Plastic bonded explosive

A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an explosive material in which explosive powder is bound together in a matrix using small quantities (typically 5–10% by weight) of a synthetic polymer. PBXs are normally used for explosive materials that are not easily melted into a casting, or are otherwise difficult to form. PBX was first developed in 1952 in Los Alamos National Laboratory, as RDX embedded in polystyrene with dioctyl phthalate plasticizer. HMX compositions with teflon-based binders were developed in 1960s and 1970s for gun shells and for Apollo Lunar Surface Experiments Package (ALSEP) seismic experiments, although the latter experiments are usually cited as using hexanitrostilbene (HNS).

Polymer-bonded explosives have several potential advantages:

Fluoropolymers are advantageous as binders due to their high density (yielding high detonation velocity) and inert chemical behavior (yielding long shelf stability and low aging). They are however somewhat brittle, as their glass transition temperature is at room temperature or above; this limits their use to insensitive explosives (e.g. TATB) where the brittleness does not have detrimental effect to safety. They are also difficult to process.

Elastomers have to be used with more mechanically sensitive explosives, e.g. HMX. The elasticity of the matrix lowers sensitivity of the bulk material to shock and friction; their glass transition temperature is chosen to be below the lower boundary of the temperature working range (typically below -55 °C). Crosslinked rubber polymers are however sensitive to aging, mostly by action of free radicals and by hydrolysis of the bonds by traces of water vapor. Rubbers like Estane or hydroxyl-terminated polybutadiene (HTPB) are used for these applications extensively. Silicone rubbers and thermoplastic polyurethanes are also in use.

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