Rheological and isothermal crystallization characteristics of neat and calcium carbonate‐filled syndiotactic polypropylene

Abstract

Steady-state and oscillatory shear behavior of three neat syndiotactic polypropylene (s-PP) resins and a s-PP resin (s-PP#8) filled with CaCO 3 particles of varying content, size, and type of surface modification were investigated. All of the neat s-PP resins investigated exhibited the expected shear-thinning behavior. Both the storage and loss moduli increased with decreasing temperature. The shift factors used to construct the master curves were fitted well with both the Arrhenius and the Williams-Landel-Ferry (WLF) equations. The inclusion of CaCO 3 particles of varying content, size, and type of surface modification, to a large extent, affected both the steady-state and oscillatory shear behavior of s-PP/CaCO 3 compounds, with the property values being found to increase with increasing content, decreasing size, and surface coating of the CaCO 3 particles. Lastly, the effects of melt-annealing and crystallization temperatures on isothermal crystallization behavior of s-PP#8 filled with CaCO 3 particles of varying content, size, and type of surface modification were also investigated. The half-time of crystallization of neat s-PP#8 exhibited a strong correlation with the choice of the melt-annealing temperature (T f ) when T f was less than about 160°C, while it became independent of T f when T f was greater than about 160°C. On the other hand, the half-time of crystallization of s-PP#8/CaCO 3 compounds did not vary much with the T f . Generally, the observed half-time of crystallization decreased with increasing CaCO 3 content and increased with increasing CaCO 3 particle size. Finally, coating the surface of CaCO 3 particles with either stearic acid or paraffin reduced the ability of the particles to effectively nucleate s-PP#8.

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