Shear rheology and melt compounding of compatibilized-polypropylene nanocomposites: Effect of compatibilizer molecular weight

Direct melt compounding was used to prepare nanocomposites of organophilic montmorillonite (o-mmt) clay dispersed in maleated polypropylenes (PPgMA) as well as nanocomposites of organoclay and polypropylene (PP) modified with various grades of PPgMA compatibilizers. The thermal effect on the rheology and melt compounding was first investigated with a plastic-order. The shear viscosities and the melt flow indices (MFI) of the PPgMA compatibilizers were sensitive to the blending temperature, which had to be varied with the compatibilizer grade to achieve desirable level of torque for extensive exfoliation of organoclay in the plastic-order. However, for low molecular weight oligomer, the clay dispersion was poor because of low shear viscosity and thermal instability. Next, the PPgMA-modified PP/organoclay nanocomposites were prepared on a corotating twin-screw extruder. The nanoscale dimensions of the dispersed clay platelets led to significantly increased linear viscoelastic properties, which were qualitatively correlated with the state of exfoliation in the nanocomposites. The relative viscosity (relative to the silicate-free matrix) curves revealed a systematic trend with the extent of clay exfoliation. Furthermore, the degree of clay dispersion was found to increase with the loading of compatibilizers; however, high loading of compatibilizer compromised the final moduli of the nanocomposites.