Keizo Miyasaka

Dispersion of fillers and the electrical conductivity of polymer blends filled with carbon black

Dispersion state of carbon black(CB) was studied in polymer blends which are incompatible with each other. It was found that CB distributes unevenly in each component of the polymer blend. There are two types of distribution. (1) One is almost predominantly distributed in one phase of the blend matrix, and in this phase fillers are relatively homogeneously distributed in the same manner as a single polymer composite. (2) In the second, the filler distribution concentrates at interface of two polymers. As long as the viscosities of two polymers are comparable, interfacial energy is the main factor determining uneven distribution of fillers in polymer blend matrices. This heterogeneous dispersion of conductive fillers has much effect on the electrical conductivity of CB filled polymer blends. The electrical conductivity of CB filled polymer blends is determined by two factors. One is concentration of CB in the filler rich phase and the other is phase continuity of this phase. These double percolations affect conductivity of conductive particle filled polymer blends.

Electrical conductivity of carbon-polymer composites as a function of carbon content

The electrical conductivity of carbon particle-filled polymers was measured as a function of carbon content to find a break point of the relationships between the carbon content and the conductivity. The conductivity jumps by as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point varies depending on the polymer species and tends to increase with the increase in the surface tension of polymer. In order to explain the dependency of the critical carbon content on the polymer species, a simple equation was derived under some assumptions, the most important of which was that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a “universal value”, Δg*, the carbon particles begin to coagulate so as to avoid any further increase of the energy and to form networks which facilitate electrical conduction. The equation well explains the dependency through surface tension, as long as the difference of the surface tensions between the carbon particles and the polymer is not very small.

Double percolation effect on the electrical conductivity of conductive particles filled polymer blends

Electrical conductivity of carbon black (CB) filled polymer blends which are incompatible with each other was studied as a function of the polymers blend ratio. Transmission electron microscope (TEM) analysis shows that CB distributes unevenly in each component of a polymer blend. TEM photographs of phase structure of solvent extracted HDPE/PMMA blend and solvent extraction experiments of PMMA/PP blend detect the blend ratio at which the structural continuity of filler rich phase is formed. The electrical conductivity of polymer blends is found to be determined by two factors. One is the concentration of CB in the filler rich phase and the other is the structural continuity of this phase. This double percolation affects the conductivity of conductive particle filled polymer blends.

Tensile yield stress of polypropylene composites filled with ultrafine particles

For polypropylene composites filled with ultrafine or particles of the order of microns, (SiO2 and glass, respectively), yield stress was measured as functions of temperature, the rate of strain and filler content. The yield stress of the composites filled with ultrafine particles increased with the filler content and decreased with the filler size, while for the composites filled with glass particles, these relations were reversed. For SiO2 filled composites, the tensile yield stress was found to be reducible with regard to temperature, the rate of strain and the filler content. The Arrhenius plot of the shift factors for composing the logarithmic strain rate — temperature master curve formed a single curve irrespective of the filler content and size. The curve comprised three linear regions with breaks appearing at 60 and 110° C, where the transition of the matrix polymer took place. The master curves obtained for different contents of a given size filler could be further reduced into a grand composite curve by shifting them along the axis of logarithmic strain rate, with the logarithmic second shift factors proportional to the square root of the volume fraction of the filler. The dependence of the filler volume fraction on the second shift factor was related to the dispersion state of fillers in PP matrix, namely, the promotion of the aggregation with filler content. The dependences of the yield stress on the filler volume fraction and size were explained by a modified equation based on the dispersion strength theory, with an aggregation parameter incorporated.

Effect of melt viscosity and surface tension of polymers on the percolation threshold of conductive-particle-filled polymeric composites

Abstract The electrical conductivities of carbon-black-filled low-density polyethylene (LDPE), poly(methyl methacrylate) (PMMA), and poly(vinyl chloride)-vinyl acetate (PVC/ VAc) copolymer were measured as functions of carbon content and melt viscosity of the matrix at the temperatures at which the composites were prepared. Sharp breaks in the relationship between the carbon filler content and the conductivity of composites were observed in all specimens at some content of the carbon filler. The conductivity jumps as much as 10 orders of magnitude at the break point. This phenomenon has been known as the “percolation threshold”. The critical carbon content corresponding to the break point

Effect of reducible properties of temperature, rate of strain, and filler content on the tensile yield stress of nylon 6 composites filled with ultrafine particles

