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

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.