Impact of <scp>APP</scp> Modified With <scp>DOPO</scp> Group‐Containing Silane Coupling Agent on Flame Retardancy and Mechanical Properties of Epoxy Resin

ABSTRACT Surface modification of ammonium polyphosphate (APP) by silane coupling agent is an effective method to enhance the performance of APP. Using (3‐isocyanatopropyl)‐triethoxysilane (IPTS) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) as reagents, a DOPO group‐containing silane coupling agent, IPTS‐P, was developed and utilized for the surface modification of APP. When the weight ratio of APP to IPTS‐P was maintained at 17:3 during the preparation of IPTS‐P‐modified APP, the resulting product, APP‐IPTS‐P 17:3 , showed excellent performance in improving the flame retardancy and mechanical properties of flame‐retardant epoxy resin (EP). Adding 8% APP‐IPTS‐P 17:3 to EP, the prepared flame‐retardant EP (EP/APP‐IPTS‐P 17:3 ) passed the V‐0 rating in the vertical burning test (UL‐94). Meanwhile, during the limiting oxygen index (LOI) test, a 30.2% LOI value was obtained. Compared with EP containing 8% APP, the total heat release (THR) of EP/APP‐IPTS‐P 17:3 was reduced by 22.89%, and the tensile strength and impact strength of EP/APP‐IPTS‐P 17:3 was increased by 23.6% and 135.1%, respectively. Consequently, the flame retardancy of EP can be improved while maintaining the good mechanical properties of EP through the addition of IPTS‐P‐modified APP to EP.