| Abstract: | There 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. © 1993 John Wiley & Sons, Inc. |
