US 2707695 A
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Patented May 3, 1%55 COMPOSITION CQMPRESING CYANE OR DI- CYANDIAMEE FOR FQRMENG AEROSOLS AND METHGD 0F MAKENG SAME Armand Jean Courtier, Mention, France, assignor to Socrete Anonyme des Manufactures ties Glaces ct Produits ghrnnques de Saint-Gobain, Chaney & Cirey, Paris,
rance No Drawing. Application May 23, 1951, Serial No. 227,945
5 Claims. (Cl. 167---li) gants which are projected into the surrounding atmossphere at substantial velocity by the volatilization of a propellant. Within the term fumigant is included insecticides, fungicides, bacteriacides, and smudges for the protection of orchards from frost. Standard fumigants are employed in the processes and DDT (dichlorodiphenyltrichloroethane) and hexachlorocyclohexane, being frequently found in standard aerosol solutions, are used herein for exemplary purposes, but it is to be understood that they are merely representative of fumigants in general and that they do not constitute a limitation.
The standard method of forming an aerosol is to dissolve or suspend a fumigant such as DDT in a compressed liquid which vaporizes at ordinary temperature, the compressed liquid being retained in a metal bomb provided with an atomizer, the aerosol being formed by vaporization when the atomizer is opened to the air and penetrating rapidly throughout the space toward which the atomizer is directed. it has also been proposed in British Patent No. 584,853 to impregnate paper or other absorbent, combustible material with an insecticide and then to disseminate the insecticide by burning the paper. In the same British patent, it is proposed to also impregnate the paper with a free burning salt such as potassium nitrate to enhance the combustibility of the impregnated paper.
The two methods thus outlined, one involving the atomization of a liquid and the other the combustion of a solid, are both useful but have inherent limitations which it is an object of this invention to avoid. The liquid method involves the use of a heavy metal bomb capable of withstanding whatever internal pressures are generated therein, the use of an atomizer'which,being of fine workmanship is costly, and occasionally gets out of order, and the use of an expensive carrier liquid. In the use of solid material impregnated with the insecticide,
combustion has always been involved, making its use undesirable under many circumstances where flame would entail risk; the burning destroys a substantial percent of the insecticide and reduces the eifectiveness of the application, and mere combustion is a very ineffective way of attempting to spread an insecticide. The imperfection of combustion has been realized and an attempt has been made in United States Patent No. 2,440,082 to carry out the combustion in a very special way, flamelessly and at lower temperature, but still involving the oxidation reaction that is the characteristic of combustion. Regardless of the method of combustion employed, the efiective range of the burning is small and not comparable to the range of the atomizer.
It is an object of this invention to propagate a fumigant by a new method which does not involve combustion or the use of a liquified, confined gas.
Another object is to prepare a new solid composition of matter capable of forming an aerosol.
Another object of the invention is to prepare a soiid of the type described which is capable of limited use so that the formation of the aerosol may be started and finished at the will of the user and which need not proceed to completion once it has started.
Another object of the invention is to propagate the fumigant out of a solid as an aerosol at material velocity so that the aerosol will be driven to a considerable distance and widely disseminated as though by an explosion.
The objects of the invention are accomplished, generally speaking, by a composition of matter containing the fumigant, such as DDT, and, as impellant, cyanamide or dicyandiamide. When this composition is made up as a powder, or as a solid stick or pellet and heated, the cyanamide or dicyandiamide decomposes violently, at a temperature below that at which the fumigant decomposes, the decomposition is exothermic, facilitating the further decomposition and the fumigant is impelled in all directions at material velocity, in very fine aerosol form that penetrates even the tiniest cracks and crannies and remains suspended for long periods. At the same time the aerosol is comparatively heavy, does not dissipate itself rapidly upward, as in the case of combustion type compositions, but remain sufiiciently close to the ground and persists so long that it is capable of being used not only as an insecticide but as a smudge for the protection of orchards and growing crops against frosts.
