Flame retardancy of polypropylene (nano)composites containing LDH and zinc borate

Polypropylene (PP)/organically-modified layered double hydroxides (LDH) and PP/organo-LDH/zinc borate (BZn) (nano) composites were prepared by the melt blending method. The structures and morphologies of (nano) composites were characterized by X-ray diffraction and TEM. The flammability properties and thermal stability were studied using TGA, cone calorimeter, limiting oxygen index (LOI), and the UL94 protocol. The basal spacing of organo-LDH increases to 3.89 nm from 0.76 nm in pristine LDH. When 10% of the organo-LDH was melt blended with PP, the basal spacing of the LDH increases to 4.01 nm. The onset temperature and thermal decomposition temperature of the PP/organo-LDH and PP/organo-LDH/zinc borate (nano) composites have no significant change compared to pristine PP, but the amount of non-volatile residue remaining at 600 degrees C is significantly higher than that in pure PP. The cone calorimetric results show a 38% reduction in the peak heat release rate for PP/10%BZn and 48, 50 and 63% reductions for PP/organo-LDH/10%BZn (nano) composites at 3, 5 and 10% organo-LDH loading. The limiting oxygen indices of all samples increase by a slight amount and all samples can obtain a UL-94 HB rating. The char content of PP/LDH/BZn and PP/BZn/organo-LDH (nano) composites is much greater than that of PP/LDH, PP/BZn and PP/organo-LDH. Copyright (C) 2011 John Wiley & Sons, Ltd.