Electron Microscopy (TEM) and X-ray Spectromicroscopy (STXM) of PP/MMT/PP-g-MA and PP/MMT/SEBS Nanocomposites
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1257-O08-09
Electron Microscopy (TEM) and X-ray Spectromicroscopy (STXM) of PP/MMT/PP-g-MA and PP/MMT/SEBS Nanocomposites Zulima Martin1, M. Angeles Gomez1 and Ignacio Jimenez2 1 Instituto de Ciencia y Tecnologia de Polimeros, CSIC. Madrid 28006. Spain 2 Instituto de Ciencia de Materiales de Madrid. CSIC. Madrid 28049. Spain . ABSTRACT Here we present a study on the polypropylene/montmorillonite interaction based on x-ray diffraction, transmission electron microscopy (TEM) and scanning transmission x-ray microscopy (STXM) measurements, which provides a complete picture of the intercalation and exfoliation processes taking place. INTRODUCTION Phenomena and processes at the nanometric scale have opened revolutionary possibilities in the development of new nanostructure materials. In polymer systems, the addition of layered silicates leads to a great improvement in the properties of the matrix such as thermal stability and mechanical performance with very low filler contents, because the high surface area of these particles with nanometric dimensions increases the interfacial interactions between matrix and clay. However, the properties depend strongly on the interfacial interactions between particle and matrix. In the case of non-polar polymers like polyethylenes or polypropylenes, the interactions are hindered by the polar character of the silicates and the non-polar nature of the matrix and, hence, require the incorporation of compatibizing agents to overcome this problem. In this work we have considered nanocomposites of montmorillonites (MMT) in a poypropylene matrix (PP) made by melt processing, using as additives (i) polypropylene-graft maleic anhydride (PP-g-MA), a common polar compatibilizer and (ii) poly(styrene-b-ethylene butylene-b-styrene) (SEBS).
EXPERIMENTAL Materials. The polypropylene (PP) used as matrix was an isotactic homopolymer, with a polydispersity of 4.77, provided by REPSOL. It is characterized by an isotacticity of 95%, determined by solution NMR, and a viscosity average molecular weight of 179,000 g/mol.1,2 The organically modified montmorillonite (MMT) clay used in this study was Cloisite 20A (C20A) obtained from Southern Clay Products. The individual platelets are typically 1 nm in thickness, with an aspect ratio larger than 50. It is modified with N,N-dimethyl dihydrogenated tallow quaternary ammonium chloride. Tallow is the mixture of octadecyl (major component (>60%)), hexadecyl and tetradecyl. The modifier concentration is 95 meq/100 g clay, with a weight lost on
ignition of 38%, and the interlayer spacing, determined by XRD, is d001 = 2.52 nm. The common compatibilizer used was a polypropylene-graft-maleic anhydride (PP-g-MA) with a maleic anhydride content of 0.42 wt % and a viscosity average molecular weight of 83,500 g/mol, EXXELORPO1015 provided by EXXON. The elastomer used was a triblock copolymer SEBS (Calprene H-6110) provided by DYNASOL, with 30 wt % of styrene content, a molecular weight value of Mw = 85,000 g/mol and Mw/Mn = 1.45, as determined by gel permeation chromato
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