CA1039426A

CA1039426A - Mouldable compositions containing polyvinyl nitrate

Info

Publication number: CA1039426A
Application number: CA206,523A
Authority: CA
Inventors: Louis J. Leneveu
Original assignee: Societe Nationale des Poudres et Explosifs
Current assignee: Societe Nationale des Poudres et Explosifs
Priority date: 1973-08-09
Filing date: 1974-08-07
Publication date: 1978-09-26
Also published as: DE2436743A1; NL7410601A; IT1016803B; DE2436743B2; SE7410182L; GB1443289A; LU70682A1; NL164884C; SE436127B

Abstract

ABSTRACT OF THE DISCLOSURE

A mouldab1e thermoplastic composition comprises (i) polyvinyl nitrate, (ii) nitrocellulose and/or polyvinyl acetate and (iii) 2-nitro-diphenylamine and may be used to form combustible articles such as cartridge cases. Preferably, the composition comprises from 30 to 90% by weight of polyvinyl nitrate based on the total weight of components (i) and (ii).
The composition may comprise up to about 30% by weight, based on the weight of components (i) and (ii), of at least one additive selected from cellulose acetate, dinitrotoluene, phthalates, non-volatile esters, heterocyclic ketones, ureas and ABS copolymers. The combustible articles may be formed by compression moulding or injection moulding. Preferably the mouldable composition is formed into granules using the "with solvent" technique for making single base propellants, and the granules are mixed with a porous powder comprising nitro-cellulose prior to being moulded to form the combustible article.

