Polymer-bonded explosives, also calledPBX orplastic-bonded explosives, areexplosive materials in which explosive powder is bound together in a matrix using small quantities (typically 5–10% by weight) of a syntheticpolymer. 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 atLos Alamos National Laboratory, asRDX embedded inpolystyrene withdiisooctyl phthalate (DEHP)plasticizer.HMX compositions withteflon-based binders were developed in 1960s and 1970s forgun shells and forApollo Lunar Surface Experiments Package (ALSEP)seismic experiments,[1] although the latter experiments are usually cited as usinghexanitrostilbene (HNS).[2]
Polymer-bonded explosives have several potential advantages:
Fluoropolymers are advantageous as binders due to their highdensity (yielding highdetonation velocity) and inert chemical behavior (yielding long shelf stability and lowaging). They are somewhat brittle, as theirglass 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.[4]
Elastomers have to be used with more mechanically sensitive explosives likeHMX. 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).Crosslinkedrubber polymers are however sensitive to aging, mostly by action offree radicals and byhydrolysis of the bonds by traces of water vapor. Rubbers likeEstane orhydroxyl-terminated polybutadiene (HTPB) are used for these applications extensively.Silicone rubbers andthermoplastic polyurethanes are also in use.[4]
Fluoroelastomers, e.g.Viton, combine the advantages of both.
Energetic polymers (e.g. nitro or azido derivates of 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.[1]
Explosive yields can be affected by the introduction of mechanical loads or the application of temperature; such damages are calledinsults. 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, andphase 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).
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 (fracturing of crystals, vaporization of components) or decreasing it (melting of components). The size distribution of the crystals can be also altered, e.g. byOstwald 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 (e.g. crystal/binder). Presence of defects in crystals (cracks, voids, solvent inclusions...) may increase the explosive's sensitivity to mechanical shocks.[4]
| Name | Explosive ingredients | Inert ingredients | Usage | |
|---|---|---|---|---|
| AFX-757 | RDX 25%, ammonium perchlorate 30%, aluminium 33% | HTPB 4.44%, dioctyl adipate 6.56% | Used in warheads forJASSM,GBU-39 Small Diameter Bomb and similar weapons.[5] Has high air blast equivalent, 1.39 times more thanComposition B, but low brisance due to low high explosive content.[6] | [7] |
| EDC-8 | PETN 76% | RTV silicone 24% | [8] | |
| EDC-28 | RDX 94% | FPC 461 6% | [9] | |
| EDC-29 | β-HMX 95% | HTPB 5% | UK composition[4] | |
| EDC-32 | HMX 85% | 15% Viton A 15% | [9] | |
| EDC-37 | HMX 91%,NC 1% | K-10 liquid 8% | [9] | |
| LX-04 | HMX 85% | Viton-A 15% | High-velocity;nuclear weapons (W62,W70)[9] | |
| LX-07 | HMX 90% | Viton-A 10% | High-velocity;nuclear weapons (W71)[9] | |
| LX-08 | PETN 63.7% | Sylgard 182 (silicone rubber) 34.3%, 2% Cab-O-Sil | [10] | |
| LX-09-0 | HMX 93% | 2,2-dinitropropyl acrylate (pDNPA) 4.6%; FEFO 2.4% | High-velocity;nuclear weapons (W68). Prone to deterioration and separation of theplasticizer andbinder. Caused serious safety problems. FEFO is 1,1-[methylenebis(oxy)]-bis-[2-fluoro-2,2-dinitroethane], liquid explosive.[3] | |
