Effect of Phosphorus‐Containing Silane Coupling Agents Modified Ammonium Polyphosphate on the Flame Retardancy and Mechanical Properties of Epoxy Resin

ABSTRACT Two phosphorus‐containing silane coupling agents (PSCAs), KH550‐P and KH560‐P, are successfully prepared by reacting 10‐hydroxy‐9,10‐dihydro‐9‐oxa‐10‐phosphorus‐10‐oxide (DOPOOH) with (3‐aminopropyl) triethoxysilane (KH550) and 3‐glycidyloxypropyltrimethoxysilane (KH560), respectively. These two PSCAs are used as the surface modification agents of ammonium polyphosphate (APP). The flame retardancy and mechanical properties of epoxy resin (EP) with PSCA‐modified APP are investigated. When the weight ratio of APP to PSCAs is 18:2 and the addition amount of PSCA‐modified APPs, APP‐KH550‐P 18:2 and APP‐KH560‐P 18:2 , in EP reaches 8%, the resulting flame‐retardant EP composite materials, EP/APP‐KH550‐P 18:2 and EP/APP‐KH560‐P 18:2 , exhibit good flame retardancy of a V‐0 rating in the vertical combustion test (UL‐94). The limiting oxygen index values of both EP/APP‐KH550‐P 18:2 and EP/APP‐KH560‐P 18:2 are higher than 30%. The peak heat release rates of EP/APP‐KH550‐P 18:2 and EP/APP‐KH560‐P 18:2 decrease by 13.8% and 28.5%, respectively, compared to EP containing 8% APP (EP/APP). Both KH550‐P and KH560‐P demonstrate similar performance in enhancing the flame retardancy of APP. When APP‐KH550‐P 18:2 is added to EP, the mechanical properties of EP/APP‐KH550‐P 18:2 are found to be similar to those of EP/APP. Conversely, the tensile strength and impact strength of EP/APP‐KH560‐P 18:2 increase by 23.8% and 74.3%, respectively, compared to EP/APP. KH560‐P shows significantly better performance in the flame‐retardant EP.