The data obtained by experiments with ultrasonic energy supply (black markers), however, follow a different trend indicating a higher reaction rate at low conversion values which slows down drastically towards high conversion values compared to values obtained with energy supply through microwaves. This trend is most accurately described by a diffusion model (D2) or a third order kinetic (F3). A 2D diffusion could be explained by the rate limiting mechanism for the dissolution of the PA 6 cylinders being the diffusion of Ca 2+ ions and EtOH into the polymer bulk. It is also possible that a product barrier layer of solvated polymer chains -described as the swelling of PA 6.6 fibers by Rietzler et al. ( ) -or a stagnant fluid layer caused by the absence of stirring inhibits further dissolution . An explanation for a third order reaction model as the rate limiting mechanism can be abduced: As proposed by Rietzler et al. ( ) for PA 6.6, the Ca 2+ ions form a complex with EtOH which breaks down hydrogen bonds, transfers the Ca 2+ to the PA chain and releases the EtOH. Therefore all three components (CaCl 2 , EtOH, amide) could be contributing to the dissolution leading to a third order reaction kinetic behavior. At this stage, a final conclusion on the dissolution mechanism remains open.