Viscoelastic properties of a sap and a lac of Japanese lac trees (Rhus vernicifera) were investigated. For the sap, in the low frequency range, the frequency dependence of η′ was considerably large, whereas the frequency dependence of G′ was smaller than that in the audiofrequency range. These behaviors may be explained as follows : fine droplets of an aqueous gum solution dispersing in urushiol interact with each other and construct temporary network structures with long relaxation times, which vanish with the progress of making the lac from a sap.
The behavior of the lac is similar to that for the ordinary synthetic polymer solutions in the low frequency range, but the values of G′ and η′ in the audiofrequency range are almost independent of the frequency. These viscoelastic behaviors are likely to be intermediate between those for rigid rods and flexible chains in solutions. It is thought that as the lac-making process proceeds, water molecules gradually evaporate, and molecular chains of the gummy substances may take the more shrunk conformation. It is presumable that the restricted segmental motion of the polysaccharides may contribute to the peculiar viscoelastic behaviors of Japanese lac at the higher frequencies.

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Submicron powders of TiO₂-Fe₂O₃ were prepared by the vapor phase reaction of the TiCl₄-FeCl₃ (or FeCl₂) -O₂ system at 800° to 1,050°C. The phases appeared were anatase-TiO₂, Fe₂TiO₅, and ca-Fe₂O₃. As the Fe/Ti ratio in reacting gas mixture increased, the major phase in products varied from TiO₂ to Fe₂TiO₅ and then to co-Fe₂O₃. The fraction of Fe₂TiO₅ exhibited a maximum at 1. 2-1. 6 of the Fe/Ti ratio. Concerning the reaction temperature, the maximum content of Fe₂TiO₅ was obtained between 900° and 1,000°C. The reactions at 800°C and 1,050°C favored the formation of TiO₂ and Fe₂O₃, respectively. Particles produced at temperatures between 800° and 1,000°C with the Fe/Ti ratio of 0. 8 and above were roundish with average sizes ranging from 0. 04 to 0. 07 μm, and their sizes decreased with raising reaction temperature or with decreasing the concentration of metal-halides, although platelets and large particles were formed under the other conditions. The particles were generally single crystals of Fe₂TiO₅, Fe₂O₃, or TiO₂. The color of TiO₂-Fe₂O₃ powders changed from light brown to reddish brown with increasing the ratio of Fe/Ti. In the formation process of TiO₂-Fe₂O₃ particles, it was considered that the preferential nucleation of Fe₂O₃ and the growth by codeposition of both TiO₂ and Fe₂O₃ components occur.

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The effects of pigments on the adhesive strength of alkyd enamel films pigmented with surface treated titanium dioxides (S-1, S-2 and S-5) were studied. The adhesive strength of the films having various pigment volume concentration was measured by means of Adherometer, ultrasonic wave method, torque method and crosshatch test. In order to analyze the experimental results on adhesion internal stress, stress-strain properties, dynamic viscoelastic properties and degree of water absorption for paint films, and sedimentation volume in the alkyd resin solution were investigated. Main results were as follows : 2) Results of the sedimentation volume, gloss, viscoelasticity and water absorption showed that the pigment-vehicle interaction for S-2 or S-1 films was larger than that for S-5 films. 2) The increasing tendency of the adhesive strength was remarkable for the sample which the interaction between pigment and vehicle was large. 3) The internal stress increased with increasing PVC, and that for S-5 films was larger than that for S-2 or S-1 films. The adhesive strength was small in the films which the internal stress was large.

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