United States Patent 19 11 Patent Number: 4,867,902 Russell 45 Date of Patent: Sep. 19, 1989

54 MICROENCAPSULATED 4,490,272 12/1984 Malafosse et al...... 252/186.43

GENERATORS ECE SEEmelect a . E. 75) Inventor: Donald H. Russell, Cherry Hill, N.J. 4,731,197 3/1988 Eckstein et al...... 252/186.32

73) Assignee:o Z-Gard,y Inc.,ay Kansas City, Mo 4,756,844 7/1988 Walles et al...... 252A186.32 X Primary Examiner-Brooks H. Hunt 21 Appl. No.: 172,731 Assistant Examiner-Virginia B. Caress 22 Filed: Mar. 23, 1988 Attorney, Agent, or Firm-Hedman, Gibson, Costigan & 51 Int. Cl...... A62D 9/00; CO1B 15/043 '" 52 U.S. C...... 252/186.32; 252/186.27; 57 ABSRACT 252/186.33; 25: 3592 An oxygen generating microencapsulated composition 58 Field of Search s 52/186 2. 186.32 includes an oxygen generating core material and a coat 252/18633,427M213.36: 428M402 24 ing which is water swellable. When exposed to water, oww. ow v. 8 the coating ruptures in an exfoliating manner, exposing 56 References Cited the core material to water and thereby generating oxy U.S. PATENT DOCUMENTS gen. The rate of oxygen release from the microcapsule can be controlled by altering wall continuity, thickness, 3,645,911 2/1972 Besauw ...... 252/186.33 3,691,090 9/1972 Kitajima et al...... 428/402.24 capsule diameter, and coating characteristics. In other 3,992,317 11/1976 Brichard et al...... 252/186.32 embodiments, combustion resistant materials are in 4,020,833 5/1977 Rind ...... 252/186.32 cluded in the wall material. 4,120,812 10/1978 Lutz ...... 252/186.32 4,178,351 12/1979 Klebe et al...... 252/186.32 30 Claims, No Drawings 4,867,902 1. 2 , which is expensive. Powdered MICROENCAPSULATED OXYGENGENERATORS superoxide reacts instantly and efficiently with water and does not crust, but its reaction rate cannot be con FIELD OF THE INVENTION trolled. The present invention relates to novel micro-encap 5 Attempts to solve the above-mentioned problems sulated formulations of oxygen generating compounds, which are inherent in these oxygen generating systems such as potassium and superoxide. The micro have been attempted in the prior art, but for the most encapsulation of these compounds provides products part these systems have been cumbersome and only with controllable reactivity which generate less exo partially effective. For instance, U.S. Pat. No. 3,574,561 thermic heat when mixed with water and which do not 10 (Nickerson et al.) discloses an improved technique for form carbonate crusts. controllably releasing oxygen from perox ide or superoxide by spraying water upward onto the BACKGROUND OF THE INVENTION chemical contained in a downwardly directed elon It is well known in the art to use alkali metal and gated cartridge, and providing for gravity escape of the alkaline earth metal peroxide and superoxide chemicals 15 sprayed water plus hydroxide product This apparatus as oxygen sources. Methods for releasing the oxygen allows the solid state chemical to be progressively dis have included introducing the chemical into a water solved, and avoids the cleaning problems caused by the containing reactor. For example, potassium superoxide formation of carbonate sludge. The released oxygen is is well known to react vigorously and almost instantly funneled into a delivery tube. with water to evolve heat and oxygen with potassium 20 It has now been surprisingly found that microencap hydroxide as the by-product. sulation of alkali , etc., in a water swellable Chemical source respirators and use two chemicals almost exclusively; namely potassium super capsule material provides particles with controllable (KO2) and anhydrous lithium hydroxide. In these reactivity which do not form carbonate crusts. In addi applications, moisture in the breath is used as the activa 25 tion, these microcapsules exhibit less exothermic heat tor. Both of these chemicals, which are in solid form, release when reacted with water, thus greatly reducing react with water exothermically to produce a hydrated the need for separate heat exchangers. The microcap metal hydroxide. LH does not liberate O2, but effec sule technique also can be used advantageously with tively absorbs CO2 in its hydrated form. It is limited to anhydrous lithium hydroxide to inhibit carbonate crust use in emergency rebreathers of short service life since 30 formation during CO2 absorption by the hydrate. no additional oxygen is provided. Potassium superoxide SUMMARY OF THE INVENTION reacts with water to produce oxygen