Crystallisation of polypropylene containing nucleators

The crystallisation of polypropylene in the presence of sodium benzoate, graphite powders, Millad 3988 (1,3:2,4-bis(3,4-dimethyl-benzylidene sorbitol)) and NA-11 (sodium 2,2′-methylene bis-(4,6-di-tert-butylphenyl)phosphate) was studied. As a parameter for the effectiveness of nucleators, a free-energy parameter for the nucleation was estimated, on the basis of a theory, from the nucleation temperature during cooling at various rates. The density of actual nuclei was estimated from the radial growth rate of spherulites and the bulk growth rate, the latter obtained by the analysis of crystallisation isotherms. The dispersibility of nucleator particles calculated with reference to the mean volume of particles was various, the cluster size being ranged between unity to several hundred. The Young's modulus of films prepared from the polymer-nucleator mixtures has been found to correlate with the nucleus density without respect to the kind of nucleator.