Development and evaluation of a novel binder based on natural rubber and high-energy polyurethane/composite propellants

Hydroxyl terminated natural rubber (HTNR) was prepared by the depolymerization of masticated natural rubber in the presence of H₂O₂ in toluene. Probable mechanisms leading to the formation of side reaction products are proposed based on the analytical data. A comparative study of some formulation variables was made for their effect in improving the flow characteristics and mechanical properties of an aluminized polyurethane (PU) propellant system based on HTNR. This PU system has also been compared for its theoretical performance characteristics with some other state-of-the-art systems.     

Effect of temperature on the rheological behavior of hydroxyl terminated polybutadiene propellant slurry

Hydroxyl terminated polybutadine (HTPB) based composite solid propellants have gained prominence in advanced missiles and launch vehicles including the Space Shuttle's Inertial Upper Stage (IUS) motor (1). To achieve a blow-hole free well performing casting, the knowledge of the processability characteristics and rheological behavior of the propellant slurry are of vital interest. In our earlier communication (2) we had discussed the effect of compositional aspects, namely solid loading, oxidizer particle size distribution, and aluminum content on the rheology of HTPB propellant. For an optimized solid loading with corresponding oxidizer particle size distribution and aluminium content, the effect of temperature on the processability and the pot life are studied and reported in this paper. This study establishes the fact that the HTPB slurry shows a complex rheological behavior having thixotropy and yield stress. The thixotropic index and yield stress show minimum values at an optimum temperature. This optimum temperature shifts to lower values as time elapses. Activation energies have been calculated for the cure reaction based on yield stress and viscosity. It is observed that the activation energy values reach asymptotic levels after about three hours of curative addition.     

Rheology of HTPB propellant. I. Effect of solid loading,oxidizer particle size,and aluminum content

Composite solid propellants based on hydroxyl-terminated polybutadiene (HTPB) have become the workhorse propellants in the present-day solid rocket motors. The other major ingredients of a composite propellant are the crystalline oxidizer and metallic fuel. As the solid loading of such propellants is as high as 86–90%, their rheological behavior is very complex. The propellant slurry needs to have reasonably low viscosity and a long pot life for better casting and, hence, for a defect-free rocket motor. The primary factors affecting the solid propellant viscosity are solid content, particle size, shape, and distribution. The present study concerns the variations of solid loading from 80 to 89% at constant aluminum cotent, variation of aluminium from 0 to 22% at constant solid loading, and the coarse-to-fine ratio of the oxidizer. The plots of yield stress, consistency index, pseudoplasticity index, and thixotropic index at different time intervals are drawn for all these parametric changes. Based on these rheological studies, the optimum ratio of oxidizer coarse-to-fine ratio, aluminum content, and level of solid loading have been determined.     

Room temperature cured polyurea-urethane propellant with unique mechanical properties

A polyurea-urethane propellant based on an NCO-terminated prepolymer, a diamine and a triol has been developed. This is a room temperature curing propellant which is case-bondable. This has been standardized at 3-kg level and then scaled upto grains of 300-mm diameter and 2250-mm length weighing 250 kg. This propellant has a tensile strength of about 4 kg/cm² and an elongation of 150 percent. Because of low cost, case bondability and room temperature curability this can be used in large solid boosters.     

The usefulness of static condensation in the finite element analysis of stiffened submersible cylindrical hulls

The usefulness of the static condensation technique in the finite element analysis of stiffened submersible. cylindrical hulls is examined in this paper. The finite element formulation used herein is essentially the same as outlined by the authors in an earlier paper wherein the stiffener is modeled rigorously using axisymmetric thin annular plate elements for the web and axisymmetric thin shell elements for the flange. The static condensation technique has been applied in this paper to reduce these stiffener finite elements so that their effect can be transferred to the shell node at the point of attachment of the stiffener with the shell. The advantage of such condensation of the stiffener elements is the smaller number of equations to be solved without the rigor of the stiffener modeling being lost in any way. The manner of incorporating the condensation in the computer program has been described. Examples of several stiffened submersible cylindrical hulls have been considered as an illustration of the use of the program.     

A study on leaching behaviour of cement blocks used as matrix for fixation of Cs activity along with ferric

Study on the cementation of the regenerated activity (from spent resin using ferric as regenerant) containing ferric in cement matrix showed that compressive strength and leaching behaviour are better when the ferric strength was < 5 N. The diffusion coefficient of Cs from the cement matrix was found to be in the range 2.4 × 10⁻⁵ cm²/day and 5.9 × 10⁻⁵ cm²/day with ferric solutions of strength in the range 0.5–3 N. When bentonite and vermiculite were included in the cement matrix, the diffusion coefficient of Cs was found to be in the range 6.2 × 10⁻⁷ cm²/day to 1.26 × 10⁻⁵ cm²/day with ferric strength in the same range.     

Rheology of HTPB Propellant: Development of generalized correlation and evaluation of pot life

Composite solid propellants based on hydroxy-terminated polybutadiene (HTPB) have become the workhorse propellants in the present-day solid rocket motors world-wide. Because of the high solid loading, the rheological behavior of such propellants is quite complex. The effect of solid loading, oxidizer particle size and aluminium content has been studied and reported. Similarly, the effect of temperature and mixer kinematics and mixing cycle time have also been studied and reported. In the present paper a generalized correlation has been developed for shear stress-shear rate based on the rheological parameters like yield stress, consistency index and pseudoplasticity index which are in turn functions of solid volume fraction, cure time, t, and temperature, and has a correlation coefficient of 0.94 with the experimental values. Also a commonly used term in propellant industries, pot life, has been defined and evaluated for the HTPB propellant system.     

Anodic oxidation of phenolics found in coal conversion effluents

Solutions of phenol, o-cresol, p-cresol, 2,3-xylcnol, 3,4-xylenol, resorcinol, and catechol at concentrations below I g/L were oxidized at constant current on a packed bed lead dioxide electrode with electrolyte recirculation. The effects of applied current and initial concentration on the extent of oxidation with time were explored. The observed ranking in ease of oxidation was phenol > 2,3-xylenol > resorcinol > p-cresol > 3,4-xylenol > o-cresol. Although the phenolics were largely destroyed, organic degradation products of the quinone and hydroquinone type remained in solution. A mixture of five monohydric phenols showed 96% destruction of phenolics, a 50% reduction in B.O.D. but a reduction in total organic carbon of only 22%.     

Tuning the Photophysical and Electrochemical Properties of Aza-Boron-Dipyridylmethenes for Fluorescent Blue OLEDs

A series of substituted aza-boron-dipyridylmethene ( aD ) compounds are demonstrated as fluorescent dopant emitters in blue organic light emitting diodes (OLEDs). Replacing the meso-carbon of a dipyridylmethene dye with nitrogen to form the aD chromophore leads to a destabilization of the highest occupied molecular orbital in aD , as evidenced both from their experimentally determined photophysical and electrochemical properties. These properties are consistent with theoretical calculations of the molecular energetics. These aD derivatives emit violet to blue light, peaking between 400 and 460 nm with photoluminescent quantum yields over 85%. The aD compounds have small energy differences (<400 meV) between their singlet and triplet excited states. OLEDs fabricated with an aza-boron-dipyridylmethene emitting fluorophore give an external quantum efficiency of 4.5% on glass substrates, close to the theoretical maximum for fluorescent OLEDs.