and hydrated . In a second reaction, the hydrate In accordance with the above, the present invention absorbs respired CO2 to form a carbonate/bicarbonate relates to a microencapsulated composition comprising mixture. Surface-crusts of carbonate sludge are formed 35 (i) a core material comprising an oxygen generating with both of these chemicals due to agglomeration compound; and which interferes with continued water reaction and gas (ii) a coating comprising an acceptable wall-forming absorption. polymer which is swellable in water. Due-to the formation of the carbonate sludge, the In preferred embodiments, the core material com practical use of these chemical sources of oxygen has prises an alkali metal superoxide or peroxide, while the been shown to be inefficient. For instance, at high coating comprises any of a large number of polymeric breathing rates (where moisture and CO2 levels are very systems including blends and alloys suitable for capsule high) there can be a 30-to 40% efficiency loss due to wall materials. Preferably, the coating comprises ole crusting of carbonates sludge. In practice, the efficiency finic homopolymers or copolymers with vinyl com loss is compensated for by using large excesses of these 45 pounds, polyamides, polyurethanes, gelatins, starches, chemicals which is wasteful. In the case of potassium gums and the like. superoxide enough exotherm heat is created to require In other embodiments, the coating may be dispersed external heat exchangers on the potassium superoxide "it in a neutral solid diluent. cannisters. However, this requires bulky oversized The present invention also relates to microencapsu equipment. In addition, potassium superoxide is espe 50 lated oxygen generating compounds which are surface cially difficult to handle because its reaction with water coated with small amounts of hydrophobic materials in is extremely fast and uncontrollable. order to inhibit or slow the absorption of moisture by Because of the extremely rapid reaction of potassium the capsule. This surface coating may be used concur superoxide and the like with water, many uses require rently or in place of capsulation. that it be made into compressed briquette or blocks in 55 order to control the rate of reaction. The increased Other embodiments of the present invention include density of the potassium superoxide in briquette form providing a wall material for the oxygen generating slows the diffusion of moisture into the chemical and compound which is combusion resistant, i.e., fire retar extends the oxygen delivery time. dent or resistant. Water activated release of oxygen in For instance, chemical oxygen masks based on potas this type of wall materials may be accomplished by sium superoxide and the like use external cannisters including leachable water soluble salts, or by creating with heat exchangers to hold the chemical, which is controlled cracks in the wall material on curing or dry usually in the form of compacted blocks and arranged in ing In preferred embodiments, the combustion resistant a fashion that allows for air circulation. The cannisters wall material comprises ceramics, certain sol-gel com have to be remote from the breathing mask because of 65 positions, char forming phenolic resins, organic poly their size, weight, and heat output. The inherent disad mers having large amounts of heavy metals attached to vantages of this type of remote unit are obvious. These the polymer backbone, low melting silicates and bo units are cumbersome and wasteful of the potassium rates, mixtures of organic polymers with certain metal 4,867,902 3 4. and non-volatile halogen-containing composi the formed carbonate sludge is prevented. In addition, tions. the exotherm heat which is created by the reaction is much less than that created by the prior art methods and DETALED DESCRIPTION OF THE can be quickly dissipated. INVENTION Microcapsule rupture mechanism: It is believed that Encapsulation, and more specifically microencapsu absorbed moisture plasticizes the capsule wall material, lation, is a technique for producing controlled release and changes its physical properties from hard and tough delivery systems The capsule walls protect the core to soft and relatively weak. Water transport through the material from hostile environments, but can release the swollen walls to the reactive potassium superoxide par interior core under specific stimulus (heat, pressure, pH, 10 ticles is facilitated, and the