Construction of a fully bio-based intumescent flame retardant for improving the flame retardancy of polyacrylonitrile

Lignin (L), casein (C), and phytic acid (PA) were chosen to construct a fully bio-based intumescent flame retardant (IFR) for endowing polyacrylonitrile (PAN) with good flame retardancy. L/C/PAN was fabricated by solution blending of L and C with PAN, and the flame retardant PAN composite (FR-PAN) was prepared by the reaction of PA with L and C in L/C/PAN. FTIR and XPS confirmed the successful construction of fully bio-based IFR. FR-PAN achieved UL94 V-0 rating during a vertical burning test. Moreover, the char residue of FR-PAN at 800 °C in N2 and air reached 59 and 8 wt%, respectively, showing good char-forming ability. Furthermore, SEM-EDS revealed that phosphorus-rich and intumescent char residues were formed after the combustion of FR-PAN. The peak of heat release rate (PHRR) and smoke production rate (PSPR) of FR-PAN were reduced by 71.4% and 64.8%, respectively, and the pyrolysis products of FR-PAN were significantly reduced. Besides, the flame-retardant mechanism of the fully bio-based IFR on FR-PAN was proposed.