干喷湿纺聚丙烯腈纤维结构形成及其演变过程的研究

发布时间：2018-03-23 04:12

本文选题：干喷湿纺　切入点：PAN初生纤维　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：聚丙烯腈(PAN)原丝质量是提高碳纤维性能的关键因素,针对干喷湿纺工艺中的各阶段纤维结构与性能展开系统性研究,全面了解PAN初生纤维结构成形以及后续纺丝各阶段的纤维结构转变过程,对改善PAN原丝质量和提高碳纤维拉伸强度具有实际指导优化的作用。本文中我们采用了 X射线衍射仪(XRD)、高分辨透射电镜(HRTEM)、扫描电镜(SEM)、差示扫描量热法(DSC)、热重分析(TG)等测试分析技术,对不同纺丝原液参数和凝固浴条件的初生纤维结构与性能,以及制备过程当中PAN纤维的结构转变规律展开了系统性研究工作。干喷湿纺初生纤维阶段是PAN原丝结构形成的最初以及最关键的制备过程。初生纤维结构对原丝质量有重要的影响。研究了凝固浴不同温度、牵伸比以及不同黏均分子量、固含量对PAN初生纤维结构和性能的影响。凝固浴温度能够影响初生丝条的双扩散过程,能够影响初生纤维截面形状;随着牵伸倍数的提高,初生纤维结晶度、晶粒尺寸和沸水缩率逐渐增长,分子链紧密排列,微孔尺寸和数量降低,初生纤维的纤度降低、拉伸强度增大、断裂伸长率升高,同时其相应的离散系数也变小;随着黏均分子量和原液固含量的增加,纺丝原液中PAN分子链的缠结点密度增加,原液黏度升高,初生纤维纤度减小,拉伸强度升高。固含量较高的纺丝原液对干喷湿纺工艺制备优质初生纤维有利。研究了干喷湿纺过程中各阶段PAN纤维微观结构,以及结晶结构对PAN原丝的力学性能和热性能的影响。干喷湿纺制备的PAN纤维表面光滑、杂质少、表面缺陷较少。在原丝制备过程中,PAN纤维的晶粒尺寸升高、结晶度呈上升趋势,结晶结构随之完善,其中,牵伸能够提高结晶度,致密化和热定型能够增进晶粒生长;随着纺丝的进行,PAN纤维纤度减小,致密性提高,拉伸强度升高,断裂伸长率降低。原丝的晶体结构对其力学性能和热性能有重要的影响,结晶结构越完善,对原丝的力学性能越有益,预氧化过程中的环化反应越难发生,反应的起始温度趋于高温,而且能够预防PAN分子链热分解。利用HRTEM表征PAN纤维微观结构,利用环氧树脂对纺丝各阶段PAN纤维进行包埋,采用超薄切片技术,得到与纤维轴向相垂直的横向切片和相平行的纵向切片,切片厚度为50-70nm,有利于电子束穿透纤维切片。其中,环氧树脂只起固定纤维的作用,对图像衬度没有增强效果。初生纤维内部组织是片层结构,片层垂直于纤维轴向排列,片层之间的孔隙较多;在凝固浴预牵伸阶段,开始出现微原纤结构,微原纤平行于纤维轴向排列,在多级牵伸和致密化后,微原纤排列更为紧密,微原纤之间并不是平行排列,微原纤之间会有交错、缠绕,微原纤的直径约30-50nm。微原纤之间存在孔隙,孔隙在拉力的作用下,截面为狭长型,在纺丝过程中,孔隙数量减少,但不能完全消除。
[Abstract]:The quality of polyacrylonitrile (pan) precursor is the key factor to improve the properties of carbon fiber. A comprehensive understanding of the formation of the primary fiber structure of PAN and the process of fiber structure transformation at various stages of subsequent spinning, In this paper, we adopt X-ray diffractometer, high resolution transmission electron microscope, scanning electron microscope, scanning electron microscope, differential scanning calorimetry, thermal gravimetric analysis. Test and analysis techniques such as TG, The structure and properties of primary fibers with different spinning solution parameters and coagulation bath conditions were studied. The structure transformation of PAN fiber was studied systematically. The initial and most critical preparation process of PAN precursor was the stage of dry spray wet spinning primary fiber. The primary fiber structure of PAN fiber was the most important one. Quality has an important effect. The different temperature of solidification bath is studied. The effects of drawing ratio, average molecular weight of different viscosity, solid content on the structure and properties of PAN primary fiber, the effect of solidification bath temperature on the double diffusion process of primary filament strip and the shape of primary fiber section, and the effect of the drawing ratio on the structure and properties of the primary fiber, The crystallinity, grain size and boiling water shrinkage of the primary fibers increased gradually, the molecular chains were arranged tightly, the size and number of micropores decreased, the size of the primary fibers decreased, the tensile strength increased, and the elongation at break increased. With the increase of viscosity average molecular weight and solid content of raw solution, the entanglement point density of PAN molecular chain in spinning solution increased, the viscosity of original solution increased, and the size of primary fiber decreased. The higher tensile strength and the higher solid content of the spinning solution are beneficial to the preparation of high quality primary fibers by dry spray wet spinning. The microstructure of PAN fibers in different stages of dry jet wet spinning is studied. And the effect of crystal structure on the mechanical and thermal properties of PAN precursor. The PAN fiber prepared by dry spray wet spinning has a smooth surface, less impurity and less surface defects. The grain size of pan fiber increases and the crystallinity increases during the preparation process. The crystalline structure was improved, among which, the crystallinity was increased by drawing, and the grain growth was improved by densification and heat setting, and the fineness, densification and tensile strength of pan fiber decreased with spinning. The crystal structure of the precursor has an important effect on its mechanical and thermal properties. The more perfect the crystal structure, the more beneficial to the mechanical properties of the precursor, and the more difficult the cyclization occurs during the preoxidation process, The initial temperature of the reaction tends to be high, and it can prevent the thermal decomposition of PAN molecular chain. The microstructure of PAN fiber is characterized by HRTEM, and the PAN fiber in all stages of spinning is encapsulated by epoxy resin. The horizontal and vertical sections perpendicular to the axial phase of the fibers were obtained. The thickness of the slices was 50-70 nm, which was favorable for the electron beam to penetrate the fibers. There is no enhancement effect on image contrast. The inner structure of primary fiber is lamellar structure, the lamellae is perpendicular to the axial arrangement of the fiber, and there are more pores between the lamellae, and the microfibrillar structure begins to appear in the predraft stage of solidification bath. The microfibrils are arranged in parallel to the axial direction of the fibers. After multistage drafting and densification, the arrangement of the microfibrils is more compact, and there is no parallel arrangement between the microfibrils, and there will be interlacing and winding between the microfibrils. The diameter of the microfibrils is about 30-50 nm. There are pores between the microfibrils. The cross-section of the microfibrils is narrow and narrow under the action of tensile force. During spinning, the number of pores decreases, but it can not be completely eliminated.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ342.31

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