Molecular composition of surface sizing starch prepared using oxidation, enzymatic hydrolysis and ultrasonic treatment methods

Surface sizing that contains a degraded starch solution is used to refine the surface properties of paper. Starch degradation is traditionally done in the paper mill. The starch undergoes either thermal oxidation or enzymatic degradation, both of which use a jet cooking process. Ultrasonic treatment of the jet cooked solution may prove to be an environmentally friendly way to produce starch degradation. The aim of this article is to compare the molecular composition of starch sizing solutions that have been prepared using different processes. A thermo‐oxidised starch solution was found to have a higher molar mass than the enzymatically degraded starch yet it had a comparable solution viscosity. The application of mild ultrasonic treatment resulted in a molecular composition comparable to that of thermo‐oxidation. Strong ultrasonic treatment caused a strong degradation of the amylopectin, primarily splitting the α‐1,6‐glycosidic linkages at the branching points. The least amount of amylose degradation occurred with the ultrasonic treatment method, followed by thermo‐oxidation and enzymatic hydrolysis.