Description

3~4Z6 The present invention relates to mouldable compo-sitions comprising polyvinyl nitrate. The compositions may be employed in the manufacture of combustible articles, such as cartridge cases, mortar shell ends or detonator tubes which have a very high potential and thus contribute energy for propelling a self-propelled projectile of which the combustible art;cle forms a part.
The thermoplastic properties of polyvinyl nitrate and its value in manufacturing moulded articles have been described in French Patent No. 911,759, but the energizing properties of these articles were not discussed in this patent and the patent does not contain any indication as to the nature of the mouldable composition to be used for a particular application.
The desirability of combustible articles in the fields of self-propulsion and artillery has long been apparent.
In the field of self-propulsion, for example, the metal fins or certain metal parts of the stabilizer assembly add to the weight of the article for the entire duration of the flight, although they are useful only at the start of the trajectory, and require an increase in the powder charge in order to effect their propulsion. In the field of artillery, it has been found that the accumulation of empty cartridge cases in a tank poses problems, both because the empty cases clut~er up the space in the tank, and because the cartridge cases also contain gases produced by the combustion of the powder, which pose toxicity problems for the occupants of the tank. These problems are far from negligible, because a lowering in the efficiency of military personnel in a tank in which a large quantity of empty cartridge cases has accumulated, has been observed.
It is known to make combustible articles, especially combustible cartridge cases, by replacing a part only of the ~ L~3~Z~;
metal casing by a combustible composition. Thus French Patent No. 1,349,818 describes cartridge cases made in two parts, namely a component made f~om a combustible material, namely nitrated cellulose, and a metal base. A serious problem with this arrangement is the difficulty of obtaining reliable joining of the metal and the nitrocellulose, and, of course, such cartridge cases are only partly combustible since they still contain a metal componen~. French Patent No. 1,573,822 describes consumable rocket fins which are destroyed during the flight of the machine, but these fins, which are made of a fusible metal, of a solid propulsion material which is not described in the patent, or of an inert plastics mater~al, do not, on being consumed, contribute energy to propel the rocket.
An attempt has been made to manufacture combustible cartridge case bases made of a readily combustible synthetic material. Such a proposal is described in French Patent No.
1,499,078, but no mention is made in this patent of the use of a high energy thermoplastic material, such as polyvinyl nitrate.
Attempts have also been made to use materials with a high energy of combustion so that the combustion of the article would provide energy ~hich could be used for assisting propulsion of the projectile. One technique, described in French Patent No. 2,003,848, comprises using, as the combusti-ble material, a f~brous cellulosic base ~for example, kraft), the potential of which is increased by adding crystalline explosives such as pentaerythritol tetranitrate, hexogen and octogen. However, the use of such explosives makes the prepa-ration o~ the cartridge a del;cate and long procedure because the entire manufacturing process is carried out in aqueous media and requires prolonged drying at the end o~ the manu-~L~3~26 facturing process. Another technique, described in FrenchPatent No. 2,103,794, comprises compressing a synthetic foam made of polyvinyl acetal~ polyurethane or polystyrene, but this technique is restricted to the particular materials just men-tioned because it is restricted to the use of foams, and thus cannot employ a vinyl compound which is highly energi-zing but cannot readily be made in the form of a foam, such as polyvinyl nitrate.
We have now developed certain msulda~le compositions which are highly energizing and which may ~e used to form wholly combustible articles which, during combustion of the article, generate a substantial amount o~ energ~ ~hich can be used to assist the propulsion of a projectile ~it~ which the article is associated.
According to the invention, there is prov~ded a mouldable thermoplastic composition which comprises ~i~ pol~-vinyl nitrate, (ii) nitrocellulose andlor polyvin~l acetate, and ~iii) 2-nitro-diphenylamine.
The invention also comprises a method of making a combustible article from a composition according to the invention, which comprises forming granules of a mouldable thermoplastic composition which comprises ~i~ polyvinyl nitrate, (ii) at least one material selected from the group consisting of nitrocellulose and polyvinyl acetate, and (iii) 2-nitro-diphenylamine, using the "with solvent" technique for making single base propellants, and moulding the granules so formed to produce the combustible article.
The use of polyvinyl nitrate is advantageous in that, in contrast to nitrocellulose, polyvinyl nitrate softens when hot, and since the decomposition temperature is markedly higher than the temperature at which softening starts, the product is ~ 39~.,6 easy to work with using injection moulding techniques.
Since polyvinyl nitrate possesses poor mechanical strength, i~ is not used alone, but in admi~ture with nitro-cellulose and~or polyvinyl acetate, the proportion hy ~eight of polyvinyl nitrate preferably being from 3~ to 90%. ~hen more than 90% of polyvinyl nitrate is used, the product possesses inadequate mechanical strength for some purposes and does not sufficiently retain its shape after moulding, whîlst if less than 30% of polyvfnyl nitrate is used, either the difference bet~een the decomposition temperature and the softening temperature becomes too small (~hen nitrocellulose is present), or the heat of combustion decreases too much ~when polyvinyl acetate is present~.
~ hen nitrocellulose is used, a nitrocellulose with a low nitrogen content is preferably employed. The greater the nitrogen content of the nitrocellulose, the smaller the differ-ence between the temperature at which softening starts and the decomposition temperature.
The mechanical properties of polyvinyl nitrate are such that it is not desirable to manufacture the combustible article from polyvinyl nitrate directly, but, rather, it is much preferred to proceed in two stages. In a first ctage, small granules of the mouldable composition of the invention are manufactured, and we have found, surprisingly, that it is possible to manufacture these granules using the well-known "with solvent" technique for preparing single-base powders, the so-called "B powders". In a second stage, the article is then moulded, either directly from the powder granules previ-ously prepared, or by mixing granules of porous powder com-prising nitrocellulose with the powder granules prevlouslyprepared.

