US3376175A - Prereaction of binders for quickmix processing of propellants - Google Patents

Description

April 2, 1968 R. D. SHEELINE 3,376,175

PREREACTION OF BINDERS FOR QUICKMIX PROCESSING OF PRQPELLANTS Filed April 18, 1965 Y h s O c S V SOLUBILITY SOLUBILI TY I OR VISCOSITY TIME CURATIVE TANK PRE-POLYMER TANK INVENTOR.

E N L E E H s D L L A D N A R United States Patent PREREACTION 0F BINDERS FOR QUICKMIX PROCESSING OF PROPELLANTS Randall D. Sheeline, Woodland Hills, Califi, assignor to North American Rockwell Corporation, a corporation of Delaware Filed Apr. 18, 1963, Ser. No. 274,021

2 Claims. (Cl. 149-19) This invention relates to an improvement in a process for dispersing solids in polymeric binder materials. More particularly, the invention relates to a process for reducing the solubility of materials in an inert carrier utilized in a process for dispersing solids in polymeric binder materials.

InUnited States Patent No. 3,022,149, there is described a process for the manufacturing of polymers containing substantially uniformly dispersed solid materials therein. The process broadly provides at least one dispersion of non-solvent polymerizable materials and non-solvent reactant materials in a non-reactive liquid dispersion media, and at least one dispersion of filling substances in nonsolvent and non-reactive liquid dispersion media, the dispersion mediums being mutually miscible, mixing the dispersions together, permitting the dispersed materials and the dispersed substances to coalesce and form an agglutinate to substantially uniformly disperse filling substances in the polymerizable materials. Curing agents, catalysts and other ingredients besides the filling substances can be added to produce certain compositions. The mass may then be cured at ambient or elevated temperatures to provide a plastic polymer with dispersed solid material therein.

While the method described in the aforementioned patent may be performed as a batch process, it is preferred to carry out the process in a continuous manner which eliminates the requirement for mechanical agitation to insure thorough mixing of the polymer and the solid being dispersed therein. This is accomplished by bringing separate streams of the polymeric materials and solid dispersions together into a common stream and effecting mixing by the turbulence set up at the point at which the two streams join. One method of accomplishing this is by metering a flow of one dispersion into a stream of the other dispersion as it is conducted from the dispersion container to a receiving vessel through a pipe or other appropriate channel.

Another method of mixing is by bringing two channels of separate dispersions together and allow mixing to be aflFected by the turbulence set up at the point of junction of the two channels. The proportions in which the two dispersions are combined is controlled by regulating the rate of feeding the separate components into their respective dispersing containers from where they flow into the channels.

The vehicles which are used as the dispersion mediums must be non-solvent with respect to the dispersed substances. The same medium may be used for both the polymeric material and the solid substances or conversely different vehicles or dispersion mediums may be employed for the polymer and the solid components. It is required only that the dispersion mediums for the two types of components be non-reactive to eitherthe polymeric substances or the solid material and that the mediums employed for each of the polymeric and solid components be mutually miscible. It has-been found, however, that a problem arises with regard to the solubility of some normally-utilized binder materials in the available dispersion mediums for the process. Any of the binder material that solubilizes in a dispersion medium will not react to form the desired product, thus it is desirable that as high a percentage of insolubility be reached as possible. Of course it is desired that the binder material approach 100 percent insolubility in the carrier.

Thus, it is an object of this invention to provide a method for decreasing the solubility of a binder and curative material in a liquid carrier.

A further object of this invention is to provide a novel apparatus for accomplishing a reduction in solubility of a binder and curvative material in a liquid carrier.

Normally, in the process involved, curing agents or catalysts are added in minor amounts to the dispersions. Some curing catalysts normally possess a high solubility in the carriers utilized and it is desirable to reduce this solubility. It has been discovered, and as a result thereof forms the basis of this invention, that the solubility in the carrier material of the prepolymer and curing agent can be greatly and unexpectedly reduced by their partial reaction prior to introduction into the process without increasing the viscosity beyond the point that the product is no longer castable.

It is believed that the invention will be further understood from the following description together with the drawings in which:

FIG. 1 represents a plot of viscosity or solubility versus time for the reaction of a hypothetical prepolymer and curing agent,

FIG. 2 represents the schematic outline of the system for the prereaction of the binder and curative agent utilized,

FIG. 3 is a cross-sectional view of the mixing portion of the prereactive device utilized,

FIG. 4 taken along lines 44 of FIG. 3 shows a mixing plate utilized in the pre-reactor device.

