Robust, Perchlorate-Free Propellants With Reduced Pollution (PP-1404)SERDP/ESTCP Technical Symposium and Workshop • Washington, DC • Dec 4-6, 2007
The Problem: Ammonium PerchlorateGroundwater Contamination
An estimated 24 million pounds of ammonium perchlorate (AP) are manufactured every year, mostly for DoD use. The perchlorate ion is extremely soluble and stable, percolating into and persisting in surface and groundwater. Perchlorate has been detected in the groundwater at rocket motor manufacturing and testing sites. (C. Hogue, Chem & Eng. News 8/10/03)
The perchlorate ion blocks iodine uptake in the thyroid, and thus is a human health concern
New technologies are needed in order to replace AP in energetic materials formulations. A perfect AP replacement, with all its virtues and none of its environmental problems, is an extremely unlikely discovery
Solid Rocket Propellant Characteristics Solid propellants contain a fuel and an oxidizer in an elastomeric binder
Common fuel is aluminum; common oxidizer is AP; common binder is a polybutadiene rubber
Solid propellants require good mechanical properties to withstand explosive ignition, rough handling etc.
Good mechanical properties require chemical bonding between the solid fillers and the binder system
Special bonding agents have been developed for use with AP. These do not generally work with other oxidizers
Ammonium Perchlorate As A Propellant OxidizerIn many ways, AP is the ideal propellant oxidizer
1. It is inexpensive to manufacture
2. It is stable in shipping, storage and use
3. It is easily and safely ground to any particle size, and processes well
4. It is compatible with most other formulation ingredients and binder cure reactions, developing excellent mechanical properties
5. Bonding agents, specific to AP, have been developed which chemically link the AP crystals and the propellant binder, strengthening the composite into a tough, rubbery material
6. It has very good combustion characteristics, producing oxygen and gaseous byproducts, with a
low burn rate pressure exponent. Burn rates can be tailored via particle sizes and catalysts specific to AP
A “Green” Energetic Oxidizer To Replace Ammonium Perchlorate
A “green” AP replacement must be “like AP, only better.”
1. It must process well with low mix viscosity, allowing for a good pot life and easy casting
2. It must be compatible with binder cure (or vice versa)
3. It must contribute to good mechanical and aging properties. Its particles should chemically bond to the binder
4. It must have no solubility issues, decompositions or unwanted physical or chemical reactions during storage
5. It must have or contribute to good safety properties
6. It must have minimal environmental impact in manufacture and use
7. It must be at least as energetic as AP; the higher the performance the better
Approved for public release; distribution is unlimited.
Coating and Bonding of ADN
Coatings for particulate energetic ingredients are desirable because a coating can reduce sensitivity to unwanted initiation, or reduce reactivity with other formulation ingredients. Coatings make the ingredients safer to handle and prolong the service life of the composite. Coatings for ADN have been applied and evaluated
If the coating compound is also a bonding agent, it allows the particle to chemically interact with the composite polymer matrix, reinforcing and strengthening the composite. Without bonding agents, the particles tend to weaken the tensile properties of the composite
ADN does not have the proper chemistry to utilize the coating and bonding agents which have been developed for AP. Other coating agents and methods of coating and bonding are under development for AP replacements. Dendrimeric molecules having multiple end groups for association or partial solution in the ADN crystal surface have been synthesized and tested. Some of the dendrimer end groups have been derivatized to cure into the binder materials
AP Replacement Candidates
Some Crosslinkers and Binders Synthesized for Evaluation
Varying structures of oligomers and crosslinkers allows tailorability of the properties of the polymer binder
Varying the number of reactive sites on the oligomer and/or the crosslinker influences the crosslink density
Increasing the crosslink density increases stress in the binder
Lengthening chains between crosslinks increases strain in the binder
Varying the polymer chain structure influences stress, strain and glass transition temperature
Trading off these properties gives the propellant the proper balance of hardness, toughness, and resistance to environmental stresses
The pressure exponent of most AP replacement candidates tends to be high. It can sometimes be lowered by additives or physical changes in the ingredients. Only formulation experience with replacement ingredients can reduce the exponent; no theory or road-map exists. Non-AP formulations with moderate pressure exponents have been made
