Intercalation of organic and inorganic anions into layered double hydroxides for polymer flame retardancy

Abstract A series of novel organic and/or inorganic-intercalated MgAl layered double hydroxides (SxMoy-LDH) were designed and prepared via calcination-reconstruction, where the organic anion was stearic (S) and inorganic anion was MoO42− (Mo). The intercalation of stearic and/or MoO42− anions into the interlayer galleries of the LDH host layers was controlled by adjusting the mass ratios (x/y) of stearic acid to (NH4)2MoO4, in which the stearic-intercalated LDH was obtained above the 1: 1 of the x/y mass ratio, and the MoO42−-intercalated LDH was synthesized below the 1: 1 of the x/y mass ratio. Especially at x/y mass ratio of 1: 1, stearic and MoO42− anions were co-intercalated into the interlayers of the S1Mo1-LDH to confer excellent flame-retardant properties. The morphology, chemical composition and structure of the as-prepared S1Mo1-LDH determined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy and energy dispersive spectrometer (SEM/EDS) and thermogravimetry (TG) confirmed the co-intercalation of stearic and MoO42− anions into the interlayer galleries. After adding the SxMoy-LDH materials into polypropylene (PP) matrix, the flame retardant performance of the PP-composites was significantly enhanced compared with the neat PP. It was also noticed that different interlayer anions could provide different retardant performances, and the stearic-MoO42−-co-intercalated LDH (S1Mo1-LDH) exhibited the highest thermostability and the best flame retardant performance owing to the synergistic effect of the interlayer stearic and MoO42− anions as well the LDH host layers. Therefore, it was possible to obtain a certain intercalation state of the organic and inorganic anions by modulating the mass ratios (x/y) of organic to inorganic anions.