CA1086955A - Polyester bonding agents for htpb propellants - Google Patents
Polyester bonding agents for htpb propellantsInfo
- Publication number
- CA1086955A CA1086955A CA292,954A CA292954A CA1086955A CA 1086955 A CA1086955 A CA 1086955A CA 292954 A CA292954 A CA 292954A CA 1086955 A CA1086955 A CA 1086955A
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- Canada
- Prior art keywords
- binder
- propellant
- polyester
- amount
- antioxidant
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
A curable binder for use in forming a castable propellant of the hydroxy-terminated polybutadiene type of the structural formula
A curable binder for use in forming a castable propellant of the hydroxy-terminated polybutadiene type of the structural formula
Description
~69SS
This invention relates to composite solid propellants and more particularly to an impr~ve~d~ hydroxy-terminated polybutadiene (HTPB) binder system for such propellants which includes a mixture of two bonding agents.
The subject matter of this application is related to that disclosed and claimed in applicant's co-pending Canadian application Serial No. 243,659, filed 16 January 1976.
Castable propellants using polybutadiene-based binders in conjunction with, for example, ammonium perchlorate oxidizer are well known. The mechanical and ballistic properties of such composite solid propellants are very dependent upon the quality of the adhesive bond between the binde} and the oxidizer, as discussed in United States Patent 3,745,074 issued July 10, 1973, to Allen. In the prior art, systems are known which have reasonably good adhesion between the fuel binder and oxidizer but such systems have other disadvantages.
One such system utilizes carboxyl-terminated polybutadiene (CTPB) binders cured with a system involving aziridines or epoxides ~ -or a mixture thereof. Propellants using such binder systems have high elongation over a wide temperature range and a relatively high ability to carry solid particles, referred to as solid loading.
The~binder-oxidizer adhesion is fairly good as the preferred aziri~int~
curing agent, tris(2-methyl aziridinyl-l) phosphine c~xide known as MAPO, polymerizes around the ammonium perchlorate oxidizer particles to form a strong layer linked to the main portion of t~ binder by chemical bonds. However, this system has the disadvantages that it involves a complicated curing system, the propellants have poor aging chara~t~s-~it~ when exposed to high temperature, and the ; properties of the polymer binder vary from one batch to another.
Another system which was developed in an attempt to overcome the disadvantages of the foregoing system is that of the HTPB-based composite propellants, which utilizes hydroxy-terminated polybuta-~P' ,, . " ..,...:.,.
, ~ ,, .
~869SS
diene prepolymers. These systems are cured with diisocyanates. These pro-pellants required the use of a bonding agent to provide good adhesion of the binder to the oxidizer particles. Aziridine polyesters are efficient bonding agents for these propellants, a preferred aziridine polyester being a reaction product of MAPO with diacids. However, this preferred bonding agent must be synthesized on site in relatively small quantities as it has a short shelf life at room temperature and must be kept at low temperature to prolong its usefulness, and a relatively high concentration is required, about 2 to 3 per cent of aziridine polyester in the binder, to provide efficient adhesion between the oxidizer and binder particularly when the solid loading is high, The invention described in applicant~s aforesaid Canadian Application No. 243,659, is based on the finding that a combination of two bonding agents, an aziridine polyester (PAZ) and an amine polyester (PAM), with the HTPB-type propellants provides proper adhesion to maintain the stress-strain capability of the propellant, and enables a reduction by a factor of 3 to 4 in the amount of aziridine polyester required as compared to the known systems. Propellant systems according to the present invention have for example enhanced mechanical properties, including improved elongation at maximum load and at rupture with comparable tensile strength and initial moduli with reference to HTPB p~opèllant sy~tems u~iLizing o~ly aziridine polyester bonding agent.
More specifically, a curable binder for use in forming a castable propellant is disclosed which comprises:
1. a hydroxy-terminated butadiene polymer, -
This invention relates to composite solid propellants and more particularly to an impr~ve~d~ hydroxy-terminated polybutadiene (HTPB) binder system for such propellants which includes a mixture of two bonding agents.
The subject matter of this application is related to that disclosed and claimed in applicant's co-pending Canadian application Serial No. 243,659, filed 16 January 1976.
Castable propellants using polybutadiene-based binders in conjunction with, for example, ammonium perchlorate oxidizer are well known. The mechanical and ballistic properties of such composite solid propellants are very dependent upon the quality of the adhesive bond between the binde} and the oxidizer, as discussed in United States Patent 3,745,074 issued July 10, 1973, to Allen. In the prior art, systems are known which have reasonably good adhesion between the fuel binder and oxidizer but such systems have other disadvantages.
One such system utilizes carboxyl-terminated polybutadiene (CTPB) binders cured with a system involving aziridines or epoxides ~ -or a mixture thereof. Propellants using such binder systems have high elongation over a wide temperature range and a relatively high ability to carry solid particles, referred to as solid loading.
The~binder-oxidizer adhesion is fairly good as the preferred aziri~int~
curing agent, tris(2-methyl aziridinyl-l) phosphine c~xide known as MAPO, polymerizes around the ammonium perchlorate oxidizer particles to form a strong layer linked to the main portion of t~ binder by chemical bonds. However, this system has the disadvantages that it involves a complicated curing system, the propellants have poor aging chara~t~s-~it~ when exposed to high temperature, and the ; properties of the polymer binder vary from one batch to another.
Another system which was developed in an attempt to overcome the disadvantages of the foregoing system is that of the HTPB-based composite propellants, which utilizes hydroxy-terminated polybuta-~P' ,, . " ..,...:.,.
, ~ ,, .
~869SS
diene prepolymers. These systems are cured with diisocyanates. These pro-pellants required the use of a bonding agent to provide good adhesion of the binder to the oxidizer particles. Aziridine polyesters are efficient bonding agents for these propellants, a preferred aziridine polyester being a reaction product of MAPO with diacids. However, this preferred bonding agent must be synthesized on site in relatively small quantities as it has a short shelf life at room temperature and must be kept at low temperature to prolong its usefulness, and a relatively high concentration is required, about 2 to 3 per cent of aziridine polyester in the binder, to provide efficient adhesion between the oxidizer and binder particularly when the solid loading is high, The invention described in applicant~s aforesaid Canadian Application No. 243,659, is based on the finding that a combination of two bonding agents, an aziridine polyester (PAZ) and an amine polyester (PAM), with the HTPB-type propellants provides proper adhesion to maintain the stress-strain capability of the propellant, and enables a reduction by a factor of 3 to 4 in the amount of aziridine polyester required as compared to the known systems. Propellant systems according to the present invention have for example enhanced mechanical properties, including improved elongation at maximum load and at rupture with comparable tensile strength and initial moduli with reference to HTPB p~opèllant sy~tems u~iLizing o~ly aziridine polyester bonding agent.
More specifically, a curable binder for use in forming a castable propellant is disclosed which comprises:
1. a hydroxy-terminated butadiene polymer, -
2. a diisocyanate curing agent, and
3. a bonding agent system of an aziridine polyester which is the reaction product of an aziridinyl phosphine oxide and at least one polycarboxylic acid, and an amine polyester which is the reaction product of an alkanolamine and a saturated 695S.
aliphatic polycarboxylic acid. Additionally, an an~ioxidant such as di-tert-butylhydroquinone or phenyl-beta-naphthyl amine may be included, together with isodecyl pelargonate as a plasticizer.
Further disclosed is a castable propellant utilizing the afore-mentioned binder and having dispersed therethrough a finely divided perchlorate oxidizer in di or trimodal distributions, and other optional ingredients such as a metal additive. The invention still further provides a method for preparation of the composite propellant which provides good dispersion of the ingredients, and reproduclbility in processing, mechanical and ballistic properties.
The HTPB prepolymers suitable for use in that binder and propellant system are, for example, of the type described in Canadian Patent 891,562 issued January 25, 1972, to Boivin and Tremblay, and United States Patent 3,792,003 issued February 12, 1974, to Duchesne. The prepolymers therein described are hydroxy telechelic polybutadienes" particularly hydroxy-termin-ated polybutadienes which are desirably rich in cis isomer. They are obtained by the reaction of a mono-epoxy compound and the corresponding carboxy polymers.
The product is a polymer having hydroxyl groups including primary and secondary such groups attached adjacent the ends of the polymer molecule, and preferably at the ends of the molecule. The mono-epoxy compound is an organic compound containing a single epoxy group including mono-epoxy resins; particularly preferred are epoxy compounds of the formula:
O ' ~ , l\
R - C - C - R' .`. ' wherein each of R and R' is hydrogen, aryl, or an alkyl preferably lower `
alkyl group, and more particularly 1,2-alkylene oxides such as propylene oxide and 1,2-butylene oxide which produce secondary hydroxyl groups ~lfl6~SS
when reacted~,with the carboxylitelechelic polymer. The c`arboxy~erminated~polybutadilèn~sear~ sui~tably.ibhose~lsupplied under the trade mark HC 434 by Thiokol Chemical Corporation and under the trade mark HYCAR-CTB by B. F. Goodrich and Company.
A typical hydroxy-terminated polybutadiene prepolymer has a molecular weight of about 3200 and is believed to have the following formula t 2_CH=CH_CH2~CH2_CH toH
CH2~
Y
wherein x = 1-75 for Ci9 and trans butadienes and y = 0-30 for vinyl, but y/x should be between O and 0.4.
Up to now, a preferred HTPB prepolymer is that sold under the trade mark Poly bd R-45M by Arco Chemicals Co. and has the following formula:
HO ~ (CH2-CH=CH-CH2) .2 fCH2 ~ ~ (CH2-CH=CH-CH2) ~ OH
H=CH2 /
wherein n = 44-60 and the polybutadiene structure is 60% trans-1,4, 20% cis-1,4, and 20% vinyl-1,2.
Over the last six or seven years, R-45M prepolymer has been widely accepted as the best polymer for most of the hydroxyl-terminated polybutadiene (HTPB) propellants presently in use or in development in m~ny countries. Despite this preference for R-45M by the propellant industry, composite propellants accounted for only a small portion of the total demand for R-45M. Recently, major consumers of this product in other industries shifted to a related prepolymer sold under the trade mark R-45HT, also by Arco. As a result, the price of R-45M is now more than double that of R-45HT. Because most propellant compositions comprise less than 10 percent prepolymer, the net effect on the total cost of the propellant is relatively " ~C3B695S
low. It was therefore difficult to justify a shift to another prepolymer e.g. R-45HT on cost considerations alone. However~ the possibility that R-45M will become difficult to procure in the future due to a very reduced market spurred on applicant's efforts.
In view of the similar structure of R-45M and R-45HT, it was decided to experiment with the latter as a possible alternative.
If R-45HT was to be employed instead of R-45M, a further problem was to find a substitute for N-phenyl-beta-naphtylamine (PBNA), the antioxidant normally used in HTPB propellants based on R-45M.
Moreover~ within a few years PBNA will probably disappear from the market because it has been identified as a carcinogenic material and a possible danger to human health.
- According to one embodiment of the present invention, a curable binder system for use in forming a castable composite propellant is contemplated comprising ~i) a hydroxy-terminated butadiene polymer of the structural formula - ~ \
H0 ~ (GH2-CH=CH-CH2) 2 ~ H2-CH ~ (CH2-CH=CH-CH2) ~ OH --~ \ CU=CH2 / 2 wherein n = 57-65 (ii) a diisocyanate curing agent, and (iii) a bonding agent system of an aziridine polyester which is the reaction product of an aziridinyl phosphine oxide and a poly-carboxylic acid, and an amine polyester which is the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid.
According to another embodiment of the invention, a method for the manufacture of a composite propellant is also contemplated, comprising (i) mixing together liquid ingredients comprising a hydroxy-terminated butadiene prepolymer of the structural formula ,; ' ' .; ' . . , ' :
J.Ci ~95~
HO ~ (CH2-CH=CH-CH2) 2 ~ CH2-CH ~ (CH2-CH=CH-CH2) 6 ~ OH
~ CH=CH2 ~ .2 wherein n = 57-65 a plasticizer and a bonding agent system of cm aziridine polyester which is the reaction product of an aziridinyl phosphine oxide and a polycarboxylic acid, and an amine polyester which is the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid at atmospheric pressure, (ii) adding solid ingredients comprising finelly divided aluminu~ metal, ferric oxide as burning rate catalyst and about 75% of the total amount of ammonium perchlorate oxidizer and mixing to substantially even dispersion, (iii) heating}at abouts60!C under vacuum for about 1 h~ur, (iv) releasing the vacuum, ~v) adding the remainder of the ammonium perchlorate oxidizer and a diisocyanate curing agent, and mixing (vi) reapplying vacuum and heating to about 60C for about 45 minutes, (vii) casting the resulting mixture into molds under vacuum.
R-45HT has the same formula as R-45M above, the difference being in the value of "n" which in the case of R-45HT is 57-65. Other differences and similarities will be apparent from the following table.
TABLE I
Typical F~mctionality 2.1 - 2.3 2.6 - 2.9 OH (m. equiv./g) 0.75 0~83 Typical Equivalent Weight 1320 1200 Viscosity (poises) at 30C 50 50 Moisture (%/w) 0.05 0.05 ss The HTPB prepolymer is used as the major ingredient in the propellant binder system, suitably in an amount of about 50-85 wt. %, prefera-bly in an amount of about 60-65 wt. ~/O of the binder composition. Suitably, an antioxidant is utilized with the prepolymer and may be for example the phenyl-beta-naphthylamine (PBNA), the bisphenol AO-2246 (American Cyanamid) or various compounds having the chemical group p-phenylenediamine.
When using R-45HT as the HTPB prepolymer, an antioxidant consist-ing of one or more of the following substances may be used:
_ 6a -~369S~
:
.
TABLE II
Tradename Supplier Chemical Name PBNA Uniroyal Phenyl-beta-naphthylamine A02246 Cyanamid Hindered bis-phenol NAUGARDQ Uniroyal Polymerized trimethyl dihydroquinoline OCTAMINE~ Uniroyal Diphenylamine-diisobutylene reaction product FLEXZONE~7L Uniroyal N-phenyl, N'-(1,3 dimethyl-butyl)-p-phenylene diamine FLEXZONE~6H Uniroyal N-phenyl, N'-cyclohexyl-p-phenylene diamine UOP-36 Universal Qil N-phenyl, N'cyclohexyl-p-Oil Products phenylene diamine DTBHQ Eastman Di-tert-butylhydroquinone A synergistic effect on the pot lifes of mixes was obtained when a combination of DTBHQ with UOP-36 or FLEXZONE 7L was added to the propellant mix to the extent of 1 per cent of the prepolymer.
