Kenji Iwakura

Properties and structure of poly(vinyl alcohol)/silica composites

The relationships between the properties and structure are discussed for poly(vinyl alcohol)(PVA)/silica composites prepared through the sol-gel process. The composites became stiff and brittle with increasing the silica content. The properties of the composites were changed drastically at around the composition of PVA/silica = 70/30 wt %. For example, there was no large change in the Youngs modulus above 30 wt % of silica content (Pure PVA: 31.8 MPa, silica 30%: 52.6 MPa, silica 50%: 55.2 MPa). Consequently, it was considered that the three-dimensional network structure of silica could be formed in the composite with more than 30 wt % of silica in PVA. From this behavior, it could be considered that the crystal growth of PVA was remarkably inhibited by silica network.

The effect of compatibility on toughness of PPS/SEBS polymer alloy

Abstract The effect of compatibility on the improvement of the toughness of polyphenylenesulfide (PPS) blended with styrene–ethylene–butylene–styrene block copolymers (SEBS) has been studied. In PPS/SEBS polymer alloy having SEBS, which was highly modified by maleic anhydride, it was confirmed that the elastomers were dispersed finely because of high compatibility with the PPS matrix, and the toughness was improved efficiently by the release of constraint of the strain due to void formation in the elastomer particles. On the contrary, in the PPS/SEBS polymer alloy having the conventional SEBS or SEBS, which was lightly modified by maleic anhydride, the diameter of dispersed elastomer particles was larger, and the particles were deformed into a rod-like shape, and oriented along to the direction of injection flow, particularly in high content of elastomer. These oriented particles were fractured easily, and many cracks, which were distributed along to the direction of flow were formed. These cracks would result in suppression of improvement or decrease in toughness of the polymer alloy.

Effect of ionic interaction on linear and nonlinear viscoelastic properties of ethylene based ionomer melts

The effect of ionic interaction on linear and nonlinear viscoelastic properties was investigated using poly(ethylene-co-methacrylic acid) (E/MAA) and its ionomers which were partially neutralized by zinc or sodium. Dynamic shear viscosity and step-shear stress relaxation studies were performed. Stress relaxation moduli G(t, y) of the E/MAA and its sodium or zinc ionomers were factorized into linear relaxation moduli G°(t) and damping functions h(y). The relaxation modulus at the smallest strain in each ionomer agreed with the linear relaxation modulus calculated from storage modulus G′ and loss modulus G″. In the linear region, the ionic interaction shifted the relaxation time longer with keeping the same relaxation time distribution as E/MAA. In the nonlinear region, the ionic interaction had no influence on h(y) when the ion content was low. At higher ion content, however, the ion bonding enhanced the strain softening of h(y).

COMPRESSIVE MODULUS OF FERRITE CONTAINING POLYMER GELS

The mechanical properties of magnetic gel have been investigated. Magnetic gels, which consist of finely dispersed powder of barium ferrite (BaFe12O19) and poly vinyl alcohol (PVA), have been synthesized. The diameter of barium ferrite is less than 45 μm. The magnetic gels varying with ferrite concentration, crosslinking densities were prepared by mixing 10 wt.% PVA aqueous solution and barium ferrite using glutaraldehyde as a crosslinking agent in the presence of HCl. The diameter of barium ferrite is large enough to have a permanent magnetic moment. We applied a 10 kOe magnetic field in order to saturate the magnetic moment of barium ferrite. After magnetization, the compressive modulus was estimated with an ultrasonic method in order to find the influence of magnetization. Ultrasonic measurements were carried out using burst waves at 10 MHz and 295.5 K. The modulus of magnetized gel was found to depend on the concentration of magnetic substance, the crosslinking density, and the degree of swelling. It was clear that the modulus of magnetized gel was higher than the gel without magnetization for all samples. The change in modulus to the initial modulus ΔM′/M′o for 10 wt.% and 15 wt.% of ferrite concentration was about 0.28% and 0.4% in a lower density region, respectively. Moreover, the change in modulus ΔM′/M′o was constant in a lower density region however it strongly depends on the density in a higher density region. When the stress direction is perpendicular to the magnetization, the change in modulus increased. On the contrary, the change in modulus decreased when the stress direction is parallel to the magnetization. As increasing the density, the distance between magnetic substances become short and therefore the magnetic interaction is more significant in a higher density region.

Anisotropy in longitudinal modulus of polymer gels containing ferrite

The effects of magnetization direction on the longitudinal modulus of magnetic gels, which consist of magnetized barium ferrite and poly(vinyl alcohol), have been investigated using 10 MHz ultrasonic waves. The modulus change due to magnetization depends on both the crosslinking density and magnetization direction. The modulus change increased and decreased when the strain direction was perpendicular and parallel to magnetization, respectively.

Anomalous temperature dependence in the elongational viscosity of ethylene-based graft copolymer melts

Abstract The ethylene-based graft-copolymerized structure exhibited an increase in non-linearity in the elongational viscosity with temperature. This behaviour has not been observed in homogeneous polymer melts. Possible sources of the positive increase in non-linearity with temperature are indicated.

Rheological properties of magnetic paints containing barium‐ferrite fine particles with various aspect ratios

Static flow properties of magnetic paints containing hexagonal shaped barium‐ferrite fine particles have been investigated in terms of their diameter/thickness aspect ratio. The Ba‐ferrite paints showed typical pseudoplastic flow behaviors with different yield stresses. The flow curves were divided into three types of flow components using Kuin equation as follows: (1) yield stress part, (2) Newtonian flow part, (3) viscoelastic deformation of flocs with stress relaxation. Each flow curve for the Ba‐ferrite paint could be well‐fitted to the theoretical trace by the Kuin equation, and four kinds of rheological parameters were obtained from those procedures. We found that such parameters except for the Newtonian viscosity increase with increasing particle aspect ratio or particle specific surface area. This implies that the rheological properties of Ba‐ferrite paints are strongly governed by the particle interaction forces associated with particle characteristics.