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.

We show the linear response theory of spatial-scale-dependent relaxation moduli for overdamped Brownian particle systems. We employ the Irving-Kirkwood stress tensor field as the microscopic stress tensor field. We show that the scale-dependent relaxation modulus tensor, which characterizes the response of the stress tensor field to the applied velocity gradient field, can be expressed by using the correlation function of the Irving-Kirkwood stress tensor field. The spatial Fourier transform of the relaxation modulus tensor gives the wavenumber-dependent relaxation modulus. For isotropic and homogeneous systems, the relaxation modulus tensor has only two independent components. The transverse and longitudinal deformation modes give the wavenumber-dependent shear relaxation modulus and the wavenumber-dependent bulk relaxation modulus. As simple examples, we derive the explicit expressions for the relaxation moduli for two simple models the non-interacting Brownian particles and the harmonic dumbbell model.

The microscopic deformation behaviors of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) under uniaxial stretching were investigated using rheo-Raman spectroscopy. The crystalline chains of LDPE were oriented uniaxially into the stretching direction beyond the first yielding point, which was accompanied by applying stretching load to the crystalline chains. In contrast, at the first yielding point of HDPE, the orientation of crystalline chains was suppressed and compression load was applied to the amorphous and crystalline chains owing to lateral shrinkage of the specimen. Additionally, the orthorhombic crystalline regularity was significantly disordered at the first yielding point for HDPE, concomitant with the fragmentation of the rigid lamellar crystals. In comparison, the disordering of the crystalline regularity of LDPE was induced at the second yielding point, when the orientation of the crystalline chains was nearly complete, owing to the application of a strong stretching load to the highly oriented crystalline chains.