Introduction
Many different chemicals can be used in the production of a solid rocket motor. These chemicals can be combined to achieve a variety of different effects. Chemicals in known use are listed below
Chemicals
Binder
Binders form the mechanical linkage in the rocket fuel. Some binders are also used as fuels. These binders are known as "energetic binders" and are normally hazardous.
R-45 M - A type of Hydroxyl Terminated Polybutadiene (HTPB) . Contains a pre-mixed anti-oxidant for long term storage
R-45 HTLO - A type of HTPB that contains no anti-oxidants. Lower viscosity than R-45M
Low Molecular Weight HTPB - Very low viscosity HTPB. Lower molecular weight. May improve castability and performance. May detrimentally affect density.
Polybutadiene Acrylonitrile (PBAN) - Common hobby binder. Requires Cure schedule. Also used in the Space Transportation System's Solid Rocket Boosters.
Curative
These chemicals begin the polymerization of the binder
Isocyanate MDI
Isophorone Diisocyanate (IPDI)
PAPI
Plasticizer
These chemicals reduce the viscosity of the uncured propellant. They make mixing and casting of propellants easier and facilitate higher solids loading.
Isodecyl Pelargonate
Dioctyl Adipate (DOA)
Dioctyl Sebacate
Opacifiers
These chemicals increase the infrared energy transfer from the flame front into the propellant face and prevent premature ignition or detonation of propellant behind the burning face.
Powdered Graphite - Black Powder
Prussian Blue - Blue Powder. Produces a blue tinted propellant after curing.
Methylene Blue - Blue stain. Liquid. Helps lower solid loading.
Nigrosin - Best opacifier by mass.
TiO2 - Opacifier. Rejects radiative heating. Creates white propellant.
Fuels
Aluminum - More energetic than magnesium but requires a larger motor to properly take advantage of. Large incompletely burned particle can damage nozzle. Tendency to deposit slag inside motor.
Magnesium - Powdered. Burns completely, faster than aluminum. Useful in smaller motors.
Oxidizers
Substances which oxidize the fuel and binder to facilitate combustion.
Ammonium Perchlorate - Most common in amateur and professional composite propellants
Ammonium Nitrate - Extremely hygroscopic. Tends to produce a slower burning propellant than ammonium perchlorate.
Potassium Nitrate - Used commonly in "rocket candy" formulations. Lower performance than ammonium perchlorate or ammonium nitrate.
Stabilizers
Magnesium Oxide
Phenylnaphthalene
DTBHQ - 2,5-ditert-butylhydroquinone
Processing Aids
Lecithin
Silicon Oil - Reduces adherence to mixing bowl. Makes propellant pour better.
Polydimethylsiloxane (PDMS) - Surfactant, reduces sticking to the bowl and aeration during mixing. Allows for mixing at higher speeds. Improves particle wetting.
Binding Agents
Binding agents form a bond between the surface of Ammonium Perchlorate particles and the polymer matrix, embedding the particles strongly in the propellant web. This slightly slows burn rate and increases hardness.
HX-752 - Does not cause foaming. Requires refrigeration. Smells bad.
HX-878 (Tepanol) - May cause foaming due to ammonia generation during curing.
HX-868 - (Dynamar) Co-active with HX-752, increases functionality and decreases migration
Cross Linking Agents
Castor Oil - provides additional sites for the polymer chains to cross link with the curative and castor oil. Increases cured propellant hardness.
Chromatic Burn Additives
Copper Oxychloride - Blue (5%-10% by mass)
Strontium Carbonate - Red.
Flame Retardants
Melamine - Used when using HTPB as a liner material
Zinc Borate - improves char layer formation