The diisocyanate curing agent for use in the binder comp-osition according to the present invention is for example 2,4-tolylene diisocyanate (TDI), 1,6-hexamethylene diisocyanate (HMDI), or DDI
which is a mixture of isomers of diisocyanate containing 36 carbon atoms prepared by dimerization of 18 carbon fatty acids. The preferred diisocyanate is DDI for the purposes of the present propellant binder systems. The isocyanate/hydroxyl (NCO/OH) ratio is adjusted to optimize the mechanical properties of the resulting propellant as recognized with previous systems. For the present purposes a typical NCO/OH equivalent ratio is in the range of 0.65 - 0.95.
~denotes trademark - 6b -, , ~ . .. . . .....
~, ,. . , . ~.;
....... ~ .;.. ~, . .
.
... .
In order to facilitate mixing of the binder composition with the solid oxidizer in preparing the castable propellants of the invention, a plasticizer is suitably included in the binder composition in a proportion of about 15 to 30 per cent based on total weight of the binder composition. Compounds suitable as plasticizers are well known in the polymer art, and in the present composition may be for example dioctyl adipate (DOA), diethyl hexyl azelate (DE~), or isodecyl pelargonate (IDP). However, the preferred plasticizer is IDP.
The aziridine polyester component of the bonding agent system is, as indicated, the reaction product of an aziridinyl phosphine oxide with a polycarboxy~ic acid. These materials are disclosed in for example United States Patents 3,745,074 and 3,762,972. More specifically, they are the reaction products of di- or tri-functional aziridinyl phosphine oxide or its derivatives with organic molecules ;
which are polyfunctional with respect to carboxyl groups and which may contain one or more hydroxyl groups in their structures. The reactants may be represented by the formula O O
Xl I X2 (I) and R - C - OH (II) Xl where Xl represents an aziridine group of the structure I / Ql - N \ ¦
I\
and Ql and Q2 are either hydrogen or alkyl groups of one to four carbon atoms (Ql and Q2 may be the same or different), X2 may be ~86~55 the same as Xl or may be an organic radical such as phenyl, benzyl, methyl, ethyl, etc., R is an alkyl that contains at least one active hydrogen atom or an organic entity of molecules that contain one or more hydroxyl groups, and n is 2, 3, or 4. The reaction product is a mixture of compounds, the nominal structure of which may be represented by:
3 ~
\ Xl--P - N - C C O - 1 R (III) ~ X2 /n wherein Xl, X2, Ql' Q2' R and n are as already defined.
The optimum proportions are such that essentially sll carboxyl groups in (II) are reacted and nominally one aziridine group in (I) is reacted, i.e., one mole of (I) for each carboxyl equivalent of (II).
The preferred aziridine polyester materials for use according to the present invention are prepared from tris-l- (2-methyl aziridinyl) phosphine oxide which is commonly known as MAPO and diacids such as adipic acid, malic acid, sebacic acid, succinic acid, and tartaric acid.
PAZ is a condensation product of MAPO, tris (2-methyl aziridin~yl-l) phosphine oxide with a straight chain diacid of general formula HOOC (CH2)X COOH (x being 2 to 8 and preferably 4,',5 or 6) and a second substituted diacid of general formula HOOC CH(R) (CH2)y CH(Rl) COOH in which R and Rl can be similar or different being H or OH and y = O to 6 being preferably 0, 1 or 2.
In a typical synthesis, 3 to 8 moles of MAPO, and preferably 5 to 6 moles, are condensed with 0.5 to 1.0 mole of the substituted diacid and 1.75 to 205 moles of the straight chain diacid at 50 to 65C for
aliphatic polycarboxylic acid. Additionally, an an~ioxidant such as di-tert-butylhydroquinone or phenyl-beta-naphthyl amine may be included, together with isodecyl pelargonate as a plasticizer.
Further disclosed is a castable propellant utilizing the afore-mentioned binder and having dispersed therethrough a finely divided perchlorate oxidizer in di or trimodal distributions, and other optional ingredients such as a metal additive. The invention still further provides a method for preparation of the composite propellant which provides good dispersion of the ingredients, and reproduclbility in processing, mechanical and ballistic properties.
The HTPB prepolymers suitable for use in that binder and propellant system are, for example, of the type described in Canadian Patent 891,562 issued January 25, 1972, to Boivin and Tremblay, and United States Patent 3,792,003 issued February 12, 1974, to Duchesne. The prepolymers therein described are hydroxy telechelic polybutadienes" particularly hydroxy-termin-ated polybutadienes which are desirably rich in cis isomer. They are obtained by the reaction of a mono-epoxy compound and the corresponding carboxy polymers.
The product is a polymer having hydroxyl groups including primary and secondary such groups attached adjacent the ends of the polymer molecule, and preferably at the ends of the molecule. The mono-epoxy compound is an organic compound containing a single epoxy group including mono-epoxy resins; particularly preferred are epoxy compounds of the formula:
O ' ~ , l\
R - C - C - R' .`. ' wherein each of R and R' is hydrogen, aryl, or an alkyl preferably lower `
alkyl group, and more particularly 1,2-alkylene oxides such as propylene oxide and 1,2-butylene oxide which produce secondary hydroxyl groups ~lfl6~SS
when reacted~,with the carboxylitelechelic polymer. The c`arboxy~erminated~polybutadilèn~sear~ sui~tably.ibhose~lsupplied under the trade mark HC 434 by Thiokol Chemical Corporation and under the trade mark HYCAR-CTB by B. F. Goodrich and Company.
A typical hydroxy-terminated polybutadiene prepolymer has a molecular weight of about 3200 and is believed to have the following formula t 2_CH=CH_CH2~CH2_CH toH
CH2~
Y
wherein x = 1-75 for Ci9 and trans butadienes and y = 0-30 for vinyl, but y/x should be between O and 0.4.
Up to now, a preferred HTPB prepolymer is that sold under the trade mark Poly bd R-45M by Arco Chemicals Co. and has the following formula:
HO ~ (CH2-CH=CH-CH2) .2 fCH2 ~ ~ (CH2-CH=CH-CH2) ~ OH
H=CH2 /
wherein n = 44-60 and the polybutadiene structure is 60% trans-1,4, 20% cis-1,4, and 20% vinyl-1,2.
Over the last six or seven years, R-45M prepolymer has been widely accepted as the best polymer for most of the hydroxyl-terminated polybutadiene (HTPB) propellants presently in use or in development in m~ny countries. Despite this preference for R-45M by the propellant industry, composite propellants accounted for only a small portion of the total demand for R-45M. Recently, major consumers of this product in other industries shifted to a related prepolymer sold under the trade mark R-45HT, also by Arco. As a result, the price of R-45M is now more than double that of R-45HT. Because most propellant compositions comprise less than 10 percent prepolymer, the net effect on the total cost of the propellant is relatively " ~C3B695S
low. It was therefore difficult to justify a shift to another prepolymer e.g. R-45HT on cost considerations alone. However~ the possibility that R-45M will become difficult to procure in the future due to a very reduced market spurred on applicant's efforts.
In view of the similar structure of R-45M and R-45HT, it was decided to experiment with the latter as a possible alternative.
If R-45HT was to be employed instead of R-45M, a further problem was to find a substitute for N-phenyl-beta-naphtylamine (PBNA), the antioxidant normally used in HTPB propellants based on R-45M.
Moreover~ within a few years PBNA will probably disappear from the market because it has been identified as a carcinogenic material and a possible danger to human health.
- According to one embodiment of the present invention, a curable binder system for use in forming a castable composite propellant is contemplated comprising ~i) a hydroxy-terminated butadiene polymer of the structural formula - ~ \
H0 ~ (GH2-CH=CH-CH2) 2 ~ H2-CH ~ (CH2-CH=CH-CH2) ~ OH --~ \ CU=CH2 / 2 wherein n = 57-65 (ii) a diisocyanate curing agent, and (iii) a bonding agent system of an aziridine polyester which is the reaction product of an aziridinyl phosphine oxide and a poly-carboxylic acid, and an amine polyester which is the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid.
According to another embodiment of the invention, a method for the manufacture of a composite propellant is also contemplated, comprising (i) mixing together liquid ingredients comprising a hydroxy-terminated butadiene prepolymer of the structural formula ,; ' ' .; ' . . , ' :
J.Ci ~95~
HO ~ (CH2-CH=CH-CH2) 2 ~ CH2-CH ~ (CH2-CH=CH-CH2) 6 ~ OH
~ CH=CH2 ~ .2 wherein n = 57-65 a plasticizer and a bonding agent system of cm aziridine polyester which is the reaction product of an aziridinyl phosphine oxide and a polycarboxylic acid, and an amine polyester which is the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid at atmospheric pressure, (ii) adding solid ingredients comprising finelly divided aluminu~ metal, ferric oxide as burning rate catalyst and about 75% of the total amount of ammonium perchlorate oxidizer and mixing to substantially even dispersion, (iii) heating}at abouts60!C under vacuum for about 1 h~ur, (iv) releasing the vacuum, ~v) adding the remainder of the ammonium perchlorate oxidizer and a diisocyanate curing agent, and mixing (vi) reapplying vacuum and heating to about 60C for about 45 minutes, (vii) casting the resulting mixture into molds under vacuum.
R-45HT has the same formula as R-45M above, the difference being in the value of "n" which in the case of R-45HT is 57-65. Other differences and similarities will be apparent from the following table.
TABLE I
Typical F~mctionality 2.1 - 2.3 2.6 - 2.9 OH (m. equiv./g) 0.75 0~83 Typical Equivalent Weight 1320 1200 Viscosity (poises) at 30C 50 50 Moisture (%/w) 0.05 0.05 ss The HTPB prepolymer is used as the major ingredient in the propellant binder system, suitably in an amount of about 50-85 wt. %, prefera-bly in an amount of about 60-65 wt. ~/O of the binder composition. Suitably, an antioxidant is utilized with the prepolymer and may be for example the phenyl-beta-naphthylamine (PBNA), the bisphenol AO-2246 (American Cyanamid) or various compounds having the chemical group p-phenylenediamine.
When using R-45HT as the HTPB prepolymer, an antioxidant consist-ing of one or more of the following substances may be used:
_ 6a -~369S~
:
.
TABLE II
Tradename Supplier Chemical Name PBNA Uniroyal Phenyl-beta-naphthylamine A02246 Cyanamid Hindered bis-phenol NAUGARDQ Uniroyal Polymerized trimethyl dihydroquinoline OCTAMINE~ Uniroyal Diphenylamine-diisobutylene reaction product FLEXZONE~7L Uniroyal N-phenyl, N'-(1,3 dimethyl-butyl)-p-phenylene diamine FLEXZONE~6H Uniroyal N-phenyl, N'-cyclohexyl-p-phenylene diamine UOP-36 Universal Qil N-phenyl, N'cyclohexyl-p-Oil Products phenylene diamine DTBHQ Eastman Di-tert-butylhydroquinone A synergistic effect on the pot lifes of mixes was obtained when a combination of DTBHQ with UOP-36 or FLEXZONE 7L was added to the propellant mix to the extent of 1 per cent of the prepolymer.
The diisocyanate curing agent for use in the binder comp-osition according to the present invention is for example 2,4-tolylene diisocyanate (TDI), 1,6-hexamethylene diisocyanate (HMDI), or DDI
which is a mixture of isomers of diisocyanate containing 36 carbon atoms prepared by dimerization of 18 carbon fatty acids. The preferred diisocyanate is DDI for the purposes of the present propellant binder systems. The isocyanate/hydroxyl (NCO/OH) ratio is adjusted to optimize the mechanical properties of the resulting propellant as recognized with previous systems. For the present purposes a typical NCO/OH equivalent ratio is in the range of 0.65 - 0.95.
~denotes trademark - 6b -, , ~ . .. . . .....
~, ,. . , . ~.;
....... ~ .;.. ~, . .
.
... .
In order to facilitate mixing of the binder composition with the solid oxidizer in preparing the castable propellants of the invention, a plasticizer is suitably included in the binder composition in a proportion of about 15 to 30 per cent based on total weight of the binder composition. Compounds suitable as plasticizers are well known in the polymer art, and in the present composition may be for example dioctyl adipate (DOA), diethyl hexyl azelate (DE~), or isodecyl pelargonate (IDP). However, the preferred plasticizer is IDP.
The aziridine polyester component of the bonding agent system is, as indicated, the reaction product of an aziridinyl phosphine oxide with a polycarboxy~ic acid. These materials are disclosed in for example United States Patents 3,745,074 and 3,762,972. More specifically, they are the reaction products of di- or tri-functional aziridinyl phosphine oxide or its derivatives with organic molecules ;
which are polyfunctional with respect to carboxyl groups and which may contain one or more hydroxyl groups in their structures. The reactants may be represented by the formula O O
Xl I X2 (I) and R - C - OH (II) Xl where Xl represents an aziridine group of the structure I / Ql - N \ ¦
I\
and Ql and Q2 are either hydrogen or alkyl groups of one to four carbon atoms (Ql and Q2 may be the same or different), X2 may be ~86~55 the same as Xl or may be an organic radical such as phenyl, benzyl, methyl, ethyl, etc., R is an alkyl that contains at least one active hydrogen atom or an organic entity of molecules that contain one or more hydroxyl groups, and n is 2, 3, or 4. The reaction product is a mixture of compounds, the nominal structure of which may be represented by:
3 ~
\ Xl--P - N - C C O - 1 R (III) ~ X2 /n wherein Xl, X2, Ql' Q2' R and n are as already defined.
The optimum proportions are such that essentially sll carboxyl groups in (II) are reacted and nominally one aziridine group in (I) is reacted, i.e., one mole of (I) for each carboxyl equivalent of (II).
The preferred aziridine polyester materials for use according to the present invention are prepared from tris-l- (2-methyl aziridinyl) phosphine oxide which is commonly known as MAPO and diacids such as adipic acid, malic acid, sebacic acid, succinic acid, and tartaric acid.
