Comparative Mechanical and Dielectric Relaxational Study of Low-Density Polyethylene

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Abstract
Some polymers show varying dynamic responses according to the technique employed to measure them. The polyethylenes are a good example, with a wide range of circumstances complicating the analysis of mechanical and dielectric relaxation spectra. First, the polyethylenes are nonpolar polymers that require oxidation or chlorination to obtain consistent dielectric activity; second, the relaxation spectrum is highly complicated in each of the three characteristic zones (γ, β, and α); and finally, the response to an alternative stimulus differs according to its physical origin. Thus it is well known that differences arise between dynamic mechanical and dielectric spectra when they are compared (McCrum et al., 1967; Morozuni et al., 1970; Ribes-Greus, 1986). Moreover, to obtain reasonable conclusions, it is necessary to use the same type of polymer in all cases; and to control the crystalline morphology of the specimen, a constant thermal history is needed.