PAN基碳纤维预氧化过程中的结构演变和动力学分析
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摘要
在聚丙烯腈(PAN)基碳纤维的制备过程中,原丝的预氧化是影响碳纤维质量、碳收率和生产效率的关键工艺。深入研究原丝在预氧化过程中的热行为和反应机理,明确纤维结构的演变规律,对于进一步优化预氧化工艺,从而获得高性能碳纤维具有重要意义。
PAN原丝在预氧化过程中,时间和温度是两个重要的参数,本论文采用差示扫描量热仪(DSC)、傅里叶变换红外光谱(FTIR)、元素分析仪(EA)、核磁共振(NMR)、体密度测试等分析手段,研究了预氧化时间、温度对处理后纤维热性能和结构演变的影响规律,以及纤维预氧化过程中的环化反应动力学。研究结果表明：
1.环境气氛对原丝的热行为有明显的影响。氮气中,纤维的放热集中；空气中放热较缓和,且在反应初期,氧可促进预氧化反应的发生,使初始反应温度比氮气中的低,在反应后期,氧阻碍反应的发生,使终止温度移向更高温度。
2.预处理纤维中的含氧结构对其后续反应有明显的影响,导致预处理纤维的DSC放热峰出现双峰现象。
3.时间效应与温度的高低有密切关系。180℃时,随预处理时间的增加,纤维的环化度、密度、相对环化率等的变化不明显,温度高于180℃时,随预处理时间的增加,纤维的环化度、密度、相对环化率等逐渐增加,且随着时间的延长,其增加趋势逐渐变缓。
4.温度对纤维的环化程度、体密度等具有明显的影响作用。随处理温度的升高,环化程度和体密度都明显增加,且增加趋势逐渐加大，说明温度效应大于时间效应。
5.由纤维的环化度可以计算其环化反应动力学,且与传统的Kissinger、Ozawa方法所得结果一致。
Pre-oxidation of polyacrylonitrile(PAN) precursor fibers is an essential process that affects the quality of carbon fibers. It is important to study intensively on the thermal behavior and reaction mechanism of PAN fibers, and on the structrul evolution during the oxidative stabilization process.
Time and temperature are two important technological conditions in oxidative stabilization processes. In this paper, the effects of pre-oxidation time and pre-oxidation temperature upon thermal behavior, structure evolution, cyclization kinetics of fibers were studied by means of differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), element analysis (EA), nuclear magnetic resonance (NMR),density, and so on. The results showed that:
1.Thermal behavior of PAN precursor can be affected by atmospheres obviously. In nitrogen, the centralized exothermic phenomenon of PAN fibers is apparent. While in air, the exothermic phenomenon is relieved, and in the initial stage of pre-oxidative reaction, it can be promoted by oxygen and the initial reaction temperature is lowered, in the later stage, the reaction is restrained by oxygen and the end temperature is increased.
2.Oxygen-containing structure of pretreatment fibers can affect consequent reaction obviously, generating double peak of DSC exotherm.
3.The effect of pre-oxidation time is related to temperature, at 180℃, the cyclization index, density, relative cyclization index remain virtually unchanged over time. At higher temperature, they increase gradually over time and the trend slow down.
4.Pre-oxidation extent and density of PAN fibers are affected greatly by pre-oxidation temperature. With the temperature rising, the pre-oxidation extent increase obviously and the trend become pretty obvious, which showed that the effect of temperature on them are more obvious than the effect of time.
5.Cyclization kinetics parameter can be obtained by cyclization index and the result is consistent with Kissinger method and Ozawa method.
PAN原丝在预氧化过程中,时间和温度是两个重要的参数,本论文采用差示扫描量热仪(DSC)、傅里叶变换红外光谱(FTIR)、元素分析仪(EA)、核磁共振(NMR)、体密度测试等分析手段,研究了预氧化时间、温度对处理后纤维热性能和结构演变的影响规律,以及纤维预氧化过程中的环化反应动力学。研究结果表明：
1.环境气氛对原丝的热行为有明显的影响。氮气中,纤维的放热集中；空气中放热较缓和,且在反应初期,氧可促进预氧化反应的发生,使初始反应温度比氮气中的低,在反应后期,氧阻碍反应的发生,使终止温度移向更高温度。
2.预处理纤维中的含氧结构对其后续反应有明显的影响,导致预处理纤维的DSC放热峰出现双峰现象。
3.时间效应与温度的高低有密切关系。180℃时,随预处理时间的增加,纤维的环化度、密度、相对环化率等的变化不明显,温度高于180℃时,随预处理时间的增加,纤维的环化度、密度、相对环化率等逐渐增加,且随着时间的延长,其增加趋势逐渐变缓。
4.温度对纤维的环化程度、体密度等具有明显的影响作用。随处理温度的升高,环化程度和体密度都明显增加,且增加趋势逐渐加大，说明温度效应大于时间效应。
5.由纤维的环化度可以计算其环化反应动力学,且与传统的Kissinger、Ozawa方法所得结果一致。
Pre-oxidation of polyacrylonitrile(PAN) precursor fibers is an essential process that affects the quality of carbon fibers. It is important to study intensively on the thermal behavior and reaction mechanism of PAN fibers, and on the structrul evolution during the oxidative stabilization process.
