Degradation of polyamide‐6 by using metal salts as catalyst

Abstract

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 ZnCl2 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 ZnCl2 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. Copyright © 2003 John Wiley & Sons, Ltd.

Effects of bleaching and functionalization of kaolinite on the mechanical and thermal properties of polyamide 6 nanocomposites

“…31 This transformation from a to thermodynamic g structures is generated by the capability of the amide groups along the PA6 polymer chain to form intrachain hydrogen bonds with the OH ions in the basal plane of the kaolinite and become aligned along the crystallographic direction of the a-axis. 32 As listed in Table 3, it can be seen that there is a minor change in the T m2 of the neat PA6 and PA6 nanocomposites with pristine, bleached and intercalated kaolinite; a maximal shi occurs from 225.51 C for the neat PA6 to 223.42 C for the PA6/KS nanocomposite. Probably, the kaolinite nanoparticles did not act as a nucleating agent, which generally favors the formation of crystal nuclei.…”

Chemical Recycling of End‐of‐Life Polyamide 6 via Ring Closing Depolymerization

“…With respect to chemical recycling of Nylon 6 some procedures have been developed. For instance, depolymerization of Nylon 6 involving acidic hydrolysis yielding 6‐aminocaproic acid as well as oligomers has been studied . Thermal decomposition under pyrolytic conditions and sub‐ und supercritical fluids applying high temperature and pressure results in the formation of low molecular weight chemicals.…”

“…For instance, depolymerization of Nylon 6 involving acidic hydrolysis yielding 6aminocaproic acid as well as oligomers has been studied. [22][23][24][25][26] Thermal decomposition under pyrolytic conditions [27][28][29][30][31][32][33][34] and sub-und supercritical fluids [35][36][37][38][39] applying high temperature and pressure results in the formation of low molecular weight chemicals. However, high energy input and extensive separation is required.…”

Polymer Degradation Under Microwave Irradiation

“…PA-6 can be recycled by hydrolysis, normally catalyzed by mineral acids, to its monomer ε-caprolactam. Klun and Krzan [51,52] presented microwave-assisted PA-6 hydrolysis in the present of phosphoric acid as catalyst. The very high dipole moment of H 3 PO 4 also makes it an excellent microwave absorbent.…”

“…Using the triflate salt, no such interaction could be observed, indicating that the degradation and catalysis mechanisms differ for the chloride and triflate salts. Five water-stable lanthanide triflates showed no catalytic effect on the reaction [52]. …”