Abstract. Sodium alginate obtained from the extraction of brown algae is used as the backbone for the synthesis of superabsorbent nanocomposite copolymerization. The first stage of extraction is the demineralization process using 0.1 M HCl solution and then 2% Na2CO3 solution for 2 hours at 60°C. The rendement of sodium alginate obtained was 44.32% with molecular weight of 40680 g/mol with measurement of the intrinsic viscosity. FTIR spectra of sodium alginate showed mannuronic acid functional group at wavenumber 884 cm -1 and the uronic acid at wavenumber 939 cm -1 , OH functional group at wavenumber 3200-3400 cm -1 , and CH2 stretching at wavenumber 2928 cm -1 . The diffraction pattern of isolated sodium alginate has specific 2θ at 13.068 and 21.096, amorphous intensity found specific 2θ at 18.058, and the obtained crystallinity degree of the sodium alginate is equal to 29.292% from the XRD analysis. The morphological analysis by SEM shows fibrils of isolated sodium alginate. The success isolation of sodium alginate from brown algae is supported by DSC which shows the decomposition temperature of pure sodium alginate and isolated alginate have close values, namely 251.12°C for pure sodium alginate and 229.90°C for isolated sodium alginate.

A nanocomposite comprising cellulose and nanomagnetite based on rice husk cellulose was used as the catalyst for the formation of methyl esters from oleic acid as an alternative method for biodiesel production. The resulting nanocomposite properties supported by FTIR, XRD, SEM and TEM characterization revealed that nanomagnetite Fe3O4 had impregnated the acetylated nanocellulose. The nanomagnetite Fe3O4 obtained had an average size of 30 nm. The best conversion of oleic acid to methyl esters for the catalytic application of the nanocomposite was 89.21%, which was achieved at a reaction temperature of 60°C, reaction time of 5 hours, catalyst concentration of 1.5 wt.%, and ratio of oleic acid to methanol of 3:1. Kinetic analysis at different temperatures (40, 50, 60 and 70°C) was performed, and a low activation energy of 16.56 kJ/mole was obtained. These results indicate that the biopolymer-based nanocomposite utilizing nanocellulose from rice husks composited with inorganic Fe3O4 nanoparticles has good potential for use as a green biocatalyst, and the proposed reaction can be used as an innovative new method to produce biodiesel in the future.

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