Among the polymeric binder materials that are used in the process and which form the basis for the pre-reaction of this invention, substances such as polymerized di-(thioethoxy) methylene, silicone polymers and rubbers of the type described in a text, Chemistry of the Silicones by E. G. Rochow, 2nd ed. (1951), published by John Wiley and Sons, Incorporated, New York. An example of a silicone polymer is a silicone gum obtained by heating a hydrolysate of a mixture of mol percent dirnethyldichlorosilane and 10 mol percent of diphenyldichlorosilane in the presence of a small amount of iron chloride. The composition is subjected to heating only for a period of time suflicient to obtain a viscous liquid. Another polymer material that can be used is an epoxy compound such as a product as obtained by the reaction of a mole of 2,2- bis(4-hydroxyphenyl)-propane with one or more mols of epichlorohydrine in the presence of a base such as sodium hydroxide. This gives a glycidyl' polyether having terminal epoxy groups. Another example of a polymeric material is a polyurethane material such as a co-polymer of polypropyleneglycol and toluene diisocyanate. Other examples of the polymeric materials utilized are the telechelic polymers such as carboxy-terminated linear polybutadiene. Further materials include hydrocarbon saturated and unsaturated resins such as the co-polymer of butadiene and acrylic acid, materials such as nitrocellulose and nitramine. Additionally, high nitrogen binders can be utilized such as polyvinyl tetrazole, polyethylene hydrazine, triaminoguanidine azide reacted with aldehyde, diamino tetrazene reacted with formaldehyde. Also fluoropolymers of the a,a,w-trihydrofluoroalkyl acrylate esters and nitroso rubbers. Other resins and polymeric substances can be used and will be apparent to those skilled in the art.

Non-limiting examples of catalysts used for curing purposes are aluminum chloride, bis-tri-methylsilyl borate and benzoylperoxide. Other well known curvatives such as MAPO which is tris I-(Z-methyl)-aziridinyl]phosphine oxide and PAPI which is polymethylene, polyphenylisocyanate are additional examples of the curative materials that are contemplated. The curatives are added in amounts of 0.1 to about 10 weight percent based on the weight of the polymer resin or elastomer. Preferably, 0.1 to 6 weight percent of the curative is utilized.

The vehicles which are used as dispersion mediums are those which are generally non-solvent with respect to the dispersed substances as previously described. Examples of these dispersion mediums or carriers which are employed include aliphatic and olefinic hydrocarbons having about 3 to about 16 carbon atoms. Examples of these are propane, butane, hexane, heptane, particularly n-heptane, octane, dodecane and hexadecane as well as 2-octene, 1- dodecene, l-hexadecene, etc. Examples of cyclic hydrocarbons are cyclohexane, rnethylcyclohexane, etc. Examples of aromatic and alkyl aromatic compounds which are employed as dispersion mediums include compounds having from 1 to about 16 carbon atoms such as benzene, toluene, zylene, 2,4-dipentabenzene, phenyldecane, decalin, l-hexyldecalin, etc. Halogen derivatives of the above hydrocarbons are also employed as dispersion mediums. Examples of these include ethylenedichloride, trichloroethylene, methylenedichloride, chlorobenzene, bromobenzene, iodobenzene. Compounds of the Freon type such as dichlorodifiuoromethane and dichlorotetrafluoroethane, etc. may also be employed.

Other possible dispersion mediums are alcohols having from 1 to about 12 carbon atoms and from 1 to about 3 hydroxyl groups. Examples of these are methyl alcohol, ethyl alcohol, benzyl alcohol, glycerin, dodecyl alcohol, etc. The means may also be used which have from about 2 to about 12 carbon atoms and from 1 to about 3 nitrogen atoms. These include such compounds as ethylene diamine, diethylene, triamine, dodecylamine, pyridine, etc. Ethers, ketones, aldehydes and esters having from about 2 to about 16 carbon atoms are also used. Examples of these are ethyl ether, acetone, propiona'ldehyde, ethyl acetate, butyldodecanoate, butylcellosolve, etc. Obviously other materials may be used as the carrier providing that they are non-reactive with the binder or curative material and that the binder and curative material are relatively insoluble therein.

The concept of this invention is illustratively seen in the chart plotted in FIG. 1. It has been found that as the reaction time at a particular temperature between a hypothetical prepolymer and curing agent increases, the solubility will decrease while the viscosity will increase. If the prereaction is allowed to progress for a time ranging between time A and time B, a marked decrease in solubility is obtained without too great an increase in viscosity. It is to be pointed out that the simple graph FIG. 1 is merely illustrative and is not sealed for values of solubility and viscosity. It is the purpose of this invention to pro-react the curative and binder material to a time of reaction between the theoretical points A and B such that the solubility in the carrier greatly decreases while the viscosity of the product of the reaction has not reached such a point where it can not be carried in the overall continuous process involved.

