Tocopherol stabilisers for nitrocellulose-based propellants

Abstract

The present disclosure is directed to a nitrocellulose-based propellant composition comprising: (a) a nitrate ester based propellant comprising nitrocellulose; and (b) a stabilizer consisting of a tocopherol compound with a general formula (I), ##STR00001##
wherein: X is oxygen; R.sup.1 is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, carboxylic acid, carboxylate, ester, saccharide, alkoxy-linked saccharide, alcohol, and ethers; R.sup.2 is selected from the group consisting of hydrogen methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; R.sup.3 is selected from the group consisting of hydrogen, methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; R.sup.4 is selected from the group consisting of methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; and R.sup.5 is selected from the group consisting of alkyl and alkenyl.

Claims

1. A nitrocellulose-based propellant composition comprising: (a) a nitrate ester based propellant comprising nitrocellulose; and (b) a stabiliser consisting of a tocopherol compound with a general formula (I), ##STR00031## wherein: X is oxygen; R.sup.1 is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, carboxylic acid, carboxylate, ester, saccharide, alkoxy-linked saccharide, alcohol, and ethers; R.sup.2 is selected from the group consisting of hydrogen methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; R.sup.3 is selected from the group consisting of hydrogen, methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; R.sup.4 is selected from the group consisting of methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; and R.sup.5 is selected from the group consisting of alkyl and alkenyl.

2. The propellant composition according to claim 1, wherein the nitrate ester based propellant consists of nitrocellulose alone as a single base or of a mixture comprising nitrocellulose in combination with at least a blasting oil and/or at least one energetic additive as a double or higher base.

3. The propellant composition according to claim 1, wherein the stabiliser is a component capable of reacting by H-abstraction with radical alkoxy groups formed by degradation of the nitrate ester to form a first by-product capable of reacting with NOx formed by degradation of the nitrate ester to form a second by-product comprising no NNO groups.

4. The propellant composition according to claim 3, wherein the second by-product is capable of reaction with radical alkoxy groups or with NOx formed by degradation of the nitrate ester to form a third and subsequent by-products capable of reacting with such radical alkoxy groups or with NOx.

5. The propellant composition according to claim 2, wherein the blasting oil comprises at least a nitrated polyol obtainable by nitration of a polyol selected from a group consisting of glycerol, glycol, diethylene glycol, triethylene glycol and metriol, and wherein the at least one energetic additive is an energetic plasticizer selected from the group of nitramines, such as butyl-NENA, dinitrodiazaalkane (DNDA), or is an explosive comprising RDX, HMX, FOX-7, FOX-12, and/or CL20.

6. The propellant composition according to claim 1, wherein the stabiliser consists of a component selected from a group consisting of alpha-tocopherol, beta-tocopherol, gamma-tocopherol, delta-tocopherol, alpha-tocotrienol, beta-tocotrienol, gamma-tocotrienol, delta-tocotrienol and a mixture thereof.

7. The propellant composition according to claim 1, wherein the stabiliser consists of a component selected from a group consisting of (+)-alpha-tocopherol, (+)-beta-tocopherol, (+)-gamma-tocopherol, (+)-delta-tocopherol, ()-alpha-tocopherol, ()-beta-tocopherol, ()-gamma-tocopherol, ()-delta-tocopherol and a mixture thereof.

8. The propellant composition according to claim 7, wherein said stabiliser consists of a mixture comprising (+)-alpha-tocopherol.

9. The propellant composition according to claim 1, wherein the stabiliser is present in the composition in an amount comprised between 0.1 and 5.0 wt. %, with respect to the total weight of the composition.

10. The propellant composition according to claim 1, wherein the nitrate ester-based propellant comprises not more than 60 wt. % nitroglycerine, with respect of the total weight of nitrate ester based propellant.

11. The propellant composition according to claim 1, having a stability measured according to STANAG 4582 (Ed. 1) at a temperature of 90 C. without heat generation above 350 W/g of at least 3.43 days.

