Case Study 605 Wet-granulation Behaviour II
This case study investigates how the surface energy and wettability of primary particles influence agglomeration kinetics and granule morphology in a top‑spray fluid‑bed wet granulation process. Using a controlled model system of mono‑disperse glass beads that are either hydrophilic (AF) or hydrophobic (AF‑225) and a 2 % w/w aqueous hydroxypropyl‑cellulose (HPC) binder, the authors measured particle surface properties with inverse gas chromatography (IGC SEA) and contact‑angle techniques. Granulation was performed under identical fluid‑bed conditions (400 g batch, 110 mL binder at 5 mL min⁻¹, inlet air 60 °C, flow 0.3‑0.5 m³ min⁻¹). Results show that hydrophobic particles produce a broader granule size distribution, larger maximum granule sizes (d₅₀ = 336 µm vs 275 µm for hydrophilic), and more compact, round granules, whereas hydrophilic particles yield a narrower distribution but limited growth due to a thin, uniform binder coating. SEM imaging reveals that hydrophilic particles are coated by a thin binder film, leaving little binder to form solid bridges, while hydrophobic particles develop thick solid bridges at inter‑particle contacts because the binder de‑wets the surface. IGC SEA “fingerprints” confirm that hydrophilic granules retain a surface composition identical to pure HPC (indicating complete coating), whereas hydrophobic granules retain a mixed fingerprint, reflecting partial coating. The study concludes that better wettability does not necessarily translate to superior granulation performance; instead, surface energy governs binder distribution and thus granule growth mechanisms. IGC SEA is highlighted as a valuable analytical tool for characterising both primary particles and resulting granules, providing quantitative “fingerprints” of surface composition.
Topics
Surface Energy as a Driver of Wet‑Granulation Behaviour
Explores the hypothesis that primary particle surface energy governs agglomeration rate and granule growth in fluid‑bed wet granulation.