【作者】 林治涛；

【导师】 朱波；

【作者基本信息】 山东大学 ， 材料学， 2014， 博士

【摘要】 PAN基碳纤维生产过程有干燥致密化前上油、热定型前上油、电化学表面改性等表面处理工序。对表面处理工序进行研究有助于保证生产过程的顺利进行和提高最终成品碳纤维的品质。本文以PAN基碳纤维原丝生产过程中的上油工艺和碳纤维后处理工序中的电化学表面改性工艺为研究对象,主要研究两个方面的内容：(1)通过油剂对碳纤维生产中各阶段纤维结构和性能的影响,研究油剂种类和上油率对干燥致密化过程、预氧化过程的影响。(2)电化学表面改性处理工艺对碳纤维表面特性、碳纤维复合材料界面特性的影响,并对电化学改性机理经行了研究。使用三种硅系油剂分别在干燥致密化前和热定型前上油,通过改变上油浓度来控制上油率,研究油剂对PAN基碳纤维生产过程的影响。研究发现上油率和上油浓度成正比例关系。在于燥致密化前上油,上油率随上油浓度的增加提高幅度比较小,使用的油剂浓度比较高；在热定型前上油,上油率随上油浓度的增加提高幅度比较大,使用的油剂浓度比较低。油剂对致密化过程中PAN纤维和最终原丝的影响主要是表观特性的变化。上油率合适时,可以有效防止粘连并丝,减少毛丝,提高纤维的抗静电性能和集束性等。油剂不仅影响预氧丝表观特性,对其力学性能和晶体结构也有影响。油剂会促进原丝在预氧化过程中晶体结构的转变,提高预氧丝的芳构化程度。油剂对原丝在预氧化过程中的热解反应有一定的阻碍作用,使放热量降低,预氧化过程易于控制,上油率越大,阻碍作用越大。油剂的使用会使碳纤维的力学性能提高,但过高的上油率会起到相反的作用。与未上油原丝制得的碳纤维相比,使用#1、#2和#3三种油剂后,上油率为1%时,碳纤维的拉伸强度分别提高4.5%,5.4%和8.2%。本文选择#3油剂作为生产高性能碳纤维的油剂。选择致密化前上油后PAN纤维的上油率为0.4%,原丝的上油率为1%。以NH4H2PO4水溶液为电解液对碳纤维进行电化学表面改性处理。对不同处理程度的碳纤维的表面形貌、表面化学性、表面颜色、表面微观结构、拉伸强度及其复合材料界面性能的分析。研究发现,电化学表面处理以后,湿纺碳纤维表面沟槽加深,干喷湿纺碳纤维表面变的凹凸不平。随着处理程度的增加,首先比较薄的表皮层被刻蚀成片剥落,然后里面暴露的皮层继续被刻蚀,一层层的剥落,继续刻蚀使碳纤维表面出现深的裂纹。过度氧化会使碳纤维表面产生平行于纤维轴的纵向裂纹,垂直于纤维轴的竹节状裂纹或与纤维轴成一定角度的螺旋状裂纹,这些有规则的裂纹与碳纤维表面和内部的结构和缺陷有关。电化学表面处理以后,碳纤维表面的碳元素含量降低,氧元素和含氧官能团的含量增加,随着通过纤维束电量的增加,碳纤维表面碳元素、氧元素和含氧官能团的相对含量起初变化很大,后来变化不大。随着处理程度的增加,碳纤维表面的颜色发生改变。碳纤维表面颜色的变化与氧化过程中碳纤维表面生成的不饱和含氧官能团有关,不饱和官能团共同作用形成共轭生色官能团,碳纤维表面每种官能团的含量变化使共轭生色团吸收的光的波长发生变化,使碳纤维呈现不同的颜色。电化学改性处理以后,碳纤维的一级拉曼光谱图中D峰和G峰有一定程度的分开,表面微.观结构发生了变化。碳纤维表面的石墨片层微晶边缘被氧化刻蚀,晶粒尺寸变小。碳纤维表面的无定形碳结构、脂肪结构、类烯烃结构等被氧化生成含氧官能团,使碳纤维表面的无序度增加。随着处理程度的提高,无定形碳等结构被氧化刻蚀掉,石墨碳的含量增加,无序度减小。所以R值先增大后减小。ID2/IG和ID3/IG与R有着相同的变化规律。随着处理程度的增加,碳纤维的线密度、断裂伸长率和拉伸强度均有所下降,层间剪切强度先升高后降低。在该实验条件下,通电量小于160C/g时,电化学处理对碳纤维拉伸强度的损伤小于5%,层间剪切强度可以提高39.6%。过度氧化产生的薄弱片层、裂纹等会大大降低碳纤维的拉伸强度和层间剪切强度。采用循环伏安法来研究电解质种类、温度、浓度等对碳纤维表面电化学特性的影响。研究发现在较小的扫描范围里,电解液中水没有电解不产生活性氧,碳纤维表面没有被氧化,不产生氧化反应电流。电解体系中析氧反应产生的活性氧是碳纤维表面被氧化的前提。扫描速度会影响到水的析氢、析氧反应和碳纤维表面的氧化反应电流强度,扫描速度与电流强度正相关。碳纤维在不同的电解质水溶液中的循环伏安曲线形状不同,说明碳纤维表面的电化学特性不同。碳纤维在强酸性的硫酸电解液中可以观察到两个氧化反应极限电流,而在强碱性的氢氧化钠电解液中没有观察到氧化反应极限电流。主要原因是在酸性的电解液中碳纤维表面比较容易被氧化,氧化电流比较明显,阴极扫描还原电流比较大,表面生成的氧化产物比较多。另外电解液的碱性增加,循环伏安曲线会朝低电位方向移动,水析氧反应开始电压减小,析氧反应剧烈,使碳纤维表面氧化反应电流在循环伏安曲线上难以观察。温度和浓度都会影响碳纤维表面电化学特性。电解液温度会影响电解液中水的析氧析氢反应以及碳纤维表面氧化反应的难易程度和反应速度。电解液浓度不会对水的析氧析氢反应以及碳纤维表面氧化反应的难易程度产生影响,但是会影响反应速度。通过对在不同电解质溶液中电化学处理前后碳纤维表面元素和含氧官能团变化的分析,发现五种电解质的氧化能力不同。五种电解质的氧化能力顺序为：NH4H2PO4>H2SO4>(NH4)2HPO4>NH4HCO3>NaOH。通过对在不同电解质溶液中电化学处理前后碳纤维表面微观结构的分析,发现碱性电解液在较低的电流密度时R值就能达到比较高的值,之后随着电流密度的增加R值减小。酸性电解液在较高的电流密度R值比较大。通过对在NH4H2PO4、NH4HCO3和(NH4)2HPO4三种铵盐溶液中处理后碳纤维拉伸强度及其复合材料层间剪切强度的分析,发现电化学处理造成碳纤维拉伸强度降低主要是因为刻蚀作用,在酸性电解液中主要是电化学氧化刻蚀,在碱性电解液中主要是物理刻蚀。拉伸强度与拉曼光谱参数有着密切的联系。R值较大时,刻蚀作用比较强,拉伸强度降低的幅度比较大。层间剪切强度既与表面含氧官能团有关,也与表面粗糙度有关。最终选择的工艺参数：以NH4H2PO4为电解质时选择的电流密度为160C/g,以NH4HCO3和(NH4)2HPO4为电解质时选择的电流密度为80C/g。更多还原

【Abstract】 In the production process of PAN based carbon fibers, there are some surface treatment processes such as finish process before collapsing, finish process before heat setting, electrochemical surface modification. Study on surface treatment process helps us to enable the production process to be smooth and improve the performance of the final carbon fibers. This paper focused on finish process in PAN based carbon fibers precursor production and electrochemical surface modification process in carbon fibers reprocessing, and the major contents include:(1) Through the influence of finish oil on fiber structure and performance in different stages of the production of carbon fibers, the influence of the types of finish oil and oil rate on collapsing and oxidative stabilization process were studied.