EXPLANATION OF ORIENTATION PATTERNS DETERMINED FOR SHEET MATERIALS BY MEANS OF MICROWAVES

Unstretched, biaxially stretched, and uniaxially stretched poly(ethylene terephthalate) (PET) films showed different types of three-dimensional pattern, i.e., the frequency and angular dependencies of transmitted microwave intensity. The resonance frequency and the intensity at the resonance frequency for the biaxially and uniaxially stretched PET films changed with rotation angle, while those for the unstretched PET films stayed unchanged. Thus these properties reflected the dielectric anisotropy of the polymer films. The angular dependence of transmitted microwave intensity at a fixed frequency, i.e., the orientation pattern, gave an orientation angle and a maximum-to-minimum ratio of transmitted microwave intensity. The orientation pattern can be obtained by cutting the three-dimensional pattern at the fixed frequency. This frequency should be selected above the resonance frequency, where the transmitted microwave intensity is one-half that at the resonance frequency in the resonance curve which is located at the low-frequency side. The fixed frequency so chosen is most appropriate, since the maximum-to-minimum ratio and the orientation angle are most sensitive around it. The molecules in polymer films are arrayed on an average in the direction specified by the orientation angle where the transmitted microwave intensity is the smallest because of the shift of the resonance curve to the low-frequency side. The orientation pattern reflecting the dielectric anisotropy is very convenient for determining the orientation of molecules or fibers quickly and nondestructively.