The influence of the cooling rate on the nucleation efficiency of isotactic poly(propylene) with bis(3,4- dimethylbenzylidene)sorbitol

The phase behavior of isotactic poly(propylene) (i-PP) and 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) was studied by using differential scanning calorimetry (DSC), rheology and optical microscopy and can be characterized by a simple binary monotectic phase diagram. DMDBS isa well-known nucleating and clarifying agent for i-PP that forms a fibrillar network upon cooling from a homogeneous melt within a specific concentration range. The influence of the cooling rate and the residence time in regime II of the phase diagram on the formation of the fibrillar network and the ratio between the a- and mesophase is investigated. This shows that DMDBS is actually a better nucleation agent for i-PP when it is given less time for gelation, since the formation of a 'secondary' structure, in which the thin elementary nano-fibrils form bundles of thicker fibrils, results in a decrease of the surface area that is available for nucleation.