Role of expandable graphite on flame retardancy, smoke suppression, and acid resistance of polypropylene/magnesium hydroxide composites

In this work, expandable graphite (EG) was introduced to the composite of polypropylene/magnesium hydroxide (PP/MH) by melt compounding, fire performance, thermal degradation behavior, and acid resistance of the PP/MH/EG composites were investigated. The results demonstrate that the flame retardant efficiency of MH is very low by itself and there is a noticeable synergism between MH and EG in PP. The addition of proper EG can enhance flame retardancy, smoke suppression, and acid resistance of the PP/MH composite significantly at the same time. Replacing 8.7 wt% MH with 8.7 wt% EG reduces the filling grade needed for V-0 from 63 wt% MH to 56.5 wt% MH/EG mixture. The presence of EG on the composite surface hinders acid erosion of MH. There is no chemical reaction between MH and EG. Continuous intumescent char can be produced on the composite surface upon combustion, which is responsible for the much-improved flame retardancy and smoke suppression, regardless of the presence of MH on the surface area.