Abstract:The synergistic effect of compound oxides with intumescent flame retardant on the properties of polypropylene composites was researched. Compound oxides (MgAl-LDHO, MgAlFe-LDHO) were obtained with calcining layered double hydroxide (LDH) precursors and prepared by hydrothermal method. X-ray diffraction (XRD) was employed to characterize the structure of LDH and LDHO mentioned above, and the results indicate that the calcination of LDH at 500 ℃ gives rise to formation of ill-crystallized MgO phase and spinel phase. The PP/IFR composites with these different LDHO were then fabricated through melt blending process. The thermal stability and flame retardancy of resulting composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning test(UL94) and cone calorimeter. TGA data shows that LDHO could improve the thermal stability of PP/IFR. LOI and UL94 tests show that LDHO could increase the LOI of PP/IFR composite. Cone calorimeter results reveal that LDHO could clearly enhance the char layer quality, consequently result in significant reduction of PHRR. The PHRR of PP/IFR/MgAl-LDHO composite decreases 71%, compared with that of PP/IFR composite. The char residue after cone test was characterized by scanning electron microscope (SEM). The residue characterization demonstrates that LDHO could promote formation of the homogeneous and compact intumescent char layer. Taking all results into account, a conclusion can be draw that LDHO could be used as an effective synergistic agent for PP/IFR composites to enhance its flame retardancy through improving the char quality in the condensed phase.