Effects of γ-irradiation on molar mass and properties of Konjac mannan

Konjac mannan (KM) is a water-soluble glucomannan with high molar mass. Here, the effects of γ-irradiation on the structure of KM, its viscosity, molar mass distribution and the state of sorbed water were studied after irradiation at reduced pressure. These changes were investigated using ESR, FT-IR, UV, viscometer, SEC–MALS and DSC. Free radical yields increased with absorbed dose. Irradiation led to chain scission, but introduced no significant new chemical groups into the structure, apart from a small increase in content of carbonyl groups. The intrinsic viscosity, molar mass and radius of gyration decreased rapidly with increasing dose up to 10 kGy and then at a slower rate. The Mark–Houwink–Sakurada equation for the KM gave [η]=5.30×10−4 M0.78. The α value showed that KM molecules are solvated in the form of random coils in water. There are three types of sorbed water in irradiated KM as in the original KM. There is no significant change in water binding ability for KM with MW greater than 2×105.