Flocculation studies on model colloids using chitosan

Ashmore, M.H., 2000. Flocculation studies on model colloids using chitosan. PhD, Nottingham Trent University.

Preview

Text 10290310.pdf - Published version Download (30MB) | Preview

Abstract

Chitosan, a biodegradable and renewable resource commodity, is a naturally occurring copolymer of poly[B(l->4)-2-acetamido-2-deoxy-D-glucopyranose] and poly[B(l->4)-2-amino-2-deoxy-D-glucopyranose], which becomes soluble and positively charged in acidic media and therefore may be used to flocculate anionic dispersions. A series of well- characterised chitosan samples spanning a wide range of molecular weights, having been homogeneously acetylated to produce varying degrees of linear charge density, were used to flocculate "model colloid" polymer latices. Latices were selected to cover a wide range of charge densities and were sized between 85nm and 2.1 .The optimum flocculation concentrations were identified using both residual turbidity and initial rate methods together with electrophoretic mobility measurements. A charge neutralisation mechanism with an enhancement of rate in comparison to the rate of rapid coagulation indicative of a "charge patch" effect was confirmed, except in the case of the 2.1 particles. The optimum flocculation concentration of the latter fell below that of rapid coagulation, an effect ascribed to the influence of adsorbed chitosan upon the drainage between particles on close approach. Both molecular weight and degree of acetylation of the chitosans had a small effect upon the optimum flocculation concentration, with efficiency increasing with increase in both molecular weight and linear charge density. Increasing the ionic strength of the dispersion medium broadened the flocculation concentration range and diminished the enhancement of rate produced by the charge patch mechanism. The effects of changing the pH of the dispersion medium were also investigated and it was determined that optimum flocculation dose was increased considerably between pH 3 to pH 7, broadly in line with predictions from pKa calculations. With doses of chitosans in excess of the optimum for flocculation, charge reversal occurred and the cationic latices were rather more stable to electrolyte addition than their anionic precursors and were shown to be electrostatically rather than sterically stabilised.

Item Type:	Thesis
Creators:	Ashmore, M.H.
Date:	2000
ISBN:	9781369325591
Identifiers:	Number Type PQ10290310 Other
Divisions:	Schools > School of Science and Technology
Record created by:	Laura Ward
Date Added:	06 Jul 2021 09:40
Last Modified:	10 Apr 2024 15:10
URI:	https://irep.ntu.ac.uk/id/eprint/43336

Actions (login required)

Edit View

Views

Downloads