N doped carbon nanosheet and B N co-doped carbon (BNC) nanosheet are first prepared through exfoliation of carbon of Schiff based covalent organic frameworks (COFs) under ultrasound using sodium lignin sulfonate as the intercalation agent and modifier. Then poly (vinyl alcohol) (PVA)/BNC nanocomposite with enhanced thermal oxidation stability, good mechanical performances and enhanced flame retardancy has been prepared through solution blending. The temperature at 5 wt% weight loss and peak heat release rate of PVA loaded with 4 wt% of BNC nanosheet increase by 31.9 °C and 57.3% compared with that of untreated PVA, respectively. A new fire hazard evaluation system based on analytic hierarchy process (AHP) is raised to comprehensively estimate fire risk of prepared sample. It is deduced from AHP that PVA loaded with 4 wt% BNC nanosheet shows the lowest fire risk (77.9 score). The effect of BNC nanosheet on pyrolysis mode of PVA in gaseous and condensed phase has also been investigated to figure out the reason for low fire risk of treated PVA.

N掺杂碳纳米片和BN共掺杂碳（BNC）纳米片首先使用木质素磺酸钠作为嵌入剂和改性剂，在超声作用下通过剥落Schiff基共价有机骨架（COF）的碳来制备。然后通过溶液共混制备了具有增强的热氧化稳定性，良好的机械性能和增强的阻燃性的聚乙烯醇（PVA）/ BNC纳米复合材料。与未处理的PVA相比，负载4 wt％的BNC纳米片的PVA在5 wt％的重量损失下的温度和峰值放热速率分别提高了31.9°C和57.3％。提出了一种基于层次分析法（AHP）的火灾隐患评估系统，可以对所制备样品的火灾隐患进行综合评估。从AHP推论出，负载了4 wt％BNC纳米片的PVA具有最低的火灾危险性（77.9分）。还研究了BNC纳米片对气相和冷凝相中PVA的热解模式的影响，以找出处理后的PVA着火危险低的原因。