| LX-09-1 | HMX 93.3% | pDNPA 4.4%; FEFO 2.3% | ||
| LX-10-0 | HMX 95% | Viton-A 5% | High-velocity;nuclear weapons (W68 (replaced LX-09),W70,W79,W82)[9] | |
| LX-10-1 | HMX 94.5% | Viton-A 5.5% | ||
| LX-11-0 | HMX 80% | Viton-A 20% | High-velocity;nuclear weapons (W71) | |
| LX-14-0 | HMX 95.5% | Estane & 5702-Fl 4.5% | [9] | |
| LX-15 | HNS 95% | Kel-F 800 5% | ||
| LX-16 | PETN 96% | FPC461 4% | FPC461 is avinyl chloride:chlorotrifluoroethylene copolymer and its response to gamma rays has been studied.[11] | |
| LX-17-0 | TATB 92.5% | Kel-F 800 7.5% | High-velocity,insensitive;nuclear weapons (B83,W84,W87,W89) | |
| PBX 9007 | RDX 90% | Polystyrene 9.1%;DOP 0.5%;rosin 0.4% | [9] | |
| PBX 9010 | RDX 90% | Kel-F 3700 10% | High-velocity;nuclear weapons (W50,B43)[9] | |
| PBX 9011 | HMX 90% | Estane and 5703-Fl 10% | High-velocity;nuclear weapons (B57 mods 1 and 2)[9] | |
| PBX 9205 | RDX 92% | Polystyrene 6%;DOP 2% | Created in 1947 at Los Alamos, later given the PBX 9205 designation.[12] | |
| PBX 9404 | HMX 94%,NC 3% | Tris(b-chloroethyl)phosphate (CEF) 3% | High-velocity;nuclear weapons, widely used (B43,W48,W50,W55,W56,B57 mod 2,B61 mods 0, 1, 2, 5,W69). Serious safety problems related to aging and decomposition of the nitrocellulose binder.[13] | |
| PBX 9407 | RDX 94% | FPC461 6% | [9] | |
| PBX 9501 | HMX 95%, BDNPA-F 2.5% | Estane 2.5% | High-velocity;nuclear weapons (W76,W78,W88). One of the most extensively studied high explosive formulations.[4] BDNPA-F is 1:1 mixture of bis(2,2-dinitropropyl) acetal and bis(2,2-dinitropropyl) formal.[3] | |
| PBS 9501 | - | Estane 2.5%; BDNPA-F 2.5%; sieved white sugar 95% | Inert simulant of mechanical properties of PBX 9501[4] | |
| PBX 9502 | TATB 95% | Kel-F 800 5% | High-velocity,insensitive; principal in recent USnuclear weapons (B61 mods 3, 4, 6–10,W80,W85,B90,W91), backfitted to earlier warheads to replace less safe explosives.[9] | |
| PBX 9503 | TATB 80%;HMX 15% | Kel-F 800 5% | Also known as X-0351.[9] | |
| PBX 9604 | RDX 96% | Kel-F 800 4% | ||
| PBXN-101 | HMX 82% | |||
| PBXN-102 | HMX 59%, Aluminum 23% | |||
| PBXN-103 | Ammonium perchlorate (AP) 40%, Aluminum 27%,TMETN 23% | TEGDN 2.5% | Mk 48 torpedoes | |
| PBXN-104 | HMX 70% | |||
| PBXN-105 | RDX 7%, AP 49.8%, Aluminum 25.8% | |||
| PBXN-106 | RDX 75% | polyethylene glycol/BDNPA-F binder | Naval shells | |
| PBXN-107 | RDX 86% | polyacrylate binder | BGM-109 Tomahawk missiles | |
| PBXN-109 | RDX 64%, Aluminum 20% | HTPB, DOA (dioctyladipate), and IPDI (isophorone diisocyanate) | Used in some versions of theMark 82,Mark 83 andMark 84 general-purpose bombs.[14] | |
| PBXN-110 | HMX 88% | 5.4% Polybutadiene, 5% Isodecylpelargonate | [15] | |
| PBXN-111 | RDX 20%, AP 43%, Aluminum 25% | |||
| PBXW-114 | HMX 78%, Aluminum 10% | |||
| PBXW-115 | RDX 20%, AP 43%, Aluminum 25% | |||
| PBXN-1 | RDX 68%, Aluminum 20% | |||
| PBXN-3 | RDX 85% | Nylon | AIM-9X Sidewinder Missile | |
| PBXN-4 | Diaminotrinitrobenzene (DATB) 94% | |||
| PBXN-5 | HMX 95% | fluoroelastomer 5% | Naval shells | |
| PBXN-6 | RDX 95% | |||
| PBXN-7 | RDX 35%, TATB 60% | |||
| PBXN-9 | HMX 92% | HYTEMP 4454 2%,Diisooctyl adipate (DOA) 6% | ||
| XTX 8003 | PETN 80% | Sylgard 182 (silicone rubber) 20% | High-velocity, extrudable;nuclear weapons (W68,W76) | [15] |
| XTX 8004 | RDX 80% | Sylgard 182 (silicone rubber) 20% | [15] |