Indonesia, one of the world's largest tapioca starch producers, generates abundant cassava starch waste (onggok) that remains underutilized. This study aimed to enhance the value of onggok by synthesizing a superabsorbent polymer (SAP) through graft copolymerization using acrylic acid monomer and cerium(IV) initiator. Grafting was optimized by varying monomer concentrations (10–40% w/w) while maintaining the initiator concentration at 1.70% (w/w) and a reaction temperature of 53 °C. The optimal grafting occurred at 20% monomer concentration, yielding a grafting percentage of 14.83% and a monomer conversion of 74.15%. FTIR analysis showed increased absorbance ratios of –OH to C=O functional groups, confirming successful grafting. SEM images revealed a transformation from granular to porous structures, while DSC analysis demonstrated a shift in gelatinization temperature from 45.91 °C (raw onggok) to 46.69 °C (grafted), and retrogradation temperature from 140.67 °C to 141.67 °C. The water absorption capacity of the grafted copolymer reached 4.2450 g/g (5.20 g total), nearly double that of raw onggok (2.2716 g/g or 3.20 g), confirming its effectiveness as a SAP material.
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