12. The propellant composition according to claim 1, further comprising one or more of the following compounds as complementary stabilisers: (a) a substituted phenol compound having the general formula (13-I): ##STR00032## wherein: R.sup.6 represents: (i) H, (ii) alkyl substituted or not, or (iii) an alkoxy group; and R.sup.7 and R.sup.8 are same or different, and represent (i) alkyl substituted or not, or (ii) alkoxy group; (b) a trialkoxy benzene having the general formulae (14-1) or (14-II): ##STR00033## wherein R.sup.9, R.sup.10 and R.sup.11 are same or different and represent C.sub.1-5 alkyl unsubstituted or substituted with an alkoxy group; (c) an aromatic compound having a general formula (15-I): ##STR00034## wherein: R.sup.12 represents, alkyl substituted or not; R.sup.13 represent (i) H, (ii) unsaturated alkyl group, (iii) ##STR00035## (iv) ##STR00036## or (v) ##STR00037## R.sup.14 represents, H, alkyl substituted or not, or OR.sup.18; R.sup.15 represents, alkyl substituted or not, aromatic ring substituted or not, or OR.sup.18; R.sup.16 represents, alkyl substituted or not, aromatic ring substituted or not, or OR.sup.19; R.sup.17 represents, aromatic ring substituted or not; R.sup.18 represents, alkyl substituted or not, or aromatic ring substituted; and R.sup.19 represents, alkyl substituted or not, or aromatic ring substituted; and (d) a substituted phenol compound having the general formula (16-I): ##STR00038## wherein: R.sup.20, R.sup.21 and R.sup.22 are the same or different and represent: (i) alkyl-substituted or not, (ii) alkoxy group; (e) a substituted phenol compound having the general formula (17-I): ##STR00039## wherein: R.sup.23, R.sup.24, R.sup.25 and R.sup.26 are the same or different and represent: (i) alkyl-substituted or not, (ii) alkoxy group; and (f) a compound of the ionone-type, with a general formula (18-I), (18-II), (18-III) or (18-IV): ##STR00040## wherein R.sup.27 represents a ketone, hydroxyl, carboxyl, aldehyde or unsaturated alkyl group.

13. The propellant composition according to claim 1, further comprising one or more of the following additives: (a) a potassium salt, such as potassium nitrate (KNO.sub.3), in an amount comprised between 0.001 and 1.5 wt. %; (b) combustion moderators such as phthalates, Cl and citrate derivatives, in an amount comprised between 1.0 and 10.0 wt. %; (c) an anti-static agent such as graphite, in an amount comprised between 0.01 and 0.5 wt. %; and (d) calcium carbonate, in an amount comprised between 0.01 and 0.7 wt. %, wherein the wt. % are expressed in terms of the total weight of the propellant composition.

14. A method comprising: stabilising a nitrate ester based propellant comprising nitrocellulose with a component of a general formula (I): ##STR00041## wherein: X is oxygen; R.sup.1 is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, carboxylic acid, carboxylate, ester, saccharide, alkoxy-linked saccharide, alcohol, and ethers; R.sup.2 is selected from the group consisting of hydrogen methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; R.sup.3 is selected from the group consisting of hydrogen, methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; R.sup.4 is selected from the group consisting of methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide; and R.sup.5 is selected from the group consisting of alkyl and alkenyl.

15. The method according to claim 13, wherein the component of general formula (I) is selected from a group consisting of: (a) alpha-tocopherol, beta-tocopherol, gamma-tocopherol, delta-tocopherol, alpha-tocotrienol, beta-tocotrienol, gamma-tocotrienol, delta-tocotrienol and a mixture thereof, or from a group consisting of: (b) (+)-alpha-tocopherol, (+)-beta-tocopherol, (+)-gamma-tocopherol, (+)-delta-tocopherol, ()-alpha-tocopherol, ()-beta-tocopherol, ()-gamma-tocopherol, ()-delta-tocopherol and a mixture thereof.

16. The propellant composition according to claim 9, wherein the stabiliser is present in the composition in an amount comprised between 0.2 and 2.0 wt. %, with respect to the total weight of the composition.

17. The propellant composition according to claim 16, wherein the stabiliser is present in the composition in an amount comprised between 0.5 and 1.0 wt. %, with respect to the total weight of the composition.

