| Summary: | Polyaspartic acid (PASP)-based green scale inhibitor has great potential application in water treatment. Here, we first synthesized PASP in ionic liquid. Then, an effective PASP-based green scale inhibitor was synthesized by ring-opening graft modification of PASP with both aspartic acid (ASP) and monoethanolamine (MEA). Its chemical composition was characterized by gel chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and 1H nuclear magnetic resonance (<sup>1</sup>H NMR). Scale inhibition efficiency was measured by static scale inhibition tests. The results showed that the new PASP-based scale inhibitor has high scale inhibition to both CaCO<sub>3</sub> and Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>. When the concentration was increased to 2 mg/L, the inhibition efficiency of the new PASP-based scale inhibitor was 99% for CaCO<sub>3</sub>, while when the concentration was raised to only 4 mg/L, its inhibition efficiency increased to 100% for Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the changes of crystal structure for CaCO<sub>3</sub> and Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> after adding the new PASP-based scale inhibitor. The crystal size of CaCO<sub>3</sub> and Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> became smaller and the crystal form became amorphous after adding the modified PASPs compared with adding pure PASP. Moreover, the modified PASP showed good biodegradation performance.
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