【作者】 张敏；

【导师】 朱波；

【作者基本信息】 山东大学 ， 材料学， 2010， 博士

【摘要】 界面对碳纤维复合材料性能的发挥起着非常重要的作用,复合材料通过界面传递载荷,可以使碳纤维与基体形成一个有效发挥综合性能的整体。在界面的研究中,提高其结合强度是改善碳纤维复合材料力学性能的关键。因此,剖析各种因素对碳纤维复合材料界面结合强度的影响,对于提高复合材料的综合性能具有十分重要的意义。本文采用扫描电镜(SEM)、X射线光电子能谱(XPS)、激光拉曼光谱(LRS)、X射线衍射(XRD)、傅立叶变换红外光谱(FTIR)以及力学性能测试等技术,考察了不同制备工艺对碳纤维结构及性能的影响,探讨了湿法纺丝制备PAN基碳纤维的电化学改性工艺以及电化学改性处理过程中碳纤维表面结构和性能的演变规律,获得了碳纤维表面除胶的合理性工艺,深入研究了碳纤维电化学改性处理、上浆剂以及基体改性对碳纤维复合材料界面结合强度的影响,提出了碳纤维电化学改性机理以及基体改性机理。对不同工艺制备的碳纤维结构及性能进行了对比分析,结果表明：与湿法纺丝工艺制备的碳纤维相比,干喷湿纺工艺制备的碳纤维内部致密性高,轴向微孔尺寸小,表面非碳元素相对含量低。从X射线衍射来看,干喷湿纺工艺制备的碳纤维石墨层面间距d002较小,更接近于石墨单晶的层面间距；微晶堆砌厚度Lc较高,石墨网平面尺寸La较大,石墨微晶的平均堆叠层数较多,这说明采用干喷湿纺工艺制备的碳纤维具有较高的石墨化程度,其结构完整性更高。湿法纺丝和干喷湿纺工艺制备的碳纤维其表面结构基本相同,但表面形貌存在很大差异。湿法纺丝工艺制备碳纤维表面粗糙,有许多轴向沟槽,而干喷湿纺工艺制备的碳纤维表面光滑无沟槽,沟槽的存在可以增加纤维与基体间的机械铰合作用,有利于提高复合材料的界面结合强度。另外,洁净的生产环境及精细的加工设备有利于减少碳纤维的表面缺陷。采用XPS技术研究了湿法纺丝工艺制备的PAN基碳纤维在电化学改性处理过程中表面特性随改性工艺的变化,结果表明：电化学改性初期,碳纤维表面改性效果明显。随着电化学改性处理时间的延长,变化趋势减慢,达到一定程度时趋于稳定。电解液的浓度和温度越高,电化学改性处理时间越长,电流密度越大,碳纤维表面改性效果越明显。大量电解质试验表明,NH4H2PO4对碳纤维表面电化学改性效果最佳。采用LRS技术系统研究了湿法纺丝工艺制备的碳纤维在电化学改性处理过程中表面结构的变化,结果表明：电化学改性处理后,碳纤维表面拉曼光谱中的G线和D线交叠度减小,尺值增大,D2线与G线的比值减小,D3线与G线的比值增大。随着电化学处理时间的增加,尺值不断增大,D2线与G线的比值以及D3线与G线的比值发生一定程度的改变,但变化趋势并不明显。所有代表无序结构的拉曼谱峰积分面积总和与石墨结构积分面积之比与R值的变化趋势基本一致,它可以更全面地表征电化学处理过程中碳纤维表面结构无序性的变化,对于深入分析碳纤维电化学改性处理中表面微结构的变化规律具有重要意义。选用高电流密度,浓度为1mol／L的NH4H2PO4为电解质,设定处理时间为4min,对碳纤维进行电化学改性处理,试验结果表明,电化学改性处理后碳纤维的表面结果和性能发生改变。碳纤维的表面结构被破坏,无序度增大,表面晶粒尺寸减小。比表面积增大,表面粗糙度增加,有利于提高碳纤维的表面极性,增大树脂的浸润性；同时更多含氧官能团的生成也有利于增大碳纤维表面与基体间的化学作用力,使得碳纤维增强树脂基复合材料的界面结合强度提高。其中,碳氧单键含量的增加对界面化学作用力的增强起主要作用。系统研究了过度电化学改性处理对T700碳纤维和石墨纤维结构的影响,结果表明：电化学改性是一种碳纤维表面改性处理的有效方法,它仅对纤维表面产生作用,并不改变纤维的本体结构。在相同的处理条件下,碳纤维表面部分结构破坏严重,轴向沟槽消失,部分结构保持完整,且破坏是沿纤维轴向进行的,破坏区域显示出微坑形貌；石墨纤维表面基本没有变化。电化学改性处理过程中,碳纤维中非碳元素的存在是石墨片层结构破坏的主要原因,也是表面结构破坏的根源。纤维表面结合力弱的区域容易被破坏,导致表面轴向沟槽增多并加深。采用不同上浆剂对碳纤维进行表面处理,研究了不同上浆剂对碳纤维以及复合材料界面结合强度的影响,结果表明：碳纤维经上浆剂处理后,很好地抑制了纤维的毛丝和断丝现象,而且上浆剂均匀附着于碳纤维表面,使纤维较好分散,有效地避免了纤维之间的粘连。上浆剂的种类对碳纤维复合材料的界面结合强度影响较大。日本生产的上浆剂基本可以改善碳纤维的表面润湿性,提高复合材料的界面结合强度。与进口上浆剂相比,国产上浆剂处理制备的碳纤维复合材料,其界面结合强度偏低,与普通环氧树脂的效果接近。采用FESEM、XPS、LRS和XRD等多种分析技术对不同除胶工艺处理的碳纤维结构及性能进行了研究,结果表明：丙酮浸泡工艺对碳纤维表面上浆剂的去除效果不佳；瞬时高温处理工艺虽然可以达到部分清除上浆剂的效果,但对纤维表面结构产生较大损伤；采用氮气保护下的高温除胶处理工艺,不仅可以有效地去除碳纤维表面上浆剂,而且可以通过工艺参数的合理配置,有效抑制处理过程中碳纤维表面的氧化以及上浆剂裂解产物的残存。通过对比分析确定,氮气保护下的高温除胶工艺是碳纤维表面上浆剂去除的有效方法。以羟基硅油为共聚改性剂对酚醛树脂基体进行改性,系统研究了基体改性对碳纤维复合材料界面结合强度及力学性能的影响,结果表明：随着羟基硅油添加量的增加,碳纤维复合材料的界面结合强度呈现先增大后减小的变化趋势,材料的弯曲强度逐渐增大,拉伸强度的变化趋势与界面结合强度的变化趋势基本一致。羟基硅油添加量不当会导致基体缺陷增加,使得复合材料界面结合性能变差,影响材料整体性能的发挥。当羟基硅油与酚醛树脂的质量百分比为2.5%时,碳纤维增强树脂基复合材料的界面结合强度最高,同时材料的拉伸强度和弯曲强度也得到改善。基体改性对复合材料界面结合强度的改善效果不如碳纤维表面改性对其效果提高明显。适当的原料配比以及合理的制备工艺是减少碳纤维复合材料内部缺陷以及改善复合材料性能的关键因素。更多还原

【Abstract】 The interface between carbon fibers and matrix is a main component of the composite. Good adhesion is a precondition for stress transfer in carbon fiber reinforced resin composites and is helpful to effectively improve the mechanical properties of composites. On the investigation of interface, it is the key to enhance interfacial bonding strength. Therefore, it is important to comprehensively understand the effect of various factors on the interfacial bonding strength of composites. In this paper several technologies, such as scanning electron microscopy （SEM）, X-ray photoelectron spectroscopy （XPS）, Laser Raman spectroscopy （LRS）, X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR） and some mechanical properties tests were used to investigate the effect of different preparation technologies on the properties and structures of carbon fibers, discuss the process of electrochemical treatment of wet-spinning PAN-based carbon fibers and the evolution of surface property and structure during electrochemical treatment systemically, grope reasonable surface desizing technology of carbon fibers, study the effect of electrochemical treatment of carbon fibers, surface sizing agent and matrix