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Development Of Crystallization Process And Forms Of Polymer Under Temperature Controlled Gradient Stage

Posted on:2015-03-06Degree:MasterType:Thesis
Country:ChinaCandidate:G H ZhangFull Text:PDF
GTID:2251330428473613Subject:Polymer Chemistry and Physics
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The crystallization and growths of polymer were strongly affected by many factors, and the temperature plays an important role on the growth process of polymer and the final crystallization morphology. In this thesis, the nucleation, growth, morphology and the mechanism of biodegradable poly(3-hydroxybutyrate) was investigated by Polarizing optical microscope (POM), Atomic force microscope (AFM) isothermally, non-isothermally and under temperature gradient, respectively.1. The spherulitic growth process, kinetics behaviors and morphology of PHB thin films crystallized isothermally from the melt were observed by POM and AFM. And we conclude that the banded and non-banded spherulites were formed isothermally depending on different crystallization temperature. It was found that the competition of the crystallization rate of the crystalline entities of polymer entities and the diffusive displacement rate of melt molecules was employed to explain this. Both the crystallization rate and the diffusive displacement rate of melt molecules are very small in the lower crystallization temperature, the crystallization rate is bigger than the diffusive displacement rate of melt molecules with the increase of the crystallization temperature; however, the diffusive displacement rate is bigger than the crystallization rate as the crystallization temperature reached higher crystallization temperature. The corresponding morphology of PHB is non-banded, banded, non-banded, respectively. Meanwhile, the morphology of PHB is uniform circular due to the same growth rate in every direction.2. The spherulitic morphology of PHB thin films crystallized under temperature gradient from the melt was observed by POM and AFM not only determined by crystallization temperature but also determined by nucleation temperature and the position of nucleation. What’s more, the growth of PHB spherulite is another important factor to determine its final morphology. The banding spacing formed under temperature gradient is smaller than formed isothermally. The mechanism of PHB isothermally is same as crystallized under temperature gradient and the banded spherulites formed in thin films may mainly come from lamellar twist and discontinuity growth, when a depletion zone of the PHB melt may be formed at the growth fronts of the spherulites.3. The spherulitic morphology of PHB thin films crystallized non-isothermally with different descent rate from the melt was observed by POM. It was concluded that the spherulite morphology of PHB formed on-isothermally is banding no matter at different descent rates. What’s more, the spherulite nucleation becomes smaller with the increasing of the cooling rate.
Keywords/Search Tags:PHB, Banded spherulite, Temperature, Temperature gradient, Crystallization
PDF Full Text Request
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