Quantification of highly oriented nucleating agent in PP-R by IR-microscopy, polarised light microscopy, differential scanning calorimetry and nuclear magnetic resonance spectroscopy

To relate a morphological structure of polymeric specimens to the applied conditions of the production process requires to be able to analyse the morphology and composition of the specimen with high spatial resolution, ideally with a single technique. Infrared microscopy (μFTIR) is a highly attractive technique to map the crystallinity and additive content of polymer samples due to its simplicity and spatial resolution. However, no methods exist yet which allow to exploit these advantages for oriented minority phases with high aspect ratio, and to study the degree of crystallinity in oriented polymer samples. Based on a theoretically derived approach we show for the first time that the spatial distribution of the β-nucleating agent N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide (NU-100) in random ethylene propylene copolymer (PP-R) can be determined by μFTIR from the sum of the absorption intensities in three directions of inspection. Using the same approach the degree of crystallinity of the polymer can be profiled, thus eliminating the problem arising from dichroism inferred by chain orientation. The newly developed method was applied to specimen of PP-R prepared by extrusion, injection and compression moulding. The results regarding the NU-100 content are in good agreement with results from nuclear magnetic resonance (NMR) and the results regarding morphology confirm those from polarised light microscopy (PLM) and differential scanning calorimetry (DSC). This method development opens the perspective to establish process → structure relationships for samples having an arbitrary degree of orientation with regard to the main phase as well as the minority phase.