Roles of organic chain structure in flame retardancy and mechanical properties of epoxy coating

Chain structure of flame retardants plays an important role in the performance of epoxy (EP) coatings. Three flame retardants containing hexyl, cyclohexyl and naphthalene were synthesized and marked as DAH, DAC and DAP, respectively. The three flame retardants were used to regulate the flame retardant and mechanical performances of EP coatings. The EP containing 3 wt% DAH displays a UL-94 V0 rating and a limiting oxygen index (LOI) 29.4 vol%, while 6 wt% DAC and >8 wt% DAP are needed to achieve the UL-94 V0 rating. The order of flame-retardant efficiency in UL-94 test is DAH > DAC > DAP, while that in cone calorimetry test is the opposite. The gas-phase effect plays a key role in the former, and the condensed-phase effect decides the heat release behaviors in the later. In addition, the improvement of mechanical property is EPC > EPH > EPP, the EPC4 has an impact strength of 13.4 kJ/m2 which is 168 % higher than that of EP. Toughening is contributed by the increased free volume, flexibility of cyclohexyl and microphase separation.