Rheology of polypropylene

Amorphous polypropylene (aPP) of low molecular weight has been know for over 100 years as an oily or waxy substance of low viscosity. The isotactic polypropylene (iPP), discovered in 1954, has a regular structure, a high degree of order and crystallinity. Recently, two members were added to the industrial polypropylene family isotactic PP with long-chain branching, and syndiotactic polypropylene (sPP), both produced using metallocene catalysts. 

As for other pol)Tners, the viscosity of PP depends on temperature, deformation rate, additives, molecular weight (MW), molecular weight distribution (MWD), etc. For MW = 7kg/mol (M is the entanglement MW) the zero-shear viscosity at T = 190°C follows the dependence [2]  

According to Zeichner and Patel s observations, (Z-P), the crossover point of the storage and loss shear moduli = G (m) = G (w), pro- 

The above relationships are valid for linear PP homopolymer, and should not be used either for branched PP, chemically crosslinked PP, or multiphase systems, e.g. for blends, composites, and lubricated formulations, viz. with siloxane or fluorinated additives. Furthermore, PP is sensitive to stress degradation (facilitated by peroxides, spedaUy in the 

The multiphase nature of polymeric systems (blends or composites) leads to complex rheological behavior [6]. Since flow depends on morphology, which in turn is determined by the flow field, the measurements in different flow fields usually show different behavior the basic assumptions of the continuum mechanics are invalid for multiphase materials. Furthermore, since the deformation rate at the interface is discontinuous whereas stresses are continuous, the rheological dependencies should be analyzed as stress, not strain-rate dependent. 

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Solomon J. Michael, Almusallam S. Abdulwahab, Seefeldt F. Kurt, Somwangthanaroj Anongnat, and Varadan Priya. Rheology of polypropylene/clay hybrid materials. 

Solomon MJ, AlmusaUam AS, Seefeldt KF, Somwangthanaroj A, Varadan P. Rheology of polypropylene/clay hybrid materials. Macromolecules 2001 34 1864-1872. 

Muke, S., Ivanov, I., Kao, N., Bhattacharya, S.N. Extensional rheology of polypropylene melts from the Rheotens test , J. Non-Newton. Fluid Mech. 101(1-3) (2001), 77-93... 

Sugimoto, M., Masubuchi, Y., Takimoto, J., Koyama, K. Melt rheology of polypropylene containing small amounts of high-molecular weight chain. 2. Uniaxial and biaxial extensional flow. Macromol... 

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