PAZ is a condensation product of MAPO, tris (2-methyl aziridin~yl-l) phosphine oxide with a straight chain diacid of general formula HOOC (CH2)X COOH (x being 2 to 8 and preferably 4,',5 or 6) and a second substituted diacid of general formula HOOC CH(R) (CH2)y CH(Rl) COOH in which R and Rl can be similar or different being H or OH and y = O to 6 being preferably 0, 1 or 2.
In a typical synthesis, 3 to 8 moles of MAPO, and preferably 5 to 6 moles, are condensed with 0.5 to 1.0 mole of the substituted diacid and 1.75 to 205 moles of the straight chain diacid at 50 to 65C for
4 hrs. under N2.
The proportion of the aziridine polyester bonding agent in the binder system according to the present invention is between about 0.1 and 1% by weight of total binder composition.
1~6gS~ :.
The other component of the bonding agent combination used in binders according to the present invention is the amine polyester material which is as indicated the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid. The preferred amine polyester for the present purposes is a polymer derived from N-methyldiethanolamine and sebacic acid which is known as Polymer N-8. Suitable N-8 Polymers have the following specifications Mn (number average Mw) 1200-2000; preferred 1500-1800 acidity <0.02 eq./100 g equivalent OH : 1-1.5 meq./g; preferred 1.1-L.3 humidity : 0.15 % wt.
Other suitable agents have the following formulas HO-fH-CH2-N-CH2-jCHO- LCO(CH2)nCOOCH-CH2 IN 2 R " R " ' RIV R " R " ' Rlv wherein R " and R~V~can~be the same or different`and can be an hydrogen or a saturated alkyl chai~ having one or two carbon atoms;
R " ' can be a saturated alkyl chain with one to eighteen carbon atoms; n is an integer from 2 to 16, the preferred one being 8;
and~ is an integer between 3-10, the preferred ones being 5-7. This bonding agent is used in;an amount of about 0.1 to 0.5% by weight of the total binder composition.
To form the castable propellant according to the present invention t~ binder before curing is admixed according to a preferred process which will be described in detail herein, with finely divided ammonium perchlorate as oxidizer in dimodal or trimodal distributions of fine powders with average si7es of 1-400~m. A preferred particle size distribution of the ammonium perchlorate is 1.7/2.7/1.0 parts of 400 ~ m size, 200~am size, and 17~ m size respectively For high temperature applications the ammonium perchlorate may be substituted by potassium perchlorate. Suitably an anticaking agent, e.g. tricalcium , . . . .
... . .
-6~5 phosphate, is included in an amount oE about 1% by weight of the 17/am perchlorate. A metallic additive may be included in the propellant composition if desired in a concentration of 0 to 20% by weight of the total propellant. This additive may be finely divided aluminum or magnesium powder, preferably having an average particle size of 5-50~ m. Another solid material suitably included in the over-all composition is a burning rate additive or catalyst which may be for example iron oxide, copper chromite, or an organometallic compound.
The preferred additive or catalyst for the present purposes is ferric oxide in an amount of 0.1-1% by weight of propellant composition.
In composite propellant compositions it is of course desir-able to obtain as high solid loading as possible, and with the propellant compositions according to the present invention the total solids content can vary between about 85 to 90% by weight of total composition, of which of course the ammonium perchlorate will constitute the major part and may be between 68 and 88% by weight of total propellant composition. The other solid components are adjusted accordingly therein. Thus, the polymeric binder will constitute about 10 to 15% by weight of the total propellant composition.
In order to obtain good dispersion of all the ingredients in preparation of the propellant composition and also reproducibility of properties from one batch to another, the preferred procedure is to first add to a mixer the liquid ingredients which are the prepolymer, the plastici~er, and the two bonding agents. The aluminum or other metal powder when used and the ferric oxide burning rate additive are then added and the contents mixed for 15 minutes at atmospheric pressure. Then approximately three quarters of the total amount of ammonium perchlorate is added to the mixture and mixing continued for a further 10 minutes. Vacuum ~0~69S5 -is applied and the contents of the mixer heated to 60C for about 60 minutes.
The vacuum i9 then released and the remaining amount of ammonium perchlorate added and mixing continued for a further 5 minutes at atmospheric pressure.
~he diisocyanate curing agent is then added to the other ingredients in the mixture and mixing continued for 5 minutes at atmospheric pressure. After this vacuum is again applied and mixing continued for 45 minutes at a temper-ature of 60C. The propellant is then cast into molds under vacuum.
Certain compositions may be difficult to process. If this problem occurs, the diisocyanate curing agent may be added and aclmixed prior to addition of the remaining ammonium perchlorate oxidizer.
In drawings which illustrate embodiments of the invention, Figure 1 is a graph of the effect of prepolymer type on the pot life of HTPB propellants, Figure 2 is a graph of the effect of antioxidants on the pot life of HTPB propellants based on R-45HT (prepolymer lot 403245), Figure 3 is a graph of the effect of FLEXZONE 6H and DTBHQ antioxi-dants on the pot life of HTPB propellants (R-45HT prepolymer lot 606095), Figure 4 is a graph of the effect of mixture of antioxidants on the pot life of HTPB PROPELLANTS (R-45HT prepolymer lot 606095)~
Figure 5 is a graph of the effect of UOP-36 and FLEXZON ~ 6H on the pot life of HTPB propellants (R-45HT prepolymer lots 403245 and 606095), Figure 6 is a graph of the effect of PAZ/PAM bonding agents on pot life of HTPB propellants (R-45HT prepolymer, lot 606095; antioxidant type D).
The following examples illustrate the use of the binder system according to the present invention in preparing composite solid propellants.
The examples are intended to be illustrative of the present invention but are not to be taken as limiting to the scope thereof. The propellant compositions set out in the examples were each prepared according to the method described in the paragraph bridging pages 10 and 11.
', ' ' ~: ' ' '. ' ;95i5 The mechanical properties tested for the propellant compos-tions according to the present invention were tensile strength (~m)~
elongation at maximum load (~m), elongation at rupture (r)~ and initial moduli (E). These tests were carried out on an Instron~
apparatus at a cross-head speed of 2 in./min. corresponding to a strain rate of 0.741 min. 1 for the ICRPG "durnbell" specimen.
Propellant compositions were prepared having the following proportions of ingredients expressed in weight per cent: ;
1.7 parts Ammonium perchlorate average diameter (400~m) 2.7 parts Ammonium perchlorate average diameter (200 ~m) ) 69.4 1.0 parts Ammonium perchlorate average diameter ( 17~ m) Aluminum (spheroidal grade average diameter (22~ m) ) 18.0 Ferric Oxide Catalyst average diameter (1~ m) ) 0.6 HTPB Binder ) 12.0 For testing four binder compositions were used in the foregoing propellant composition. Binders I, II and III contained R-45M prepolymer including 1% PBNA and binder IV contained R-45HT
including 1% of an equi-mixture of DTBHQ and FLEXZONE 6H. Isodecyl pelargonate was included as plasticizer, and DDI diisocyanate as curing agent. In one binder composition the two bonding agents according to the invention were not utilized but rather only the aziridine polyester for comparative purposes. In the other three compositions both bonding agents were included.
The binder compositions were as follows I II III IV
Prepolymer (including 1% antioxidant) 62.91 62.91 62.91 62.66 DDI 12.09 12.0912.0912.34 Aziridine polyester 2.40 0.9 0.6 0.8 Amine polyester (N-8) - 0.2 0.2 0.2 IDP plasticizer ,22.60 23.9 24.2 24.0 denotes trademark s~ ~
The aziridine polyester of this example was prepared by reacting 0.15 mole of d-tartaric acid and 0.3 mole of adipic acid with 1 mole of MAPO (phosphine~oxide2ein,theYprocessOp~eviQusly des~rlbed hereinr.s The~amine polyestér~N*8~!ofilthisi)e~amplelhad ~hel,ollo~ing properties:
(i) OH equivalent 1~19 M equiv./g.
(ii) Acidity 0.016 equiv./100 g.
(iii) Molecular weight (Mn) 1430 determined by VPO.
The processing and mechanical properties obtained for the propellant compositions using the aforementioned binders were:
~-I II III IV
Aziridine/amine polyester 2.4/- 0.9/0.2 0.6/0.2 0.8/0.2 `;
(% in binder) End-of-mix viscosity (~P/60 C) 2.5 2.7 Z.7 3.6 Pot life to 10 kP (hr) 4.2 4.2 4.5 6.6 Mechanical Properties (initial) ~m at 22.8C (MN/m2) .58 .79 .63 .65 at " (%) 30.6 36.9 41.6 32.5 É at " `(MN/m2) 3.41 4.04 3.24 3.66 ~m at -45.6C (%) 48.2 58.8 65.6 50.8 20r at " (%) 54.5 59.8 68.5 55.6 Mechanical Properties (56 days at 60 C
o; ( / 2) .58 .79 .73 .81 ~m at " (%) 35.2 35.9 39.1 25.0 at " (MN/m2) 3.37 4.82 3.85 5.45 ~m at -45.6C (%) 49.4 48.9 59.5 38.1 , r at " (%) 50.7 50.4 60.9 40.0 It will be seen from the foregoing results that the proc~ss-ing characteristics, that is end-of-mix viscosity and pot life, ' . ' ' ~ - ' ' ' . ' .. . . , !
for the propellants according to the present invention were substantially the same as these properties for the propellants (I, II and III). However, the amount of aziridine polyester utilized according to the invention is consider-ably less than that required for the reference composition I. Also, the propellants according to the invention show improved elongations at maximum load and at rupture while the tensile strength and initial moduli are com-parable to the reference composition I.
The following additional examples serve to emphasize the advantages of using R-45HT in combination with various novel binder systems.
Preparation of R-45HT/antioxidant Batches Due to marked differences in the pot lives of propellants based on two lots of R-45HT, it has been decided to discuss the results for each lot separately.
Premixes of R-45HT (99 percent) and antioxidant (1.0 percent) were prepared by heating and agitating the components at 60C during approximately one hour. Because di-tert-butylhydroquinone (DTBHQ) is not soluble in R-45HT
in excess of 0.2 percent, but is soluble in IDP plasticizer, premixes of R-45H/IDP/DTBHQ were prepared with the following composition: R-45HT at 75.0 percent, IDP at 24.25 percent and DTBHQ at 0.75 percent. The relative concen-tration of DTBHQ with R-45HT was thus maintained at 1.0 percent. Unless otherwise stated, all the antioxidants were tested at a cencentration of one percent of the prepolymer.
Propellant Mixing and Casting Propellant batches were manufactured in a Cone-Vertical 8-CV
mixer operating at a batch size of 6.5 kg (approximately 50 percent of the mixer capacity). The same mixing and casting procedure was followed during the whole program. The liquid ingredients ( the prepolymer including the antioxidant, the plasticizer and the two bonding agents ) were Eirst added to the mixer. The aluminum and the ferric oxide were then added and the content mixed for 15 minutes at atmospheric pressure with the jacket temperature maintained at 60 C. Then approximately three quarters of the total amount of ammonium perchlorate was added to the mixture and mixing continued for a further 10 minutes. Vacuum was applied and the contents of the mixer heated to 60 C for 60 minutes.
The vacu~m was released and the remaining amount of ammonium perchlorate added and mixing continued for a further 5 minutes at atmospheric pressure. The diisocyanate curing agent was added to the other ingredients in the mixer and mixing continued for 5 minutes at atmospheric pressure. After this vacuum was again applied and mixing continued for 45 minutes at a temperature of 60 C. The propellant was then cast into molds under vacuum.
Viscosity and Pot Life Measurements The end of-mix (EOM) viscosities were obtained with a Brookfield apparatus Model HAT mounted on a Helipath stand. All the measurements were made with a spindle type D at a rotational speed of 2.5 rpm and at a nominal casting temperature of 60C. Pot life data was taken with Rotovisko apparatus (Gebruder Haake, Berlin) coupled with special ' ' controls for continuous recording of the torque and automatic retracting of the viscometer probe. The pot life is defined here as the period between the initial addition of the polymerizing agent (DDI) and the time required for the viscosity~to reach 10 kilopoises (kP) at 60C.
, Measurements of Mechanical Properties and Data Reduction Mechanical properties were measured after curing and after accelerated a~n~ ~n ,, circulating air at 60 C. Enough propellant was cast (usually a 15 x 15 x 13-cm block) for full evaluation at -53.9, -45.6 and 22.8C. After a normal curing period of five days at 60 C, the block was X-rayed and cut into slabs 1.27 cm + 0.05 thick; ICRPG
~ .
/~
S~
dogbones were die-cut and measurements taken of the minimum section.
Four samples were tested on the Instron tester at an extention rate of 0.0847 cm/s at each of the three temperatures. For accelerated aging tests, the machined slabs of propellant were individually wrapped in polyethylene bags.
R~SULTS AND LlSCUSSION
Propellants Based on R-45HT Lot 403245 Effect of Polymer Type on Pot Life The two lower curves of Figure 1 illustrate the effect of the prepolymer (R-45M versus R-45HT) on the propellant viscosity variation with the time elapsed after addition of DDI curative agent. With PBNA
as the reference antioxidant, the pot lives (to attain a viscosity of 10 kP) are 4.5 and 3.3 hours respectively for R-45M and R-45HT.
Effect of the Antioxidants on Pot Life The two upper curves of Figure 1 show the beneficial effect of PBNA antioxidant on the pot life of a typical HTPBIR-45HT propellant.
Without antioxidant, the R-45HT propellants would show a pot life of only 2.3 hours. It is therefore important to select an antioxidant which also slows down the initial polymeri~ation rate of the propellant.
Each of the three propellants of Figure 1 had two bonding agents at a concentration of PAZ/PAM o~0'~6/,0~-~21perdent~ o -th-~ b~der.
Six of the seven antioxidants listed in Table II (excluding FLEXZONE 6H) were tested separately in a similar propellant based on R-45HT lot No. 403245. Three antioxidants yielded a pot life shorter than R-45HT/PBNA propellant; they are, as shown on Figure 2, AO-2246, NAU&ARDQ Q and 9eTA~E. AO-2246 was the worst one with pot lives of 1.5 and 2.1 hours at concentrations of 0.5 and 0.25 percent in the prepolymer. The three other antioxidants yielded pot lives longer than R-45HT/PBNA propellant (UOP-36 at 3.6 hours, FLEXZONE 7L at 4.2 hours and DTBHQ at 4.4 hours).
i95S
Effect of Combinations of Antioxidants on Pot Life A synergistic effect was observed (Table III) when a combination of DTBHQ with UOP-36 or FLEXZONE 7L was added to the propellant mix to the extent of 1 percent of the prepolymer.
