Mitsukazu Ochi

Enhanced partial discharge resistance of epoxy/clay nanocomposite prepared by newly developed organic modification and solubilization methods

Frequency accelerated partial discharge (PD) aging of epoxy nanocomposite with 5 wt % additions of clay was investigated in comparison with that of epoxy without clay in terms of PD erosion depth. It was found that the change in the erosion depth is far smaller in specimens with clay than those without clay. The newly developed organic modification and solubilization methods give comparable PD resistance characteristics. The latter would be more resistant to PDs than the former, if specimens were prepared properly. It was clarified that nano-micro mixed composites were superior to the single nanocomposite. Nano segmentation with some interaction zone effect is proposed as a mechanism of improvement in PD resistance.

Dielectric properties of epoxy/clay nanocomposites - effects of curing agent and clay dispersion method

Effects of the differences in the curing agent and filler dispersion method on the dielectric properties were examined for epoxy/clay nanocomposites. Irrespective of the clay dispersion method, relative permittivity and electrical conductivity are higher in the samples cured with the amine. Moreover, negative heterocharge accumulates in the vicinity of the anode in the amine-cured samples, whereas positive homocharge accumulates in the acid anhydride-cured samples. From the results of UV photon absorption and PL measurement, the bandgap or the energy at which the photon absorption increases drastically is smaller in the amine-cured samples than in the acid anhydride-cured samples. Ion migration can occur easily in the amine-cured samples whose electrical conductivity and relative permittivity are higher than the acid anhydride-cured samples. The curing agent gives the strongest effect, while the existence of clay affects secondly and the filler dispersion method has the weakest effect.

Phase structure and toughness of silicone-modified epoxy resin with added silicone graft copolymer

To disperse RTV-silicone elastomer as fine particles in a bisphenol-A-type epoxy resin, silicone-methylmethacrylate graft copolymer was added as a compatibilizer. The molecular weight of the silicone segment and the MMA segment between silicone branches in the graft copolymer strongly affected the effectiveness of compatibilizer. It was revealed that the graft copolymer which acts as a more effective compatibilizer was more highly concentrated at the interface between the silicone-dispersed phase and the epoxy matrix. The interfacial tension around the silicone-dispersed phase decreased with the formation of the interphase which is mainly composed of the graft copolymers. The diameter of the dispersed phase decreased with a decrease in the interfacial tension. The fracture toughness of the modified resins increased with a decrease in the diameter of the silicone phase.

Effect on the toughness and adhesion properties of epoxy resin modified with silyl-crosslinked urethane microsphere

Abstract In order to give a toughness and improve adhesion properties of the cured epoxy system, modified epoxy resins, which have pre-reacted urethane microspheres formed using dynamic vulcanization method in liquid diglycidylether of bisphenol A, were prepared. It was found that the size of the particles decreased to sub-micro order with increase in solubility of urethane oligomers in epoxy resin, and coefficient of variance in the particle size distribution resulted in less than 15%. Fracture energy G 1c of the cured system was highly improved. Lap shear strength and peel strength were also improved. These mechanical and adhesion properties do not depend on any curing condition of epoxy resin because of the existing stable particles in the epoxy resin before curing.

Effect of the addition of aramid-silicone block copolymer on phase structure and toughness of cured epoxy resins modified with silicone

Abstract To improve the toughness of silicone-modified epoxy resin, an aramid-silicone block copolymer was used as a compatibilizer. Fine silicone phases could be uniformly and stably dispersed in the epoxy matrix by the addition of the block copolymer. The relative ratio of the molecular weight of epoxy and silicone segments in the block copolymer strongly affected the effectiveness of the compatibilizer. The block copolymer which acted as a good compatibilizer was mainly concentrated in the interfacial area around the silicone phase. The main values of fracture toughness and impact strength in the silicone-modified system increased with a decrease in the diameter of the silicone phases. Their maximum value increased to about 2.0–2.5 times that of the unmodified system. Observations of the damage zone with an optical microscope revealed that the improvement in the toughness in the silicone-modified system is due to the increase in the area of the damage zone caused by the formation of fine silicone phases.

