Temperature dependence of the properties of low‐density polyethylene

The dynamic mechanical properties of low‐density polyethylene melts were measured as a function of frequency and temperature using the Orthogonal Rheometer. These results were expressed in terms of the components G′ and G″ of the dynamic modulus and the components η′ and η″ of the dynamic viscosity. The functions J′, J″, η*, and G* were also calculated from the results. The method of reduced variables or time‐temperature superpositions was attempted on the results. The classical method was found to require modification to be applied to these low‐density polyethylenes. From this modified form of the reduced variables technique, the temperature dependence of the elastic and viscous parts of the response could be separated. The experimentally determined temperature dependence of the elastic part of the response was found not to be in accord with the accepted theory of rubber elasticity. The temperature dependence of the viscous part of the response is discussed in terms of the concept of flow activation energy, and clarification of this term is explored. It is concluded that the temperature dependent properties of polymer melts are best compared at equivalent time scales of response in the non‐Newtonian region. In order to do this the temperature dependence of the elastic part of the response must be included explicitly in the reduction scheme.