聚丙烯腈碳纤维预氧化阶段分子结构调控与碳化性能的研究

Theoretically, the strength of polyacrylonitrile (PAN)-based carbon fibers is 180 GPa. However, the highest tensile strength of carbon fibers manufactured in laboratory reported to be 9.03 GPa, which is only 5% of the theoretical value. There is still a large gap between the tensile strength of commercial carbon fibers and that of the theoretical value. It is believed that the mechanical properties of carbon fibers are determined by the structural defects, such as orientation of crystallites, microvoids, skin-core structure and surface defects. In this proposal, the combination of low-temperature thermal stabilization and gradient elevation of temperature stabilization will be used to regulate the molecular structure of stabilization. Heat-resistance cyclized structure will be formed by intramolecular cyclization reaction during low-temperature thermal stabilization which reduce the pyrolysis of molecular chains during stabilization and carbonization process. As a result, the char yield and mechanical properties of carbon fibers will be increased. Moreover, the effect of molecular structure produced during low-temperature thermal stabilization on the structures and properties of carbon fibers will be studied by using infrared spectroscopy, small angle X-ray scattering and mechanical properties measurement. This research will provide a new way in preparing high-performance carbon fibers.

聚丙烯腈(PAN)碳纤维的理论拉伸强度为180 GPa，目前实验室制备的碳纤维的最大拉伸强度为9.03 GPa，仅为理论值的5 %，碳纤维拉伸强度的提高仍有很大的空间。碳纤维是一种缺陷控制材料，其力学性能受控于微晶取向度、微孔、皮芯结构、表面裂纹等结构缺陷。本项目拟采用低温热氧化与梯度升温预氧化相结合的方法对预氧化阶段分子结构进行调控，利用PAN分子在低温热氧化阶段发生分子内环化反应，形成具有一定耐热性能的环化结构，抑制链段在预氧化和碳化阶段的裂解，减少缺陷的产生，从而提高碳纤维的碳收率和力学性能；利用红外光谱、小角X射线散射和力学性能测试等手段进一步研究低温热氧化产生的分子结构变化对碳纤维结构与性能的影响，为高性能碳纤维的制备提供新方法。

碳纤维的理论拉伸强度为180GPa，然而工业化生产的碳纤维的强度远远低于其理论强度，目前实验室制备的碳纤维的最大拉伸强度为9.03GPa，仅为理论值的5%。因此，碳纤维拉伸强度的进一步提高仍有很大的空间。造成碳纤维的实际强度远远低于理论强度的主要原因是由于纤维的结构缺陷，如微孔、裂纹、皮芯结构，以及微晶非取向所致。工业化碳纤维碳收率低是造成碳纤维力学性能低的另一个原因。聚丙烯腈(PAN)纤维在预氧化过程中分子链逐步发生分子内环化以及分子间交联反应，转化为具有耐热的梯型结构，碳化过程未发生环化的分子进一步发生交联反应，逐渐形成碳网平面结构，同时未环化的线型链段和端基在高温下裂解成小分子逸走，因此，工业化生产的碳纤维实际碳化收率低于50%，而PAN原丝的理论碳化收率为68%左右，碳收率低不仅影响碳纤维的性能也影响产量。本项目围绕如何降低碳纤维生产工艺过程缺陷的产生以及减缓链段裂解提高碳收率，从而提高碳纤维力学性能为目标，提出低温热氧化的方法来促进PAN分子发生部分环化和氧化反应，减少链段在高温下的裂解，将碳纤维的碳收率提高了25%。采用傅里叶红外光谱仪(FTIR)、热重分析仪(TG)、差示扫描量热仪(DSC)、X射线衍射仪(XRD)、小角X射线散射仪(SAXS)、扫描电子显微镜(SEM)等技术表征PAN纤维在低温热处理过程化学结构、热性能、晶体结构等变化；以及低温热处理方法对PAN纤维预氧化以及碳化行为的影响，为高性能碳纤维的制备提供新方法。