PROPERTIES OF CATIONIC STARCHES OBTAINED BY REACTIVE EXTRUSION
Two different methods, namely chemical and physical modification in the Druvather® reactor DVT5 and Krauss Maffei twin-screw extruder ZE25R x 40D UTXi were used to prepare cationically modified starches, and the properties of those were compared. The reactive extrusion process consisted of two stages. In the first one, the mixture of reaction components at the molar ratio starch : 2,3-epoxypropyltrimethyl-ammonium chloride : NaOH : H2O = 1 : 0.125 : 0.04 : 3.5 was obtained. In the second one, the derived mixture was extruded by using a twin-screw extruder. The extrusion temperature varied from 20 to 140 °C, the screw speed was 50 rpm, and the mixture feed rate was about 1.5 kg/h. Four different samples of extruded cationic starches were obtained. The main characteristics such as the degree of substitution of cationic groups (DS), reaction efficiency, particle size and the polydispersity index were determined and compared with those of a non-extruded control sample of cationic starch of similar DS. Also, the parameters well defining the behavior of samples in water, such as the swelling power (SP) and the solubility index (SOL) at 75 °C were determined for extruded and control samples. It was established that the properties of extruded and non-extruded cationic starches were different. The following observations can be drawn with respect to the obtained data: the particle size of the extruded samples is much lower and the SP values are 7–13 times lower than those of the control sample; the SOL values of the extruded samples are twice as high, reaching 76–92 %, and even might be higher.