Start
Mar 05, 2009 - 16:00
End
Mar 05, 2009 - 17:00
Venue
Creativity Hall (Room 118) Chemical Engineering
Event Type
Speaker
Dr. Sachin Jain Global Polymer Research BASF-SE Ludwigshafen Germany
Title
Nano-scale events with macroscopic effects in PP/silica nanocomposites
It is well established that above a certain threshold value for the molar mass Mc the terminal (zero shear) viscosity 0 of polymer melts scales with molar mass to the power 3.4. The strong increase of the viscosity with increasing molar mass is related to entanglement coupling and the presence of a physical entanglement network characterized by an average molar mass between the physical crosslinks Me between the macromolecules. But high molar masses are required for materials properties notably toughness and strength rendering the production of polymer products an area of unfortunate compromises. Therefore we designed a novel approach which would enable high molar mass materials to flow better without compromising the properties. The melt viscosity of poly(propylene) is found to reduce dramatically through the addition of a minute amount of silica nanoparticles. We attribute this unique effect to “selective adsorption of high molar mass polymer chains” on the surface of the nanofillers. This represents a paradigm shift regarding commonly-accepted relations between the molar mass and viscosity of molten polymers (Einstein’s equation). This particular rheological behaviour is accompanied by strong effect on the crystallization behaviour during flow. The flow-induced crystallization (FIC) behavior of nanocomposites has been studied using in-situ SAXS and WAXD. The viscosity drop caused by the selective adsorption provides the possibility of creating a more uniform and isotropic morphology in a product. The X-ray scattering study shows that orientation is minimal at 0.5 wt% silica concentration at which the viscosity also shows a minimum. In comparison to pure PP the flow-induced crystallization is faster in silica-filled PP but this enhancement is lowest for the concentration where the orientation is minimal.