This paper describes the applicability of a new quality control test method, the full-notch tensile fatigue (FNTF) test, using fatigue behavior. As quality control test methods for PE pipes, stress rupture tests, environmental stress crack resistance tests (ESCR tests), etc. for testing long-term strength have been conducted, all of which are prescribed in the JIS. However, as the time to failure is extremely long in these tests, quality is not judged by the actual time to failure but is judged acceptable if the time exceeds a certain limit. To accelerate failure, the FNTF test was proposed, in which the test specimen is notched all around and a repetitive load is applied to it. The significance of this test was studied. The test, conducted with a square wave in a complete tension mode at an elevated temperature of 80°C and at a frequency of 0.5Hz, enables practical and efficient quality control of polyethlene pipes. In this test method, failure is accelerated to about 1/100 of the time specified for the stress rupture test in the JIS, and it is possible to determine a failure curve, from which the change in the performance of a resin product by an actual time to failure can be determined. From the test result, it has been shown that the time to failure due to pure creep can be predicted by studying the creep-fatigue interaction at various frequencies.

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The experimental study of elongational flow for solution treated ultra-high molecular weight polyethylene (polyethylene gel) was carried out using an elongational rheometer. Three different molecular weight polyethylenes, M_w=1.0×10ⁿ, 2.0×10⁶, 2.5×10⁶ were used. Solutions were prepared by dissolving 10wt% of the polyethylenes in decalin. The solution treated ultra-high molecular weight polyethylenes were uniformly elongated in constant strain rate elongation experiments. The elongational viscosity-time relation at 140°C shows the same behavior as polymer melts except at high viscosity. The elongational strain (draw ratio) at high temperature are much smaller than that in lower temperature experiments. A rapid increase in elongational viscosity appears at ca. 200sec for strain rate of 0.008sec^-1. The degree of the viscosity increase of the solution treated polyethylene is much steeper than that of polymer melts. The steep increase in the viscosity was discussed in terms of the structure development of the solution treated polyethylene.

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The measurement of the filament temperature along a spinline in a high speed melt spinning process provides information on the cooling behavior and crystallization behavior of running filament. The filament temperature was analyzed through simultaneous measurements of infrared radiation intensity and the diameter of the filament. The determined empirical formula for the evaluation of the cooling of the running filament predicts a slower cooling rate than that obtained from the Kase and Matsuo equation. The diameter profile for a poly (ethylene terephthalate) spinline at a take-up velocity of 6km/min showed a so-called neck-like deformation at 140-150cm down from the spinneret, and the temperature profile showed a maximum just after the end of the deformation. This temperature increment reflects the heat of crystallization induced by molecular orientation. The rate of crystallization in the spinline, which is estimated from the temperature and diameter profiles, at a temperature of ca. 160°C and birefringence of 0.108 is 10⁵ times greater than that of the isotropic state. It is suggested that crystallization proceeds rapidly just after the end of the neck-like deformation in a high speed spinning process.

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