STUDIES ON THE THERMAL PROPERTIES OF HOT DRAWN P. E. T. FIBERS

In the previous paper, taking notice of the temperature range of the maximum shrinkage (85°_??_90°C) and the abnormal elongation (in the vicinity of 115°C) for successive heating and coolling at a constant rate, the effects of time-dependence on the dimensional change at a constant temperature were investigated in the temperature range of 85°_??_115°C. Especially, the effects of the load on the dimensional change for lower stretched P. E. T. fibers, which were shown markedly abnormal elongation at heating, were studied. Thermal changes in the fine structure are discussed based on the X-ray diffraction patterns. The results obtained are as follows:<br>1) The shrinkage for most of the stretched fibers, except for higher stretched (draw ratio: 3.8), becomes larger with the time passed in silicone oil bath at 85°C under less load. The shrinkage of the intermediate oriented fiber (draw ratio: 2.5), having an unstable structure, becomes larger; the a-axis oriented (non-drawn and lower stretched fibers) are medial; next in order, the fiber-like oriented fiber (draw ratio: 3.8) becomes less so. The higher stretched fiber (draw ratio: 3.8) shows a slight elongation beyond 90min. The higher stretched fiber continues to have extension monotonously at 102°C, but other stretched ones change shrinkage for extension in a short time with increased draw ratio. The shrinkage _??_ time curves at 115°C are similar to the shrinkage behavior at 102°C.<br>2) Effects of the dimensional change at 102°C for lower stretched fibers are remarkable, The abnormal elongation on the shrinkage-time curve may have been superposed on the thermal creep effect due to the elongation that becomes larger with increased load over the spontaneous elongation caused by the cold-crystallization<br>3) When the shrinkage and logarithmic time curves under less load for the same fiber at different temperatures are compared, it is found that they may be superposed by a simple lateral shift along logarithmic time scale within the temperatures of this experiment.<br>4) In contrast with the time-dependence on dimensional change under tensionless condition, higher stretched fiber shows shrinkage at all times on the degree of the heat-set and logarithmic time curves under a constant length, or, intermediate stretched . fibers always show elongation. On the other hand, the lower stretched fibers may change elongation for shrinkage during the heating.