Polymer-bonded explosives have several potential advantages:
If the polymer matrix is an elastomer, it tends to absorb shocks, making the PBX very insensitive to accidental detonation, and thus ideal for insensitive munitions.
Hard polymers can produce PBX that is very rigid and maintains a precise engineering shape even under severe stress.
PBX powders can be pressed into a particular shape at room temperature, when casting normally requires hazardous melting of the explosive. High pressure pressing can achieve density for the material very close to the theoretical crystal density of the base explosive material.
Many PBXes are safe to machine—to turn solid blocks into complex three-dimensional shapes. For example, a billet of PBX can, if necessary, be precisely shaped on a lathe or CNC machine. This technique is used to machine explosive lenses necessary for modern nuclear weapons.
Binders
Fluoropolymers
s are advantageous as binders due to their high density and inert chemical behavior. They are however somewhat brittle, as their glass transition temperature is at room temperature or above; this limits their use to insensitive explosives where the brittleness does not have detrimental effect to safety. They are also difficult to process.
Energetic polymers can be used as a binder to increase the explosive power in comparison with inert binders. Energetic plasticizers can be also used. The addition of a plasticizer lowers the sensitivity of the explosive and improves its processibility.
Insults (potential explosive inhibitors)
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
Thermomechanical mechanisms involve stresses by thermal expansion, melting/freezing or sublimation/condensation of components, and phase transitions of crystals.
Thermochemical
Thermochemical changes involve decomposition of the explosives and binders, loss of strength of binder as it softens or melts, or stiffening of the binder if the increased temperature causes crosslinking of the polymer chains. The changes can also significantly alter the porosity of the material, whether by increasing it or decreasing it. The size distribution of the crystals can be also altered, e.g. by Ostwald ripening. Thermochemical decomposition starts to occur at the crystal nonhomogeneities, e.g. intragranular interfaces between crystal growth zones, on damaged parts of the crystals, or on interfaces of different materials. Presence of defects in crystals may increase the explosive's sensitivity to mechanical shocks.
