Smoke suppression, flame retardancy, and fire toxicity of polypropylene containing melamine salt of pentaerythritol phosphate halloysite

Polypropylene (PP) was melt blended with a new mono molecular intumescent flame retardant, melamine salt of pentaerythritol phosphate halloysite (MPPH) to enhance its thermal stability, flame retardancy, and smoke suppression properties. The structure of MPPH was elucidated by Fourier transform infrared (FTIR), H-1 NMR, X-ray diffraction (XRD), and energy dispersive X-ray (EDX) analysis. PP composites results showed that MPPH increased the thermal stability of PP at high temperatures in all PP composites. The horizontal flammability test (UL94H) showed that MPPH stopped flame propagation in PP composites. Vertical burning rate test (UL94V) revealed that PP composites can attain V-0 rating at loading levels 25, 30, and 35 wt.% of MPPH. Limiting oxygen index (LOI) data indicated that adding 20, 25, 30, and 35 wt.% of MPPH to PP increased the LOI value of PP (19.2%) to 27.1%, 32.5%, 35.4%, and 38.7%. MPPH succeeded in reducing the maximum specific optical density (Ds(max)), mass specific optical density (MOD), and rate of smoke generation during the first 4 min (VOF4) of PP composites compared to PP alone. FTIR gas analyzer results revealed that MPPH decreased the emission of CO and CO2 in the gas phase during the combustion process. Digital photos and scanning electron microscope (SEM) images of char residues remained after the smoke density test revealed that MPPH succeeded in forming a cellular and cohesive char layer on the PP surface. The new data is expected to increase the use of PP in rigid packaging applications.

Automated summary

In this study, a new mono molecular intumescent flame retardant, melamine salt of pentaerythritol phosphate halloysite (MPPH), was added to polypropylene (PP) to improve its thermal stability, flame retardancy, and smoke suppression properties. The addition of MPPH increased the thermal stability of PP and stopped flame propagation in PP composites. PP composites achieved V-0 rating in the vertical burning rate test with different loading levels of MPPH. The addition of MPPH also increased the LOI value of PP and reduced smoke generation during combustion.