Prepardtion And Properties Of Multi-Walled Carbon Nanotube/Polyamide66Composites

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.