Synergistic effects of magnesium oxysulte whisker and multiwalled carbon nanotube on flame retardancy, smoke suppression, and thermal properties of polypropylene

Abstract In this work, multiwalled carbon nanotube (MWCNT)‐modified magnesium oxysulfate whisker (MOSw) (MOSw‐MWCNT) is successfully synthesized via a facial hydrothermal method. MWCNT is bonded on the surface of MOSw via a bidentate bridging mode of the carboxylate ligation without changing their crystal structures. Then MOSw‐MWCNT is incorporated into polypropylene (PP) matrix to prepare series of PP/MOSw‐MWCNT composites via melt blending. Cone calorimetry test, horizontal and vertical test, and limit oxygen index (LOI) results all show a significant synergistic effect of MOSw and MWCNT on flame‐retardant PP. PP/7MOSw‐3MWCNT composite exhibits the lowest peak heat release rate, total heat release, peak smoke production rate, total smoke production, and burning speed of 332.3 kW/m 2 , 87.4 MJ/m 2 , 0.0212 m 2 /s, 47.7 m 2 and 23.2 mm/min, respectively. The LOI value of PP/7MOSw‐3MWCNT composite is increased to 23.1% from 18.0% of neat PP. The scanning electron microscopy and Raman spectra of residue char indicate that the degree of graphitization and compactness of the residue char are increased with the amount of MWCNT. The introduction of MOSw and MWCNT both improves the thermal stability of PP matrix, but the excess MWCNT leads to the decomposition of the unstable residue char since its excellent thermal conductivity.