(2) The effect of electrochemical surface modification process on the surface properties of carbon fibers, and carbon fiber composite material interface properties. The electrochemical modification mechanism was also studied in this paper.Three kinds of silicone oil were used as finish oil respectively before collapsing and heat setting. Control oil rate by changing the oil concentration, and the effect of finish oil on the PAN based carbon fibers production process were studied. It was found that finish oil rate ought directly proportional to finish oil concentration. During finish process before collapsing, it was relatively small that finish oil rate increased with the increase of the oil concentration, and the used oil concentration was high. During finish process before heat setting, it was relatively obvious that finish oil rate increased with the increase of oil concentration, and the used oil concentration was low. The influence of finish oil on PAN fibers after collapsing and the precursor was mainly the change of the apparent characteristics. When the finish oil rate was appropriate, it could effectively avoid adhesion and fusion between filaments, reduce broken filaments and improve the antistatic performance of fibers and integrity, etc. Finish oil rate not only affected the apparent characteristics of stabilized fibers, but also the mechanical properties and crystal structure. Finish oil could improve the degree of aromatization, decrease the mechanical performance of the stabilized fibers. Finish oil could hinder the pyrolysis reaction and reduce heat flow during oxidative stabilization process. As the finish oil rate increased, the block effect were higher. The use of finish oil would increase the mechanical properties of carbon fibers, but high finish oil rate would have the opposite effect. Compared to carbon fibers made from unfinished precursor, after using#1,#2and#3finish oils, when the finish oil rate was1%, the tensile strength of the carbon fibers respectively increased by4.5%,5.4%and8.2%.#3finish oil was use to produc high-performance carbon fibers. The finish oil rate of PAN fibers after collapsing was0.4%, and the finish oil rate of precursor was1%.NH4H2PO4agueous solution was used as electrolyte, and carbon fibers was electrochemical modified with different treatment intensity. Surface morphology, surface chemical properties, surface color, surface microstructure structure, tensile strength of carbon fibers and ILSS of CFRP were investigated. It was found that the carbon fibers surface groove deepened and the surface became uneven. With the increase of treatment intensity, thin skin layer of carbon fibers was etched into flake, then the exposed layer continued to be etched. When the treatment intensity was higher, the carbon fibers surface appeared deep cracks. Carbon fibers surface appeared longitudinal crack parallel to the fiber axis, bamboo-like crack perpendicular to the fiber axis or spiral crack with a certain angle to fiber axis after excessive oxidation. The regular crack was associated with the carbon fibers surface and internal structure and defect. After electrochemical surface treatment, the carbon content of the carbon fibers surface decreased, oxygen and oxygenated functional group increased. With the increase of electricity passing through the fiber bundle, the content of carbon, oxygen, and oxygenated functional group changed rapidly at first and then remained almost constant. With the increase of treatment intensity, the color of the carbon fiber surface changed, which was related with unsaturated oxygenated functional group generated in electrochemical surface modification process. These unsaturated functional groups worked together to form multiple conjugated chromophores. With the change of treatment intensity, the content of each surface functional groups changed and the absorbed wavelength of light changed, so the appeared color of the carbon fibers would change. D band and G band separated to a certain extent in the first-order Raman spectra after electrochemical modification treatment, which indicated that the surface microstructure changed. The edge of microcrystalline graphite flake layer on the carbon fibers surface was etched. Big graphite crystallite was etched into small graphite crystallite. Crystallite size decreased and disorder graphite lattice increased. Aliphatic structure, olefins structure