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

Abstract

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°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 © 2011 John Wiley & Sons, Ltd.