Mechanical properties of polymeric materials are determined by the chemical structure of the chain and the resulting morphology. While the chain structure is given by the synthesis the morphology depends also processing conditions such as temperature, pressure and/or mechanical stress additionally have a strong influence. Thus, to tailor mechanical properties morphological characteristics have to be characterized on both macroscopic and microscopic scale. Crystallinity and chain orientation are important characteristics for semicrystalline polymers. Besides X-ray diffraction Raman is a suitable tool since it is not only sensitive to chemical variations but also to conformational changes of the chain. Thus, determination of the crystallinity, crystalline polymorphs or the orientation of polymeric chains is possible. Since Raman spectroscopy can be combined with an optical microscope it enables to investigate these structural characteristics on the sub-scale. Raman microscopy was applied to investigate processing induced changes in polymer microstructure of isotactic polypropylene (iPP) used as model system. For iPP samples either melt crystallized or as solvent casted or extruded films average crystallinities, depolarization ratios and orientation functions were estimated and the data obtained by Raman were compared to DSC and WAXS data. Since all values are in good agreement the method was applied to determine the distribution of crystallinity and orientation performing Raman images of pressure crystallized samples before and after subjecting to additional shear load. Local variations in the characteristic values such as the local orientation can be estimated (Figure 1).

Investigation of microscopic properties of polymer surface in contact with liquids: A combined SFM-Raman study

249th National Meeting (2015)

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