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表面改性提升碳纤维界面性能中科院宁波材料技术与工程研究所复合材料研究团队日前在碳纤维表面改性方面取得进展。研究人员将氧化石墨烯引入环氧基上浆乳液中,采用浸渍法对碳纤维进行表面改性,可以有效调控碳纤维复合材料的界面微观结构,进而显著改善碳纤维复合材料的界面性能。这一成果为制备高性能碳纤维复合材料提供了一种新的方法和思路。研究结果表明,氧化石墨烯均匀分散在碳纤维表界面层中,改性碳纤维复合材料的界面剪切强度比未上浆和未改性的材料,分别提高了70.9%和36.3%,     

碳纳米材料接枝碳纤维的复合材料界面增效研究进展

界面作为复合材料的重要组成部分,起着传递载荷的作用,影响复合材料的整体性能。碳纤维表面属于石墨乱层结构,微晶有序取向,惰性大,不易与树脂基体结合。对碳纤维进行适当的表面改性,增加纤维的比表面积、粗糙度和引入活性官能团,都能改善表面润湿情况,实现机械结合和化学结合,提高复合材料的界面性能。碳纳米材料接枝到碳纤维表面,是提高界面性能的有效方法之一。因此,对碳纳米管、氧化石墨烯接枝碳纤维的制备方法、界面增效设计以及界面增强机制的国内外研究现状进行综述和分析,在此基础上,展望了碳纳米材料接枝碳纤维表面和界面性能评价方法的研究趋势和前景。     

含碳纳米管上浆剂上浆改性碳纤维及其界面研究

碳纤维(CF)是一种高强度、高模量的高性能纤维,被广泛应用于复合材料中,但是纤维表面的活性官能团含量低,与基体之间的界面结合性能较差。本文利用含氨基化碳纳米管(NH_2-CNTs)上浆剂对光威GQ4922/12K型碳纤维表面进行改性,改善碳纤维与环氧树脂之间的界面结合性能。通过傅里叶红外光谱、扫描电镜、X射线光电子能谱、接触角和微脱粘对改性后的纤维表面组成、表面形貌、表面自由能和界面剪切强度进行分析,发现NH_2-CNTs可成功接枝到碳纤维表面,改性后纤维表面的氧(氮)元素含量增加,与水接触角从67.1°降低到50.5°,表面自由能从32.2 mN/m增加到了41.1 mN/m;界面剪切强度在氨基化碳纳米管质量浓度为0.6%时达到最大,相比未改性纤维从62.3 MPa提高到76.8 MPa,提高了23.3%。结果表明通过在上浆剂中引入氨基化碳纳米管,可以增加碳纤维表面活性,提高碳纤维与基体树脂的界面结合性能。     

碳纤维表面处理和上浆剂的研究进展

复合材料的界面特性与其宏观力学性能密切相关:界面层的厚度和模量决定了界面处应力的传递,界面层的化学组成也会间接影响界面粘结强度,因此研究复合材料界面层组成及性能的影响因素是十分必要的。因此,碳纤维自身的表面物理、化学性质和碳纤维表面涂覆的上浆剂成为了重要考虑因素。本文结合日本东丽关于碳纤维表面处理、上浆剂种类及上浆工艺的专利及其它文献,综述了表面处理方法和上浆剂种类对界面粘结性能的影响。     

碳纤维多尺度增强体的研究进展

介绍了碳纳米管、石墨烯、碳纳米纤维等碳纳米材料修饰的碳纤维多尺度增强体的构筑方法（化学气相沉积法、化学接枝法、电化学沉积法、上浆剂复合法和“grafting to”法）及其对复合材料界面力学性能的影响机理.针对碳纤维多尺度增强体的优势和不足,指出需通过界面设计进一步提高碳纤维与碳纳米材料之间的作用强度,氧化石墨烯/碳纤维复合增强体及其对复合材料性能的增强机制是下一步研究的焦点,连续生产碳纤维多尺度增强体也将成为重要的发展方向.     

