Long period analysis in blends of high-density and lowdensity polyethylene

Long period calculations from small angle X-ray scattering experiments (SAXS) is a well-known way to describe biphasic polymeric systems. In the case of semi-crystalline homopolymers, more and more sophisticated models have been proposed to account for the SAXS intensity profiles. However, they use too many parameters to be applied to systems including two crystalline phases and an amorphous phase. Therefore, we propose a crude alternative, based on a generalization of the old paracrystalline Hoseman model, in order to consider the case of blends of high-density (HDPE) and low-density (LDPE) polyethylene. The crystalline lamella thickness distribution function is taken as the sum of two Gaussians (bimodal function 2G). As far as the amorphous domain thickness distribution function is concerned, either an exponential distribution (E) or a Gaussian distribution (G) is used. The model 2G/G proves to be much more realistic than the model 2G/E, with respect to the long period evolution as a function of HDPE/LDPE blend composition.