Structure‐property relationship of HTPB‐based propellants. II. Formulation tailoring for better mechanical properties

Abstract

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.'

Mechanical properties of HTPB-IPDI-based elastomers

“…3 The effect of crosslinking agents on the structure and properties of polyurethane elastomer composite poly-Polyurethane elastomers are widely used engimers has been studied for various mixtures of dineering materials and are well known for their cumyl peroxide and toluene diisocyanate dimer, 4 outstanding mechanical, thermal, and adhesive trimethylolpropane and toluene diisocyanate, 5,6 properties. Polyurethanes are also used as a liner and trimethylolpropane and 4,4-diphenylmethmaterial for HTPB-based composite solid propelane diisocyanate.…”

HTPB-Polyurethane: A Versatile Fuel Binder for Composite Solid Propellant

“…A PU propellant grain should have sufficient tensile strength and elongation to withstand various types of stresses experienced during handling and transportation, thermal cycling, sudden pressurization on ignition, and acceleration load during flight of the rocket motor. A tensile strength of approximately 7-8 kgf/cm 2 , an elongation of 40-50 % and initial modulus of 40-50 kgf/cm 2 are reasonable for a typical case bonded rocket motor (Manjari et al, 1993). The PU binder accounts to 10-15 % of the composite propellant, and usually consists of three components: (1) a prepolymer (polyol), (2) an isocyanate curator, and (3) a chain extender (butan-1,4-diol) and cross-linking agent (trimethylol propane).…”

Experimental Study on the Rate Correlativity of Particulate-filled Composite

“…Composite propellant, as a heterogeneous propellant, the differences of formula would cause the change of the mechanical properties, but would not have intrinsic distinction [12] .Thus, the composite propellant of the same batch, consisting of polyether polyurethane and diethyleneglycol dinitrate as adhesive and ammonium perchlorate, aluminum powder, cyclotetramethylene tetranitramine as fuel particles. Referring to QJ924-85 standard, the material was cut to dumbbell specimens, as pictured in Fig 1. Experiments were carried out on QJ211B electronic universal test machine in room temperature under the tensile rates of 5mm/min, 20mm/min, 50mm/min, 100mm/min, 200mm/min, 500mm/min.…”