oxygen generating reaction etc.). The release can be instantaneous or preferably at begins. Expanding oxygen inside the capsule ruptures a Constant rate. the capsule and the wall material folds back or exfoli Essentially, microencapsulation entails applying thin ates instead of fragmenting as expected. It is the physi coatings reproducibly to small particles of solids, drop cal properties of the water plasticized wall material that lets of liquids, or dispersions, thus forming microcap 5 allows retention of the broken capsules contiguously sules. This technique can be readily differentiated from with each particle of core chemical. Agglomeration and other coating methods in that the size of the particles crusting of the reaction debris is prevented by the pres which are to be coated range from severals tenths of a ence of these plastic buffers. micron to 5,000 microns in size. Controlled and uniform reaction rates are achieved ... The basic microencapsulation process used to pro 20 because the capsules exfoliate gradually, and the con duce the oxygen generating microcapsules of the pres tained cores emerge and react over an extended period ent invention involves three steps: (1) dispersion of the instead of suddenly. Conventional microcapsules rup core material in a continuous fluid; (2) precipitation of a ture by fragmentation (pressure and/or dissolution) and wall former (usually a polymer) onto the dispersed the total surfaces of the core and released immediately. phase with which it is non-reactive under dry condi 25 Since there is no means of shielding the core surfaces, tions; and (3) hardening of the polymer wall by appro reaction rate is uncontrolled and no mechanism for priate means. The encapsulated product is isolated and crusting prevention is available. Although capsules of dried to remove any volatiles. different dissolution rates can be used, the chemical The deposition of the liquid polymer around the core release would be in a series of bursts rather than by material occurs only if the polymer is absorbed at the 30 gradual reaction. interface formed between the core material and the Besides potassium superoxide, other chemicals that liquid vehicle phase. Moreover, the hardening of the release oxygen by reaction with water and which can be polymer wall may be accomplished by heat, crosslink microencapsulated and used alternatively are the alkali ing, or dissolution techniques. and alkaline earth metal , superoxides, triox The equipment required for microencapsulation of 35 ides, percarbonates, and permanganates, Moisture reac the oxygen generating compositions of the present in tive compounds that liberate gases other than oxygen vention is relatively simple. It consists of mainly of and which can be encapsulated are the alkali and alka jacketed tanks with variable speed agitators. However, line earth hydrides (hydrogen release) and carbides any of the well-known devices used in the art for micro (acetylene release). Ammonium salts of weak acids encapsulation may be used in the production of the 40 (carbonate or sulfide) will release ammonia. microcapsules of the present invention. Anhydrous lithium hydroxide (ALH) and the anhy In the microcapsules of the present invention, the drous oxides and hydroxides of alkali and alkaline earth core material is released under the stimulus of moisture. metals all form monohydrates with water and in this More particularly, the alkali metal superoxide, etc., form they become selective CO2 absorbers. In all cases microcapsules which are appropriately located in the 45 the CO2 reaction products form watery sludges that respirator or are exposed to moisture which agglomerate into crusts. The crusting inhibits further is generated by the user's respired air. This moisture is gas absorption and efficiency is reduced. ALH is the absorbed by the wall material of the microcapsule. The most effective CO2 absorber of this group and is used microcapsule wall material becomes softened and commercially in rebreathers, but it does not liberate swollen as increased amounts of moisture are absorbed. 50 oxygen. Additional moisture permeates the swollen wall and The oxygen generating compounds which are within begins to react with the core material. Eventually, tears the scope of the present invention include the alkali and in the capsule wall propagate and the wall is peeled alkaline earth oxides, peroxides, superoxides, hydrox back in an exfoliation manner to expose gradually in ides, percarbonates. In preferred embodiments, the oxy creasing amounts of the surface of the core material. 