RELAXATION BEHAVIOR OF POLYETHYLENE ORIENTED BY VARIOUS TECHNIQUES

Stress relaxation of high-density polyethylene extrudates and those cr ystallized from highly deformed melt (PE-1) have been investigated in a wide range of temperatures (-50 to +120-degrees-C) and draw ratios f rom 5.5 up to 12.2 at the different constant tensile strains from 1 up to 20%. The experimental data obtained have been summarized by the ti me-temperature superposition principle. Relative intensity of stress r elaxation (the stress drop in 10(3) s divided by the initial stress) h as been observed to increase together with the growth of draw ratio de spite the enhancement of the short-term properties. The radiation cros s-linking of the PE-1 samples may only decrease the stress relaxation intensity by 30%. The relaxation properties of a number of oriented po lyethylene samples produced by various techniques were compared. It ha s been established that all the investigated materials are characteriz ed by similar values and high relative drops in stress, whereas the sh ort-term properties are essentially different. It points out to the re laxation processes being intensive both in the oriented and unoriented PE.