modification on the interfacial bonding strength of carbon fiber reinforced resin composites, put forward electrochemical treatment mechanism of carbon fibers and matrix modification mechanism.Analysis of properties and structures of carbon fibers with different preparation technologies show that compared with carbon fibers prepared by wet-spinning process, the compactness of carbon fibers prepared by dry-jet wet spinning process is higher and the axial pore size is smaller, while the content of non-carbon elements on the surface of carbon fibers is lower. From X-ray diffraction, the structural parameters of both carbon fibers vary. For carbon fiber prepared by dry-jet wet-spinning process, its interlayer spacing d₀₀₂ is smaller than that prepared by wet-spinning process. The crystallite size Lc and La are larger and stacked layers of graphite lamella increases. The results show that carbon fiber prepared by dry-jet wet-spinning process has a higher degree of graphite and more integrated structure. The surface micro-structure of both carbon fibers is almost the same, while there is a big difference in surface morphology. The surface of carbon fibers prepared by wet-spinning process is rough and possesses many axial grooves, which are beneficial to increase the mechanical hinge effect between carbon fibers and resin matrix and improve the interfacial bonding strength of composites, while the surface of carbon fibers prepared by dry-jet wet-spinning process is smooth. In addition, clean production environment and fine processing equipment are beneficial to the reduction of carbon fiber surface defects.The surface properties of wet-spinning PAN-based carbon fibers was investigated with the treatment technologies by XPS during electrochemical treatment. The results indicate that the effect is obvious at early stage. However, the trend of surface treatment effect become gently forward. Higher electrolyte concentration, higher electrolyte temperature, longer treatment time and larger current density are helpful to the electrochemical treatment. Experimental determination is that NH4H2PO4 is the most suitable electrolyte for electrochemical treatment of carbon fibers.LRS was used to study on the surface structure change of wet-spinning PAN-based carbon fibers during electrochemical treatment. And the characteristics of first-order Raman spectra of carbon fibers with different treatment time were investigated. The results indicate that the peak separation between D band and G band increases in the first-order Raman spectra after electrochemical treatment, so does R value and ratio of D3 band and G band, while the ratio of D2 band and G band decreases. R value gradually increases with the treatment time, while the variation trends of the ratio of D2 band and G band and the ratio of D3 band and G band are not obvious. The ratio of all the disordered structure and G band increases continuously, and its change trend is consistent with that of R value, which can be used to comprehensively explain the variation of the surface disordered structure of carbon fibers. So the change rules of the structure of carbon fibers can be investigated by laser Raman spectroscopy during electrochemical treatment.The carbon fibers electrochemically treated in 1mol/L NH4H2PO4, for 4 mininutes, and high current density.were investigated. The results show that after electrochemical treatment specific surface area enlarges, surface roughness increases while oxygen content and oxygen-containing functional groups increase. These factors can improve the surface polarity and increase wettability of resin matrix. More oxygen-containing functional groups are helpful to enhance chemical action between carbon fibers and resin matrix to improve