Chitosan‐graft‐acrylamide polyelectrolytes: Synthesis, flocculation, and modeling

Abstract

A series of chitosans have been grafted with quaternary ammonium cationic monomers, as well as acrylamide using Ce(IV) to induce macroradical formation on the polysaccharide backbone. The materials, which have long chain branches per molecule between 0.3 and 5.5, are shown to provide very high specific flocculation efficiency, at the very least equal to the entirely synthetic materials which have been previously documented in the literature. A charge ratio, determined from the polymer concentration at which flocculation takes place, the charge density of the polymer, and the surface charge of the suspended matter are proposed as metrics to evaluate the occurrence of charge neutralization and bridging or charge patch flocculation mechanism. Furthermore, a window of application (WA) for flocculants, which characterizes the region of concentration wherein the polyelectrolyte can remove 99% of the supernatant turbidity, has been defined. It was shown to depend on the square root of the ionic strength and varies inversely with the Debye length, providing a fundamental basis for the concept of the WA. A mathematical expression is presented which links the WA with the salt concentration and the number of branches of the grafted polymer. Grafted chitosans have been shown to be more robust than polyacrylamides in testing against model kaolin suspensions.

Preparation of cationic chitosan-polyacrylamide flocculant and its properties in wastewater treatment

“…For municipal waste water treatment, synthetic cationic polymers are almost exclusively employed. In recent years, graft copolymers of chitosan were prepared to treat wastewater (Feng et al, 2005;Lin et al, 2005;Laue and Hunkeler, 2006;Chu and Sun, 2008), most of which are of limited charge. The flocculation in many applications requires high molar charge densities.…”

“…In acidic solutions, the amine groups of chitosan are protonated and form a cationic macromolecule. Chitosan has been successfully used to prepare Semi-IPN Hydrogels (Mahdavinia et al, 2008), membranes (RMP, 2008), flocculant (Laue and Hunkeler, 2006;Chu and Sun, 2008), porous beads resin (Cai, 1999), sizing agent (Hebeish et al, 2006) and paper-strengthening agent (Ma and Qiu, 2007).…”

The flocculating properties of chitosan‐graft‐polyacrylamide flocculants (I)—effect of the grafting ratio

“…Based on previous research reports related to chitosan-g-PAM flocculants, the influence of external factors such as pH and dose has already been investigated. 12,13 However, there is little research about the effects of structure factors, such as the grafting ratio, on flocculating properties. In fact, structure factors are the most important factors for the performances of materials.…”

Study on chain deformation of polyacrylamides in solutions and its flocculation performance during the flocculation process

“…Polyacrylamide (PAAm) is one of the widely used organic flocculants for wastewater treatment 1, 2. The flocculation performance of PAAm flocculants primarily depends on the type of flocculants, the ionic‐PAAm and nonionic‐PAAm,3, 4 the ionic content,5 the molecular weight,6, 7 the type of wastewater, and their suspensions concentrations,8 and also depends on some operation processes such as the shear rate 9. In our previous work,10, 11 the effect of the flocculant dose and the parent solution concentration on the flocculation performance of PAAm flocculants has also been documented.…”