Preparation of a ternary hybrid of P‐g‐C3N4@PGS‐Ti and its enhancement of the flame retardancy of epoxy resins

Summary A novel ternary hybrid flame retardant named P‐g‐C3N4@PGS‐Ti was prepared through step‐by‐step method. First, titanium dioxide was loaded on PGS to make PGS‐Ti (where PGS = palygorskite), and then, PGS‐Ti was decorated by phosphor‐doped g‐C3N4 (abbreviated as P‐g‐C3N4) to prepare a ternary flame retardant of P‐g‐C3N4@PGS‐Ti. It showed that P‐g‐C3N4@PGS‐Ti could efficiently improve the flame retardancy of epoxy resins (EP). The structure and the morphology of P‐C3N4@PGS‐Ti were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scaanning electron microscopy and hermogravimetric analysis (TGA). The flame retardancy and the burning behavior of 5 wt% P‐g‐C3N4@PGS‐Ti composited EP were well investigated through TGA, limiting oxygen index (LOI), cone calorimeter test (CCT) and vertical burning test (UL‐94 standard). It was found that the peak heat releasing (pk‐HRR) of the EP/P‐g‐C3N4@PGS‐Ti composite reduced 36% (from 1459 to 852 kW/m2) with the addition of 5 wt% of P‐g‐C3N4@PGS‐Ti flame retardant to the matrix of EP. The combustion residue analysis showed that the EP/P‐g‐C3N4@PGS‐Ti composite gained the most continuous and firmest char yield due to the synergistic effect of PGS, TiO2 and the introducing of P element. The mechanism proved that the combination of gas phase and condensed phase flame‐retardant processes were well coordinated to improve the fire retardancy for EP. We tested and studied the mechanical properties of EP/P‐g‐C3N4@PGS‐Ti composites. Only 2.4% decreasing of flexural strength and 23.5% decreasing of impact strength in EP/P‐g‐C3N4@PGS‐Ti composites compared to pure EP, respectively. But according to the test results of EP/P‐g‐C3N4@PGS‐Ti composite material and the control sample in the system, EP/P‐g‐C3N4@PGS‐Ti composite material had the highest flexural modulus and impact strength.