The overall system for affecting the desired result of this invention is shown in FIG. 2 wherein a heated prepolymer tank and a curative tank are disposed in relation to gear pumps or feeders 13 which feed the polymer and curative respectively into the pre-reactive section 14. The reactive portion of the pre-reactor 14 is jacketed with a cylindrical casing 15 which has an inlet 16 and outlet 17 through which hot water or steam is passed when needed to cause a sufficient pre-reaction of the two materials utilized. From the pre-reactor the pre-reacted polymers and curative pass into the mixer section 18 where it is combined with filling substances in dispersion mediums being emitted from lines 19 and 20. The resultant slurry then leaves the mixer from line 21. Alternative to that shown the pre-reacted material may be first formed in a separate dispersion prior to entering the mixer.

Reference is now made to FIG. 3, particularly disclosing the pre-reactor portion of the device utilized to effect the desired results of this invention. The feed line 11 from the curative storage tank enters the housing 22 for the pre-reactor and extends concentrically therein. The feed line 12 from the prepolymer storage tank terminates at the housing 22 for the pre-reactor at a point intermediate of the disposed length of the curative feed line 11 within the pre-reactor housing 22. The curative material is emitted from the feed line 11 through a plurality of radial apertures 23 situated adjacent its closed end within the pre-reactor housing 22. Upon leaving the apertures 23, the curative begins its mixing with a prepolymer material that substantially fills the pre-reactor housing 22. A plurality of plates 24 are placed downstream from the terminal end of the polymer feed line 11 within the easing 22, three being shown by way of example. These plates, as shown in FIG. 4, are provided with a plurality of apertures 25 therein, such apertures shown by way of example in FIG. 4 particularly. The function of a plate within the housing is to accomplish good mixing of the curative with the polymer material as it passes through the heated pre-reactor. This mixing being affected by the passage of the polymer and curative through the succeeding apertures in each plate. For ready access, the plates 24 are secured within the housing 22 with standard fittings such as those available for use with AN tubing wherein tube 22 is in section held together by AN fittings and containing plates 24 (not shown).

Example To clearly illustrate this invention, a carboxy terminated linear polybutadiene, which is a commonly used prepolymer, was mixed in a conventional carrier using the described process. The carrier was isopropyl alcohol. To illustrate the solubility of the prepolymer, 20 grams thereof was stirred in a beaker in grams of isopropyl alcohol for five minutes. The beaker was maintained in a F. bath. After completion of the stirring, the alcohol was decanted from the beaker and analyzed for nonvolatiles which would, of course, be the prepolymer. It was found that 0.4 gram of the prepolymer had solubilized in the alcohol carrier material. However, the curative MAP0 and isopropyl alcohol are essentially completely soluble in each other. A common binder composition consists of these two materials in the ratio of 19.4 parts of prepolymer and 0.6 part of curative. When 19.4 grams of prepolymer and 0.6 gram of MAP0 curative were mixed with isopropyl alcohol at 140 F., all the MAP0 and 0.4 gram of the prepolymer dissolved in the alcohol carrier. This clearly would indicate that the MAPO, which is a highlydesirable curative, could not be feasibly used in the overall process since it would not react with the binder material if it were all in a state of solubility in the alcohol carrier. To prove the feasibility of the invention, the prepolymer and the curative MAPO were then metered in a 19.4:0.6 ratio into the pre-reactor device previously described. The jacket temperature was maintained at 240 F. with a residual time of four minutes in the reacting device and then mixed with isopropyl alcohol for five minutes at 140 F. The alcohol was then decanted from the resultant product and analyzed for non-volatile matter. It was found that only 0.2 gram of such non-volatile material existed in the isopropyl alcohol. Further analysis showed that no measureable amount of MAP0 could be found dissolved in the isopropyl alcohol. The results as set forth in Table I are clearly indicative of the surprisingly unexpected improvement obtained from the pre-reaction of the two components.

