Effect of two types of iron MMTs on the flame retardation of LDPE composite

Both MMT synthesized by hydrothermal method (Fe-OMMT) and MMT prepared by modifying MMT using Fe3+ (Fe-MMT) were used to prepare flame-retardant low-density polyethylene (FR-LDPE) together with an intumescent flame retardant (IFR). The effects of two types of MMTs on the flame retardation of FR-LDPE were investigated by different measurements. Combustion tests showed that the limiting oxygen index (LOI) of LDPE/IFR28/Fe-MMT2 was increased to 34.6 from 29 of LDPE/IFR30, and the UL-94 rating of the former reached V-2 from no rating of the latter. Cone calorimeter (CC) test demonstrated that both Fe-OMMT and Fe-MMT improved the combustion behaviors of LDPE/IFR at about 2 wt%. LDPE/IFR/Fe-MMT had a lower heat release rate (HRR), lower total heat release (THR) and more residues than LDPE/IFR/Fe-OMMT at the same loading in the range from 0.5 to 3 wt%. Scanning electron microscopy (SEM) observation showed that both Fe-MMT and Fe-OMMT could promote the formation of continuous and compact intumescent char layer in LDPE/IFR. Both CC and UL-94 tests vitrified that Fe-MMT had better contribution to IFR in fire resistance test. Thermogravimatric (TG) and Mossbauer spectrum etc. revealed that the different efficiency of Fe-OMMT and Fe-MMT should mainly be resulting from the structure difference between Fe-MMT and Fe-OMMT, in which the essential difference might be the different existing state of Fe in two types of MMTs.