The influence of polymer chemistry on adsorption and flocculation of talc suspensions

The adsorption and action of four starch polymers in talc flocculation has been studied. The polymers include: two chemically modified starch polymers (carboxymethyl (CM) and phenyl succinate (PS) starch), with similar molecular weight but variation in terms of added aromatic functionality; and two unmodified starch polymers, Gelose 80 and Gelose 50, which vary in their amylose:amylopectin ratio. The adsorption behaviour of the polymers indicated that the carboxyl groups of the functionalised polymers discouraged adsorption at low ionic strength, with the non-charged Gelose polymers adsorbing to higher densities in spite of having lower molecular weights. AFM imaging and contact angle measurements indicated that the polymers interact similarly with the talc basal plane in terms of coverage and effect on hydrophobicity, with minor differences in adsorbed layer thickness. CM and PS starch had an equal and best effect on the flocculation behaviour of talc suspension. The settling rate of bare talc was 0.14 m h−1; the two functionalised starch polymers increased the settling rate to 1.7 and 2 m h−1 for CM and PS starch, respectively (at 8 mg L−1 concentration). Whereas different chemical substitution had no pronounced effect on the settling behaviour, the relative content of amylose to amylopectin did produce differences in settling. Gelose 80 (80% amylose; 1.3 m h−1 settling rate at 40 mg L−1 concentration) performed better when compared Gelose 50 (50% amylose; 0.65 m h−1 settling rate at 40 mg L−1 concentration). Of the two unmodified starch polymers, Gelose 80 gave the best overall settling performance, highlighting the effect of the linear starch chains in encouraging good bridging flocculation.

► The influence of starch chemistry on adsorption and flocculation.
► Chemistry influences adsorption, contact angle, and adsorbed layer thickness.
► Flocculation not affected by a variation in polymer substitution chemistry.
► Flocculation is significantly affected by variation in polymer branching ratio.