THERMOLUMINESCENCE STUDY OF PET FIBERS FOR TIRE-CORD USE

Abstract

Commercial PET fibers for tire-cord use were characterized by Thermoluminescence method (TL). TL experiments were performed separately at low and high temperatures: In the low temperature experiment, samples were irradiated by x-ray from a Copper-tube at -180°C for 1 hour and then heated up to room temperature at a rate of 3°C/min. to measure the TL intensity as a function of temperature. In the high temperature experiment, the x-ray irradiation was made at room temperature and heated up at the same rate of heating as in the low temperature experiment. In the Low temperature TL, asymmetric-shaped intensity curves with the maxima between -150°C and -130°C were observed commonly for all specimens. However, big difference was observed in the magnitude of the low temperature TL intensity among the specimens: the intensity of a specimen with the strongest TL was one order of magnitude larger than that of the specimen with the weakest TL. The high temperature TL curves had maxima at about 80°C corresponding to the Tg, and the specimens with very weak low temperature TL had another maxima at 160°C as well as at 80°C. The fibers were repeatedly extended to a fixed strain at a rate of 105 rep./min. at room temperature, and the change of TL with the extension was measured. The high temperature TL intensity increased with extension but decreased with time after the stop of the repeated extension: the intensity measured after long time was weaker than before extension, with an exception of the specimen from FII company. In this fiber the increase in the TL intensity with the extension was much larger than in other specimens, and the intensity did not become weaker than before extension even after a long time. Low temperature TL intensity remarkably increased in the specimens with weak low temperature TL before extension, while it almost remained as before in the specimens with strong TL intensity before extension. The results obtained in the study suggested that TL method may be effectively used for the characterization of PET tire-cord fiber and also the study on the fatigue properties of the fibers.