碳纤维/环氧复合材料界面优化研究进展

从界面粘合理论、碳纤维表面改性、树脂基体改性等方面对碳纤维/环氧复合材料界面性能的研究进展进行了综述。表明界面对碳纤维/环氧复合材料充分发挥其优异性能起关键作用,其界面优化设计主要从碳纤维表面改性和树脂增韧改性入手,研究已取得一定进展;但亟需在界面作用机理、界面改善处理的工业化生产、纳米材料改性的技术难题等方面期待突破。     

碳纤维/聚醚酮酮界面强度影响因素的研究进展

碳纤维(CF)增强聚醚酮酮(PEKK)复合材料具有强度高、韧性好、工艺简易等优点,已成为一种极具潜力的热塑性复合材料。现有方法制备的复合材料中CF和PEKK的界面黏结强度依然不高,给其实际应用造成了困难。本文对CF/PEKK复合材料研究现状进行总结,通过分析界面结构及性能对应力传递所发挥的作用,归纳影响界面强度的关键因素。其中浸润理论、化学键理论、物理吸附理论可有效用于界面改性的机理分析。而针对CF/PEKK复合材料,可通过调节PEKK分子中的对苯和间苯比例或发展聚醚酮类上浆剂来进一步提高其界面性能。     

环氧树脂上浆剂对PAN基碳纤维性能的影响

分别以KD-213,YD-128环氧树脂、复合环氧树脂及油酸酰胺改性的复合环氧树脂(改性环氧树脂)为主体的上浆剂对聚丙烯腈基碳纤维(PANCF)进行上浆,对上浆纤维的加工性能、表面形貌及其界面剪切强度(IFSS)进行了研究。结果表明:上浆剂改善了PANCF的耐磨性、毛丝量、耐水性及其复合材料的IFSS。其中改性环氧树脂上浆剂为最佳,可在PANCF表面形成一层完整的柔韧性光滑薄膜,上浆后的PANCF的耐磨次数为1887,毛丝量为0.14mg,吸水率小于等于0.005%,复合材料IFSS较未上浆纤维提高38.5%,达87.26GPa。     

自乳化环氧上浆剂对碳纤维复合材料性能影响

以过硫酸铵为催化剂,用不同相对分子质量聚乙二醇(PEG400、800、1000、1500、2000、4000、6000)与氢化双酚A环氧进行加成聚合反应,滴加去离子水制得改性环氧乳液。分别从乳液稳定性、化学结构、耐热性和复合材料表面以及断面形貌和力学性能表征上浆剂乳液及其复合材料性能。结果表明:PEG2000改性环氧乳液上浆剂稳定性与耐温性好,平均粒径0.866μm,经其处理后碳纤维复合材料的力学性能优异,界面结合能力强。     

耐高温PPBES溶液型碳纤维上浆剂的制备及性能

碳纤维增强高性能树脂基复合材料具有质轻、耐腐蚀性、力学强度高等特点,提升树脂与纤维界面强度可以优化复合材料综合性能。利用杂萘联苯聚芳醚树脂所具有的优异溶解性,选择氯仿∶N-甲基吡咯烷酮=2∶8混合溶液作为溶剂,制备耐高温溶液型上浆剂。通过对碳纤维进行上浆操作,在碳纤维表面包覆杂萘联苯聚芳醚砜树脂基团,纤维表面活性增加,当溶液上浆剂质量浓度为1.0%～1.5%时,树脂在碳纤维表面分散性较好,通过对比使用不同上浆剂的碳纤维增强树脂基复合材料的界面性能,使用浓度为1.5%的溶液上浆剂处理后的碳纤维相较于脱浆碳纤维,玻璃化转变温度从未处理的214℃提升至223℃,损耗因子从未处理的0.38下降到0.33,所制备的复合材料弯曲强度提升了12.0%,层间剪切强度提升了11.1%,证明溶液型上浆剂的使用提升了纤维与树脂间的界面性能。综上,溶液型上浆剂的使用能够提升碳纤维的表面活性,进而提升复合材料的弯曲强度、界面剪切强度,且提升效果优于市售常见环氧上浆剂,加工方便,有着广阔的市场应用前景。     

