Desenvolvimento e caracterização de composições elastoméricos de EPDM com redução no teor de óxido de zinco

Abstract

Zinc oxide nanoparticle (nano ZnO) is a kind of inorganic multifunctional filler, which has extensive uses in rubber additives. Notably, most of relevant researches about nano ZnO focused on using them as a substitute of conventional ZnO and an essential cure activator for rubber crosslinking by sulfur or sulfur donors in rubber composites. In this work, the effect of three kinds of ZnO on the properties of ethylene, propylene and diene (EPDM) elastomeric compounds was investigated. Standard ZnO (sZnO), nano ZnO (ZnO 40) and nano ZnO dispersed in CaCO3 (ZnO 30) were used and their characteristics were analyzed. The characterizations of these ZnO were carried out by atomic absorption spectrometry, X-ray diffraction, surface area, scanning electron microscopy, pore and particle size distribution. The elastomeric composites were processed in an industrial two-roll mill and the different ZnO were added in a laboratory two-roll mill. A usual composition to bus body rubber profile were prepared with varying the proportion of ZnO (1, 2, 3, 4 and 5 parts per hundred of rubber (phr)). To ZnO 40 and ZnO 30 ten composites were developed (1, 2, 3, 4 and 5 phr), including a compound without ZnO (White sample). The cure properties were determined in an oscillating disk rheometer. The unvulcanized compositions are also characterized by a Mooney viscometer and a rubber process analyzer (RPA). After vulcanization, the compositions had their physical- mechanical properties analyzed, as well as scanning electron microscopy. The thermal oxidative aging, the parameters and degradation kinetic mechanisms were studied for the compounds with the same mass content of Zn (sZnO 4 phr, ZnO 30 3 phr and ZnO 40 2 phr), as well as the white sample. The results of these investigations showed that ZnO 30 and ZnO 40 have a smaller particle size and higher surface area, making them more reactive and classifying them as nano ZnO. The results of the investigation of the effect of different types of zinc oxide in the EPDM composites were satisfactory, since the same results were obtained with lower amounts of ZnO, particularly with the use of nano ZnO. The non-isothermal degradation process of EPDM rubber compounds were investigated with thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), using the different calculation procedures. It was found that the values of activation energy of the composition with ZnO 30 and ZnO 40 showed higher results to sZnO, confirming the higher thermal stability. The degradation reaction mechanism determined by the method Coats Redfern (CR) and confirmed by Criado method was the F1 type, can be described by the random scission mechanism, in terms of the first order kinetics. Thus, the use of nano ZnO in elastomeric compositions became interesting, economically viable, important for the environment and it could be a reduction of Zn in the compositions without prejudice to the mechanical performance of the artifacts.