then react with the chlorite anions in the particles to form gas. The filler controls the release of chlorine dioxide gas by forming a barrier to the diffusion of hydronium ions. The amount of alkali or filler in the core can be adjusted to change the time period before the gas is released from the particles. For example, if a longer delay in gas release is required, the concentration of the alkali or filler can be increased. During the preparation of silicate particles or powders containing particles, the alkali or filler can stabilize chlorite. The amount of alkali in the particles can be adjusted to change the time period of gas release and improve thermal stability. Based on the total weight of the particles, up to about 50% by weight of the alkali can be included.

[0034] Any base or any filler that reacts with hydronium ions can be incorporated into the silicate particles or powders. Suitable bases or fillers include, but are not limited to, 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, bicarbonates of transition metal ions, protonated primary, secondary or tertiary amines, or quaternary amines such as ammonium bicarbonate, carbonates of transition metal ions, protonated primary, secondary or tertiary amines, or 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, hydroxide salts of transition metal ions, protonated primary, secondary or tertiary amines, or quaternary amines such as ammonium hydroxide, alkali metal phosphides, phosphates such as dibasic or tribasic phosphates, alkaline earth metal phosphates such as dicalcium phosphate or tricalcium phosphate, 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 ammoniums 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 ammoniums, 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; hydroxide salts of transition metal ions; protonated primary, secondary or tertiary amines, or quaternary amines such as ammonium hydroxide. Sodium hydroxide is preferred.

[0036] In the process of the present invention, the aqueous suspension may be an azeotrope. When the aqueous suspension is an azeotrope, the spray drying inlet temperature may be as high as 537°C (1000°F) while still avoiding decomposition of sodium chlorite. The azeotrope may include a mixture of solvents including, but not limited to, acetone, acetonitrile, acrylonitrile, alcohols (e.g., ethanol, methanol, isopropanol, tert-butyl alcohol), enols, alkanes (e.g., hexane, 2-methylpentane), alkenals, halogenated alkanes (e.g., dichloromethane, trichlorotrifluoroethane), nitroalkanes (e.g., nitromethane), aniline, cycloalkanes (e.g., cyclopentane, cyclohexane), benzene, alkylbenzenes, halogenated benzenes, 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), halogenated alkenes, alkenyl chlorides, trifluoroacetic acid, toluene, xylene, or any combination thereof.

[0037] For example, the aqueous suspension may include an azeotrope comprising 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.

[0038] Preferably, the silicate particles are formed from an aqueous suspension containing sodium silicate and sodium chlorite. The anhydrous material is preferably magnesium sulfate. The inorganic acid releaser 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 various sources. Before being used in the powder preparation process, the ingredients are stored in a dry atmosphere.

[0040] An inert atmosphere, such as a nitrogen blanket, may be used during the process. An inert atmosphere may 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] The aqueous suspension can be prepared by mixing its ingredients in any order of addition. For example, sodium chlorite can be mixed with water and a silicate to form an aqueous suspension, and optionally a solvent can be added to the suspension to form an azeotrope. Alternatively, the silicate and sodium chlorite can be mixed prior to mixing with water to form an aqueous suspension. When preparing the 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, for example, any known atomization method, such as a nozzle or a rotating disk. Typically, the inlet temperature is maintained at about 482°C to about 537°C (900°F to 1000°F), and the outlet temperature is maintained in the range of about 121°C (250°F) to about 143°C (290°F). The spray drying process usually occurs quickly (e.g., within about 60 seconds at most). If desired, the silicate particles can then be further dried by any conventional method. The silicate particles are stored in a dry atmosphere.

[0043] Although not limited thereto, it is believed that spray drying of an aqueous suspension forms solid or hollow spheres consisting of a solid solution (such as a substantially amorphous silicate matrix) in which the anions are uniformly dispersed and encapsulated. This uniform dispersion and encapsulation enhances the thermal stability of the silicate particles and powders containing silicate particles. It is believed that powders containing silicate particles release significantly more gas than powders containing crystalline cores. Gas release efficiencies of 75% to 100% are typical of the powders of the present invention.

