Flocculating agents based on cationic agarose

PRADO, H. J.; MATULEWICZ, M. C.; BONELLI, P. R.; CUKIERMAN, A. L.

Rosario, Santa Fe, Argentina

Workshop; 1st Argentinien Workshop on Environmental Science; 2009

Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario

The adsorption of polymers onto colloidal particles can cause changes in their colloidal stability leading to improved flocculation. Although cationic polyelectrolyte flocculants are widely based on polyacrylamide derivatives, concerns regarding biodegradability and high cost have encouraged research towards natural polymers. In that sense, we synthesized novel cationic agaroses with different degrees of substitution (DS) and tested their performance in the destabilization of kaolin dispersions. The cationic agaroses were prepared by the reaction of agarose in alcaline aqueous solution with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC). In order to obtain agaroses with different DS and to find the best reaction conditions for each case, the molar ratio agarose:CHPTAC:NaOH, reaction time and temperature were varied. The reaction products were characterized by means of different techniques: FT-IR spectra allowed confirming the occurrence of the substitution; the DS was calculated by elemental analysis and 1H NMR spectroscopy. The products were also characterized using monodimensional and bidimensional NMR techniques. The molecular weight of the products was determined by means of the quantification of the reducing ends and by HPSEC-MALLS. Products with DS between 0.04 and 0.77 were obtained. As opposed to the natural agarose whose gelling temperature was 31°C, these products did not form gels. During the reaction, sulphate groups, originally present in the agarose, were eliminated. A defect in the concentration of NaOH for each concentration of CHPTAC, led to a lower DS, to the incomplete elimination of sulphate, and to the obtention of an anphiphilic product that presented gellification. An excess of base also lowered the DS and enhanced polysaccharide degradation. The kinetic study showed that for a molar relation of 1.0:2.0:4.6 at 50°C the reaction was completed in 2 h for a DS of 0.19. The increase of the temperature to 80°C did not substantially improved the DS. The flocculation behaviour of cationic agaroses with four different DS (0.04, 0.19, 0.55 and 0.77) was tested by turbidimetry at 500 nm, 15 min after the addition of the flocculant and thorough. Best results were obtained with the modified agarose presenting a DS of 0.19 with a concentration of 2-4 mg of flocculant per g of kaolin. For agaroses with DS of 0.55 and 0.77, better results were achieved for a specific concentration of flocculant, being this concentration lower, the more sustituted the agarose was. At a higher than optimal dose the cationized agarose may cover most of available anionic sites on each kaolin particle and impart an electric positive charge to them, causing mutual repulsion. Agarose with a DS of 0.04 stabilized the suspension and made flocculation slower. Cationized agarose constitutes a natural polymer with potential application in flocculation of aqueous suspentions.