| Engineering plastics shows the predominant advantages of light-weight, erosion-resistance and easy-to-molding for the extensive application in the mechanical and electronical fields. However, in order to meet the requirement of special applications, it become the key problems needing to be solved on how to ehance the mechanical and triboligical properties of engineering plastics. In this thesis, the carbon fiber (CF) has been used to modify nylon6(PA6) plastics in order to improve the mechanical and triboligical performances, and especially the effects of the CF length, other fillers and other polymers as the component of matrix on the PA6/CF copomsites were also investigated. The main work in this thesis is depicted as follows:(1) The CFs with two different lengths have been used to reinforce the PA6plastics. The strength, stiffness and hardness of the composites filled with longer CF (SCF) were simultaneously enhanced by117%,422%and17%, respectively, while the composites filled with shorter CF (CFP) showed a signnificant increase in toughness by2.43fold over that of the PA6plastics. However, the addition of CF resulted in the decrease of friction stability and the friction coefficient of the PA6/CF composites located in the range of0.21～0.24under the load f20N and the sliding speed of2000rpm. On the other hand, the wear resistance of the composites containing SCF was enhanced. Especially, when the loading-level of SCF was20wt%, the resultant composites showed the best performance of wear resistance, and the wear rate was measured as4.36x10-5mm3/Nm under the load of20N and the sliding speed of2000rpm. At the same time, the addition of CFP resulted in lower wear resistance. The SEM observation showed that the wear mechanism of the composites containing SCF and CFP were adhesive wear and abrasive wear, respectively. The wearing degree of the former decreased with an increase of the SCF content, but the wearing degree of the latter argumented with an increase of the CFP content. With an increase in the load, the sliding speed and the working temperature, the friction coefficient of the PA6/CF composites decressed together with the increase of wear rate. SCF showed better wear performances. Overall, the enhancement of SCF on the mechanical and tribological properties of the PA6/CF composites was better than that of CFP, and especially the composites filled with SCF had the predominant wear performances under high load, high sliding speed and high temperature.(2) For the PA6/SCF composites, the simultaneous addition of graphite (Gr) and CFP resulted in the further enhancement of strength, modulus, toughness and plasticity, while the CFP-filled PA6/SCF composites just shown slightly improvement on the toughness. However, the friction stability decreased together with the increase of friction coefficient. On the other hand, it is worth of note that the wear rate decreased slightly. At the same time, in contrast with the CFP-filled PA6/SCF composites, the Gr-filled PA6/SCF composites exhibited higher friction stability and lower friction coefficient and wear rate, with the friction coefficient of0.22-0.24and wear rate of4.35～5.75x10-5mm3/Nm at the condition of2000rpm and20N. With an increase of the load, the sliding speed and the working temperature, the friction coefficient slightly decreased and the wear rate significantly increased for the PA6/SCF composites modfied with CFP and Gr. The SEM observation showed that the further addition of CFP resulted in the transformtion from adhesive to abrasive wear for the reultant composites while the further addition of Gr did not interfere with the adhesive mechanism of the PA6/SCF composites. In conclusion, the Gr showed more predominant effects of enhancing mechanical and tribological performances than CFP.(3) To regulate the mechanical performances of the shorter PA6/CFP composites, other polymer was introduced as the component of matrix. The addition of polyphenylene sulfide (PPS) resulted in the enhancement of strength, rigidity and hardness for the PA6/CFP composites while the thermoplastic polyurethane (TPU) significantly improved the toughness of PA6/CFP composites. Although the friction stability of the PA6/PPS-CFP composites was poorer than that of the PA6/TPU-CFP composites, the PA6/PPS-CFP composites showed the predominant ability of wear-resistance. As a result, the enhancement of rigidity and hardness contributed to the wear-resistance. With an increase of load and sliding speed, both the friction coefficient and wear-resistance of the PPS-and TPU-modified PA6/CFP composites decreased. At this time, the modification of TPU contributed to low friction coefficient and high wear-resistance. The SEM observation of the wearing surface showed that the wear mechanisms of the PPS-and TPU-modified PA6/CFP composites were mainly assigned to adhesive wear and abrasive wear, respectively.(4) Based on the effects of other filler and other polymer as the component of matrix on the PA6/CF composites, it can be concluded that the simultaneous addition of Gr and SCF contributed to better function of wear-resistance and resulted in the decrease of wear rate by30%, and the resultant composites exhibited the best tribological performances among all the composites in this thesis, including the only SCF-filler composite and the PPS-and TPU-modified PA6/CFP composites.(5) The effects of composit modification on the performances were investigated, and hence the relationships between mechnical and tribologiical properties were estabilished. The results suggested that the enhancement of strength, modulus and hardness contributed to good triboligical properties. At the same time, the introduction of other fillers and other polymers as the component of matrix could also be used to regulate the mechnical and tribological properties of the resultant composites.Based on the results mentioned above, the effects of the CF length on the mechanical and tribological properties for the PA6/CF composites were understood, and it is the first time to enhance the mechanical and tribological properties by combining the fiber reinforcement with the blending of polymer matrix simultanesouly. Furthremore, the tribological mechanisms for the composites prepared by many modification methods were concluded. The effects of composite modification on the performances of the as-prepared materials were proved, and hence the relationships between mechnical and tribologiical properties were estabilished. These valuable results provided the fundamental theory as a guide for the design and manufacturing of high-performance CF-filled engineering plastics-based parts. |
PDF Full Text Request