THE EFFECT OF IONIZING GAMMA RADIATION ON THE STRUCTURAL-MECHANICAL PROPERTIES OF STARCH GELS

Samples of potato starch were subjected to Co/sup 60/ gamma doses of 1.0 x 10/sup 6/ to 18.2 x 10/sup a/sr at a dose rate of 2000 r/min. The variation in plasticity of a standard gel with l2% dry starch was measured. Moderate amounts of radiation (1 to 3 x 10/sup 6/ r) caused an increase in the plastic strength of the gel, but larger doses (>4 x 10/sup 6/ r) caused a rapid decrease in the plastic strength. It is assumed that these changes in plastic strength are associated with changes in the number of hydroxy groups which promote the formation of a gel by hydrogen bonding. A series of relations is derived that include the dose, Avogsdro's number, the energy necessary to disrupt a single bond, a factor for the number of hydroxyl groups formed in breaking a single bond, the average molecular weight of unirradiated starch, and the value of the plastic strength of the gel. The observed phenomena are explained satisfactorily in terms of an initial increase in the number of hydroxyl groups due to bond breaking whose rate varies linearly with the dose with a subsequent decrease in the number of hydroxyl groups due tomore » depolymerization whose rate varies as the square of the dose. (TTT)« less