Effectively, the pot life of the DTBIIQ/UOP-36/R-45HT and DTBHQ/FLEXZONE 7L/R-45HT propellants were longer than those observed on DTBHQ/R-45HT, UOP-36/R-45HT and FLEXZONE/R-45HT
propellants.
Twelve of the 15 mixes prepared with combination~s of DTBHQ
and UOP-36 or FLEXZONE 7L yielded pot lives longer than 4.5 hours.
On the average, pot lives of DTBHQ/UOP-36 propellants were 4.9 hours and those of DTBHQ/FLEXZONE 7L propellants were 4.5 hours.
i, - TABLE III
. ~ . , .
Effect of Comb;nations of Antioxidants On Pot Life of ~-45HT Propell ants , Combinations of Antioxidants Pot Li~e at 10 kP Viscosi tY
DTBHQ UOP-36FLEXZONE 7L (hr) 100 _ _ 4,4
The proportion of the aziridine polyester bonding agent in the binder system according to the present invention is between about 0.1 and 1% by weight of total binder composition.
1~6gS~ :.
The other component of the bonding agent combination used in binders according to the present invention is the amine polyester material which is as indicated the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid. The preferred amine polyester for the present purposes is a polymer derived from N-methyldiethanolamine and sebacic acid which is known as Polymer N-8. Suitable N-8 Polymers have the following specifications Mn (number average Mw) 1200-2000; preferred 1500-1800 acidity <0.02 eq./100 g equivalent OH : 1-1.5 meq./g; preferred 1.1-L.3 humidity : 0.15 % wt.
Other suitable agents have the following formulas HO-fH-CH2-N-CH2-jCHO- LCO(CH2)nCOOCH-CH2 IN 2 R " R " ' RIV R " R " ' Rlv wherein R " and R~V~can~be the same or different`and can be an hydrogen or a saturated alkyl chai~ having one or two carbon atoms;
R " ' can be a saturated alkyl chain with one to eighteen carbon atoms; n is an integer from 2 to 16, the preferred one being 8;
and~ is an integer between 3-10, the preferred ones being 5-7. This bonding agent is used in;an amount of about 0.1 to 0.5% by weight of the total binder composition.
To form the castable propellant according to the present invention t~ binder before curing is admixed according to a preferred process which will be described in detail herein, with finely divided ammonium perchlorate as oxidizer in dimodal or trimodal distributions of fine powders with average si7es of 1-400~m. A preferred particle size distribution of the ammonium perchlorate is 1.7/2.7/1.0 parts of 400 ~ m size, 200~am size, and 17~ m size respectively For high temperature applications the ammonium perchlorate may be substituted by potassium perchlorate. Suitably an anticaking agent, e.g. tricalcium , . . . .
... . .
-6~5 phosphate, is included in an amount oE about 1% by weight of the 17/am perchlorate. A metallic additive may be included in the propellant composition if desired in a concentration of 0 to 20% by weight of the total propellant. This additive may be finely divided aluminum or magnesium powder, preferably having an average particle size of 5-50~ m. Another solid material suitably included in the over-all composition is a burning rate additive or catalyst which may be for example iron oxide, copper chromite, or an organometallic compound.
The preferred additive or catalyst for the present purposes is ferric oxide in an amount of 0.1-1% by weight of propellant composition.
In composite propellant compositions it is of course desir-able to obtain as high solid loading as possible, and with the propellant compositions according to the present invention the total solids content can vary between about 85 to 90% by weight of total composition, of which of course the ammonium perchlorate will constitute the major part and may be between 68 and 88% by weight of total propellant composition. The other solid components are adjusted accordingly therein. Thus, the polymeric binder will constitute about 10 to 15% by weight of the total propellant composition.
In order to obtain good dispersion of all the ingredients in preparation of the propellant composition and also reproducibility of properties from one batch to another, the preferred procedure is to first add to a mixer the liquid ingredients which are the prepolymer, the plastici~er, and the two bonding agents. The aluminum or other metal powder when used and the ferric oxide burning rate additive are then added and the contents mixed for 15 minutes at atmospheric pressure. Then approximately three quarters of the total amount of ammonium perchlorate is added to the mixture and mixing continued for a further 10 minutes. Vacuum ~0~69S5 -is applied and the contents of the mixer heated to 60C for about 60 minutes.
The vacuum i9 then released and the remaining amount of ammonium perchlorate added and mixing continued for a further 5 minutes at atmospheric pressure.
~he diisocyanate curing agent is then added to the other ingredients in the mixture and mixing continued for 5 minutes at atmospheric pressure. After this vacuum is again applied and mixing continued for 45 minutes at a temper-ature of 60C. The propellant is then cast into molds under vacuum.
Certain compositions may be difficult to process. If this problem occurs, the diisocyanate curing agent may be added and aclmixed prior to addition of the remaining ammonium perchlorate oxidizer.
In drawings which illustrate embodiments of the invention, Figure 1 is a graph of the effect of prepolymer type on the pot life of HTPB propellants, Figure 2 is a graph of the effect of antioxidants on the pot life of HTPB propellants based on R-45HT (prepolymer lot 403245), Figure 3 is a graph of the effect of FLEXZONE 6H and DTBHQ antioxi-dants on the pot life of HTPB propellants (R-45HT prepolymer lot 606095), Figure 4 is a graph of the effect of mixture of antioxidants on the pot life of HTPB PROPELLANTS (R-45HT prepolymer lot 606095)~
Figure 5 is a graph of the effect of UOP-36 and FLEXZON ~ 6H on the pot life of HTPB propellants (R-45HT prepolymer lots 403245 and 606095), Figure 6 is a graph of the effect of PAZ/PAM bonding agents on pot life of HTPB propellants (R-45HT prepolymer, lot 606095; antioxidant type D).
The following examples illustrate the use of the binder system according to the present invention in preparing composite solid propellants.
The examples are intended to be illustrative of the present invention but are not to be taken as limiting to the scope thereof. The propellant compositions set out in the examples were each prepared according to the method described in the paragraph bridging pages 10 and 11.
', ' ' ~: ' ' '. ' ;95i5 The mechanical properties tested for the propellant compos-tions according to the present invention were tensile strength (~m)~
elongation at maximum load (~m), elongation at rupture (r)~ and initial moduli (E). These tests were carried out on an Instron~
apparatus at a cross-head speed of 2 in./min. corresponding to a strain rate of 0.741 min. 1 for the ICRPG "durnbell" specimen.
Propellant compositions were prepared having the following proportions of ingredients expressed in weight per cent: ;
1.7 parts Ammonium perchlorate average diameter (400~m) 2.7 parts Ammonium perchlorate average diameter (200 ~m) ) 69.4 1.0 parts Ammonium perchlorate average diameter ( 17~ m) Aluminum (spheroidal grade average diameter (22~ m) ) 18.0 Ferric Oxide Catalyst average diameter (1~ m) ) 0.6 HTPB Binder ) 12.0 For testing four binder compositions were used in the foregoing propellant composition. Binders I, II and III contained R-45M prepolymer including 1% PBNA and binder IV contained R-45HT
including 1% of an equi-mixture of DTBHQ and FLEXZONE 6H. Isodecyl pelargonate was included as plasticizer, and DDI diisocyanate as curing agent. In one binder composition the two bonding agents according to the invention were not utilized but rather only the aziridine polyester for comparative purposes. In the other three compositions both bonding agents were included.
The binder compositions were as follows I II III IV
Prepolymer (including 1% antioxidant) 62.91 62.91 62.91 62.66 DDI 12.09 12.0912.0912.34 Aziridine polyester 2.40 0.9 0.6 0.8 Amine polyester (N-8) - 0.2 0.2 0.2 IDP plasticizer ,22.60 23.9 24.2 24.0 denotes trademark s~ ~
The aziridine polyester of this example was prepared by reacting 0.15 mole of d-tartaric acid and 0.3 mole of adipic acid with 1 mole of MAPO (phosphine~oxide2ein,theYprocessOp~eviQusly des~rlbed hereinr.s The~amine polyestér~N*8~!ofilthisi)e~amplelhad ~hel,ollo~ing properties:
(i) OH equivalent 1~19 M equiv./g.
(ii) Acidity 0.016 equiv./100 g.
(iii) Molecular weight (Mn) 1430 determined by VPO.
The processing and mechanical properties obtained for the propellant compositions using the aforementioned binders were:
~-I II III IV
Aziridine/amine polyester 2.4/- 0.9/0.2 0.6/0.2 0.8/0.2 `;
(% in binder) End-of-mix viscosity (~P/60 C) 2.5 2.7 Z.7 3.6 Pot life to 10 kP (hr) 4.2 4.2 4.5 6.6 Mechanical Properties (initial) ~m at 22.8C (MN/m2) .58 .79 .63 .65 at " (%) 30.6 36.9 41.6 32.5 É at " `(MN/m2) 3.41 4.04 3.24 3.66 ~m at -45.6C (%) 48.2 58.8 65.6 50.8 20r at " (%) 54.5 59.8 68.5 55.6 Mechanical Properties (56 days at 60 C
o; ( / 2) .58 .79 .73 .81 ~m at " (%) 35.2 35.9 39.1 25.0 at " (MN/m2) 3.37 4.82 3.85 5.45 ~m at -45.6C (%) 49.4 48.9 59.5 38.1 , r at " (%) 50.7 50.4 60.9 40.0 It will be seen from the foregoing results that the proc~ss-ing characteristics, that is end-of-mix viscosity and pot life, ' . ' ' ~ - ' ' ' . ' .. . . , !
for the propellants according to the present invention were substantially the same as these properties for the propellants (I, II and III). However, the amount of aziridine polyester utilized according to the invention is consider-ably less than that required for the reference composition I. Also, the propellants according to the invention show improved elongations at maximum load and at rupture while the tensile strength and initial moduli are com-parable to the reference composition I.
The following additional examples serve to emphasize the advantages of using R-45HT in combination with various novel binder systems.
Preparation of R-45HT/antioxidant Batches Due to marked differences in the pot lives of propellants based on two lots of R-45HT, it has been decided to discuss the results for each lot separately.
Premixes of R-45HT (99 percent) and antioxidant (1.0 percent) were prepared by heating and agitating the components at 60C during approximately one hour. Because di-tert-butylhydroquinone (DTBHQ) is not soluble in R-45HT
in excess of 0.2 percent, but is soluble in IDP plasticizer, premixes of R-45H/IDP/DTBHQ were prepared with the following composition: R-45HT at 75.0 percent, IDP at 24.25 percent and DTBHQ at 0.75 percent. The relative concen-tration of DTBHQ with R-45HT was thus maintained at 1.0 percent. Unless otherwise stated, all the antioxidants were tested at a cencentration of one percent of the prepolymer.
Propellant Mixing and Casting Propellant batches were manufactured in a Cone-Vertical 8-CV
mixer operating at a batch size of 6.5 kg (approximately 50 percent of the mixer capacity). The same mixing and casting procedure was followed during the whole program. The liquid ingredients ( the prepolymer including the antioxidant, the plasticizer and the two bonding agents ) were Eirst added to the mixer. The aluminum and the ferric oxide were then added and the content mixed for 15 minutes at atmospheric pressure with the jacket temperature maintained at 60 C. Then approximately three quarters of the total amount of ammonium perchlorate was added to the mixture and mixing continued for a further 10 minutes. Vacuum was applied and the contents of the mixer heated to 60 C for 60 minutes.
The vacu~m was released and the remaining amount of ammonium perchlorate added and mixing continued for a further 5 minutes at atmospheric pressure. The diisocyanate curing agent was added to the other ingredients in the mixer and mixing continued for 5 minutes at atmospheric pressure. After this vacuum was again applied and mixing continued for 45 minutes at a temperature of 60 C. The propellant was then cast into molds under vacuum.
Viscosity and Pot Life Measurements The end of-mix (EOM) viscosities were obtained with a Brookfield apparatus Model HAT mounted on a Helipath stand. All the measurements were made with a spindle type D at a rotational speed of 2.5 rpm and at a nominal casting temperature of 60C. Pot life data was taken with Rotovisko apparatus (Gebruder Haake, Berlin) coupled with special ' ' controls for continuous recording of the torque and automatic retracting of the viscometer probe. The pot life is defined here as the period between the initial addition of the polymerizing agent (DDI) and the time required for the viscosity~to reach 10 kilopoises (kP) at 60C.
, Measurements of Mechanical Properties and Data Reduction Mechanical properties were measured after curing and after accelerated a~n~ ~n ,, circulating air at 60 C. Enough propellant was cast (usually a 15 x 15 x 13-cm block) for full evaluation at -53.9, -45.6 and 22.8C. After a normal curing period of five days at 60 C, the block was X-rayed and cut into slabs 1.27 cm + 0.05 thick; ICRPG
~ .
/~
S~
dogbones were die-cut and measurements taken of the minimum section.
Four samples were tested on the Instron tester at an extention rate of 0.0847 cm/s at each of the three temperatures. For accelerated aging tests, the machined slabs of propellant were individually wrapped in polyethylene bags.
R~SULTS AND LlSCUSSION
Propellants Based on R-45HT Lot 403245 Effect of Polymer Type on Pot Life The two lower curves of Figure 1 illustrate the effect of the prepolymer (R-45M versus R-45HT) on the propellant viscosity variation with the time elapsed after addition of DDI curative agent. With PBNA
as the reference antioxidant, the pot lives (to attain a viscosity of 10 kP) are 4.5 and 3.3 hours respectively for R-45M and R-45HT.
Effect of the Antioxidants on Pot Life The two upper curves of Figure 1 show the beneficial effect of PBNA antioxidant on the pot life of a typical HTPBIR-45HT propellant.
Without antioxidant, the R-45HT propellants would show a pot life of only 2.3 hours. It is therefore important to select an antioxidant which also slows down the initial polymeri~ation rate of the propellant.
Each of the three propellants of Figure 1 had two bonding agents at a concentration of PAZ/PAM o~0'~6/,0~-~21perdent~ o -th-~ b~der.
