Mechanochemical decomposition of poly(acrylic acid - acrylamide) hydrogels in aqueous solutions, influence of ultrasonic power and pulse



Polymers and gels may need to be degraded. For certain applications, polymers with lower molecular mass have advantages over the high molecular mass candidates. 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). It can be observed that there is a drastic decrease in viscosity of these solutions at first and a more moderate decrease after about 30min. 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.