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Piezoelectric properties of elongated films of cellulose diacetate and cellulose triacetate were investigated in a temperature range from -160°C to +160°C. The sinusoidal stress was given to a film specimen cut at 45 degrees obliquely to the orientation axis at frequency 20c/s, and measurement was taken of the electrical polarization that appeared on the faces of the film. Not only the absolute value of piezoelectric constant but also the phase difference between the stress and the polarizatian was detected. Defining the complex piezoelectric modulus as d*=d'-id", d' and d" were quantitatively determined as a function of temperature.In cellulose diacetate, d' increased with the rise of temperature accompanied by a peak of d" with a positive sign, indicating that the polarization lagged behind the stress. On the contrary, in cellulose triacetate, d' decreased with the rise of temperature, accompanied by a trough of d" with a negative sign, indicating that the polarization overreached the stress. Such results may be called as piezoelectric dispersion and absorption with temperature.Dynamic viscoelastic and dielectric measurements were also carried out for the same specimens. Comparison of the results indicated that piezoelectric, elastic, and dielectric absorptions took place over the same range of temperature, and that the piezoelectric absorption was the sharpest among them.The oriented polar molecules or oriented crystallites are supposed to be the units responsible for the piezoelectric polarization in the elongated polymer films. Distribution of mechanical stress and dielectric shielding around these units and even piezoelectric moduli of units themselves can be altered by the thermal variation of the molecular motion in polymers.

Temperature Variation of Complex Piezoelectric Modulus in Cellulose Acetate