The contributions of dipoles and trapping electrons to the thermally stimulated current (TSC) spectra (-170∼130°C) in dry wood electrets were investigated not only by examining the collecting voltage-dependence of the TSC but also by substituting acetyl groups for hydroxyl groups in wood.
When the polarizing voltage (VP) and the collecting voltage (VC) were applied, the current (IPC) was proportional to (VP-VC) in the low temperature dispersion. In the high temperature dispersion, the VC-depenence of the current became higher than the VP-dependence with rising temperature and the polarity reverse of the current was observed.
When the collecting voltage was applied without the polarizing voltage, the current (IC) showed a high value in the higher temperature region. This phenomenon can be explained by means of the presence of conduction current. The difference between IPC and IC was given by the following equation: IPC-IC=kVP+IT(VP, VC), where IT(VP, VC) is the current due to trapping electrons. When VP was constant and VC was varied, this value (IPC-IC) was held constant in the rising part of the high temperature dispersion as well as in the low temperature dispersion. The value at 80°C tended to decrease with an increase in VC, and so trapping electrons may take part in the current.
The current in the high temperature region except near 130°C as well as in the low temperature region markedly decreased with an increase in acetyl value.
It is possible to conclude from the above results that the TSC in the rising part of high temperature dispersion as well as in the low temperature dispersion results from the polarization due to dipoles but trapping electrons may take part in the high temperature part of the high temperature dispersion.