Six of the seven antioxidants listed in Table II (excluding FLEXZONE 6H) were tested separately in a similar propellant based on R-45HT lot No. 403245. Three antioxidants yielded a pot life shorter than R-45HT/PBNA propellant; they are, as shown on Figure 2, AO-2246, NAU&ARDQ Q and 9eTA~E. AO-2246 was the worst one with pot lives of 1.5 and 2.1 hours at concentrations of 0.5 and 0.25 percent in the prepolymer. The three other antioxidants yielded pot lives longer than R-45HT/PBNA propellant (UOP-36 at 3.6 hours, FLEXZONE 7L at 4.2 hours and DTBHQ at 4.4 hours).
i95S
Effect of Combinations of Antioxidants on Pot Life A synergistic effect was observed (Table III) when a combination of DTBHQ with UOP-36 or FLEXZONE 7L was added to the propellant mix to the extent of 1 percent of the prepolymer.
Effectively, the pot life of the DTBIIQ/UOP-36/R-45HT and DTBHQ/FLEXZONE 7L/R-45HT propellants were longer than those observed on DTBHQ/R-45HT, UOP-36/R-45HT and FLEXZONE/R-45HT
propellants.
Twelve of the 15 mixes prepared with combination~s of DTBHQ
and UOP-36 or FLEXZONE 7L yielded pot lives longer than 4.5 hours.
On the average, pot lives of DTBHQ/UOP-36 propellants were 4.9 hours and those of DTBHQ/FLEXZONE 7L propellants were 4.5 hours.
i, - TABLE III
. ~ . , .
Effect of Comb;nations of Antioxidants On Pot Life of ~-45HT Propell ants , Combinations of Antioxidants Pot Li~e at 10 kP Viscosi tY
DTBHQ UOP-36FLEXZONE 7L (hr) 100 _ _ 4,4
- 5.0, 5,6, 4,8, 4.1 50 - - 5,2, 5.1, 4.9 . -- 4.6 ~:
- 100 - 3.8 - 50 4.3 - 75 4.5, 4.8, 4.2,~4.6, 4.5, 5.0 - - 100 4.1 - - Under~lined results were obtained with PAZ/R-45~ formulations.
, .'' : ' , ' ' Screening of Antioxidants Based upon the da~a presented above ~he pot lives of R-45HT
propellants appear to be strongly dependent upon the type of anti-oxidant added to the composition. To reduce the scope of the program, f/ it was decided that the three antioxidants yielding a shorter pot life than R-45HT/PBNA propellant (AO-2246, NAUGARD Q and OCTAMINE) would be dropped from this study. On the other hand, accelerated aging tests at 60C, would be carried out on propellants containing one or two of threelother candidates UOP-36, FLEXZONE 7L and DTBHQ) to evaluate their effectiveness as an antioxidant.
Mechanical Property Data Eleven propellant mixes based on R-45HT Lot 403245 were tested for mechanical properties; their binder compositions are shown in Table IV. The solids composition is as described previously.
A reference propelLant (mix 29) was formulated without antioxidant.
Four mixes had a single antioxidant; mix 26 (FLEXZONE 7L), mix 28 (UOP-36), mixes 25 and 35 (DTBHQ). Their mechanical properties after curing (t = O) and upon aging (14, 28 and 56 days at 60C) are shown in Table V. The mechanical properties of six propellant mixes incorporating two antioxidants (UOP-36/DTBHQ or FLEXZONE 7L/
DTBHQ are listed in Table VI.
':, . , ' ";, ~' ', ' . - ' i9S5 TABLE IV
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Binder Compos_tions based on R-45HT Lot 403245 MixAntioxidant NCO/OH Compos_tion (~ t~ _ No. Type Ratio R-45HT DDI IDP PAZ PA~
29 ni 1 0 . 85 62.03 12.9724.20 0.6 0.2 26 FLEX.7L 0.875 61.72 13.2824.00 n . 8 0.2 28 UOP-36 0.85 62.03 12.9724.20 0.6 0.2 DTBHQ 0.85 62.03 12.9724.20 0.6 0.2 DTBHQ 0.85 62.03 12.9724.20 0.6 0.2 07 75DTBHQ 0.85 62.03 12.9724.20 0.6 0~2 -25 UOP-36 ,~
08 " " 0.85 62.03 12.9722.60 2.4 0.0 09 25 DTBHQ 0,875 61.72 13.2824.20 0.6 0.2 __ .
75 ~lex-7L
16 " " 0.85 62.03 12.97 22.60 2.4 0.0 17 " " 0,85 62.03 12,97 22.60 2.4 O.G
18 " " 0,85 - 62.03 12.97 22.60 2.4 0.0 - :
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TABLE v Mechani cal Property Data For Three ~nti oxi dants ~R-45HT, Lot 403245) _ . _ _ _ _ Propsrties at TsOmp. Da~r 29 26 28 2s 35 am ~kP~22.8 0 703 590 406 681 746 m c%~ 16,5 34.7 37.8 30.5 ~1.7 E ~kPa) " " 6784 2906 1981 4153 4677 m (%)-45.6 " 18.9 48.1 56.8 43.9 46.9 r ~%) " 20,7 52.0 65. g 50.2 51,1 m (%) -53-9 " 15,1 42.8 43.9 33.1 39.5 r (~ 17.1 47.7 47.1 41.1 43.7 ~m (kPa) 22.8 14 738 662 479 759 795 Em (%) " " 9.1 31.0 34.2 33.9 29.8 E (kPa) " " 10790 4259 2565 4871 5034 am (kPa) 22.8 2& 492 680 565 769 861 Em (%) ll ll 3.4 31.5 33.8 27.6 26,7 E (kPa) " " 18612 4049 3218 5444 5870 Em ~%)_45.6 6,2 57.7 50.2 52.5 41.9 (%) 6,4 61.0 53.8 55.6 43.7 m y ~m (kPa) 22.8 56 438 782 648 857 904 Em C~ " " 2,2 29,5 30.5 21.7 22.0 E ~kPa) 2 " 29582 4890 3656 7443 7423 Em ~%)-45.6 " 3,7 43.5 47.1 31.5 33.8 Er (%) " " 3,8 45.8 48.6 35.1 37.1 Antioxidant Type - FLEX,7L unP-36 nTBHQ DTBII~) ~' '' ` ' ' ' .
.. ~. , , , ~ , . : ; . .: . ;
J~8169~i5 TAB LE ~/ I
Mechan; cal Property Data for ~i xtures of Anti ox] dants ~R-45HT, Lot 403245) Properties at lOmp, AgingMixes _ .
r Cl rDa~ 07 08 09 16 ]7 18 ~m (kPa)22,8 0 622 848 483 611 743 835 m C%) " " 27,723,0 41,8 29,5 27.4 26.3 E ~kPa) " " 31585767 1439 3132 3778 4710 m' ~) -45.6 " 33.237,0 55,7 40.9 ~9.3 38,1 Er (%) ll ~l 39.238.2 60.2 44.8 42.5 41.0 m (%) ~53 9 " 22.832.0 27.0 36.3 37.4 35.2 ~r (%) " " 32.735.9 48,0 39.1 39.6 37.7 ~m ~kPa) " " 660 1083 554 813 946 953 ~m (%) " " 28.624,1 38.0 23.7 21.7 22.8 E (kPa) " " 26596986 2431 4873 5933 6302 , ~m ~kPa) 22.8 28 722 1060 594 836 9176 1043 ~ ~%) " ~,26.0 25.636.624.8 22,6 23.O
E ~kPa) " " 4500 633924675273 6575 6583 m ( )-45,6 ~ 32,0 36,548,636,7 34.0 35.1 ~ ~%) " " 36,0.37,5 52,7 38.1 35,0 36,3 om ~kPa?22,8 56 730 100I 608 927 1079 1031 ~m ~%) " " 23,425, S 32,8 26,7 24.5 23, A
E CkPa~ " " 53717466 3492 6407 7~760 7220 ~m c~ -45,6 " 30,735,8 46.4 37,0 33.8 35.5 `
~r ~%) " " 35.336,4 50.7 38.2 34.6 36.0 DTIIBQ ~O o~ R-451~) 0,750,75 0,25 0,25 0.25 0.25 UOP-36 ~" " " ) 0,250,25 - - - -FLEX,7L (~ ,o . 750,75 n . 75 0,75 - ~ - - -- - - ~21 - -.
1~86g55 R-45HT Propellant Without Antioxidant As expected, an unprotectecl R~45HT propellant looses its mechanical properties veryrapidly upon aging; its stress and strain at room temperature fall from 703 kPa and 16.5% at t = O to 438 kPa and 2.2% only after 56 days of aging at 60C. Conversely, the modulus increases from 6784 to 29582 kPa. Obviously, an unprotected R-45HT
propellant is very susceptible to oxidation.
Effectiveness of UOP-36, FLEXZONE 7L and DTBHQ
Results for mixes 26, 28, 25 and 35 (Table V) tend to indicate that each of the above three candidates provides efficient protection against oxidation. All four mixes however, shaw some degree of post-curing as evidenced by the increasing 6 and E upon aging.
Effectiveness of Mixtures of Antioxidants It has been shown above that a combination of DTBHQ with UOP-36 or FLEXZONE 7L yielded improved pot lives. Aging results for mixes 07, 08, 09, 16,17 and 18 (Table VI) indicate that the combinations of two antioxidants also provide efficient protection against oxidation.
Good batch-to~batch reproducibility while aging at 6~C was obtained with mixes 16, 17 and 18.
Propellants Based on R-45HT Lot 606095 ' ':
Thirteen (13) propellant compositions based on R-45HT
Lot 606095 were tested for processing characteristics and accelerated aging properties; their binder compositions are listed in Table VII.
The main variables under study were: the type of antioxidant(s), the concentration of isocyanate/h~droxyl groups (NCO/OH) and the concentration of bonding agents. Two antioxidants were evaluated alone (DTBHQ and FLEXZONE 6H) and thrae combinations of DTBHQ
with FLEXZONE 6H or FLEXZONE 7L were tested with the solids system described previously.
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~86955 TABLE VII
Binder Compos;tions Based on_~-45HT Lot 606095 Mix Antioxidant NCn/oH Compositions ('O !~'t) No Tvoe fl) Ratio R-451~ DDI IDP PAZ PA~l -~ . . .. , . _ .
41 DTBHQ 0,80 62,03 12,97 24,2 0,6 0,2 47 " 0.80 61.98 1~.02 24.0 0,8 0,2 64 " 0,725 63,01 11,99 24.0 0.& 0,2 71 " 0,70 63,36 11,64 24,0 0,8 0,2 72 FLEX.6H 0,75 62,66 12,34 24,0 0,8 0,2 C 0,75 62,66 12,34 24,0 0.8 0,2 66 C 0,725 63,01 . ll.9g 24.0 0,8 0,2 73 E 0,75 62,66 12,34 24,0 0,8 0,2 D 0.725 63,01 11.99 24,0 0,8 0,2 61 D 0,75 62,66 12,34 24,0 0,8 0,2 68 D 0,75 62.66 12,34 24.4 0.4 0,2 69 D 0,75 62,66 12,34 23,6 1.2 0.2 D 0,75 62.66 12,34 23,8 0,8 0,4 ~ . . . . .
~1) Type C is-a 50/50 mixture of DTBHQ/FLEXZONE 7L, Type D is a 50/50 mixture of DTBHQ/FLEXnNE 6H.
Type E is a 25/75 mixture of DTBHQ/FLEXZONE 6H, .
.~
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~al86~SS
Effect of Antioxidant on Processing Characteristics As aan be seen on Table VIII, very satisfactory EOM
viscosities and pot lives were obtained with DTBH~ and combinations of DTBHQ with FLEXZONE 7L or FLEXZONE 6H. The pot lives of 12 of the 13 mixes were longer than 5.5 hours for a mix viscosity of 10 kP
at 60C. This is well above the target of 4.5 hours, as the average for 12 mixes is 6.6 hours. This is further illustrated in Figures 3 and 4. The propellant containing FLEXZONE 6H alone as antioxidant (Mix 72) displayed a pot life of 3.9 hours (Figure 5); this compares advantageously with UOP-36, another commercial name for N-phenyl, .
N'-cyclohexyl-p-phenylene diamine.
TABLE VIII
.
Processing Character;stics of ~-45HT Propellants Lot 606095 -- . . . .. . . . . . .
Mix-Antioxidant E.~.M. Viscosity Pot Lives Chrl No_ Types (1~ _kP / C at 10 kP ~0Clat 20 kP (60Cl : :
41 DTBHQ 2.5 / 59 7.5 10.6 47 " . 3.4 / 57 7.9 10.6 64 It 4,4 / 55 5.9 71 ~ 4.5 / 58 6.0 8.6 72FLEX.6H 5.6 / 59 3.9 6.0 C 3,~ / 57 7.8 10.2 66 C 4.1 / 58 6.4 9.2 73 E 4,3 / 59 5.5 7.8 D 4.2 / 57 6.2 8.6 61 D 4.1 / 56 6.6 9.2 68 D 4.3 / 58 6.4 8.8 69 D 4.4 / 58 6.7 8.9 D 5,6 / 59 6.1 8.2 .
tl) Type C is a 50/50 mixture of DTBHQ/FLEXZONE 7L.
Type D is a 50/50 mixture of DTBHQ/FLEXZnNE 6H.
Type E is a 25/75 mixture of DTB~IQ/FLEXZONE 6H.
, ., . .. . .. ~' ,~ . ' ` , 9ss Effect of Antioxidants on Mechanical Properties The mechanical properties at t = O and upon aging at 60C
for four propellant mixes (41, 47, 64 and 71) containing DTBHQ
antioxidant are listed in Table IX. The optimized concentration NCO/OH appears to be 0.725, since ~m~ ~m and E at 22.8 C are respect-ively 686 kPa, 33.4% and 3742 kPa, and at -53.9C, m is as high as 45.8%. Again, the four mixes show some degree of post-curing.
Results in Table X indicate that i) the initial 6m at room temperature is too low for the FLEXZONE 6H/R-45HT propellant (mix 72?;
ii) propellants containing combinations of DTBHQ with FLEXZONE 7L
and FLEXZONE 6H have satisfactory aging properties; iii) an NCO/OH
ratio of 0.75 yields better propellant than 0.725 (cf. mixes 60 and 66).
