Inhibition of Double-Base Propellants

1) Interpositioning of barrier coats resistant to NG migration, before application of flexible polymeries as main inhibitor and 

EP-4 developed by ERDL is a very flexible polyester based on polyethylene glycol with molecular weight-200 (PEG-200), isophthalic acid (IPA) and maleic anhydride (MAn). Before its use, it is blended with styrene monomer (1 1) and cured at room temperature using cobalt naphthenate (as an accelerator) and methyl ethyl ketone (MEK) peroxide (as a catalyst). This meets the requirements of the main inhibitor and is used for inhibition of DB and CMDB propellants after the application of a barrier coat (generally a rigid polyester such as PR-3). However, it is observed during manufacture of EP-4 that there is a lot of batch-to-batch variation in properties in spite of the strict quality control measures adopted during its manufacture. 

This is perhaps attributed to variation in molecular weight (mol.wt.) of PEG-200 as, most of the time, mol.wt. of 200 is achieved by blending PEGs of different molecular weights. In view of this, an unsaturated polyester based on triethylene glycol (TEG), IPA and MAn was developed and this meets the requirements [302]. The properties of three typical batches of TEG-based polyester are given in Table 4.15. 

Visual Observation Reddish brown Reddish brown Reddish brown 

It is evident from the data that the batch-to-batch variation is within the specification limits. It is, therefore, considered a better substitute of EP-4 and is likely to substitute ERDL, EP-4 for inhibition of DB and CMDB rocket propellants in future. 

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