Case Study 611 D-Mannitol Flowability
This case study investigates how surface chemical modification influences the flow behavior of D‑mannitol powders. Using inverse gas chromatography with surface energy analysis (iGC SEA), the authors map the dispersive and specific (acid‑base) surface energy distributions of both as‑received (AR) and silanised (methylated) D‑mannitol. The methylation reaction replaces surface hydroxyl groups with –Si(CH₃)₂ groups, producing a more homogeneous, hydrophobic surface. Surface energy profiles reveal that AR D‑mannitol exhibits a wide range of dispersive (≈37–53 mJ m⁻²) and specific (≈2.7–4.3 mJ m⁻²) values, whereas silanised material shows narrowly clustered values (≈34 mJ m⁻² dispersive, ≈1.6 mJ m⁻² specific). Powder flow properties are measured with an FT4 Powder Rheometer, assessing dynamic, bulk, and shear characteristics, as well as flowability energy, aerated energy, stability index, consolidation index, and wall friction angle. AR D‑mannitol displays high, variable flowability energy (up to 333 mJ) and unstable aeration behavior, indicating strong cohesion. In contrast, silanised D‑mannitol shows lower, more consistent flow energies (≈75 mJ) and reduced cohesion, reflected in lower work of cohesion and a smaller wall friction angle (24.9° vs 26.2°). The study demonstrates a clear correlation: reduced surface energetic heterogeneity and lower specific surface energy lead to diminished cohesive forces and improved, repeatable flow performance. The authors conclude that iGC SEA provides a rapid, quantitative means to predict powder flow behavior from surface energy maps, offering practical value for pharmaceutical formulation and processing.
Topics
iGC SEA Mapping of Surface Energy Heterogeneity in D‑Mannitol
Application of inverse gas chromatography with surface energy analysis to generate dispersive and specific surface energy profiles as a function of surface coverage for AR and silanised D‑mannitol.
Methylation (Silanisation) of D‑Mannitol Surface Hydroxyls
Chemical modification using dichlorodimethylsilane to replace surface –OH groups with –Si(CH₃)₂, producing a hydrophobic, energetically homogeneous surface.
FT4 Powder Rheometer Characterization of Flow Metrics
Measurement of dynamic, bulk, shear, flowability energy, aerated energy, stability index, consolidation index, and wall friction angle for both powder variants.
Correlation Between Surface Energy Profiles and Cohesive Strength
Demonstration that broader surface energy distributions correspond to higher work of cohesion and variable flowability, while narrow, low‑energy profiles reduce cohesion.
Effect of Surface Homogenisation on Powder Flowability
Quantitative comparison showing silanised D‑mannitol’s lower flowability energy, reduced aerated energy, and more stable flow indices versus AR material.
Implications for Pharmaceutical Powder Processing
Discussion of how rapid iGC SEA surface energy mapping can guide formulation decisions to achieve consistent, free‑flowing powders.