Flame resistance and aging mechanism of flame retardant polycarbonate sheet containing linear phenolic resin charring agent

The preparation of halogen-free flame retardant thin-wall polycarbonate (PC) sheet with high performance is a global challenge. In our research, a composite flame retardants system composed of polysiloxane and perfluorinated sulfonate combined with a macromolecular charring agent, linear phenolic resin (LPR) could endow PC sheets (thickness: 0.4 mm) with UL94-V0 rating, showing high flame resistance efficiency. Regrettably, this efficient flame retardant system made the aging properties of PC seriously deteriorated due to the transesterification reaction between the phenolic hydroxyls and PC macromolecular chains, thus losing practical applied value. Introducing a small amount of boron acid (HB) could solve the fatal shortcoming through a quick coordination reaction between the boron atom and phenolic hydroxyl to effectively protect the PC backbone chains, and meanwhile further improve the flame retardance by increasing the charring stability of LPR due to the formed B-O bond with higher energy.