Kinetic aspects of chitosan fragmentation by femtosecond laser

Kinetics of chitosan fragmentation by ultrafast laser pulses, and the effects of reactor shape, saturation of solution with oxygen and chitosan molecular weight on fragmentation were investigated. The degree of fragmentation and molecular weight distribution of the fragments were followed by viscometry and size exclusion chromatography. Chain scission increased with light pulse energy, irradiation time in sigmoidal manner, and dose in biphasic manner. It also increased with molecular weight of chitosan, indicating that larger molecules were preferentially fragmented. The polydispersity of fragments increased with irradiation time. There was only a minor change in chain scission when chitosan solution was saturated with oxygen suggesting that secondary processes involving oxidation–reduction reactions may play only a minor role, and fragmentation proceeds mainly through multi-photon absorption.