Abstract The use of controlled extension flows associated with processing with predominant shear flows can bring gains in the dispersive capacity of nanofillers during the processing of nanocomposites. In this work, we use a controlled flow device coupled to the matrix of a single-screw extruder to process PP matrix composites containing 0.5% and 2.5% (v/v) of MWCNT. The nanocomposites were evaluated by optical microscopy and oscillatory rheological analysis. The clusters size analysis showed that in PP/0.5MWCNT-el, 70.5% of all its clusters were below 1µm2 while its analog processed without the extensional flow showed 59.8% of its clusters below this value. The rheological analysis allowed to verify that the compositions processed with the presence of the extensional flow have their crossover frequencies shifted to lower values, that is, longer relaxation times corroborating that improved degrees of dispersion were achieved.

Abstract The structure and properties of semi-crystalline polymers can be drastically tailored by extensional flows. In this work, polypropylene (PP), Polyvinylidene fluoride (PVDF) and Low Density Polyethylene (LDPE) were melt extruded through a sequence of rings designed to apply controlled extensional flows in the polymer melts. The effects of extensional flow on the structure and properties of the extruded filaments were then evaluated by mechanical tensile tests, dynamic-mechanical analysis (DMA) and Differential Scanning Calorimetry (DSC). The DMA and tensile tests revealed a significant increase in terms of static and dynamic moduli for the polymers extruded through the extensional flow device. PP, PVDF and LDPE had their dynamic moduli enhanced 19%, 40% and 77%, respectively. These results were ascribed to the enhancement in crystallinity and orientation degree of the polymer chains induced by the extensional flow. The crystallinity was increased around 9% for PP, PVDF and LDPE extruded under extensional conditions.

The purpose of the present paper was to test the validity of the nonlinear regression method for calculating the non-isothermal crystallization rate constant of the Nakamura's model of a rotational molding grade LLDPE directly from non-isothermal crystallization experiments carried out in a single cell DSC. Cooling rates of 50, 40, 30, 20, 10 and 5 oC/min were used with samples of 3.0 mg under nitrogen atmosphere. Here, good agreement was observed between the experimental relative crystallinity curves and the simulated ones using the calculated parameters by nonlinear regression. It shows that this method can be used to determine the Nakamura's non isothermal rate constant for using in simulation of the cooling phase of rotational molding. In this paper it was used 10-3, 10-4 and 10-14 as the initial crystallinity in the Nakamura's model. However the best average results for all cooling rates was obtained when 10-4 was used. Average spherulitic dimensions of LLDPE studied in this paper did not change significantly with different cooling conditions.