US3597288A - Explosive containing nitrocellulose coated with an alkylated diphenyl amine and preparation thereof - Google Patents

Abstract

NITROCELLULOSE EXPLOSIVE CHARGES ARE PROVIDED WITH IMPROVED MOISTURE RESISTANCE BY TREATMENT WITH AN ALKYLATED DIPHENYL AMINE.

Description

United States Patent 3,597,288 EXPLOSIVE CONTAINING NITROCELLULOSE COATED WITH AN ALKYLATED DIPHENYL AMINE AND PREPARATION THEREOF Frederic C. Merriam, Danvers, Mass., assignor to USM Corporation, Boston, Mass. No Drawing. Filed May 15, 1969, Ser. No. 825,033 Int. Cl. C06b 19/02 US. Cl. 149-11 11 Claims ABSTRACT OF THE DISCLOSURE Nitrocellulose explosive charges are provided with improved moisture resistance by treatment with an alkylated diphenyl amine.

The present invention relates to explosive charges and more particularly to nitrocellulose explosive charges.

Nitrocellulose explosives are notoriously hydrophilic in nature. Under humid conditions nitrocellulose takes on directly about two percent of water and this may go as high as four percent. Then, in the usual situation where the charge is produced as a compacted mass of particles or fibers, the same charge may blot up as much as ten to twenty percent of dry Weight, taken into capillary spaces of the charge.

On taking on moisture or Water, which as indicated they do readily, even under humid air conditions, the ability of nitrocellulose charges to be ignited conveniently is interfered with, and ignition or'firing reliability is greatly lessened. This latter is a major concern where the charges are designed for use as propellants or, as sometimes re' ferred to, as low explosive charges. For ordinary commercial propellant usage, water resistance which protects firing reliability after a period of about an hour, exposure to moisture is acceptable, but nevertheless difiicult to obtain. For military and some commercial uses the time requirement so far as the moisture resistance is more stringent, with periods of 24 hours or greater moisture resistance being called for. l

Various attempts have been made to improve the moisture resistance of nitrocellulose explosive charges. Generally these have taken the form of coatings, the latter intended to include deposits, impregnants, etc. as well; most of which are waxes or polymeric in nature. And, while they have been successful in improving moisture resistance, these coatings have done so with the sacrifice of ignition ability and reduction in power output of the charges so coated. This is probably for the reason that the coating materials used are combustion resistant in nature under the ignition conditions ordinarily used. As a result, and, because of the amounts needed to be used to contribute the desired moisture resistance, residues are left on ignition which interfere particularly with repeated ignitions or firings, and as well cut down on power output of the charges so coated.

Accordingly, it is an object of the present invention to produce nitrocellulose explosive charges exhibiting improved moisture resistance.

Another object is to produce the indicated charges and to do so without significantly lessening ignition reliability and power output of those charges.

Those and other objects of the present invention are attained in an explosive charge exhibiting improved moisture resistance comprising a mass of nitrocellulose coated with an alkyl substituted diphenyl amine having the formula "Ice wherein R is a hydrogen or alkyl radical, R is an alkyl radical and the combination of R and R contains a total of 8 to 40 carbon atoms, the amine comprising about 0.1 to 5.0 weight percent based on the weight of nitrocellulose.

Nitrocellulose explosive charges are provided in various convenient sizes and shapes. In the case of propellant or low explosive charges they may be produced as caseless type pellets, pills, sheets, matrices or the like, and, as well they may be produced for cased type, cartridges, etc. Similarly, high explosive charges are provided in shapes and sizes as desired. Under any of those situations, it is necessary to produce charges of uniform nature at least insofar as energy output is concerned, and to do so in a safe manner. The latter has reference to the instability and dangers attendant to handling nitrocellulose explosives. As a result it is customary to produce specific explosive charges from nitrocellulose by a method which maintains the material wet during production, and accordingly in a relatively safe handling condition. In one convenient method for doing that the nitrocellulose in particulate form, that is, as fibers, fines, particles or the like is first provided as a slurry, suspension, sol or gel in water, and, incidentally, some solubilization may also take place. Various additives such as dye stuffs, stabilizers, fillers, binders, ignition and burning agents, as well as other treating agents such as those to improve water resistance, etc. may also be included. The system so obtained, with some dewatering optional, may be then directed into shaping or die cavities and pressed to partial dryness. Thereafter the charges so obtained are repressed and dried to final size and density. For convenience the present invention is described in relation to this method and particularly by treatment carried out on the nitrocellulose while in slurry or suspension form. However, the invention may be effected by other practices such as by treating a finished charge pellet, etc. by dipping, coating, spraying or other application of the alkylated diphenyl amine.

