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United States Patent [151 3,669,924 Daume Et A1 United States Patent [151 3,669,924 Daume et a1. [451 June 13, 1972 [54] STABILIZED POLYVINYL NITRATE [51] Int. Cl. ......................................................... ..C08l 1/92 AND PROCESS [58] ?eldofSearch ............................ ..260/9l.3 VA,45.9R [72] Inventors: Eduard Daume; Jurg Breitenmoser, both [56] References Cited of Zurich, Switzerland [73] Assignee: Werkzeugmaschinenfabrik Oerlikon-Buh UNITED STATES PATENTS rle AG, Zurich, Switzerland 2,118,487 5/1938 Burrows et al ....................... ..260/1 44 Filed: Sept. 11, 1969 [22] Primary Etaminer—.loseph L. Schofer [21] Appl. No.: 857,234 Assistant Examiner-Stanford M. Levin Att0rney--Wenderoth, Lind & Ponack [30] Foreign Application Priority Data [5 7] ABSTRACT Sept. 19, 1968 Switzerland ....................... .. 14042/68 A novel stabilized polyvinylnitrate and a process for the production thereof including the precipitation of the com [52] US. Cl. .............. ..260/45.9 R, 260/77.5 A, 260/78.4 R, pound from organic solutions containing same. 260/791, 260/913 VA, 260/942 R, 260/220, 149/88 12 Claims, No Drawings 3,669,924 1 2 STABILIZED POLYVINYL NITRATE AND PROCESS Polyvinylnitrate may be produced by nitration (esterifica tion) of polyvinyl alcohol with pure concentrated nitric acid The present invention relates to stabilized polyvinylnitrate or with a so-called mixed acid, consisting of concentrated (PVN), and to methods for producing same. nitric acid and concentrated sulfuric acid. Nitration (ester-iii In the development of fuels for rocket motors, it is en cation) is preferably carried out at 0° C. The polyvinyl nitrate deavored to produce fuel compositions which are as energy formed is thereby completely or partly soluble in the nitrating rich as possible, in order thereby to be ableto deliver large acid depending upon the selected excess thereof. After nitra payloads with small volumes of fuel. In the ?eld of solid-fuel tion, the product is precipitated in water. During this rockets, the so-called “double-base" fuels are mainly used to precipitation process, a considerable heat of dilution is this end. They consist essentially of a mixture of nitrocellulose produced, which causes the polyvinylnitrate precipitating in and nitroglycerine, to which additives are admixed for modify the water to coagulate. ing the combustion properties. Moreover, inorganic oxidizing Although the particle size of the polyvinyl nitrate formed agents such as ammonium perchlorate, ammonium nitrate as may be relatively well controlled according to the conditions well as metal powder may also be admixed to these fuels in of precipitation, an acid inclusion cannot be avoided. The order to increase the energy content thereof. Apart from the 15 conventional methods used in the explosives and fuel industry “double-base" fuels, the so-called “composite” fuels are also for washing out the nitration product formed and sub known, which are substantially based on the use of inorganic sequently treating with alkaline agents such as sodium bicar oxidizing agents with organic bonding agents. These bonding bonate or ammonium bicarbonate and the like, do not lead to agents are for example polybutadiene, polyurethane, polysul the target, since the included acid cannot be reached by the al tide, polyester and the like. The oxidizing agents are mixed 20 kalis. It was also proposed to treat the polyvinylnitrate with an with the still ?uid organic components for producing these alkaline solvent~water mixture and in this way to remove the fuels and are subsequently subjected to a curing process, this residual acid. Also, this method does not produce good stabili resulting in a solid resilient mass of predeterrninated fonn. ty values. Finally, it is known that it was attempted to dissolve Metal powder may also be added to these fuels in order to in the polyvinylnitrate in acetone and to reprecipitate the 25 crease the energy content thereof. lacquer solution after its neutralization in water. When using rockets for military purposes, it is in many cases In this way, good stability values may be obtained, but the necessary that the propellants burn without the formation of process is only to be carried out with considerable dilution and smoke. This property exists, in the conventional fuels, on the is therefore uneconomical. The precipitate coagulates at basis of nitrocellulose and nitroglycerine, and, in the com 30 higher concentrations. posite fuels, on ammonium nitrate. The limit of capacity, ex It is therefore an object of this invention to procure a new pressed as speci?c impulse, is about 230 to 240 seconds in the and improved process to prepare stabilized PVN from the double-base fuels, without the addition of ammonium crude product which may in turn be prepared by conventional perchlorate and metal powder. However, in order to obtain means. such capacities, a fairly high proportion of nitroglycerine is 35 It is a further object of the invention to produce a stabilized necessary, which causes the fuel already to begin to deform PVN having