Preparation of Nonwoven Carbon Materials from Fabrics Based on Flax Cellulose and Viscose Fibers

A method for obtaining nonwoven carbon materials by the staged heat treatment of cellulose felt is developed. Fabrics produced from fibrous flax cellulose and viscose fibers by needle punching are used as nonwoven precursors. To obtain carbon fabric precursors the optimum ratios of components are chosen from the data on the formation of nonwoven fabrics and the thermal analysis of various blend formulations. It is shown that the content of flax fibers in the system should be at least 50%. Viscose fibers play the role of a reinforcing material and so far cannot be fully excluded from the system. With an increase in the content of flax cellulose the value of carbon yield grows. The mechanical properties of the carbon felt are provided by the physical network of friction and dispersion contacts between individual fibers. Upon heat treatment of the composite nonwoven material, the morphological features of precursor fibers remain unchanged. The interplanar distances of carbon layers in the carbon material are calculated using X-ray diffraction analysis and transmission electron microscopy. The fraction of carbon upon heat treatment to 1700°С is at least 90%, and after graphitization to 2400°С the purity of the product is above 99%. The maximum values of carbon yield at this temperature may be as high as 25‒27%. The coefficients of thermal conductivity of the carbon felt are measured, and the values obtained are 30% lower than the corresponding parameters of carbon fabrics.