A model study for the recovery of polyamides using the dissolution/reprecipitation technique

A model dissolution/reprecipitation. process is studied for the recycling of both poly-epsilon-caprolactam (PA 6) and polyhexamethyleneadipamide (PA 6 6). This process comprises dissolution of each of the aforementioned polyamides in an appropriate solvent, reprecipitation by addition of a nonsolvent and finally recovery of the polymers through washing and drying. Dimethylsulfoxide/methyl-ethyl-ketone (DMSO/MEK) proved to be the most suitable solvent/nonsolvent system for the recovery of PA 6, while formic acid/methyl-ethyl-ketone was used as a potential pair of solvent/nonsolvent in the case of recovering PA 6 6. The recycled polyamides were evaluated in terms of the following characteristic properties: molecular weight (based on end-group analysis and intrinsic viscosity determination), crystallinity and grain size analysis. In all cases, the recycled materials present excellent retention of the properties studied. Finally, the solvent mixtures involved are separated by distillation for reuse.