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Effects of Shear-Flow on Isotatic Polypropylene Isothermal Crystallization

Author: WangBo
Tutor: ShenChangYuï¼›ChenJingBo
School: Zhengzhou University
Course: Materials Processing Engineering
Keywords: Rheology Isothermal crystallization Induced crystallization Induction time
CLC: TQ320.66
Type: Master's thesis
Year: 2007
Downloads: 169
Quote: 0
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Abstract


The crystallization behavior of the crystallinity of the polymer affect its microstructure and decided that a key factor of the products final properties. Its crystallization behavior of the polymer in the molding process by shearing, drawing, etc. to be changed. In the actual processing in the production process, the polymers are subject to flow shearing action. Therefore, the study of the crystallization behavior of the polymer in the shear field, in-depth understanding of polymer crystallization kinetics and guide the production, improve the mechanical properties of the product are of great significance. In this paper, the study of the rheological behavior of the crystallization process under steady-state and dynamic shearing shear field and shear history of the i-PP Isothermal crystallization process. Its main work is as follows: 1. Using the steady-state shear field in the viscosity (stress) versus time curve, and studied the influence of the shear rate and temperature in the steady-state shear field in the crystallization induction time. Through research found that at the same temperature, as the shear rate increases, the viscosity (normal stress) mutations of time in advance, the crystallization induction time is reduced; at the same shear rate as the temperature decreases, the viscosity (normal stress) mutations in ahead of time, crystallization induction time decreases. 2. The steady-state shear field in the induction time and the relation curve of the shear rate (temperature), temperature (shear rate) for the crystallization-inducing time changes the role of the (temperature) at a shear rate relationship. Through research found that the larger the change in amplitude of the crystallization induction time at high temperature or under a small shear rate. 3. Analysis of the relationship between induction time viscosity and France, respectively crystallized stress characterization. Through the study found, the viscosity and the normal stress has a mutation process, can be used to characterize the isothermal induced crystallization process. Small shear rates, the viscosity of the mutated time earlier than the method to stress mutated time; high shear rate, the normal stress mutated back to a viscosity mutated time. 4. Small amplitude oscillatory the relaxation modulus shear flow versus time curve, study shear calendar (pre-shearing time, pre-shear rate and the pre shear strain) on the isothermal crystallization process, through the study found. crystallization induction time with the pre-shear time, pre-shear rate and pre-shear strain increases shortened. But to play a leading role in the system crystallization induction time is the size of the pre-shear strain, and large shear strain can shorten the crystallization induction time. 5. Study the dynamic measurement parameters - amplitude and frequency of the isothermal crystallization process, the results show that the role of the small strain amplitude (0.5% -10%) and vibrational frequencies (1rad/s-50rad/s) less impact in the crystallization process, negligible.

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