The title of this review,“ High Performance Paper,” was named after the High Performance Paper Society, which has been working on researches of specialities and/or characteristics of paper for twenty-five years. The“high performance paper” may be classified among the“special paper”in the paper industry, though the difference is not very clear at present. This review describes recent developments in the manufacturing of the high performance paper in the modern sense. The following three groups of newly developed high performance paper and their properties are discussed: 1) Paper made with inorganic, carbon and metallic fiber and with other materials. High performance of this group of paper is based on properties of raw materials. 2) Paper used for separation technology. Separation function of the paper originates in the structure of paper. 3)“Paper Ceramics.”New characteristics appear through treatments of paper.
Rheological behavior of optically isotropic pitches derived from petroleum crude oils and coal tars were reviewed in relation to their dependence on molecular weight and temperature. Studied were the hydrodynamic characteristics (intrinsic viscosity, [η], and diffusion coefficient) of dilute pitch solutions, glass transition behavior, viscoelastic properties, and dielectric dispersion-electric conductivity characteristics of fractionated pitches with different molecular weights, which were prepared using the difference in solubility of the pitches in n-hexane and benzene. The hydrodynamic studies yielded an important information on the shape and dimension of constituent pitch molecules, i. e., oblate ellipsoid with the axial ratio of 1-3, and 10-20Å in equatorial diameter. The glass transition temperature, Tg, which decreased linearly with the inverse of number averaged molecular weight, was found to play an important role on the molecular weight dependence of steady-state shear viscosity, η, and steady-state shear compliance, Je0. The dependence of Je0 on temperature suggests that the elastic process in pitches is enthalpic, not entropic as observed in usual organic polymers. The dielectric behavior of pitches were described well by so-called Cole-Cole relation except prominent energy dissipation due to electrically conductive carriers in the region of low electrical frequency at high temperature. The importance of the rheological studies of mesophase pitches was emphasized in relation to the technical development of anisotropic carbon fibers with high elastic modulus and high strength
A comparative study of the rheological properties of nine molecularly characterized polyethylene melts is presented. This includes three high density polyethylenes (HDPE), three low density polyethylenes (LDPE) and three linear low density polyethylenes (LLDPE). The HDPE's respond quantitatively similar to other vinyl polymers in their dependence upon molecular weight distribution. This is most notably seen in its shear viscosity-shear rate dependence or η/η0vs. η0γ, which may be quantitatively interpreted in terms of Mw/Mn. The rheological properties of LLDPE's depend upon molecular weight distribution in a manner identical to the HDPE's. The long chain branched LLDPE's exhibit strikingly different behavior especially in uniaxial extension where they exhibit strain hardening behavior.
PVC melts have viscoelastic properties. Moreover PVC melts have additional flow characteristics such as slippage on the wall of solid surfaces. The velocities on the wall of most polymer melts are usually zero, but those of PVC melts are not zero but finite. In the present paper, the slip velocities were measured by a simple method using some grooved nozzles, which can stop the slippage on the wall over a certain shear rate range. The measured values of the slip velocities were found to be from 10 to 60% of the average velocities. It was found that grooved nozzles should be suitably designed for various compounds, flow conditions, geometries, etc. The true flow curves, defined as those in which the effect of the slippage is removed, had almost the same property as the flow curves of the other polymer melts without slippage. A simple model of two-layer flow was introduced in order to predict the slip velocities and deepen understanding of the slippage mechanism. A very thin layer of a low molecular weight liquid is assumed to ooze out on the wall from a bulk flow layer of the PVC compound. The slip velocities could be predicted approximately from the model. It may be concluded that the very thin layer really exists, since the slip velocities had almost the same values regardless of the differences in the surface metals of the nozzles.
When a viscoelastic fluid flows out from a horizontally placed rectangular duct, many cracks and upheavals are formed on the upper surface of jet: the jet looks like a packed row of cylinders. As far as the authors know, this anomalous phe-nomenon has not yet been reported. The occurrence of this phenomenon is not affected by inlet flow condition and duct shape. The state of the jet surface varies with increasing flow rate. At low flow rates, the surface is smooth and the jet is stable. As the rate increases, the surface becomes to be composed of cracks and upheavals, which are replaced by new ones from time to time. At relatively low rates of flow, an upheaval breaks into two. These grow and push aside the neighboring ones, and the one at the end of the row vanishes. At higher rates of flow, an upheaval is suddenly formed in the crack, grows, and pushes aside the neighboring ones. In the anomalous stage of flow, many air bubbles rush into the duct from the upper edge of exit when the flow is suddenly stopped.
Dynamic mechanical properties of ABS polymers with various rubber contents were measured in the glass transition temperature region of the rubber phase over a wide range of frequency. Time-temperature superposition could be applied well. The temperature dependence of the shift factors for all the ABS polymers was expressed by a common WLF equation with suitable choice of the reference temperature, Ts. log aT=-17.44 (T-Ts)/(51.6+T?Ts). The reference temperature was regarded as the glass transition temperature, Tg. Tg thus obtained decreased with a decrease in rubber content. Thermal stresses in ABS polymers estimated from the pressure dependence of Tgwere in good agreement with the theoretical values calculated from the difference in thermal expansion coefficient between the two phases and the rigidity, and increased with decrease of the rubber content. It was found that the two phases were bonded together with sufficient strength by grafted chains.