“One-pot” synthesis of crosslinked silicone-containing macromolecular charring agent and its synergistic flame retardant poly(l-lactic acid) with ammonium polyphosphate

A crosslinked silicone-containing macromolecular charring agent (CSi-MCA) was synthesized via “one-pot” process, and it was combined with ammonium polyphosphate (APP) to synergistically improve the flame retardancy of poly( l -lactic acid) (PLA). The chemical structure of synthesized CSi-MCA was characterized by Fourier transform infrared spectroscopy and solid-state 13 C nuclear magnetic resonance. The thermal gravimetric analyzer indicated that the CSi-MCA displayed good thermal stability and high residue via the catalytic crosslinking. Furthermore, the flame retardant effect of CSi-MCA and APP as intumescent flame retardants in PLA system was investigated by limited oxygen index, UL94, and cone calorimeter test. When the content of CSi-MCA was 5 wt% and APP was 10 wt% (CSi-MCA/APP = 1/2), the limited oxygen index value of composites was 33.6 and UL94 classed a V-0 rating. The peak heat release rate and total heat release of PLA composites containing both APP and CSi-MCA decreased significantly in comparison with those with APP or CSi-MCA alone. The flame retardancy mechanism was investigated via analyzing residual chars by scanning electron microscopy and X-ray photoelectron spectroscopy as well as the possible chemical reaction between APP and CSi-MCA by thermal gravimetric analyzer and Fourier transform infrared spectroscopy. The results showed that the enhanced flame retardancy was attributed mainly to synergistic effect of CSi-MCA and APP, which could form a compact, continuous, and protective layer during combustion. Copyright © 2017 John Wiley & Sons, Ltd.