In-situ SAXS study of the mesoscale deformation of polyethylene in the pre-yield strain domain: Influence of microstructure and temperature

The deformation of polyethylene spherulites at the scale of the lamellar stackings is investigated by in-situ SAXS as a function of draw temperature in comparison with the macroscopic strain. Local elongation strain in equatorial region and local compressive transverse strain in polar region both increase in absolute value and follow linear relations versus macroscopic strain in the visco-elastic range. However, local strains turn out heterogeneous over the whole spherulite volume. This is attributed to the different type of mechanical coupling between the crystalline lamellae and the amorphous layers in the polar and equatorial regions. Increasing the temperature in the range 50–100 °C gradually promotes homogeneous distribution of strain at the local scale. The origin of this phenomenon is discussed in terms of activation of the chain mobility in the crystalline phase that modifies the mechanical coupling between the two phases. This ratio between local and macroscopic deformation increases with temperature up to the macroscopic value.