Preparation of Crosslinked Grafted Modified Anionic Starch-Based Flocculants and Their Dye Removal Performance

Abstract This study addresses two critical limitations of conventional flocculants applied to textile dyeing and printing wastewater: their poor biodegradability and persistent toxic residues. It also tackles the suboptimal performance commonly observed with single-modified starch flocculants. To overcome these challenges, a novel cross-linked, graft-copolymerized anionic flocculant—termed CSPA—was synthesized using cassava starch (St) as the backbone polymer, acrylamide (AM) and sodium acrylate (AANa) as co-grafting monomers, N,N′-methylenebisacrylamide (MBA) as the cross-linker, and an ammonium persulfate/sodium bisulfite redox system as the initiator. The dye removal efficiency of a composite coagulant composed of CSPA and polyaluminium chloride (PAC) was evaluated under ambient conditions. Structural and compositional characteristics of CSPA were systematically elucidated via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and solid-state ¹³C nuclear magnetic resonance (¹³C-NMR) spectroscopy. Using Disperse Red FB and Disperse Yellow RGFL as model dyes, the effects of key synthesis parameters—including the St-to-monomer mass ratio, AM-to-AANa molar ratio, MBA dosage (wt% relative to total reactants), initiator dosage (wt% relative to total reactants), and reaction temperature—on decolorization performance were rigorously investigated. Optimal flocculation performance was achieved at a St:AM:AANa molar ratio of 1:1:1, with MBA and initiator dosages of 0.2 wt% and 0.6 wt%, respectively (both calculated relative to total reactant mass), and a synthesis temperature of 70°C. Under these conditions, CSPA–PAC achieved removal efficiencies of 98.97% for Disperse Red(FB) and 99.56% for Disperse Yellow(RGFL). Moreover, the system demonstrated robust operational flexibility, maintaining > 90% decolorization across a broad CSPA dosage range (40–70 mg/L) and acidic-to-neutral pH range (pH 1–7).