【作者】 谢怀玉；

【导师】 李常清；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2011， 硕士

【摘要】 PAN纤维的稳定化(预氧化)是制备碳纤维的关键步骤之一。研究PAN纤维官能团的化学反应,掌握PAN纤维热处理过程化学结构、化学反应与温度之间的关系,为今后稳定化控制PAN纤维预氧化结构的生成和最终碳纤维结构都有重要意义。本文以均聚PAN纤维作为研究对象,在氮气保护下,从低温到高温连续对PAN纤维进行热处理,研究了各温度下PAN纤维形成的化学结构,研究了PAN纤维官能团的优势反应与温度的依赖性,推测反应机理。借助DSC、FT-IR和NMR等手段研究了氮气气氛中均聚PAN纤维稳定化过程的热效应、化学结构、化学反应与温度的关系。研究发现：1、PAN纤维热稳定化过程中的热反应存在温度时间效应。在氮气下,PAN纤维热反应活化能大,达到反应能垒要较高的温度；在空气下,氧的参与使得PAN纤维热反应活化能降低,在较低温下发生热反应。同等温度下,PAN纤维在氮气中的化学反应常数远大于空气。2、在惰性气氛中,PAN纤维的官能团CN、CH2、CH化学反应活性不同,CN受热激发生成自由基的活化能较低,首先发生热化学反应,150℃时CN先形成自由基引发环化反应,形成C=N结构；CH2\CH受热激发生成自由基活化能较高,170℃时CH2\CH才表现出脱氢反应,生成C=C结构,此C=C结构与已生成的C=N转化为六元环上的-C=N-C=C-共轭结构。3、170℃-260℃温度区间,PAN纤维同时发生环化和脱氢反应,纤维内部-C=C-C=N-共轭骨架结构逐渐增加,230℃前环化反应程度大于脱氢反应,高于230℃氰基反应基本完成,但脱氢反应还很明显。4、高于260℃,PAN纤维分子内发生异构化反应,分子间发生交联反应,最终形成平面内稳定梯形结构。更多还原

【Abstract】 The stabilization of polyacrylonitrile precursor fibers (pre-oxidation) process is one of the key steps of carbon fiber technology. Investigating the chemical reaction of PAN fiber functional groups, mastering the relationship between the chemical structures, chemical reactions and temperature, which have significant importance for controlling the structure that the PAN fiber stabilization turns forming and the final structure of carbon fiber.In this paper, we take PAN fibre from homopolymers as research target, taking heat treatment under N2 in temperature sequence from low to high in order to study the new generative structures at different temperature,then figure out how the dominant reactions of PAN fiber functional groups dependence on temperature and speculate the reaction mechanism.In virtue of DSC、FT-IR and NMR techniques, we work over the heat effect, chemical structures, the relationship between chemical reactions and temperature. And found that:1. Under N2 atmosphere, the heat reaction of PAN fibre has high activation energy, which means it need high temperature to reach to the energy barrier. Whereas, owing to the presence of oxygen under air, the activation energy is low so the heat reaction could be carry through at low temperature. And at the same temperature, the reaction constant under N2 is much bigger than that of under air.2. PAN fiber’s functional groups CN, CH2, CH have different chemical reactivity, C=N bond in PAN molecules has a low activity energy prior to form free radicals, its initiate cyclization reaction and then transforms into a C=N bond at 150℃. CH2\CH group need a higher activation energy to initiate dehydrogenation. At 170℃, the C=N bond reacts with a C=C group that resulted from CH2/CH-functional-group dehydrogenation. This reaction contribute to the conjugate structure,-C=N-C=C-3. At the range of 170℃-260℃, Cyclization and dehydrogenation reactions occur during the heat treatment,then the conjugated skeleton structure of-C=C-C=N-is gradually increased. Before 230℃, nitrile group leads a dominant reaction, it evidently disappear at 230℃. Over 230℃, dehydrogenation reaction still happens. 4. Over 260℃, Polyacrylonitrile intramolecular occurs isomerization reaction, and crosslinking reaction occurs between molecules,finally PAN fibers form the stable ladder structure in a plane.更多还原