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 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 (esterifica tion) of with pure concentrated 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 produced, which causes the polyvinylnitrate precipitating in and nitroglycerine, to which additives are admixed for modify the water to coagulate. ing the 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 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 ~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 and to reprecipitate the 25 crease the energy content thereof. lacquer 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 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 . 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 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. with an aqueous solution of an alkaline agent, e.g. NaOH, A polyvinylnitrate puri?ed in this way, produced from NaHCOa or NazCQq or other alkali metal hydroxides, car polyvinyl alcohol with a saponi?cation number of 99 mole %, bonates or bicarbonates until neutralization or weak basicity is to which 0.5 percent 2-nitrodiphenylamine were added, is reached, this necessitating considerable amounts of the al thermally stable and satis?es for example the Heat-Test ac kaline agent, according to the residual acid content which was included in the PVN particles. cording to US-MIL-Standard at 120° C. in 65 min., at l34.5° C. in 25 min. and the Abel-Test at 80° C. in 40 min. The term “weakly basizity" or “slightly alkaline” as used The nitrogen content of such a product, determined accord herein is to be understood as comprising pH values in the range of about 7 to about 9, preferably between about 7 and ing to the Dumas method, gives 15.5 percent and corresponds about 8.5. to the theoretical value in which the saponi?cation number of When neutralization is ?nished, the neutralized or slightly the starting product and the proportion of stabilizer are taken alkaline PVN solution is separated from the salts formed, i.e. into account. generally from the alkali-nitrates or their solution, if an aque This product has an explosion heat of 909 cal/g and a com ous neutralizing solution was used. To this end, the solution is 20 bustion heat of 2,963 cal/g. generally allowed to stand and the separation of the salts or The process according to the present invention is further il the salt solution is awaited. The separation usually occurs by lustrated by the following non-limiting Examples. All parts are itself after a short time, the supernatant PVN solution has by weight unless otherwise stated. clari?ed and may be drawn off for further processing. If it ap pears advantageous, the PVN solution may be subjected to a 25 EXAMPLE 1 post-sedimentation, e. g. by centrifugation. 20.4 parts of crude humid polyvinylnitrate, produced by the From the beginning, such solutions are generally used which nitration (ester-ification) of a polyvinylalcohol with a saponi? are good to process. For neutralization, a 20 percent by weight cation number of about 99 mole % and an approximate solution of PVN in ethyl acetate is for example particularly 30 molecular weight of 100,000 (“Mowiol N 90-99” sold by suitable. The content of the solutions will vary depending Farbwerke Hoechst AG), subsequent dilution with water and upon the molecular weight or viscosity of the crude PVN. Too filtration (water content about 50 percent by weight) were strongly diluted solutions represent volumes which are dif dissolved in 40.8 parts of ethyl acetate. (The crude product ficult to handle, while too concentrated solutions are very contains nitrating acid still included therein. It would there viscous and are dif?cult to neutralize. 35 For further processing of the solution, i.e. for the precipita fore be senseless to determine the nitrogen content.) tion of the solutes, the solution may be diluted after The solution obtained was mixed, with stirring, with a 5 per neutralization. cent by weight aqueous solution of NaHCO3, until the CO2 Solutions which are more diluted than those described evolution had stopped and the mixture had a pH-value of 7 to 7.5. To this end, 1.5 parts of the NaHCOa solution were neces above generally produce purer products. After dilution, the 40 solid content of the solution is advantageously assayed, e.g. by sary. After the mixture had been allowed to stand for 20 evaporating a sample until it is dry. Before precipitation, a sta minutes, two layers had formed. The upper organic layer was bilizer for the PVN may be added to the solution, preferably 2 separated off. 1.0 parts thereof were dried in vacuo, and the nitrodiphenylamine; however, the process according to the residue amounted to 0.2 parts. The neutralized PVN solution present invention mainly consists in a stabilization by purify 45 was therefore still 20 percent by weight. By the addition of 50 ing the PVN. parts of ethyl acetate, an about 10 percent by weight PVN The precipitating bath used consists, in the simplest case, of solution was produced. 