Abstract The yield stress of nylon 6 (Ny6) composites filled with ultrafine and micron-sized (SiO2 and glass) particles was measured as a function of temperature, rate of strain, and filler content. The yield stress of the composites filled with ultrafine SiO2 particles increased with filler content and decreased with filler size, whereas for composites filled with glass particles, this relation was reversed. For ultrafine SiO2 filled composites, the tensile yield stress was found to be reducible with regard to temperature, rate of strain, and filler content. At a given filler content, composite curves were obtained for yield stress plotted against the logarithm of the strain rate. The Arrhenius plot of the shift factors for composing the strain rate-temperature master curve formed a single curve irrespective of the filler content and size. The curve comprised two linear regions with a break appearing at 110[ddot], corresponding to a transition of the matrix polymer. The master curves obtained for differe...

Electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer as a function of vinyl acetate content

The electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer was measured as a function of carbon and vinyl acetate (VAc) content. For the composites whose matrices contain less than 32 wt% ofVAc content, a sharp break point of the relation between carbon content and conductivity was observed. The conductivity jumps as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point can essentially be predicted by our previous model. This model was derived under certain assumptions, the most important of which is that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a “universal value”,Δg*, the carbon particles begin to coagulate so as to avoid any further increase of energy and to form networks which facilitate electrical conduction. On the other hand, for the composites whose matrices contain more than 32 wt% ofVAc content, a sharp break of the relation between the carbon content and conductivity cannot be observed and conductivity increases continuously with increasingVAc content. In this region ofVAc content, carbon particles were dispersed well in theVAc rich matrices. This is because the presence of polar groups in aVAc component enhances its bonding to conductive fillers. In this case, the interfacial excess energy,Δg, seems to be the caseΔg≤0. Better dispersibility of fillers in this region ofVAc content can be shown from an electron micrograph (TEM).

At study of ion permeation across a charged membrane in multicomponent ion systems as a function of membrane charge density

Abstract The authors have described an ion flux across a charged membrane in multicomponent systems by the theories (based on the Donnan equilibrium and the Nernst-Planck equation) in the previous paper. In the present study, the permeation coefficients of ions in various kinds of electrolyte systems are calculated as functions of membrane charge density by this theory. The theory predicts that permeability coefficients of multi-valent ions will be lower than those of univalent ions according to the low charge density, and that the permeability coefficients of multi-valent ions will become negative if the membrane has high charge density. That is, they are transported against their concentration gradient. This phenomenon in 1-1- and 2-1-type electrolyte systems was examined for negatively charged membranes, which were composed of poly (vinyl alcohol) (PVA) and poly (styrenesulfuric acid) (PSSA) mixtures, and a positively charged one, which was composed of a PVA and poly(allylamine) (PAAm) mixture. The theoretical prediction agreed well with the experimental results. The uphill transport of a multivalent ion occurred under the appropriate membrane charge density. This result shows that the direction of multivalent ion transport changes with charge density. This phenomenon is applicable in a new mechanism to control ion transport direction.

Simulation of the transport of ions against their concentration gradient across charged membranes

Abstract In a multi-ionic system, changes in ion concentration in two cells containing strong- and weak-acid ion-exchange membranes were simulated as a function of time, to obtain the flux of each ion in the system from only the charge density and ion mobility in the membrane and the ion concentrations in the two cells. This enables a determination of how the concentrations of the other ions change if one ion is transported against its concentration gradient. From this, the mechanism of uphill ion transport across ion-exchange membranes is clarified. These phenomena are confirmed experimentally using cation-exchange and poly(vinyl alcohol) membranes. Although ion transport across ion-exchange membranes has formerly been explained as active transport by a proton jump mechanism and across poly(vinyl alcohol) membranes by ring opening/closing reactions, we will describe such transport in terms of uphill transport across a strong- and weak-acid ion-exchange membrane. The theoretical predictions coincide well with experimental data.

Structural studies on ethylene-tetrafluoroethylene copolymer 1. Crystal structure

Abstract The crystal structure for an ethylene-tetrafluoroethylene (ETFE) alternating copolymer film containing highly ordered crystal regions was determined. The unit cell is orthorhombic with the dimensions: a = 8.57 A , b = 11.20 A , and c ( chain axis ) = 5.04 A . Four planar zigzag chains are packed in the unit cell. The lateral packing mode is similar to that of orthorhombic polyethylene (PE). A study on the mode of double orientation confirmed that the crystal structure of ETFE, which has been assumed to be pseudo-hexagonal, is indeed orthorhombic as described above, although it has paracrystalline disorder.