Polypropylene-Layered Silicate Nanocomposites: Filler Matrix Interactions and Mechanical Properties

Abstract

Various alkyl ammonium cations were ionically exchanged with the sodium cations of montmorillonites with two different cation exchange capacities (CECs). The organo-montmorillonites were compounded with polypropylene (PP) and the effect of filler-matrix interactions on the intercalation-exfoliation behavior and the mechanical properties of the composites were investigated. With increasing the chain packing density, an increase in the d-spacing was observed and for the same cation, the d-spacing of the OMMT was higher for the higher CEC clay. Covering the surface with molecules of higher cross-sectional area led to large basal plane spacing which was helpful in achieving the partial delamination of the filler in the PP matrix even without the use of conventional compatibilizers. The modulus of PP organo-montmorillonite composites was significantly enhanced, but the other tensile properties decreased indicating the increased brittleness and lack of stronger attraction forces at interface. Augmenting the filler volume fraction also led to a significant increase in the stiffness which was compared to the theoretical predictions using the Halpin Tsai model and its modified versions.