Materiais à base de magnésio sintetizados em presença de extratos de plantas para aplicação em vulcanização de borrachas nitrílicas

Abstract

This work aims to comparatively evaluate the potential of magnesium-based activators (G-MgO and Mg2+-P) synthesized in the assistance of colony leaf extract in the vulcanization of nitrile rubbers, NBR, as a substitute for the usual activator ZnO. The compounds, G-MgO and Mg2+-P, were synthesized with the assistance of the hydroalcoholic extract of colony leaves (Alpinia Zerumbet). The compounds were characterized by Fourier Transform Infrared Absorption Spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TG and DTG), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), high resolution scanning electron microscopy (SEM-FEG) and determination of particle size distribution by dynamic light scattering (DSL). The green Mg-O (G-MgO) presented the cubic crystalline structure, average crystallite diameter in the range of 8 nm and nanometric particles around 51 nm. Mg2+-P showed bands characteristic of the formation of the magnesium(II)-polyphenol complex, amorphous structure and agglomerated particles with no defined shape. In order to study the technical feasibility of using green magnesium compounds as activators in the vulcanization of NBR, replacing ZnO, compositions NBR-33%-GMgO, NBR-33%-Mg2+-P and NBR-33%-ZnO were prepared. Comparisons were made with regard to rheometric properties, density of cross-links (DLC), vulcanization kinetics, mechanical properties, thermal stability and thermo-oxidative aging. It was observed that the compositions containing Mg compounds showed a different vulcanization process to those containing ZnO. This behavior was more evident in the kinetic study with the “free model”. The compositions with G-MgO showed a higher density of cross-links and higher thermal stability, while the compositions with Mg2+-P showed similar behavior to those with ZnO. As for mechanical properties, the compositions with G-MgO and Mg2+-P showed promising results, especially with lower stress relaxation values. A study was carried out to compare the performance of NBR compositions with 45% and 33% acrylonitrile (ACN) containing G-MgO and ZnO as activators. Comparisons were made with regard to rheometric properties, DLC, vulcanization kinetics, mechanical properties, thermal stability and thermo-oxidative aging. In this case, it was observed that the compositions with G-MgO did not undergo significant changes with the different ACN contents, however, in the compositions containing ZnO, the rheometric properties and vulcanization kinetics showed changes in the vulcanization system in the NBR-45%-ZnO composition, making G-MgO a more attractive activator for vulcanizing NBR containing a higher acrylonitrile content. Another study was carried out using FTIR to understand the difference in the vulcanization mechanism of MgO versus ZnO, where it was possible to observe that the interaction of magnesium oxide with the components of the vulcanization system is different from that of zinc oxide, especially in the formation of magnesium and zinc stearates, suggesting that the vulcanization mechanisms are influenced by the activators used.