Self-Assembly of Temperature Sensitive Additives in Polypropylene Melt and Its Influence on Viscoelasticity

The use of a temperature-sensitive nucleating agent (NA) for polypropylene (PP), besides its influence on the crystallization characteristic, provides a platform to affect the rheology of molten PP by controlling its self-assembly behavior. In this study, in order to clarify the dependence of the melt rheology properties on the self-assembly behavior of N,N′,N′′-tricyclohexyl-1,3,5-benzenetricarboxylamid, changes in the NA content and final process temperatures (Tf) were used to control the self-assembly behavior of the NA molecules. The morphological and rheological behavior of samples were studied at 180 °C and evaluated by using central composite design-response surface methodology (CCD-RSM). The polarized optical microscopy results showed a fibril shape structure with a length in the range of 26–94 μm and diameter of 3–11 μm. The regression analysis models revealed that the increase in NA wt % and Tf favored the formation of larger fibrils in length and diameter, and the impact of NA wt % was more significant than Tf. Shear rheometry results indicated that the fiber size and its distribution were both directly related to an increase in complex viscosity and storage modulus. The study of the zero shear viscosity, crossover frequency, Cole–Cole plot, and also ANOVA analysis indicated that the optimal value for Tf is 270 °C and for NA is 0.5 wt %.