Nitrocellulose comes in various forms depending upon its explosive characteristics. The present invention is particularly attractive for use in providing water resistance to nitrocellulose of the low explosive type or use, or that which is designed for use in propellant charges. Nitrocellulose materials having a nitrogen content of 12 to 15 percent are well adapted for this. Also, as indicated previously, nitrocellulose in particulate form, and more specifically fiber or fibrous in nature is particularly well adapted for practice of the present invention.

In providing the nitrocellulose in suspension, about 2 to 20 weight percent, and more preferably about 5 to 12 weight percent of the particulate nitrocellulose may be used, together with water as the suspending medium. The resulting suspension may be also described as a slurry, and it may take the form of a so] or gel, or combination of both. In providing the suspension it is pre ferred that ambient temperatures be used. With increase in temperature, and at boiling, a slurry or suspension of smoother consistency may be obtained. However, in doing so the nitrocellulose becomes strongly acid. It is preferred to maintain the nitrocellulose at a pH of 5-8. When the nitrocellulose is more strongly on the acid side, difiiculty is met in acquiring good coating effect, while if it goes on the more strongly alkaline side decomposition of the nitrocellulose takes place.

In addition to nitrocellulose, the suspension may contain a number or additives, including dyestuifs, fillers such as carbon black; stabilizers such as diethyl diphenyl urea, hydroquinone monobenzyl ether; binders such as polyvinyl alcohol; as well as ignition and burning agents such as tricresyl phosphate, and others. It is preferred that the additives be kept below about 2.0 weight percent. Otherwise, they may interfere in an adverse manner, with the ignition reliability and power output of the explosive charges produced eventually from the subject nitrocellulose.

Moisture resistance of the nitrocellulose is obtained by coating with a specific class of alkyl substituted diphenyl amines. Those may be represented by the formula where R is either a hydrogen or an alkyl radical, R is an alkyl radical and the total number of carbons contained in the radicals R and R total 8 to 40 with the preferred total number ranging 10 to carbon atoms for those substituents. Monoalkylated diphenyl amines which may be used include monooctyl diphenyl amine; monononyl diphenyl amine; monodecyl diphenyl amine; monohendecyl diphenyl amine; monododecyl diphenyl amine; monotridecyl diphenyl amine; monopentadecyl diphenyl amine; monohexadecyl diphenyl amine; monooctadecyl diphenyl amine; monononadecyl diphenyl amine; etc. Dialkylated diphenyl amines which may be used include dibutyl diphenyl amine; diamyl diphenyl amine; dihexyl diphenyl amine; diheptyl diphenyl amine; dioctyl diphenyl amine; dinonyl diphenyl amine; didecyl diphenyl amine; dihendecyl diphenyl amine; dodecyl pentyl diphenyl amine; di(2-ethylhexyl)diphenyl amine; etc.

The preferred alkyl substituted diphenyl amines are dioctyl diphenyl amine; di(2-ethyl hexyl) diphenyl amine; dinonyl diphenyl amine; didodecyl diphenyl amine; etc. Water resistance so far as the period of time the nitrocellulose may be exposed to moisture increases with increase in the number of carbon atoms contained in the alkyl substituents. At the same time, however, energy output may be affected, and the desired effect required based on anticipated end use, environment of use, etc. must be taken into account in choosing the particular alkylated diphenyl amine, or mixture of same to be used on a given occasion.

The amount of alkylated diphenyl amine deposited or coated, which term or terms include impregnated as well, ranges about 0.1 to 5.0 weight percent on the nitrocellulose. A more preferred range is about 0.5 to 2.0 weight percent. Some variation may be exercised within the indicated ranges based on the choice of alkylated diphenyl amine and the amount of water resistance desired. The latter aspect will, of course, be governed to some extent by the conditions anticipated to be met in using the finished charges, storage time before use, etc.

The alkylated diphenyl amine is prepared as a solution and in that form is added to the nitrocellulose suspension, where it coats the nitrocellulose particles, or other forms of the same as are found there. The solution uses an organic solvent. Solvents for use include, for example, methanol, ethanol, propanol, as well as other alcohols, acetone and other ketones, methyl Cellosolve, ethyl Cellosolve, etc. Solvents which are somewhat miscible with water, and also convenient to remove after treatment are preferred as, for example, ethanol.

The concentration of alkylated diphenyl amine in solution preferably may range about 3 to 10 weight percent, with some variation based on the nature of the particular amine and solvent system used.

