High radiation dose studies of kappa-carrageenan in dilute aqueous solution

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Crosslinking or degradation of polysaccharides is one of the most important applications of radiation processing. Kappa-carrageenan (κ-carrageenan), one of the most frequently studied polysaccharides, is known to undergo degradation when exposed to ionizing radiation. In this work, irradiation of 1% κ-carrageenan solution (Mw 1.14 × 106 Da) at high radiation doses of 100–300 kGy resulted in an increase in molecular weight. The average molecular weight (Mw) increased from 5600 to 60,000 Da and 7500 to 69,000 Da with gamma and electron-beam irradiation, respectively. UV analyses of irradiated 1% solution showed an increasing absorbance at 265 nm, while FT-IR spectra still displayed some important functional groups and showed an increasing carbonyl and double bond groups with doses up to 300 kGy. The antioxidant properties also increased with dose but leveled off at 100 kGy. Further irradiation to 500 kGy led to the formation of microgels with a size of <5 μm under SEM, indicating the presence of a crosslinked chain of κ-carrageenan. The lowering of solution pH due to the release of sulfate groups during irradiation and the radical formation on the alkyl group of the side chain may be responsible for the radiation crosslinking of κ-carrageenan. The results of this study would be beneficial in understanding the radiation-induced changes in the structure and properties at different irradiation conditions, which may pave the way for various applications of carrageenan-based materials.