Biodegradation of polyamide 6 by Lysinibacillus sp, Alcaligene faecalis and Enterococcus faecalis

Polyamide 6 (PA6, polycaprolactam, Nylon 6) is a thermoplastic polymer widely used in construction, automotive, packaging, etc. It is a semi-crystalline polymer known for its good mechanical properties, and chemical, and thermal stability, with a low price, compared to the other polyamides. PA6 can be synthesized by anionic polymerization of ε-caprolactam, initiated by sodium hydride, and activated by N-acetylcaprolactam. This poorly biodegradable material has quickly proven to be a source of considerable pollution both visually and in terms of ecosystem preservation, particularly due to its increasing annual global production. This issue raises the need to develop environmentally friendly protocols for the degradation of this waste. One of the methods that can prove to be effective is the degradation by microorganisms. The objective of our research is to study the degradation of PA6 by the bacteria Lysinibacillus sp. (LB), Alcaligene faecalis (AF), and Enterococcus faecalis (EF) isolated from the landfill. The three bacteria, isolated and previously identified, were able to show proliferation in minimal media using PA6 as the sole source of carbon and nitrogen. The weight loss of the PA6 pellets was evaluated at 21% for L. bacillus, 27% for A. faecalis, and 13% for E. faecalis after 48 days of incubation. The biodegradation of PA6 was also confirmed by FTIR and SEM coupled to the elemental detector scanning EDS, which revealed the structural, morphological, and elemental changes that PA6 underwent.