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Composite Propellants use a polymer binder to hold their constituent components in place. The composite binder has a curing process that chemically results in the linking of chains of molecules via an a dehydration reaction . To enable this reaction a curative agent needs to be added. In order to see the best mechanical properties in the cured propellant all of the possible cross linking sites should be linked. This would require that the same number of donating sites and receptor sites exit. Many chemicals in a generic composite propellant formulation can interact with the polymerization. The way to handle this interaction is with a value known as the equivalent weight. Equivalent weight accounts for the relative number of linking sites accepted or donated, and the relative mass of a compound.
Software
This formula uses the equivalent weight of the binder, curative, and castor oil to calculate the fractions of HTPB and curative, given the sum of HTPB/curative and fraction of castor oil.
The following python file will walk you through this calculation.
Balancing the Equivalent Weight of a Formulation
A succinct overview of correctly determining the proper amount of curative for a given formulation was done by John DeMar, and is linked below.
https://wikis.mit.edu/confluence/download/attachments/122621517/Curative_calculation.pdf?api=v2
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