Ultrasonic Degradation of Poly(acrylic acid co acrylamide) Hydrogels in Aqueous Solutions

Continuous exposure to high-energy ultrasonic waves depolymerizes macromolecules in solutions and produces a permanent reduction in viscosity. Different factors affect the efficiency of this process. In this work ultrasonic degradation of one commercially important hydrogel based on acrylic acid and acrylamide was carried out in aqueous solution at room temperature (25°C). Also, the effect of sonication parameters (power and pulse) on the rate of degradation was investigated. A method of viscometry was used to study the degradation behavior of the hydrogel and a first order kinetic equation was employed to calculate the degradation rate constants. The experimental results indicated that the rate of ultrasonic degradation increased with increasing ultrasonic power and pulse. FT-IR and UV spectrometry measurements confirmed that the degradation proceeds by mechanical forces and also involves radical scission mechanism. Finally a mechanism was proposed according to the experimental data. The elucidated merits of the present ultrasonic process are: a) The process does not require any chemicals and additives; b) The process can be simple and rapid, which means that the process is cost effective; and c) The process will not induce large changes in the chemical structure, and in particular, the properties of hydrogel. Also, the ultrasonic process has been confirmed to be applicable for many kinds of hydrogels and gels.