Studies on chain scission and extension of polyamide 6 melt in the presence of ultrasonic irradiation

The ultrasonic degradation of polyamide 6 (PA6) melt was conducted in a specially designed reactor. The effects of initial molecular weight of PA6, irradiation time, ultrasonic intensity as well as ultrasonic irradiation distance on the ultrasonic degradation of PA6 melt were investigated. Some surprising experimental results show that for low molecular weight PA6 (LPA6), the viscosity-average molecular weight of LPA6 increases in the presence of ultrasonic oscillations due to extension reaction of end groups (-COOH and -NH2), while for high molecular weight PA6 (HPA6), the viscosity-average molecular weight of HPA6 decreases with irradiation time, and passes through a minimum, then increases with irradiation time, up to a limiting molecular eight. Ultrasonic degradation kinetics of HPA6 melt obey the equation: M-t = M-infinity + Ae(-kt). FTIR analysis and a microtitration method confirm that the chain scission of HPA6 under ultrasonic irradiation occurs at C-N bonds. A plausible ultrasonic degradation model of the polymer melt based on molecular movement is proposed. Published by Elsevier Ltd.