Awaiting some final ingredients I started to characterize the old-stock HTPB. I expect the HTPB I have is similar to R45HTLO so an EW of 1190 is used in the curative calculations. Small 50gr batches (measured to a hundreds of a gram) were made to evaluate the different Cure Indexes 0.9 – 1.3. The curative used is from a fresh can of PS120b – MDI with an EW of 133 (%NCO 31.5).

Attached is a graph of the results. The Shore A hardness was determined with a Bareiss durometer and showed consistent results over several measurements on the same sample. The Cure Index is an approximation since I don’t know the exact EW of the HTPB. Compared to the 24h and 72h / 1 week results, the HTPB significantly hardens over time.