Controlled Air Oxidation for Surface Functionalization of Pyrolytic Carbon Black

Abstract

It is known that the chemical composition of pyrolytic carbon black changes considerably after the pyrolysis process of the tire owing to the presence of a high level of charge which alters the homogeneity of its surface and therefore affects the efficiency of the interactions of pyrolytic carbon black with polymers. Thus, when used in composites, the presence of these impurities causes a nonhomogeneous distribution of the pyrolytic nanofillers in the matrix. This results in the agglomeration of the pyrolytic fillers, which limits their effectiveness as reinforcing materials. Surface treatment techniques have been developed to reduce the chemical activity of impurities, but innovative practical techniques to improve the structural surface properties of the pyrolytic filler enhancing its effectiveness in composites are still needed. To do so, the main objective of these innovations is to improve the surface chemical properties to enhance the surface chemical activity of the pyrolytic black. It is in this context that this work is intended. The functionalization of the surface of pyrolytic carbon blacks involved a precise control of oxidation by air, which allowed grafting acidic oxygen functional groups. The objective is to reinforce the activity of the surface properties to allow better adhesion between the filler and the polymers for the possible development of composites with a plastic matrix. In this study, the functionalization technique is quite ecological, and the oxidizing agent used was oxygen from air. This technique made it possible to carry out controlled oxidation of different samples of pyrolytic carbon black over different initial temperature ranges (Top), namely, from 25 to 370 °C, from 370 to 385 °C, and above 385 °C. In each experiment, the evolution of the oxidation temperature of the treated sample was monitored, and the final product was characterized by a variety of physicochemical characterization techniques including thermogravimetric analysis, the physisorption isotherm of nitrogen to determine the specific surface area (Brunauer–Emmett–Teller method) and diameter and pore size distribution estimated by nonlocal functional density theory. Also, the concentration of oxygenated acid functions was evaluated using Boehm titration, and infrared spectroscopy with Fourier transform in attenuated total reflection mode ATR–FTIR was carried out as well on each oxidized sample. Raman spectroscopy was utilized to examine possible modifications of the carbon ordering. Transmission electron microscopy was also applied. For samples oxidized over the initial temperature range of 370–385 °C, the process allowed generating maximum concentrations of surface acidic oxygen groups with only insignificant weight loss. Also, the injection of water vapor at selected oxidation time into the reactor allowed good control of the local temperature distribution in the sample, which is particularly important for the temperature of the hot spots likely to form at the points on the surface where oxidation begins.