Nucleation, athermal observation

When the filler is pressent at polypropylene crystallization, can be expected that this affects its crystalline order, being the Avrami parameter n the key to these changes. In our study, whereas in the isothermal crystallization of unfilled polypropylene the value of n is near three, i.e. similar to the values reported in the literature (4) corresponding to a tridimensional athermal nucleation, in the composites containing the block copolymer, sepiolite or talc, apart from deviating notably from the value found for unfilled polypropylene, it does not remain constant with filler concentration. The dif ferent behaviour observed between the composites containing the different fillers points toward the qualitative fact that different fillers promote different structures in the polypropylene composites containing them, which undoubtlessly has an impact on their physical properties. 

II. For shear rates higher then I/t, but lower then 1/xr, only orientation effects enhance the point nucleation that is, on top of the normally observed athermal nucleation, the flow causes an additional sporadic nucleation. The number of extra nuclei depends on the flow strength and the flow duration. For the Weissenberg numbers it now holds Wio 1, W4 < 1. 

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