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

[0045] The wall thickness of the hollow particles can be varied by changing process conditions, such as 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, for example, particle size, solids concentration, viscosity, surface tension or temperature of the feed solution.

[0046] The crystallinity of the silicate particles is varied by varying the silicate used to prepare the particles.

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

[0048] Once a colloidal suspension comprising an inorganic acid releaser, anhydrous material and water is formed, it can be spray dried to form a powder by any method known in the art, including, for example, any known atomization method, such as a nozzle or a rotating disk. Typically, the inlet temperature is maintained at about 482°C to about 537°C (900°F to 1000°F), and the outlet temperature is maintained at about 121°C (250°F) to about 143°C (290°F) in the range. The spray drying process usually occurs quickly (for example, in about 60 seconds at most). If desired, the powder can 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, silicon dioxide, silicates such as sodium silicate, sodium metasilicate, sodium sesquisilicate, sodium orthosilicate, borosilicates, aluminosilicates, zeolites, sodium sulfide, or a combination thereof.

[0050] The powder may 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 may contain: 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 a 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 a silicate, and between about 1% and 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 a silicate, and between about 0.5% and about 5% by weight of sodium chlorite.

[0052] The chlorine dioxide release rate for effective disinfection can be, for example, in the range of about 0.08 ppm / minute to about 50 ppm / minute over a period of about 2 hours to about 72 hours. The release rate can be increased by increasing the amount of chlorite in the powder, for example to achieve a release rate of 100 ppm / minute, 200 ppm / minute, or more over a period of about 2 hours to about 72 hours or longer.

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

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

[0055] As a second aspect of the present invention, a moisture activated powder is provided. The moisture activated powder is prepared by the method described in the first aspect and examples of the present invention. When exposed to moisture or relative humidity, the powder is capable of generating a controlled release of a disinfecting effective amount of chlorine dioxide from the powder without releasing a detectable amount of chlorine and / or chlorite or chlorate.

[0056] The application of powder is very extensive. They can be used in most of any environment that may be exposed to moisture or relative humidity. Powder can be formed into solid by molding or sintering. Powder 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, films, engineering materials, paints, coatings and adhesives, thereby for a wide range of end-use applications. Powder is particularly useful for preparing any injection molded product, compression molded product, thermoforming (thermoforming) product or extrusion molded product, such as cast or blown film. The thermal stability of powder allows them to be used in injection molding processes.

[0057] The powder of the present invention is preferably incorporated into the plastic product of injection molding, compression molding, thermoforming or extrusion molding, which is by compounding and granulating the powder via conventional means, and mixing the pellets with the material before conventional molding or molding process. Suitable materials for forming these products include any polymer, multi-component polymer (such as copolymer, terpolymer or oligomer) and their polymer alloys or blends or any wax. Representative polymers include polyolefins, such as polyethylene and polypropylene, polyethylene terephthalate, polyvinyl chloride, polyurethane, metallocene polymers, polyesters, polyacrylates, acrylic acid, polystyrene, polycarbonate, polyamide, polyesteramide, ethylene-vinyl acetate copolymer, ethylene-methacrylate copolymer and polyacetal. Suitable wax includes microcrystalline wax, paraffin and synthetic wax, such as chlorinated wax, polyethylene wax, polyethylene glycol and polypropylene glycol. Preferably, polymer is biodegradable.

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

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

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

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

[0062] A multilayer composite material can be formed to generate gas within a housing formed by the composite material. Such a composite material includes a gas generating layer and a barrier layer. The gas generating layer includes a powder. The barrier layer is adjacent to the surface of the gas generating layer. The barrier layer is permeable to moisture so that it transmits 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. When exposed to moisture or relative humidity, the gas generating layer is capable of generating and releasing chlorine dioxide after activation.