interfacial bonding strength of composites, in which the content increase of carbon-oxygen bond plays a main part in improving interfacial bonding strength of composites. The surface micro-structure of carbon fibers is destroyed after electrochemical treatment, the surface disordered degree increases and surface grain size becomes larger.The structures of T700 carbon fibers and graphite fibers after excessive electrochemical treatment were analyzed. The results indicate that electrochemical treatment is a kind of effective method, which has effect on the surface structure and does not destroy bulk structure. Under the same treatment condition, surface striations disappear and surface of T700 become rough along axial direction of carbon fibers. The surface of graphite fibers is almost unchanged. Modification mechanism is analyzed in the way of internal structure of carbon fibers. The existence of surface non-carbon elements is the main reason to destroy the structure of graphite layers, and the region of poor bonding force is easily destroyed to expose more axial grooves on the surface of carbon fibers.Carbon fibers were treated by different sizing agents, the effect of sizing agents on carbon fibers and interfacial bonding strength of composites were investigated. The results show that after sizing the broken filaments decrease. Sizing agents uniformly attach to the surface of carbon fibers. The dispersion property of sized carbon fibers is good to effectively avoid adhesion between carbon fibers. But different sizing agents result in different interfacial bonding strength of composites. Most sizing agents made in Japan can improve the surface wettability of carbon fibers, which is beneficial to improve the interfacial bonding strength of composites. Compared with imported sizing agent, the domestic is poor in improving interfacial bonding of composites, whose effect is close to ordinary epoxy resin.The structures and properties of carbon fibers treated by different desizing technology were investigated by FESEM, XPS, LRS and XRD. The results indicate that the immersion technology in acetone has little action to remove surface sizing agent. The instant high-temperature treatment can melt surface sizing agent, but it also damages the surface micro-structure of carbon fibers. The high-temperature treatment in N2 can effectively remove the surface sizing agent, eliminate the residue of the pyrolytic products of sizing agent and prevent the damage of the carbon fibers surface at high temperature under reasonable technology parameters. In summary, the high-temperature treatment in N2 is most effective to remove the surface sizing agent.Phenolic resin modified by hydroxyl silicone oil was used as matrix to prepare carbon fibers reinforced resin composites. It is found that when the content of hydroxyl silicone oil increases, the interfacial bonding strength of composites firstly increases and then decreases, flexural strength gradually increases and the variation trend of tensile strength is basically identical with that of interfacial bonding strength. Unsuitable addition of hydroxyl silicone oil leads to more defects in matrix and poor interfacial bonding of composites. When the weight percent of hydroxyl silicone oil to phenolic resin is about 2.5%, the interfacial bonding strength of composite is highest, meanwhile tensile strength and flexural strength enhance. But the effect of matrix modification on interfacial bonding strength of composites is inferior to that of carbon fiber treatment. In addition, suitable proportion design of matrix and proper operation in the preparation of carbon fiber composites are key factors to avoid structure defects and improve interfacial bonding strength of composites.更多还原