Effect of plasma power on degradation of chitosan

The depolymerization of chitosan by plasma in the presence of oxygen (O 2 ) and nitrogen (N 2 ) was investigated with various PECVD power. The degree of the depolymerization was determined by measuring the viscosity. With 100W of PECVD, the average molecular weight (M w ) decreased from 93,000 of raw chitosan to about 41,000 with plasma-treating time of 5 min in N 2 , and 45,000 in O 2 . The depolymerization of chitosan increased with increasing PECVD power from 100W to 400W, and with increasing PECVD treating time from 1min to 5 min. FT-IR showed the absorption band peaks of the amine (-NH) band at 1,541–1,549 cm −1 and the carbonyl (C=O) band at 1,654 cm −1 and 3,422–3,488 cm −1 substantially decreased. The decrease in band peaks means that the chain of chitosan macromolecules was broken into smaller unit which results in decreasing viscosity. Therefore, plasma treatment in the presence of O 2 or N 2 is a potentially applicable technique for the production of low molecular chitosan.