SYNOPSISThere has been a constant endeavor to improve the mechanical properties of hydroxylterminated polybutadiene ( HTPB ) -based composite solid propellants. A systematic study has been conducted on different batches of HTPB resins with varying molecular weights and hydroxyl values. Propellant formulation experiments were conducted wherein the ratio of chain extender to crosslinker was systematically varied, with a view to achieve the maximum possible strain capability and moderately high tensile strength, keeping all other parameters constant. The influence of increasing hydroxyl content from trimethylolpropane at the expense of hydroxyl content from butanediol, on the mechanical properties of the finished propellant, has been depicted on 3-dimensional graphs. The isoproperty lines, plotted as a triangular chart with the percentage hydroxyl contents from the three constituents, can be used to arrive at the suitable formulation for a specified application depending upon the OH value of the resin. HTPB resins with high molecular weight, low functionality, and low hydroxyl value require higher levels of trifunctional curing agent and higher NCO/ OH ratios to obtain outstanding mechanical properties, especially elastic properties, compared to low molecular weight, high functionality resins. The impact of hard and soft segment domain structure on the mechanical behavior of the cured systems is more pronounced in the low molecular weight resin formulations due to the higher hard segment content compared to those attainable in high molecular weight resin formulations. I NTRO DUCT10 NThere has been a constant endeavor to improve the mechanical properties of HTPB-based composite solid propellants. In order to have a better understanding of the influence of resin variabilities like hydroxyl value, molecular weight, functionality, etc. on the resultant propellant properties, a coordinated program was undertaken. Under this scheme, a series of HTPB resins with varying molecular weights and hydroxyl values were produced at Vikram Sarabhai Space Centre.' Details of the first set of experiments conducted on these batches of resins by varying the ratio of curing agent to resin, i.e., R values, keeping the chain extender to crosslink ratio the same, have been reported in Part 1.'

In this paper a comparative analysis on the energetics of ester type plasticizers such as dioctyl adipate (DOA), dioctyl phthalate (DOP), dibutyl sebacate (DBS), isodecyl pelargonate (IDP), trioctyl phosphate (TOF), diethyl phthalate (DEP), tricresyl phosphate (TCP) and dibutyl phthalate (DBP) and hydrocarbon type plasticizers such as polybutene (PB), spindle oil, naphthenic oil, polymer extender oil (PEO) and poly isobutylene (PIB) and the impact of some of the plasticizers on the workability, pot life and mechanical properties of propellants based on two selected polymeric binders namely polybutadiene-acrylic acid-acrylonitrile (PBAN) ter polymer and hydroxyl terminated polybutadiene (HTPB) have been reported. The compatibility of all the plasticizers on HTPB binder was also studied at different concentration levels and temperatures using Brookfield viscometer and reported. The mechanism of plasticization is also reviewed.

A systematic study has been conducted on a composite solid propellant formulation using hydroxyl-terminated polybutadiene ( HTPB ) prepolymer with varying molecular weights and hydroxyl values. Fairly extensive regions of resin parameters have been studied. Contours of important propellant properties have been laid down. In this set of experiments, varying levels of diol and trio1 contents were used at two different NCO/OH ratios to arrive at the optimum level needed for different grades of HTPB resin. It is seen that different grades of HTPB resin require varying levels of diol-trio1 contents to give similar properties for the end product. Also, for the best performance, varying the diol-trio1 ratio at the optimum level of the diol-trio1 content is necessary.