Synthesis of cationic flocculants based on acrylamide and [2-(acryloyloxy)ethyl]trimethylammonium chloride copolymers by semicontinuous inverse microemulsion polymerization. Part II: influence of initiator addition conditions, initial temperature, pH and comonomer concentration on flocculating performance

The influence of initiator concentration, specific flow rate of initiator addition (Q(sp)), initial copolymerization temperature (T-i), aqueous phase pH and total comonomer concentration (TCC) on flocculating performance of latex particles of acrylamide and [ 2( acryloyloxy) ethyl] trimethylammonium chloride copolymers with a cationic charge density of 40%, obtained by inverse microemulsion copolymerization by using a surfactant blend of Arlacel 83 and Softanol 90 as emulsifier and Rolling M-245, a mixture of n-decane and n-tetradecane in about 40/60 weight ratio, as oil phase, has been studied for high TCC, ranging from 28 to 34.5% (w/w). Comonomer inverse microemulsion copolymerizations were carried out in the semicontinuous mode by adding continuously an aqueous solution of sodium metabisulfite as initiator into stirred inverse comonomer microemulsions. Initiator concentration has a strong influence on viscosity, viscometric structuring degree (VSI) and average weight molar mass (M-w) of copolymers in the range from 5 to 25 g/L. Both viscosity and M-w decrease with increasing initiator concentration. Best flocculating performance is obtained from 10 to 20 g/L, values at which VSI shows a minimum. Under the experimental conditions used, Q(sp) (153 to 310 mL/h/kg of comonomer), T-i ( 25 to 35 degrees C) and aqueous phase pH (2.5 to 4.5) have almost no influence on both viscosity and VSI and, hence, on flocculating performance. On the contrary, TCC has a slight influence on copolymer viscosity but a strong one on VSI which increases dramatically with TCC, being the worst flocculating performance obtained at the highest TCC studied (34.5% (w/w)). Flocculating performance results are explained in terms of copolymer structuring degree and collapsed state of copolymer chains inside latex particles as well as in terms of the composition drift with conversion.