Abstract
This paper investigates the char forming effect of para-aramid fiber and the flame-retardant efficiency of para-aramid fiber synergizing with ammonium polyphosphate on polypropylene/ethylene propylene diene monomer. Para-aramid fiber was firstly modified by phosphoric acid, and then modified by 3-aminopropyltriethoxy. Para-aramid fiber and modified para-aramid fiber were characterized by field-emission scanning electron microscope, energy-dispersive analysis and Fourier transform infrared spectroscopy. Fourier transform infrared spectroscopy illustrated that P–O groups and Si–O groups appeared on the surface of modified para-aramid fiber. The intumescent flame retardants containing para-aramid fiber/ammonium polyphosphate or modified para-aramid fiber/ammonium polyphosphate was introduced into polypropylene/ethylene propylene diene monomer. The flame-retardant efficiency of polypropylene/ethylene propylene diene monomer composites were investigated by limiting oxygen index, UL-94 vertical burning and cone calorimeter test. The polypropylene/ethylene propylene diene monomer composite containing 34.5 wt% ammonium polyphosphate and 0.5 wt% modified para-aramid fiber achieved a UL-94 V0 rating with a limiting oxygen index of 28, as well as showed a 23.6% reduction of total heat release and a 47.0% reduction of total smoke release. The thermal stability of polypropylene/ethylene propylene diene monomer composites were investigated by thermogravimetric analysis. The residual char layers of polypropylene/ethylene propylene diene monomer composites were analyzed by field-emission scanning electron microscope. The tensile and tear strength of polypropylene/ethylene propylene diene monomer composites were also tested. After 1 phr modified para-aramid fiber was added, the tensile strength and tear strength increased by 33.3% and 35.9%, respectively. The results indicated that modified para-aramid fiber/ammonium polyphosphate/polypropylene/ethylene propylene diene monomer had better flame-retardant efficiency, thermal stability, smoke suppression and mechanical properties with the synergistic effect of P, N, Si elements.
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