Molecular mass distribution and degradation rate of xylan sonicated in acid and alkaline media

The molecular mass distribution of birch wood xylan sonicated in H2SO4 or KOH solution was investigated for elucidating the effect of medium on the change of molecular distribution. A recycling-style ultrasonic spray system, mainly composed of a 20 kHz frequency generator and a spraying nozzle, was used. Xylan was repeatedly sonicated for 0–15 cycles, and the molecular mass of xylan was determined by high-performance size-exclusion chromatography (HPSEC). Results indicated that the molecular mass of sonicated xylan decreased with increasing sonication cycle in alkaline solution, whereas no significant reduced in acid solution was observed. Moreover, the change of molecular mass of xylan treated with sonication in 2% KOH was higher than in 1% KOH solution. The degradation of xylan sonicated in alkaline solution was manifested by a decrease in weight ratio of higher molecular mass component. The changes on degradation rate constant (k) and average-number of chain splitting ratio (ANCS) of sonicated xylan indicate that the molecule is rapidly degraded within the first 5 cycles of sonication in 2% KOH solution. However, occurrence of aggregation was observed in H2SO4 solution (k<0). Results indicate that alkaline solution is a better medium than acid solution for xylan sonication.