The studies of structural characteristic improvement of pyrolysis carbon black by synchrotron radiation X-ray nano-computed tomography

Pyrolysis carbon black (CBp) from waste tires not only has significant economic benefits but also addresses the urgent environmental problem of waste tire disposal. To date, many studies have been conducted to improve the properties of CBp in order to enhance its reinforcing effects. However, due to the structural complexity of CBp, it is crucial to quantitatively evaluate its structural discrepancies and identify the subtle distinctions between CBp and commercial carbon black (CB) in order to guide the improvement of CBp's properties. In this study, synchrotron radiation X-ray Nano-CT, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) were employed to carefully investigate the spatial and chemical structures of CBp before and after nitric acid (HNO₃) treatment. We believe the main reasons for the low structurer (fractal dimension: 2.162 for CBp, lower than 2.307 for commercial CB), inhomogeneous size distributions, and inert chemical surface properties of CBp are the presence of rubber residues (volume ratio: 3.6 %) and other oxides remaining on the surface. These substances block pores, cover the active sites for chemical groups, and cause smaller particles to adhere to larger ones. After the residues were removed through HNO₃ treatment, the spatial and chemical structures of CBp were significantly improved (pore volume ratio increased from 2.7 % to 6.5 %), bringing its properties closer to those of commercial CB. The aim of this study is to identify subtle microstructural changes that can guide the optimization of conditions for producing CBp with the potential to replace commercial CB in tire fabrication.