outstanding properties of purity and ability to be plastically when the ambient temperature is increased, this stored for comparatively long periods of time, substantially having a disadvantageous effect on combustion at high tem without decomposition. peratures. However, an addition of ammonium nitrate to the Finally, it is another object of the invention to develop solid double-base fuels does not bring a substantial increase in ener fuel compositions superior to the known ones for use as gy, so that this possible solution can only be applied in rare propellants in rocket motors. cases. Composite fuels based on ammonium nitrate are only It has now been found that pure and stabilized polyvinyl~ used for special purposes, e.g. for gas generators, since the nitrate, usually with a nitrogen content of more than 15 per adiabatic ?ame temperature is very low and therefore only cent (theoretical maximum value about 15.7 percent), can be speci?c impulses in the order of 160 to I80 seconds can be 45 produced from the raw, decomposable PVN. The new stabil achieved. All other fuels of the composite class produce a con ized polyvinylnitrate generally forms free ?owing, non caking siderable amount of smoke during combustion, which smoke powders which was not possible until now. is composed, according to the choice of the oxidizing agent, of Brie?y spoken, the process according to the invention com solid combustion products, e.g. potassium chloride, potassium prises the steps of oxide, sodium oxide and lithium chloride. When using am 50 a. providing a solution of raw acid containing polyvinyl monium perchlorate as oxidizing agent, gaseous hydrochloric nitrate in an organic solvent, acid is produced which forms heavy fumes particularly when b. neutralizing or rendering slightly alkaline said solution, the atmosphere is damp. The hydrochloric acid is also disad c. separating said solution from non-dissolved products of vantagous due to its corrosive effect on the ground installa’ the neutralization, tion. The addition of metal powder, in particular aluminum or 55 d. introducing said puri?ed solution of step (c) into a hot magnesium, also increases the formation of smoke since the precipitating bath in which said organic solvent is insolu corresponding metal oxides are produced during combustion. ble or only partially soluble, whereby said solvent is High-energy fuels which do not present these disadvantages stripped and stabilized polyvinylnitrate is of smoke formation and the corrosive effect on ground instal precipitated,and whereby the rate of introduction of said lations, may be produced, on the basis of the present inven 60 puri?ed solution corresponds to the stripping rate of said tion, from stabilized polyvinylnitrate. This purely synthetically solvent so that steady-state conditions are maintained, produceable material has good thermoplastic properties and and whereby a solvent is selected in step (a) the pure boil may be gelatinized with many organic nitric esters or other ing point of which or the azeotropic boiling point of known plasticizers. In this form, it is capable of absorbing which with the precipitating bath is below the boiling larger amounts of known explosives in pure or mixed form, 65 point of the pure precipitating bath. such as for example trimethylenetrinitroamine, nitropenta, As precipitating bath, either pure water or an aqueous trotyl or even ammonium nitrate. From such mixtures, propel medium which contains certain additives which are given lants may be formed, which deliver completely smoke-less hereinbelow by way of example, is preferably used. With combustion products and high speci?c impulses. aqueous precipitating baths, such solvents are preferably used Polyvinyl nitrate was already under consideration in the 70 in the PVN-solution which form with the water an azeotrope 40's as component in fuels and explosives, but its use in this with minimum boiling point, this usually being immediately ?eld has, up to the present, not been able to penetrate. The the case when using solvents which are not or only partially main disadvantage is stated to be the difficulty in the stabiliza miscible with water. Examples of such solvents are esters and tion process. PVN decomposes more or less quickly during ketones, such as ethyl and butyl acetate or methylethylketone storage and/or heating. 75 and methylisobutylketone. Ethyl acetate is preferred. 3,669,924 3 4 As PVN starting product, a direct product of nitration of continued. Then the stirring device is switched 05. The polyvinyl alcohol after precipitation with water, ?ltration and precipitated, stabilized PVN settles in the reaction vessel. The washing-out with water until neutrality is reached, is ad supernatant liquid is drawn off and replaced by the same vantageously used. This product can immediately be dissolved quantity of water. Thereupon, stirring is again continued for in humid state without drying, e.g. in ethylacetate. about 1 hour. Subsequently, the product is ?ltered off, washed One proceeds best by agitating the solution of the raw PVN and dried in vacuo.
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