Nanographite-reinforced carbon/carbon composites

Carbon/carbon composites (C/Cs) with nanographite platelets (NGP) filler in a matrix derived from phenolic resin were produced. Different weight concentration (0.5, 1.5, 3, 5 wt.%) NGP were introduced by spraying the NGP during the prepreg formation. The NGP-reinforced C/Cs were characterized for effect of NGP concentration on microstructure, porosity, interlaminar shear strength (ILSS), flexural, ultrasonic and vibration damping behavior. At 1.5 wt.% NGP C/C, the highest values of ILSS observed was 10.5 MPa (increased by 22%), flexure strength of 142.4 MPa (increased by 27%), flexural modulus of 59.2 GPa (increased by 68%) and porosity of 18.8% (reduced by 17.5%) in comparison to neat (without NGP) densified C/C. Ultrasonic testing revealed an average increase of 15% through the thickness Young’s modulus of NGP-C/C; (3.12 GPa at 1.5 wt.% NGP). A 20% average decrease in the damping ratio of the first four modes of vibration was observed in 1.5 wt.% NGP densified C/C. At low concentration (⩽1.5 wt.%) the NGP filled in the pores, cracks and debonded interface but at concentration higher than 1.5 wt.% NGP lost their effectiveness due to agglomeration. The required cycles for desired density/properties are projected to be less compared to neat C/C due to less porosity observed in ⩽1.5 wt.% NGP concentration C/C.     

Pulsed electrodeposition of carbon nanotubes-hydroxyapatite nanocomposites for carbon/carbon composites

Carbon nanotubes-hydroxyapatite (CNTs-HA) composite coatings, which behaved like single composites, were synthesized by a combined method composed of electrophoretic deposition and pulsed electrodeposition. The phase compositions and the microstructure of the composite coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed that the CNTs-HA composite coatings protected the bare carbon/carbon composites from corrosion in simulated body fluid (SBF) solution. The adhesion strength of CNTs-HA composite coating prepared by the combined method is 14.57±1.06 MPa achieved at the CNTs EPD time of 10 min. Compared to the other CNTs-HA composite coatings with different content of CNTs, the CNT-HA composite coating with the electrophoretic deposition of 10 min showed the best corrosion resistance. The morphology of CNTs-HA composite coatings immersed in SBF solution rendered the formation of HA crystallites. In addition, in vitro cellular responses to the CNTs-HA composite coatings were assessed to investigate the proliferation and morphology of mouse cells 3T3 cell line.     

Single-walled carbon nanotube buckypaper and mesophase pitch carbon/carbon composites

Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.     

Kinetics of pyrolytic carbon infiltration for the preparation of ceramic/carbon and carbon/carbon composites

Carbon/carbon and zeolite/carbon composites have been prepared by pyrolytic carbon infiltration of organic and inorganic substrates with different porous structures. The chemical vapour infiltration kinetics of these substrates has been studied in a thermogravimetric system at atmospheric pressure, using benzene as pyrolytic carbon precursor. The rate of pyrolytic carbon infiltration seems to depend on the porosity of the substrate available to the pyrolytic carbon precursor, irrespective of the nature of the substrate studied. Activation energy values of about 180 kJ/mol were found for the different substrates used in the temperature range of 700-800 °C, where the cracking reaction of benzene takes place, predominantly, in a heterogeneous form. At higher temperatures homogeneous reactions compete with heterogeneous ones and higher values of activation energies (280-380 kJ/mol) were obtained. The oxidation of the pyrolytic carbon deposited on the different substrates studied takes place in the same range of temperature, which suggests the presence of a similar pyrolytic carbon structure on substrates of different nature or a similar accessibility to the deposited layer.     

