【作者】 邱丽；

【导师】 刘旭光；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2013， 博士

【摘要】 随着人们对能源消耗问题的关注,对摩擦和磨损方面的研究越来越重视。高分子聚合物摩擦材料,因其具有强度/质量比高、制造工艺简单以及优异的化学稳定性和摩擦学特性,可以明显减轻材料重量,降低材料的磨损,被广泛应用于航空、航天、化工、纺织、机械、仪器仪表、汽车及医学等领域。尼龙66作为一种典型工程塑料,具有很高的机械强度,耐热性,磨擦系数低,耐磨损,自润滑性,吸震性,耐油,耐弱酸、弱碱,电绝缘性好；而且在较高温度也能保持较高的强度和刚度,特别是耐热性和耐油性好,适合制造汽车发动机周边部件和容易受热的部件。为了提高尼龙66作为齿轮、轴承等材料的耐磨性。本论文在多壁碳纳米管(MWCNTs)表面改性的基础上,采用熔融共混法制备了一系列MWCNTs/尼龙66复合材料,研究了MWCNTs的修饰改性和胺化碳纳米管(D-MWCNTs)含量对复合材料的加工流变性和产物分散性的影响,通过对复合材料结晶性能和力学性能的研究,得到MWCNTs的修饰方法和D-MWCNTs含量对复合材料摩擦性能的影响。具体研究结果如下：(1) MWCNTs的表面改性。通过对MWCNTs进行酸化和胺化处理,分别在MWCNTs表面接枝了羧基、羟基、羰基,以及胺基官能团。确定了最佳混酸处理和胺化修饰改性条件,制备了分散均匀、表面含有胺基官能团的MWCNTs。(2) MWCNTs/尼龙66复合材料的制备。通过转矩流变仪制备了一系列MWCNTs/尼龙66复合材料,研究显示,MWCNTs的胺化处理,改善了MWCNTs与尼龙66之间的相容性,提高了MWCNTs在尼龙66基体中的分散性。确定了最佳复合材料制备过程的工艺参数。(3MWCNTs/尼龙66复合材料的结晶性能和热性能。研究了MWCNTs修饰方法和D-MWCNTs含量对尼龙66非等温结晶熔融行为、结晶结构及热稳定性的影响。1)由于D-MWCNTs的诱导作用,添加D-MWCNTs复合材料的熔融焓增大。随着D-MWCNTs含量的增加,复合材料的熔融温度降低,结晶峰值温度增加,熔融焓呈现先增大后减小的趋势。2)MWCNTs/尼龙66复合材料非等温结晶动力学研究证明,D-MWCNTs的添加阻碍了尼龙66分子链运动,使尼龙66在较高温度下开始结晶,结晶增长变缓,复合材料的结晶速率减小,改变了尼龙66的成核和生长机理,改变了复合材料的结晶和增长过程。3) MWCNTs/尼龙66复合材料结晶结构研究表明,D-MWCNTs的添加,改善了MWCNTs与尼龙66的相容性,减弱了MWCNTs对复合材料结晶结构的影响；当D-MWCNTs含量为2.5wt%时,对复合材料结晶结构的影响最小。4) MWCNTs/尼龙66复合材料的热稳定性研究表明,在惰性气氛下,MWCNTs没有改变复合材料的降解趋势,随着D-MWCNTs含量的增加,复合材料的最终热分解温度增加,热稳定提高；最终失重率相应增加,且与预混质量相当,说明改性MWCNTs在尼龙66基体中分布均匀。(4) MWCNTs/尼龙66复合材料的力学和摩擦性能。重点研究了尼龙66和MWCNTs/尼龙66复合材料的力学性能及干态、非润滑、反共形接触摩擦磨损性能,分析了MWCNTs对复合材料摩擦磨损机理的影响,并利用纳米压痕仪分析了摩擦前后复合材料的微观性能的变化。1)当MWCNTs含量相同时,酸化碳纳米管(A-MWCNTs)和D-MWCNTs的添加,使复合材料的拉伸强度和弹性模量增加,同时,由于MWCNTs具有刚性,导致所有材料的断裂伸长率较纯尼龙66明显下降；随着D-MWCNTs含量的增加,复合材料的拉伸强度和弹性模量都呈现先增加后减小的趋势,当其含量为2.5wt%时,达到最大值。2)当MWCNTs含量相同时,在稳定摩擦阶段,MWCNTs的表面改性有效降低了复合材料的摩擦系数和磨损率；当D-MWCNTs含量为2.5wt%时,摩擦系数最小,磨损率最低。3)当MWCNTs含量相同时,由于D-MWCNTs与尼龙66基体之间存在良好的界面相容性,仅在D-MWCNTs/尼龙66复合材料的磨损表面形成了转移膜,其余材料表面都产生了微裂纹；当D-MWCNTs含量增加至5wt%时,复合材料表面的转移膜消失,微裂纹再次出现,说明当MWCNTs含量过多时,导致MWCNTs在尼龙66基体中团聚,使复合材料性能下降。4)当MWCNTs含量相同时,摩擦使尼龙66的硬度和模量明显增加,而D-MWCNTs/尼龙66复合材料的最大压痕深度、硬度和弹性模量在摩擦前后没有明显变化；在摩擦前后,D-MWCNTs含量不改变复合材料的性能。更多还原

