Three different starch-based flocculants with various chain architectures and charge properties have been prepared through etherification, graft copolymerization , or their combination. Two of the flocculants (starch- graft -poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride] and starch-3-chloro-2-hydroxypropyl triethyl ammonium chloride , denoted as STC- g -PDMC and STC-CTA respectively) are cationic, and another one (carboxymethyl starch- graft -poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride], denoted as CMS- g -PDMC) is amphoteric. Those three flocculants have shown far different flocculation efficiency and floc properties for the removal of humic acid (HA) from water due to their distinct structural features. The effects of pH, flocculant dose, and initial HA concentration have been studied systematically. Accordingly, STC- g -PDMC and CMS- g -PDMC with strongly cationic branch chains have much better flocculation performance than polyaluminum chloride (PAC) and STC-CTA, the latter of which features linear chain architecture and strongly cationic pieces lying on its chain backbone. It indicates that the architecture of cationic branch chains plays an important role in HA flocculation due to their significantly enhanced bridging effects. Moreover, STC- g -PDMC has higher HA removal efficiency and better floc properties than CMS- g -PDMC, suggesting that charge neutralization effects make notable contributions to HA removal and that the additional anionic pieces on CMS- g -PDMC can weaken its flocculation performance. In addition, STC- g -PDMC used as coagulant aid for PAC has also been tried, which observably reduces the optimal dose of the inorganic coagulant.
Two series of cellulose-based antiscalants with different chain architectures, i.e., linear carboxymethyl cellulose (CMC) and branch-shaped carboxymethyl cellulose- graft -poly(acrylic acid) (CMC- g -PAA), were synthesized. The carboxyl groups were distributed on CMC backbone but mainly on the grafted chains of CMC- g -PAA. The addition of CMC and CMC- g -PAA can both increase the surface energy of CaCO 3 scale and decrease its crystal nucleation rate, thereby inhibiting CaCO 3 scale formation. The structural effects of these cellulose-based antiscalants, especially the chain architectures, on the scale inhibition were investigated in detail. High degree of carboxymethyl substitution caused better inhibition effect of linear CMC. However, CMC- g -PAA with an appropriate content of carboxyl groups but high average number of PAA grafted chains can achieve high inhibition performance. Besides, with similar contents of carboxyl groups, CMC- g -PAA showed much better inhibition performance than CMC due to the distinct multi-dimensional spatial structure of graft copolymer in solution, causing the enhanced chelation and dispersion effects. Characterization of CaCO 3 crystal by scanning electron microscopy and X-ray diffraction confirmed that crystal distortion effect obviously existed in CMC but quite minor in CMC- g -PAA. The differences between the scale-inhibition performance of CMC and CMC- g -PAA should be attributed to the different scale-inhibition mechanisms originated in their distinct chain architectures.
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