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Explosive materials where powder is bound together in a matrix with synthetic polymer

Polymer bonded explosives, also called PBX or plastic bonded explosives, are explosive materials 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 at 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,

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 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 effects on safety. They are also difficult to process.

Explosive yields can be affected by the introduction of mechanical loads or the application of temperature; such damages are called insults. The mechanism of a thermal insult at low temperatures on an explosive is primarily thermomechanical, at higher temperatures it is primarily thermochemical.

Thermomechanical mechanisms involve stresses by thermal expansion (namely differential thermal expansions, as thermal gradients tend to be involved), melting/freezing or sublimation/condensation of components, and phase transitions of crystals (e. g. transition of HMX from beta phase to delta phase at 175 °C involves a large change in volume and causes extensive cracking of its crystals).