The influence of frequency on the mechanical and radical effects for the ultrasonic degradation of dextranes

The ratio of mechanical and radical effects for the ultrasonic degradation of dextranes in aqueous solutions was studied in dependence of frequency and molecular weight of the dextranes. For low ultrasound frequency (35 kHz) a stronger increase of the polymer degradation with increasing molecular weight was found as expected on the basis of the radicals present. This is due to the mechanical effects of ultrasound. Applying higher frequencies (> 500 kHz) only radical reactions are responsible for the degradation. Below a molecular weight limit of 40000 the mechanical effects vanish.