[0063] The gas-releasing powders, films or other compositions of the present invention can be used to retard, kill, prevent or control microbial contamination or biochemical decomposition on the surface of a material, in the material or in the atmosphere surrounding the material by placing the material adjacent to the composition of the present invention and exposing the composition to moisture or relative humidity to release chlorine dioxide from the composition into the atmosphere surrounding the material. Microbial contaminants may include bacteria, viruses, molds and fungi.

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

[0065] As used herein, delaying, preventing or controlling biocontamination is also referred to as "sanitization," "disinfection," or "sterilization." Biocontamination can include bacteria, viruses such as coronaviruses (e.g., SARS-COV-2 and variants thereof such as Delta or Omicron variants), molds, and fungi.

[0066] The composition 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 and release it from the composition into the atmosphere surrounding the material. For example, chlorine dioxide is used to inactivate biological contaminants (e.g., anthrax) after biological warfare or for other military decontamination.

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

[0068] The composition may also be used to deodorize the surface of a material or the atmosphere surrounding the 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 to generate and release chlorine dioxide from the composition 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 materials by placing the material adjacent to the composition and exposing the composition to moisture or relative humidity to generate and release chlorine dioxide from the composition into the atmosphere surrounding the material.

[0070] In the above method, 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 the composition can be enclosed in a container. When the composition is enclosed in a container, the container can be hermetically sealed, or partially sealed so that some gas leaks from the container.

[0071] The chlorine dioxide-releasing powder can be impregnated into containers for storing food, soap, laundry detergent, documents, clothing, paint, seeds, medical equipment, devices and supplies (such as catheters and sutures), personal care products, medical or biological waste, sports shoes, ostomy bags, footwear and garbage, for example. Such powders can also be impregnated into covers for medical, hospital, household or commercial equipment or covers for storage. Pouches, pouches, "tea bags" or other breathable containers of powder can be included in the storage container to provide a chlorine dioxide micro-atmosphere when activated. The chlorine dioxide-releasing powder can also be impregnated into paper or polymeric materials (e.g., shower mats, shoe insoles or shoe insoles, bandage materials, cutting boards, food packaging materials, food packaging trays, seed packets, or air filters); incorporated into wax or polymer coatings applied to cardboard containers or other surfaces; incorporated into films, such as packaging films or coverings for storage or medical, hospital, household, or commercial equipment; formed into porous portions to sterilize water; mixed with materials to create a micro-atmosphere of chlorine dioxide around materials (e.g., soil); or mixed with other powders to kill microorganisms, enhance freshness, or deodorize (e.g., foot powders, bath powders, powders for treating soft surfaces such as carpet powders, desiccants for removing moisture).

[0072] These powders may also be used to: neutralize odors, delay, prevent, inhibit or control chemotaxis (ie, the attraction of living organisms to chemicals); or reduce or eliminate bacteria in animal feed and potentially reduce the bacterial load in the intestines of animals consuming the feed.

[0073] The compositions of the present invention effectively release gas at temperatures (including refrigeration temperatures) commonly encountered in the above-mentioned applications. Compositions that release chlorine dioxide can be used, for example, to package medical supplies, food, or other materials that require refrigeration to sterilize or deodorize the material. Multilayer films including barrier layers can also be used to form packages, such as for medical supplies or food. The barrier layer retains the generated gas in the package, for example, to increase shelf life and prevent mold growth in food or to improve the sterilization of medical supplies.

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

[0075] Example

[0076] The following non-limiting examples are provided to illustrate the invention.

[0077] Example 1

[0078] The moisture activated powder was produced by a two-step spray drying process to produce multilayer particles with a D10 particle size distribution of 0.79 microns, a D50 particle size distribution of 13.24 microns, and a D90 particle size distribution of 30.99 microns.

[0079] Preparation of core powder. A liquid slurry was prepared in a blending tank which was spray dried to form the core powder. The blending tank had an agitator which was turned on during the addition of all ingredients.

