New starch phosphate carbamides of high swelling ability: Synthesis and characterization

The paper describes the synthesis of starch phosphate carbamides by reacting starch with phosphoric acid and urea. A solid state technique in vacuum at elevated temperatures is used. The degree of substitution of phosphate (DSP) and carbamide groups (DSC) can be adjusted by the molar ratio of starch: phosphoric acid: urea, the reaction temperature, and time. The starch derivatives prepared show remarkable swelling if the DSP ranges between 0.2 and 0.3. With increasing content of urea in the reaction mixture the water-holding ability is still significantly improved, which is explained by chemically and especially physically introduced urea into the starch polymer. Furthermore, the ratio of amylose: amylopectin of the starch samples influences both the DS values and the physicochemical properties, e.g., swelling power and multivalent metal ion adsorption of the products. The structure of the new polymers was determined by means of FTIR, C-13- and P-31 NMR spectroscopy as well as by gel permeation chromatography (GPC).