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This article reports the piezoelectric moduli of wood d 31 , d 32 , and d 36 . The piezoelectric moduli of wood d 31 and d 32 have not been previously reported, although there has been much research on the d 14 and d 25 moduli of wood. The moduli d 31 , d 32 , and d 36 were measured carefully because their absolute values were considerably smaller than those of d 14 and d 25 . For Softwoods, d 36 values were mostly negative, whereas the values for hardwoods had either positive or negative values. The other moduli, d 31 and d 32 , were a mixture of positive and negative values in softwoods and hardwoods. The existence of d 31 and d 32 suggests the presence of an electrical polarity of the cellulose crystal in the fi ber direction of the wood. The polarities of d 31 and d 32 became clear from wood in the outer part of the trunk, where the crystallinity of cellulose is large and the alignment of the crystals becomes parallel to the fi ber direction.

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The piezoelectricity of cyanoethylated hydroxyethylcellulose was investigated. Elastic, piezoelectric, and dielectric relaxations were observed at -80 ° to -60°C and 0 ° to 20°C at a frequency of 10Hz. The activation energy is about 9-15kcal/mol in the low temperature region and about 30-45kcal/mol at room temperature. These relaxations in the low temperature region may be caused by the motion of the cyanoethyl group and those at room temperature mostly by the motions of the main chain. Cyanoethylated hydroxyethylcellulose has a high piezoelectric strain constant (d25), which is the largest value among the cellulose derivatives and is almost the same as the value for polyvinylidene fluoride. The electromechanical coupling factor for cyanoethylated hydroxyethylcellulose was small.