Propellants energetic binders

There are a number of inert binders such as polyester, epoxy, polysulfide, polyurethane which have been reported as binders for composite propellants and plastic bonded explosives (PBXs). At present, hydroxy-terminated polybutadiene (HTPB) is regarded as the state-of-the-art workhorse binder for such applications. However, the recent trend is to use energetic binders such as poly [3,3-bis(azidomethyl oxetane)] [poly(BAMO)], poly (3-azidomethyl-3-methyl oxetane) [poly(AMMO)], PNP, GAP diol and triol, nitrated HTPB(NHTPB), poly(NiMMO), poly(GlyN) and nitrated cyclodextrin polymers poly(CDN) for PBXs and composite propellants in order to get better performance. 

The chemistry and properties together with applications of other energetic binders such as GAP, NHTPB, poly (NiMMO), poly (GlyN) and poly (CDN) will be described in Chapter 4 on propellants because of their extensive use in that segment of explosive industry. 

Binders A binder plays an important role in resisting conductive ignition by hot metal particles. Propellants whose binders decompose endothermically are considered excellent in this context. On the other hand, propellants with exothermically decomposing binders ignite as easily as nitrate ester propellants. Binders can be classified as inert and energetic binders. 

To summarize, the cost of production of NHTPB is lower than that of poly(NiMMO) or Poly(GlyN). However, NHTPB s performance is poor in comparison to them. On the basis of trials conducted so far, it seems likely that poly(GlyN) will prove to be a world leader in the field of energetic polymers. A summary of the properties of energetic binders for use with both explosives and propellants is given in Table 4.6a,b. 

Table 4.6b Some thermal and explosive properties of energetic binders for explosives and propellants.

Similar to the effects of Alex addition in pyrotechnics and solid propellants, replacement of conventional micron-sized A1 powder by nanosized A1 powder (Alex) increases the detonation velocities and heats of detonation of TNT/A1 formulations. The increase of VOD is more pronounced in small diameter charges, close to the critical diameter. On the contrary, n-Al powder does not increase the VOD of aluminized PBXs based on inert binders. It is very interesting to observe that the VOD of PBXs based on an energetic binder decreases on substitution of micron-sized A1 by Alex [119, 120]. Reshetov and his coworkers [121] reported in the early 1980s that the addition of Alex enhanced VOD of RDX. More recently, an increase in both VOD as well as brisance was demonstrated for a number of TNT-based tritonal and H-6 formulations containing Alex. The improvements in VOD -200-300ms1 and brisance up to 27% were observed in a number of tritonal charges on replacement of conventional or micron-sized A1 by Alex [122]. 

As discussed under explosives and propellants, a number of energetic binders GAP, NHTPB, poly(NiMMO), poly(GlyN), poly(BAMO), poly(AMMO) and BAMO-AMMO copolymers etc. have been reported in the recent past and are at various stages of development and introduction for bulk production of explosives and propellants for various applications. These polymeric binders are reasonably stable and are of established compatibility with a wide range of ingredients used for explosive and propellant formulations. The data on their explosive properties impact, friction and electric spark sensitivities, indicate that it is safe to handle these materials. However, there appears to be no report in the open literature on... 

By very carefully controlling the reaction of pentaerythritol in nitric acid, PETRJN (Figure 3.29) instead of PETN can be obtained. PETRIN is not a particularly desirable explosive, but because of the hydroxyl group left on the last of the outer carbons, this material has one particularly useful feature. The hydroxyl can be reacted to the acid group in acrylic acid to form a polymerizable material, PETRJN-acrylate. PETRJN-acrylate polymer, a plastic, is used as an energetic binder in some composite rocket propellants. 

Compositions that hold together a charge of finely divided particles and increase the mechanical strength of the resulting propellant grain when it is consolidated under pressure. Binders are usually resins, plastics, or asphaltics, used dry or in solution (-> Energetic Binders). 

Poly-AMMO is synthesized via cationic polymerisation from the monomer 3-azidomethyl-methyl-oxetane (AMMO). The polymerisation reaction is quenched with water to get polymer chains with hydroxyl endgroups which enable to react these pre-polymers later with isocyanate for curing reaction. Poly-AMMO is suggested as - energetic binder component in -< composite propellants and is in the scope of actual research. 

Epichlorohydrin or chloromethyloxirane is manufactured from allyl chloride, and, in 2006, had a merchant price of US 1.66 kg [4]. It is used as a building block in the manufacture of plastics, epoxy resins, phenoxy resins, and other polymers, and as a solvent for cellulose, resins, and paints, and has also found use as an insect fumigant. Epoxy resins (aryl glycidyl ethers) are manufactured successfully in large scale (1.2 x 10 metric tons in 2000) [26] and are widely used in a variety of industrial and commercial applications [27]. These are made by addition reactions of epichlorohydrins or by epoxidation of allyl ethers or esters (Table 1.1). Epichlorohydrin can be reacted with an alkali nitrate to produce glycidyl nitrate, an energetic binder used in explosive and propellant compositions. 

A. J., and Schoyer, H. F. R., New Solid Propellants Based on Energetic Binders and HNF, IAF-92-0633, 43rd Congress of the International Astronautical Federation, Paris (1992). 

---