[0080] First, a blending tank was filled with a certain amount of deionized water to provide a 27.3% liquid slurry before spray drying. Sodium chlorite powder (2.7 wt %) was added to the water, followed by sodium silicate (70 wt %) to form a clear slurry with a light yellow hue. The amounts listed are based on the total weight of the liquid slurry before spray drying. The slurry was then transferred to the feed tank of the spray dryer, which was also equipped with an agitator.

[0081] About 22.8 kg (50 lbs) of a liquid slurry containing dissolved sodium chlorite and suspended sodium silicate was pumped into the 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 a pH of 12.8. The inlet temperature of the spray dryer ranged from 510°C (950°F) to 527°C (980°F) throughout the run. The outlet temperature ranged from 121°C (250°F) to 124°C (255°F). The slurry was spray dried to produce a powder.

[0082] The resulting fine white hygroscopic powder was screened through a 50 micron screen into a polymer drum lined with two opaque plastic bags. A perforated hose connected to a nitrogen bottle was inserted into the drum to facilitate cooling. Once the temperature dropped to 32°C (90°F), the bags and drums were sealed.

[0083] Preparation of finished core-shell powder. A liquid slurry was prepared in a blending tank containing deionized water maintained at a temperature of 7.2°C (45°F). Sodium polyphosphate was added to the cold water and stirred until dissolved. Magnesium sulfate was then added, which resulted in a colloidal suspension that periodically accumulated on the side walls of the blending tank, which was periodically removed from the side walls and redeposited in the pH 6 mixture.

[0084] The core powder was then added and mixed with the colloidal suspension in the blending tank. The final slurry had a pH of 7 and had the following ingredients 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 out feed tank to be pumped into the spray dryer. The absolute viscosity of the slurry containing 24.1% solids was 58.72 centipoise at a pH of 7.0. The inlet temperature of the spray dryer ranged from 510°C (950°F) to 527°C (980°F) throughout the run. The outlet temperature ranged from 121°C (250°F) to 124°C (255°F). The powder was produced by spray drying the slurry.

[0085] The resulting fine white powder with an average moisture content of 4.6% was screened through a 50 micron screen into a polymer drum lined with two opaque plastic bags. A perforated hose connected to a nitrogen bottle was inserted into the drum to facilitate cooling. Once the temperature dropped to 32°C (90°F), the bags and drums containing the final powder (subjected to a nitrogen inert atmosphere) were sealed.

[0086] Four samples of the finished powder were collected throughout the run and tested for chlorine dioxide production when exposed to a saturated sponge. After 60 seconds of exposure of 5 grams of powder to moisture, production of more than 250 ppm of chlorine dioxide was consistently observed. Longer exposure to moisture produced chlorine dioxide levels greater than 1,000 ppm from 5 grams of powder. All four samples produced the same results, i.e., greater than 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.

[0087] Example 2

[0088] Pellets Formation: The spray dried powder of Example 1 was compounded into pellets using a range of polymers such as 2 to 20 melt index linear low density polyethylene (LLDPE) resins at a concentration of 20% powder and 80% resin. The pellets were packaged under nitrogen and stored in a dry atmosphere.

[0089] Film Formation: Pellets were blown into films using a range of resins such as 2 to 20 melt index LLDPE resins (50% dilution). The resulting films contained about 10% powder by weight. The films were stored in a dry atmosphere.

[0090] Moisture Activation of Film: The film samples were placed in a jar with a 0 ppm to 10 ppm chlorine dioxide electrochemical detector attached to the lid (desiccant included to produce 0% relative humidity). No chlorine dioxide was generated during this period. The introduction of moisture, relative humidity or water resulted in the generation of chlorine dioxide.

[0091] Example 3

[0092] The moisture content of the powder product of Example 1 was considered to be an incorrect measurement. Therefore, the moisture content of the powder produced in Example 1 was tested again. The powder had been stored in a polyethylene bag which was inside an aluminum flexible foil bag and sealed for more than one year.

