【作者】 王亮；

【导师】 金日光；

【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原丝的预氧化过程在整个聚丙烯腈(PAN)基碳纤维的制备过程中起到承上启下的作用。优异的预氧化纤维能够制得性能更好的碳纤维。本文深入研究PAN原丝的热性能和制定优异的预氧化参数之间的关系。牵伸是预氧化过程中一项不可或缺的参数,研究正牵伸和负牵伸(主要是高温负牵伸)对今后的预氧化工作有一定的指导意义。采用差示扫描量热仪(DSC)、热重分析仪(TG)、傅里叶变换红外光谱(FTIR)、元素分析仪、广角X射线衍射仪(WAXD)、扫描电镜(SEM)、以及强度测试等方法来系统地研究PAN原丝的热性能、预氧化过程中参数的制定、以及正牵伸和负牵伸对纤维晶体结构、化学结构和力学性能的影响。PAN原丝的热分析是制定预氧化工艺参数的重要依据,结果表明,共聚单体的加入改善了原丝的热性能,使放热峰加宽、放热速率减缓,失重率低,并且在较低温度下引发环化反应。对于共聚PAN原丝,在空气中的放热峰宽、失重率都低于在氮气气氛。在空气气氛下,随着升温速率的升高,DSC放热曲线整体向高温方向移动,并且峰形变窄,因此原丝的预氧化要在较低的升温速率或较小的温度梯度、空气气氛下进行。同时原丝中C、H、N、O四种元素含量在预氧化前期变化幅度较小,在预氧化中后期,氧化反应比较剧烈,C、N、H含量逐渐减少,O含量剧烈增加。牵伸实验结果表明,无论正牵伸还是负牵伸对纤维的FTIR图谱和XRD图谱的形状和位移没有显著的影响。正牵伸条件下,晶面间距d在20=17°附近时先减小后增大,而在20=25°附近时却是总体增大,并且强度随着牵伸的增大而逐渐降低。负牵伸条件下,d在20=17°附近的反映和20=25°的反映恰好相反,纤维强度在较低负牵伸下较高,负牵伸加大则强度下降。运用第四统计力学解释了预氧化过程中非晶形与晶形的竞争过程以及定量分析牵伸与预氧化纤维强度的关系。预氧化过程中的FTIR图谱表示,C=N和CH2等原有基团经过预氧化后逐渐减少,而出现了C=N、C=C、C=O等新的吸收峰。同时XRD图谱上显示出,由于预氧化初期施加一定的牵伸使20=17°的衍射峰强度有所增加,但随着预氧化反应的进行,其衍射峰强度逐渐降低,同时在20=25°附近出现了新的衍射峰。相对环化率和芳构化指数都随温度的增大而增大。相对环化率在低温下增幅较大,而芳构化指数则在高温下增幅较大,表明预氧化反应首先发生在无定形区而后进入有序区。更多还原

【Abstract】 Preoxidation process plays an important role and it is a critical step curing the conversion from polyacrylonitrle(PAN) fibers to carbon fibers. Excellent preoxidized fiber can be prepared carbon fiber with good performance. The relations between thermal properties of PAN precursor and the preoxidation parameters have been deeply studied in this thesis. Stretching is an indispensable parameter in preoxidation process, so studying positive stretching and negative stretching(especially at high temperature) could be very meaningful to the future work. Several technologies, such as differential scanning ealorimetry(DSC), thermal gravimetry(TG), Fourier infrared spectroseopy(FTIR), elemental analyzer, wide diffraetion(WAXD), scanning electron microscopy(SEM), and strength testing were used to systemically investigate thermal properties of PAN precursor, determination of preoxidation parameters, and the effect of positive and negative stretching on the crystal structure, chemical structure and mechanical properties. Thermal analysis of PAN precursor can be referred as to as a guide of preoxidation process and the results indicated that comonomer can improve thermal properties of PAN precursor including broadening exothermic peak, slowing down heat release rate and reducing weight loss and also initiate cyclization reaction at low temperature. For PAN copolymer, the exothermic peak was wider and the weight loss was lower in air than that in nitrogen atmosphere. With the increasing of heating rate, the overall DSC curve moves to the higher temperature and the shape of exothermic peak become narrower. So the preoxidation should be carried out with lower heating rate or smaller temperature gradient in air. At the initial stage of preoxidation, there is little variation in C, H, N, O content. At later stage, due to the acute oxidation reaction, the content of O increases obviously along with the gradual decrease of C, H and N.Experimental results of stretching show that whatever positive or negative stretching, there is no obvious influence on the shape and displacement of the FTIR spectrum and the XRD patterns. At positive stretching, the d-spacing decreased at first around 20=17°and then increased, while d-spacing around 20=25°increased with the increasing positive stretching ratio, meanwhile the tensile strength decreased gradually. When negative stretching was carried out, the trend of d-spacing around 20=17°was opposite to that around 29=25°. The tensile strength was higher at low negative stretching ratio, but the strength was lower are high negative stretching ratio. The competive process of amorphous and crystal phase and the relationship between stretching and strength have been investigated.The FTIR spectrum showed that the original functional groups such as C=N and CH2 disappeared, but new groups such as C=N, C=C, C=O appeared in preoxidation process. Meanwhile, as shown in XRD patterns, the intensity of peak around 26=17°increased because of the stretching at low temperature, but it decreased with the preoxidation, and a new peak appeared around 20=25°. Cyclization rate and aromatization index both increased with increasing temperature. Cyclization rate increased at lower temperature but aromatization index increased conspicuously at higher temperature, which indicated that cyclization was initiated first in the amorphous region and then propagated to the boundaries of the orderedphase. At high temperatures, the reactions developed to the crystalline region.更多还原