Ballistic TailoringSmall Motors for Evaluation of Propellant
A rocket motor needs a specific burning rate at specific pressure. It also needs a low burn rate pressure exponent, otherwise combustion rates can increase disastrously at high pressures. AP propellants are easily tailored for burn rate and typically have low pressure exponents
Mechanical Properties Testing With Instron Test Machine
Mechanical properties of propellant formulation must satisfy missile require-ments. Determinations include stress, strain and elastic modulus at high, low and ambient temperatures
Propellant sample in Instron test apparatus
Below is a recording of the sample being pulled in the Instron. As the propellant stretches (strain; X-axis) it resists with its own force (stress; Y-axis). If the particles of oxidizer (green) are bonded to the binder matrix, they resist pulling away from the particles (dewetting; yellow), and the propellant resists breaking
ConclusionsThe triazole cure has been shown to be a more robust alternative to the more conventional urethane cure
Prilling of ADN can be done to produce round particles of desired sizes
Dendrimers show promise of leading to improved processing and improved mechanical properties in non-AP propellants
ADN (Ammonium Dinitramide)CL-20
(Hexaazahexanitroisowurtzitane)
O2NN NNO2
O2NN NNO2
O2NN NNO2
O2NN NNO
O2NN NNO2
NNO
Ammonium Nitrate
N—NO2NO2N—
NF2
NF2
F2N
F2N
Tetrakis (Difluoramino)Octahydro-Dinitro-Diazocine (HNFX)
NO3-NH4
+NO2
+ NNO2
NH4 N-
Improved Oxidizer Utilization
More RobustRubbery Binders
Better Prilling/Particle Resizing/
Propellant Formulation
New Coatings and Bonding Agents
New Ingredients, Ballistic ModifiersMulti-property Tailoring
Evaluation
Safety/Sensitivity Mechanical Ballistic
AgingEnvironmental
Optimized Propellant
Technical Objective
Develop a Technology Base For AP Replacement Candidates, Which Will Allow Their Use Despite Any Deficiencies, Compared To AP, They Might Possess
1. Develop more robust binders for better compatibility with alternative oxidizers such as ADN, AN, and organics, and advanced fuels. Current binders often exhibit cure problems with these reactive new materials
2. Concurrently, develop modifications of ADN and other energetic ingredients to enhance their compatibility with binders, curatives, and other propellant ingredients. Advanced methods of particle sizing and shaping, as well as coatings and bonding agents will be developed
3. The new ingredients will thus be tailored to the formulation, and vice versa. Other properties will be tailored as needed
Technical Approach
Binder System ImprovementsThe cyclization of polyazides and polyacetylenes to form triazole rings (the “triazole cure”) is a robust reaction which allows use of AP replacements whose reactivity interferes with conventional urethane polymer cures. Both reactions link molecular chains into solid, rubbery networks (see below)
Many oligomers have been derivatized with acetylene and azide terminations and many acetylene crosslinkers have been synthesized. Monitoring of the cure reaction by heat-flow calorimetry, IR and NMR has been done. Determinations of the extent of polymerization, the molecular weights and the polydispersities of the triazole polymers are underway. We are working to mimic the diversity of feedstocks available for the urethane cure in triazole precursors, in order to make the triazole cure as universally applicable as the urethane cure is
Urethane Linkage
R N
C
O
N
C
O
R'OH OH+
DI-ISOCYANATE DIOL
NH
C
O
ROR' NH
C
O
O R'
URETHANE-LINKED POLYMER STRUCTURE
Triazole Linkage
DI-AZIDE
RN
N+
-N
N
+NN-
R'C CCHHC
DIACETYLENE
N
N
RN
TRIAZOLE-LINKED POLYMER STRUCTURE
R'C CH
N
NN
R'CHC
Synthesis of Polyazido and Polyacetylenic Oligomers and Curatives
OOH
HO
n
OOTs
TsO
n
ON3
N3
n
OONO2
O2NO
n
p-TsCl
NaN3
HNO3
NaN3
Direct AZIDE Substitution
PolyolStarting Material
O
n
O
n
N3OH
O
N3O
O
N3
O
O
C OH
OHC
CO
O
HCC
O
O
CH
Azidoesterification
Polyacetylene Derivatization
Photomicrograph and scanning-electron microscope pictures of ADN prills
Prilling is a process where solids are melted and the molten material is sprayed into droplets, which are cooled and quenched into spheres
The spherical shapes process better in formulations than the irregular-shaped crystals of the original solid material
ADN Priller
• Melt zone
• Droplet formation
zone
• Solidification zone
ADN Prilling For Processibility
Publications Sponsored by PP-1404
“Further Developments in Triazole Binders and Propellants” D. A. Ciaramitaro, T. Jacks, J. M. Hitner and T. Bui. JANNAF PEDCS-S&EPS Meeting, Seattle, WA July 26-29, 2004. CPIA Publication JSC CD 34 (2004)
“Triazole Crosslinked Polymers in Recyclable Energetic Compositions and Method of Preparing the Same” D. A. Ciaramitaro. U. S. Patent No. 6,872,266, March 29, 2005
“High-Energy Propellant with Reduced Pollution” D. A. Ciaramitaro and R. Reed. US Patent 6,805,760B1, Oct 19, 2004.