[0093] Three samples were taken from the bag and analyzed for moisture content by placing the samples in an oven at 215 degrees Fahrenheit (101.67 degrees Celsius). After weighing, the samples were placed in the oven for one hour and then weighed again. The samples were then placed in the oven for an additional 2 hours and weighed again at the end of the 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 are as follows ("na" indicates unavailable due to loss of some powder during the test):

[0094] Sample No. Water content at 1 hour (weight %) Water content at 3 hours (weight %) 1 0.024 0.024 2 0.029 na 3 0.027 0.029

[0095] The data obtained show high reproducibility. The average moisture content of the powder of Example 1 during the two drying times was 0.027 wt %. The data also show that the drying time has a sufficient duration. According to these results, the average moisture content of the powder of Example 1 was 0.027 wt % both when the powder was prepared and after storage for at least one year.

[0096] definition

[0097] As used herein, the term "suitable substituent" is intended to mean a chemically acceptable functional group, preferably a part that does not counteract the activity of the compounds of the present invention. Such suitable substituents include, but are not limited to, halide groups, perfluoroalkyl groups, perfluoroalkoxy groups, alkyl groups, alkenyl groups, alkynyl groups, hydroxyl groups, oxo groups, sulfhydryl groups, alkylthio groups, alkoxy groups, aryl or heteroaryl groups, aryloxy or heteroaryloxy groups, aralkyl or heteroaralkyl groups, aralkyloxy or heteroaralkyloxy groups, HO-(C=O)-groups, heterocyclic groups, cycloalkyl groups, amino groups, alkylamino and dialkylamino groups, carbamoyl groups, alkylcarbonyl groups, alkoxycarbonyl groups, alkylaminocarbonyl groups, dialkylaminocarbonyl groups, arylcarbonyl groups, aryloxycarbonyl groups, alkylsulfonyl groups, and arylsulfonyl groups. It will be appreciated by those skilled in the art that many substituents may be substituted with additional substituents.

[0098] As used herein, the term "alkyl" refers to a straight chain, branched chain or cyclic hydrocarbon group, 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, isobutyl, sec-butyl and tert-butyl. Alkyl groups can be unsubstituted or substituted with one or more suitable substituents.

[0099] As used herein, term "alkenyl" refers to a straight chain, branched or cyclic hydrocarbon group, 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 vinyl, 1-propenyl, 2-propenyl (allyl), isopropenyl, 2-methyl-1-propenyl, 1-butenyl and 2-butenyl. Alkenyl groups can be unsubstituted or substituted by one or more suitable substituents, as defined above.

[0100] The term "alkynyl" as used herein refers to a straight chain, branched or cyclic hydrocarbon group, 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.

[0101] The term "aryl" or "ar" as used herein alone or as part of another group (e.g., aralkyl) means a monocyclic, bicyclic or tricyclic aromatic group such as phenyl, naphthyl, tetrahydronaphthyl, indanyl, etc., optionally substituted with one or more suitable substituents, preferably 1 to 5 suitable substituents, as defined above. The term "aryl" also includes heteroaryl.

[0102] "Arylalkyl" or "aralkyl" means an aryl group attached to a parent molecule through an alkylene group. The number of carbon atoms in the aryl group and the alkylene group 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.

[0103] As used herein, the term "cycloalkyl" refers to a monocyclic, bicyclic or tricyclic carbocyclic group (e.g., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclopentenyl, cyclohexenyl, bicyclo[2.2.1]heptyl, bicyclo[3.2.1]octyl and bicyclo[5.2.0]nonyl, etc.); optionally containing 1 or 2 double bonds. The cycloalkyl group may be unsubstituted or substituted with one or more suitable substituents, preferably 1 to 5 suitable substituents, as defined above.

[0104] The term "-ene" used as a suffix as part of another group represents a divalent group in which a hydrogen atom is 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 represents a divalent alkyl group, such as ethylene (-CH2CH2-) or isopropylene (-CH2(CH3)CH2-). For clarity, the addition of the -ene suffix is ​​not intended to change the definition of the main word, except for indicating a divalent group. Thus, continuing with the above example, alkylene represents an optionally substituted straight-chain saturated divalent hydrocarbon group.