55 gen generating compound is potassium superoxide. Although the capsule walls peels back in this exfoliation A large number of polymeric systems, including manner, the capsule wall remnants do not fragment. blends and alloys, are suitable for the capsule wall mate Rather, the capsule wall remnants stay in place around rials of the present invention. The primary requirements the reacting core material and act as a shield or buffer for these polymeric systems are film forming capability against contact between exposed reactive particles. and controlled absorption and swelling in water. The The release rate from the microcapsules of the pres various polymer structures can be manipulated to ob ent invention can be controlled by altering wall conti tain desired features. nuity and thickness, capsule diameter, and polymer In particular, the polymeric wall materials may com characteristics. Those skilled in this technology can prise olefin copolymers with vinyl acetate, vinyl alco adjust these various parameters to achieve balances of 65 holderived from hydrolyzed vinyl acetate, acrylic acid, extended controlled release. In this manner, the ex methacrylic acid and their salts, the alkyl, hydroxy tremely rapid reaction of the alkali metal superoxide alkyl and amino alkyl, acrylic and methacrylic esters, with water can be slowed so that the agglomeration of maleic anhydride, maleate esters and maleate salts, vinyl 4,867,902 5 6 alkyl ethers, vinyl pyridine, vinyl pyrollidone, and vinyl The silica particles, which are much smaller (approxi sulfonic acid, its esters and salts, and the like. Suitable mately 0.1 microns) than the microcapsules, become olefins include ethylene, propylene, isobutylene, sty lodged in their surface interstices. A discontinuous silica rene, mixtures of any of the foregoing and the like. The layer is formed which inhibits or slows moisture uptake, polymeric wall material may also include homopoly but does not block it completely. It also acts as an anti mers of the vinyl monomers, acrylics, and maleic anhy blocking agent for possible microcapsule caking. dride systems mentioned above. Also suitable for use as It is also contemplated that the microcapsules of the polymeric wall materials are the anhydrous high molec present invention comprise an oxygen generating com ular weight (greater than 500 MW wt. av.) polymeric pound as a core material and a combustion resistant wall alkylene oxide polyols and alkoxy derivatives. An ex 10 material which also allows the core material to produce ample of these are the Carbowax polyols, available from oxygen at a controlled rate when the microcapsule is Union Carbide. Blends, alloys, and dispersions of the exposed to moisture. Combustion resistance for the above-named polymers with each other, or in neutral purposes of the present invention can mean completely solid diluents such as paraffin waxes are also suitable. non-flammable, decreased flammability, and/or self Other suitable polymeric wall materials include poly 15 amides and polyurethanes which have been modified extinguishing. for high hydrophilicity. When a non-flammable coating is desired, a number In addition to the above, gelatins, starches, natural of materials are suitable, including effective amounts of and synthetic gums and their chemically modified and ceramic or ceramic-organic cements, sol-gel composi /or cross-linked forms may also be used to comprise the 20 tions derived from alcoholates of Al, B, Si or Ti, and wall materials. metal rich cements of zinc oxide with certain terpenic As previously stated, microcapsules in accordance compounds such as zinc oxide/eugenol dental cement. with the present invention may generally range in size When decreased flammability is desired, effective from about several tenths of a micron to about 5000 amounts of char-forming phenolic resins which convert microns in diameter. In preferred embodiments, the 25 thermally to non-combustible structural carbon residues diameter of the microcapsules ranges from about 250 are suitable. Also suitable are organic polymers with microns to about 1000 microns. large amounts of heavy metals chemically attached to Another way of controlling the reactivity of the al the polymer backbone. Examples include copolymers kali metal superoxides and the like is by means of slow with acrylates and methacrylates of Zn, Zr, Fe, Ti, Sn release monolithic coatings or castings utilizing water 30 or W, or olefin-maleic anhydride adducts of the same soluble but chemically non-reactive binders. This metal series. Other compounds, such as intumescent method does not give uniform reactivity control and is agents, including low melting silicate and borate com useful only in less demanding applications. Typical pounds are also suitable. reactivity of the monolithic systems is non-linear and Self-extinguishing wall materials can be provided by decreasing step-wise as a function of binder solubility. 