THE EFFECT OF DIFFERENT METHODS OF CATIONIZATION ON THE STARCH GRANULE AND ITS GELATINIZATION PRODUCT

The effect on the form and structure of starch granules caused by cationisation using a solvent, by dry cationisation and by cationisation in a water slurry has been studied by means of scanning electron microscopy (SEM). By means of energy‐dispersive X‐ray analysis (EDXA) and electron spectroscopy (ESCA) analyses have been made of the chemical elements in the surface layer and inner part of the cationised granules and in gelatinised products prepared from the cationised granules. Cationisation does not change the form of the granules. In granules cationised in a water slurry a slight swelling can be observed. Cationisation gives the starch granules a thin shell‐like outer surface. In the case of solvent‐cationised and especially of dry‐cationised granules there are abundant quantities of small particles in the surface of the granules. These are the remains of chemicals added during cationisation. The ESCA analyses show that the amount of N in the surface layer of solvent‐cationised, dry cationised and water‐cationised granules studied is 3.1, 0.71 and 0.37% (w/w), respectively. In the gelatinised samples prepared from the cationised granules the amount of N in solvent‐ and water‐cationised granules is the same but in dry‐cationised granules it is only half as much, i.e. 0.35% (w/w). The amount of Cl in the surface layer is for solvent‐, dry‐ and water‐cationised granules 88, 47 and 21% of the N content, respectively. The Cl content in the gelatinised products of solvent‐ and water‐cationised granules is approximately the same as before gelatinisation but in the dry‐cationised product it is 50% less. Judging from the analyses it would seem that the cationic amino groups are evenly distributed throughout the granule in the case of solvent‐ and water‐cationised granules. In dry‐cationised granules, however, these groups are concentrated to starch molecules in the outer part of the granule. The significance from the paper‐manufacturing viewpoint of even distribution of the cationic groups throughout the granule, of a low Cl content and of the existence of remains of chemicals in cationic starch is briefly addressed. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim