Thermoplastic molding has been prepared from beech wood flour steamed at 180°C or at higher temperatures without any additives. It exhibited a smooth and lustrous surface and had a high density of approximately 1.45 g cm-3. The internal structure of molding revealed that the flour particles were completely surrounded by black resin-like substance which was thermoplasticized by heat and pressure during the molding process. The chemical composition of the steamed flour and physical properties of molding were examined as a function of steaming temperature. Maximum bending strength and Young's modulus of molding reached 63 MPa and 11 GPa, respectively, at 180°C of steaming, which were much higher than those of a hardboard. The water absorption of the molding was 8% or less and decreased with the steaming temperature.

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Keyaki wood is the most suitable material for the ''Wadaiko, a traditional Japanese drum.'' However, the amount of wood with excellent quality available for producing the wadaiko has decreased in recent years. Wadaiko shells made of artificial materials are an effective substitute for the traditional wooden wadaiko. In this study, prototypes of the wadaiko were made using a wood plastic and their sound characteristics were examined. The vibrational properties of the wood plastic were investigated and compared with those of keyaki and sen woods used for the traditional wooden wadaiko. The sound characteristics of the wood plastic wadaiko were more complex than those of the keyaki wadaiko. The Chladni experiment on the wood plastic wadaiko clarified that the respective modal patterns appeared at two or three resonant frequencies with increasing the degree of the modes. The sound components of the wood plastic shell did not affect the overall sound characteristics of the wadaiko. The internal friction of wood plastic was larger than those of keyaki and sen, whereas the specific Young's modulus in the grain direction was smaller than those of keyaki and sen. The results of this study indicated that the mechanical properties of wadaiko shell materials strongly affected both the tension of the membrane and the boundary condition between the membrane and shell. A large specific Young's modulus as well as high strength comparable to that of keyaki is necessary for wood plastics to be used as a substitute material for the wadaiko shell.

We report the first results of persistent spectral hole burning of dendrimer porphyrins having three‐, four‐, or five‐layered aryl ether dendritic arrays. We evaluate structural relaxations of dendrimer framework around the porphyrin core at low temperatures. A large environmental change around the porphyrin core, as evaluated from the hole area, was suppressed in dendrimer porphyrins of higher generation numbers, whereas a small environmental change, as evaluated from hole width, showed no dependence on the number of generations. The dendrimer porphyrins showed sharp holes at 20 K, suggesting a long dephasing time and the suppression of spontaneous spectral diffusion. The results of dendrimer‐embedded polymer sample indicated that the structural relaxation of polymer chain outside the dendrimer does not have an influence on the resonant frequency of the porphyrin core. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 210–215, 2002

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