Expandable graphite (EG) enhanced fire performance and reduced smoke with magnesium hydroxide in polypropylene. Polypropylene was tested with 0 – 63% magnesium hydroxide (MH), 9 – 30% EG and a combination of 4 – 17% EG with MH to a total of 57% PIN FR. Replacing c. 9% MH by EG enabled total PIN FR load needed to achieve UL 94 V-0 (3 mm) in polypropylene to be reduced from 63% to 57% with the same LOI as with 63% MH. The authors note that there is no chemical reaction between EG and MH and that the improved fire performance and smoke suppression was because EG on the polymer surface hinders acid erosion of MH.
“Role of expandable graphite on flame retardancy, smoke suppression, and acid resistance of polypropylene/magnesium hydroxide composites”, S. Liang et al., Polym. Eng. Sci. 2022;1–12, https://doi.org/10.1002/pen.26093