碳纤维的硝酸氧化及表面的化学分析探讨

分别运用化学衍生法与X光电子能谱(XPS)分析了硝酸氧化前、后的碳纤堆表面所发生的化学变化。结果表明,高模量碳纤维表面化学基团含量要明显低于低模量碳纤维的含量;硝酸氧化对于低模量碳纤维表面改性显著大于高模量碳纤维;硝酸氧化使得碳纤维表面相应羟基含量得以减少,而碳纤维表面羟基含量却有所增加。     

碳纤维的表面处理对其力学性能和结构的影响

通过X射线衍射、扫描电镜、拉曼光谱、X射线电子能谱及电子拉力等分析表明,硝酸、空气中氧化、烧灼等处理可使中强碳纤维的力学性能得到改善.硝酸处理使碳纤维表面产生氧化形成一些活性基团和表面粗化.而空气中氧化、灼烧等处理未能改变碳纤维的表面化学结构.     

碳纤维的性能

PAN基碳纤维作为复合材料中的增强材料应用得最为广泛。这类纤维最主要的特点是各向异性。在低中级模量纤维中,通常沿纤维轴向取向的层状集合较小,而高模量碳纤维通常有较高取向度的表皮。高模量纤维的缺点是强度一般较低。模量的提高可简单地通过层面的取向来完成,而强度的控制却是个复杂问题。 PAN基碳纤维至少分三类:高级、中级和低级模量碳纤维。表5列出了高品化碳纤维的性能和价格。     

碳纤维表面处理

介绍了碳纤维表面气相氧化、液相氧化、阳极氧化、化学涂层、电聚合涂层和冷等离子体等6种处理方法。用冷等离子体方法处理碳纤维表面可提高复合材料层间剪切强度、模量、耐湿热性能及材料的韧性,是目前最有发展前途的处理方法之一。     

碳纤维增强聚合物界面相的研究进展

碳纤维增强聚合物具有重量轻、强度高、模量高、耐高温等优良性能,在国防、航空航天和高端民用产品领域具有广泛的应用前景。本文主要综述了碳纤维增强树脂基复合材料的表面特性,包含碳纤维的表面形貌和粗糙度、碳纤维表面的化学成分等,叙述了碳纤维增强复合材料界面结合强度的表征方法,介绍了碳纤维的表面改性方法,包含氧化处理、等离子体处理及化学气相沉积法等。     

碳纤维表面基团化学分析法探讨

化学分析法是目前应用效果较好的碳素材料表面基团分析法,其缺点是分析误差较大。本法较系统地分析了误差发生的原因。有效地改进了化学分析法,用改进后的方法分析硝酸氧化处理1小时碳纤维表面酸性基团,最大偏差5％,取得了较好的效果。为今后碳纤维表面基团分析提供了可靠的分析方法。     

PAN基高模量碳纤维及其应用现状

高模量碳纤维由于其高模量、尺寸稳定等优势在航空航天等领域有着重要的应用。综述了高温石墨化制备高模量碳纤维的原理,以及石墨化过程中纤维理化性能的变化。同时介绍了高模量碳纤维的主要表面改性方法,以及国内外高模量碳纤维的发展应用情况。     

中间相沥青基碳纤维电化学氧化表面处理的正交优化设计

利用正交法研究了电化学氧化法对中间相沥青基碳纤维表面处理过程中各因素对表面处理效果的影响,获得了优化的表面处理条件。利用傅里叶变换红外光谱扫描、X射线光电子能谱分析等手段,对优化的最佳条件下的表面处理效果进行表征。实验结果表明：采用浓硝酸预处理后,再进行电化学氧化表面处理可使碳纤维复合材料的层间剪切强度（ILSS）进一步提高,可达45.324 MPa,较未经硝酸预处理而直接进行电化学氧化表面处理的碳纤维提高了24.1%,较未表面处理碳纤维提高了49.4%     

PAN原丝改性对碳纤维结构和性能的影响

采用高锰酸钾对 PA N原丝进行化学改性 ,借助扫描显微镜、透射电镜、化学分析等方法 ,对化学改性处理后的纤维形貌、表面及内部结构进行了初步的研究 ,并对化学改性得到的碳纤维力学性能进行了初步探讨。结果表明 :高锰酸钾在预氧化中能降低环化温度 2 0℃左右 ,改性后的碳纤维强度提高了15 %～ 3 0 %、模量提高了 5 %～ 10 %。     

液相氧化对碳纤维表面性能影响的研究

为了提高碳纤维表面的性能,采用丙酮和硝酸及其混合溶液对碳纤维表面进行了处理,然后采用电子扫描显微镜(SEM)对表面处理后的碳纤维进行了表面形态结构分析,采用X射线光电子能谱仪研究了碳纤维经过表面处理后其表面官能团的变化情况.结果表明,丙酮和硝酸混合处理120 min后,碳纤维表面粗糙度最大,且表面的羟基官能团含量达到58.16％,有利于提高碳纤维与热塑性塑料的界面结合力.     

