Effect of calcium ion (cross-linker) concentration on porosity, surface morphology and thermal behavior of calcium alginates prepared from algae (Undaria pinnatifida)

Alginic acid and metal (sodium) alginates was prepared from fresh algae using hot extraction method. Calcium alginates are also prepared from sodium alginate by varying calcium ion (calcium chloride) concentrations. FTIR spectra indicate that alginic acid is converted into metal alginate. Surface morphology as well as total intrusion volume, porosity (%) and pore size distribution changes by changing calcium ion (cross-linker) concentrations. Thermal degradation of calcium alginates showed a stepwise weight loss during thermal sweep, indicating different types of reactions during degradation. Calcium alginate (Calg0.6) prepared at low calcium ion concentration is least stable whereas at highest calcium ion concentration, the alginate sample (Calg20) is most stable at final degradation temperature (800 °C). Kinetic analysis was performed to fit with TGA data, where the entire degradation process has been considered as four consecutive 1st order reactions.