35 the addition of effective amounts of oxides known to The materials of choice are solid high molecular weight confer self-extinguishing properties to organic poly polyethylene glycols (PEGs) which are avaiable in a mers. Although many such metal oxides such as Zn, Sb range of molecular weights and degrees of water solu and Ti are suitable, alumina trihydrate is the preferred bility. These polyethylene glycols are also useful as oxide because it also liberates 3 moles of water on mod binders for moisture activated controlled release sys erate heating. Non-volatile halogen containing com tems, such as the microcapsules of the present inven pounds and polymers can also be used. However, these tion. Carbowax polymers, which are solid at room tem compounds present separate health hazards by the pro peratures and which are available in a range of molecu duction of halogen gases and vapors. lar weights and water solubilities are the PEGs of Water activated release of oxygen from the cores of choice. They are mutually compatible and can be 45 these combustion resistant materials is achieved by in blended to achieve desired properties. Thus, the car bowaxes may be used to control the degree of moisture cluding effective amounts of leachable water soluble sensitivity and rate of solution in water, since the hygro salts, such as sodium or potassium chlorides, carbonates scopicity and water solubility of carbowaxes decrease " or phosphates, or by selecting systems in which shrink with their increasing molecular weight. 50 age stresses create controlled defects or cracks through Blends of the carbowaxes with the alkali metal supe which moisture can be controllably absorbed on drying. roxides, etc., are made by first melting the glycols, stir DESCRIPTION OF THE PREFERRED ring in the powdered chemicals, casting coatings or EMBODIMENTS DETAILED layers, and then allowing them to resolidify at room temperature. The resulting products remain stable when 55 Specific embodiments of the present invention are stored in dry air. Although the polymeric glycols are taught in the following examples which are not limiting not reactive with the alkali metal superoxides, etc., they in any way. must first be thoroughly dehydrated to remove any EXAMPLE 1. V entrained water. The resulting mats or fabrics are use able as filters in breathing masks and provide slow re 60 Microcapsules were prepared using a core material lease of oxygen. comprised of potassium superoxide ground and sieved An additional means of controlling the rate of mois to specific particle sizes. The microcapsules which were ture absorption by the microcapsules of the present prepared by grinding commercial lump grade KO2 invention is to surface coat them with small amounts of (Aldrich Chemical Co.) to a powder in a mortar and hydrophobic grade colloidal silica. An example of such 65 pestle within a dry box with a dry N2 atmosphere, and is Cab-O-Sil(R)TS-720, available from Cabot Corp. The then seived to a nominal 20-24 mesh (0.84-1.0 mm.) for coating is accomplished by simple mechanical tumbling use in making microcapsules. A typical seive analysis of the dry blends of microcapsules and colloidal silica. WaS: 4,867,902 7 8 Final drying was done in a vacuum oven at RT for 36 hours. Tyler Screen No. % by retained Hydrolysis was estimated from spectrographic analy 12 0 sis of resin films at about 10-20% of the contained vinyl 14 2 acetate. 6 3.5 18 5 The hydrolysed resin was made into a 5% solution in 2O 43.5 dry toluene, and used to coat sized KO2 particles as in 24 39 Example 2. The resulting microcapsules had 78% core 28 6 material and a wall thickness of about 30 microns. When 32 1. 