and crystallite structure edge carbon were oxidized to generate oxygenated functional group. With the increase of treatment intensity, R increased firstly and then decreased. Linear density, elongation at break and tensile strength decreased. ILSS of CFRP increased at first, then decreased.When the electricity was160C/g, tensile strength of carbon fibers decreased by5%and ILSS of CFRP increased by39.6%. The weak layer and crack could reduce the tensile strength and ILSS obviously.Cyclic voltammetry was used to study the electrochemical behavior of carbon fiber under different experimental conditions in different electrolyte aqueous solution. The influence of the types of electrolyte, temperature and concentration on anodic oxidation reaction were studied. It was found that the scan range was different in different electrolyte aqueous solution, which was mainly determined by the pH of the electrolyte. As the pH value increases, the scan range moved toward the direction of the lower potential. In the smaller scan range, the water in the electrolyte did not produce reactive oxygen, so the carbon fibers surface was not oxidized. There was no oxidation reaction electricity. If only the oxygen evolution reaction of water happened, the carbon fibers surface can be oxidized. Oxygen evolution reaction of water was the precondition of the carbon fibers surface oxidation reaction. Scan rate had a positive relationship with surface oxidation reaction, hydrogen evolution and oxygen evolution reaction current intensity. CV curve was different in different electrolytes, which showed that the mechanism of carbon fibers surface oxidation reaction was different. Two oxidation limiting current could be observe in strong acid sulfate electrolyte, however there was oxidation limiting current in strong alkaline sodium hydroxide electrolyte. On the one hand, it was related to the pH of electrolyte. On the other hand it was because the carbon fibers surface could be easily oxidized in acidic electrolyte. The oxidation and reduction current were obvious, which showed that more surface oxidation products were generated. Temperature and the concentration would affect anodic oxidation reaction. Electrolyte temperature could affect the difficulty and reaction speed of the oxygen evolution reaction of water and oxygen reaction of carbon surface. The electrolyte concentration would not affect the difficulty of the oxygen evolution reaction and oxygen reaction of carbon fibers surface, however it could affect the reaction rate.Through the analysis of carbon fibers surface element content and functional groups before and after treated in different electrolytes, it was found that oxidation ability of the five electrolytes was different. The oxidation ability order of the five electrolytes was NH4H2PO4>H2SO4>(NH4)2HPO4>NH4HCO3>NaOH2Through the analysis of surface microstructure treated in different electrolyte, it was found that R could achieve high value at low current density in alkaline electrolyte, then R value decreasesd with the increase of the current intensity. R value was large at higher current density in acidic electrolyte. Through the analysis of the tensile strength of carbon fibers and ILSS of CFRP before and after treated in NH4H2PO4, NH4HC03and (NH4)2HPO4, the main reason of the decrease of carbon fibers tensile strength was the etching effect. Electrochemical oxidation etching mainly occurred in acidic electrolyte. Physical etching mainly occurred in alkaline electrolyte. The tensile strength of carbon fibers had a close relation with R value. When R value was larger, etching effect was stronger, and the tensile strength decrease rapidly. ILSS of CFRP had a close relation with surface chemical properties and surface roughness of carbon fibers. The optimum current density was160C/g in NH4H2PO4electrolyte. The optimum current density was80C/g in NH4HCO3and (NH4)2HPO4electrolyte.更多还原