Degradation kinetics of poly (vinyl-pyrrolidone) under ultrasonic irradiation

Ultrasonicaton has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Solution of poly (vinyl-pyrrolidone) in chloroform with different concentrations and different molecular weights at a fined temperature were subjected to ultrasonic degradation. This study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The results were indicated that the polymers with height molecular mass degraded faster than the polymers laving low molecular mass thus the rate of ultrasonic degradation increased with increasing molecular weight. It was found that rate constant decreases as the concentration increases. The calculated rate constants correlated in terms of inverse concentration and relative viscosity of PVP solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased. The experimental results show that the viscosity of polymers decreased with ultrasonic irradiation time and approached a limiting value, below which no further degradation took place.