TECHNOLOGY AREAS: Air Platform, Materials/Processes, Space Platforms

ACQUISITION PROGRAM: Strategic Systems Programs ACAT I

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: To develop a new class of bonding agents for high energy propellants that improve aging, insensitive munitions (IM) characteristics, reduced cycle costs of rocket motor propellants and can provide safety enhancements to existing systems.

DESCRIPTION: Bonding agents are critically important components of solid rocket propellants which affect processing, mechanical properties, ballistics, safety, aging, temperature cycling, and IM propellant characteristics. A bonding agent is defined as a material that interfaces with the surface of the oxidizer and is chemically reacted to the polymeric binder network during the propellant cure process. Both requirements are necessary to have an effective bonding agent. Bonding agents are a small component (0.3-0.5%) of the overall propellant formulation, but is the most important ingredient in the formulation. Processing is improved with higher solids loading above 75% solids by wetting the solids and improving stress-strain curves and eliminating dewetting (voids and micro porosity) in the propellant. The elimination of micro porosity lowers the burning rate slope and Pi sub k. Safety, aging, temperature cycling, and IM can also be improved by the elimination of micro porosity as it improves the shot-gun tests as when the pellet is broken-up, the fragments are still coated with the polymeric binder rather than forming a porous bed of uncoated oxidizer. When the coated fragments burn, the burning slope is lowered and prevents a deflagration to detonation scenario. Similarly, the aging and temperature cycling capability can be improved by the elimination of dewetting as the dewetting will increase the chance of grain cracking and crack propagation. During the fragment and bullet impact the elimination of dewetting results in a less violent event and can restrict the throwing of chunks of propellant to less than 50 feet, thus resulting in an IM type propellant. The critical diameter can also be improved, especially for larger diameter motors, as the elimination of porosity will prevent a deflagration to detonation. Bonding agents have been developed and are typically used in ammonium perchlorate (AP) oxidized propellants using a hydroxyl terminated polybutadiene (HTPB) binder. However, effective bonding agents do not exist for multi-functional oxidizers (ammonium perchlorate (AP), ammonium nitrate (AN), nitramines, glycidyl azide polymer (GAP), ammonium dinitramide (ADN), etc.) with nitrate esters in polyether binder systems. A need exists to improve the strain capability of these propellants so that their rocket motors can be aged temperature cycled, and fired over a wide temperature range without cracking the propellant grain. As rockets based on this technology are developed because of their enhanced safety, environmental as well as high energy performance advantages, the importance of suitable bonding agent ingredients becomes a critical technology. The newly developed bonding agents should meet the following requirements: Meet the complete definition of bonding agents; interact with the surface of the oxidizers and be chemically reacted to the polymeric binder during the propellant cure process; function for a number of different oxidizers (AP, AN, potassium perchlorate (KP), cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitrate (RDX), ADN, etc.) in the presence of nitrate esters; have functional groups that will react with the propellant binder; be neutral or slightly acidic to avoid decomposition of nitrate esters and oxidizers such as HMX/RDX/AND; be soluble in different binder systems [hydroxyl terminated polybutadiene (HTPB), polyethers, etc.]; be functional for cure systems with isocyanate/hydroxyl (NCO/OH) ratios of 1/1 or less than 1/1; and be cost effective and domestically produced. Because of crosslink density, more than one bonding agent maybe required. The metric of success is a bonding agent meeting all the stated characteristics above and that doubles the tensile strength and triples the elongation at maximum stress of the propellant. There are three problems that may occur in developing bonding agents: The surface attractions for the bonding agent may not work; there may be physical instability (loosening of the attraction) after thermal cycling; and long term aging may change the properties of the bonding agent. Solving any one of these problems can exacerbate the other two. R&D is required to simultaneously solve all three problems.

PHASE I: Synthesize and characterize bonding agents. Produce 50-100 grams of multifunctional bonding agents. Perform compatibility test between bonding agents and high energy propellants and / or individual propellant ingredients.

PHASE II: Scale-up bonding agents to pilot plant level (kg). Formulate high energy propellants with the new bonding agents. Characterize propellant mixes for processing, mechanical properties, ballistics, safety, aging, temperature cycling, burning rates and IM propellant characteristics. Do small scale high energy propellant mixing with the new bonding agents.

PHASE III: Commercialize bonding agents. Scale-up and characterize high energy propellant rocket motors.

PRIVATE SECTOR COMMERCIAL POTENTIAL.DUAL-USE APPLICATIONS: Bonding agents developed in the SBIR effort could be commercially used in a wide range of binders and oxidizers for use in space as well as defense solid rocket propulsion systems. Beside rocket propulsion, these additives could also be of value in ordnance and pyrotechnic applications involving the use of binders and multi-functional oxidizers. Beyond the energetic application area, a potential also exists for these bonding agents in general polymer applications such as plastics, adhesives and sealants.

REFERENCES: 1. J.P. Consaga, ''Universal Bonding Agents'', CPIA Proceedings of the 1974 JANNAF Propulsion Meeting, San Diego, Ca 22-23 Oct 1974.

2. J.P. Consaga, ''Dimethyl Hydantoin Bonding Agents in Solid Propellants'', U.S. Patents 4,214,928, 29 Jul 1980.

3. J.P. Consaga, ''Bonding Agents and Processing'', CPIA Proceedings of the 1995 JANNAF Propulsion Meeting, Tampa, Fl. 4-8 Dec 1995.

4. CPIAC publication LS87-04 "HTPB Processing Aids and Bonding Agents"

5. CPIAC publication LS89-14 "Composite Propellant Bonding Agents and Binder Filler Interaction"

6. "Principles of Solid Propellant Development" by A.E. Oberth

7. "Adhesion of solid rocket materials" by Heidi L. Schrueder-Gibson, Rubber World Nov 1990

KEYWORDS: bonding agents; tactical propellants; high energy propellant; gas generators; strategic propellants

TPOC: Carlos Lopez
Phone: (703)601-9377
Fax: (703)601-9399
Email: SP27315@ssp.navy.mil
2nd TPOC: Keith Klaber
Phone: (703)601-9374
Fax: (202)764-2105
Email: SP2731@ssp.navy.mil

** TOPIC AUTHOR (TPOC) **

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