Using ultrasonic (US)-initiated template copolymerization for preparation of an enhanced cationic polyacrylamide (CPAM) and its application in sludge dewatering.

In this study, the ultrasonic (US)-initiated template copolymerization was employed to synthesize a novel cationic polyacrylamide (CPAM) characterized by a microblock structure using dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM) as monomers, and sodium polyacrylate (NaPAA) as template. The polymers structure property was analyzed by Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance spectroscopy (1H NMR) and thermogravimetric analysis (TGA). The results showed that a novel cationic microblock structure was successfully synthesized in the template copolymer of DMDAAC and AM (TPADM). Meanwhile, the analysis result of association constant (MK) provided powerful support for a I Zip-up (ZIP) template polymerization mechanism and the formation of the microblock structure. The factors affecting the polymerization were investigated, including ultrasonic power, ultrasonic time, monomer concentration, initiator concentration, mAM:mDMDAAC and nNaPAA:nDMDAAC. The sludge dewatering performance of the polymers was evaluated in terms of specific resistance to filtration (SRF), filter cake moisture content (FCMC), floc size (d50) and fractal dimension (Df). Flocculation mechanism was also analyzed and discussed. The sludge dewatering results revealed that the polymer with the novel microblock structure showed a more excellent flocculation performance than those with randomly distributed cationic units. A desirable flocculation performance with a SRF of 4.5 × 1012 m kg-1, FCMC of 73.1%, d50 of 439.156 µm and Df of 1.490 were obtained at pH of 7.0, dosage of 40 mg L-1 and the molecular weight of 5.0 × 106 Da. The cationic microblock extremely enhanced the polymer charge neutralization and bridging ability, thus obtaining the excellent sludge dewatering performance.