A study on the effect of hydrophobically modified cationic acrylamide copolymers on flocculation properties of kaolin suspension
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Date
2009
Authors
Lee, Khai Ern
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Abstract
A series of hydrophobically modified cationic polyacrylamides were
synthesized via free radical solution copolymerization using ammonium
persulphate/sodium hydrogen sulphite as the redox initiator. Epichlorohydrin,
acrylamide and trialkylamine were used to synthesize the hydrophobic cationic
monomer 3-acrylamido-2-hydroxypropyltriakylammonium chloride (AHPTAAC) in
which the trialkyl group was trihexylamine, trioctylamine and tridodecylamine. Low
concentration (1-6 mol %) of cationic monomer from each group were
copolymerized with acrylamide to obtain hydrophobically modified cationic
polyacrylamides. Copolymer obtained at high concentration of cationic monomer
was insoluble in the aqueous medium due to its high hydrophobicity and
entanglement effect. Results show that the intrinsic viscosity and molecular weight
of the copolymers decreases with the increase in concentration of the hydrophobic
cationic group, whereas charge density indicates the reverse behaviour. Fourier
Transform Infrared (FTIR) and Transmission Electron Microscopy (TEM) were also
carried out to elucidate the functional groups and structures of the copolymer
respectively. A correlation analysis has been done between molecular weight and
charge density of the copolymers. It was found that there is a significant inverse
correlationship between molecular weight and charge density in this study. The
effect of hydrophobically modified cationic polyacrylamide of varying molecular
weight and charge density on flocculation of a kaolin suspension has been
investigated. High molecular weight was found to be ideal in flocculating kaolin suspension. Comparison of different hydrophobic groups and monomer substitution
ratio on turbidity removal was done. Hexyl group copolymer which had the highest
molecular weight of 2.13x106g/mol shows the best flocculation activity and reduced
turbidity by 99%. 1 mol % of hydrophobic cationic monomer concentration in
copolymers was found to be the best system in flocculating the kaolin suspension.
Bridging was the dominant mechanism in flocculating the kaolin suspension.
Copolymer with a dodecyl group had the least water retention in the flocculated
sludge compared to octyl and hexyl groups.
Description
Master
Keywords
Biological Science , Hydrophobically , Kaolin suspension