Time and temperature are two important technological conditions in oxidative stabilization processes. In this paper, the effects of pre-oxidation time and pre-oxidation temperature upon thermal behavior, structure evolution, cyclization kinetics of fibers were studied by means of differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), element analysis (EA), nuclear magnetic resonance (NMR),density, and so on. The results showed that:
1.Thermal behavior of PAN precursor can be affected by atmospheres obviously. In nitrogen, the centralized exothermic phenomenon of PAN fibers is apparent. While in air, the exothermic phenomenon is relieved, and in the initial stage of pre-oxidative reaction, it can be promoted by oxygen and the initial reaction temperature is lowered, in the later stage, the reaction is restrained by oxygen and the end temperature is increased.
2.Oxygen-containing structure of pretreatment fibers can affect consequent reaction obviously, generating double peak of DSC exotherm.
3.The effect of pre-oxidation time is related to temperature, at 180℃, the cyclization index, density, relative cyclization index remain virtually unchanged over time. At higher temperature, they increase gradually over time and the trend slow down.
4.Pre-oxidation extent and density of PAN fibers are affected greatly by pre-oxidation temperature. With the temperature rising, the pre-oxidation extent increase obviously and the trend become pretty obvious, which showed that the effect of temperature on them are more obvious than the effect of time.
5.Cyclization kinetics parameter can be obtained by cyclization index and the result is consistent with Kissinger method and Ozawa method.
引文
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[2]胡兴军.碳纤维在汽车上的应用[J].汽车与配件,2008,(50)：44-45
[3]曹永友,李青青,王强.汽车工艺与材料[J].汽车与配件,2008,(10)：54-57
[4]武学刚.碳纤维复合材料在混凝土栈桥加固工程中的应用[J].黑龙江科技信息,2008,(24)：237-238
[5]赵亚.碳纤维在桥梁加固中的应用[J].交通世界,2008,(09)：124-126
[6]钱水林.碳纤维的应用及市场需求分析[J].石油化工技术与经济,2008,24(1)：26-29
[7]杨国华.碳素材料(下册).北京：中国物质出版社[M],1999,30-30
[8]王茂章,贺福.碳纤维的制造、性质及其应用[M].北京：科学出版社,1984,20-299
[9]刘国昌,徐淑琼.聚丙烯腈基碳纤维及其应用[J].机械制造与自动化,2004,33(4)：41-43
[10]贺福.碳纤维及其应用技术[M].北京：化学工业出版社,2004,2-250
[11]贺福,杨永岗.突破原丝“瓶颈”是碳纤维产业化的必备条件[J].高科技纤维与应用,2001,26(6)：1-5
[12]张旺玺.聚丙烯腈基碳纤维的新进展[J].高科技纤维与应用,2001,26(5)：12-14
[13]Bhat G S, Cook F I, Abhiraman A S. New aspects in the stabilization of acrylic fibres[J]. Carbon,1990,28(2):377-385
[14]Belte L A, Gustafson R R. Cyclization kinetics of polyacrylonitrile [J]. Carbon,1996, 34(5):561-566
[15]刘洪波,徐仲榆.炭纤维石墨化处理技术[J].炭素技术,1995,(2)：25-25
[16]张乃武,王培华.PAN共聚纤维预氧化反应动力学的研究[J].青岛化工学院学报,1991,12(2)：21-25
[17]王平华,刘杰,岳中仁,等.PAN纤维连续预氧化过程的研究.纤维的物化行为[J].碳素,1991,(3)：15-19
[18]Houtz RCA research on the control method for oxidation process of precursor fiber[J]. Textile Research Journa,1950,20:786-786
[19]Burlant W J, Parsons J L. Pyrolysis of polyacrylonitrile[J]. Journal of Polymer Science, 1956,22(101):249-256
[20]La Combe E M. Color formation in polyacrylonitrile[J]. Journal of Polymer Science,1957, 24(105):152-154
