The impact of blue organic and inorganic pigments on the crystallization and rheological properties of isotactic polypropylene

Viscosity behavior is used to illustrate the relative sensitivity of the rheological properties to the morphological structure imposed by the presence of organic copper phthalocyanine and inorganic ultramarine blue pigments in isotactic polypropylene. While the inorganic pigment showed a small effect, the organic pigment was responsible for greatly increasing the nucleation rate and rapidly increasing the viscosity. This was also accompanied by a lowering of the degree of supercooling and the formation of a fibrous morphology. The results indicate that copper phthalocyanine is an excellent nucleating agent, drastically reducing the onset time of crystal formation and increasing the crystallization kinetics. Dynamic rheological properties also suggest that the organic pigment acts as a softening agent in the supercooled melt. Percent concentration and shear rate were not found to be major factors accelerating the rate of crystallization. This study details contributing factors including the particle size differences of the pigments under scanning electron microscopy, which provides further insight into the non-spherulitic morphology observed under a Linkam device. A possible correlation between the pigment morphology, the crystallization kinetics and rheology is discussed.