The processes and the compositions that constitute this invention overcome the disadvantages and accomplish the advantages which are indicated hereinabove and hereinafter. In its preferred form, the invention contemplates mixing the fumigant with cyanamide and/ or dicyandiarnide, and raising the mixture to a temperature sufficient to decompose the propellant. When the cyanamide and dicyandiamide are thus heated they decompose violently and exothermically, acting as a propellant for the fumigant. This decomposition is accompanied by the release of great quantities of fumes; it is a very complex reaction which appears to involve not only decomposition but also polymerization. It has been shown by the applicant that under these conditions substantially all of the dispersed fumigant is transformed to an aerosol, the losses of fumigant inherent in combustion type reactions being substantially eliminated. Inasmuch as those losses were particularly grave in the case of DDT and hexachlorocyclohexane, materially reducing the effectiveness of their aerosols, the invention is of material value as it permits the maintenance of higher concentrations of fumigant in aerosols.
Under some circumstances, applicant has discovered that it is advantageous to include in the fumigant composition a compound capable of generating internal heat within the composition and to this end the composition may include a selected proportion of ammonium nitrate, or of the following compounds: hydrazine nitrate, methylarnine nitrate, ethylamine nitrate and other volatile amine nitrates. Ammonium nitrate being very useful, is employed for purposes of illustration in the following examples.
The usual aerosol forming fumigants are all useful in this invention, the following examples being based upon the use of DDT and hexachlorocyclohexane, and
Example 1 10 grams of DDT are crushed with 25 grams of crystallized cyanamide. The mixture is placed in a metal box of 250 cc. capacity which is placed over an alcohol lamp in an enclosure containing about 64 cubic meters of space. After 1 minute of heating, the exact temperature of which was not determined, a violent reaction occurred, fumes were produced in abundance and were projected from the box into surrounding space, heating was continued until, after about minutes, the release of fumes ended. The following eifects were observed:
a. A screen cage containing 60 insects (drosophiles) was left for minutes in the enclosure. The insects were severely attacked by the aerosol. Thirty minutes after having been withdrawn from their 15 minutes exposure in the chamber, they had all fallen onto the bottom of the cage and after an hour none of them could move more than their feet.
b. To measure the action of the aerosol on the walls of the chamber, a dozen filter paper discs of about .6 square decimeter surface area were applied to the walls. The discs were in contact with the atmosphere for minutes. They were then withdrawn and each one was placed in a glass box with two crickets. After two days, half of the crickets were dead.
c. To measure the yield of the dispersion 800 liters of the gas in the enclosure was removed shortly after the dispersion and passed across the surface of a piece of blotting paper having one square decirneter of surface, 3 minutes being required for the passage. The paper was then digested in boiling alcoholic potash of half normal concentration. This solution was neutralized with nitric acid and the chlorine was titrated by the method of Volhard. The titration showed the presence of a quantity of chlorine corresponding to 112 mgrs. of DDT, which corresponds to 9 grms. of this insecticide within the 64 cubic meters of the enclosure, compared to the 10 grms. which was in the cartridge that was disintegrated by heat in the enclosure. Thus, 90% of the DDT was in the state of an aerosol, no computation being made for that which had adhered to the walls of the container.
d. The size of the particles in the atmosphere of the enclosure 8 minutes after the dispersion was measured as follows: at 50 cm. from the bottom of the enclosure there was vertically disposed a microscope object glass which was placed between two electrodes 3 cm. apart. For 8 seconds a tension of 10,0000 volts was maintained between the two electrodes. The object glass was then examined under a microscope with an enlargement of 500X. There were only two spots having an apparent diameter above 5 mm, about spots of about 3 mm., and several hundred spots having a diameter less than 2 mm. The quasitotal of particles therefore possessed an actual diameter positively less than 5 microns. This explains the stability of the aerosol, which remained in suspension for many hours.