“Monitoring Binder Cure Kinetics with Microcalorimetry” L. Lusk, D. A. Ciaramitaro, H. M. Matheke and A. Chafin. JANNAF PCDS-S&EPS Meeting, Seattle WA July 26-29, 2004. CPIA Pub JSC CD 34 (2004).
“Advanced Rocket Motor Formulations with Alternative Binder Cures” D. A. Ciaramitaro, T. Jacks and A. Lieux. JANNAF PEDCS-S&EPS Meeting, Destin, FL, March 6-9, 2006. JSC CD 42 (2006).
“Ammonium Dinitramide Prilling Process” K. P. Ford, D. L. Dean, C. P. Waltz, D. P. Pate, and J. J. Hosto. JANNAF PEDCS-S&EPS Meeting, Destin, FL, March 6-9, 2006. JSC CD 42 March 2006
“Robust, Insensitive Propellant for Air Launched Missile Systems” D. L. Dean, D. A. Ciaramitaro, S. Nguyen, F. J. Dodson, R. W. Pritchard, T. S. Ward and K. P Ford. JANNAF PEDCS-S&EPS Meeting, Destin, FL, March 6-9, 2006. JSC CD 42 March 2006
“Triazole-Oligomers by 1,3-Dipolar Cycloaddition” A. R. Katritzky, S. K. Singh, N. K. Meher, J. Doskocz, K. Suzuki, R. Jiang, G. L. Sommers, D. A. Ciaramitaro and P. J. Steel. ARKIVOC 2006, (v), 43-62.
“Dendrimers for Improved Mechanical Properties of Composite Propellants” Peter Zarras, David Ciaramitaro, David Dean, Samantha Hawkins, Kara D. Lormand and Lawrence Baldwin. 231st ACS National Meeting, Polymeric Materials Science & Engineer-ing 94, 258 (2006).
“New Polymerization Reaction Promises Less Toxic, More Robust, More Environmentally Friendly Composite Materials” D. A. Ciaramitaro. Currents, the Navy’s Environmental Magazine Spring Issue, April 2006
“Triazole-Cured Binder Structure/Property Correlations” D. A. Ciaramitaro, K. Baum, W. Lin, A. R. Katritzky, R. Duran and N. K. Meher. JANNAF PEDCS-S&EPS Meeting, Reno NV, August 13-16, 2007. In press.
“Getting the AP Out: What it Means to Make a Greener Propellant” D. L. Dean, F. J. Dodson, S. Nguyen. JANNAF PEDCS-S&EPS Meeting, Reno NV, August 13-16, 2007. In press.
“Preparation and Characterization of 1,2,3-Triazole-Cured Polymers from Endcapped Azides and Alkynes” A. R. Katritzky, N. K. Meher, S. Hanci, R. Gyanda, S. K. Tala, S. Mathai, R. S. Duran, S. Bernard, F. Sabri, S. K. Singh, J. Doskocz, D. A. Ciaramitaro. J. Polym. Sci.: Chemistry 2007. In Press.
“Dendritic-Based Bonding Agents for High Density Insensitive Munitions (IM) Propellant Formulations” Peter Zarras, David Dean, David Ciaramitaro, Suong Nguyen, Fred J. Dodson, Lee R. Cambrea and Lawrence Baldwin. 235th ACS National Meeting, Polymeric Materials Division, New Orleans, LA. April 6-10, 2008. ACS Polymer Preprints. In Press.
