Characterization of crystalline and spray-dried amorphous α-cyclodextrin powders

• Published in: Powder technology 2015-11, Vol.284, p.585-594
• Main Authors: Ho, Thao M., Howes, Tony, Bhandari, Bhesh R.
• Format: Article
• Language: English
• Subjects: Amorphous α-cyclodextrin powder; Moisture adsorption; Re-crystallization; Relative humidity; Spray drying
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2015.06.027

Alpha-cyclodextrin (α-CD) powder has been used to adsorb organic compounds for various applications. In order to study the complexation of α-CD powder with guest compounds, an understanding of physical properties α-CD powder including molecular structure and water adsorption behavior is essential. Two known types of α-CD powder structure are crystalline and amorphous. However, commercial α-CD powder exists only in crystalline form and there is no reported information on properties of amorphous α-CD powder. This study aims at characterization and comparison of those properties of commercial (crystalline structure) and spray-dried α-CD powders. The results of SEM, X-ray, FTIR, DSC, PSD, TGA and 13C solid-state NMR analyses indicated that spray-dried α-CD powder was in an amorphous form with spherical shape particles (mean diameter ~13.28μm) and its glass transition temperature (Tg) was about 83.4°C. The spray-dried α-CD powder crystallized when kept above 65.30% Equilibrium Relative Humidity (ERH), corresponding to 13.70–14.97g of moisture 100g−1 of dry solids. In moisture adsorption study, at the same ERH levels, amorphous α-CD powder adsorbed moisture much higher than crystalline α-CD powder did, and its adsorption isotherm data were fitted well with both BET and GAB models at a low RH range (