Abstract:
The flame retardant effect of single phosphaphenanthrene and phosphazenes was limited. In order to improve the flame retardant effect of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide (DOPS) on epoxy resin (EP), DOPS and hexa (phenoxy) cyclotriphosphazene (HPCTP) were compounded and applied in EP. When the total P content was 1.2wt%, DOPS and HPCTP were added to EP by adjusting the ratio of P content in the phosphaphenanthrene and phosphazene groups to prepare EP composites. The limiting oxygen index test (LOI), vertical flame test (UL-94), thermogravimetric analysis (TGA), cone calorimeter test (CONE), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) and thermogravimetric-infrared spectroscopy analysis (TG-IR) were used to study the effects of different proportions of phosphaphenanthrene and phosphazene groups on the thermal stability, and combustion performance of EP, and explored the law and mechanism of double groups synergistic flame retardancy. The results show that there is synergistic flame retardancy between P and S elements. When the total P content is 1.2wt%, the LOI value and UL-94 grade of HPCTP-DOPS/EP increase with the increase of S content in the composite system. and the ratio of P content between HPCTP and DOPS is 0.2∶1, the LOI of HPCTP-DOPS/EP composite system is 30.4%, reaching UL-94 V-0 grade, the total heat release (THR) and peak heat release rate (PHRR) decreased significantly, The EP/HPCTP/DOPS composite has a more dense and stable expanding carbon layer after combustion, which is superior to the flame retardant effect of the two flame retardants on EP solely, there is a synergistic flame retardant effect between the phosphazene and phosphaphenanthrene flame retardants. From the perspective of flame retardant mechanism, DOPS and HPCTP plays a flame retardant role in gas phase and condensed phase respectively.