10 placed in water, oxygen release occurred over 8-9 min utes and demonstrated the increased water sensitivity of A 10% bw solution of Elvax 40W (60% the wall material. ethylene/40% vinyl acetate having a number average The microcapsules may be made in the size range of mol. wt. of about 80,000 and a melt index of 48-66 from about 10 to about 1000 microns by varying the decigram/min ASTM D 1238 (mod) was prepared in a 5 procedure set forth above. Examples 3-9 provide the solvent blend of 1/1 toluene/n-butanol as follows 50 measurements of seven different microcapsules having gms. of Elvax 40W (dried 24 hrs. in a vacuum dessica varying capsule diameters, wall thickness, and varying tor) were added to 500 ml of solvent (dried over mole amounts of oxygen generating core material, deter seives) in a 1 liter three-necked round bottom pyrex mined as a percentage by weight of the total weight of flask fitted with a stirrer, powder funnel, and a reflux 20 core material and wall material. The results are shown condenser through which a stream of dry N2 was intro in Table 1. duced. The mixture was heated to 50-60 C. with a Microscopic observations of the water wetted potas Glascol mantle and stirred until solution was com sium superoxide microcapsules exposed to human pleted. breath showed that the exfoliated capsule fragments The Elvax 40W solution maintained at 50-60' C. 25 prevented the agglomeration of the formed carbonate was transferred to the dry box and 10 gms of sized KO2 sludge. The microcapsules thus retained high levels of added slowly through the powder funnel with stirring oxygen release efficiency. maintained. After complete powder addition, stirring The unit weight and size of the capsules was low, and was continued for 5 minutes, and then the slurry was moisture and gas diffusion times were negligible. The allowed to settle. 30 exothermic heat produced by the reaction of the potas The supernatant liquid was decanted, the coated par sium superoxide and water was quickly dissipated. ticles transferred to a large heated Buchner funnel con As can be seen from the results provided in Table 1, taining a glass fiber filter sheet, and vacuum filtered to the microcapsules exposed and wetted by moisture from a damp condition. The particles had to be stirred in the human breath released the entire amount of oxygen funnel to prevent their adhesion to each other. A sol 35 generated by the reaction of the potassium superoxide vent hardening step was inserted prior to vacuum filtra and water over a range of from about 3 minutes to about tion to eliminate particle/particle adhesion. 40 minutes, depending upon the relative capsules diame The resulting capsules were free flowing, non-tacky, ter, wall thickness and percentage of potassium super and spherical with about 72% bw core KO2 and about oxide by weight as a percentage of the total weight of 36 micron wall thickness. When placed in RT water, 40 the microcapsule. In addition, substantially uniform oxygen release occurred over a period of 28-30 min (near zero order) oxygen release rates were attained. utes. Furthermore, these results show that both the rate and After removal of supernatant liquid as above, the duration of the oxygen production can be controlled by damp, coated particles were slurried-in 1 liter of naph manipulation of the encapsulation parameters. tha (mineral spirits) at RT for about 5 minutes to solvate 45 residual toluene/n-butanol and harden the coating. EXAMPLES 10-15 Vacuum filtration was done according to the procedure Microcapsules having the same composition as those supra, and final drying was done in a vacuum oven set forth in Examples 2-9 were prepared. Thereafter, (Napco Model 5851) at 60°C/100 mm Hg for 24 hours. the microcapsules were coated with colloidal silica by 50 mechanically tumbling a 50:50 dry blend of microcap EXAMPLES 2-9 sules and colloidal silica (Cab-O-Sil (R) TS-721) for 3-6 Example 1 was repeated using a 5.5% Elvax 40W minutes. Examples 10-12 had a capsule diameter, wall solution and yielded capsules with 84% core material thickness, and weight percentage of potassium superox and a 29 micron wall thickness. Oxygen was released ide similar to that of Example 1 prior to coating with the for 15-18 minutes when these capsules were put in RT 55 colliodal silica, while Examples 13-15 were similar to Water. Example 9. The amount of oxygen release upon expo A 2% solution of Elvax 40W in anhydrous methanol sure to moisture was measured. However, the percent was made by heating under reflux with stirring. Solid age of colloidal silica by weight of the total microcap NaOH was added to a level of 0.05gm/gm of resin in sule was varied between 0 (thereby