Improving flame retardancy of IFR/PP composites through the synergistic effect of organic montmorillonite intercalation cobalt hydroxides modified by acidified chitosan

Abstract To improve the flame retardancy of IFR/PP composites, organic montmorillonite (Mt) intercalation cobalt compounds (Co-OMt) were prepared and modified by acidified chitosan to further expand the interlayer spacing of Mt. The Co-OMt/IFR/PP nanocomposites were fabricated via melt blending method. The results indicated that cobalt hydroxides and acidified chitosan were successfully intercalated into interlayers of Mt, which promoted the fine dispersion of Co-OMt in PP matrix. The results of limiting oxygen index (LOI) and vertical burning (UL-94) tests indicated that IFR/PP composites only reached V-2 rating and the LOI value was 26.5%. With addition of 4 mass% Co-OMt, 4 mass% Co-OMt/IFR/PP nanocomposites passed UL-94 V-0 rating and the LOI value was high to 32.1%. Furthermore, the cone calorimeter tests results confirmed that peak heat release rate (PHRR), total heat release (THR) and peak smoke production rate (PSPR) of 4 mass% Co-OMt/IFR/PP nanocomposites decreased by 33.7%, 11.8% and 16.7% compared with those of IFR/PP composites. The notably improved flame retardant and smoke suppression properties were attributed to the fine dispersion of Co-OMt with layered structure and excellent catalytic performance in PP matrix, which promoted the fully cover of consolidated and compact residual layers on the surface of polymer during combustion, ultimately suppressing heat and mass transfer between polymer matrix and flame zone.