Poly (vinylidene fluoride) (PVDF) has been widely explored to produce polymer nanocomposites possessing outstanding combinations of properties. In this work, the impact of extensional melt flows on the dispersion, relaxation and crystallinity of PVDF nanocomposites filled with multiwalled carbon nanotubes (MWCNT) and montmorillonites (MMT) was studied. Extrusion was employed to produce nanocomposites containing 3 wt% of fillers, named: (i) PVDF/3 wt% MWCNT, (ii) PVDF/3wt%MMT, and (iii) PVDF/1.5wt%MWCNT/1.5 wt% MMT. The results showed that applying a sequence of extensional flows through the melts improved the dispersion of both fillers in the PVDF matrix. Moreover, extensional flows significantly enhanced the viscosity and relaxation of MWCNT nanocomposite, but had marginal effects on MMT nanocomposite. On the other hand, MMT favored the crystallization of the β piezoelectric phase of PVDF over the α phase and the extensional flow enhanced its crystallinity content. Therefore, these new insights prospect a vast horizon toward the use of extensional flows for tailoring synergic combinations of properties in hybrid PVDF/MWCNT/MMT systems.

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.

In the present work, we prepared modified and unmodified microscale and nanoscale silica particles using spray-drying and the spray-pyrolysis process, respectively, which could be an alternative for the production of this kind of product in industrial scale. For it, modified Stöber method was used to synthetize the precursor solution including tetraethyl orthosilicate (TEOS) and triethoxy(octyl)silane (ETOS) as precursors and 3-(Trimethoxysilyl)propyl methacrylate (γ-MPS) as template for the functionalization. The silica sol passed into both equipment to obtain the final powder. The surface morphology was investigated with Scanning Electron Microscopy (SEM), and the Fourier Transform Infrared spectroscopy (FT-IR) was used to describe the functionalization of the final powder. SEM results show that we successfully synthetized spherical microscale and nanoscale particles with spray-drying and spray-pyrolysis process, respectively. The FT-IR analysis show the functionalization of the silica powder obtained with both technologies. It is possible to consider these technologies as a simple way to produce modified spherical silica particles in an industrial scale.

This paper has been partially presented at the 16th Brazilian Polymer Congress,held on-line, 24-28/Oct/2021.

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, dynamicmechanical 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.