A new concept of the nature of the crystalline relaxation (αc) mechanism of high-density polyethylene was proposed. This concept is based on the mechanical properties observed in the αc temperature range for as-grown single crystals mats and samples of bulk crystallized material. The decomposition of the αc multiple relaxiation process into the α1-and α2-processes was carried. It was concluded that the α1-and α2-relaxiation mechanisms might be attributed to the deformation of intermosaic block region and that of interlamellar crystalline region, respectively. Threfore, the α1 process was strongly affected by slight elongation and fatigue cycling of the sample. The surface relaxiation process for the monodisperse polystyrene (PS) films with different number-average molecular weight, Mn was investigated on the basis of lateral force microscopy (LFM) and scanning viscoelasticity microscopy (SVM). SVM measurements showed that the surface of the monodisperse PS film with Mn lower than 30 k was in a glass-rubber transition state or in a rubbery state even at 293 K, even though the bulk Tg was far above 293 K. It was revealed from the temperature-dependent LFM that the magnitude of activation energy for the surface αa- relaxiation process is almost half as much as that for the bulk one. The molecular weight dependences of the Tgs for the monodisperse PS film with various chain end groups were also investigated on the basis of temperature-dependent SVM measurement. The Tgs was strongly dependent on a difference of surface free energy between chain end group and main chain.
Translational and rotational diffusion coefficients as well as the zero-shear viscosity of stiff-chain polymers in dilute through concentrated solutions were formulated on the basis of the fuzzy cylinder model. To test the validity of the theory, the results formulated were compared with zero-shear viscosities and mutual diffusion coefficients measured using well-characterized samples of various stiff polymers [schizophyllan, xanthan, poly (n-hexyl isocyanate), and cellulose tris(phenyl carbamate)] as functions of the polymer concentration and molecular weight. Agreements between theory and experiment were satisfactory for stiff polymer samples having the Kuhn-segment number less than ca. 20. The dielectric dispersion of a type-A stiff polymer, poly (n-hexyl isocyanate), and dynamic electric birefringence of poly (γ-benzyl L-glutamate) in solution were also favorably compared with the fuzzy cylinder model theory near the rod limit.
Polymer blend is one of the materials which has shown a highest growth rate in the polymer industries. One of the key factors to obtain the polymer blends with superior performance is to control the phase morphology and higher order structure of the blends. Sea-island morphology in the incompatible blends has to be controlled in the flow fields during shaping process. Even in the compatible blends, control of the crystalline higher order structure has to be carried out in the processing, if at least one of the component is crystalline. This report presents some of the researches related to the processability and the mechanical properties of polymer blends, including the researches on “PLLA/PDLA blend fibers”, “Polymer blends which involve a liquid crystalline polymer as a component”, and “Observation of deformation and recovery of minor phase in an incompatible polymer blend”.
This paper summarizes our studies on the numerical flow analysis of polymeric liquids and its application to the industrial problems in the polymer processing. The contents include three parts. The first part is a review about development of numerical technique of viscoelastic flow analysis to obtain the solution at high deformation rate. We used the streamline-upwind (SU) finite element method with the sub-elements for stress components to simulate the extrudate swell at high Weissenberg number (We). The calculation using the Giesekus model with a single relaxation time was feasible over hundreds of We in the planar and capillary extrude swell, but the calculation was impossible for We > 3 in the annular extrudate swell. We proposed the new technique of under-relaxation method, which introdnced the virtual Newtonian stress in order to increase the numerical stability. The calculation by the new technique combined with the SU method was successful in obtaining the solution over hundreds of We in the annular extrudate swell problem. The second part is a review of numerical studies on polymeric liquid flow in the basic flow fields. We performed the viscoelastic flow analysis using the several kinds of constitutive models in the contraction flow and extrudate swell. The simulation results using the viscoelastic model with a single relaxation time were compared with the experimental data of stress field measured by the flow birefringence technique and the agreement better than 20~30% in accuracy was obtained in the lower shear rate region. The simulation results also gave the several explanations about the mechanism of corner vortex and entrance pressure drop in the contraction flow, swelling phenomena in the extudate swell, etc. On the other hand, the simulation using the constitutive models with multiple relaxation times gave the useful information, especially on the effect of material polymer. The last part is application to the industrial problems in polymer processing. The technique of viscoelastic flow analysis was applied to the film casting and the effect of elongational viscosity on the film shape was found. The technique was also applied to the development of prediction of prison formation in blow molding. The viscous non-Newtonian flow analysis was applied to the three-dimensional flow analysis and the evoluation of mixing performance in the twin screw extruder.
Rheological properties of emulsified inks are important for controlling printability because printing inks are emulsified by dampener water on press. This newly developed instrument can evaluate rheological properties of emulsified inks in the high shear rate region. Consequently, this instrument has greatly contributed for the designing of new products.
Chemorheology of an epoxy resin with 90wt% silica fillers was investigated using a parallel-plates viscometer. Viscosity-time curves at four frequencies were measured at intervals of 10°C in the range of 50°C to 130°C. Within the range of 130°C to 180°C, viscosity-time curves of samples, in which the concentrations of a curing catalyst had been decreased in order to lower the rate of reaction, were measured. Parameters of an Arrhenius type equation, considering the frequency dependence, were obtained from these data for the prediction of the resin viscosity variation during cure. In particular, the parameters at high temperature were estimated by extrapolation of the normal concentration of a curing catalyst. The calculated viscosity profile coincided with the experimental data. The gel point at 100°C was obtained using two methods: (i) crossover of the tanδ-time curves at several frequencies (ii) same power law dependence of G'(ω) and G"(ω) on frequency. Both values coincided. Values of the power exponent from the two methods were 0.62 and 0.70, respectively. These values were in agreement with the value predicted by the dynamic scaling theory. The appearance of an insoluble fraction at the gel point was confirmed by GPC. The degree of cure at the gel point was 0.50 by DSC.
Rheological properties of cellulose fibrous suspensions were measured with a cone-plate type rheometer. Effect of particle concentrations, c, and salt concentrations of the systems on the properties were studied. The flow curve of the fully dialyzed system showed Newtonian flow at a particle concentration of 0.1 wt%. However, it showed plateau regions of shear stress over a particle concentration of ca. 0.3 wt%, which is consistent with the critical concentration c0 calculated from the aspect ratio of the fiber particle. The dynamic moduli of the systems were almost independent of angular frequency. They were in proportion to c9/4. The absolute value of zeta potential of the cellulose particle was decreased with increasing salt concentration of the suspension. When the particle concentration was lower than c0, salt concentration had no influence on the flow properties of the system. At higher particle concentration, however, the yield stress was exponentially decreased with decreasing the absolute value of zeta potential of the particle. These facts indicate that the shear stress consists of two different contributions: one is caused by friction of the effective volume of the particles and the other arises from overlapping of the electric double layer of the particles.