Selective dispersion of nanoplatelets of MDH in a HDPE/PBT binary blend: Effect on flame retardancy

Selective dispersion of 10 phr of magnesium dihydroxide nanoplatelets into 80/20 HDPE/PBT blends was successfully achieved by adjusting the processing temperatures, without any surface modification of the MDH nanoparticles. Three morphologies were achieved where nanoplatelets of MDH are dispersed only in the PBT dispersed phase (M1), only in the HDPE matrix (M2) or in both polymers (M3). An original extraction method (coupled with TGA results) allowed confirming the microstructures obtained by SEM and determining the amount of nanoplatelets in each phase. At microscale, the flame retardancy is somewhat dependent on the morphology. The first degradation peak assigned to early PBT degradation by water released from MDH is slightly shifted to higher temperature for M2. Moreover, a significant decrease of peak of heat release rate in cone calorimeter is observed for M2 associated to a more efficient barrier effect. This is due to the structure of the mineral residue which is thicker and more cohesive for this morphology than for M1 and M3, leading to a more insulating layer. This work emphasizes the strategy consisting in optimizing the morphology to improve the flame retardancy at low or moderate flame retardant amounts.