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.

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

Extensive Molecular Dynamics, MD, calculations of the Lennard-Jones, LJ, rheological equation of state have been made. Non-equilibrium MD permits evaluation of shear thinning of the dense LJ liquid which adheres in behaviour quite closely with that of more complex “real molecules”. However, quantitative correspondence with simple analytic formulae for non-Newtonian behaviour used in the treatment of experimental data is hindered by poor prediction of certain key parameters. For example, at low shear rates, the equilibrium Newtonian viscosity and, at high shear rates, a limiting shear stress are often required. Both are difficult to obtain by simulation in the portion of the LJ phase diagram which exhibits significant shear thinning and using present techniques. Suggestions for improving the Eyring model for shear thinning are made.

Shear thinning of the Lennard-Jones fluid by molecular dynamics

L'origine biologique de la cellulose (coton ou bois) influe sur l'extrusion des propergols a double base et sur les proprietes physiques des propergols seches

The Rheological Properties of Plasticized Nitrocellulose as a function of nitrocellulose precursor

Dans le processus de melange Batch de propergols solides composites, de faibles variations lors du melange peuvent entrainer des modifications indesirables des proprietes et des performances du bloc de propergol. Une nouvelle strategie de melange a boucle fermee est proposee pour ameliorer l'insensibilite du processus de melange vis-a-vis de ces petites modifications et reduire ainsi les modifications du produit final d'un processus Batch a un autre. La nouvelle strategie de melange se base sur l'hypothese selon laquelle la reproductabilite du resultat du melange peut etre amelioree en executant le processus de melange de la meme maniere et que l'efficacite peut etre amelioree par un controle continu des performances. On justifie cette hypothese. L'efficacite de la nouvelle strategie de melange est demontree par des simulations en utilisant un modele de processus base sur des mesures et des analyses pendant un processus de melange reel avec un propergol composite nitrate d'ammonium. Les resultats montrent que la nouvelle strategie ameliore la reproductabilite du processus de melange par reduction des fluctuations lors du melange et elimination des fluctuations lors de la repetition du processus Batch. La nouvelle strategie de melange s'avere realisable. Etant donne que cette nouvelle strategie donne des resultats positifs avec une large marge de manoeuvre pour ce processus de melange difficile, elle devrait etre egalement efficace pour le processus Batch dans le domaine des propergols solides composites.

The Control of Power for Efficient Batch Mixing

When two simple fluids are mixed together to form a blend the resulting viscosity sometimes obeys a mixture rule of a log additive nature:

$$ \log \eta _{12} = \phi _1 \log \eta _1 + \phi _2 \log \eta _2 $$

(6.1)

The morphology and rheology of liquid crystal polymer blends

Using especially modified torque and capillary extrusion rheometers the rheological behaviour of a typical triple-base gun propellant has been examined as a function of such processing variables as temperature, solvent content, time taken to incorporate, filler content and filler shape. Propellant doughs flow according to the law where σ is the shear stress applied to the dough to maintain a shear rate of γ, σ0 is the yield stress at which flow commences, K is the consistency index and n is the flow behaviour index. Variations in these constants as a function of the above mentioned variables are presented and their implications discussed. Resultant changes in the physical properties of the dried extruded propellant also are monitored.

R. E. Carter

Papers

Processing Characteristics of Gun Propellants