【作者】 徐志伟；

【导师】 黄玉东；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2007， 博士

【摘要】 本文研究了碳纤维的截面形状由圆形变为腰形后,纤维表面、复合材料界面及纤维在复合材料中分布的变化。采用高效、节能和便捷的γ射线辐照接枝技术对腰形截面碳纤维进行改性,分析研究了γ射线辐照对腰形纤维表面物理化学性能、复合材料界面性能和纤维本体结构的影响。采用X射线光电子能谱(XPS)、扫描电子显微镜(SEM)和表面能测试对腰形和圆形截面碳纤维表面进行研究。结果表明,腰形截面碳纤维的表面能及其非极性分量高于圆形截面碳纤维,二者的截面不同,表面元素组成相同。BET吸附测试则发现,腰形截面碳纤维的比表面积和表面孔径明显高于圆形截面碳纤维,结果前者对环氧树脂和酚醛树脂的浸润性也略高于后者。由XRD分析可知两种纤维的石墨化程度基本相同。使用层间剪切强度(ILSS)和界面剪切强度(IFSS)评价复合材料界面性能,腰形纤维环氧复合材料的界面粘接性能优于圆形截面纤维,前者的IFSS比后者高33%。腰形纤维复合材料的拉伸、压缩和弯曲强度也略高于圆形纤维复合材料。通过SEM和金相显微镜研究了复合材料的断口形貌和横断面,结果发现:腰形纤维的凹面与树脂基体之间相互嵌合形成了“锚钉”效应,腰形截面碳纤维凸凹面相扣的抱团现象使纤维和树脂基体的界面不易受到破坏,腰形截面碳纤维凹面与凹面相对的现象则不利于树脂对纤维的浸润,腰形截面碳纤维在复合材料中的分布均匀性差。通过实验,确定了腰形截面碳纤维合适的辐照接枝剂量为300kGy,辐照剂量率为6kGy/h。选定环氧树脂/丙酮溶液共辐照、环氧氯丙烷共辐照和丙烯酸预辐照为主要研究对象。实验还发现硝酸镨溶液的共辐照处理对腰形纤维的表面改性也颇为明显。SEM和原子力显微镜(AFM)分析发现,共辐照和预辐照处理后纤维表面的沟槽更清晰,纤维表面分布着一些不均匀的粘附物。采用XPS元素分析后发现,纤维表面O/C升高,羧基和羰基官能团明显增加,纤维表面未形成接枝层。辐照处理后纤维表面能增加。尝试采用热重分析(TGA)的方法研究吸附树脂后的碳纤维热分解性能,以分析纤维辐照处理前后对树脂的吸附性,结果发现除空气中辐照处理外,其它辐照处理方法都不同程度的提高了纤维对树脂的吸附能力。采用复合材料的ILSS评价各种辐照接枝改性的效果,丙烯酸的预辐照效果优于共辐照,环氧氯丙烷的共辐照效果略好于预辐照,环氧树脂丙酮溶液共辐照的改性效果最明显,环氧复合材料的ILSS提高了20.2%。γ射线辐照接枝达到了等离子体的处理效果,并高于涂层和超声处理。通过SEM分析还发现,辐照处理后复合材料破坏断面粘附了大量的树脂,纤维和树脂基体间“锚钉”效应明显。根据电子顺磁共振谱(ESR)测试结果,推断纤维与辐照介质之间发生了自由基接枝反应,并探讨了接枝过程和复合材料界面改善机理。为研究γ射线辐照对腰形纤维本体各部分结构变化的影响,采用XRD和Raman光谱对腰形纤维、石墨粉和无定型碳粉进行结构分析。结果表明,随着辐照剂量的增加,纤维的(002)晶面间距逐渐减小,趋向于理想石墨的晶面间距,在2000kGy辐照剂量下d002的最大变化可达0.066nm,纤维表层石墨微晶尺寸La则随吸收剂量则先增加后减小。辐照处理后石墨(002)晶面间距变小,石墨化程度提高,无定型碳粉结构则并未发生变化仍以无定型碳的形式存在。采用浮沉法测试纤维密度,随着辐照剂量的增加,碳纤维的密度先增加而后逐渐稳定下来。分别使用碳纤维复丝和单丝测试,并使用双参数Weibull模型评价纤维力学性能的变化,实验表明腰形纤维的抗拉强度随辐照剂量的增加先增加后减小,辐照剂量超过1000kGy时抗拉强度低于未处理纤维。杨氏模量随着辐照剂量的增加持续升高,但增加幅度逐渐减小。辐照处理后纤维的均匀性和稳定性被提高。检验了腰形纤维改性效果的时效性,退化实验表明纤维表面改性的退化效应与纤维的存放方式有关,而纤维的力学性能不存在退化效应。更多还原