[0105] As used herein, the term "ether" refers to a divalent (ie, difunctional) group that includes at least one ether linkage (ie, -O-).

[0106] As used herein, the term "heteroaryl" refers to a monocyclic, bicyclic or tricyclic aromatic heterocyclic group containing one or more heteroatoms (e.g., 1 to 3 heteroatoms) selected from O, S and N in the ring. Heteroaryl groups include, but are not limited to, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, thienyl, furanyl, 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, benzofuranyl and indolyl. A heteroaryl group may be unsubstituted or substituted by one or more suitable substituents, preferably 1 to 5 suitable substituents, as defined above.

[0107] The term "hydrocarbon" as used herein describes a compound or radical consisting solely of the elements carbon and hydrogen.

[0108] The term "substantially amorphous" is defined as comprising no more than 20%, preferably no more than 10%, and more preferably no more than 2% crystalline content.

[0109] The term "substituted" means that in the group in question, at least one hydrogen atom bonded to a carbon atom is replaced by one or more substituents, such as hydroxyl (-OH), alkylthio, phosphino, amido (-CON(RA)(RB), wherein RA and RB are independently hydrogen, alkyl or aryl), amino (-N(RA)(RB), wherein RA and RB are independently hydrogen, alkyl or aryl), halide (fluorine, chlorine, bromine or iodine), silyl, nitro (-NO2), ether (-ORA, wherein RA is alkyl or aryl), ester (-OC(O)RA, wherein RA is alkyl or aryl), ketone (-C(O)RA, wherein RA is alkyl or aryl), heterocycle, etc. When the term "substituted" introduces or follows a list of possible substituent groups, the term is intended to apply to each member of the group. That is, the phrase "optionally substituted alkyl or aryl" should be interpreted as "optionally substituted alkyl or optionally substituted aryl". Likewise, the phrase "alkyl or aryl optionally substituted by fluorine" should be interpreted as "alkyl optionally substituted by fluorine or aryl optionally substituted by fluorine".

[0110] When introducing elements of the present invention or the preferred embodiments thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more elements. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements besides the listed elements.

[0111] From the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

[0112] As various changes could be made in the above products and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

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

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

3. The method of claim 2, wherein the dispersant comprises a nonionic surfactant.

4. The method according to claim 3, wherein the nonionic surfactant comprises 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, polyvinyl pyrrolidone, copolymers of polyvinyl alcohol and polyvinyl pyrrolidone, copolymers of (meth)acrylic acid and (meth)acrylates, or any combination thereof.

5. The method according to any one of claims 1 to 4, wherein the pH of the aqueous suspension is from about 9 to about 14.

6. The method of any one of claims 1 to 4, wherein the pH of the colloidal suspension is from about 5 to about 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. The method according to any one of claims 1 to 7, wherein the inorganic acid-releasing agent comprises tetraalkylammonium polyphosphate, potassium dihydrogen phosphate, potassium polymetaphosphate, sodium metaphosphate, borophosphate, aluminum phosphate, silicophosphate, sodium polyphosphate, potassium tripolyphosphate, sodium-potassium phosphate, or any combination thereof.

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, dehydrated silica gel, alumina, zeolite, clay, potassium permanganate, molecular sieves, or any combination thereof.

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

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

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

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

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

16. The method of any one of claims 1 to 15, wherein the disinfecting effective amount is in the range of about 0.08 ppm / minute to about 50 ppm / minute over a period of about 2 hours to about 72 hours.

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

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

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

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

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

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

23. A moisture activated powder which, when exposed to moisture, is capable of generating a controlled release of a disinfecting effective amount of chlorine dioxide from the powder without releasing detectable amounts of chlorine, chlorate and / or chlorite, said powder being prepared by the method of any one of claims 1 to 22.

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

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