A novel insight into the origin of toughness in polypropylene–calcium carbonate microcomposites: Multivariate analysis of ss-NMR spectra

Abstract

Interface has been long time recognized as crucial for changing and optimizing mechanical properties of polymer composites and nanocomposites. Spectroscopic identification of this interface, however, remains a great challenge. This study combining solid-state 13C NMR spectroscopy with a principal component analysis (PCA) proposes a novel strategy to explore the role of interfacial area at vicinity of filler particles on toughness of polymer composites. Samples of commercial-grade isotactic polypropylene (PP), both neat and modified with various types of calcium carbonate (CaCO3) microparticles, were subjected to a combination of fracture mechanical testing and solid-state NMR analysis. Temperature-induced transformation between the free and constrained amorphous phases was monitored using the factor analysis of 13C MAS NMR spectra. The three-dimensional correlation plots clearly separated the prepared PP/CaCO3 microcomposites into the well-defined clusters, allowing the systems with differing quantities of partially ordered amorphous domains to be identified. These differences perfectly correlated with the toughness of the prepared composites. The results thus confirmed that the changes in the toughness of the microcomposites are closely related to the increased formation of the partially ordered trans-crystalline fraction of PP chains.