Multi‐Modal Imaging of the Loading Heterogeneity in Blended Films of Amorphous and Semi‐Crystalline Polymers During Stretching
Martin Kreuzer, Maria Stec, Graeme Moad, Peter Halley, Marianne Impéror‐Clerc, Stéphan Rouzière, Jennifer Bodin, Jan Ilavsky, Emigdio Chávez‐Ángel, Aitor Mugarza, Francisco Martínez López, Juan Carlos Martínez Guil, Marc Raventós Tato, Marc Malfois, Bronwyn Laycock, Christopher J. GarveyABSTRACT
Spatially correlated spectroscopic and X‐ray scattering are used to identify the load bearing structures in melt blended poly(lactic acid) (PLA) with medium‐density polyethylene (MDPE) and high‐density polyethylene (HDPE). Regions of failure during uniaxial tensile deformation of films were identified using optical microscopy; crazes and domains oriented orthogonally to the extension direction are micron‐scale in pure PLA but expand to millimeter‐scale in the blended materials. Polarized infrared and Raman microspectroscopy reveals specific molecular orientation of the PLA and PE chains in the failure regions. Spatially localized X‐ray scattering provided information on crystalline (wide angle X‐ray scattering, WAXS) and meso‐scale domains (small angle X‐ray scattering, SAXS) and orientational information on these domains. The phase‐separated PE structures are shown to play a role in the distribution of load in the blend during extension, inhibiting the formation of PLA fibrils. These results indicate that the improved mechanical performance arises from a local redistribution of stresses in the brittle PLA by the PE phase in the craze region. A simple representation, pixel mapping of extracted parameters, from the large data sets would be suitable for more rapid and advanced multivariate analysis for mechanistic understanding and further materials improvement.