Binder System for Propellants and Explosives (1964)
U.S. Patent No. 3,140,210, granted on July 7, 1964, to Henry T. Sampson, addresses a critical engineering hurdle in the field of aerospace and ballistics: how to manufacture a solid rocket fuel or plastic-bonded explosive that is powerful, easy to pour, and highly stable.
At the time of this filing, Sampson was based in Urbana, Illinois. His invention provided a solution to a major logistical problem in military and space research—most existing binders were too thick (high viscosity) to allow for a high percentage of explosive crystals to be added, and they required dangerously high curing temperatures.
The Innovation: The Low-Viscosity High-Energy Matrix
The core of Sampson’s invention is a polyurethane-based binder system that incorporates a nitrated plasticizer. Unlike standard binders that simply hold the fuel together, this system contributes its own chemical energy to the explosion or thrust.
1. Solving the Loading Problem
To maximize the power of a rocket, engineers want to pack as much solid fuel (like ammonium perchlorate) into the mix as possible. Sampson’s binder starts as a low-viscosity liquid, allowing manufacturers to stir in a high volume of solid ingredients while the mixture remains “castable”—meaning it can be poured into a rocket motor casing or a warhead like liquid rubber.
2. Thermal Stability and Safety
Traditional binders often require extreme heat to “set” (cure), which is inherently risky when working with explosives. Sampson’s composition utilizes a chemical reaction that can be controlled at lower temperatures (120°F), resulting in a bubble-free, structurally sound propellant.
Key Chemical Components
The binder is a precise chemical cocktail designed to be both a structural adhesive and a high-energy fuel.
| Component | Range (%) | Function |
| Castor Oil (CasO) | 30% – 40% | The primary polymer backbone; provides the necessary flexibility to prevent the fuel from cracking under pressure. |
| 2,4-Tolylene Diisocyanate (TDI) | 20% – 30% | The cross-linking agent that causes the liquid oils to “cure” into a solid, rubbery mass. |
| TMETN (Trimethylolethane Trinitrate) | 15% – 35% | The “Energy Booster.” A nitrated plasticizer that significantly increases the specific impulse of the propellant. |
| Dipropylene Glycol (DPG) | 11% – 15% | Works in tandem with the castor oil to control the final hardness and stretch of the binder. |
Performance: Strength and Flexibility
A solid rocket fuel must be tough enough to maintain its shape but elastic enough to handle the intense pressure of ignition. Sampson’s patent data demonstrates how varying the TMETN levels changes the material’s properties:
- Standard Mixture: A blend with 24.5% TMETN achieved a tensile strength of 270 p.s.i. and a massive 290% elongation (stretch).
- High-Stiffness Version: By reducing the plasticizer, the binder reached a tensile strength of 665 p.s.i.
- The “Pure” Plastic: Without the explosive plasticizer, the binder reached 2,500 p.s.i., showing the immense structural strength of the polyurethane base.
The Manufacturing Process
The patent outlines a specific “cold-mix” strategy to ensure the chemicals react safely:
- Initial Mix: Castor oil, DPG, and TDI are mixed at 32°F for twenty minutes to prevent a runaway heat reaction.
- Temperature Control: The mixture is kept below 120°F to manage viscosity.
- Vacuum Degassing: Because the reaction produces carbon dioxide, it must be mixed under a vacuum to ensure the final propellant is bubble-free (bubbles can cause a rocket to explode).
- Final Cure: The mixture is poured into the casing and cured for five days at 120°F.
About the Inventor: Henry T. Sampson
Dr. Henry Thomas Sampson was a pioneering African American nuclear engineer and inventor whose work was vital to the U.S. Navy and the broader aerospace industry.
- University of Illinois: It was during his time here that he developed the chemical foundations for this binder system.
- Government Service: The patent was assigned to the United States Government, meaning it was developed for use in national defense and space exploration without the need for private royalties.
- Scientific Legacy: Beyond rocketry, Dr. Sampson is famously known for his contributions to the Gamma Electric Cell, furthering his impact on how we capture and use high-energy radiation.
Summary of Claims
The patent explicitly claims:
- A specific ratio of Castor Oil, DPG, TDI, and TMETN to create a high-energy binder.
- The ability to use Polypropylene glycol as a substitute to tailor the physical properties of the propellant.
- A specific commercial-grade formulation (Example IV) consisting of 32.5% Castor Oil and 33.4% TMETN for maximum energy output.