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~98695~i TABLE IX
Mechanical Propcrt~es of ~-45llT Propellants Lot 606095; D'l'IIBQ Antio~;dant -- _ , . .
Properties at Temp. Aging ~ es ~C) (Day) 4ï 47 6i 71 _ .. _ _ _ ~ . . . . _ . _ _ _ _ . . . _ am ~kPa) 22.8 0 859 899 686 605 Em (%) " " 26.4 20,1 33.4 ~4.9 E ~kPa) " " 5783 8096 3742 3117 Em (%) -45.6 " 37.2 30,3 52.0 54,5 Er ~%) ~ ~I 41.7 33.3 58.1 56.7 ~m ~%) ~53-9 " 27.7 27.5 45.8 47.7 Er ( ) 33.6 30.3 48.9 50.6 ~m ~kPa) 22.8 14 895 959 746 693 ~m ~%) " " 24.8 20.6 30.0 29.8 E ~kPa) " " 6587 8089 4424 4059 `~m ~kPa) 22.8 28 916 980 794 754 Em (%~ " " 24.0 21.0 29.8 29.6 E (kPa) " " 6570 825~ 4773 4463 Em (%) -45.6 " 35.9 28.8 48.0 48.4 Er ~%) ~ 40.1 31.8 50.5 51.1 ~m (kPa) 22.8 56 873 996 811 799 Em ~%) ~ 22.1 20.9 24O5 23.5 E (kPa) " " 6402 9713 5626 5642 Em (%) -45.6 " 27.7 22.9 38.3 32.3 E~ f%) " 32,5 26.8 40,4 33,6 , R ~NCo/nH ratio) 0.80 0.80 0.725 0,70 ~: :: . ' ~L~8695iS
TABLE X
.
M hanical Propert;es of R-45}~ Propellants Lot 606095; Fl,EX.61I, Types C and E Antioxidants Properties at Temp. Aging Mi xes _ (C) ~ay) 72 60 66 73 m CkPa)22.8 0 483 674 499 584 m ~%) " " 35.7 31.4 35.7 28.2 E CkPa) " " 2461 3663 2641 3835 m C%) -45.6 " 49,8 47,8 50.9 49.9 E r ~%) "- " 56.0 50.8 58.1 52.5 m ~%) ~53 9 " 44~0 42.8 45.9 45.4 r (%~ 47.6 43.5 49.0 47.1 am (kPa)22.8 14 614 720 611 724 ~%) ~ 29.9 30.6 31.3 28.7 E ~kPa) " " 3510 4207 3490 4517 a ~kPa)22.8 28 654 793 571 814 ~%) 1l 1l 29.1 29.1 30.0 27.8 E (kPa) " " 3725 4647 3819 5281 m (%) -45.6 " 49.6 43.4 49.9 45.2 (%) 1l 1~ 52,1 46.2 51.7 46.8 am ~kPa)22.8 56 722 849 739 797 m (%) " " 26.8 26.6 28.5 23.9 E (kPa) " " 4306 5526 4701 6142 m ~%) -45.6 " 43.1 39.4 44,6 34.8 r ~%) " " 44.7 40.5 46.7 37.3 R NCO/OII ratio 0.75 0.75 0.725 0.75 FLEX.6H (% of R-4511T) 1.00 - - 0.75 DTB~IQ (~ of R-4511T) - 0.50 0.50 0.25 FLEX.7L (O of R-4511T) - 0.50 0.50 .
~ ~ 27 .~ .
. i .
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~ 6~iS
Optimization of Bonding Agents in Propellants Containing Type D Antioxidcmts Two propellants (mixes 65 and 61) containing the 50/50 mixture of DTBHQ/FLEXZONE 6H (type D antioxidants) performed very well with respect to pot lives (Table VIII) and mechanical properties (Table XI). Mix 61, in particular, having an NCO/OH ratio of 0.75 showed 6ml ~m and E of 6.50 kPa, 32.5% and 3657 kPa at room temperature and ~m of 50.8 and 44.9% at -45.6 and _53 9C respectively. In most of the previous compositions, the concentration of PAZ/PAM
bonding agents was kept at 0.8/0.2 percent of the binder. Three propellants having an NCO/OH of 0.75 (lmixes 68, 69 and 70) were formulated to verify the effect of changing the PAZ/PAM concentrations to 0.4/0.2, 1.2/0.2 and 0.8/0.4 percent. All the pot lives were longer than 6 hours (Fig. 6) and the mechanical properties were excellent. The preferred PAZ/PAM ratio is that of mix 70 (0.8/0.4) which yielded an ~m of 45.8 percent at -45.6C after 56 days of aging. `~
... . .
695~i TABLE Xl Mechanical Properties of R-45~ PTopellants Lot 606095; Type D ( ) Antiox;dant Propcrties at ~'emp. Aging Mixes (C)~Day~ 65 61 68 69_ 70 am (kPa) 22,8 o 529 650 616 714 578 ~m (%) " .. 32~ 32~5 37,7 30,835,4 E (kPa) " " 2929 3657 3210 41013078 Em (%)-45,6 " 52,5 50,8 55,9 48,952,5 ~r (%) " 57,0 55,6 58,8 51,557,2 Em (%)-53'9 '' 46,7 44.9 48.2 43.148.7 Er (%) " " 51,0 48.1 49.8 45,850.9 am ~Pa)22.8 14 635 724 676 800 673 m (%) " " 29,7 30.2 33.1 27,032.5 E ~kPa) "i ~ 3940 4297 38404836 3~7 m (kPa) 22.8 28 700 819 731 818 713 E (%) 1l 11 29.7 28.6 30.1 27.730.9 E (kPa) " " 4451 5089 42864781 3932 Em ~%)-45.6 " 51.0 44.1 45.9 45.349.3 ~r (%) " " 54.8 45.9 48.4 48.154.7 -m ~kPa) 22,8 56 766 816 718 825 779 ~m (%) " 26,2 25,0 24,6 25,6 279 E (kPa) " " 5428 5445 51735260 4768 ~%~45,6 " 44,0 38,1 - 33,7 40.145.8 ~r (%) " ~ 47.2 40,0 35,6 41,9,48,0 R NCO/OII ratio 0,725 0,75 0,75 n ~ 75 0.75 PAZ (% wt of binder) 0,8 0,8 0,4 1,2 0,8 PAM (% wt of binder) 0,2 0,2 0,2 0,2 0,4 ~1) Type D antioxid~nt is a 50/50 mixture of DTB~lQ/rlJrA~7nNr 611.
.
:
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.: . . . . .:
Comparison Be~ween the Two Lots of R-45HT
The Lon er Pot Lives of Propellants Based on Lot 606095 ~g The longer pot lives obtained with Lot 606095 are not easily explicable. Various laboratory tests were conducted on the R-45HT
prepolymers Lots 403245 and 606095. No significant difference could be found to date with such tests as the equivalent weight (OH groups), the water content, the GPC and VPO. Viscosity measurements over the temperature range of 20 to 60C Led to almost identical results for both lots. It is possible, however, that the two-year period elapsed between the manufacturing of Lot 403245 and the addition of an anti-oxidant could have contributed to a certain deterioration of the prepolymer by homopolymerization. In an attempt to minimize the degradation of the product, the second lot of R-45HT was purchased with the additional specification "that the material must be delivered within six months after its manufacture". j ~ -! Mechanical P~ r~
Very little difference could be found between the mechanical properties of propellants based on R-45HT Lot 403245 and those from Lot 606095. The proper~ies of two propellants containing DTBHQ, mix 25 (Lot 403245) and mix 64 (Lot 606095) are compared in Table XII.
For nearly identical ~ m (681 versus 686 kPa), mix 64 shows slightly hlgher~el~gà~t~s~atll~owtte~pe~at~u~e~ IT~herr~dûG~e!d~val~ès,;~ich are an indication of the stability of the two propellants upon accelerated aging at 60C, are also nearly the same. Some post-curing is obvious with increases of 6m~ E and reduction in the elongation.
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1ai8~9~;S
TABLE XIT
Mechanical Propertics of R-45liT Propellant~s Containin~ 1% OTBI!~ -~Lots 4U3~4~ and ~06095) Reduced Value A~ Mix 25, Lot 403245 t - O t . 56 t56/to a `(XPa) @ 22.8C 681 857 1.20 m (%) ll 30.5 21.70.71 E (kPa) " " 4154 7443 1.79 m (%) @ -45.6 43.9 31.5 0.72 Er (%) " " 50.2 35,1 0.70 ~%) @ 53 9 33.1 T ( ) 41.1 B) Mix 64, Bot 606095 a (kPa) ~ 22.8C 686 811 1.18 ~m C%) " 33.4 24.5 0.73 E (kPa) " " 37¢2 5626 1.50 F (%) @ -45.6 . 52.0 38.3 0.74 m r (%) " " 58.1 40.2 0.70 m- (%) @ ~53 9 45.8 - _ r (%) " " 48.9 ~ ~
(1) t = O for initial properties.
t _ 56 for properties after 56 days of aging at 60C.
.
': :
.
. .. . - ,, ., ~ , . . , . , :
:.: ,:, :' . ~ :. . . , . . , ' . . :
,.. . . . .
~a~sss The Preferred Antioxidant (g) Based on the data collected during this study, it appears difficult to assign a relative value to each of the candidate anti-oxidants. Because of the unacceptable processing properties of the resulting propellants, three antioxidants (AO-2246, NAUGARD Q and OCTAMINE) were eliminated early during the study. The four other candidates (DTBHQ, FLEXZONE 7L, FLEXZONE 6H and UOP-36) used alone in the case of DTBHQ or in combinations (DTBHQ with the three others) ,yie'W eAdiexcellent!)processing~aharactbr~s~icsian!d-!ac2eptable~mechanical ~' properties. In compositions incorporating a single antioxidant DTBHQ is the only candidate that meets the objective of a pot life of at least 4.5 hours, notwithstanding a more pronounced post-curing effect. Combinations of DTBHQ with one of the p-phenylene diamines (FLEXZONE 7L, FLEXZONE 6H or UOP-36) also yielded excellent results. A preferred combination would be type D (50150 mixture of DTBHQ~FLEXZONE 6H) on account of its superior mechanical properties.
.. . . . . . . .
:
.' ' ' . ' . '~ ' : ' ' . ' .
:, . . .
,. ~ ' ' : ~. ,
- 100 - 3.8 - 50 4.3 - 75 4.5, 4.8, 4.2,~4.6, 4.5, 5.0 - - 100 4.1 - - Under~lined results were obtained with PAZ/R-45~ formulations.
, .'' : ' , ' ' Screening of Antioxidants Based upon the da~a presented above ~he pot lives of R-45HT
propellants appear to be strongly dependent upon the type of anti-oxidant added to the composition. To reduce the scope of the program, f/ it was decided that the three antioxidants yielding a shorter pot life than R-45HT/PBNA propellant (AO-2246, NAUGARD Q and OCTAMINE) would be dropped from this study. On the other hand, accelerated aging tests at 60C, would be carried out on propellants containing one or two of threelother candidates UOP-36, FLEXZONE 7L and DTBHQ) to evaluate their effectiveness as an antioxidant.
Mechanical Property Data Eleven propellant mixes based on R-45HT Lot 403245 were tested for mechanical properties; their binder compositions are shown in Table IV. The solids composition is as described previously.
A reference propelLant (mix 29) was formulated without antioxidant.
Four mixes had a single antioxidant; mix 26 (FLEXZONE 7L), mix 28 (UOP-36), mixes 25 and 35 (DTBHQ). Their mechanical properties after curing (t = O) and upon aging (14, 28 and 56 days at 60C) are shown in Table V. The mechanical properties of six propellant mixes incorporating two antioxidants (UOP-36/DTBHQ or FLEXZONE 7L/
DTBHQ are listed in Table VI.
':, . , ' ";, ~' ', ' . - ' i9S5 TABLE IV
.
Binder Compos_tions based on R-45HT Lot 403245 MixAntioxidant NCO/OH Compos_tion (~ t~ _ No. Type Ratio R-45HT DDI IDP PAZ PA~
29 ni 1 0 . 85 62.03 12.9724.20 0.6 0.2 26 FLEX.7L 0.875 61.72 13.2824.00 n . 8 0.2 28 UOP-36 0.85 62.03 12.9724.20 0.6 0.2 DTBHQ 0.85 62.03 12.9724.20 0.6 0.2 DTBHQ 0.85 62.03 12.9724.20 0.6 0.2 07 75DTBHQ 0.85 62.03 12.9724.20 0.6 0~2 -25 UOP-36 ,~
08 " " 0.85 62.03 12.9722.60 2.4 0.0 09 25 DTBHQ 0,875 61.72 13.2824.20 0.6 0.2 __ .
75 ~lex-7L
16 " " 0.85 62.03 12.97 22.60 2.4 0.0 17 " " 0,85 62.03 12,97 22.60 2.4 O.G
18 " " 0,85 - 62.03 12.97 22.60 2.4 0.0 - :
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., , :
TABLE v Mechani cal Property Data For Three ~nti oxi dants ~R-45HT, Lot 403245) _ . _ _ _ _ Propsrties at TsOmp. Da~r 29 26 28 2s 35 am ~kP~22.8 0 703 590 406 681 746 m c%~ 16,5 34.7 37.8 30.5 ~1.7 E ~kPa) " " 6784 2906 1981 4153 4677 m (%)-45.6 " 18.9 48.1 56.8 43.9 46.9 r ~%) " 20,7 52.0 65. g 50.2 51,1 m (%) -53-9 " 15,1 42.8 43.9 33.1 39.5 r (~ 17.1 47.7 47.1 41.1 43.7 ~m (kPa) 22.8 14 738 662 479 759 795 Em (%) " " 9.1 31.0 34.2 33.9 29.8 E (kPa) " " 10790 4259 2565 4871 5034 am (kPa) 22.8 2& 492 680 565 769 861 Em (%) ll ll 3.4 31.5 33.8 27.6 26,7 E (kPa) " " 18612 4049 3218 5444 5870 Em ~%)_45.6 6,2 57.7 50.2 52.5 41.9 (%) 6,4 61.0 53.8 55.6 43.7 m y ~m (kPa) 22.8 56 438 782 648 857 904 Em C~ " " 2,2 29,5 30.5 21.7 22.0 E ~kPa) 2 " 29582 4890 3656 7443 7423 Em ~%)-45.6 " 3,7 43.5 47.1 31.5 33.8 Er (%) " " 3,8 45.8 48.6 35.1 37.1 Antioxidant Type - FLEX,7L unP-36 nTBHQ DTBII~) ~' '' ` ' ' ' .
