Temperature Mediated Adsorption of Poly(N-isopropylacrylamide) onto a-Alumina
A range of various molecular weight poly(N-isopropyl acrylamide) (PNIPAM) polymers have been synthesised for use as temperature sensitive flocculants. The conditions investigated include the ratio of initiator to monomer, monomer concentration and reaction time. It was found that by controlling these variables polymers with molecular weights between 100 kDa and 10 MDa could be produced. The lower critical solution temperature (LCST) was investigated by UV-vis spectroscopy. The response of PNIPAM dosed, alpha-alumina suspensions to various pH and temperature conditions was investigated through adsorption studies and batch settling tests. It was shown that the lower critical solution temperature (LCST) of the PNIPAMs was invariant with molecular weight. At all temperatures, higher PNIPAM doses were required to effect flocculation and settling at the extremes of pH than at neutral pH. However it was also found that at all pH values, the minimum PNIPAM dosage necessary for flocculation and settling, decreased when temperature conditions were raised above the LCST. Anionic flocculants were prepared as co-polymers of PNIPAM and poly acrylic acid.