Influences of 4ZnO·B2O3·H2O whisker based intumescent flame retardant on the mechanical, flame retardant and smoke suppression properties of polypropylene composites

Abstract

AbstractIn this work, the influences of 4ZnO·B2O3·H2O zinc borate (ZB) whisker based intumescent flame retardant (IFR) containing ammonium polyphosphate and dipentaerythritol on the mechanical, flame retardant and smoke suppression properties of polypropylene (PP) composites were characterized by the universal testing machine, UL‐94, limiting oxygen index (LOI), and cone calorimeter tests, respectively. The results indicate that only 1 phr of ZB could effectively improve the LOI value and slow down the burning rate of PP composite. The peak heat release rate, average of HRR, total heat release, peak smoke production rate, and total smoke production values are all decreased from 413.8 kW/m2, 166.3 kW/m2, 82.3 MJ/m2, 0.0995 m2/s, and 17.9 m2 for PPc/20IFR composite to 267.8 kW/m2, 128.3 kW/m2, 66.8 MJ/m2, 0.0478 m2/s, and 12.6 m2 for PPc/20IFR/1ZB composite, respectively. The scanning electron microscopy images, energy dispersive spectrometry, and Raman spectra of char residue reveal that ZB is helpful to form a compact and graphitized intumescent char residue so that the heat diffusion and oxygen transmission are greatly hindered. The thermogravimetry analysis‐fourier transform infrared spectroscopy (TGA‐FTIR) results show that less combustible volatiles and more H2O vapor are generated with the appearance of ZB. Hence, the combustion mechanism in gas phase is suppressed.