2 Four minutes at 240 F.

It should be understood that the length of the pre-reactor, the rate of feed of the reactants, the temperature of the pre-reactor and quantities of materials used are all variables being this is essentially a polymeric reaction which transpires. The viscosities of the pre-reacted material are often in the range of 250,000 to 500,000 centipoiscs, though by no means limited to this range. In fact, the material may be so viscous that it can be removed only by shaking. The objective herein is to partially react the curative and the prepolymer material. Normally the curatives and prepolymers utilized have a multiplicity of reactive groups. For example, with the MAPO molecule there are normally an average of three to four reactive sites present. The objective of the herein invention is to pre-react the curative with the prepolymer so as to tie up only one, or two at the most, of the reactive sites present on the curative with the prepolymer material. Then, after the pre-reacted composition polymer meets the solids fed into the mixer, and they become a homogeneous mass, the remaining reactive sites are reacted during a curing operation, which may consist simply of heating. By the term heating, it is contemplated that the reaction may occur between ambient conditions for polymers curing at same and 300 F., though temperatures without this range are possible depending on the polymers.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by Way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

I claim:

1. In a process for the manufacture of a composition comprising substantially uniformly dispersed solid particulate substances in an organic polymer, which comprises mixing, under turbulent conditions, (1) at least one dispersion of a liquid organic material in a non-reactive dispersion medium which material forms a binder upon curing with (2) at least one dispersion of a solid particulate selected from the class consisting of fuels and inorganic oxidizers filling substance having a particle size of at least one micron in a non-reactive dispersion medium, said turbulent conditions operating to combine said filling substance and said liquid organic material into a dispersion on contact such that said dispersion, upon the release of turbulent conditions and in the absence of added colloid coagulating agents separates from said carrier, and upon curing said dispersion is further characterized in that it forms a solid cohesive substance of substantially uniform composition, the improvement comprising intimately mixing a polymer-forming material with a curative for a sufficient period of time to partially cure said polymer-forming material prior to forming said dispersion (1).

2. In a process for the manufacture of mixtures of polymeric materials and filling substances which comprises providing (1) at least one dispersion of polymerforming materials in non-reactive liquid organic dispersion mediums, wherein said polymer-forming materials consist essentially of at least one component selected from the class consisting of silicone polymers, silicone rubbers, glycidyl polyethers having terminal epoxy groups, polyurethane material, polymerized di-(thioethoxy) methylene, partially polymerized materials having the general formula:

in which R is a hydrocarbon group and n is a number selected from the series, 1, 2, 3 and isocyanate resins having the general formula:

wherein n is as defined above and such that the molecular weight of the resin is from about 2,000 to about 3,000, and wherein the ratio by weight of polymer-forming materials-to-dispersion mediums in (1) is from about 1:19 to about 1:1 and (2) at least one dispersion of solid particulate filling substances consisting essentially of inorganic perchlorates in non-solvent and non-reactive liquid organic dispersion mediums, said dispersion mediums being mutually miscible, providing an individual stream of each of said dispersions, bringing said streams together under conditions of turbulence to form a common stream of uniform composition, permitting said dispersed polymerized materials and said dispersed filling substances to coalesce and form an agglutinated composition of substantially uniformly dispersed filling substances in said polymerizable materials, the improvement comprising intimately mixing said polymer-forming material with a curative for a sufficient period of time to partially cure said polymer-forming material prior to forming said dispersion.

References Cited UNITED STATES PATENTS 2,213,577 9/ 1940 Cordier 260-30.2 2,282,948 5/1942 Dietzel 26030.2 2,788,337 4/1957 Preiswerk et a1 26037 2,849,417 8/1958 Tsang 26037 2,987,381 6/1961 Carter et al. 23--284 3,042,500 7/ 1962 Godel 23-284 2,962,368 11/1960 Guth l4919 3,022,149 2/1962 Cramer 14919 3,018,203 1/1962 Guth 14919 3,296,043 l/ 1967 Fluke et al 14919 BENJAMIN R. PADGETT, Primary Examiner.

MORRIS LIEBAM, Examiner.

J. W. BEHRINGER, Assistant Examiner,

Claims (1)

1. 2. IN A PROCESS FOR THE MANUFACTURE OF MIXTURES OF POLYMERIC MATERIALS AND FILLING SUBSTANCES WHICH COMPRISES PROVIDING (1) AT LEAST ONE DISPERSION OF POLYMERFORMING MATERIALS IN NON-REACTIVE LIQUID ORGANIC DISPERSION MEDIUMS, WHEREIN SAID POLYMER-FORMING MATERIALS CONSIST ESSENTIALLY OF AT LEAST ONE COMPONENT SELECTED FROM THE CLASS CONSISTING JOF SILICONE POLYMERS, SILICONE RUBBERS, GLYCIDYL POLYETHERS HAVING TERMINAL EPOXY GROUPS, POLYURETHANE MATERIAL, POLYMERIZED D--(THIOETHOXY) METHYLENE, PARTIALLY POLYMERIZED MATERIALS HAVING THE GENERAL FORMULA:

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