Use of Differential Scanning Calorimetry and Thermogravimetric Analysis To Characterize the Thermal Degradation of Crystalline Sucrose and Dried Sucrose−Salt Residues

Abstract

Thermal degradation of pure sucrose in concentrated aqueous solution (100 °C, ∼65 °Brix) in the presence of KCl, LiCl, NaI, and Na2B4O7 was investigated. Polarimetry was used to quantify sucrose degradation, and pseudo-first-order kinetic constants of initial degradation rates were calculated. All salts significantly increased sucrose degradation; colored degradation products were only formed in the presence of Na2B4O7. Thermal degradation characteristics of crystalline sucrose and dried, crystalline residues from sucrose−salt model solutions heated at 100 °C for 0 and 3 h were further investigated by differential scanning calorimetry (DSC), thermogravimetric (TG), and differential thermogravimetric (DTG) analyses. Rate of heating was 15 °C/min from 50 to 500 °C. DSC and TG studies confirmed the catalytic nature of salts on the thermal degradation of sucrose. Salts affected thermal degradation in various ways. The initial condensation degradation reactions were more rapid than expected, and subsequent elimination reactions were slower. The thermal analysis results indicate that complexation between the salt and sucrose is occurring, and further study at the molecular level is required. Keywords: Sucrose thermal degradation; DSC; TG, DTG; salts; crystalline sucrose; amorphous sucrose