Structure and melt rheology of long-chain branching polypropylene/clay nanocomposites

Abstract

Long-chain branching polypropylene (LCB-PP)/clay nanocomposites were prepared by melt blending in a twin-screw extruder. The microstructure and melt rheology of these nanocomposites were investigated using x-ray diffraction, transmission electron microscopy, oscillatory shear rheology, and melt elongation testing. The results show that, the clay layers are intercalated by polymer molecular chains and exfoliate well in LCB-PP matrix in the presence of maleic anhydride grafted PP. Rheological characteristics, such as higher storage modulus at low-frequency and solid-like plateau in tan-ω curve, indicate that a compact and stable filler network structure is formed when clay is loaded at 4 phr (parts per hundred parts of) or higher. The response of the nanocomposite under melt extension reveals an initial decrease in the melt strength and elongational viscosity with increasing clay concentration up to 6 phr. Later, the melt strength and elongational viscosity show slight increases with further increasing clay concentration. These results might be caused by a reduction in the molecular weight of the LCB-PP matrix and by the intercalation of LCB-PP molecular chains into the clay layers. Increases in the melt strength and elongational viscosity for the nanocomposites with decreasing extrusion temperature are also observed, which is due to flow-induced crystallization under lower extrusion temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011