Alginates: Extraction, Characterization, and Properties

C.G. GOMEZ; M. RINAUDO; M.A VILLAR

Santiago de Chile, Chile

Conferencia; 10th International Conference on Frontiers of Polymers and Advanced Materials; 2009

Universidad de Chile

Extraction of sodium alginate from brown seaweeds (M. pyrifera) was performed in order to understand the influence of purification methods on the yield and final properties of the polymer. Direct polymer precipitation with ethanol (1/1 volume ratio) leads to the best yield. Purified alginates isolated under the sodium salt form were characterized by size exclusion chromatography (SEC) equipped with three detectors on line: a differential refractometer, a viscometric detector, and a multiangle laser light scattering (MALLS). Chemical composition of extracted alginates was obtained by 1H-NMR. Gelation ability of sodium alginate solutions in the presence of calcium ions was carried out by dialysis through a porous cellulosic membrane. The rheological behaviour of the solutions and gels was determined using a parallel plate rheometer at 25 ◦C. Oxidation reactions on –OH groups at C-2 and C-3 positions of the uronic units of sodium alginate were performed with sodium periodate, and the influence of degree of oxidation on physical properties of the oxidized derivatives was analyzed. The molar mass decreases rapidly until an oxidation of 10 mol% and then remains nearly constant. Polymers with a degree of oxidation higher than 10 mol% were no more able to form gels with calcium ions. Both elastic modulus (G`) and swelling degree (SD) of alginate gels decrease as the degree of oxidation increases. This behavior was attributed to the decreasing in the cooperative interactions between calcium ions and carboxylate groups due to a decrease in both the molar mass and the number of unreacted G units. Selective chemical modification of both b-cyclodextrin (b-CD) and sodium alginate (Alg) was performed in order to produce an alginate derivative possessing pendant b-CD cavities along the chain. A sodium alginate derivative modified with adipic dihydrazide (Alg-ADH) and a b-cyclodextrin derivative possessing an aldehyde function on the primary face were synthesized, and both were selectively coupled by a reductive amination-type reaction. The aim of this work is to find new active functional groups on alginates, which is a polymer of interest as support in drug-controlled delivery systems.