Preparation of flame-retardant HDPE composites with synergistic strategy by the combination of phosphorus-containing modifier and magnesium oxychloride cement

Magnesium oxychloride cement (MOC), as an inorganic gel material with 5Mg(OH)2·MgCl2·8H2O as its main component, has higher heat absorption and water yield during thermal decomposition than that of magnesium hydroxide (MH). It can also be used in flame-retardant polymer materials like MH. The flame retardancy of HDPE/MOC composites increases with the addition of MOC. Compared with pure HDPE, when the MOC filling amount is 60 wt%, the total heat release and total smoke production decrease by 50.6% and 50.8% respectively, and the total heat release per mass for HDPE decreases from 53 kJ/g to 32.2 kJ/g. Phosphoric acid (PA) shows a good synergistic flame-retardant effect with MOC while improving the water resistance of MOC. After adding 1 wt% PA, the peak heat release rate and peak smoke production rate of HDPE/MOC/PA (50/49/1) decrease by 30% and 25.6% respectively, and the fire growth index (FGI) decreases by 24.6%. Phosphorus-containing coupling agent (isopropyl tri(dioctylpyrophosphate) titanate) can improve the size distribution of MOC, and also has synergistic flame-retardant effect with MOC in HDPE/MOC composites.