Encapsulation and Release Characteristics of Carbon Dioxide in α-Cyclodextrin

Encapsulation and release of carbon dioxide (CO₂) into and from α-cyclodextrin (α-CD) was studied. Initial moisture content of α-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 α-CD solution produced the inclusion complex crystal of similar inclusion ratio to solid α-CD. The release characteristics of inclusion complexes were also monitored at various relative humidities at 25 °C. Predominantly, increase in storage humidity accelerated the release of CO₂. The inclusion complex crystal prepared from saturated α-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 α-CD cavities in gaseous state rather than being bound to the hydroxyl groups of α-CD. Powder X-ray diffractometry was carried out to investigate the crystal lattice structure of α-CD and inclusion complexes. Scanning electron microscopy was also performed for morphological examination.