University Of Florida, GainesvilleAlan R. Katritzky Heterocyclic chemistry expertiseRandolph S. Duran Polymer engineering Nabin K. Meher Triazole reaction mechanism Sandeep K. Singh Small samples Srinivasa R. Tala Reactivity studiesSureyya Hanci Analysis techniques Chunming Cai Direct azido-substitutionYuming SongReena Gyanda Firouzeh SabriDiana GomezLing WangSophie Bernard
Fluorochem, Inc.Kurt Baum Synthesis scaleupWendy Lin Samples, Analyses ATK Thiokol, Inc.Alex Paraskos Energetic materialsScott Lusk Synthesis and samples CD Systems, INC.Victor Crainich Particle coating samples of materials
Air Force Research Lab, Edwards AFBTom Hawkins Rocket motor firings
SERDP SponsorsCharles Pellerin and Bruce Sartwell
NAWCWPNS China Lake David A. Ciaramitaro Project managementDavid L. Dean Sample evaluationPeter Zarras Formulation, evaluationFred Dodson Evaluation Alan Turner ADN prilling, sizing Terrie Jacks Dendrimer coating synthesis Suong Nguyen Coating evaluationsTrent Ward Methodology Kevin WardCristina LovernAndrew Lieux
conc. HClHO
C
OH
OH
HO
H2C CH
CN
THF
NaN3
DMF
C O NH
O OH
OHOH
C O NH
O N3
N3N3
C O CN C O COOH
C OOH
C OOMs
C ON3
C ONH2
C O CN
C O CN C ONH2
H2C CH
CN
C ON
CN
CN
conc. HClC O
N
COOH
COOH
C ON
OH
OH
C ON
N3
N3
acrylonitrileDI water
pentaerythritol
+
Tetrakis(5-cyano-2-oxabutyl)methane (Tetranitrile)
1hr, 70-75oCTetrakis(5-carboxy-2-oxabutyl)methane,
Triton B
(Tetraacid)
Tetrakis(5-hydroxy-2-oxapentyl)methane (Tetraol)
BH3*THF, dry THF
25oC, 24 hours
MsCl/Et3N
Tetrakis(5-mesyloxy-2-oxapentyl)methane (Tetramesylate)
Tetrakis(5-azido-2-oxapentyl)methane (Tetraazide)
1. MeOH, dry HCl, 2 hours
2. Tris 6
4
Dodecylol (12-mer)
1. MsCl/Et3N
2. NaN3/DMF
4
Dodecylazide, 12-mer)
4 4
4 4
4
Pd/C, H2
25oC, 7 hrs4
Tetrakis(5-amino-2-oxapentyl)methane (Tetraamine)
4
Tetranitrile
4
Tetranitrile
BH3*THF, dry THF
70oC, 24 hours 4Tetraamine
MeOH/H2O
0-80oC
Octanitrile
1hr, 70-75oC
Octanitrile
BH3*THF, dry THF
25oC, 24 hours
4
4
4Octaol
1. MsCl/Et3N
2. NaN3/DMF
4Octaazide
SERDP Dendrimer Synthesis
NH4+N-
N
N
O
O O
O
CO
OO
OH
OH
HO
OHO
Structural Correlations With Triazole Reaction Rates
1. The activation of the acetylenic function by an ester group allows lower reaction temperatures for faster cure
2. Lack of this activation requires longer cure times and higher temperatures
3. Steric hindrance of the acetylenic function slows the reaction rate
4. The azido-oligomer structure also influences the rate of cure
5. These differences in reactivity cause changes in the mechanical properties of the polymer, which will enable tailoring as needed for any application
A propellant formulation for a specific missile needs a specific burning rate at specific pressure. AP propellants are easily tailored for burn rate
The firing of small motors on static fixtures (test stands) allows burn rate and other data to be developed with a minimum expenditure of material. Such a facility is valuable when the ingredients and binders are in short supply, as they invariably are early in their development
The picture above is a schematic of a small motor assembly, with the cured formulation in green. The one at right shows a small motor being fired. The test stand can be instrumented to take pressure and temperature data, as well as thrust readings
Propellant Burning Rate Versus Pressure
1 0 0 0 1 0 0 0 0
P re s s u re - P s ia
P r o p e l l a n t w i t h L o w P r e s s u r e E x p o n e n t
P r o p e l l a n t w i t h H i g h P r e s s u r e E x p o n e n t
Schematic of Dendrimer Bonding Agent with ADN