~3g4~6 The granules of the mouldable composition can be manufactured in a conventional powder production line so that industries which already work with nitrated cellulosic compounds do not need to introduce new installations, and, in contrast to the maj~rity of known techniques, the manufacture of the articles themselves i5 ver~ simple and reliable and can be rendered automatic without danger since the granules of the mouldable composit;on can be checked before use.
In order that the invention may he better understood, a preferred method of putting the invention into practice is described below, by way of example.
As noted above, granules of t~e mouldable composition may be manufactured using the "with solvent" technique in the production of "B powders". The polyvinyl nitrate is preferably .. .. .
dehydrated with isopropyl alcohol, and pre-ground in a hammer mill rotating at 3,000 revolutions~minute. Since the fibres of polyvinyl nitrate are very short, it is advisable to line the draining press ~ith non~nitrated cotton linters in order to prevent loss of the fibres. The polyvinyl nitrate is then preferably placed in a Werner-type mixer together with nitro-cellulose andlor polyvinyl acetate. Acetone is then preFerably added in an amount of 60 cc per 100 g of dry material and 2-nitro-diphenylamine is added, as a stabili~er, preferably in an amount of 3 parts by weight per 100 parts of the mixture of polyvinyl nitrate, nitrocellulose andlor polyvinyl acetate.
According to a further preferred feature of the invention, additives are added to the mixture, preferably in an amount of up to 30 parts by weight per 100 parts of the mixture of poly-vinyl nitrate, nitrocellulose and/or polyvinyl acetate. These additives are preferably selected from cellulose acetate, dinitrotoluene, a phthalate, a non-volatile ester, a hetero-1~394Z6cyclic ketone ~such as camphor), a urea ~such as centralite) or an acrylonitrile-butadiene-styrene copolymer (ABS copolymer).
The mixing pre~erably lasts for between 2 and 3 hours, and after mixing, the fibres are stretched at the press and are cut immediately after stretching; in t~is context, it should be noted that the spinning pressure must remain very low ~prefer-ably between 80 and 100 bars). The granules of the mouldable composition may then be dried in air~ preferably at ~5C. for 100 hours. The granules thus obtained are ready to be used for moulding.
Examples of preferred compositions o~ granules o~ the mouldable composition, together with their main p~sical properties are given below.
The polyvinyl nitrate used had an average molecular ~7 ~eight of 89, its nitrogen content ~as 14.7% and its potential was 990 calorieslg-1) Compositions comprising polyvinyl acctate and polyvinylnitrate ... ............... - . . : .
_ _ Composition 1 Composition 2 _ .
Polyvinyl acetate 20 parts by weight 30 parts by weight Polyvinyl nitrate 80 " " " 70

2~nitro-diphenylamine 3 " " " 3 " " "
Chemical stability ~ 70 hours > 70 hours Impact sensitivity 0.5 kg x m 0.5 kg x m Potential 617 caloriesl9 595 calories/g * Vieille stability test at 108.5C. (period of time for which a sample of powder has to be heated in order to cause litmus paper to change colour).
", ', 1~3g~
2) Compositions comprising nitrocellulose (11.15% N) and polyvinyl nitrate 2.1) Compositions containing ABS (Compcsitions 3 to 10) Compositions 5 Polyvinyl nitrate 80 parts 70 parts 70 parts Nitrocellulose 10 parts 30 parts 10 parts 2-nitro-diphenylamine 3 parts 3 parts 3.3 parts ABS 10 parts 10 parts 20 parts Chemical stability > 70 hours > 70 hours 70 hours Impact sensitivity 0.3 kg x m 0.3 kg x m0.3 kg x m . Potential 480 cals/g 590 cals/g565 cals/g 6 - 7 8 . 9. . . .10 60 parts 80 parts 50 parts 60 parts50 parts 40 parts 20 parts 50 parts 40 parts50 parts 2.5 parts 3 parts 3 parts 3 parts3 parts 10 parts 10 parts 10 parts 5 parts5 parts : ~ 70 hours > 70 hours > 70 hours > 70 hours > 70 hours 0.3 kg x m 0.3 kg x m 0.3 kg x m 0.3 kg x m0~3 kg x m 584 cals/g 602 cals/g 642 cals/g 605 cals/g594 cals/g .. ........... ... . . . . . . . . .
_ _ ~03~26 2.2) Compositions containing dinitrotoluene (Compositions 11 to 13~ _ 1112 ~13 Polyvinyl nitrate ~0 parts 70 parts 80 parts Nitrocellulose 10 parts 30 parts 20 parts 2-nitro-diphenylamine 3 parts3 parts 3 parts Dinitrotoluene 10 parts 10 parts 20 parts Chemical stability > 70 hours > 70 hours > 70 hours Impact sensitivity 0.3 kg x m 0.3 kg x m 0.3 kg x m Potential 684 cals/g 683 cals/g 674 cals/g