18. The propellant composition according to claim 10, wherein the nitrate ester-based propellant comprises between 5 and 45 wt. % nitroglycerine, with respect of the total weight of nitrate ester based propellant.

19. The propellant composition according to claim 18, wherein the nitrate ester-based propellant comprises between 7 and 22 wt. % nitroglycerine, with respect of the total weight of nitrate ester based propellant.

20. The propellant composition according to claim 11, having a stability measured according to STANAG 4582 (Ed. 1) at a temperature of 90 without heat generation above 350 W/g of at least 10 days.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1: shows a reaction of spontaneous decomposition of nitrocellulose with formation of free radicals and NOx.

(3) FIG. 2: shows the assumed stabilisation mechanisms of akardite (AkII) and diphenylamine (DPA) (prior art).

(4) FIG. 3: shows the normalised heat flow expressed in W/g generated by propellant compositions stabilised with various amounts of a stabiliser of formula (Ia) for (a) single base nitrocellulose propellants, (b) double base nitrocellulose/nitroglycerine (80/20 wt. %) propellants and (c) double base nitrocellulose/nitroglycerine (60/40 wt. %) propellants.

DETAILED DESCRIPTION OF THE INVENTION

(5) As illustrated in FIG. 1, degradation of nitrocellulose forms free oxide radicals 2 (RO) and NOx. These degradation products are capable of reacting further and with nitrocellulose 1, which can rapidly lead to an explosion of the nitrate ester-based propellant due to excess heat generation. The most commonly used stabilisers are certainly akardite (AkII) 4 and diphenyl amine (DPA) 5 as illustrated in FIG. 2(a). Akardite (AkII) 4 when exposed to NOx, forms carcinogenic NNO compounds 6 as illustrated in reaction (A) of FIG. 2(a). Simultaneously or sequentially, it dissociates upon exposure to heat to form diphenyl amine (DPA) 5 following reaction (B) of FIG. 2(a). Whether used directly as stabiliser, or present in the composition following heat dissociation (B) of akardite 4, diphenyl amine (DPA) 5 stabilises a propellant composition by the following mechanism. A free radical alkoxy group generated by the propellant abstracts the hydrogen of the amine group of DPA 5 to form a stable compound (ROH, 9) (cf. reaction of FIG. 2(a)). The radical formed on the amine 8 can react with a NOx to form stable N-nitrosodiphenylamine 10 (cf. reaction (D) of FIG. 2(a)). The NNO group of N-nitrosodiphenylamine 10 is, however, carcinogenic and should be avoided for safety reasons. Triphenylamine has been tested in the past in order to prevent formation of NNO groups, but with little success in stabilisation properties. Hindered phenols as illustrated in FIG. 2(b) effectively react with free oxide radicals (RO) but forming stable components which are unlikely to further react with NOx (cf. reaction {circumflex over (1)} of FIG. 2(b)). The efficiency of such stabilisers is limited to short periods of time only because of rapid phenol depletion.

(6) A stabiliser as used in the present invention has a general formula (I)

(7) ##STR00013##
wherein:
X is oxygen;
R.sup.1 is selected from the following: hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, carboxylic acid, carboxylate, ester, saccharide, alkoxy-linked saccharide, alcohol and ether groups;
R.sup.2 is selected from the group consisting of hydrogen methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester and saccharide;
R.sup.3 is selected from the group consisting of hydrogen, methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester, and saccharide;
R.sup.4 is selected from the group consisting of methyl, benzyl carboxylic acid, benzyl carboxylate, benzylester, and saccharide;
R.sup.5 is selected from the group consisting of alkyl and alkenyl.

(8) Not wishing to be bound by any theory, it is believed that a stabiliser (I), as defined in the present invention contains a very labile proton which can react with radical alkoxy groups 2 and NOx species (FIG. 1) formed by degradation of the nitrate ester 1. Successive by-products are likely formed, and are also capable of reacting with NOx and alkoxy radicals from the degradation of the nitrate ester 1, increasing the efficiency of stabiliser function. Since no harmful NNO groups are formed due to the lack of nitrogen atoms in compound (I) structure, the stabiliser according to the present invention produces little to no carcinogenic and mutagenic by-products.

