Delamination of organically modified montmorillonite for reducing the filler networking with carbon black in poly(1,4-cis-isoprene) based nanocomposites

This work presents the correlation between the organization of an organically modified montmorillonite (OMt) and the dynamic-mechanical properties of polymer nanocomposites containing a hybrid filler system, based on carbon black (CB) and OMt. Clay polymer nanocomposites (CPN) were prepared by melt blending synthetic poly(1,4-cis-isoprene) (PI), carbon black (CB) and OMt. Two types of OMt were used: with ammonium cations intercalated between the clay mineral layers (I-OMt) and delaminated (D-OMt). The latter was obtained via ball milling of I-OMt and presented a degree of delamination higher than 95%, as revealed by X-ray diffraction (XRD) analysis. The structure of CPN was studied with XRD and transmission electron microscopy (TEM) analyses. The mechanical behavior of uncrosslinked masterbatches and of nanocomposites crosslinked with sulfur based systems was assessed with dynamic shear experiments, by measuring the time needed to recover the initial modulus after a large strain perturbation and by obtaining master curves for the dependence of the storage modulus on frequency. I-OMt is shown to promote the filler networking phenomenon more easily than D-OMt: the storage modulus has a stronger reduction with the strain amplitude and a longer rubbery plateau is featured on the frequency scale. Modulus recovery measurements revealed that the structure of CPN can be restored after the application of large strain amplitudes. The extent of OMt delamination is presented as a key feature to control the dynamic-mechanical properties of CPN containing a filler, such as CB, suitable to establish an intimate interaction with OMt. The partial substitution of CB with D-OMt allowed the preparation of crosslinked nanocomposites with lower Payne effect.