Flow Function of Pharmaceutical Powders at Low-Stress Conditions Can Be Inferred Using a Simple Flow-Through-Orifice...

Area of Science:

• Pharmaceutical Engineering
• Materials Science
• Powder Technology

Background:

• Many pharmaceutical powder processing operations occur at stress levels significantly lower than those typically employed in standard laboratory shear cell testing.
• A gap exists in accurately characterizing powder flow properties under these low-stress conditions, impacting process efficiency and product quality.

Purpose of the Study:

• To develop and validate a reliable method for determining intrinsic powder flow properties, specifically the flow function (FFc), under low-stress conditions relevant to pharmaceutical manufacturing.
• To bridge the gap between empirical measurements and theoretical understanding of powder flowability at low consolidation stresses.

Main Methods:

• Utilized a commercially available flow-through-orifice device (Flodex™ apparatus).
• Developed a theoretical framework integrating Jenike's radial stress field analysis with Flodex experimental data.
• Applied the method to 10 distinct pharmaceutical powders, estimating major principal stresses around 100 Pa.

Main Results:

• Successfully derived major principal stress and flow function (FFc) from Flodex experiments under low-stress conditions (approx. 100 Pa).
• Obtained FFc values generally consistent with extrapolated data from ring shear testing.
• Demonstrated that FFc decreases with decreasing consolidation stress for pharmaceutical powders, consistently remaining above 1.

Conclusions:

• The integration of radial stress field theory with a simple flow-through-orifice experiment enables reliable determination of intrinsic powder flow properties under low stresses.
• The flow function (FFc) threshold for assessing powder flowability requires careful consideration and potential adjustment under low-stress conditions.
• This method provides valuable insights into powder behavior in pharmaceutical processes operating at lower stress regimes.