Selective decomposition of isopropanol using as prepared and oxidized graphite nanofibers

Three types of as prepared and treated graphite nanofibers (GNFs) were used as catalysts in the decomposition of isopropanol to propene and acetone in the presence of oxygen to evaluate the surface chemistry of the fibers. As prepared herringbone fibers were found to produce higher selectivity for propene compared to the as prepared platelet and ribbon fibers at all temperatures explored. Herringbone fibers that had undergone oxidative treatment with nitric acid, phosphoric acid, ruthenium tetroxide or potassium permanganate were also evaluated at a 290 °C. Effects of oxidation treatments on fiber structure were evaluated using a host of analytical techniques including BET, SEM/EDS, TGA, XPS, and fluorescence labeling of surface species. Selectivity for acetone dehydrogenation product or propene dehydration product could be achieved by the appropriate surface treatment. Nitric acid was the mildest treatment and the treated fibers showed minimal changes. (Potassium permanganate was a harsh treatment that almost completely degraded fiber structure, creating amorphous carbon.) Phosphoric acid treated fibers were found to produce very high conversions and almost pure selectivity for propene. Ruthenium tetroxide did not appear to have a large affect on fiber morphology; however, selectivity for acetone was much higher when GNFs were treated with ruthenium tetroxide.     

Surface modification and adsorption of eucalyptus wood-based activated carbons: Effects of oxidation treatment, carbon porous structure and activation method

The incorporation of oxygen functional groups onto the surface of eucalyptus activated carbon and its surface chemistry were investigated as a function of oxidation conditions, carbon porous properties and carbon preparation method. Under all treatment conditions of increasing time, temperature and oxidant concentration, liquid oxidation with HNO₃, H₂O₂ and (NH₄)₂S₂O₈ and air oxidation led to the increase of acidic group concentration, with carboxylic acid showing the largest percentage increase and air oxidation at the maximum allowable temperature of 350 °C produced the maximum content of both carboxylic acid and total acidic group. Nitric acid oxidation of chemically activated carbon produced higher total acidic content but a lower amount of carboxylic acid compared to the oxidized carbon from physical activation. The increased contents of acidic groups on oxidized carbons greatly enhanced the adsorption capacity of water vapor and heavy metal ions.     

Morphological aspects of the interface in the PEEK-carbon fiber system

Although high modulus PAN based carbon fibers (HMS) induce transcrystallinity in PEEK and a wide variety of other semi-crystalline polymers, the interfacial strength is lower than PEEK in contact with low modulus carbon fibers (AS4) where transcrystallinity is not induced. In the PEEK/HMS system, crystalline lamellae were found to be oriented edge-on to the fibers, while in AS4 they were oriented flat-on, reflecting the difference in surface energies between the two fibers. The intrinsic effect of transcrystallinity on the fiber matrix interaction is therefore obscured when the chemistry of the interaction varies.     

Influence of surface treatment of carbon fibers on interfacial adhesion strength and mechanical properties of PLA‐based composites

In the present study C/PLA composites with different fiber surface conditions (untreated and with nitric acid oxidation for 4 h and 8 h) were prepared to determine the influence of surface treatment on the interfacial adhesion strength and mechanical properties of the composites. A chemical reaction at the fiber–matrix interfaces was confirmed by XPS studies. Nitric acid treatment was found to improve the amount of oxygen‐containing functional groups (particularly the carboxylic group, —COOH) on carbon fiber surfaces and to increase the surface roughness because of the formation of longitudinal crevices. The treated composites exhibited stronger interface adhesion and better mechanical properties in comparison to their untreated counterparts. There was a greater percentage of improvement in interfacial adhesion strength than in the mechanical properties. The strengthened interfaces and improved mechanical performance have been mainly attributed to the greater extent of the chemical reaction between the PLA matrix and the carbon fibers. The increased surface roughness also has had a slight contribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 367–376, 2001     

Effects of treatment on the surface composition and energy of carbon fibers

The surface composition and energy of carbon fiber has been carefully analyzed and quantified. Untreated, AU, surface-treated, AS, and heat-treated AHT fibers were all studied. AS fiber was surface-treated by an electrolytic oxidation process. AHT fiber was heat-treated at elevated high temperatures under vacuum. X-ray photoelectron spectroscopy (XPS or ESCA) was used to investigate the surface elemental concentration of carbon fibers. The corresponding surface free energies of these fibers were calculated from the contact angles measured by a dynamic contact angle analyzer. Results showed a strong correlation between the surface treatment and heat-treatment history and the surface chemistry of carbon fibers. After oxidation treatment, the surface free energy was increased by adding functional group elements (oxygen and nitrogen). However, these added elements could be removed by high temperature treatment under vacuum. The diffusion of O, N, and Na was discussed. The correlation between oxygen and nitrogen concentration and carbon fiber surface free energy has been plotted. These fibers would be used to quantify the relationship between carbon fiber surface free energy and the interfacial shear strength of the fiber-polymer interface.     