Improving Epoxy-based Insulating Materials with Nano-fillers toward Practical Application

A primary concern in recent nanocomposite research is practical application. In this study, various kinds of epoxy-based nanocomposites were made and their properties evaluated to determine their applicability as insulating materials for heavy electric apparatuses. Experimental results demonstrated that nano-fillers enhance insulation breakdown properties in nanocomposites. Moreover, nano- and micro-filler combinations were adopted as an approach toward practical application of nanocomposite insulating materials. These nano- and micro- filler mixed composites had the same low thermal expansion as aluminum, and insulation breakdown properties superior to those of conventional insulating materials. Consequently, an aluminum conductor and a vacuum interrupter were molded by the nano- and micro-filler mixed composites for the first time in nanocomposite research.

Comparison of dielectric properties between epoxy composites with nanosized clay fillers modified by primary amine and tertiary amine

Epoxy-based nanocomposites (NCs) were prepared using clay modified by either primary amine or tertiary amine, and the effect of the difference in modifier on the thermal and dielectric properties of the NCs were discussed. The NC with clay fillers modified by the primary amine, 1C, shows a glass transition end temperature (Teg) at a temperature 20°C lower than the neat epoxy (N). This indicates that the resin of 1C is less crosslinked than that of N. On the other hand, the sample 3C, in which the clay was modified by the tertiary amine, shows a DSC spectrum close to that of N. Namely, 3C has a high crosslinking density similar to N. While the three samples show a relaxation peak in their dielectric loss spectra, the peak appears at high frequencies in 1C compared to N and 3C. Moreover, ionic conduction current flows more at high temperatures in 1C than in N or 3C. These facts are ascribable to the difference in their crosslinking densities.

Effect of the network structure on thermal and mechanical properties of mesogenic epoxy resin cured with aromatic amine

The epoxy resin containing a typical mesogenic group such as biphenol was cured with catechol novolak and aromatic diamines which have neighboring active hydrogens. In the biphenol-type epoxy resin cured with catechol novolak, 4,4′ diaminodiphenylmethane, and p-phenylenediamine (PPD), the glass-rubber transition almost disappeared, and thus a very high elastic modulus was obtained in the high temperature region. It is clear that the thermal motion of the network chains is significantly suppressed in these cured systems. In addition, in the PPD-cured system, a characteristic pattern like a schlieren texture was clearly observed under the crossed polarized optical microscope. Thus we conclude that the mesogenic group contained in the epoxy molecule is oriented in the networks when the mesogenic epoxy resin is cured with phenols and diamines which have neighboring active hydrogens. On the other hand, the biphenol-type resin cured with 3,3′,5,5′-tetraethyl-4,4′-diamino diphenylmethane (TEDDM) showed a well-defined glass-rubber transition and, thus, a low rubbery modulus. In this cured system, no characteristic pattern was observed under the crossed polarized light. These results show that the large branches, such as ethyl groups on the network chains, prevent the orientation of network chains which contain the mesogenic group.

Bonding properties of epoxy resin containing mesogenic group

A liquid crystalline epoxy resin with a mesogenic group was synthesized and its adhesive bonding properties are compared to that of the bisphenol-A type epoxy resin. The bonding strength of the former resin system was higher than that of the latter. This suggested that the high bonding strength of the liquid crystalline epoxy system was due to the large deformation of this system along the stress direction. Bonding strength of all the cured systems had a maximum peak during curing, due to the increase in the internal stress which occurred during the curing shrinkage of the epoxy resins. To decrease the internal stress, we cured the epoxy resin with an excess amount of curing agents. Bonding strength of the system with the added excess amount of curing agent showed a higher value than that for the system with an equivalent amount of curing agent. It was considered that the high bonding strength of the former system was due to the low internal stress in this system.

Mechanical relaxation mechanism of epoxide resins cured with diamines

Abstract The mechanism of mechanical relaxation, which is observed between 50° and 90°C in epoxide resins cured with aromatic and alicyclic diamines, has been investigated by comparing dynamic mechanical properties and chemical structures of these networks. This relaxation is denoted here as the α′ relaxation. The occurrence of the α′ relaxation depends on the existence of p -phenylene groups, and is independent of the degree of cure in the cured epoxide resins. Moreover, the intensity of the α′ relaxation increases linearly with increasing the concentration of p -phenylene groups in the networks. From these results, it is concluded that the α′ relaxation of the cured epoxide resins is attributed to the motion of p -phenylene groups in the network structures.