Example 2 Following the method set forth in Example 1, the same tests were carried out using the following mixture:
10 grms. of DDT l0 grms. of crystallized cyanamide l0 grms. of ammonium nitrate The results were similar to those in Example 1 except that all the insects (drosophiles) were dead, as well as of the crickets. The particles deposited on the object glass had the same dimensions as in Example 1.
Example 3 Operating in the same way but with a mixture of 8 grms. of dicyandiamide and 10 grms. of DDT, the titration of the insecticide showed that only 4 grms. had been dispersed, no crickets died, but the insects had fallen to earth after 2 hours. The yield was not as favorable, which is attributed to the fact that the transformation of dicyandiamide is less exothermic than that of cyanamide. It was therefore concluded to be advantageous to boost the heat output of dicyandiamide by adding some ammonium nitrate to the composition.
Example 4 Example 5 10 grins. of commercial hexachlorocyclohexane were pulverized with 20 grms. of dicyandiamide. The mixture was poured into an iron box of 400 cubic centimeters capacity and heated over a gas flame in an enclosure of about 64 cubic meters capacity. After 2 minutes of heating there was a liberal yield of fumes which yield continued for 2 minutes. On the wall of the enclosure there had been vertically applied a dozen discs of filter paper having about .6 square decimeters of surface. These discs were left in contact with the atmosphere of the enclosure for 10 minutes and each was then put in the glass boxes with two crickets. In 24 hours all of the crickets were dead.
Example 6 Operating as in Example 5 but with 10 grms. of hexachlorocyclohexane, 1O grms. of ammonium nitrate and 10 grms. of dicyandiamide it was found that the results were analogous to those of Example 5.
Example 7 Operating as in Example 5 and 6 with a mixture of 10 grms. of hexachlorocyclohexane and 20 grms. of crystallized dicyandiamide, the results were the same as in the preceding examples.
In a particular phase of the invention, the fumigant composition is made up as a dense solid under the form of cartridges or pencils, which are even more useful than the powders described hereinabove. This is particularly valuable when dicyandiamide is mixed with ammonium nitrate and an insecticide. This result is obtained easily by melting the insecticide with a mixture of dicyandiamide and ammonium nitrate. The dicyandiamide and ammonium nitrate being in the relative proportion of between and 30% by weight of dicyandiamide to 25 to 70% by weight of ammonium nitrate. The melted mass forms two layers which are easily emulsified by agitation and which can be solidified by cooling the emulsion. The emulsion persists during and after solidification, no decantation is necessary and the final product is a solid which is compact and contains the insecticide in a state of fine dispersion in the solidified emulsion. Dicyandiamide and ammonium nitrate, the applicant has discovered, formed an eutectic mixture having a minimum fusion point at about 112 C., this eutectic contains 66 parts by weight of ammonium nitrate to 34 parts by weight of dicyandiamide.
It is advantageous in preparing cartridges or pencils of aerosol forming type to choose a mixture which approaches the composition of the eutectic closely in order to carry out the fusion at the lowest possible temperature. The invention is not limited to the use of a mixture of dicyandiamide and nitrate of ammonium having the composition of an eutectic but it is advantageous not to pass the proportion of 70% by weight of ammonium nitrate because the mixture would then risk, at the moment of the formation of the aerosol by heat, decomposition by combustion, and flames would partially destroy the insecticide. At the other end of the range, the emulsion of dicyandiamide and ammonium nitrate melts at a temperature which is higher as the content of ammonium nitrate is the less. it is not recommended to use less than 25% of the ammonium nitrate in such compositions.
