| Polymer blending is the simplest and most practical method to obtain new high-performance polymer materials. It’s feasible to control the microstructure and thus regulating the macro-properties of blend materials through tuning the miscibility and phase separation process of the components. Among different kinds of polymer blends, there is a kind of blend that is miscible in the melt state while phase-separated in the solid state due to the occurrence of crystallization of one component. The crystallization and phase separation of miscible polymer blends during the solidification process can be influenced by many factors, including composition, interactions between the components and molecular weights of each component. Recently, it has been proven that adding nanoparticles into such blends also influences the phase separation and/or crystallization processes. The effects of nanoparticles on crystallization and phase separation are closely related to the shape, dimension, types of functional groups on the surface and other properties of the nanopariticles. Carbon nanotubes (CNTs) are typical one-dimensional nano fillers which have attracted much attention of researchers. Because of the large aspect ratio and surface area, as well as the similar chain conformation characteristic to that of polymer, CNTs exhibit strong affinity to many kinds of polymers. It can be expected that CNTs have a influence on the crystallization and phase separation when introduced into the above mentioned miscible blend. It is meaningful to investigate the effects of CNTs in such kind of miscible blend from both a perspective of academic research and industrial production.The present thesis is focused on investigating the influencing mechanism of CNTs on poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) miscible blend. Carboxyl functinanlized CNTs were introduced into PVDF/PMMA miscible blend to prepare the ternary nanocomposites. The dispersion states and the microstructures of CNTs were firstly characterized. The nonisothermal and isothermal crystallization behaviors of the binary blends and the ternary nanocomposites were systematically investigated. At the same time, the phase separation behavior and the subsequent crystallization behavior were also investigated for a better understanding of the role of CNTs in the ternary nanocomposites. At last, the influences of molecular weight on the crystallization and phase separation of the blends and nanocomposites were studied. The main results obtained in the present thesis are listed as follows:(1) For the PVDF/PMMA(60/40, wt/wt) blend, in which PVDF exhibits crystallization behavior under common crystallization conditions, the results showed that CNTs exhibited stronger interfacial affinity to PMMA. Homogeneous dispersion of CNTs in the nanocomposites was achieved, even if the content of CNTs was increased up to 2.0wt%. The crystallization ability of PVDF in the blend was greatly enhanced by adding CNTs. Largely enhanced crystallization temperature and increased crystallinity of PVDF were obtained during the nonisothermal crystallization process. The results obtained from isothermal crystallization process proved that both the crystallization temperature and the content of CNTs exhibited great influence on the crystalline morphology of PVDF. Specifically, the presence of CNTs induced the concentration fluctuation in the sample, which resulted in the formation of spherulites with different types, i.e. the ring-banded spherulites and compact spherulites.(2) For the PVDF/PMMA blend (50/50, wt/wt), which remains amorphous state at a cooling rate of 5℃/min or higher, the results showed that the crystallinity during nonisothermal crystallization process was largely improved and the muleaation density during isothemal crystallization process was increased remarkably, that is to say, crystallization of PVDF component from miscible PVDF/PMMA blend was greatly accelerated by adding CNTs. Specifically, it was observed for the first time that the two types of spherulites, i.e. ring-banded spherulites and compact spherulites, which were simultaneously induced during the isothermal crystallization process, exhibited different degrees of thermal stability. The latter spherulites exhibited higher thermal stability compared with the former spherulites. The crystallization of PVDF component could be further enhanced after the samples being melt-annealed at high temperatures. It was suggested that the accelerated crystallization of PVDF component from miscible PVDF/PMMA blend was not simply attributed to the nucleation effect of CNTs but possibly attributed to the joint effects of CNT nucleation and inducing phase fluctuation during the crystallization process.(3) Different contents of carboxyl functinanlized carbon nanotubes (CNTs) were introduced into miscible PVDF/PMMA(60/40, wt/wt) blends with two different molecular weights of PMMA. The results showed that the molecular weight of PMMA had different effects on the crystallization and phase separation of binary blends and ternary nanocomposites; that is to say, larger molecular weight of PMMA benefited the crystallization of PVDF in binary blends but disfavored the crystallization of PVDF in ternary nanocomposites. What’s more, larger molecular weight of PMMA led to less numbers of compact spherulites in isothermal crystallization at relatively high temperatures. In the case of melt-annealing, it was found that larger molecular weight of PMMA promoted the phase separation in binary blends while suppressed the phase separation in ternary nanocomposites. It was suggested that in binary blends, larger molecular weight of PMMA led to poor miscibility and easier phase separation, which benefited the crystallization of PVDF; in ternary nanocomposites, larger molecular weight of PMMA led to poor mobility of PMMA molecular chains, which made it more difficult for CNTs to induce phase separation in the miscible blend, and as a result, the crystallization of PVDF was suppressed. |
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