HTPB binder

Fig. 7.33 Burning rates of HMX composite propellants composed of HTPS, HTPE, HTPA, and HTPB binders.

The presence of carbonaceous fragments can be attributed to the low oxygen content in the HTPB binder, 3.6%, compared to oxygen contents in the HTPS, HTPE, and HTPA binders of more than 25 %, as shown in Table 4.3. 

The burning rates of AP-RDX composite propellants are dependent on the physicochemical properhes of the AP, RDX, and fuel used, such as particle size, as well as on mixture raho and the type of binder. The results of burning rate measurements are reported in AlAA Paper No. 81-1582.125] Various combinahons of AP and RDX parhcles are used to formulate AP-RDX composite propellants, as shown in Table 7.6.125] pjjg particles incorporated into the propellants have bimodal combinations of sizes, where large RDX particles (RDX-I), small RDX particles (RDX-S), large AP particles (AP-I), and small AP particles (AP-S) are designated by d, d, dj, and da, respectively. HTPB binder is used in all of the propellants shown in Table 7.6. 

ISRO polyol is considered to be a substitute for HTPB binder and propellants based on it are used in sounding rockets (RH-300). Such propellants are also considered as candidate propellants [94] for the booster stages of Polar Satellite Launch Vehicle (PSLV). The easy availability of castor oil coupled with its low cost makes ISRO polyol more attractive compared with current binders [95] like PBAN, CTPB and HTPB. 

Dilutes and distributes the ferrocene derivative in the HTPB binder due to low iron content (iron content in Butacene = 8% and Catocene = 25%). 

Presently, research is on-going into trying to find alternatives to AP/A1 (see also Ch. 1.2.4). The problems with the AP/A1 mixtures which contain HTPB as a binder, are two-fold. On the one hand AP is toxic and should be substituted for this reason alone (see Ch. 1.2.4). On the other hand, such formulations are also problematic in slow cook-off tests (SCO test, see Ch. 6.2). It appears to be the case that here the AP slowly decomposes during the formation of acidic side-products. These acidic side-products then react with the HTPB binder, which can result in the formation of cracks und cavities in the composite, which consequently negatively affects the performance and sensitivity. Possible alternatives for AP are ADN, HNF and TAGNF. However, they cause other problems, such as, for example, the low thermal stability (ADN melts at 93 °C and already decomposes at 135 °C) and the binder compatibility is not always guaranteed either. Further research work is absolutely necessary in order to find better oxidizers for solid propellants. In this context, the following requirements must be fulfilled ... 

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