Delaminated and intercalated organically modified montmorillonite in poly(1,4-cis-isoprene) matrix. Indications of counterintuitive dynamic-mechanical behavior

Abstract

Montmorillonite (Mt) and Mt organically modified (OMt) with dimethyl ditalloyl ammonium cations were delaminated through ball milling. X-ray diffraction (XRD) analysis allowed the observation a more efficient delamination for OMt than for Mt. In fact, 90% delamination was obtained for OMt, without appreciable variations of the in-plane Mt order. About 60% delamination was obtained for pristine Mt, in the presence of a substantial reduction (up to 40%) of crystalline order in the structural planes. A reflection due to the rotator order of talloyl chains was found both in pristine and in extensively delaminated OMt samples. Polymer nanocomposites based on poly(1,4-cis-isoprene) were prepared with two types of OMt: OMt, unmilled, with the ammonium cation intercalated in the interlayer space (I-OMt) and 90% delaminated OMt (D-OMt). XRD analysis of clay polymer nanocomposites (CPNs) revealed the unaltered crystalline order of I-OMt and a nearly complete maintenance of the delaminated structure of D-OMt. Dynamic-mechanical characterization of CPN gave counterintuitive results. I-OMt revealed a higher tendency to give rise to the filler networking phenomenon, in samples crosslinked with a sulfur based system. Moreover, I-OMt gave rise to a more pronounced extension of the rubbery plateau at low frequencies, in uncrosslinked masterbatches. This behavior is attributed to the higher volume fraction of I-OMt, as the intercalated alkylammoniums contribute to the I-OMt volume, whereas they essentially act as compatibilizers in D-OMt. Delamination of OMt is thus presented as a powerful tool to reduce the dissipation of energy in dynamic-mechanical applications of polymer melts and elastomers.