A re-examination of the elastic modulus dependence on crystallinity in semi-crystalline polymers

The elastic modulus versus crystallinity linear relationship in Polyethylene (PE) is re-examined via meticulous measurements over a wide set of PE. First, large discrepancies to linearity are observed; moreover, Raman spectroscopy revealed that the content of the so-called interphase exhibits considerable variations over the set of PE. Therefore a novel strategy based on DMA is developed for a better identification of the modulus of each phase along the temperature. one hand, below the α and β relaxations, the young modulus proved to be linearly dependant on the sum of the crystal and interphase content. On the other hand, between the α and β relaxations, the interphase appears surprisingly as stiff as the crystal. In addition, the quenched samples exhibit a particular behavior. A simple model has lead to the conclusion that their mechanical coupling and/or amorphous modulus are significantly different as compared with all others materials.