To further understand the effect of ultrasound on the dissolution of polyamide we conducted microscopic experiments that to some extend resembled the treatment in the ultrasound bath. Details on the results of these visualizations can be found in the supplementary information (S8) †. The application of ultrasound generates stable cavitation bubbles which oscillate around and on the PA strings staying attached to the strings due to hydrophobic interactions, as can be seen in figure . These bubbles seem to be responsible for the higher dissolution as they act as local micro-mixers enhancing the local mass transfer. Possibly this is the reason why k dis could be higher in the case of ultrasonic energy supply compared to energy supply through microwaves.