Mapping Structural Evolution of Semi-crystalline Polymers to SAXS Patterns: An Explanation of the Butterfly Pattern

Coupling the micromechanical behavior of semi-crystalline polymers under various processing conditions to the morphological and structural evolution of crystalline/amorphous regions has been the subject of study for decades. However, even with a wealth of experimental data via Small Angle X-ray Scattering (SAXS) there is currently no clear understanding of the underlying structural features that give rise to the observed scattering patterns, even less so describing the associated morphology evolution during transformation from one type of pattern to another. A unique type of SAXS pattern, commonly referred to as butterfly pattern, has been observed since the first SAXS studies on polymers, but has not been satisfactorily explained. In this presentation we model the morphologies, simulate the experimental SAXS data, and refine the model using key morphological parameters to fully explain the observed patterns in terms of chain slip and lamellar shear as the essential deformation modes. Not only does this approach illustrate the static SAXS pattern, it also reveals the transformation from e.g., a butterfly pattern to a simple 4-point pattern, often observed in semi-crystalline polymer processing.