Flame retardant modification of benzoxazine resin and its glass fiber reinforced composites

Ammonium polyphosphate (APP) was used as flame retardant to modify benzoxazine (BOZ) resin and glass fiber (GF) /BOZ composites. The flame retardant mechanism of material was investigated by thermal analysis and microstructure analysis. The results show that APP can significantly improve the flame retardancy of BOZ resin. With the increase of APP content, the limiting oxygen index of resin system increase gradually. The limiting oxygen index of 3wt% APP-BOZ resin increases from 31.5% of matrix to 34.5% and the UL 94 of V-0 is obtained. The APP-BOZ modified resins decompose earlier than BOZ resin, and the glass transition temperatures reduce a little. The curing reactions of modified resin system start at lower temperatures and operate more mildly. With the incorporation of APP, the flame retardancy of GF/BOZ composites gets further improved, and the limiting oxygen index of 10wt% GF/APP-BOZ composites increases from 51.0% of GF/BOZ to 57.7%. Microstructure analysis shows that APP can help to form denser char of APP-BOZ modified resins and GF/APP-BOZ composites to improve the flame retardancy.