Starch Derivatives of High Degree of Functionalization, 8. Synthesis and Flocculation Behavior of Cationic Starch Polyelectrolytes

Abstract

Water soluble starch derivatives with a high degree of substitution (DS) up to 1 containing quaternary ammonium groups were prepared by reacting starch with 3-chloro-2-hydroxypropyltrimethylammonium chloride (QUAB®188) in ethanol/sodium hydroxide/water or preferably with 2,3-epoxypropyltrimethylammonium chloride (QUAB®151) in aqueous-alkaline solution. The DS values of the samples can be controlled by adjusting the molar ratio of cationization agent to anhydroglucose unit and is only slightly dependent on the amylose content of the starting starch material. The structure of the cationic starch derivatives was confirmed by means of NMR spectroscopy. Dewatering experiments with the cationic starch derivatives were conducted on a harbor sediment suspension using a laboratory pressure filtration apparatus. The cationic starches were used alone and in combination with a high-molar-mass synthetic polyanion. Both dependence on the DS of the sample and influence of the amylose/amylopectin ratios of the initial native starch were observed. The highest dewatering index of 63 was found for the cationic polyelectrolyte based on the amylopectin-rich waxy maize starch in monoflocculation. In case of dual flocculation using additionally a poly(acrylamide-co-acrylate) a dewatering index of even 85 was attained.