US3708359A

US3708359A - Hydrazinium nitroformate propellant with saturated polymeric hydrocarbon binder

Info

Publication number: US3708359A
Application number: US00074862A
Authority: US
Inventors: G Low; V Haury
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1970-09-23
Filing date: 1970-09-23
Publication date: 1973-01-02
Anticipated expiration: 1990-01-02

Abstract

A solid propellant composition containing hydrazinium nitroformate as an oxidizer, utilizing a saturated polymeric hydrocarbon binder and a polyisocyanate as a curing agent to prevent deterioration of the propellant.

Description

United States Patent Low et 211.

Jan. 2, 1973 Appl. No.: 74,862

US. Cl ..l49/19, 149/36 llnt. Cl. ..C06d 5/06 Field of Search ..l49/19, 20, 36, 44

References Cited UNITED STATES PATENTS 3,418,183 12/1968 Rice ..149/36 X 3,586,552 6/1971 Potts et al 3,511,725 5/1970 Stevens et al 3,535,173 10/1970 Spenadel et a1. ..l49/36 X Primary Examiner-Benjamin R. Padgett Attorney-Monte F. Mott, J. H. Warden and John R. Manning [57] ABSTRACT A solid propellant composition containing hydrazinium nitroformate as an oxidizer, utilizing a saturated polymeric hydrocarbon binder and a polyisocyanate as a curing agent to prevent deterioration of the propellant.

8 Claims, No Drawings HYDRAZINIUM NITROFORMATE PROPELLANT WITH SATURATED POLYMERIC HYDROCARBON BINDER ORIGIN OF THE INVENTION Aeronautics and Space Act of 1958, Public Law 83-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is in the field of solid propellants, more particularly the invention relates to solid propellants which contain hydrazinium nitroformate which are stable and have a satisfactory shelf life.

2. Description of the Prior Art Hydrazinium nitroformate, HNF, is a valuable oxidizer in that it is very energetic, producing high performance in the propellants in which it is incorporated. When HNF is utilized with conventional unsaturated hydrocarbon binders, such as carboxyl terminated polybutadiene, the propellant will deteriorate on aging at ambient temperatures. It appears that the HNF attacks the double bonds in the unsaturated hydrocarbon binder, producing a gas-forming reaction. The propellants thus become porous and lose structural strength. Not only is there porosity due to the gas formation, but further, the attack of the double bonds breaks down the backbone of the binder, softening and weakening the propellant. One method for overcoming the deterioration of the propellants containing HNF and unsaturated hydrocarbon binders, is to utilize nitroguanidine as an additive to the propellant mixture. As disclosed in copending application Ser. No. 74,861, now US. Pat. No. 3,658,608 filed concurrently herewith, to the same inventor, there is described adding nitroguanidine to solid propellant formulations comprised of carboxyl terminated polybutadiene and HNF. Further, the invention is particularly directed to utilizing triethylene melamine as a type of curing agent, since it has been found that some curing agents are also attacked by HNF in addition to the propellant binder. Thus, as disclosed in the aforementioned copending application, one system has been developed to practically allow the utilization of HNF as an oxidizer in solid propellants. This system, however, is limited to carboxyl terminated polybutadiene, or as also indicated in the disclosure, polyisoprene. Further, the invention as disclosed in the copending application, is particularly limited to curing agents that do not react with HNF yet will cure the unsaturated type of binders. Since it is desirable to utilize HNF as an oxidizer, it is further desirable to enlarge the type of solid propellant systems in which this material can be used so that one would not be limited solely to the system disclosed in the copending application.

SUMMARY OF THE INVENTION The herein invention is directed to a novel propellant composition comprised of a saturated polymeric hydrocarbon binder, particularly of a hydroxyl terminated specie, such as hydroxyl terminated hydrogenated polybutadiene. It has been found that HNF can be incorporated as a solid particulate oxidizer in these saturated binders to produce a propellant having satisfactory shelf life if a proper curing agent is utilized. Specifically, it has been found that if a polyisocyanate type curing agent such as polymethylene polyphenylisocyanate, PAPI, is utilized the aforegoing results are achieved in a propellant having satisfactory shelf life results. Although other polyisocyanates such as toluene diisocyanate, TDI and hexamethylene diisocyanate HMDI can also be used, PAP] is preferred.

