Pressure Effect on the Rheological Behavior of Highly Filled Solid Propellant During Extrusion Flow

Area of Science:

• Materials Science
• Chemical Engineering
• Polymer Science

Background:

• Solid propellants (SPs) contain high concentrations of micro-/nanoscale particles, posing challenges for understanding their rheological behavior.
• The shear-extrusion behavior of SPs, particularly their viscosity under processing conditions (80-95 °C), is not well understood.
• Existing research on highly filled polymers does not fully capture the unique rheology of SP melts.

Purpose of the Study:

• To investigate the pressure dependence of solid propellant (SP) melt viscosity during steady-state shear flow.
• To quantify the impact of pressure on SP rheology within the practical processing temperature range.
• To identify factors influencing the pressure sensitivity of SP viscosity.

Main Methods:

• Utilized a twin-bore capillary rheometer for steady-state shear measurements.
• Employed capillary dies with varying diameters and lengths to analyze viscosity.
• Measured viscosity under controlled temperature and shear rate conditions across a pressure range of 3-30 MPa.

Main Results:

• Solid propellant viscosity exhibits a strong dependence on melt pressure, deviating significantly from pressure-independent models.
• Interface defects between octogen particles and the polymer matrix contribute to significant melt pressures.
• Pressure sensitivity (β) of viscosity is strongly influenced by the solvent and solid particle content.
• Observed discrepancies are linked to the compressibility of particle-particle and particle-polymer networks.

Conclusions:

• Pressure effects are critical and non-negligible for accurately characterizing the rheological properties of solid propellants.
• The compressibility of internal networks within SPs under pressure significantly alters flow behavior.
• Accounting for pressure dependence is essential for optimizing SP manufacturing processes and ensuring reliable performance.