PIEZOELECTRIC RELAXATION OF WOOD III - TH E EFFECT OF DELIGNIFICATIONON THE PIEZOELECTRIC RELAXATION OF WOOD IN LOW-TEMPERATURE REGION

To clarify the effects of chemical constituents on the piezoelectric b ehavior of wood, the dielectric, elastic and piezoelectric properties of delignified wood as well as untreated wood were measured at 10 and 100 Hz over a temperature range of -150 degrees C to 0 degrees C. As t he lignin content of wood decreased, the peak location of the dielectr ic loss and the loss modulus shifted to lower temperatures with a decr ease in magnitude. On the other hand, the piezoelectric loss remained almost unchanged by delignification, although the peak location at abo ut -110 degrees C for untreated hoonoki shifted slightly to lower temp eratures with decreasing lignin contents. The value of the piezoelectr ic constant for the untreated hinoki wood changed from negative to pos itive at about - 120 degrees C, while that of the delignified hinoki w ood was positive over the temperature range tested. The analysis by us ing a two-phase model showed that the piezoelectric constant of wood, d, could be expressed by the following equation: d= d(c)phi(c)+d(a)phi (a) where d(c) and d(a) are the piezoelectric constants of the crystal line and oriented amorphous regions, respectively. The dielectric and elastic dispersions of hemicellulose were observed at about -110 degre es C and -120 degrees C, respectively. However, the piezoelectric cons tant and loss for hemicellulose were about 0.4x10(-14) C/N and 0.3x 10 (-14) C/N, respectively. This fact suggested that hemicellulose was in volved in the oriented amorphous region of the cell walls, and that th e difference in the piezoelectric relaxation between softwood and hard wood was ascribed to the hemicellulose content.