Effects Of Shear-Flow On Isotatic Polypropylene Isothermal Crystallization

The structure, morphology and ultimate properties of semicrystalline polymers are strongly dependent on the crystallization behavior of them. When a semicrystalline polymer is subjected to flow, as invariably happens during processing the crystallization behavior change to some extent. In fact, all the polymers were be sheared in the process of manufacturing. In order to understand the crystallization kinetics thoroughly and obtain the better properties, it is needed for us to study the crystallization behavior under flow conditions of polymers.In this thesis, the isothermal crystallization course of isotactic polypropylene(i-PP) on shearing and the history of shear were studied by rheology method. And all the works as follow::1. We studied the influence of temperature and shear-rate on crystallization induction time by the curve of shear viscidity (Normalforce) versus times. The results show that it can bring forward the time of shear viscidity (Normalforce) breaking and short the induction time with higher shear rate under isothermal conditions; and it can bring forward the time of shear viscidity (Normalforce) breaking and short the induction time with lower temperature under the same shear-rate conditions.2. We study the effects of temperature (shear-rate) on the induction time utilizing the curve of induction time versus shear-rate (temperature). The results show that the induction time changed speedy under higher temperature or lower shear-rate.3. Studies on induction time depended on the shear viscidity and normalforce we carried out. It is found that we can token the induction time by viscidity and normalforce. But, the time of shear viscidity breaking ahead of the time of normalforce breaking under lower shear-rate and it is oppositional under higher shear-rate.4. We studied the effect of shearing history on isothermal crystallization process by the curve of shear modulus versus times. The results indicate that the induction time will be shorter along with the longer pre-shear time, the higher shear-rate and the bigger pre-shear stain. Especially, the pre-shear stain was emphasized, the pre-shear stain larger, the induction time shorter.5. Studies on the influence of swing and frequency on isothermal crystallization process we got. It is found that the influence of swing (0.5%-10%) and (1rad/s-50rad/s) was faintness.