(9) In a preferred embodiment, the stabiliser is selected from a group consisting of alpha-tocopherol, beta-tocopherol, gamma-tocopherol, delta-tocopherol, alpha-tocotrienol, beta-tocotrienol, gamma-tocotrienol, delta-tocotrienol or a mixture thereof.

(10) In a preferred embodiment, the stabiliser is selected from a group consisting (+)-alpha-tocopherol, (+)-beta-tocopherol, (+)-gamma-tocopherol, (+)-delta-tocopherol, ()-alpha-tocopherol, ()-beta-tocopherol, ()-gamma-tocopherol, ()-delta-tocopherol or a mixture thereof.

(11) A preferred stabiliser is (+)-alpha-tocopherol, of formula (Ia):

(12) ##STR00014##

(13) The propellant composition may be a single base propellant, wherein the nitrate ester propellant consists of nitrocellulose only or a double base propellant, wherein nitrocellulose is combined with a blasting oil and/or at least one energetic additive. The most common blasting oil is nitroglycerine. FIG. 3(a) illustrates the stability of a single base propellant composition stabilised with a stabiliser (Ia) according to the present invention. FIG. 3(b) illustrates the same for a double base propellant composition wherein the nitrate ester propellant comprises 80 wt. % nitrocellulose and 20 wt. % nitroglycerine, a commonly used blasting oil. FIG. 3(c) illustrates the same for a double base propellant composition wherein the nitrate ester propellant comprises 60 wt. % nitrocellulose and 40 wt. % nitroglycerine. Energetic additives can be an energetic plasticiser selected from the group of nitramines such as butyl-NENA, dinitrodiazaalkane (DNDA), or an explosive such as RDX, HMX, FOX7, FOX12, CL20. A double base propellant composition according to the present invention preferably comprises a nitrate ester based propellant comprising not more than 60 wt. % blasting oil (such as nitroglycerine) or energetic additive with respect to the total weight of nitrate ester based propellant. More preferably, it comprises between 5 and 45 wt. %, most preferably between 7 and 22 wt. % blasting oil or energy additive, with respect of the total weight of nitrate ester based propellant. A preferred blasting oil is nitroglycerine.

(14) A propellant composition according to the present invention comprises a stabiliser of formula (I), preferably in an amount comprised between 0.1 and 5.0 wt. %, more preferably between 0.2 and 2.0 wt. %, most preferably between 0.5 and 1.5 wt. %, with respect to the total weight of the composition. FIG. 3(a) compares the stability as a function of time of a single base propellant composition stabilised with DPA (dotted line, =prior art), and with 1 wt. % of a stabiliser according to formula (Ia) (solid line, =invention). FIGS. 3(b) & (c) plot the same stability curves as a function of time for double base propellant compositions (20 and 40% nitroglycerine, respectively) stabilised with DPA (dotted line) and with 1 wt. % of a stabiliser according to formula (Ia). It can be seen in FIG. 3 that a stabiliser of Formula (1a) maintains the level of energy released perfectly stable below 100 W/g for over a week and longer. The stabilising properties of a stabiliser according to the present invention are at least as goodand often substantially betterthan the ones of DPA, without forming any carcinogenic NNO-components.

(15) Even longer stabilisation times can be obtained by combining a stabiliser as defined in the present invention with a complementary stabiliser in the form of an aromatic compound. The complementary stabiliser is preferably selected from the following group: (a) a substituted phenol compound (13) having the general formula (13-I):

(16) ##STR00015##
wherein: R.sup.6 represents: (i) H, (ii) alkyl substituted or not, or (iii) an alkoxy group; and R.sup.7 and R.sup.8 are same or different, and represent (i) alkyl substituted or not, or (ii) alkoxy group; (b) a trialkoxy benzene (14) having the general formulae (14-I) or (14-II):

(17) ##STR00016##
wherein R.sup.9, R.sup.10 and R.sup.11 are same or different and represent C.sub.1-5 alkyl unsubstituted or substituted with an alkoxy group; and (c) an aromatic compound (15) having a general formula (15-I):

(18) ##STR00017##
Wherein: R.sup.12 represents, alkyl substituted or not; R.sup.13 represent (i) H, (ii) unsaturated alkyl group, (iii)

