Highly efficient flame retardant poly(lactic acid) using imidazole phosphate poly(ionic liquid)

Because of good thermal stability, nonflammability and rich structural designability, ionic liquids (ILs) have been used as flame retardants for poly(lactic acid) (PLA). However, as a small molecule, IL has the disadvantages of poor thermal stability and water resistance, and so on. In this paper, an imidazole-type poly(ionic liquid) (PIL) containing a phosphate anion was synthesized using 1-vinylimidazole, triethyl phosphate, and 1,2-divinylbenzene and marked as PDVE[DEP]. The PDVE[DEP] was used to improve the flame retardancy of PLA. The flame retardancy and thermal degradation behaviors of PLA/PDVE[DEP] composites were investigated by the limited oxygen index (LOI), UL-94 vertical burning, cone calorimetry, and thermal gravity analysis, and so on. The results showed that only 1.0 wt% PDVE[DEP] allows PLA to achieve the UL-94 V0 rating and obtain LOI value 25.6 vol%. The PDVE[DEP] improve the flame retardancy of PLA by melting-away mode. In addition, it catalyzes the transesterification of PLA and changes the degradation products.