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Critical processing factors affecting rheological behavior of a wax based formulation
W Phuapradit1, N H Shah, Y Lou
1Pharmaceutical and Analytical R&D, Nutley, NJ 07110, USA.
Summary
Controlling shear and cooling rates is crucial for wax-based drug formulations. These factors significantly impact viscosity, ensuring consistent drug content and capsule quality in pharmaceutical manufacturing.
Area of Science:
- Pharmaceutical Sciences
- Materials Science
- Rheology
Background:
- Wax-based vehicles stabilize drugs prone to hydrolysis and oxidation.
- Uniform viscosity is essential for reproducible drug content and encapsulability in soft gelatin capsules.
Purpose of the Study:
- To identify critical processing factors influencing the rheological behavior of wax-based vehicles.
- To understand how temperature, shear rate, and cooling rate affect vehicle viscosity.
Main Methods:
- Rheological evaluation using a CSL Rheometer with parallel plates.
- Shear rate sweeps and viscosity-temperature profiles at varying cooling rates (1.3–20 °C/min).
- Analysis of phase transitions (sol, gel-sol, gel) via Arrhenius plots.
Main Results:
- Three distinct phase regions identified: sol (>50 °C), gel-sol (30–45 °C), and gel (<30 °C).
- Newtonian behavior in the sol region; thixotropic behavior (hysteresis loop) in the gel region.
- Cooling rate significantly impacts viscosity due to wax recrystallization; faster cooling leads to higher viscosity.
Conclusions:
- Shear rate and cooling rate are critical processing parameters for controlling final product viscosity.
- Precise control of these factors is necessary for consistent pharmaceutical manufacturing of wax-based formulations.