Regulating the radial structure of polyacrylonitrile fibers during pre-oxidation and its effect on the mechanical properties of the resulting carbon fibers
-
摘要: 预氧纤维结构及其分布直接影响炭纤维的性能，优化预氧结构径向分布，构建预氧结构与炭纤维力学性能的关系，对制备高性能炭纤维具有指导意义。本文采用固体核磁、光学显微镜、热失重等表征方法，通过温度控制预氧化反应速率，研究预氧化反应速率对纤维结构和径向分布及炭纤维性能的影响。结果表明，整体提高预氧化反应速率，在促进预氧结构向纤维更深区域扩展的同时，也导致含氧结构增加较多，热稳定性降低，影响炭纤维的性能；而提高预氧化初期反应速率，有效改善预氧结构径向分布的同时纤维含氧结构增加较少，热稳定性提高，最终炭纤维的石墨化程度和致密性较高，力学性能显著提升，获得一种具有高强中模特征、直径相对较大的炭纤维。Abstract: The radial structure of polyacrylonitrile fibers oxidized before carbonization and its distribution directly affect the performance of the resulting carbon fibers. Optimizing the radial distribution of the oxidized structure and establishing a relationship between this structure and the mechanical properties of the final carbon fibers will help optimize the oxidation conditions for the preparation of high-performance carbon fibers. Solid-state nuclear magnetic resonance spectroscopy, optical microscopy, thermogravimetric analysis, and mechanical tests were used to investigate the effect of the oxidation reaction rate on the radial distribution of the structure of the oxidized fibers and the mechanical properties of the resulting carbon fibers. The oxidation reaction rates were controlled by regulating the oxidation temperature gradient. Results show that the degree of oxidation increases with both the average and initial oxidation rates. By increasing the average oxidation reaction rate, the oxidized structure penetrates deeper into the core region of the fibers, the content of oxygen-containing functional groups increases, the thermal stability of the fibers decreases, and the degree of graphitization of the final carbon fibers increases, but the density of the fibers is decreased and their mechanical properties are degraded. Compared with sample obtained with the lower initial oxidation rate, the number of oxygen-containing functional groups, thermal stability, degree of graphitization and density of the final carbon fibers of the sample with the higher initial oxidation rate are higher, and its tensile strength and modulus are respectively 4.2% and 2.2% higher. A new type of carbon fiber with high strength, medium modulus and a relatively large diameter is obtained under the optimized oxidation conditions.
-
Figure 1. Schematic diagram of the measuring positions of the optical density of a pre-oxidized fiber.
Figure 2. Radial distribution of the pre-oxidation degree in sample 1 fibers: (a) Micrograph of the fiber cross section and (b) radial optical density distribution of the fiber cross section.
Figure 3. Micrographs of the cross sections of pre-oxidized fibers prepared with different pre-oxidation rates: (a) Sample 1, (b) 2 and (c) 3.
Figure 4. Radial optical density distribution of pre-oxidized fibers subjected to different pre-oxidation reaction rates.
Figure 5. Effect of the pre-oxidation reaction rate on thermal stability of pre-oxidized fibers.
Figure 6. Radial distribution of the pre-oxidation degree in fibers: (a) Micrograph of the fiber cross section of sample 4 and (b) optical density distribution of the fiber cross section for sample 1 (black) and 4 (red).
Figure 7. Effect of the initial reaction rate on the thermal stability of pre-oxidized fibers.
Figure 8. Radial distribution of the g values of carbon fiber samples determined from Raman spectra.
Table 1. Pre-oxidation furnace temperatures (°C) used to prepare samples 1-4.
Sample 1 2 3 4 5 6 1# 200 215 238 255 260 265 2# 200 213 235 250 255 260 3# 200 220 243 255 265 270 4# 210 225 238 255 260 265 Note: processing time: 1 h, atmosphere: air. 
下载: 导出CSV
Table 2. 13C ssNMR analysis results for pre-oxidized fibers subjected to different pre-oxidation reaction rates.
Sample C＝C 115×10−6 C＝CH 139×10−6 C＝N 153×10−6 —C＝O 176×10−6 RCI(%) Gh(%) RC＝O/C＝N(%) △RC＝O/C＝N(%) 1# 14.21 8.86 20.41 4.61 55.3 65.3 22.6 0.0 2# 14.24 8.84 20.11 4.51 54.5 65.0 22.2 -0.4 3# 15.60 9.69 21.10 5.21 56.7 78.0 24.7 +2.1
下载: 导出CSV
Table 3. Optical density analysis results of PAN fibers pre-oxidized at different reaction rates.
Sample OD0 OD±1 OD±2 OD±3 OD±4 OD±5 ODm 1# 0.555 0.546 0.531 0.505 0.500 0.494 0.508 2# 0.559 0.553 0.540 0.525 0.519 0.512 0.522 3# 0.543 0.530 0.478 0.418 0.412 0.408 0.436
下载: 导出CSV
Table 4. Characteristic structural parameters of PAN fibers pre-oxidized at different initial reaction rates.
Sample RCI
(%)Gh
(%)RC＝O/C＝N
(%)△RC＝O/C＝N
(%)ODm 1# 55.3 65.3 22.6 0.0 0.508 4# 56.6 69.8 22.7 +0.1 0.492
下载: 导出CSV
Table 5. Structures of different pre-oxidized fibers and properties of corresponding carbon fibers.
