In fiber suspensions, fibers with three-dimensional orientation states are dramatically flow oriented in the flow-flow gradient plane when the flow starts. In contrast, large strains are required for flow orientation in the flow-vorticity plane. Under oscillatory shear flow, when the strain amplitude is small, the flow orientation in the flow-vorticity plane is weakly induced, unlike that in the flow-flow gradient plane. The orientation in the flow-vorticity plane increases with the strain amplitude. At large strain amplitudes, fibers are oriented in the flow-flow gradient plane; thus, the rotational motion of fibers in the flow-flow gradient plane is dominant, i.e., fibers are almost flow oriented in the flow-vorticity plane. However, contributions of the oscillatory behavior of fiber orientation in the flow-flow gradient and flow-vorticity planes to complex viscosity are unclear. Herein, we adjusted the two initial orientation states (random and flow-oriented states) for the strain sweep test to determine the contributions of fiber orientation in each plane to complex viscosity. Furthermore, phase transition behaviors from the random to flow-oriented state in the flow-vorticity plane with increasing strain amplitude were qualitatively estimated as the orientation angle via visualization. Consequently, when the initial orientation was random, the fibers gradually vibrated in a medium strain amplitude region and complex viscosity was higher than that of the initial flow-oriented state. We divided the complex viscosity behavior of the strain sweep test into five strain amplitude regions and clarified the dominant orientation state in each region.

One of the unsolved problems on recycling of waste plastic is the viscosity non-uniformity; the viscosity of recycling plastics is neither stable nor homogeneous as the material is a mixture of pieces of various products with different molecular weights. In this study, we propose a processing system of recycling plastics, the so-called continuous viscosity homogenization treatment system. In this system, we maintain the viscosity by blending virgin resins to waste plastics with monitoring the viscosity via an in-line rheometer. Tsenoglou's equation was used in the homogenization treatment. We evaluated the concept for mixtures of aqueous solutions of poly (ethylene oxide) which is one of the entanglement polymers. The viscosity after the homogenization treatment was in good agreement with the target viscosity.