Ultrasonic degradation of poly(vinyl alcohol) in aqueous solution

Solution of poly(vinyl alcohol) in water with different concentrations (by weight 1%, 1.5%, 2%) and different volumes (50, 75 and 100 ml) were subjected to ultrasonic degradation. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The degradation rate constant was correlated with the power input due to ultrasonic irradiation and reaction volume. It was found that rate constant decreases as the reaction volume and concentration increases. The proportionality index of the relation between rate constant, power input and reaction volume was found to be nearly equal for all concentrations studied. The proportionality constant was found to be approximately equal for 1% and 1.5% solution and for 2% solution it was approximately half the value for that of 1% and 1.5% solutions. The decrease in rate constant and proportionality constant is attributed to the fact that at higher concentration and at higher volume, the intensity of cavitation phenomenon is depressed and therefore the extent of polymer chain breaking decreases. The difference in the values of limiting viscosities (constant solution viscosity which does not decrease by further ultrasonic irradiation) for 50, 75 and 100 ml solutions for each of 1% and 1.5% concentration was negligible. But 2% solution at 100 ml volume showed slightly higher value of limiting viscosity than that for 50 and 75 ml.