(19) ##STR00018## (iv)

(20) ##STR00019##
or (v)

(21) ##STR00020##
R.sup.14 represents, H, alkyl substituted or not, or OR.sup.18;
R.sup.15 represents, alkyl substituted or not, aromatic ring substituted or not, or OR.sup.18;
R.sup.16 represents, alkyl substituted or not, aromatic ring substituted or not, or OR.sup.19;
R.sup.17 represents, aromatic ring substituted or not;
R.sup.18 represents, alkyl substituted or not, or aromatic ring substituted;
R.sup.19 represents, alkyl substituted or not, or aromatic ring substituted.

(22) In a preferred embodiment, R.sup.12 represents C.sub.1-5 alkyl-substituted or not, preferably CH.sub.3; further, it is preferred that R.sup.13 represents: (i)

(23) ##STR00021## (ii)

(24) ##STR00022## (iii)

(25) ##STR00023##
or (iv)

(26) ##STR00024##
Wherein R28 represents H, alkyl-substituted or not, or aromatic ring, substituted or not. For example, eugenol (15-III) or isoeugenol (15-IV) are suitable complementary stabilisers according to the present invention.

(27) ##STR00025##

(28) A more preferred embodiment of composition according to the present invention comprises a curcumin derivative of formula (15-II) as stabiliser,

(29) ##STR00026##
Wherein
R.sup.12 and R.sup.29 are same or different and represent alkyl substituted or not, preferably C.sub.1-5, more preferably CH.sub.3; R.sup.14 and R.sup.30 are same or different and represent H or alkyl substituted or not (e.g., C.sub.1-5 alkyl), wherein each of R.sup.12 and R.sup.29, and R.sup.14 and R.sup.30, are preferably same, and more preferably both are H. (d) a substituted phenol compound (16) having the general formula (16-I):

(30) ##STR00027##
wherein: R.sup.20, R.sup.21 and R.sup.22 are the same or different and represent: (i) alkyl-substituted or not, (ii) alkoxy group. (e) a substituted phenol compound (17) having the general formula (17-I):

(31) ##STR00028##
wherein: R.sup.23, R.sup.24, R.sup.25 and R.sup.26 are the same or different and represent: (i) alkyl-substituted or not, (ii) alkoxy group.

(32) (f) a compound of the ionone-type, with a general formula (18-I), (18-II), (18-III) or (18-IV):

(33) ##STR00029##
wherein R.sup.27 represents a ketone, hydroxyl, carboxyl, aldehyde or unsaturated alkyl group. In a preferred embodiment, R.sup.27 represents C(O)CH.sub.3 giving rise to alpha ionone (18-Ia) and pseudo ionone (18-IVb):

(34) ##STR00030##

(35) Beside a nitrate ester based propellant and a stabiliser, a propellant composition according to the present invention may comprise additives. In particular, it may comprise one or more of the following additives: (a) a potassium salt, such as potassium nitrate (KNO.sub.3) or sulphate (K.sub.2SO.sub.4), preferably in an amount comprised between 0.01 and 1.5 wt. %; (b) combustion moderators such as phthalates, centralite and citrate derivatives, preferably in an amount comprised between 1.0 and 10.0 wt. %; (c) an anti-static agent such as graphite, preferably in an amount comprised between 0.01 and 0.5 wt. %; and (d) calcium carbonate, preferably in an amount comprised between 0.01 and 0.7 wt. %,
Wherein the wt. % are expressed in terms of the total weight of the propellant composition.

(36) An example of propellant composition according to the present invention is listed in Table 1.

(37) TABLE-US-00001 TABLE 1 typical propellant compositions according to the present invention single base double base component wt. % wt. % nitrocellulose 89.0-96.0 82.0-86.0 nitroglycerine 0.0 7.0-11.0 KNO.sub.3 0.5-1.0 0.5-1.0 dibuthylphthalate 3.0-7.0 3.0-7.0 graphite 0.2-0.4 0.2-0.4 calcium carbonate <0.7 <0.7 stabiliser of formula (I) 0.15-2.0 0.15-2.0

Experimental Tests

(38) STANAG 4582 (Ed. 1) of Mar. 9, 2007 entitled Explosives, nitrocellulose based propellants, stability test procedure and requirements using heat flow calorimetry, defines an accelerated stability test procedure for single-, double-, and triple base propellants using heat flow calorimetry (HFC). The test is based on the measurement of the heat generated by a propellant composition at a high temperature. Fulfilment of the STANAG 4582 (Ed. 1) test qualifies a propellant composition for a 10 year stability at 25 C.

