Preparation of porous microcrystalline cellulose pellets by freeze-drying: Effects of wetting liquid and initial freezing conditions
✍ Scribed by Maria Balaxi; Ioannis Nikolakakis; Stavros Malamataris
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 195 KB
- Volume
- 99
- Category
- Article
- ISSN
- 0022-3549
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✦ Synopsis
The effects of wetting liquid and initial freezing conditions on the pore volume and pore size distribution of freeze-dried microcrystalline cellulose (MCC) pellets were studied with mercury porosimetry. Freeze-drying was applied after extrusion/spheronization using two wetting liquids (water and water-isopropanol) and three initial freezing conditions (À30, 80, and À1978C). Also, the effects of initial freezing were compared to those on pellets prepared with extraction of NaCl from Avicel 1 /NaCl pellets. Pellet porosity was found to increase with decreasing initial freezing temperature and the increase is greater for pellets made with water as wetting liquid. The mean pore diameter is greater for the extracted pellets, followed by nonextracted MCC pellets made with water and water-isopropanol. Also, the pore diameter is greater for freezing at À808C comparatively to that at À308C, while it is smaller for freezing at À1978C. Narrower and more symmetrical pore size distributions were obtained with waterisopropanol at À1978C. The higher porosity obtained with water alone and the smallest mean pore diameter and narrower distribution obtained with water-isopropanol may be due to the effects of H-bonding between isopropanol and water molecules on the nucleation and growth of ice crystals during the initial freezing.