Mechanism of Flow Induced Crystallization of Polymers

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[1]Direct observation of Crystallization under shear flow (Takimoto)An original device for the direct observation of crystallization under shear flow has been developed. It has been found that the nucleation rate of spherulites is strongly accelerated as the shear stress increases (i.e., shear rate and/or molecular weight increase), but the growth rate is only weakly affected. At high shear stress, the row nucleated structure is observed.[2] Simultaneous measurement of heat of crystallization and viscosity under shear flow (Koyama)We have developed a shear flow thermal rheometer which can measure the heat of crystallization and viscosity under shear flow simultaneously. It has been found that the shear viscosity η increases with the relative crystallinity Xc as η(Xc)=η(0)exp(αXc). The constant α depends on the shear rate, which indicates that the morphology at the same Xc differs for different shear rates.[3] PVT measurement under shear flow (Koyama)We have modified a PVT measurement system so that shear flow can be applied under high pressure. It has been found that i) effect of pressure on the crystallization rate can be described by the shift of the melting temperature, ii) effect of shear rate can be described by a induction strain which is independent of crystallization temperature and pressure, and iii) effect of pressure and shear rate can be separated.[4] Molecular Dynamics Simulation (Masubuchi)Crystallization of polyethylene oligomer under shear flow was studied by molecular dynamics simulation. Flow alignme of the molecules and the acceleration of the nucleation have been demonstrated.