A lysine-derived flame retardant for improved flame retardancy, crystallinity, and aqueous-phase degradation of polylactide

Polylactide (PLA) as one of the excellent representative bioplastics had attracted attention worldwide. However, high flammability and poor crystallization behavior of PLA limit its further application. Moreover, the aqueous degradation rate of the pure PLA has been reported extremely low in natural environment (e.g. in water or soil). To solve these problems, the bio-based flame retardant DL was designed and prepared in water phase without any organic solvent by using lysine (Lys), derived from animals and beans, and diethylenetriamine penta-(methylenephosphonic) acid (DTPMPA), a non-toxic scale inhibitor for water treatment, as raw materials. The combination of the flame retardant DL and polyethylene glycol (PEG) endowed PLA with UL94 V-0 rating and limited oxygen index (LOI) value of 29.4%. The crystallinity degree of PLA with 4 wt% PEG and 6 wt% DL were improved to 39.0%. Moreover, the aqueous degradation of PLA in the purified water at the ambient temperature was accelerated by the addition of DL and PEG, manifested by the 38% decrease in Mw of PLA. It is interested in the analysis of the degradation solution that the release of the oligomers of degraded PLA and the flame retardant DL was found during the aqueous degradation process, which further clarified the degradation mechanism.