DESCRIPTION OF THE PREFERRED EMBODIMENT As pointed out above, solid propellant formulations containing HNF in unsaturated hydrocarbon binders deteriorate on aging due to gas-forming reactions within a few days at ambient temperatures. Since it is postulated that this is due to the attack of HNF upon double bonds in the binder, it has led to the present disclosure that HNF could be combined with saturated hydrocarbon binders. Such saturated binders must have present functional groups which are capable of being cross-linked to form the cured network. Thus, the herein invention is particularly directed to binders that contain functional hydroxyl groupings. Examples of such binders are hydroxyl terminated polybutylene, hydrogenated hydroxyl terminated polybutadiene and hydrogenated hydroxyl terminated polyisoprene. Once a saturated binder system is chosen for the HNF, the problem of deterioration is still not overcome, as will be shown below from the results of tests performed. HNF not only will apparently attack unsaturated bonds in the polymeric binders, but further can react apparently with various curing agents utilized. Thus, for example, as disclosed in the aforementioned copending application, a particular curing agent such as triethylene melamine is preferred to cure the carboxyl terminated polybutadiene disclosed therein, having nitroguanidine as an additive. As pointed out, curing agents such as MAPO which is tris[ l-(2-methyl)- aziridinyl] phosphine oxide when used in that same system would produce a gassing and deterioration due to apparent reaction with the HNF. In the same sense, in the herein invention, the choice of curing agent is important and, in fact, determines the success of the propellant system in overcoming the shelf life problem.

It has thus been unexpectedly found that the utilization of a particular polyisocyanate type curing agent, namely, polymethylene polyphenyliscoyanate, PAPI, will cure the hydroxyl terminated saturated binders into a cured propellant system that will have a good shelf life when incorporating HNF as an oxidizer. It is to be pointed out that PAPI is a known curing agent. However, unexpectedly this particular isocyanate has been found to be more effective in preventing deterioration of the saturated binder, than similar known isocyanate curing agents such as toluene diisocyanate, TDI, and hexamethylene diisocyanate, HMDI.

In the propellant system of this invention, the saturated binder will generally comprise 5 to 25 weight percent of the propellant. The HNF oxidizer will comprise 50 to weight percent. In addition to the oxidizer it is generally required that a fuel be present. Any suitable solid propellant particulate fuel is usable. Typical example of such fuel is particulate aluminum. Other examples of metal fuels that are useful include beryllium,

boron and magnesium. The solid particulate fuel will be present in an amount that will vary from 5 to 20 weight percent. Often, the saturated hydrocarbon binders are waxy in nature and require a plasticizer such as Conoco 11-35 which is a hydrocarbon oil to be added to improve processing. Other suitable plasticizers, such as Oronite Polybutene No. 6, dioctyl azelate and isodecyl pelargonate can be used, as is conventional in the processing of these materials. The plasticizer will generally vary from 0 to 20 weight percent of the composition. As the plasticizer is increased in level, it is found that the tensile strength of the cured compositions tend to decrease. Thus, it is desirable to minimize the amount of plasticizer. This can be achieved by utilizing lower viscosity binders as well as elevating processing temperatures. In addition to the foregoing ingredients, burning rate modifiers, coolants and the like which are used in conventional propellant art, if

compatible with HNF, can be added to the compositions in amounts from 0 up to 10 weight percent.

The amount of the PAPI curing agent utilized is related to the amount of binder material. Curing transpires between the OH groups on the binder and the NCO groups on the curing agent to form urethane linkages. Thus, the critical ratio is the NCO to OH groups. As a result, sufficient PAPI should be present to provide a ratio of NCO to OH of from 0.95 to about 1.3 in the composition.

In formulating the propellant composition of the invention, the ingredients are mixed prior to the final addition of the PAPI curative. It is preferred to mix the propellant at a temperature range of to 30C. The formulated propellant compositions are then cured at a temperature between 20 and 30C for 24 to 48 hours to a point where the cure is obtained. It is believed that the invention will be further understood from the following detailed examples.

EXAMPLE I A series of propellants were formulated utilizing differing polyisocyanate curing agents selected from a class consisting of PAPI and l-IMDI. To illustrate the relative effect of each of these materials upon the shelf life of the propellant. The propellants all contained 70 weight percent I-INF, 12 weight percent aluminum and 18 weight percent of a binder. The binder was Telagen S, which is a hydrogenated hydroxyl terminated polybutadiene made by General Tire & Rubber Co. The binder contained one part by weight of Conoco 11-35 as a plasticizer to five parts of Telagen S. The amount of the various isocyanate curatives varied, and in the following Table I, the effect of the amount of curative is shown, based on the ratio of NCO to OH groups present in the binder material. The results of the test are thus shown in the below table.

