| For binary crystalline/crystalline polymer blend, both phase separation and crystal structures affect its performance. So it is important to investigate the control of the crystal structure and phase separation of polymer blends with different blend ratios and crystallization temperatures. In this thesis, the miscibility, crystallization kinetics and phase separation structure of the poly(vinylidene fluoride)(PVDF)/poly(ethylene adipate)(PEA) blend have been studied by differential scanning calorimetry(DSC), polarized optical microscopy(POM), scanning electron microscopy(SEM) and atomic force microscopy(AFM).The results show that the equilibrium melting point of PVDF decreases with the increment of PEA. From the melting point data of PVDF, a negative but quite small value of the interaction parameter χPVDF-PEA is derived using the Flory-Huggins equation, implying that PVDF shows some miscibility with PEA to some extent. Nonisothermal and isothermal crystallization kinetics suggest that the crystallization rate of PVDF decreases with increasing the amount of PEA, and a contrary trend was found when PEA crystallizes with the increase of the amount of PVDF. It was further disclosed that the blend ratio and crystallization temperature affect the texture of PVDF spherulites greatly, which determines the subsequent crystallization of PEA. At high temperature, e.g.150 oC, the band spacing of PVDF spherulites increases with the addition of PEA content and the spherulitic structure becomes more open. In this case, spherulitic crystallization of PEA is not observed for all blend compositions. At low temperature, e.g.130 oC, for the PEA-rich blends, the interpenetrated structures are eventually formed by the penetration of the spherulites of PEA growing within the pre-existing PVDF spherulites.Furthermore, the effect of PEA on the γ-phase PVDF crystalline structure has been also investigated by infrared spectroscopy(IR) and scanning electron microscopy(SEM). It was demonstrated that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and a transcrystalline-like structure develops. Subsequently, the transcrystalline layer of PEA continue to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetically results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.The effects of crystallization temperature and blend ratio on the polymorphic crystal structures of poly(butylene adipate)(PBA) in poly(butylene succinate)(PBS)/poly(butylene adipate)(PBA) blends were studied by means of wide-angle X-ray diffraction(WAXD) and atomic force microscopy(AFM). It was revealed that the polymorphismb of PBA can be regulated by the blend ratio even in a non-isothermal crystallization process. The results demonstrate that high temperature favors flat-on α-form crystals, while low temperature contributes to edge-on β-form crystals. It was also found that the effect of blend ratio on the crystallization mechanism of PBA is well coincident with that of the crystallization temperature. The increment of PBS content in the PBS/PBA blend gives rise to more β-form crystals of PBA. For those PBS/PBA blends with low PBA content, the interlamellar phase segregation of PBA makes its molecular chains so difficult to diffuse from one isolated microdomain to another that high crystallization temperature and sufficiently long crystallization time will be required if the PBA α-type crystals are targeted. |
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