C型炭纤维阳极氧化处理及其增强ABS复合材料的研究

以NH4NO3为电解质,对C型通用级沥青基炭纤维在不同条件下进行阳极氧化表面处理,并通过SEM、力学性能测试等方法考察了纤维及其复合材料的性能,发现经氧化处理后,炭纤维表面粗糙度和含氧官能团如C-O、C=O、COOH等数目明显增大,CF/ABS复合材料的界面粘结性得到有效地改善;复合材料的拉伸强度、弯曲强度及模量有所提高,断裂形式由纤维拔出转变为纤维断裂。     

Carbon phase-graphite oxide composites based on solid state interactions between the components: Importance of surface chemistry and microstructure

Composites of graphite oxide (GO) with commercial activated carbon and with two carbon blacks of different surface areas were built employing solid state interactions between the two phases. The initial materials and their composites were oxidized in air at 350 °C. The samples obtained were characterized from the view point of their porosity, surface chemistry, texture, and electronic properties. The results showed that when the surface of carbonaceous components is rich in surface functional groups and has a high level of amorphicity of the carbon matrix, it chemically interacts with that of GO reducing the surface oxygen groups. It results in an increase in DC conductivity. The composites with carbon blacks are less susceptible to oxidation than a carbon phase itself owing to meager surface chemistry. On the other hand, in the composite with amorphous carbon, the carbon phase underwent the extensive oxidation by the species released from the decomposition of GO surface groups.     

Recycling carbon fiber from composite waste and its reinforcing effect on polyvinylidene fluoride composite: Mechanical,morphology, and interface properties

Recycled carbon fiber (RCF) was reclaimed from thermoset composite waste and employed as reinforcement from 0 to 30 wt% to prepare polyvinylidene fluoride (PVDF)/RCF composite. Commercial virgin carbon fiber (VCF) was used as comparison. The surface morphology, chemistry, and tensile properties of carbon fibers were investigated by Scanning Electron Microscopy (SEM), X‐Ray Photoelectron Spectroscopy (XPS), and tensile test. Results showed that the roughness, O/C ratio and –COO content of RCF surface were significantly improved after recycling. In addition, the single fiber tensile strength and modulus of RCF was lower than that of VCF. The interfacial adhesion between RCF and PVDF was much stronger due to the high chemical activity and roughness over the RCF surface. Mechanical properties of composites were investigated by flexural test, impact test, and Dynamic Mechanical Analysis (DMA). It is found that the PVDF/RCF composite showed higher flexural properties, storage modulus, and lower impact strength, which indicated the strong interfacial adhesion, played an important role in reinforcing. The morphology of fracture further demonstrated the strong interface in PVDF/RCF composite. The fiber length distribution and crystallinity of composites were also evaluated to characterize the composites. The work develops potential for recycling and reuse of carbon fiber, and also expands the application of PVDF based composite. POLYM. COMPOS., 38:2544–2552, 2017. © 2015 Society of Plastics Engineers     

The mechanical and tribological properties of nitric acid‐treated carbon fiber‐reinforced polyoxymethylene composites

The carbon fibers have been exposed to nitric acid oxidation treatments and introduced into polyoxymethylene composites (POM/CF). The nitric acid treatment increases the number of the flaws, roughness of the surface, and disorder of carbon atoms on fiber, as well as introduces reactive functional groups, which could lead to a better mechanical bonding between fiber and the matrix. It is shown that the impact strength and fiber‐matrix adhesion in composites (POM/mCF) are superior to those for POM/CF composites. Simultaneously, the addition of mCF improves flexural strength and modulus relative to virgin POM significantly. Average friction coefficient values of POM/CF composites are lower than that of POM/mCF composites. As the percentage of fiber increases, the trend of wear ratio of the composites goes down initially and bumps up afterwards. The results indicate that the proper contents of CF and mCF in composites range from 5 wt % to 20 wt %. Scanning electron microscopy of worn surface morphology has revealed that the main wear mechanism of the composites were adhesive wear and ploughing wear. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41812.