The emulsified liquid mixture of fumigant, cyanamide and/ or dicyandiamide, with or without ammonium nitrate, may be cooled in molds of any desired shape, for instance, shaped as pencils which can be consumed progressively and to any desired extent, beginning at one end. The
solidified emulsion is hydroscopic but it may be protected against humidity by enclosing'it in a moisture proofing composition such as varnish, wax, including parafline, and moisture proof paper. Parafli'ne is particularly advantageous if a small quantity, molten, is maintained in the mold before pouring in the molten fumigant. The paraffine will completely cover the preparation, which can then be cooled, solidifying both the emulsion and the paraffine. The parafline facilitates the removal from the mold, preventing sticking. The following examples illustrate this phase of the invention:
Example 8 in a heated mixer is placed kg. of DDT, 13.3 kg. of ammonium nitrate, 6.7 kg. of dicyandiamide, which is mixed together until the temperature of the mixture reaches about 120 C. at which time a liquid emulsion has been formed. In the meantime cylindrical molds of 5 cm. diameter and 5 cm. of length have been prepared and heated and supplied with 1 to 2 centimeters of melted paraffine. The emulsion is poured into the molds, the molds are cooled, the parafline having in the meantime completely covered the emulsion. When the cylinders have solidified, they are removed and each cylinder weighs about 150 grms. 130 such cylinders were made from this batch. One of these cylinders was used to destroy the flies in a stable. The cylinder was placed in an iron box open at the top, and having a capacity of about 2 liters which was heated by a 500 watt electric resistor heater. After a quarter of an hour of heating, the whole cylinder was transformed to an aerosol and, the stable having been closed in advance, expanded into every crevice. All the flies were knocked down and after 2 hours not one fly was flying in the stable.
Example 9 Into a heated mixer there were placed 10 kg. of hexachlorocyclohexane, 13.3 kg. of ammonium nitrate and 6.7 kg. of dicyandiamide. The mixture was raised to 120 with agitation, forming an emulsion which was molded as in Example 8, forming 130 cylinders of 5 cm. diameter and 5 cm. height. 70 of these were placed in a receptacle of 80 cm. diameter and 80 cm. height which was supported on a tripod and heated by an alcohol lamp. A tripod was placed in a vineyard having an area of one hectare. The heating began at 4 a. m. in the month of May in a calm atmosphere. 4 liters of alcohol were consumed by the burner in transforming the cartridge to aerosol, the transformation being completed in a half hour. The insecticide fumes persisted in the vinyard until 6:30 a. m. The larvae of cochylis and of pyrales which were active on the young vines were destroyed.
Example 10 In a mixer there was placed 10 kg. of 1, 2, 4, 5, 6, 7, 8, 8, octochloro 4, 7, methano 3a, 7, 4, 7a tetrahydroindane, 12 kg. of ammonium nitrate and 8 kg. of dicyandiamide. The mixture was heated to about 120 after mixing and molded to produce pencils of 1 cm. diameter and .8 cm. thickness. These pencils were fed into an apparatus which delivered them at about 10 a minute to a receptacle heated by an alcohol lamp. The fumes which were released were conducted by a relief pipe to a blowing machine. The whole apparatus was mounted on a carriage capable of being moved around a field; the blowing machine comprised a fan between the fume generator and a nozzle which could be directed toward growing plants, the fan being driven by gears from the wheels of the carriage to destroy the harmful insects in the field (doryphores). 2,000 of these cartridges were employed per hectare.
Example 11 In order to protect the vines of a vineyard against spring frosts, it was suflicient to decompose 10 kg. of any of the cyanamide to be used is very variable compositions hereinabove per hectare, in boxes scattered throughout the vineyard. The aerosols obtained from these cartridges or pencils were so dense and persisted so long that they successfully prevented frost damage.
The following theory is advanced to account for the success of the invention, but it is to be understoood that the applicant is not bound by the theory: Most organic insecticides decompose below their boiling point under atmospheric pressure and they cannot be vaporized under that pressure and ordinary conditions. On the other hand these insecticides in liquid state are little or not at all soluble in cyanamide or dicyandiamide. The mass of cyanamide or dicyandiamide containing the insecticides may, at the moment of reaction, be assimilated in a mixture of two liquids that are not miscible with each other. In submitting such mixtures to what is generally called an entrainment in vapor, it is possible to distill their constituents under atmospheric pressure at a lower temperature than their point of ebullition at this pressure. It may be supposed that it is this process, involving the violent exothermic reaction of decomposition of cyanamide or dicyandiamide which entrains the insecticide and propels it as an aerosol.
