Multi-walled carbon nanotubes encapsulated by graphitic carbon nitride with simultaneously co-doping of B and P and ammonium polyphosphate to improve flame retardancy of unsaturated polyester resins

Herein, graphitic carbon nitride (g-C₃N₄) encrusted multi-walled carbon nanotubes (MWCNTs) while co-doping of B and P by one-pot hydrothermal method (BPCNT) and used as a co-effector of ammonium polyphosphate (APP) to improve the fire safety of unsaturated polyester resins (UPR). The flexural strength and toughness of UPR/BPCNT/APP were increased 59.3% and 29.2% from UPR/APP, respectively. The limited oxygen index of UPR/BPCNT/APP is increased from 19.8% of UPR to 30.6%. The total heat release, total smoke production, and CO₂ yield of the UPR/BPCNT/APP were reduced by 58.6%, 35.8%, and 62.5%, respectively, indicating that BPCNT and APP can endow excellent fire safety for UPR composites. Substantial reductions in pyrolysis gaseous products of UPR/BPCNT/APP in the gas phase were observed. B₂O₃, phenyl phosphate and MWCNTs play a synergistic role in the condensed phase to form a swelling and dense char.