【Abstract】 More and more attentions have been paid to the studies of friction and wear, as the problems of energy consumption are causing ever increasing concern. Owing to the high strength/weight ratio of polymer materials, the application of these materials can significantly reduce the total weight of machinery components and effectively prevent the wear and tear of the mechanical parts. Other advantages, such as simple manufacturing process, excellent chemical stability and tribological properties, also make polymer materials the popular candidates in aviation, aerospace, chemical, textile, machinery, instrumentation, automotive, medicaland many other industries. PA66, as a popular engineering plastics, has high mechanical strength, heat resistance, excellent wear resistance and self-lubrication properties, good shock absorption, good resistance to oil, weak acid, weak alkali and outstanding electrical insulation property. It also is capable of maintaining strong strength and stiffness at high temperature. Furthermore, its fantastic resistance to heat and oil makes it particularly suitable to be used as the material in manufacturing automobile engine parts which often operate in high temperature environment.In order to improve the abrasive resistance performance of PA66as gears, bearings and other engineering materials, a series of MWCNTs/PA66composite materials were prepared using melt blending process on the basis of the practice of surface modification of PA66by MWCNT. The effected of the modification of MWCNTs and content of aminated MWCNTs (D-MWCNTs) on the rheological property of the composite and the additive dispersibility were investigated. Based on the study on crystallization properties and mechanical properties of the composites, the frictional performance of the composites with differently modified MWCNTs and different content of D-MWCNTs was discussed. The main conclusions are listed as follows:(1) The surface modification of MWCNTs. Through acidification and amination of MWCNTs, carboxyl, hydroxyl, carbonyl, and amino functional groups were attached onto the surface of MWCNTs. The optimum modification conditions were determined, uniform dispersion of MWCNTs modified with amino functional groups was achieved.(2) MWCNTs/PA66composite preparation. A series of MWCNTs/PA66composites were prepared using torque rheometer. D-MWCNTs greatly improved the compatibility between MWCNTs and PA66and therefore enhanced the dispersion of MWCNTs in PA66matrix. The optimum technology parameters for the composite preparation process were determined.(3) The crystal properties and thermal performance of MWCNTs/PA66composite. The effects of surface modification method of MWCNTs and the effects of D-MWCNTs content on the PA66non-isothermal melting crystallization behavior, crystalline structure and thermal stability were investigated.1) Owing to the entrainment effect of D-MWCNTs, the melting enthalpy of the composites was increased by the addition of MWCNTs. With the increase of D-MWCNTs content, the melting temperature of the composites reduced and the crystallization peak temperature increased; the melting enthalpy firstly increased to a maximum and then decreased with the increase of D-MWCNTs content.2) The non-isothermal crystallization kinetics of the MWCNTs/PA66 composites demonstrates that by adding D-MWCNTs chain motion of PA66was hindered, so that PA66started crystallization at higher temperature, and the crystallization growth became slow, the crystallization rate decreased. The nucleation and growth mechanism of PA66were changed, as well as the crystallization and the growth process of the composites.3) The research on the crystalline structure of MWCNTs/PA66composites shows that:surface modification of MWCNTs to D-MWCNTs improved the compatibility of the additive with PA66and weakened the influence of MWCNTs on the crystalline structure of composites. When D-MWCNTs content was2.5wt%, the influence on crystalline structure of the composite materials was the smallest.4) TG analysis of MWCNTs/PA66composites shows that under inert atmosphere MWCNTs did not change the degradation trend of composites. With the increase of D-MWCNTs content, the final decomposition temperature of composites increased, the thermal stability was improved; the final weightlessness of composites increased, while with the increase of D-MWCNTs amount, the final residue and matched well with the expected percentage, which suggests that modified MWCNTs mixed well with PA66matrix.(4) The mechanical properties and frictional performance of MWCNTs/PA66composites. Research was mainly focused on the mechanical properties of PA66and MWCNTs/PA66composites and friction and wear properties of the composites at dry, unlubricated and anti-conformal contact condition. The influence mechanism of MWCNTs on friction and wear mechanism of the composite materials was discussed. Nano indentation was employed to analyse the changes of micro mechanical properties of the composite in the friction tests.1) When the additives with the same content were employed, acidification-and amination-modified MWCNTs increased tensile strength and elastic modulus of the composites. At the same time, owing to the rigidness of MWCNTs, all the elongation at break of the composites was markedly reduced compared with pure PA66. With the increase of the addition content of D-MWCNTs, tensile strength and elastic modulus showed a trend of decrease after the initial increase. Tensile strength and elastic modulus reached the maximum at2.5wt%addition content.2) With the identical addition content of D-MWCNTs, reduction on the friction coefficient and wear rate of the composite at the stable friction stage was observed for the surface-modified MWCNTs. The lowest friction coefficient and wear rate were achieved when2.5wt%D-MWCNTs was added in the composite.3) When the MWCNTs content was constant, as a result of the good interfacial compatibility of D-MWCNTs with PA66matrix, the formation of a transfer film was only found on wear surfaces of the MWCNTs/PA66composite, micro cracks were observed on the surface of the rest of the materials; When D-MWCNTs content further increased to5wt%, transfer film on the surface of the composite disappeared and was replaced by the micro cracks. It suggests that when the MWCNTs content was too much, the agglomeration of MWCNTs in PA66occurred and the degradation of the material performances was resalted.4) When the MWCNTs content was constant, the hardness and modulus of PA66were significantly increased after friction test. While, no considerable change in maximum indentation depth, hardness and elastic modulus were found in the D-MWCNTs/PA66composite after the friction test. D-MWCNTs content did not change the performance of the composite either before or after the friction test.更多还原