| 其他摘要 | Nylon 6 (PA6) was a kind of widely used engineering thermoplastics, but the usage was limited by its deficiencies, such as higher water absorption, lower heat distortion temperature, worse toughness at dry condition and lower temperature, notch sensitivity, etc. Therefore, in order to improve the general properties of PA6 and spread its use, carbon nanotubes (CNTs), organomontmorillonite (OMMT) and rubber (POE) were adopted to modify PA6, respectively.
In this thesis, CNTs were first treated with acids and diamine; the microstructures of PA6/CNT nanocomposites were characterized by SEM and TEM; the effect of CNTs on the mechanical properties, crystallization and melting behaviors, friction and wear behaviors of PA6 was also comparatively investigated. In this thesis, the effect of blending sequence on the microstructure and properties of PA6/POE/OMMT ternary nanocomposites was also investigated; the microstructure of ternary nanocomposites was studied by XRD, SEM and TEM; the effects of OMMT and POE on the mechanical properties, crystallization and melting behaviors, heat stability, water absorption and rheology of PA6 were also analyzed. The main results were as follows.
The stronger interaction of the polar oxygen-containing groups led to a compact stacking morphology of the acid-modified MWNTs (A-MWNTs). After further modification of A-MWNTs with ethylenediamine weakened the interaction among MWNTs, which resulted in the less compact stacking morphology of the diamine-modified MWNTs (D-MWNTs). Therefore, D-MWNTs had better dispersion and stronger interfacial adhesion with PA6 matrix compared with A-MWNTs. Although both A-MWNTs and D-MWNTs were effective reinforcements of PA6, D-MWNTs had higher reinforcing efficiency for PA6 compared with A-MWNTs.
The results of crystallization and melting behaviors showed that A-MWNTs and D-MWNTs acted as effective heterogeneous nucleating agents for PA6 and increased the crystallization temperature of PA6. During isothermal crystallization process, both A-MWNTs and D-MWNTs increased the crystallization rate of PA6, but they reduced the crystallization rate of PA6 during non-isothermal crystallization process. However, the addition of A-MWNTs and D-MWNTs almost had no influences on the melting behaviors of PA6. Compared with A-MWNTs, D-MWNTs had more influences on the crystallization of PA6 due to its better dispersion and stronger interfacial adhesion between PA6 and D-MWNTs.
D-MWNTs were effective solid lubricants for PA6, which could reduce the friction coefficient and specific wear rate of PA6 under dry- and water-lubricated sliding conditions.
The blending sequence strongly influenced the microstructure and performances of PA6/POE/OMMT ternary nanocomposites. The nanocomposite of (PA6+OMMT)+ POE, which implied that PA6 was reinforced with OMMT first and the PA6/OMMT nanocomposite was blended with POE later, had the best performances. In this nanocomposite, most exfoliated OMMT stayed in PA6. The independent dispersions of POE and OMMT in PA6 made the PA6/POE/OMMT ternary nanocomposite present a better balance between stiffness and toughness.
When the OMMT contents in nanocomposites were less than 8wt%, OMMT could be exfoliated into individual clay layer and the addition of POE had no effect on the exfoliation of OMMT. POE possessed better compatibility with PA6, but the presence of OMMT weakened the compatibility and resulted in the bigger POE particles in PA6/POE/OMMT ternary composites.
The results of mechanical properties showed that OMMT could obviously increase the strength and modulus of PA6, but reduced the toughness of PA6; on the contrary, POE greatly increased the toughness of PA6, but reduced the strength and modulus of PA6. Thus, modifying PA6 with POE and OMMT could achieve reinforcing and toughening aims for PA6, which made PA6/POE/OMMT ternary nanocomposites present a better balance between stiffness and toughness.
During isothermal crystallization process, both POE and OMMT acted as heterogeneous nucleating agents for PA6 and increased the crystallization rate of PA6, but they also increased the crystallization activation energy of PA6. However, the addition of POE and OMMT almost had no influences on the melting behaviors of PA6. During non-isothermal crystallization process, both POE and OMMT increased the crystallization temperature and crystallization rate of PA6; the presence of OMMT led to the increase of crystallinity and melting points for PA6, but the addition of POE reduced the crystallinity and melting points for PA6.
OMMT remarkably improved the heat stability of PA6 and reduced the water absorption of PA6; however, POE reduced the heat stability and water absorption of PA6. The shear viscosity of PA6 and its composites decreased with the increasing temperature and shear rate, which implied that the melts of PA6 and its composites were pseudoplastic fluids. |
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