(39) A sample of propellant composition is enclosed in a hermetically sealed vial and positioned in a heat flow calorimeter having a measuring range corresponding to 10 to 500 W/g. The sample is heated and maintained at a constant temperature of 90 C. for the whole duration of the test and the heat flow is measured and recorded. A heat flow not exceeding 350 W/g for a period of 3.43 days at 90 C. is considered to be equivalent to at least 10 years of safe storage at 25 C. The graphs of FIGS. 3(a), (b), and (c) show the stability of a composition as a function of time measured as defined above. The full scale of the ordinate (normalised heat flow) corresponds to a value of 350 W/g not to be exceeded according to STANAG 4582 (Ed. 1), and the vertical straight line indicates 3.43 days. The initial heat flow peaks of graphs of FIGS. 3a, b and c are ignored as they are not representative of any specific reaction or phase transformation of the propellant composition, provided they do not exceed an exotherm of 5 J.

(40) FIGS. 3(a), (b) and (c) show the results as solid lines of the stability tests carried out on single- and double-base nitrocellulose based propellants, the double base propellants comprising 20 wt. % (FIG. 3(b)) or 40 wt. % nitroglycerine (FIG. 3(c)), in all cases stabilised with 1 wt. % of a stabiliser according to formula (Ia), with respect to the total weight of the propellant composition. For comparison, the result of the same stability tests carried out on similar nitrocellulose based propellants, but stabilised with diphenyl amine (DPA) are plotted as dotted lines in the graphs of FIG. 3. It can be seen that the heat flow never exceeds 100 W/g for 3.43 days, when STANAG 4582 (Ed. 1) requires to maintain the heat flow below 350 W/g (full scale of the ordinate). The tests on single base propellants were carried out for a longer period, showing a prolonged stability of the compositions with a heat flow continuously lower than 150 W/g for over 12 days.

(41) Both DPA and stabiliser (1a) fulfill the requirements of STANAG 4582 (Ed. 1). Stabiliser (Ia) according to the present invention is, however, advantageous over DPA and Akardite because, (a) Contrary to DPA, stabilisers according to the present invention do not generate any NNO carcinogenic by-product upon their stabilisation activity. (b) DPA curve (dashed line) shows a sharp peak stabilising in a plateau at higher heat flow values, suggesting that all DPA was spent after only about two days (cf. reactions (C) & (D) in FIG. 2(a)) whence stabilisation probably proceeds by reactions with by-products. By contrast, no discontinuity in the heat flow can be identified with stabiliser (Ia) over 3.5 days. and even for over 12 days, as revealed in FIG. 3(a) discussed supra with respect to single base nitrocellulose propellants. (c) As revealed in FIG. 3(a) discussed supra with respect to single base nitrocellulose propellants, the stabilisers of the present invention allow the maintenance of a heat flow substantially lower than 350 W/g at a temperature of 90 C. for periods well over 12 days for single-base propellants. Double-base propellants with 20 wt. % and 40 wt. % nitroglycerine are perfectly stabilised for at least 7 or even 10 days. Longer term tests with DPA, however, are not easily performed because vials containing a composition stabilised with DPA leaked earlier than the ones stabilised according to the present invention. It is assumed that gas generation by the reactions with DPA raises the pressure inside the vials above their limit of resistance, leading to the bursting open of the vials after a few days testing. Uncontrolled pressure rises must be avoided during transportation or storage of propellant compositions for obvious reasons.

(42) The propellant compositions of the present invention mark the beginning of the use of a new generation of stabilisers which can be referred to as green or environmentally-friendly stabilisers, which combine efficient, long term stability of nitrocellulose-based propellants without formation of any detectable amounts of carcinogenic or mutagenic by-products.