The excellent yield of aerosol may be explained by the fact that the maximum temperature reached in the mass during the exothermic transformation is constantly int'erior to the temperature of the decomposition of the insecticide. On the other hand, the vaporized insecticide is found in unstable equilibrium, its vapor temperature being at original temperature much less than atmospheric pressure. It therefore condenses immediately and it is possible that the dispersion thus obtained from such a vapor is much finer than can be attained by mechanical pulverization of the insecticide or by distribution in a liquid.
The advantages of the invention include the following: The operation does not present any danger because the gases formed are not combustible, the reaction of decomposition is easily started and it suflices to keep the compositions over a small flame to produce, in a very short time, the eruption of fumes charged with fumigant as an aerosol, which remain tenuously, without rapid dispersion, near the location of their generation. No special apparatus is required for the invention. The quantity of but the applicant has observed that the best results are obtained when that quantity is on the order of 1 part by weight for 1 part of the propellant. In the case of insecticides, one may use a larger proportion of cyanamide and dicyandiamide be cause these products have an aggressive action on the chitinous tissues of insects and assist the penetration of the insecticide.
As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.
What is claimed is:
1. The method of making a fumigant cartridge that comprises melting a thermally vaporizable fumigant with ammonium nitrate and dicyandiamide in a proportion of 75-30% by weight of dicyandiamide and 25-70% by weight of ammonium nitrate relatively, the remainder to make 100% being mainly composed of the fumigant, emulsifying the mass by agitation thereof, and solidifying it.
2. An aerosol forming composition of matter comprising at least 40 parts by weight of a thermally vaporizable insecticide and 100 parts of a mixture including between and 25 parts by weight of ammonium nitrate and 30 and parts, by weight, respectively, selected from the group consisting of cyanamide and dicyandiamide.
3. An aerosol forming composition of matter consisting essentially of a thermally vaporizable fumigant, at least one of the group consisting of dicyandiamide and cyanamide, and ammonium nitrate, in proportions that require the continuous application of heat to sustain decomposition to aerosol form, the ammonium nitrate not being present in over about 66.5% of the combined weight of the ammonium nitrate and the members of said group.
4. An aerosol forming composition of matter consisting in its essential constituents of a thermally vaporizable fumigant, at least one of the group consisting of dicyandiamide and cyanamide, and ammonium nitrate, in proportions that require the continuous application of heat to sustain decomposition to aerosol form, the ammonium nitrate not being present in over about 66.5% to 70% of the weight of the ammonium nitrate and said one combined, the ammonium nitrate being present in an amount less than about one-half the total weight of the composition.
5. An aerosol forming composition of matter consisting essentially of a thermally vaporizable fumigant, at least one member of the group consisting of cyanamide and 8 dicyandiamide, and ammonium nitrate, the members of said group preferably being present in quantity about equal to that of said fumigant, and the ammonium nitrate being less than about 70% of the combined weight of the members of said group and the ammonium nitrate.
References Cited in the file of this patent UNITED STATES PATENTS 792,511 Frank June 13, 1905 2,409,111 Davis Q. Oct. 8, 1946 2,434,872 Taylor Jan. 20, 1948 2,440,082 Flanders Apr. 20, 1948 2,455,205 Whetstone Nov. 30, 1948 2,557,814 Dinsdale June 19, 1951 2,578,858 Taylor Dec. 18, 1951 2,590,054 Taylor Mar. 18, 1952 FOREIGN PATENTS 305,567 Germany Dec. 10, 1919