approximating Ex solution. Heating and stirring under reflux was contin amples 9 and 11), 0.1 and 0.3 percent by weight 1. The ued for 3-4 hours. results are shown in Table 2. The partially hydrolysed resin was precipitated by As can be seen from the results obtained, the rate of pouring the alcohol solution into a large excess of cold oxygen release was slowed as the amount of colloidal water. The precipitate was washed with 10% HCl to silica coating was increased. remove residual base, and then washed with distilled water until the washings were neutral to pH paper. TABLE 1. OXYGEN RELEASE OF MICROCAPSULES HAVING 4,867,902 9 TABLE 1-continued A POTASSUMSUPEROXDE CORE WHEN EXPOSED TO WATER Example 3 4. 5 6 7 8 9 Capsule Diameter (microns) 250-1000 250-1000 250-1000 250 250 250-1000 250-500 Capsule Wall Thickness (microns), Av. 27.5-100 27.5-100 27.5-100 27.5 27.5 27.5-100 27.5-55 Potassium Superoxide 72 88 72 72 73 72 84 (percentage by weight) PERCENTAGE OXYGEN RELEASE ASA PERCENTAGE OF TOTAL Elapsed Time (minutes 0 0.5 14.8 65 20 16.4 42 60 11.4 .0 23.8 87 44 33.8 84, 88 17.9 2.0 39.7 96 80 53.2 95 90 27.5 3.0 100 95 40 61.7 100 88 100 100 44 60 77.6 100 60 8.0 71 10.0 90 78 12.0 83 14.0 92 20.0 100 96 40.0 100

TABLE 2 EFFECT OF ADDED COLLODIAL SILICAON OXYGEN RELEASE RATE FOR MICROCAPSULES WITH POTASSIUM SUPEROXIDE CORE - Example 10 1 12 13 14 15 Capsule Diameter (Microns) 250-1000 250-000 250-1000 250-500 250-500 250-500 Capsule Wall Thickness (Microns), Av. 27.5-100 27.5-100 27.5-100 27.5-55 27.5-55 27.5-55 Potassium Superoxide 72 72 72 84 84 84 (percentage by weight) Colloidal Silica Coating (percentage by weight) O 0,1 0.3 0 0. 0.3 PERCENTAGE OXYGEN RELEASE ASA PERCENTAGE OF TOTAL Elapsed Time (minutes) 1. 23.8 19 13 11.4 10.5 8 4. 61.7 53 46 44 36.5 28.5 10 90 78 66 78 56.8 46.8 14 91 79 92 80.8 70.8 Many variations of the present invention will suggest themselves to-those skilled in the art in light of the amides; polyurethanes modified for high hydrophilicity; above detailed description. For example, many other 40 and mixtures of any of the foregoing. oxygen generating compounds other than those specifi 3. A microencapsulated composition as defined in cally named herein are contemplated for use as core claim 1, wherein said component (ii) is a copolymer materials. In addition, many other polymeric or com comprising bustion resistant coating materials well known to those (a) an olefin selected from the group consisting of skilled in the art will be suitable for use as a wall mate 45 ethylene, propylene, isobutylene and styrene; and rial. Likewise, other coating materials having similar (b) a vinyl compound selected from the group con properties to colloidal silica may be substituted in its sisting of vinyl acetate, acrylic acid and meth place. Also, while the preferable size of the particles of acrylic acid and their salts, the alkyl, hydroxyalkyl core material to be microencapsulated are detailed and amino alkyl acrylic and methacrylic esters, herein, the size of these particles may not be critical to 50 maleic anhydride, maleate esters, maleate salts, obtain a controlled release system in other environ vinyl alcohol, vinyl alkyl ethers, vinyl pyridine, ments of use. Finally, the above detailed control sys vinyl pyrollidone, and vinyl sulfonic acid, esters tems may be applied to other water sensitive organic and salts. and inorganic compounds as a method of extending 4. A microencapsulated composition as defined in reactivities. All such obvious variations are within the 55 claim 2, wherein said component (ii) is further mixed full intended scope of the appended claims. with a neutral solid diluent. I claim: 5. A microencapsulated composition as defined in 1. A microencapsulated composition, comprising claim 3, wherein said component (ii) is further mixed (i) a core material comprising an oxygen generating with a neutral solid diluent. compound which is potassium superoxide; and 6. A microencapsulated composition as defined in (ii) a coating comprising an acceptable wall-forming claim 1, wherein said component (ii) comprises a cross water swellable polymer linked gelatin, starch, or natural or synthetic gum. 2. A microencapsulated composition as defined in 7. A microencapsulated composition as defined in claim 1, wherein said component (ii) comprises olefin claim 1, wherein said component (i) comprises a particle copolymers with vinyl compounds; homopolymers of 65 ranging in diameter from about 250 microns