Polylactic acid flame-retarded by nano-compound of form II ammonium polyphosphate with montmorillonite

It is reported a convenient method to obtain flame-retardant polylactic acid composite by adding low amount of crystal form II ammonium polyphosphate (APP-II) or nano-compound of crystal form II ammonium polyphosphate with calcium-based montmorillonite. The structures and thermal properties of the crystal form II ammonium polyphosphate and crystal form II ammonium polyphosphate with calcium-based montmorillonite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Crystallography and morphologies of the polylactic acid and its composites with the crystal form II ammonium polyphosphate and crystal form II ammonium polyphosphate with calcium-based montmorillonite were measured through differential scanning calorimeter and scanning electron microscopy. In flame retardancy of the polylactic acid composites, the 5 wt% crystal form II ammonium polyphosphate could make the polylactic acid achieve the UL-94 vertical burning V-0 rating and limited oxygen index 27.3%. When using crystal form II ammonium polyphosphate with calcium-based montmorillonite in flame-retarding polylactic acid, only 3 wt% nano-compound can result in the same V-0 rating level and the limited oxygen index of 28.0%. Meanwhile, polylactic acid with crystal form II ammonium polyphosphate or crystal form II ammonium polyphosphate with calcium-based montmorillonite still keeps the good mechanical properties. The developed systems are environmentally friendly and highly effective flame retarding, which show a promising future in practical large-scale polylactic acid application.