Materiais híbridos formados pelo ânion ditiocarbimato [C7H7SO2NCS2]2- . 2 H2O e hidroxissais lamelares de zinco: síntese, caracterização e estudos de vulcanização de borracha natural

Abstract

The study of layered materials has received much attention in recent decades due to the numerous possibilities of applications, such as the preparation of adsorbent materials, catalysts, devices for releasing drugs, and sensors. In this context, inorganic-organic hybrid materials stand out, which can be formed from the interaction between inorganic matrices, with the intercalation of organic molecules between the layers of the layered component. Dithiocarbimates (DCBI), organic anions that can be intercalated in suitable layered matrices, are known in the literature for their fungicidal and bactericidal properties and the capacity to form metallic complexes, which present activities as rubber vulcanization accelerators. It is noteworthy that, so far, there are no reports in the literature about zinc hydroxy salts (hydroxynitrate or hydroxyacetate) intercalated and/or functionalized with dithiocarbimate anions. The purpose of this work was the synthesis, characterization, and evaluation of the stability in the aqueous medium of these unpublished hybrid compounds and their tests as accelerators of rubber vulcanization. The compounds obtained were characterized by X-ray diffraction (XRD), vibrational spectroscopy in the infrared region (IR), electronic spectroscopy in the ultraviolet-visible region (UV-Vis), scanning electron microscopy, and energy dispersive X-rays (SEM /EDS). All synthesized compounds were tested as accelerators in the rubber vulcanization process. The XRD results indicated that the hydroxy salts, obtained without the presence of the dithiocarbimate anion, presented good crystallinity and, after being submitted to ion exchange reactions or having been synthesized via coprecipitation, products intercalated and/or functionalized with the organic anion were obtained, maintaining the basic structure of the layered structure. FTIR data suggest that acetate anions interact with the layers in a bidentate manner, nitrate anions are free in the interlayer spaces, and DCBI anions interact with the layers through the CS2 portion. The kinetic studies carried out from data obtained through UV-vis confirmed the instability of the DCBI anion in a basic medium, however the anion was more stable than when in an aqueous medium. The release study in an aqueous medium made from suspensions of the hybrid compounds HAcZ-iDCBI, HAcZ-fDCBI, and HNZ-iDCBI indicated greater stability of the anion due to its interaction with the matrices. In addition, the results indicated the presence of an anion in the reaction medium during the synthesis time and corroborate with the data of DRXP and DCBI size in the analysis of the integrity of the anion present in the intercalated structures. SEM/EDS techniques indicate morphologies with shapes without well-defined sizes and uniform distribution of elements over the surface. Tests of solids as accelerators in the rubber vulcanization process and mechanical tests were compared with the commercial accelerator ZEDC. The samples that showed better results were HNZ, HNZ-fDCBI, and HNZ-iDCBI. All samples were active as accelerators, although slower and with lower crosslinking levels, they had an advantage in terms of pre-cure time and minimum torque. Mechanical tests indicated that the synthesized samples have lower tear resistance and higher elongation at break when compared to ZEDC.