3) Composition comprising polyvinyl nitrate, nitrocellulose and polyvinyl acetate -_ 14 _ Polyvinyl nitrate80 parts Nitrocellulose10 parts Polyvinyl acetate10 parts 2-nitro-diphenylamine 3 parts Chemical stab;lity > 70 hours ~mpact sensitivity 0.4 kg x m Potential 660 cals/g The granules of the mouldable composition thus prepared are easy to process in order to manufacture moulded combustible articles therefrom. The moulded articles can be manufactured by compression moulding or by injection moulding.
In the case of compression moulding, the desired quantity of composition is placed in the cold mould, which is heated in an oven until a temperature is reached ~hich is 20C.
above the softening temperature, that is to say approximately - .

~L~39~;~6 120C. for the preferred compositions given above. For small articles such as cartr;dge cases~ such a temperature is reached in about ten minutes. The mould is then compressed under a relatively low pressure (about ten bars is sufficient for this type of composition). The mould is allowed to cool and when cold the article is released therefrom.
In the case of injection moulding, the granules are heated until a homogeneous paste-like material is obtained, this is injected by means of a press into the mould which is allowed to cool and, when cold, the article is released there-from.
Cylindrical cartridge cases of length 1.5 cm, ; external diameter 1 cm and internal diameter 0.6 cm have been manufactured using the compression moulding technique. These cartridge cases possessed the following properties, as a function of their composition.

~394;~:6 Compos;tion of 2 the cartridge case 3 _ _ _ .
Heat of combustion 617 cals/g 595 cals/g 595 cals/g _ Rate of combustion bars 22.4 mm/s. 24~5 mm/s. 16 mm/s.
.. . .
Breaking load - 20C- 50 kg/cm 50 kg/cm2 50 kg/cm2 t 20C. 10 kg/cm2 10 kg/cm2 20 kg/cm2 10+ 50C. stretches stretches 7 kg/cm Chemical stability > 70 hours> 70 hours > 70 hours Unburnt materials under ordinary 6% 8% 4%
pressure . . . . . . . . . . . .

Mould-release slight diffi- good good . culties . .
_ .
Impact sensitivity t 20C. 0.5 kg x m + 40C. 0-4 kg x m ditto ditto ~ 60C. 0.35 kg x m . ~ 80C. 0.35 kg x m . . . . . .
_ .

softening starts ~ 30C. 3SC 35C.
__ a26 .

