Effect of pile irradiation on the dynamic mechanical properties of polyethylene

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Abstract
The effects of pile irradiation on the damping and resonant frequency of a “high pressure” polyethylene has been investigated over a temperature range from 80 to 550°K. in the audiofrequency region using an apparatus which drives rod‐like specimens in their transverse modes. Using irradiation dosages which result in approximately 4% crosslinking or greater, the mechanical loss peaks found at about 165, 265, and 355°K. in polyethylene are altered. Definite changes in the resonant frequency or modulus‐temperature plots also occur. The 355°K. peak, attributed to the melting of the crystalline portions of the sample, decreases in height and shifts to lower temperatures with increasing irradiation dose. A decrease in the height of the 265°K. peak accompained by a shift to higher temperatures takes place. The 165°K. peak initially increases in height and peak temperature but at higher dosages a marked decrease in the damping maximum occurs. The damping behavior in the 165 and 265°K. regions is discussed in terms of diffusional motion of chain segments in the amorphous polymer portions.