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A new technique to show good electroconductivity was proposed using carbon nanotube (CNT) localization in cocontinuous immiscible polymer blends comprising ultrahigh-molecular-weight polyethylene (UHMWPE) and polycarbonate (PC). When UHMWPE was added to PC/CNT in the molten state in an internal mixer, CNTs started moving to the UHMWPE phase. However, CNTs require a long time to diffuse into the UHMWPE phase owing to a low diffusion constant. Consequently, they remain at the interface between PC and UHMWPE. When the blends have cocontinuous structure, the localized CNTs at the phase boundary act as a conductive path, leading to a good electroconductivity. Although a similar morphology is obtained by adjusting the balance of interfacial tensions among polymers and CNT, it is difficult to find a system showing appropriate interfacial tensions. As the present method is applicable to various polymer blends, it will be an important technique to prepare a conductive nanocomposite.

Adding polyethylene greatly affects the rheological response of isotactic polypropylene (PP) under uniaxial elongational flow. Though strain hardening in the transient elongational viscosity barely appeared in pure PP, we induced strain hardening by adding low-density polyethylene (LDPE) to PP, even though the blends showed a phase-separated structure. During elongational flow, LDPE droplets dispersed in the PP were deformed in the flow direction. Because LDPE shows marked strain hardening in the elongational viscosity, the deformed LDPE droplets behaved as rigid fibers as the strain increased. Consequently, the PP between the fibrous LDPE droplets experienced excess localized deformation, which increased the apparent elongational viscosity. Furthermore, adding the high-density polyethylene (HDPE) increased the drawdown force—defined as the force required for uniaxial stretching of a molten polymer in the nonisothermal condition. This behavior comes from the rapid crystallization of HDPE, which causes the deformed HDPE particles to act as rigid fibers in the molten PP and enhances the PP crystallization, which increases the elongational stress.

We investigated the structure and properties of strands of high‐density polyethylene (HDPE), containing multi‐walled carbon nanotubes (MWCNTs) extruded from a capillary rheometer. Surprisingly, we found that the MWCNTs enhanced the chain orientation of HDPE, and that in the absence of MWCNTs, orientation relaxation occurred in the HDPE immediately after passing through the die. Conventional differential scanning calorimetry measurements indicated that MWCNT acts as a nucleating agent and raises the crystallization temperature 2–4 °C under quiescent condition. In the flow field, oriented MWCNTs behave like polymeric chain extended crystals “shish” and greatly accelerate the flow‐induced crystallization of the HDPE “kebab.” Consequently, the modulus was significantly increased in the flow direction. These findings demonstrate that the addition of MWCNTs is an effective method of enhancing the rigidity of HDPE. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48010.

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The rigidity of an injection‐molded isotactic polypropylene (PP) containing 1,3:2,4‐bis‐o‐(4‐methylbenzylidene)‐D‐sorbitol (MDBS) as a crystal nucleating agent can be enhanced by selection of appropriate processing conditions. A new method by differential scanning calorimetry measurements showed that the dissolution temperature of 0.4 wt.% MDBS in molten PP is around 210°C. When injection molding was performed below the dissolution temperature, for example, 190°C, the molecular orientation of PP was greatly enhanced. Although this is an anomalous condition for the system to expect good transparency, the product obtained showed a high flexural modulus. In contrast, with high‐temperature processing at 240°C, that is, conventional condition, the modulus decreased because of poor molecular orientation. Transmission electron microscopy observation revealed that MDBS fibrils strongly orient to the flow direction under the low‐temperature processing, in which network structure of MDBS fibers is not detected. The oriented MDBS fibers led to a well‐developed shish‐kebab structure, which is responsible for the pronounced rigidity.

We investigated changes to the linear viscoelastic properties of a mixture comprising polycarbonate (PC) containing 3 wt.% of a multiwalled carbon nanotube (MWCNT) and high-density polyethylene (HDPE), also containing 3 wt.% MWCNT, during post-processing annealing. The oscillatory shear moduli-i.e., the storage modulus G′ and the loss modulus G′′-gradually increased with residence time in a rheometer (i.e., annealing). The samples were prepared by compression-molding at low temperature, during which the MWCNTs became oriented by the applied squeeze flow. The marked increase in the oscillatory moduli may be attributed to the formation of a conductive MWCNT network owing to Brownian motion. Furthermore, the moduli increased more rapidly during high-temperature annealing. These increases can be expressed by a simple equation using only one characteristic time, i.e., the time required for MWCNT redistribution by Brownian motion. This characteristic time is considered one of the factors that control the structure of composites containing MWCNTs.

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