Catalytic pyrolysis and flame retardancy of epoxy resins with solid acid boron phosphate

A solid acid boron phosphate (BP) has been prepared and characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic effects of BP on pyrolysis and flame retardancy of epoxy resins (EP) were studied by various methods. Transmission electron microscopy images suggested that BP was uniformly dispersed into the EP matrix. Differential scanning calorimetry illustrated that loading of BP could slightly reduce the glass transition temperature of EP. Thermogravimetric analysis and Fourier-transform infrared spectrometry indicated that BP catalyzed EP to pyrolysis at a lower temperature, leading to a reduction of flammable gas release and an increased residue yield. Limiting oxygen index (LOI) and UL 94 data showed that when the BP loading was increased, the LOI value increased accordingly. In addition, the UL 94 level was improved from no rating to a V-1 rating. In cone calorimeter measurements, a compact intumescent "honeycomb-like" char layer was found for the EP/BP composites, which led to considerable decreases in the maximum peak of heat release rate and total heat released. A possible catalytic flame retardant mechanism for the EP/BP composites is proposed.