Aging behavior of hydroxyl-terminated polybutadiene/ammonium perchlorate (HTPB/AP)-based composite solid propellants was studied as a function of crosslink density, which is predominantly determined by the molar ratio of diisocyanate to total hydroxyl (NCO/OH ratio) and the molar ratio of triol to diol (triol/diol ratio). For this purpose, 16 propellant samples with different compositions were prepared by changing the NCO/OH ratio as 0.81, 0.82, 0.83, and 0.85 for each triol/diol ratio of 0.07, 0.09, 0.11, and 0.13, and subjected to an accelerated aging at 65°C. The changes in the mechanical properties were monitored throughout the aging period. In the initial part of the aging period, a sharp increase in stress, modulus, and hardness values and a sharp decrease in strain values were observed for all the propellants. At further stages of aging, only slight changes were observed in the mechanical properties. Concerning the aging criterion as reduction in the strain capability more than the half of the initial value, the propellants with respective NCO/OH-triol/diol ratios of 0.81–0.09, 0.85–0.09, 0.81–0.13, 0.83–0.13, and 0.85–0.13 can be considered to be aged with time. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 959–964, 2001

Aging of HTPB/AP‐based composite solid propellants, depending on the NCO/OH and triol/diol ratios

The viscoelastic aging behavior of composite solid propellant grains is studied by a three-dimensional thermoviscoelastic constitutive model with aging evolution, in which the crosslinking degree is taken as an aging variable. The resulting viscoelastic constitutive equations are numerically discretized into incremental form by integration algorithms, and the stress-updating method is presented according to incremental law. Subsequently, the Abaqus-based user material subroutine and its structural analysis module are constructed and validated through typical examples. Studies show that the results of structural analysis have high accuracy and are in well agreement with each other. The designed analysis module presents an effective aging-mechanical analysis platform for further lifespan estimation of solid rocket motors.

Three‐dimensional Structural Analysis Approach for Aging Composite Solid Propellant Grains

This is the first report on studies carried out in detail on high-pressure oxygen copolymerization (>50 psi) of the vinyl monomers styrene and α-methylstyrene (AMS). The saturation pressure of oxyg...

High-pressure kinetics of vinyl polyperoxides

Effects of thermal ageing on the properties and lifetime prediction of hydroxyl-terminated polybutadiene

Thermal oxidative polymerization of alpha-methylstyrene (AMS) has been studied at various temperatures(45-70 degrees C) and pressures (50-400 psi). Due to its high electron dense double bond, it undergoes thermal oxidative polymerization even at low temperatures fairly easily. The major products are poly(alpha-methylstyrene peroxide) (PMSP), and its decomposition products are acetophenone and formaldehyde. Above 45 degrees C the rate of polymerization increases sharply at a particular instant showing an ''autoacceleration'' with the formation of a knee point. The ''autoacceleration'' is supported from the fact that the plot, of R-p vs T shows a rapid rise, and the plot of ln R-p vs 1/T is non-Arrhenius. The occurrence of autoacceleration is explained on the basis of acetophenone-induced cleavage of PMSP during polymerization, generating more initiating alkoxy radicals, which subsequently leads to the rapid rise in the rate of polymerization. The mechanism of autoacceleration is supported by the change in. order, activation energy, and activation volume before and after the knee point.

Mechanism of ``Autoacceleration'' in the Thermal Oxidative Polymerization of α-Methylstyrene

Aging studies on carboxy terminated polybutadiene (CTPB) and CTPB-based propellants have been carried out. The increase in the cross-link density during aging has been measured using a thermomechanical analyzer. During aging, a correlation has been shown between the cross-link density and the ignition temperature of the binder as well as of the propellant. The ignition temperature vs cross-link density results were found to show an opposite trend in CTPB and CTPB-based propellants, suggesting that the two ignition mechanisms are different.

K. Sridhara

Papers

Aging studies on carboxy terminated polybutadiene (CTPB) binder and propellant

Prediction of performance of burning-rate catalysts: a group contribution approach

Thermoanalysis of ammonium perchlorate and sodium nitrate mixture

Mechanism of catalytic activity of metal oxides and chromites on ammonium perchlorate pyrolysis