to 1000 vinyl monomers; anhydrous polymeric alkylene oxide microns. polyols and alkoxy derivatives having a molecular 8. A microencapsulated composition as defined in weight greater than 500; gelatins; starches; gums; poly claim 7, wherein said component (i) comprises from 4,867,902 11 12 about 72 to about 88 percent by weight of the total (i) a core material comprising an oxygen generating composition. compound which is potassium superoxide; and 9. A microencapsulated composition as defined in (ii) a coating comprising a combustion resistant com claim 1, wherein said component (ii) has a wall thick position which is sensitive to water. ness of from about 27 microns to about 100 microns. 22. A microencapsulated composition as defined in claim 21, wherein said component (ii) comprises ceram 10. A microencapsulated composition as defined in ics, ceramic-organic cements, sol-gel compositions de claim 1, further comprising rived from alcoholates of Al, B, Si, or Ti, metal rich (iii) a surface coating comprising a hydrophobic ma cements of zinc oxide or zinc superoxide in combination terial. 10 with a terpenic compound, char-forming phenolic res 11. A microencapsulated composition as defined in ins, organic polymers with large amounts of heavy claim 10, wherein said component (iii) is a hydrophobic metals attached chemically to the polymer backbone, colliodal silica. intumescent agents, mixtures of organic polymers and 12. A microencapsulated composition as defined in metal oxides, and non-volatile halogen-containing com claim 11, wherein said component (iii) comprises from 15 pounds and polymers. about 0.1 to about 0.3 percent by weight of the total 23. A microencapsulated composition as defined in composition. claim 21, wherein said component (ii) comprises an 13. A microencapsulated composition as defined in organic copolymer with acrylates and methacrylates, or claim 1, wherein said component (ii) comprises a solid olefin-maleic anhydride adducts of Zn, Zr, Fe, Ti, Snor dehydrated high molecular weight polyethylene glycol. 20 W. 14. A microencapsulated composition as defined in 24. A microencapsulated composition as defined in claim 1, wherein said component (ii) includes an effec claim 21, which includes an intumescent agent selected tive amount of a combustion resistant compound. from the group consisting of low melting silicate and 15. A microencapsulated composition as defined in borate compounds. claim 14, wherein said component (ii) comprises an 25 25. A microencapsulated composition as defined in organic copolymer with acrylates, methacrylates or claim 21, which includes a metal oxide selected from the olefin maleic anhydride adducts of Zn, Zr, Fe, Ti, Snor group consisting of alumina trihydrate, and the oxides W of Zn, Sb and Ti. 16. A microencapsulated composition as defined in 26. A microencapsulated composition as defined in 30 claim 21, wherein said component (ii) includes an effec claim 14, wherein said component (ii) comprises a mix tive amount of a leachable water soluble salt. ture of an organic polymer with an effective amount of 27. A microencapsulated composition as defined in a metal oxide. claim 26, wherein said leachable water soluble saltcom 17. A microencapsulated composition as defined in prises sodium or , carbonate orphos claim 16, wherein said metal oxide and oxides comprises 35 phate. alumina trihydrate, and oxides of Zn, Sb and Ti. 28. A microencapsulated composition as defined in 18. A microencapsulated composition as defined in claim 21, wherein shrinkage stresses are created in said claim 14, wherein said component (ii) includes an effec coating during curing and drying. tive ampunt of a leachable water soluble salt. 29. A microencapsulated composition as defined in 19. A microencapsulated composition as defined in 40 claim 1 which includes anhydrous lithium hydroxide claim 18, wherein said leachable water soluble salt com and potassium superoxide. prises sodium or potassium chloride, carbonate or phos 30. A microencapsulated composition as defined in phate. claim 1 which consists essentially of potassium superox 20. A microencapsulated composition as defined in ide, anhydrous lithium hydroxide and a coating which claim 14, wherein shrinkage stresses are created in said 45 consists essentially of a wall forming water swellable coating during curing and drying. polymer. 21. A microencapsulated composition comprising sk k k ck

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