Degradation of polyamide‐6 by using metal salts as catalyst

Polyamide‐6 (PA‐6) is a widely used polycondensation polymer that can be recycled by hydrolysis to its monomer ϵ‐caprolactam. The reaction is normally catalyzed by mineral acids. Using microwaves as the source of heating, zinc chloride, acetate and triflate were evaluated as non‐acid catalysts for the reaction. Gravimetric and electron spray ionization mass spectrometry analysis of reaction products showed ZnCl 2 as the most effective salt catalyst. A 50wt% (versus PA‐6) addition gave 75% water‐soluble, low‐molecular‐weight oligomers, which is approximately 25% lower than when using phosphoric acid. The triflate salt was effective only when used as an addition to a mineral acid, whereas the acetate was ineffective. FTIR and NMR spectroscopy of degradation products showed that dissociated ions from ZnCl 2 bind to the amide group of the polymer. Using the triflate salt no such interaction could be observed, indicating that the degradation and catalysis mechanisms differ with the chloride and triflate salt. Five water‐stable lanthanide triflates showed no catalytic effect on the reaction.