Physicochemical properties of sodium alginate from brown algae Sargassum aquifolium and Sargassum cinereum

Abstract

Synthesis and characterization of sodium alginate from Sargassum aquifolium dan Sargassum cinereum have been successfully performed. S. aquifolium and S. cinereum were collected from the Dompu Islands, West Nusa Tenggara, Indonesia. Extraction was performed by acid pathway, due to cell disruption and the addition of Na2CO3 for extraction. The addition of HCl was to convert acid alginate into alginate, then transformed acid alginate into sodium alginate using NaOH. NaOCl and IPA were used for purification. Physicochemical properties were characterized using SEM-EDS, FTIR, and TG/DTG. The morphological structure of synthetic sodium alginate shows layer structure and fiber fibrils. Sodium alginate contained C, O, Na, and Cl elements. FTIR spectrum indicated the presence of functional groups at the following wavelengths: OH at 3343 cm−1, CH2 at 2915 cm−1, CO double bonds at 1614 cm−1, and fingerprint indicated by the presence of uronic acid, which functioned as the CH group stretched at 935 cm−1. The sodium alginate sample shows a three-step thermal degradation pattern. The first step was starting at 41.7 °C associated with dehydration and was followed by 206.4 and 241 °C associated with decomposition. TGA/DTG results showed a reduction in thermal stability at 250–300 °C. It is suitable for modification and application.