Synthesis of novel phosphonium bromide-montmorillonite nanocompound and its performance in flame retardancy and dielectric properties of epoxy resins

To enhance the flame retardancy of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) on epoxy resins (EPs), by addition reaction with allyltriphenylphosphonium bromide (ATPB), a novel DOPO-containing phosphonium bromide (DOPO-ATPB) was synthesized and its structure was characterized by Fourier transform infrared (FTIR), ¹³C nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS). By intercalating DOPO-ATPB into montmorillonite (MMT) layers and with the help of solvents, the intercalated nanocompound (DPAB-MMT) was prepared, and X-ray diffraction (XRD) confirmed a d-spacing expansion of DPAB-MMT layers (from ~1.01 to ~2.10 nm). The epoxy composites with DOPO-ATPB and DPAB-MMT were prepared, and their effects on the flame retardancy, mechanical and dielectric properties were studied by limiting oxygen index (LOI), UL-94 vertical burning test, cone calorimetry, three-point bend testing, and the impedance analyzer. The results show that DOPO-ATPB endows EPs with excellent flame retardancy and dielectric properties, and DPAB-MMT can be well dispersed in EPs. Compared with pure EP, the EP/8 wt% DOPO-ATPB increased the LOI values from 23.0% to 32.5%, achieved V-0 rating and decreased the peak heat release rate (p-HRR) by approximately 36.6%. With the 8 wt% DPAB-MMT, the LOI values of epoxy composite was increased from 23.0% to 35.9%, the p-HRR was decreased by ~25.4%, the mechanical flexural strength was enhanced by approximately 13.4% and the dielectric loss (ε″) was decreased from 0.080 to 0.052 at 100 Hz.