. . .
642 cals/g 646 cals/g 626 cals/g 650 cals/g 638 cals/g _ 17 mm/s . 17 mm/s .13 mm/s . 15 mm/s . 16 mm/s .
50 kg/cm2 > 50 k~ 50 kg/cm2 60 kg/cm2 60 kg/cm2 stretches 13 kg/cm25 kg/cm 54 kg/cm 50 kg/cm stretches stretches8 kg/cm 8 kg/cm 6 kg/cm2 _ > 70 hours > 70 hours> 70 hours > 70 hours .> 70 hours 5% 18% 5% 6% 2%
. .good . :good good good good 0.5 kg x m 0.6 kg x m 0.35 kg x m0.4 kg x m 0.35 kg x m 0.4 kg x m 0.5 kg x m 0.30 kg x m0.35 kg x m 0.30 kg x m 0.35 kg x m 0.45 kg x m0.25 kg x m 0.30 kg x m 0.25 kg x m 0.35 kg x m 0.4 kg x m 0.25 kg x m 0.25 kg x m 0.25 kg x m 35C. . .. -.40C. . 45C 50C 40C
_ .
1-0 ... 1.l........ 12..... . 13 14 _ 670 cal.s/g . 734 ca.ls./g. .712. cals/g 764 cals/g .. 6.60. cals/g . _ . :1.6 .mm/s .. .2.0 mm/.s .. . . .17 mm/s . 18 mm/s.... .2.4.. 5 mm/s .
_ 2 2 kg/cm > 50 kg/2cm > 50 kg/cm > 50 kg/cm 50 kg/cm 36 kg/cm l 5 kg/cm 11 kg/cm stretches 10 kg/cm kg/cm2 10 kg/cm2 7 kg/cm stretches stretches _ _ _ _ > 70 hours > 70 hours - > 70 hours > 70 hours > 70 hours . . -.. 2% ........ 4/0 ...... 2% 15% 4%
. . . .good . . good good good good _ 2 0.40kg x m 0.5 kg x m 0.5 kg x m 0.5 kg x m 0.5 kg/cm 2 0.35kg x m 0.45 kg x m 0.45 kg x m 0.45 kg x m 0.45 kg/cm2 0.30kg x m 0.40 kg x m 0.40 kg x m 0.40 kg x m 0.40 kg/cm 0.25kg x m 0.35 kg x m 0.35 kg x m 0.40 kg x m 0.35 kg/cm ~ 2 ~
From these results, it may be seen that the higher the proportion of polyvinyl nitrate, the more readily can the composition be moulded, but a slight lowering of the mechanical properties occurs at higher proportions of polyvinyl nitrate.
The choice between nitrocellulose and polyvinyl acetate depends on the desired ease of moulding and on the desired potential. Polyvinyl acetate facilitates moulding to a greater extent than does nitrocellulose, but lowers the potential to a greater extent than does nitrocellulose.
Likewise, in the case of the additives, it may be seen that ABS imparts better mechanical properties to the compositions than does dinitrotoluene, but lowers the potential to a greater extent than does d;nitrotoluene.
Accord;ng to a preferred embodiment of the invention, the combustible articles, especially combustible cartridge cases, possessing a high rate of combustion, are manufactured by mixing a porous powder comprising nitrocellulose with a mouldable composition of the ;nvention, prior to moulding the article. Combustible articles are thus obtained which can provide a large amount of propulsion energy and which can form, for example, either combustible cartridge cases to be filled with a conventional powder, or a propellant block to be used with or without ignition powder.
A mouldable composition comprising nitrocellulose, polyvinyl nitrate and ABS is preferred for use with the latter technique, it being preferred that the proportions o~ the various constituents lie within the following limits:
nitrocellulose: 30 to 70 parts by weight polyvinyl nitrate: 70 to 30 parts by weight ABS: 0 to ~ parts by weight.

9~339~Z~6 The nitrocellulose is preferably a nitrocellulose with a low nitrogen content (from 11 to 12.6% of nitrogen), whilst the polyvinyl nitrate is preferably highly nitrated (nitrogen content approximately 15.4%~.
According to a preferred procedure for making a combustible article from a mouldable composition of the invention, a mixture consisting of a previously prepared mouldable composition and a porous powder consisting essentially of nitrocellulose is introduced into the female part of a mould. Preferably, the proportion of the porous powder comprising nitrocellulose is up to 60% by weight of the mixture. The porous powder comprising nitrocellulose advantageously contains approximately 1% of diphenylamine.
The mould is then heated in an oven preferably to a temperature of about 110C~ and once temperature equilibrium has been achieved, it is left for about thirty seconds under the press and released from the mould after cooling. Combustible articles which burn in approximately half a millisecond may be obta;ned in this manner.
In order that the invention may be more fully under-stood, the following Example of the manufacture of combustible cartridge cases from a composition according to the invention is given by way of illustration only:
EXAMPLE
A porous powder comprising nitrocellulose known as BA-10 S powder and having the following composition, was employed:
nitrocellulose (nitrogen content: 13.2%) 100 parts by weight diphenylamine 1.20 " " "
30 potassium nitrate 125 " " "