【Abstract】 A study on the surface characteristics of kidney sectional carbon fiber (CF), interfacial properties of kidney CF/epoxy composites and distribution of kidney CF in composites was carried out. Besides, the highly efficient, energy-saving and convenientγ-ray irradiation technique was employed to activate kidney section CF surface, improve the interface adhesion of composites and optimize the structure of CF.The surface physicochemical properties of kidney and circular section CF were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and surface energy analysis. The results indicated that the kidney section CF outperformed the circular section CF in surface energy and its non-polar component. The two kinds of fibers had the same element composition, but the different cross-section shape. The Brunauer-Emmett-Teller (BET) adsorption tests showed that the kidney sectional CF had a larger specific surface area than the circular CF. Thus the former had the slightly better wettability with epoxy and phenolic resin. It was found that the graphitization degree of kidney CF was the same as that of circular CF by X-ray diffraction (XRD) analysis.According to the interlaminar shear strength (ILSS) and interface shear strength (IFSS) tests, the interfacial properties of composites were evaluated. The interfacial adhesion of kidney CF/epoxy was better than that of circular CF/epoxy and the IFSS of kidney CF/epoxy was 33% greater than that of circular CF/epoxy. The kidney CF/epoxy composites perform shortly better than circular CF/epoxy composites in tensile, flexural and compressive strength. The fracture topography of composites showed that the concave of kidney CF had a good adhesive interface with matrix and the adhesive joint looks like the mechanical anchor. The concave and convex of kidney CF mutually embraces with each other in composites, which results in the firm interface between fiber and matrix. Besides the concave of kidney CF can also embrace with each other in composites, which did harm to the interface adhesion of composites because of weak wetting with resin. It was shown that the kidney CF distributed more non-uniformly than the circular CF in composites via metallographic microscope.The irradiation dose of 300kGy and irradiation dose rate of 6kGy/h of kidney CF were determined by the optimizing experiments. Epoxy/acetone solution mutual irradiation, chloroepoxy mutual irradiation and acrylic acid pre-irradiation were selected as the representatives. Furthermore, the mutual irradiation of kidney CF in rare earth solution was found to be efficient. By the SEM and atomic force microscopy (AFM) characterization, it was found that the grooves of the irradiated fiber surface became wider and deeper compared with the original CF and more pieces of tiny fragments stuck to the fiber surface. Both the O/C rate and the amount of carboxyl and carbonyl groups were increased. The grafted layer was not formed on the fiber surface. The surface energy of kidney CF was increased after irradiation. Thermogravimetric analysis (TGA) was used to investigate the adsorption of kidney CF in resin. The results showed that the irradiation by the other methods improved the adsorption ability of kidney CF in epoxy resin, except irradiation in air.ILSS of CF/epoxy composites was selected as the evaluation criterion of various modification methods. It was shown that pre-irradiation treatment had the advantage of mutual irradiation for acrylic acid, mutual irradiation exceeded marginally pre-irradiation for chloroepoxy and ILSS value of epoxy mutual irradiated CF/epoxy reacheed the maximum with 20.2% improvement. Gamma ray irradiation grafting achieves the same effectiveness as plasma treatment and moreover performs better than coating and ultrasonic treatments. It was observed that the more resin stuck on the fiber surface in fracture surface of composites after irradiation treatment of CF and the“mechanical anchor”existed between matrix and irradiated fiber by SEM images. The results of electron spin resonance (ESR) showed that CF may graft with irradiation media by free radical mechanisms. The mechanisms of composite interface improvement were explored after irradiation grafting.To study the change of different structures in CF, Raman spectra was used to investigate the irradiated CF and XRD was employed to analyze CF, turbulent carbon and graphite. It was found that the interlayer space (d002) of CF decreases and the graphite degree of CF increases with the irradiation dose. The interlayer space of kidney section CF decreased with the maximum of 0.066nm after irradiation at 2000kGy. The size (La) of graphite microcrystallite was increased at low dose and decreased at high dose. For the graphite, the interlayer space (d002) was reduced and the graphite degree was improved after irradiation. However, the structure of turbulent carbon was not influenced byγ-ray irradiation.The density of kidney sectional CF was determined by the sink-float method. The density of CF was enhanced at the low dose and trend to stabilize at the high dose. The bundle and filament tests of CF and Weibull distribution function were applied to evaluate the mechanical performance. It was indicated that CF tensile strength was enhanced in the range of 0~300kGy and reduced with the increasing absorbed dose when the dose exceeded 300kGy. The Young’s modulus was increased and the cracking specific elongation was decreased as the dose increases at the range of 0~2000kGy. The uniformity and reliability of kidney CF was improved by irradiation treatment. The degradation experiments showed that the degradation of surface modification was decided by the storage conditions of CF and there was not the degradation of mechanical performance of kidney CF as the time flies.更多还原