Samples Structures of pre-oxidized fibers Properties of carbon fibers RCI(%) Gh(%) RC＝O/C＝N(%) Linear density(g·m−1) ρ(g·m−3) σ(GPa) E(GPa) 1# 55.3 65.3 22.6 0.0697 1.7399 5.28 273 2# 54.5 65.0 22.2 0.0682 1.7524 5.02 268 3# 56.7 78.0 24.7 0.0717 1.7384 5.21 265 4# 56.6 69.8 22.7 0.0700 1.7549 5.50 279
下载: 导出CSV
-
[1] Zhao Y H, Li Q F, Wang J W, et al. Preparation and properties of carbon fiber/polyether polyurethane composites[J]. New Carbon Materials,2014,29(06):454-460. [2] Zhang J, Chuai X B. Development and application status of carbon fiber[J]. Chemical Management,2017,23:60. [3] Yang Y H, Pan Y X, Feng Z H, et al. Evaluation of aerospace carbon fibers[J]. New Carbon Materials,2014,29(03):161-168. [4] Wu S, Gao A J, Wang Y, et al. Modification of polyacrylonitrile stabilized fibers via post-thermal treatment in nitrogen prior to carbonization and its effect on the structure of carbon fibers[J]. Fibers and Polymers,2018,53(11):8627-8638. [5] Wen Y F, Cao X, Yang Y G, et al. Carbonization of pre-oxidized polyacrylonitrile fibers[J]. New Carbon Materials,2008(02):121-126. [6] Zhang X. Pre-oxidized structure regulation of PAN fiber and the influence on high temperature thermal cracking and restructuring behavior[D]. Master Degree, Beijing University of Chemical Technology, 2015. [7] Xue Y, Liu J, Lian F, et al. Effect of the oxygen-induced modification of polyacrylonitrile fibers during thermal-oxidative stabilization on the radial microcrystalline structure of the resulting carbon fibers[J]. Polymer Degradation and Stability,2013,98(11):2259-2267. doi: 10.1016/j.polymdegradstab.2013.08.016 [8] Ruan R Y, Ye L W, Feng Hai, et al. High temperature evolution of the microstructure in the radial direction of PAN-based carbon fibers and its relationship to mechanical properties[J]. New Carbon Materials,2020, 35 (3): 295-306 [9] Liu J, Li J, Wang L, et al. The evolution of the core/shell structure of polyacrylonitrile fibers during peroxidation[J]. New Carbon Materials,2008,23(02):177-184. [10] Nunna S, Naebe M, Hameed N, et al. Evolution of radial heterogeneity in polyacrylonitrile fibres during thermal stabilization: An overview[J]. Polymer Degradation and Stability,2017,136:20-30. doi: 10.1016/j.polymdegradstab.2016.12.007 [11] Nunna S, Naebe M, Hameed N, et al. Investigation of progress of reactions and evolution of radial heterogeneity in the initial stage of thermal stabilization of PAN precursor fibres[J]. Polymer Degradation and Stability,2016,125:105-114. doi: 10.1016/j.polymdegradstab.2016.01.008 [12] Nunna S, Creighton C, Bronwyn L, et al. The effect of thermally induced chemical transformations on the structure and properties of carbon fiber precursors[J]. Journal of Materials Chemistry A,2017,5(16):7372-7378. doi: 10.1039/C7TA01022B [13] Zhao C. The research of dimensional-effect on the thermal reaction proceeding of PAN fibers[D]. PhD, Beijing University of Chemical Technology, 2012. [14] Wang J, Hu L, Yang C, et al. Effects of oxygen content in the atmosphere on thermal oxidative stabilization of polyacrylonitrile fibers[J]. Royal Society of Chemistry,2016,6(77):73404-73411. [15] Kong L, Liu H, Cao W, et al. PAN fiber diameter effect on the structure of PAN-based carbon fibers[J]. Fibers and Polymers,2014,15(12):2480-2488. doi: 10.1007/s12221-014-2480-1 [16] Nunna S, Creighton C, Hameed N, et al. Radial structure and property relationship in the thermal stabilization of PAN precursor fibers[J]. Polymer Testing,2017,59:203-211. doi: 10.1016/j.polymertesting.2017.02.006 [17] Wu S. Formation and orientation efficiency of cyclized structure of PAN-based carbon fibers under thermal stretching[D]. PhD, Beijing University of Chemical Technology, 2018. [18] Zhong S, Xu F, Lei Shuai, et al. Optical density method of radial structure of PAN-based pro-oxidized fibers[J]. Journal of Materials Engineering,2017,45(02):65-71. [19] Vollebregt S, Ishihara R, Tichelaar F D, et al. Influence of the grow temperature on the first and second-order Raman band ratios and widths of carbon nanotubes and fibers[J]. Carbon,2012,50(10):3542-3554. doi: 10.1016/j.carbon.2012.03.026 [20] Yuan J S. The relevant research on pre-oxidation process and aggregation structure of PAN fibers[D]. Master Degree, Beijing University of Chemical Technology, 2013. -
点击查看大图
计量
- 文章访问数: 717
- HTML全文浏览量: 428
- PDF下载量: 57
- 被引次数: 0
