| Crystallization temperature (Tc) plays a dominant role on aggregation structure of polymer material. As a high-throughput method, temperature gradient hot stage provides controlled range of temperature that involves continuous variation. It allows a more thorough study on the influence of crystallization temperature on crystalline morphology of various kinds of crystalline and semi-crystalline polymers. Furthermore, the employment of temperature gradient hot stage improves efficiency and accuracy of experiment at the same time.Recently, interface crystallization, especially transcrystallization (TC) has attracted tremendous attention because it has the potential to improve interface bonding between polymer matrix and fillers. In this essay, PLLA and carbon fiber were chosen to prepare CF/PLLA composite film via solution casting. Then the film was isothermally crystallized from melt on the temperature hot gradient stage with temperature ranging from 90 to 140℃ for four hours. Polarizing microscope observation indicated that typical transcrystallinity was formed on the surface of CF when Tc was during 98～132℃. As Tc decreased from 132 ℃ to 98℃, nuclei density on single carbon fiber increased and thickness of transcrystallinity layer decreased. Crystallization kinetics analysis demonstrated that onset time of nucleation and radius growth rate of TCdecreased as Tc decreased. Furthermore, kinetics analysis revealed that final size of TC was influenced by competition between transcrystallization on fiber surface and homogenous crystallization in the bulk matrix around the fiber.Poly-(vinylidene fluoride) (PVDF) is a kind of semi-crystalline polymer that has five crystalline phases. However, only β phase shows strong Piezoelectricity, a and y phases could be obtained when PVDF is crystallized from the melt. And both α and γ phase can be transformed to β phase under certain conditions. Hence, it is of great importance to study crystallization behavior of α and γ phase at different crystallization temperatures. In this essay, thin film made by solution casting was isothermally crystallized on the 110～180 ℃ temperature gradient hot stage for 8 hours. The result demonstrated that single y phase was formed when Tc was above 164℃. As Tc decreased, phase content of γ/α phase decreased according to POM observation, FTIR and DSC test. Crystallization kinetic analysis demonstated that nucleation rate of γ phase was much stronger than a phase at higher Tc while growth rate of y spherulites was much smaller than. In addition, it was found that y phase spherulites could induce nucleation of a phase.Then, transcrystallization behavior in CF/PVDF composites was researched through isothermal crystallization on the 110～180℃ temperature gradient hot stage for 4 hours. POM observation revealed that crystal phase composition of TC structure has strong dependence on crystallization temperature. Transcrystalline was composed of single y phase when Tc was above 164℃. When Tc was between 150～160℃, heterogenous nucleation on the the surface of CF was dominated by y phase though a few a phase nuclei appeared. When Tc decreased to 137℃, γ phase TC layer was suppressed by a phase.When Tc was in the range of 144～156℃,γy phase transcrystalline could induce a phase nucleation which finally developed into trancrystalline. In that case, double TC layer was formed in CF/PVDF composite.The last part of the essay deals with influence of a small amount of PVDF on crystallization behavior of PLLA.5/95 and 10/90 PVDF/PLLA blend were prepared via solution blending and melt blending. Thin films of the blends were isothermally crystallized on the temperature gradient hot stage. Nuclei density of PLLA increased and radii of spherulites decreased with the addition of 5wt% PVDF. Crystallization kinetic analysis demonstrated that nucleation rate of PLLA was impoved. DSC and WAXD test indicated that PVDF crystallized at higher temperature in the blend. And crystallization of PLLA was improved under the same condition. |
PDF Full Text Request