1039~6 The powder was manufactured in accordance with the "with solvent" process, the potassium nitrate being removed during steeping, thus rendering the powder porous. The powder was cut up into small cylinders of length 0.6 mm and diameter 0.5 mm. Its physical characteristics were as follows:
density 0.428 g/cm3 alcohol 0.044%
ether G.011%
diphenylamine 1.13%
potassium nitrate 0.145%
graphite 0.13%
potential 982 calories/g The follo~ing mouldable thermoplastic co~positions were prepared:
Composition: A B
nitrocellulose (nitrogen content: 12.5%) 50 parts 60 parts polyvinyl nitrate (nitrogen content: 15.4%) 50 parts 40 parts ABS 0 part 1 part 2-nitro-diphenylamine 3 parts 3 parts solvent 2 parts 1.16 parts Composition: A B
potential 830 calories/g 845 calories/g Completely combustible cartridge cases were produced from a mixture consisting of one of these mouldable compo-sitions and the powder BA-10 S, the weight ratio of the mouldable composition to BA-10 S powder in the mixture being 2:1. The cartridge cases thus produced had the following physical properties:

IO39~Z6 Cartridge'cases'prod'u'ced with'th'e'co'mposit'i'bn's''of'type A B
actual density 1.70 g/cm 1.72 g/cm3 residual water 0.8% 0.8%
residual solvents 1.6% 1.03%
2-nitro-diphenylamine 2.6% 2.6%
potential 880 calories/g 895 calories/g start of softening 80C. > 80C.
decomposition 200C. 196C.
impact sensitivity 0.4 kg x m 0.4 kg x m sensitivity to friction resists resists 36 kg x m 36 kg x m chemical stability 70 hours 70 hours

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A moldable thermoplastic composition which comprises (i) polyvinyl nitrate, (ii) at least one material selected from the group consisting of nitrocellulose, polyvinyl acetate and a mixture of nitrocellulose and polyvinyl acetate, (iii) 2-nitro-diphenylamine, and (iv) at least one additive selected from the group consisting of cellulose acetate, dinitrotoluene, phthalates, non-volatile esters, heterocyclic ketones, ureas and acrylonitrile-butadiene-styrene copolymers, the amount of polyvinyl nitrate being from about 30 to about 90% by weight based on the total weight of components (i) and (ii), provided that when nitrocellulose is used alone the additive can only be an acrylonitrile-butadiene-styrene copolymer.

2. A composition according to Claim 1, in which the amount of additive is up to about 30% based on the total weight of components (i) and (ii).

3. A composition according to Claim 1, in which the amount of 2-nitro-diphenylamine is about 3% of the total weight of components (i) and (ii).

4. A method of making a combustible article, which comprises forming granules of a moldable thermoplastic compo-sition comprising (i) polyvinyl nitrate, (ii) at least one material selected from the group consisting of nitrocellulose, polyvinyl acetate and a mixture of nitrocellulose and polyvinyl acetate, (iii) 2-nitro-diphenylamine, and (iv) at least one additive selected from the group consisting of cellulose acetate, dinitrotoluene, phthalates, non-volatile esters, heterocyclic ketones, ureas and acrylonitrile-butadiene-styrene copolymers.
the amount of polyvinyl nitrate being from about 30 to about 90% by weight based on the total weight of components (i) and (ii).

5. The method of Claim 4, wherein the amount of additive is up to about 30% based on the total weight of components (i) and (ii).

6. The method of Claim 5, wherein the amount of 2-nitro-diphenylamine is about 3% of the total weight of components (i) and (ii).

7. A method according to Claim 4, which comprises mixing the granules of the mouldable thermoplastic composition with a porous powder comprising nitrocellulose prior to moulding, the proportion of the porous powder comprising nitro-cellulose being up to 60% by weight of the mixture.