.. ~. , , , ~ , . : ; . .: . ;
J~8169~i5 TAB LE ~/ I
Mechan; cal Property Data for ~i xtures of Anti ox] dants ~R-45HT, Lot 403245) Properties at lOmp, AgingMixes _ .
r Cl rDa~ 07 08 09 16 ]7 18 ~m (kPa)22,8 0 622 848 483 611 743 835 m C%) " " 27,723,0 41,8 29,5 27.4 26.3 E ~kPa) " " 31585767 1439 3132 3778 4710 m' ~) -45.6 " 33.237,0 55,7 40.9 ~9.3 38,1 Er (%) ll ~l 39.238.2 60.2 44.8 42.5 41.0 m (%) ~53 9 " 22.832.0 27.0 36.3 37.4 35.2 ~r (%) " " 32.735.9 48,0 39.1 39.6 37.7 ~m ~kPa) " " 660 1083 554 813 946 953 ~m (%) " " 28.624,1 38.0 23.7 21.7 22.8 E (kPa) " " 26596986 2431 4873 5933 6302 , ~m ~kPa) 22.8 28 722 1060 594 836 9176 1043 ~ ~%) " ~,26.0 25.636.624.8 22,6 23.O
E ~kPa) " " 4500 633924675273 6575 6583 m ( )-45,6 ~ 32,0 36,548,636,7 34.0 35.1 ~ ~%) " " 36,0.37,5 52,7 38.1 35,0 36,3 om ~kPa?22,8 56 730 100I 608 927 1079 1031 ~m ~%) " " 23,425, S 32,8 26,7 24.5 23, A
E CkPa~ " " 53717466 3492 6407 7~760 7220 ~m c~ -45,6 " 30,735,8 46.4 37,0 33.8 35.5 `
~r ~%) " " 35.336,4 50.7 38.2 34.6 36.0 DTIIBQ ~O o~ R-451~) 0,750,75 0,25 0,25 0.25 0.25 UOP-36 ~" " " ) 0,250,25 - - - -FLEX,7L (~ ,o . 750,75 n . 75 0,75 - ~ - - -- - - ~21 - -.
1~86g55 R-45HT Propellant Without Antioxidant As expected, an unprotectecl R~45HT propellant looses its mechanical properties veryrapidly upon aging; its stress and strain at room temperature fall from 703 kPa and 16.5% at t = O to 438 kPa and 2.2% only after 56 days of aging at 60C. Conversely, the modulus increases from 6784 to 29582 kPa. Obviously, an unprotected R-45HT
propellant is very susceptible to oxidation.
Effectiveness of UOP-36, FLEXZONE 7L and DTBHQ
Results for mixes 26, 28, 25 and 35 (Table V) tend to indicate that each of the above three candidates provides efficient protection against oxidation. All four mixes however, shaw some degree of post-curing as evidenced by the increasing 6 and E upon aging.
Effectiveness of Mixtures of Antioxidants It has been shown above that a combination of DTBHQ with UOP-36 or FLEXZONE 7L yielded improved pot lives. Aging results for mixes 07, 08, 09, 16,17 and 18 (Table VI) indicate that the combinations of two antioxidants also provide efficient protection against oxidation.
Good batch-to~batch reproducibility while aging at 6~C was obtained with mixes 16, 17 and 18.
Propellants Based on R-45HT Lot 606095 ' ':
Thirteen (13) propellant compositions based on R-45HT
Lot 606095 were tested for processing characteristics and accelerated aging properties; their binder compositions are listed in Table VII.
The main variables under study were: the type of antioxidant(s), the concentration of isocyanate/h~droxyl groups (NCO/OH) and the concentration of bonding agents. Two antioxidants were evaluated alone (DTBHQ and FLEXZONE 6H) and thrae combinations of DTBHQ
with FLEXZONE 6H or FLEXZONE 7L were tested with the solids system described previously.
,- ' ' '' :' , . :. ' ''' :.
.::
~86955 TABLE VII
Binder Compos;tions Based on_~-45HT Lot 606095 Mix Antioxidant NCn/oH Compositions ('O !~'t) No Tvoe fl) Ratio R-451~ DDI IDP PAZ PA~l -~ . . .. , . _ .
41 DTBHQ 0,80 62,03 12,97 24,2 0,6 0,2 47 " 0.80 61.98 1~.02 24.0 0,8 0,2 64 " 0,725 63,01 11,99 24.0 0.& 0,2 71 " 0,70 63,36 11,64 24,0 0,8 0,2 72 FLEX.6H 0,75 62,66 12,34 24,0 0,8 0,2 C 0,75 62,66 12,34 24,0 0.8 0,2 66 C 0,725 63,01 . ll.9g 24.0 0,8 0,2 73 E 0,75 62,66 12,34 24,0 0,8 0,2 D 0.725 63,01 11.99 24,0 0,8 0,2 61 D 0,75 62,66 12,34 24,0 0,8 0,2 68 D 0,75 62.66 12,34 24.4 0.4 0,2 69 D 0,75 62,66 12,34 23,6 1.2 0.2 D 0,75 62.66 12,34 23,8 0,8 0,4 ~ . . . . .
~1) Type C is-a 50/50 mixture of DTBHQ/FLEXZONE 7L, Type D is a 50/50 mixture of DTBHQ/FLEXnNE 6H.
Type E is a 25/75 mixture of DTBHQ/FLEXZONE 6H, .
.~
.
~al86~SS
Effect of Antioxidant on Processing Characteristics As aan be seen on Table VIII, very satisfactory EOM
viscosities and pot lives were obtained with DTBH~ and combinations of DTBHQ with FLEXZONE 7L or FLEXZONE 6H. The pot lives of 12 of the 13 mixes were longer than 5.5 hours for a mix viscosity of 10 kP
at 60C. This is well above the target of 4.5 hours, as the average for 12 mixes is 6.6 hours. This is further illustrated in Figures 3 and 4. The propellant containing FLEXZONE 6H alone as antioxidant (Mix 72) displayed a pot life of 3.9 hours (Figure 5); this compares advantageously with UOP-36, another commercial name for N-phenyl, .
N'-cyclohexyl-p-phenylene diamine.
TABLE VIII
.
Processing Character;stics of ~-45HT Propellants Lot 606095 -- . . . .. . . . . . .
Mix-Antioxidant E.~.M. Viscosity Pot Lives Chrl No_ Types (1~ _kP / C at 10 kP ~0Clat 20 kP (60Cl : :
41 DTBHQ 2.5 / 59 7.5 10.6 47 " . 3.4 / 57 7.9 10.6 64 It 4,4 / 55 5.9 71 ~ 4.5 / 58 6.0 8.6 72FLEX.6H 5.6 / 59 3.9 6.0 C 3,~ / 57 7.8 10.2 66 C 4.1 / 58 6.4 9.2 73 E 4,3 / 59 5.5 7.8 D 4.2 / 57 6.2 8.6 61 D 4.1 / 56 6.6 9.2 68 D 4.3 / 58 6.4 8.8 69 D 4.4 / 58 6.7 8.9 D 5,6 / 59 6.1 8.2 .
tl) Type C is a 50/50 mixture of DTBHQ/FLEXZONE 7L.
Type D is a 50/50 mixture of DTBHQ/FLEXZnNE 6H.
Type E is a 25/75 mixture of DTB~IQ/FLEXZONE 6H.
, ., . .. . .. ~' ,~ . ' ` , 9ss Effect of Antioxidants on Mechanical Properties The mechanical properties at t = O and upon aging at 60C
for four propellant mixes (41, 47, 64 and 71) containing DTBHQ
antioxidant are listed in Table IX. The optimized concentration NCO/OH appears to be 0.725, since ~m~ ~m and E at 22.8 C are respect-ively 686 kPa, 33.4% and 3742 kPa, and at -53.9C, m is as high as 45.8%. Again, the four mixes show some degree of post-curing.
Results in Table X indicate that i) the initial 6m at room temperature is too low for the FLEXZONE 6H/R-45HT propellant (mix 72?;
ii) propellants containing combinations of DTBHQ with FLEXZONE 7L
and FLEXZONE 6H have satisfactory aging properties; iii) an NCO/OH
ratio of 0.75 yields better propellant than 0.725 (cf. mixes 60 and 66).
` `
-`
~98695~i TABLE IX
Mechanical Propcrt~es of ~-45llT Propellants Lot 606095; D'l'IIBQ Antio~;dant -- _ , . .
Properties at Temp. Aging ~ es ~C) (Day) 4ï 47 6i 71 _ .. _ _ _ ~ . . . . _ . _ _ _ _ . . . _ am ~kPa) 22.8 0 859 899 686 605 Em (%) " " 26.4 20,1 33.4 ~4.9 E ~kPa) " " 5783 8096 3742 3117 Em (%) -45.6 " 37.2 30,3 52.0 54,5 Er ~%) ~ ~I 41.7 33.3 58.1 56.7 ~m ~%) ~53-9 " 27.7 27.5 45.8 47.7 Er ( ) 33.6 30.3 48.9 50.6 ~m ~kPa) 22.8 14 895 959 746 693 ~m ~%) " " 24.8 20.6 30.0 29.8 E ~kPa) " " 6587 8089 4424 4059 `~m ~kPa) 22.8 28 916 980 794 754 Em (%~ " " 24.0 21.0 29.8 29.6 E (kPa) " " 6570 825~ 4773 4463 Em (%) -45.6 " 35.9 28.8 48.0 48.4 Er ~%) ~ 40.1 31.8 50.5 51.1 ~m (kPa) 22.8 56 873 996 811 799 Em ~%) ~ 22.1 20.9 24O5 23.5 E (kPa) " " 6402 9713 5626 5642 Em (%) -45.6 " 27.7 22.9 38.3 32.3 E~ f%) " 32,5 26.8 40,4 33,6 , R ~NCo/nH ratio) 0.80 0.80 0.725 0,70 ~: :: . ' ~L~8695iS
TABLE X
.
M hanical Propert;es of R-45}~ Propellants Lot 606095; Fl,EX.61I, Types C and E Antioxidants Properties at Temp. Aging Mi xes _ (C) ~ay) 72 60 66 73 m CkPa)22.8 0 483 674 499 584 m ~%) " " 35.7 31.4 35.7 28.2 E CkPa) " " 2461 3663 2641 3835 m C%) -45.6 " 49,8 47,8 50.9 49.9 E r ~%) "- " 56.0 50.8 58.1 52.5 m ~%) ~53 9 " 44~0 42.8 45.9 45.4 r (%~ 47.6 43.5 49.0 47.1 am (kPa)22.8 14 614 720 611 724 ~%) ~ 29.9 30.6 31.3 28.7 E ~kPa) " " 3510 4207 3490 4517 a ~kPa)22.8 28 654 793 571 814 ~%) 1l 1l 29.1 29.1 30.0 27.8 E (kPa) " " 3725 4647 3819 5281 m (%) -45.6 " 49.6 43.4 49.9 45.2 (%) 1l 1~ 52,1 46.2 51.7 46.8 am ~kPa)22.8 56 722 849 739 797 m (%) " " 26.8 26.6 28.5 23.9 E (kPa) " " 4306 5526 4701 6142 m ~%) -45.6 " 43.1 39.4 44,6 34.8 r ~%) " " 44.7 40.5 46.7 37.3 R NCO/OII ratio 0.75 0.75 0.725 0.75 FLEX.6H (% of R-4511T) 1.00 - - 0.75 DTB~IQ (~ of R-4511T) - 0.50 0.50 0.25 FLEX.7L (O of R-4511T) - 0.50 0.50 .
~ ~ 27 .~ .
. i .
. . .
~ 6~iS
Optimization of Bonding Agents in Propellants Containing Type D Antioxidcmts Two propellants (mixes 65 and 61) containing the 50/50 mixture of DTBHQ/FLEXZONE 6H (type D antioxidants) performed very well with respect to pot lives (Table VIII) and mechanical properties (Table XI). Mix 61, in particular, having an NCO/OH ratio of 0.75 showed 6ml ~m and E of 6.50 kPa, 32.5% and 3657 kPa at room temperature and ~m of 50.8 and 44.9% at -45.6 and _53 9C respectively. In most of the previous compositions, the concentration of PAZ/PAM
bonding agents was kept at 0.8/0.2 percent of the binder. Three propellants having an NCO/OH of 0.75 (lmixes 68, 69 and 70) were formulated to verify the effect of changing the PAZ/PAM concentrations to 0.4/0.2, 1.2/0.2 and 0.8/0.4 percent. All the pot lives were longer than 6 hours (Fig. 6) and the mechanical properties were excellent. The preferred PAZ/PAM ratio is that of mix 70 (0.8/0.4) which yielded an ~m of 45.8 percent at -45.6C after 56 days of aging. `~
... . .
695~i TABLE Xl Mechanical Properties of R-45~ PTopellants Lot 606095; Type D ( ) Antiox;dant Propcrties at ~'emp. Aging Mixes (C)~Day~ 65 61 68 69_ 70 am (kPa) 22,8 o 529 650 616 714 578 ~m (%) " .. 32~ 32~5 37,7 30,835,4 E (kPa) " " 2929 3657 3210 41013078 Em (%)-45,6 " 52,5 50,8 55,9 48,952,5 ~r (%) " 57,0 55,6 58,8 51,557,2 Em (%)-53'9 '' 46,7 44.9 48.2 43.148.7 Er (%) " " 51,0 48.1 49.8 45,850.9 am ~Pa)22.8 14 635 724 676 800 673 m (%) " " 29,7 30.2 33.1 27,032.5 E ~kPa) "i ~ 3940 4297 38404836 3~7 m (kPa) 22.8 28 700 819 731 818 713 E (%) 1l 11 29.7 28.6 30.1 27.730.9 E (kPa) " " 4451 5089 42864781 3932 Em ~%)-45.6 " 51.0 44.1 45.9 45.349.3 ~r (%) " " 54.8 45.9 48.4 48.154.7 -m ~kPa) 22,8 56 766 816 718 825 779 ~m (%) " 26,2 25,0 24,6 25,6 279 E (kPa) " " 5428 5445 51735260 4768 ~%~45,6 " 44,0 38,1 - 33,7 40.145.8 ~r (%) " ~ 47.2 40,0 35,6 41,9,48,0 R NCO/OII ratio 0,725 0,75 0,75 n ~ 75 0.75 PAZ (% wt of binder) 0,8 0,8 0,4 1,2 0,8 PAM (% wt of binder) 0,2 0,2 0,2 0,2 0,4 ~1) Type D antioxid~nt is a 50/50 mixture of DTB~lQ/rlJrA~7nNr 611.
