Encapsulation and release characteristics of carbon dioxide in α-cyclodextrin

Encapsulation and release of carbon dioxide (CO2) into and from alpha-cyclodextrin (alpha-CD) was studied. Initial moisture content of alpha-CD and CO2 pressure were found to have affected the encapsulation behavior. The increase of CO2 pressure has constantly accelerated the encapsulation rates and increased the maximum inclusion ratio, whereas the increase of initial moisture content showed no consistent effect. The saturated alpha-CD solution produced the inclusion complex crystal of similar inclusion ratio to solid alpha-CD. The release characteristics of inclusion complexes were also monitored at various relative humidities at 25 degrees C. Predominantly, increase in storage humidity accelerated the release of CO2. The inclusion complex crystal prepared from saturated alpha-CD solution showed the most stable release characteristic at all storage humidities investigated. The encapsulation and the release characteristics were analyzed using the first-order reaction equation and the Avrami's equation respectively, in order to estimate the rate processes of encapsulation and release. The FT-IR spectra of inclusion complexes presented an absorption band at wavenumber around 2338 cm(-1), indicating CO2 molecules resided inside the alpha-CD cavities in gaseous state rather than being bound to the hydroxyl groups of alpha-CD. Powder X-ray diffractometry was carried out to investigate the crystal lattice structure of alpha-CD and inclusion complexes. Scanning electron microscopy was also performed for morphological examination.