Thermal properties of alginic acid-polylysine molecular composites

Abstract

Alginic acid (Alg) is a copolysaccharide extracted from brown masse algaeconsisting of D-mannuronic acid (M component) and L-guluronic acid (G component). Sodium alginate (NaAlg) is a representative polyelectrolyte used widely in various fields, such as food and textile industries. Although NaAlg is readily dissolved in water, water insoluble alginates can be prepared when sodium ions of NaAlg are replaced by di- and trivalent cations. Among various ions, such as Fe2+, Cu2+, Ca2+, and Al2+, Ca2+ has received particular attention, since it is thought that a unique “egg-box structure” is formed when G components enclose Ca2+ ions. This chapter studies the thermal properties of alginig acid–polylysine molecular complexes. Alginic acid (Alg) - polylisine (PLys) molecular composites (Alg-PLys) are prepared by ionic crosslinking under the acidic condition. In order to investigate the effect of molecular conformation on the above composites formation, several kinds of Alg-PLys with different guluronic (G) and mannuronic acid (M) ratios are used. It also describes the thermal properties of Alg-PLys in the dry and wet states are measured by differential scanning calorimetry (DSC). The glass transition temperature of Alg-PLys composites is observed at a temperature higher than the Tg's which is calculated by assuming a simple mixing law of two components. Amorphousity of the composites is evaluated via restrained amount of non-freezing water, which is calculated from the enthalpies of melting and crystallization of water. The obtained results indicate that the molecular motion of Alg-PLys composites composed by G rich Alg is easily enhanced due to the bulky molecular conformation.