[21]Grassie N, Hay N, McNell I C. Coloration in acrylonitrile and methacrylonitrile polymers[J]. Journal of Polymer Science,1958,31(122):205-206
[22]Schurz J. Discoloration effects in acrylonitrile polymers[J]. Journal of Polymer Science, 1958,28(117):438-439
[23]Grassie N, Hay N. Thermal coloration and insolubilization in polyacrylonitrile[J]. Journal of Polymer Science,1962,56(163):189-202
[24]Robert T, Conley J B. Examination of the oxidative degradation of polyacrylonitrile using infrared spectroscopy[J]. Journal of Applied Polymer Science,1963,7(5):1757-1773
[25]Berlin A A, Dubinskaya A M, Moshkovskii S Y. Heat treatment of polyacrylonitrile in solution in dimethylformamide[J]. Polymer Science,1964,6(11):2145-2151
[26]Fester W. On the Chromophore of polyacrylonitrile[J]. Textile Rundschau,1956,20(5):1-1
[27]Grassie N, McGuchan R. Pyrolysis of polyacrylonitrile and related polymers—II:The effect of sample preparation on the thermal behaviour of polyacrylonitrile[J]. European Polymer Journal,1971,7(8):1091-1104
[28]Grassie N, Maccallum R. The kinetics of depolymerization[J]. Journal of Polymer Science, 1962,60(169):S33-S34
[29]Grassie N, McGuchan R. Pyrolysis of polyacrylonitrile and related polymers—VI: Acrylonitrile copolymers containing carboxylic acid and amide structures[J]. European Polymer Journal,1972,8(2):257-269
[30]Morita K, Murata Y, Ishitani A, Murayama K, Ono T, Nakajima A. Characterization of commereially available PAN-based carbonfibers.Pure and Applied Chemistry,1986,58(3): 455-468.
[31]BashirZ. A critical review of the stabilization of PAN[J]. Carbon,1991,29(8):1081-1090
[32]Tse-HaoKo. Influence of continuous stabilization on the Physieal properties and Mierostrueture of PAN-based carbonfibers. Journal of Applied Polymer Seienee,1991, 42(7):1949-1957
[33]潘鼎,陈惠芳,李雨华,等.PAN预氧化纤维的分段碳化工艺研究[J].中国纺织大学学报,1993,19(6)：17-23
[34]刘焕章,王成国,王延相.聚丙烯腈纤维预氧化工艺条件对其结构和性能的影响[J].高科技纤维与应用,2006,31(1)：35-35
[35]Bhat G S, Cook F L, Abhiraman A S.new aspects in the stabilization of acrylic fibers[J]. Carbon,1990,28(2-3):377-385
[36]E.Frrzer, D.J.Muller. The Influence of Oxygen on The Chemical Reactions During Stabilization of PAN as Carbon Fiber Precursor[J]. Carbon,1975,13:63-69
[37]刘杰,阳武.热氧稳定过程中聚丙烯腈纤维序态结构的变化[J].材料研究学报,2007, 21(5)：488-489
[38]Wangxi Zhang, Liu J, Gang Wu. Evolution of structure and properties of PAN precursors during their conversion to Carbon fibers. Carbon,2003,41(14):2805-2812
[39]Love G, Cox M G, Scott V D. Electron-probe microanalysis of oxygen in heat-treated Orion fibers[J]. Materials Research Bulletin,1975(10):81
[40]刘杰,李佳,王雷,等.预氧化温度对聚丙烯腈纤维皮芯结构形成的影响[J].北京化工大学学报,2006,33(1)：43-44
[41]于晓强,庄光山,丁洪太,等.PAN基碳纤维预氧化过程中环构化机理[J].山东工业大学学报,1995,25(4)：301-305
[42]Ogawa H, Saito K. Oxidation behavior of polyacrylonitrile fibers evaluated by new stabilization index[J]. Carbon,1995,33(6):783-788
[43]ZHANG Shou-chun, WEN Yue-fang, YANG Yong-gang, ZHENG Jing-tang, LING Li-cheng. Effect of itaconic acid content on the thermal behavior of polyacrylonitrile[J]. New Carbon Materials,2003,18(4):315-317
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