Preparation and characterization of flame retardant and proton conducting boron phosphate/polyimide composites

In this study novel flame retardant boron phosphate (BPO 4 )/polyimide composites were prepared. 4,4′-Oxydianiline (ODA) was reacted with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in dimethyl formamide (DMF) and mixed with BPO 4 particles to obtain a series of polyamic acids, meanwhile, corresponding polyimides were synthesized via the thermal imidization technique. The amount of BPO 4 in the composite films was varied from 0 wt% to 10 wt%. The structure, thermal and surface properties of the polyimide films were characterized by means of ATR-FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The flame retardancy of the composite materials was examined by limiting oxygen index (LOI) measurements and UL-94 VTM tests. Result showed that the LOI values of composites increased from 28 to 39. Furthermore, proton conductivity of polyimide films was measured by the four probe technique. The composite membrane containing 3 wt% of BPO 4 showed a conductivity of 0.4 mS/cm at room temperature.