.
:
. - . . - , . . : : . , , :
.: . . . . .:
Comparison Be~ween the Two Lots of R-45HT
The Lon er Pot Lives of Propellants Based on Lot 606095 ~g The longer pot lives obtained with Lot 606095 are not easily explicable. Various laboratory tests were conducted on the R-45HT
prepolymers Lots 403245 and 606095. No significant difference could be found to date with such tests as the equivalent weight (OH groups), the water content, the GPC and VPO. Viscosity measurements over the temperature range of 20 to 60C Led to almost identical results for both lots. It is possible, however, that the two-year period elapsed between the manufacturing of Lot 403245 and the addition of an anti-oxidant could have contributed to a certain deterioration of the prepolymer by homopolymerization. In an attempt to minimize the degradation of the product, the second lot of R-45HT was purchased with the additional specification "that the material must be delivered within six months after its manufacture". j ~ -! Mechanical P~ r~
Very little difference could be found between the mechanical properties of propellants based on R-45HT Lot 403245 and those from Lot 606095. The proper~ies of two propellants containing DTBHQ, mix 25 (Lot 403245) and mix 64 (Lot 606095) are compared in Table XII.
For nearly identical ~ m (681 versus 686 kPa), mix 64 shows slightly hlgher~el~gà~t~s~atll~owtte~pe~at~u~e~ IT~herr~dûG~e!d~val~ès,;~ich are an indication of the stability of the two propellants upon accelerated aging at 60C, are also nearly the same. Some post-curing is obvious with increases of 6m~ E and reduction in the elongation.
.... . . .
..
. :.. . ::
~`
1ai8~9~;S
TABLE XIT
Mechanical Propertics of R-45liT Propellant~s Containin~ 1% OTBI!~ -~Lots 4U3~4~ and ~06095) Reduced Value A~ Mix 25, Lot 403245 t - O t . 56 t56/to a `(XPa) @ 22.8C 681 857 1.20 m (%) ll 30.5 21.70.71 E (kPa) " " 4154 7443 1.79 m (%) @ -45.6 43.9 31.5 0.72 Er (%) " " 50.2 35,1 0.70 ~%) @ 53 9 33.1 T ( ) 41.1 B) Mix 64, Bot 606095 a (kPa) ~ 22.8C 686 811 1.18 ~m C%) " 33.4 24.5 0.73 E (kPa) " " 37¢2 5626 1.50 F (%) @ -45.6 . 52.0 38.3 0.74 m r (%) " " 58.1 40.2 0.70 m- (%) @ ~53 9 45.8 - _ r (%) " " 48.9 ~ ~
(1) t = O for initial properties.
t _ 56 for properties after 56 days of aging at 60C.
.
': :
.
. .. . - ,, ., ~ , . . , . , :
:.: ,:, :' . ~ :. . . , . . , ' . . :
,.. . . . .
~a~sss The Preferred Antioxidant (g) Based on the data collected during this study, it appears difficult to assign a relative value to each of the candidate anti-oxidants. Because of the unacceptable processing properties of the resulting propellants, three antioxidants (AO-2246, NAUGARD Q and OCTAMINE) were eliminated early during the study. The four other candidates (DTBHQ, FLEXZONE 7L, FLEXZONE 6H and UOP-36) used alone in the case of DTBHQ or in combinations (DTBHQ with the three others) ,yie'W eAdiexcellent!)processing~aharactbr~s~icsian!d-!ac2eptable~mechanical ~' properties. In compositions incorporating a single antioxidant DTBHQ is the only candidate that meets the objective of a pot life of at least 4.5 hours, notwithstanding a more pronounced post-curing effect. Combinations of DTBHQ with one of the p-phenylene diamines (FLEXZONE 7L, FLEXZONE 6H or UOP-36) also yielded excellent results. A preferred combination would be type D (50150 mixture of DTBHQ~FLEXZONE 6H) on account of its superior mechanical properties.
.. . . . . . . .
:
.' ' ' . ' . '~ ' : ' ' . ' .
:, . . .
,. ~ ' ' : ~. ,
Claims (26)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A curable binder system for use in forming a castable composite propellant which comprises (i) a hydroxy-terminated butadiene polymer of the structural formula wherein n = 57-65 (ii) a diisocyanate curing agent, and (iii) a bonding agent system of an aziridine polyester which is the reaction product of an aziridinyl phosphine oxide and a poly-carboxylic acid, and and amine polyester which is the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid.
2. A binder as claimed in Claim 1, wherein the aziridine polyester is the reaction product of tris-(2-methyl aziridinyl-1) phosphine oxide and a diacid selected from the group consisting of a straight chain diacid of general formula HOOC(CH2)XCOOH, x being 2 to 8, and a substituted diacid of general formula HOOC CH(R) (CH2)yCH(R1)COOH in which R and R1 may be similar or different being H or OH, and y = 0 to 6, the phosphine oxide being reacted in an amount of 1 mole per carboxyl equivalent of the acid.
3. A binder as in Claim 2 wherein the diacids are d-tartaric and adipic in the respective proportions of 0.15 and 0.3 mole per mole of the phosphine oxide.
4. A binder as claimed in Claim 1, wherein the amine polyester is a polymer derived from N-methyldiethanolamine and sebacic acid.
5. A binder as claimed in Claim 1, 2 or 4 wherein the aziridine polyester is present in an amount of 0.1-1% by weight of the total binder, and the amine polyester is present in an amount of 0.1 to 0.5% by weight of total binder.
6. A binder as claimed in Claim 1, 2 or 4, wherein the diisocyanate curing agent is DDI used in a proportion so that the NCO/OH ratio is in the range of 0.65-0.95.
7. A binder as claimed in Claim 1 which contains isodecyl pelargonate as plasticizer.
8. A binder as claimed in Claim 1, and further comprising an antioxidant selected from the group consisting of N-phenyl, N'-(1,3 dimethylbutyl) p-phenylene diamine, N-phenyl, N'-cyclohexyl-p-phenylene diamine, di-tert-butylhydroquinone, and combinations thereof in an amount of about 1% by weight of the hydroxy-terminated polybutadiene polymer.
9. A binder as claimed in Claim 8, wherein the antioxidant is di-tert-butylhydroquinone.
10. A binder as claimed in Claim 8, wherein the antioxidant is a combination of about 25-75%/w di-tert-butylhydroquinone and about 75-25%/w N-phenyl, N'-cyclohexyl-p-phenylene diamine.
11. A binder as claimed in Claim 8, wherein the antioxidant is a combination of about 25-75%/w di-tert-butylhydroquinone and about 75-25%/w N-phenyl, N'-(1,3-dimethyl-butyl)-p-phenylene diamine.
12. A binder as claimed in Claim 10, wherein the antioxidant is a combination of about 50%/w di-tert-butylhydroquinone and about 50%/w N-phenyl, N'-cyclohexyl-p-phenylene diamine.
13. A binder as claimed in Claim 8, wherein the aziridine polyester is present in an amount of 0.4-0.8% by weight of the total binder, and the amine polyester is present in an amount of 0.2-0.4%
by weight of total binder.
by weight of total binder.
14. A binder as claimed in Claim 13, wherein the aziridine polyester is present in an amount of 0.8%/w of the total binder and the amine polyester is present in an amount of 0.4%/w of total binder.
15. A castable propellant comprising the binder of Claim 1 having dispersed therethrough finely divided ammonium perchlorate as oxidizer and finely divided aluminum, the former being present in an amount of 68-88% by weight of the total propellant and the latter being present in an amount of 0-20% by weight of total propellant.
16. A propellant as claimed in Claim 15, and further comprising comprising a burning rate catalyst consisting of 0.1-1% by weight of the propellant composition of ferric oxide.
17. The propellant of Claim 16, wherein the oxidizer is present as a di or trimodal distribution of average particle size between 1 and 400 µm.
18. The propellant of Claim 17, wherein the aluminum has an average particle size in the range 5-50 µm.
19. TThe propellant of Claim 15, 16 or 18 containing isodecyl pelargonate as plasticizer.
20. The propellant of Claim 15, 16, or 18 containing DDI as curing agent.
21. The propellant of Claim 15, wherein the binder further comprises an antioxidant selected from the group consisting of N-phenyl, N'-(1,3 dimethylbutyl) p-phenylene diamine, N-phenyl, N'-cyclohexyl-p-phenylene diamine, di-tert-butylhydroquinone, and combinations thereof in an amount of about 1% by weight of the hydroxy-terminated polybutadiene polymer.
22. The propellant of Claim 21, wherein the antioxidant is a combination of about 50%/w di-tert-butylhydroquinone and about 50%/w N-phenyl-N'-cyclohexyl-p-phenylene diamine.
23. The propellant of Claim 22, wherein the aziridine polyester is the reaction product of tris-(2-methyl aziridinyl-1) phosphine oxide and d-tartaric and adipic diacids and wherein the amine polyester is a polymer derived from N-methyldiethanolamine and sebacic acid.
24. The propellant of Claim 23, wherein the aziridine polyester and amine polyester are present in amounts of 0.8% and 0.4%, respectively by weight of binder.
25. A method for the manufacture of a composite propellant which comprises (i) mixing together liquid ingredients comprising a hydroxy terminated butadiene prepolymer of the structural formula wherein n = 57-65 a plasticizer and a bonding agent system of an aziridine polyester which is the reaction product of an aziridinyl phosphine oxide and a polycarboxylic acid, and an amine polyester which is the reaction product of an alkanolamine and a saturated aliphatic polycarboxylic acid. at atmospheric pressure, (ii) adding solid ingredients comprising finely divided aluminum metal, ferric oxide as burning rate catalyst and about 75% of the total amount of ammonium perchlorate oxidizer and mixing to substantially even dispersion, (iii) heating at about 60°C under vacuum for about 1 hour, (iv) releasing the vacuum, (v) adding the remainder of the ammonium perchlorate oxidizer and a diisocyanate curing agent, and mixing (vi) reapplying vacuum and heating to about 60°C for about 45 minutes, (vii) casting the resulting mixture into molds under vacuum.
26. A method according to Claim 25, wherein the diisocynate curing agent is added and admixed prior to addition of the remainder of ammonium perchlorate oxidizer.
Priority Applications (13)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/888,542 US4427468A (en) | 1976-01-16 | 1978-03-21 | Curable propellant binding systems with bonding agent combination |
| GB19718/78A GB1604197A (en) | 1977-12-13 | 1978-05-16 | Polyester bonding agents for htpb propellants |
| DE19782830495 DE2830495A1 (en) | 1977-12-13 | 1978-07-11 | NETWORKABLE BINDING SYSTEM FOR USE FOR THE FORMATION OF A POURABLE FUEL MASS |
| FR7822599A FR2411872A1 (en) | 1977-12-13 | 1978-07-31 | COMPOSITION OF BINDER FOR PROPULSIVE POWDERS |
| BE189782A BE869617A (en) | 1977-12-13 | 1978-08-08 | COMPOSITION OF BINDER FOR PROPULSIVE POWDERS |
| IT50927/78A IT1106293B (en) | 1977-12-13 | 1978-08-31 | POLYESTER BINDING AGENTS FOR POLYBUTADIENE-BASED PROPELLANTS WITH HYDROXYL TERMINAL GROUPS |
| JP12249878A JPS5484016A (en) | 1977-12-13 | 1978-10-04 | Binder for blended propelling agent |
| NO783480A NO146492C (en) | 1977-12-13 | 1978-10-13 | HARDENABLE BINDING MATERIAL FOR USE IN THE PREPARATION OF A CASTABLE FUEL AND USING THE BINDING MATERIAL |
| DK539078A DK539078A (en) | 1977-12-13 | 1978-11-30 | HARDWARE BINDERS FOR USE IN MOLDY FUELS MOLDY FUELS CONTAINING SUCH BINDERS AND PROCEDURES FOR THE PRODUCTION OF SUCH FUELS |
| SE7812668A SE444808B (en) | 1977-12-13 | 1978-12-08 | HARDENABLE BINDING AGENT, FOR USE IN THE PREPARATION OF A CASTABLE FUEL, BASED ON A BUTADIENE POLYMER WITH FINALLY HYDROXYL |
| NL7812148A NL7812148A (en) | 1977-12-13 | 1978-12-13 | HARDABLE BINDER SYSTEM FOR USE IN FORMING A CASTABLE COMPOSITE DRIVE. |
| SE8304823A SE451068B (en) | 1977-12-13 | 1983-09-08 | FUEL OF THE POLYBUTADIA TYPE WITH HYDROXYL GROUPS IN THE END AND THE PROCEDURE FOR ITS PREPARATION |
| US06/575,727 US4517035A (en) | 1976-01-16 | 1984-02-03 | Method of making a castable propellant |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NO770011A NO144486C (en) | 1976-01-16 | 1977-01-04 | HARDENABLE BINDING AGENT. |
| NO77.0011 | 1977-01-04 | ||
| US80399277A | 1977-06-06 | 1977-06-06 | |
| US803,992 | 1977-06-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1086955A true CA1086955A (en) | 1980-10-07 |
Family
ID=26647627
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA292,954A Expired CA1086955A (en) | 1976-01-16 | 1977-12-13 | Polyester bonding agents for htpb propellants |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1086955A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115925497A (en) * | 2023-02-07 | 2023-04-07 | 北京理工大学 | HTPB (HyperText polybutadiene) based adhesive system with enhanced mechanical property and preparation method thereof |
-
1977
- 1977-12-13 CA CA292,954A patent/CA1086955A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115925497A (en) * | 2023-02-07 | 2023-04-07 | 北京理工大学 | HTPB (HyperText polybutadiene) based adhesive system with enhanced mechanical property and preparation method thereof |
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