In this paper,a bio-based flame-retardant coating with different chitosan-sulfonated graphene layers was con-structed on the surface of a RPUF by using a water-based layer-by-layer self-assembly method(LBL).The influence of different layers on the flame retardancy and smoke suppression of the RPUF was intensively investigated.The results in-dicated that the RPUF coated with the flame-retardant coating exhibited excellent flame-retardant performance,high ther-mal stability,and good smoke suppression,which were also affecting by the numbers of coating layers.The 5-layer-self-assembly coated RPUF(RPU-5BL)reached a UL 94 V-0 rating in the vertical burning test along with a limiting oxygen index of 35.1 vol％and a char yield of 34.9 wt％at 800 ℃,which were increased by 78.2％and 85.6％,respectively,compared to the untreated RPUF.Moreover,the RPU-5BL exhibited a peak heat release rate of 163.9 kW/m2,a total smoke production of 9.1 m2,a maximum smoke density of 22.9％,and a smoke density grade of 14.9,which de-creased by 30.6％,14.2％,61.9％,and 120.1％,respectively,compared to the controlled sample.
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