Structure modification of isotactic polypropylene by bi‐component nucleating systems

The efficiency of heterogeneous nucleation of isotactic polypropylenes (iPP) with various isotacticity and MWD is estimated by an increase of the crystallization temperature (Tcr). A bi‐component nucleating system, composed of a pimelic acid and a calcium stearate, was added to the polymeric matrix in the molten state. The relative increase of Tcr is found to be independent on the structure stereo‐regularity of iPP. On the contrary, dependent on the polymer structure, the investigated nucleating system influences in a different way the creation of the β‐phase. The form of the DSC melting curves, for the β‐phase rich iPP samples, is discussed in terms of various preliminary cooling conditions. The transformation from a multi‐modal form of the DSC melting peak to a simple one is related to the lowering of the cooling rate and to the increase of the heating rate.