0.05 parts of Z-nitrodiphenylamine water. However, it has proved advantageous if the precipitat were added to this solution. ing bath contains certain additives which increase the quality, A four-necked, round-bottomed ?ask with distilling at i.e. in particular the stability, of the precipitating PVN. Also 50 tachment and cooler, thermometer, dropping funnel and coming into question in particular are surface active agents, agitator is charged with 100 parts of an aqueous solution, preferably such of anion-active nature, e.g. the sodium salt of which contains 1 part of disodium dodecyldiphenyloxide disulfonated dodecyldiphenyloxide; electrolytes, e.g. sodium disulfonate, 2.5 parts of sodium sulfate, 0.4 parts of sodium sulfate; pH regulators, preferably for adjusting or maintaining bicarbonate, 2 parts of bone glue and 5 parts of ethyl acetate. slightly basic conditions, e.g. sodium bicarbonate; protective 55 The agitator (vibrator-mixer) is set into action and the ?ask is colloids, e.g. bone glue, etc. If the PVN solution contains a sol heated until the contents thereof are boiling (about 71° C.). vent or solvent mixture which is partially miscible with water, Immediately after the beginning of boiling, the above it is recommended to saturate the precipitating bath with this described PVN solution is made to drop in. Heating of the solvent or mixture or to add so much to these liquids that satu ?ask and speed of feed-in are regulated so that the liquid level ration practically occurs at precipitation temperature. In this 60 in the ?ask remains practically constant. About 20 parts of an case, the boiling temperature of such a precipitating bath cor responds to the temperature at which the continuous ethylacetate-water azeotrope with about 92 percent precipitating process proceeds. ethylacetate and 8 percent water distil per hour with a vapor The precipitating bath is preferably strongly stirred at least temperature of about 71° C. The precipitation of PVN is to be during the introduction of the PVN solution, perhaps with the 65 observed in the ?ask. After 5 hours, the dropping in of the aid of a vibrator-mixer. In this way, a uniform and ?ne PVN solution is stopped and distillation is continued until the precipitation is obtained. vapor temperature has risen to 100° C.; there are no more It has proved advantageous to strip o?‘ about one-?fth of the noteworthy amounts of ethyl acetate in the distillate. The con PVN solvent used per hour. After the end of the feed-in of the tents of the ?ask are cooled, while being stirred, to 25° C., the PVN solution, stripping is generally continued until the vapor agitator device is switched off and the precipitated PVN is al temperature has risen by about 25° - 30°, in order to be sure lowed to settle. The supernatant liquid is drawn off and that practically all solvent has been stripped off. replaced by 100 parts of de-ionized water. Stirring is con Further processing may be undertaken in any way. One tinued for 1 hour at room temperature, and the product is generally proceeds in the following manner: The precipitating drawn off, washed with water and dried in vacuo. Yield: 9.4 bath is allowed to come to room temperature, agitation being 75 parts of PVN (about 94 percent of the amount used). 3,669,924 5 6 EXAMPLE 2 EXAMPLE 4 Components, percent by 26.0 parts of crude, humid polyvinylnitrate, produced by weight the nitration (esteri?cation) of a polyvinylalcohol. with a -~ aA~r~ W — - - r — 'l‘v, L, (l . l’VN AN ll'l‘N ° K. golr. (lnw. saponification number of about 98 mole % and an approxi 5 mate molecular weight of 41,000 (“Mowiol N 50-98" sold by 35 50 1.5 2,785.3 245. l 240. l 42 ‘l0 l8 2,701’). 7 2.15.3 2401 Hoechst AG), subsequent dilution with water and ?ltration 60 30 10 2,773. l 245. 8 240.3 (water content about 40 percent), were dissolved in 36.4 parts of methylethylketone. The solution obtained was mixed, with EXAMPLE 5 stirring, in a 5 percent by weight aqueous NaHCOa solution, 10 until the CO, stopped forming and the mixture had a pH-value Components, percent by weight In, of 7. To this end, 2.5 parts of the NaHCOa solution were —————»— ‘ ~~ —~ - (ll. necessary. After the mixture was left to stand for 2 minutes, PVN AN l’hN (lvw. two phases were formed. The upper organic phase was 40 40 20 35 50 15 separated off. 2.0 parts thereof were dried in vacuo. The 15 ‘28 (i0 12 residue amounted to 0.6 parts. The neutralized PVN-solution 30 (i0 10

EXAMPLE 6 Components, percent by weight 1‘100, Stability 6| PVN PETN RDX AN HTN Russ Pb.St. 7L min/s it 120° C ;I.,'t111.3 10 l 1 0. 4'2 12. 5 240’ l. 645 10 l 1 0. 52 12. 4 230' 1.614 10 1 1 U. 78 11.0 150’ 1. 551 In the above examples of application the abbreviations signify: parts of methylethylketone, a 15 percent by weight PVN solu PVN: Polyvinlynitrate, stabilized tion was produced. 0.075 parts of 2-nitrodiphenylamine were according to the invention added to this solution. PETN: Pentraerythritoltetranitrate A four-necked round—bottomed ?ask with distillating at (Nitropenta) 30 HTN: Hexanetrinitrate tachment and cooler, thermometer, dropping funnel and AN: Ammonium nitrate agitator is charged with 100 parts of an aqueous solution PDN: Pentanedinitrate which contains 1 part of disodium dodecyldiphenyloxydisul RDX: Trimethylenetrinitroamine fonate, 2.5 parts of sodium sulfate, 0.4 parts of sodium bicar (hexogen) Pb.St.: Lead stearate bonate, 2 parts of bone glue and 5 parts of methylethylketone. 