Improving fire behavior and smoke suppression of flame‐retardant PBS composites using lignin chelate as carbonization agent and catalyst

Abstract

AbstractA copolymer of alkali lignin and polyacrylamide was fabricated by graft copolymerization, and further chelated with Fe3+. The obtained lignin chelate with star structure was used as synergistic agent and catalyst with the incorporation of intumescent flame retardants (IFRs) to prepare flame‐retarded poly (butylene succinate) (PBS) composites. The replacement of IFR by lignin chelate favors the enhancement of mechanical performance, resulting in the synchronous improvement of tensile and flexural properties. Compared with the specimen used 25 wt% IFRs (75P/25I), the tensile strength, flexural strength, and modulus of specimen prepared by 23 wt% IFRs and 2 wt% lignin chelate (75P/23I/2LC) exhibited significant increased. A synergistic effect between IFR and lignin chelate occurred when they were combined with an appropriate ratio. When IFR and lignin chelate loadings were 24 and 1 wt%, respectively (75P/24I/1 LC), the limited oxygen index (LOI) value of 36.2% and UL‐94 V0 rate of composite could be achieved. Compared with 75P/25I, the char residue mass of 75P/24I/1 LC increased by 35.7%. Moreover, SEM images indicated that a more compact, smooth, and continuous char layer of 75P/24I/1 LC could be formed during combustion. The peak heat release rate (pHRR) and total heat release (THR) of 75P/24I/1 LC decreased by 58.9% and 9.9% compared with PBS, also decreased by 10.3% and 4.8% compared with 75P/25I, respectively. TGIR and FTIR analysis also indicated that lignin chelate exhibited an excellent synergistic effect with IFRs, and gave PBS a good flame retardancy by making contribution to char‐formation and gas‐phase flame retardancy. This study provides an alternative way for the application of natural polymers such as lignin in flame retardant materials.