Mechanical behavior of two-dimensional carbon/carbon composites with interfacial carbon layers

Effect of interfacial carbon layers on the mechanical properties and fracture behavior of two-dimensional carbon fiber fabrics reinforced carbon matrix composites were investigated. Phenolic resin reinforced with two-dimensional plain woven carbon fiber fabrics was used as starting materials for carbon/carbon composites and was prepared using vacuum bag hot pressing technique. In order to study the effect of interfacial bonding, a carbon layer was applied to the carbon fabrics in advance. The carbon layers were prepared using petroleum pitch with different concentrations as precursors. The experimental results indicate that the carbon/carbon composites with interfacial carbon layers possess higher fracture energy than that without carbon layers after carbonization at 1000°C. For a pitch concentration of 0.15 g/ml, the carbon/carbon composites have both higher flexural strength and fracture energy than composites without carbon layers. Both flexural strength and fracture energy increased for composites with and without carbon layers after graphitization. The amount of increase in fracture energy was more significant for composites with interfacial carbon layers. Results indicate that a suitable pitch concentration should be used in order to tailor the mechanical behavior of carbon/carbon composites with interfacial carbon layers.     

Porous carbon/carbon composites produced from carbon black and petroleum pitch

Granular porous carbon/carbon composites were prepared by mixing carbon black, petroleum pitch and a solvent, followed by granulating the mixture and carbonization of the resulting pellets in an inert atmosphere. The pore structure of this material is studied by mercury porosimetry and scanning electron microscopy. Based on the obtained results, a model for it is proposed. The effects of carbon black type used, filler/binder ratio, heat treatment temperature and mixing time on surface area, total pore volume and strength of the finished pellets were investigated. Comparison with activated carbons indicates that the investigated material can find industrial applications as a catalyst support and as an adsorbent for adsorption of large molecules due to the meso- and macroporous structure and low ash content.     

Friction behaviors of carbon/carbon composites with different pyrolytic carbon textures

Friction and wear properties of carbon/carbon (C/C) composites with a smooth laminar (SL), a medium textured rough laminar (RL) and a high textured RL pyrolytic carbon texture were investigated with a home-made laboratory scale dynamometer to simulate airplane normal landing (NL), over landing (OL) and rejected take-off (RTO) conditions. The morphology of worn surfaces at different braking levels was observed with scanning electron microscopy. The results show that C/C composites with RL have nearly constant friction coefficients, stable friction curves and proper wear loss at different braking levels, while friction coefficients of C/C composites with SL pyrolytic carbon decrease intensely and their oxidation losses increase greatly under OL and RTO conditions. Therefore, C/C composites with a high and medium textured RL pyrolytic carbon may satisfy the requirements of aircraft brakes. The good friction and wear properties of C/C composites with RL are due to the properties of RL, which leads to a uniform friction film forming on the friction surface.     

Microstructure of carbon/carbon composites reinforced with pitch-based ribbon-shape carbon fibers

Carbon/carbon composites were prepared with ribbon-shape pitch-based carbon fibers serving as reinforcement and thermosetting PFA resin and thermoplastic pitch as matrix precursors. The composites were heat treated to 1000, 1600 and 2700 °C. Microstructural transformations taking place in the reinforcement, carbon matrix, and the interface were studied using polarized optical and scanning electron microscopy. The fiber/matrix bond and ordering of the carbon matrix in heat-treated composites was found to vary depending on the heat treatment temperature of the fibers. Stabilized fiber cleaved during carbonization of resin-derived composites. In contrast, fibers retain their shape during carbonization of pitch matrix composites. Optical activity was observed in composites made with carbonized fibers; the extent decreases with increased heat treatment of the fibers. Studies at various heat treatment temperatures indicate that ribbon-shape fibers developed ordered structure at 1600 °C when co-carbonized with thermosetting resin or thermoplastic pitches.     

Sharp indentation behavior of carbon/carbon composites and varieties of carbon

Sharp indentation tests on carbon fiber and carbon matrix composites (C/C composite) were carried out over a wide load range from 0 to 2 N on three different cross sections: normal, parallel and inclined to the fiber axis. For comparison purposes, a variety of carbons including HOPG, glassy C, and pyrocarbon films was also examined. Both the fibers and the matrices displayed first a purely elastic response and second crack-induced damage. A purely elastic behavior was also observed with most of the varieties of carbon considered. Young’s modulus was extracted from the indentation curves either at maximum or at various forces, using the Sneddon equation of elastic response on loading (elastic indentation) or a classical equation based on elastic recovery on unloading (elastoplastic indentation). Results are discussed with respect to features of structure and heterogeneity of material in the stressed volume.