Synthesis, Characterization, and Flocculation Properties of Branched Cationic Polyacrylamide

A water soluble branched cationic polyacrylamide (BCPAM) was synthesized using solution polymerization. The polymerization was initiated using potassium diperiodatocuprate, K5[Cu(HIO6)2](Cu(III)), initiating the self-condensing vinyl copolymerization of acrylamide and acryloxyethyltrimethyl ammonium chloride (DAC) monomer. The resulting copolymer was characterized by the use of Fourier-transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Its flocculation properties were evaluated with standard jar tests of sewage. The effects of initiator concentration, monomer concentration, reaction temperature, and the mass ratio of monomers on intrinsic viscosity and flocculation properties of the product were determined using single-factor experiments and orthogonal experiment. 1. Introduction The process of coagulation and flocculation is one of the physicochemical unit processes in water and wastewater treatment [1, 2]. The object of this process is to turn small particles into larger particles through the use of chemicals called coagulants or flocculants [3]. Flocculants may be inorganic or organic, small molecules or polymers [4]. Based on their ionic nature, polymeric flocculants can be classified as anionic, nonionic, and cationic [5]. Among the polymer flocculants, cationic ones have better flocculating properties [6]. Cationic polymer flocculants have been used widely in wastewater treatment, especially in sludge dewatering [7]. Most of the polymeric flocculants used at present are linear polymers [8]. When the molecular weight increases, the viscosity of the solution increases rapidly, making subsequent synthesis and purification more difficult [9]. A branched polymer has a branched molecular chain point that connects three or more chain segments [10]. Examples are graft copolymers, star-shaped polymers, comb polymers, and dendritic polymers [11]. Compared with linear polymers, branched polymers have lower viscosity and better solubility and can be dispersed more rapidly into water [12]. The synthesis of a branched polyacrylamide using a supernormal valence transition metal, such as potassium diperiodatocuprate K5[Cu(HIO6)2](Cu(III)), as an initiator, in alkaline medium, and being capable of initiating the self-condensing vinyl polymerization (SCVP) of acrylamide, and then the branched polyacrylamide was obtained [13]. The self-condensing vinyl polymerization of acrylamide has been reported [14], but has not been used as a flocculant. We previously reported the synthesis of a branched nonionic polyacrylamide (BNPAM)