35 Tc: Adiabatic combustion chamber The agitator (vibrator-mixer) is set into action and the ?ask is temperature heated until the contents thereof are boiling (about 74° C). 1,, gefr.: speci?c impulse in seconds for isentropic solidi?ed immediately after the beginning of boiling, the above expansion described PVN solution is made to drop in. Heating of the 1,, Gl.Gew.: speci?c pulse in seconds for flask and rate of feed-in are controlled so that the liquid level 40 isentropic equilibrium in the ?ask remains practically constant. About 20 parts of a expansion of an ideal gas n: Pressure exponent of the methylethylketone-water azeotrope with about 88 percent combustion MEK and 12 percent water are stripped per hour with a vapor '100: Combustion rate at lOO kg/cm2 temperature of about 74° C. The precipitation of PVN is to be pressure observed in the ?ask. After 5 hours, the dropping in of the 45 4 : density PVN-solution is stopped and distillation is continued until the What we claim is: vapor temperature has risen to 100° C.: there are no more noteworthy amounts of MEK in the distillate. The contents of l. A process for preparing a stabilized polyvinylnitrate from the ?ask are cooled, while being stirred, to 25° C., the agitator a crude starting material, comprising the steps of device is switched off and the precipitated PVN is allowed to 50 a. providing a solution of raw acid containing polyvinyl settle. The supernatant liquid is drawn off and replaced by 100 nitrate in an organic solvent, parts of de-salted water. Stirring is continued for 1 hour at b. neutralizing or rendering slightly alkaline said solution, c. separating said solution from non-dissolved products of room temperature, and the product is drawn o?‘, washed with water and dried in vacuo. Yield: 14.4 parts of PVN (about 96 the neutralization, and percent of the amount used). 55 d. introducing said puri?ed solution of step (c) into a hot Theoretically, water, as outer phase, may be replaced by aqueous precipitating bath in which said organic solvent another liquid compound in which PVN is not soluble. Suita is insoluble or only partially soluble, whereby said solvent ble solvents which form the inner phase with the dissolved is stripped and stabilized polyvinylnitrate is precipitated, PVN, should not or only partly be soluble in the outer phase. and whereby the rate of introduction of said puri?ed solu Their boiling point must be lower than that of the outer phase. 60 tion corresponds to the stripping rate of said solvent so The following examples illustrate the use of the stabilized that steady-state conditions are maintained, and whereby PVN, obtained according to the present invention, in fuels. a solvent is selected in step (a) the pure boiling point of The parts are by weight. which or the azeotropic boiling point of which with the precipitating bath is below the boiling point of the pure 65 precipitating bath. EXAMPLE 3 2. A process as in claim 1 in which step (b) is carried out by Components, percent by using an aqueous neutralizing solution of an alkali metal weight In hydroxide, bicarbonate or carbonate. -——— ———— —-—-~~—~— Te, 18, G1. PVN PE'I‘N HTN ° K. gefr. Gcw 3. A process as in claim 1 in which step (b) is carried out by 70 using an aqueous neutralizing solution of NaHCO,,. 59. 5 30 10. 5 2, 082. 5 251. 5 245. 2 51 40 i). 0 3, 058. 6 253.0 245. ‘I 4. A process as in claim 1 in which in step (a) a solvent is 42.5 50 7. 5 3,146.‘) 254.1 245. b used selected from the group comprising an ester and a ketone 25 50 25 3,103. l 253. 8 245. (l 35 50 15 3,128. 2 254. 0 245. 8 at most partially miscible with water. 75 5. A process as in claim 1 in which in step (a) ethyl acetate is used as a solvent. 3,669,924 7 8 6. A process as in claim 1 further comprising the step of group consistirvifoTelectrolytes, protection colloids and pH diluting the solutions of step (b) with the same solvent as used regulators. in step ( a)_ 10. A process as in claim 1 in which an aqueous precipitat 7. A process as in claim 1 in which a solution of about 20 ing bath is used in step (d) which has been previously satu parts by weight of crude polyvinylnitrate in about 80 parts by rated with the organic solvent of step (a) in the range between weight of ethyl acetate is prepared in step (a), and further normal room temperature and the azeotropic boiling point. comprising the dilution of the neutralized solution of step (b) 11. A process as in claim 1, further comprising the step of with ethyl acetate to a concentration of about 10 percent by vigorously agitating the precipitating bath of step ((1) during weight of polyvinyl nitrate. and after the precipitating period. 8. A process as in claim 1, further comprising the step of ad 12. A process as in claim 1, further comprising the step of ding to said solution after step (c) 2-nitrodiphenylamine as a continuing stripping off the solvent in step (d) after the feed of stabilizing agent. said polyvinylnitrate solution has been stopped until said 9. A process as in claim 1 in which the precipitating bath of precipitating bath is substantially solvent free. step (d) is selected from the group comprising pure water and an aqueous medium containing at least one additive of the 15 4! * * IF it

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