Extrusão auxiliada por fluxo elongacional de compósitos de matriz de PVDF ou PP com MMT, NTCMC ou grafite

Abstract

The structure and properties of polymers, or composites, can be drastically modified by extensional flows applied during processing. In this work, PVDF and PP were used as matrices for the production of composites containing montmorillonite (MMT), multi wall carbon nanotubes (MWCNT) or graphite as fillers. For the processing, a device capable of applying extensional flow (EFD) was built, at a rate of 33.19 s-1, during extrusion, to compare the effects caused by the controlled flow, the processing was carried out with and without the EFD for production of filaments. The impact of controlled flow in processing was evaluated on the dispersion of fillers, rheological, mechanical, and thermal properties for the different composites and for neat polymers. The results of the particle size measurements showed that the use of EFD was able to provide reductions in the agglomerates dimensions, for all the fillers used. MMT particles in PVDF matrix showed decreases of 55%. Furthermore, the extensional flow significantly increased the values of G', G", rl* and the relaxation (tr) of composites containing MWCNT or graphite, but had marginal effects for composites containing MMT, this in relation to homologous compositions processed without the EFD. Regarding the mechanical properties, the compositions processed with EFD reached higher values of E, OM and E', which is directly related to the finer dispersion of particles in the polymer matrix for the composites and the alignment of the chains in the flow direction for the PVDF-el and PP-el. The presence of MMT in PVDF favored the crystallization of the piezoelectric phase, in addition, the elongational flow increased the final crystallinity of the composites with different fillers as well as the pure matrices of PVDF-el and PP-el, where this increase was 9 %. In this case, for the pure polymers, this effect is related to the alignment of the chains that can favor the crystallization, while for the composites it is due to the more accentuated nucleating effect for the processing with the EFD.