TABLE I ACCELERATED AGING OF IMPROVED HNF PROPELLANTS (At 45C) HNF/ 12% A1 18% Binder Binder: Telagen S Conoco H-35 plasticizer NCO/HO Time Swelling Wt. Loss Curative Equ. Ratio Days Vol. Loss PAP] 0.96 12 0. 0.02 PAPI .096 24 0. 0.14 A I 1.04 12 0. 0.02 PAPI 1.04 35 0. 0.12 PAPI 1.11 12 0. 0.02 PAPI 1.11 35 O. 0.14 PAPI 1.18 12 0. 0.02 PAPI 1.18 35 0. 0.14 TDI 1.00 12 8. 0.25 TDI 1.06 12 10. 0.40 TDI 1.15 12 8. 0.44 TDI 1.25 12 0. 0.02 TDI 1.25 17 11. 0.23 HMDI 1.09 12 0. 0.02 HMDI 1.09 21 3. 0.24

with 2 parts hexanetriol added per parts Telagen S in order to improve mechanical properties.

As can be seen from the above table, the use of PAPl peculiarly more effectively inhibited the deterioration of the propellant system than did TDI and HMDI. With TDI and HMDI shelflife was increased by the use of an excess of the curing agent. PAPI is preferred because of longer shelf life with a lower NCO/OH ratio. A large excess of curing agent tends to give poor mechanical properties.

EXAMPLE II To illustrate the fact that the system requires a saturated binder, a propellant was formulated comprised of 13 weight percent R-45M which is an unsaturated hydroxyl terminated hydrocarbon manufactured by Sinclair Petrochemicals, Inc., 3.25 weight percent Conoco 11-35 as a plasticizer, 1.7 weight percent PAPI, 14 weight percent aluminum and 69 weight percent HNF. This material swelled at the end of 13 days when maintained at a temperature of 45C to indicate that when all the other ingredients in the formulation of the same including the use of PAPI, the presence of unsaturated bonds in the binder will lead to attack by the I-INF to lower the shelf life and prevent practical utilization of the material.

I claim:

1. A solid propellant composition comprising:

hydrazinium nitroformate in an amount sufficient to act as an oxidizer,

a saturated polymeric hydrocarbon binder containing hydroxyl terminal functional groups, and a polyisocyanate in an amount sufficient to cure said binder.

2 The propellant of claim 1 wherein said binder is selected from the class consisting of hydroxyl terminated polybutylene, hydrogenated hydroxyl terminated polybutadiene and hydrogenated hydroxyl ter- 5 to 20 weight percent of solid particulate metal fuel. minated polyisoprene. 6. The composition of claim 5 wherein said binder is 3. The propellant of claim 1 wherein said curing selected from the class consisting of hydroxyl teragent is polymethylene polyphenylisocyanate. minated polybutylene, hydrogenated hydroxyl ter- 4. The propellant of claim 1 further comprising: 5 minated polybutadiene and hydrogenated hydroxyl tera solid particulate metal fuel. minated polyisoprene. 5. A solid propellant composition comprising: P P P of claim 5 Whercin 5 to 25 weight percent ofa hydroxyl terminated satu- 531d curlng agent Poll/methylene yp y rated polymeric hydrocarbon binder, y 50 to 70 weight percent hydrazium nitroformate, 10 propellant Composition 0f Clalm 5 further sufficient polyisocyanate curing agent to provide a compnsmgi ratio of NCO to OH groups in said composition of up to weght Permt ofa plastlclzer- 0.95 to 11.3,

Claims

1. A solid propellant composition comprising: hydrazinium nitroformate in an amount sufficient to act as an oxidizer, a saturated polymeric hydrocarbon binder containing hydroxyl terminal functional groups, and a polyisocyanate in an amount sufficient to cure said binder. 2 The propellant of claim 1 wherein said binder is selected from the class consisting of hydroxyl terminated polybutylene, hydrogenated hydroxyl terminated polybutadiene and hydrogenated hydroxyl terminated polyisoprene.

3. The propellant of claim 1 wherein said curing agent is polymethylene polyphenylisocyanate.

4. The propellant of claim 1 further comprising: a solid particulate metal fuel.

5. A solid propellant composition comprising: 5 to 25 weight percent of a hydroxyl terminated saturated polymeric hydrocarbon binder, 50 to 70 weight percent hydrazium nitroformate, sufficient polyisocyanate curing agent to provide a ratio of NCO to OH groups in said composition of 0.95 to 1.3, 5 to 20 weight percent of solid particulate metal fuel.

6. The composition of claim 5 wherein said binder is selected from the class consisting of hydroxyl terminated polybutylene, hydrogenated hydroxyl terminated polybutadiene and hydrogenated hydroxyl terminated polyisoprene.

7. The propellant composition of claim 5 wherein said curing agent is polymethylene polyphenylisocyanate.

8. The propellant composition of claim 5 further comprising: up to 20 weight percent of a plasticizer.