The solution of alkylated diphenyl amine is introduced directly into the nitrocellulose suspension. It is recommended that stirring of the mix be carried out carefully to minimize if not prevent entrapment of air in the mix. If air becomes entrapped, it attaches to the nitrocellulose particles, interfering with flow distribution of the amine and even with coating by the latter. In addition it causes the nitrocellulose particles to float or rise to the surface of the liquid medium, Whereas otherwise on becoming coated with amine the particles drop to the bottom of the water medium and may be conveniently separated as by decanting, etc. It is recommended then that stirring be carried out, but that it be done by keeping the stirring systems submerged, and avoiding vortexing in the mix.

When the coated nitrocellulose settles to the bottom, the upper liquid may be decanted to obtain preliminary separation. Thereafter the coated nitrocellulose may be washed, rinsed, provided in a further convenient slurry form and may be processed to produce charges, for example, propellant pellets, using for example, the methods and means disclosed in US. 3,430,532.

The nitrocellulose charge or charges obtained, for example, in the form of pellets, but in other convenient forms as well, exhibit improved moisture resistance. Further improvement in moisture resistance is desirable in instances where it is anticipated that the charges will be exposed to moisture for an extended period of time. One method of accomplishing this involves treating the coated nitrocellulose charges at elevated temperature. This involves exposing the charges to a temperature above about the melting point of the alkylated diphenyl amine used in coating the charge for a period sufficient to allow the coating to melt and form into a continuous film, which sets when the charge is allowed to cool. Taking a dioctyl diphenyl amine coated nitrocellulose charge in pellet form, for example, treatment at C. for a period of at least about 10 minutes is found to contribute improved moisture resistance.

The following example is included for the purpose of further illustrating the invention.

EXAMPLE I (A) Preparation of nitrocellulose suspension A washing solution is prepared constituting 10 liters of tap water to which is added 60 ml. of 0.1 weight percent sodium lauryl sulfate and 200 ml. of 0.1 weight percent potassium citrate.

One hundred grams (7 0 grams dry weight) of refrigerated, damp nitrocellulose are mixed into 2500 ml. of the washing solution using a closed mixer. Even mixing is carried out for 2 minutes. A milky slurry or suspension is obtained. This is then stirred into the remainder of the washing solution.

After standing for 1.5 to 2.0 hours most of the nitrocellulose settles to the bottom, in fibrous form. The top layer of hazy water is poured off leaving the bulk of the nitrocellulose in the bottom 625-750 ml. The latter is rewashed by stirring in 5.0 liters of water, at room temperature containing 50 ml. of 0.1 weight percent potassium citrate. The fibrous nitrocellulose is allowed to settle to 500 ml. in 2-4 hours, and again the hazy top water is poured oif.

The concentrated, non-flowable, washed fiber slurry or suspension is increased to 1250 ml. by addition with stirring, of distilled water. The result is a slurry or suspension containing 5.6 weight percent solids of fibrous nitrocellulose.

(B) Treatment of nitrocellulose/suspension Two hundred and fifty ml. of the washed fibrous nitrocellulose suspension from pragraph A above is charged into a Waring Blendor. With the motor operating at reduced speed, 4 ml. of warm ethanol solution containing 0.17 gram of dioctyl diphenyl amine is quickly charged or poured into the stirring solution. At the same time a coloring charge of 4.0 ml. of ethanol containing 0.03 grams of National Oil Brown M and 0.03 gram of National Oil Brown Y is poured into the suspension. Stirring is continued for 15 minutes or until the dioctyl diphenyl amine has deposited on the nitrocellulose fibers. Stirring is done slowly and with care to prevent vortexing of the mix, which in turn would allow air to become entrapped in the mix.

The treated nitrocellulose suspension is vacuum filtered at 6 in. Hg using two Whatman No. 19.0 cm. filter papers,

in a Buchner funnel. It is noted that about 220 ml. of water are removed in 15 seconds.

The cake, of coated, fibrous nitrocellulose is air dried between paper towels, in relative darkness, for 24 hours. The amount of dioctyl diphenyl amine pickup is calculated to be 1.3% on dry weight of the nitrocellulose.

The procedure is repeated, withthe exception that the dioctyl diphenyl amine is substituted for by other diphenyl amine materials. The various products obtained are as follows.

Table I Nitrocellulose/ designation: Treating agent B1 Dioctyl diphenyl amine. B2 Monooctadecyl diphenyl amine. B3 Monononyl diphenyl amine. B4 Monooctyl diphenyl amine. -B5 Diphenyl amine.

(C) Preparation of nitrocellulose charges/pellets A number of samples from each of the nitrocellulose materials produced according to paragraph B above are provided in the form of propellant charge pellets.

The samples are each weighed out to .16 gram, and placed in a covered die having a cylindrical die cavity to provide a pellet having in each instance a diameter of .338 inch and a length of 0.072 inch. The pellets are pressed in the die using a laboratory press having a 1.875 inch ram, hand pump and Marsh Type 1 Master Gauge (0-3000 p.s.i.). Pressing is carried out at 1200 p.s.i. The pellets so obtained have a density of about 1.52 grams/ml.

