Investigation of the Surface Structure of Initial/Reclaimed Carbon Fibers after Chemical Treatment/Low-Temperature Solvolysis

The article examines the surface structure of carbon fibers after extraction by low-temperature solvolysis from carbon fiber and functionalization of the initial carbon fibers by Raman spectroscopy and X-ray diffraction. Contact angles of all treated fibers were measured, the values of their surface energy were found, and the mechanical properties of polymer composites based on acrylonitrile butadiene styrene were evaluated. Functionalization was carried out using nitric acid for 1, 3, 6, 16, and 24 h at room (25 °C) and elevated (60 °C) temperatures. It has been shown that an increase in processing time leads to the removal of the most reactive areas from the surface of carbon fibers and, as a result, to a decrease in wettability by more than 20%. An increase in the functionalization temperature contributes to more active oxidative processes that lead to fiber degradation and an even greater decrease in wettability (from 30%). Carbon fiber obtained by low-temperature solvolysis of carbon fiber-reinforced plastics for 1 h showed better wettability compared to 1 h of functionalization, regardless of temperature. A study of the physicomechanical characteristics of the obtained polymer composites has shown that the most effective filler is carbon fiber, functionalized within 1 h. Using reclaimed carbon fiber at the same mass concentrations yields comparable strength values to samples filled with fibers during 1 h of processing. Such a comparison of the modes of functionalization and extraction of carbon fibers will allow optimization of the conditions of low-temperature solvolysis in the future.