Rheological properties of olefinic thermoplastic elastomers (TPO), which contain fully crosslinked rubber particles in a continuous matrix of polyolefin (especially polypropylene, PP), were studied. Samples employed are a commercial TPO (Santoprene®, A. E. S. Japan) and a series of new TPOs produced from PP and acrylate rubber using a unique method, called “dynamic valcunization”. Even above melting point of matrix (PP), the TPOs behave as normal cross-linked rubber materials in the linear viscoelastic region. However, the TPOs show plastic flow due to a mutual displacement of the rubber particles. The stress σC needed for the displacement of the particles is almost independent from angular velocity or shear rate. The value of σC, however, depends strongly on a kind of oil contained in TPOs. The mechanism on this dependence is not clear, but it was confirmed that plasticizing or swelling of the matrix due to transferring oil from rubbers to matrix are not main reasons for this dependence, i. e., change the stress value σC.
Kinetics of enthalpy relaxation upon physical aging was examined for both amorphous, isotropic poly (ethylene terephthalate)(PET) and semi-crystalline, anisotropic PET samples below their glass transition temperature (Tg). After isothermal aging a DSC endothermic peak was observed near Tg and its shape, size and position were strongly dependent on the temperature and time of aging as well as sample preparation histories. For the amorphous PET sample, the experimental results were discussed on microscopic level, within a context of a modified reptation model. The relaxation mechanism of the amorphous chains in the semi-crystalline PET sample was quite different from that of the totally amorphous PET, due to the crystallites restricting the segmental rearrangements in the former. It was also found that the prolonged again of the amorphous PET accelerated cold-crystallization at temperatures above Tg, while no effect of the prolonged aging was found for the semi-crystalline PET.
A new numerical method has been developed for predicting fiber orientation in complex flows. This method combines the particle simulation method (PSM) with the finite element method (FEM) for flow analysis. PSM models a fiber as sequence of N spheres each having a diameter identical to that of the fiber, where N is the aspect ratio of the fiber. The equation of motion formulated for every sphere is solved under a flow field obtained from the FEM analysis, and the motion of the fiber is described as the combined motion of all spheres. Accuracy of PSM was examined for a test case, orientation of short fibers in two-dimentional diverging flows: The fiber orientation calculated with the method developed here was in good agreement with the known, theoretical orientation.
Flows through cylinder arrays are numerically calculated for nematic liquid crystalline polymers using the simplified model of the Lesile-Ericksen theory. The flow domain is mapped onto the square domain using a boundary-fitted curvilinear coordinate system and the flow problem is solved using a finite difference method. The director orientation is largely affected by the contraction and expansion flows and the elongational flows before and after a cylinder. The flow fields depend on the material constants β1 and β2, and are expected to change significantly from that of Newtonian fluids if the constants for the Doi theory are applied to β1 and β2.
Dynamic viscoelastic properties of W/O emulsions composed of n-paraffin (continuous oil phase) and 0.01mol/dm3 NaCl and/or MgSO4 aqueous solutions (isolated water-droplet phase) were investigated as a function of water volume fraction, Φ. The properties were hardly different for the emulsions containing NaCl and MgSO4. In addition to the viscoelastic tests, Cryo-SEM observation was carried out to examine the shape and size of the water phase. The water droplet size varied from 0.5μm to 3μm, depending on stirring conditions during emulsion preparation. Complex viscosities of the emulsion systems decreased with increasing frequency; For a given frequency, the viscosity was larger for larger Φ and smaller droplet size. For such emulsions, storage moduli for 1% strain were independent of frequency, being irrespective of Φ and droplet size. Alternatively, loss moduli showed mild peaks at low frequencies except for the smallest droplet size of 0.5μm, and the peak height increased with increasing droplet size. These results suggest that some coagulated structure of the water droplets may exist due to interaction among the droplets in the emulsion systems.
Flow of anisotropic fluids was analyzed to examine an expression for a quadratic closure approximation that enabled accurate calculation of time evolution of a second-order orientation tensor. Specifically, two dimensional fiber orientation was simulated with two methods. The first method, called a continuum method, solved the time evolution equation for the second-order orientation tensor under a quadratic closure approximation (for the fourth-order tensor involved in the equation). The second method, a statistical method, considered a large number of fibers, calculated orientation of each fiber from Jeffery's equation, and evaluated the second-order tensor as an average. For a simple shear flow, the distribution and preferred angle of fiber orientation were in agreement with known analytical results, indicating the accuracy of this method. For this flow, both statistical and continuum methods indicated that the preferred angle jumped from -45°to +45°with a frequency determined by the fiber aspect ratio and an orientation ellipse showed no flip-over behavior if the fibers were randomly orientated at the initial state. However, the flip-over behavior was observed for fibers having other initial orientation. For a developing flow in a parallel plate channel, this behavior was observed for fibers of any initial orientation because nonhomogeneous flow at the channel entrance significantly affected the fiber orientation. It was also demonstrated that the highest accuracy of the quadratic closure approximation was achieved when a tensor d:a4=dklaklaij was involved in the calculation of the continuum method.
Torque measurements for spherical Couette flow of non-Newtonian fluids are presented together with flow characteristics in a region of low rotational Reynalds number up to an onset of hydrodynamic instability. The spherical flow configuration in the present study is such that the inner sphere is rotated while the outer sphere is kept stationary. The rotational torque induced by shear stress on the inner sphere surface is measured for dilute, aqueous polymer solutions (PEO: Polyethylene oxide and PAA: Polyacrylamide) of various concentrations. The experimental results show that before the onset of hydrodynamic instability the torque characteristics are higher than those estimated for linear azimuthal velocity profile in the spherical gap. It is shown consequently that the measured torque can be well described by the integral correlation formula that considers the azimuthal non-linear velocity profile and involves the generalized Reynolds number. The critical Reynolds number associated with the onset of the hydrodynamic instability (laminar transition) is much lower than that estimated from Newtonian correlational equation (modified by the generalized Reynolds number) and is strongly dependent upon the concentration of the PEO and PAA polymer solutions.