(D) Moisture resistance testing Various of the pellets produced according to pragraph C above are subjected to moisture resistance testing.

Covered glass dishes are used which are 2.0 inches in diameter and 1.2 inches deep. A wet paper towel is placed over the inside bottom of the dishes and the pellets are then stationed on end on the wet paper. The atmospheres in the glass dishes are maintained saturated. After a period of two hours the pellets are removed, excess water wiped off and they are transferred to glass weighing bottles, and weighed for a second time to arrive at the water pickup.

The results obtained as a result of two hours exposure to the testing conditions are as follows.

Table II Nitrocellulose Moisture pickup/hrs. (2) material: percent on dry weight As indicated in Table II, nitrocellulose treated with the alkylated diphenyl amines of the present invention (B1 and B4) show unexpected improvement in moisture resistance characteristics.

(E) Firing testing/ energy output/reliability Nitrocellulose pellets produced according to paragraph C above are subjected to the moisture conditions set forth in paragraph D above for a period of 2 hours.

The pellets are then used in a Model AP300 tool to fire 1.0 inch x inch diameter drive pins into a Type 300 cast aluminum plate 1.0 inch in thickness.

The relative energy output of the pellets then may be assessed based on the depth to which the fasteners are driven into the plate. The depth is average depth on number of actual firings out of five attempts.

The reliability of the firing may be assessed in the number or percentage of firings v. misfirings had, in this case five attempts are used.

In the case of B5 there is slow burning in four out of five attempts. However, the slow burning does not amount to firing suflicient to drive the fasteners to the exte nt that they make any penetration into the test plate.

When dry control pellets based on formula B3 are tested they fire 5/5 and their average penetration into the test plate is 18.0 mm.

The results of Table III indicate that the nitrocellulose charges produced in accordance with the present invention (Bl-B4) exhibit improved moisture resistance, while nonetheless retaining good firing characteristics, both from the standpoint of energy output and firing percentage.

As indicated previously, the moisture resistance of nitrocellulose charges produced with the use of the sponsored alkylated diphenyl amines, may be further improved by subjecting the charges to a later heat treatment.

(P) Heat treatment of nitrocellulose charges TABLE IV Moisture pickup percent on dry weight Nitrocellulose pellet material 4 hours 8 hours 24 hours B1 (not heat treated) 2. 77 3. 58 4. 59 B1 (heat treated) 2.49 2. 92 3. 79

The results set forth in Table IV indicate a definite advantage in moisture resistance is obtained from the heat treatment.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above coating or impregnating method and in the nitrocellulose explosive charges set forth without departing from the scope of the inven tion, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

1. An explosive charge exhibiting improved moisture resistance comprising a mass of particulate nitrocellulose coated with an alkyl substitute diphenyl amine having the formula wherein the R is hydrogen or alkyl radical and R is an alkyl radical and the combination of R and R contains a total of 8 to 40 carbon atoms, the amine comprising 0.1 to 5.0 weight percent on weight of the nitrocellulose.

2. An explosive charge according to claim 1 wherein the combination of R and R contains a total of 10 to 20 carbon atoms.

3. An explosive charge according to claim 1 wherein the nitrocellulose is in compacted form.

4. An explosive charge according to claim 1 wherein the alkyl substituted diphenyl amine is dioctyl diphenyl amine.

5. A method for providing an explosive charge having improved moisture resistance, which comprises the steps of providing a suspension of nitrocellulose in particulate form in water, adding to the suspension a solution of alkyl substituted diphenyl amine having the formula:

wherein R is hydrogen or alkyl radical, R is an alkyl radical and the combination of R and R contains a total of 8 to 40 carbon atoms in organic solvent to coat the nitrocellulose with the said amine and thereafter separating coated nitrocellulose from the water.

6. A method according to claim wherein the coated nitrocellulose after separation from the water is heated above about the melting point of the amine.

7. A method according to claim 5 wherein the suspension contains about 2 to 20 weight percent of nitrocellulose.

References Cited UNITED STATES PATENTS 1,329,211 1/1920 Snelling et al. 14911 1,329,212 1/1920 Snelling et al. 149-11X 2,033,217 3/1936 Woodbridge 149-11 2,123,517 7/1938 Woodbridge 14911 2,125,941 8/1938 Matter 149--11X 3,303,073 2/1967 Graham et a1. 14911X 3,138,496 6/1964 Monical 149-11 CARL D. QUARFORTH, Primary Examiner S. J. LECHERT, 1a., Assistant Examiner US. Cl. X.R. 14994,