Effect of coal tar pitch modification on the structure and char yield of pyrolysis epoxy resin carbons

Epoxy resin carbons are of high strength, high temperature resistance, and corrosion resistance, which are widely used as the precursor of carbon composite materials. However, the applications of epoxy resin carbons are greatly limited for the characteristic of non-graphitization and low char yield (22 wt%). In this paper, coal tar pitch was used to modify epoxy resin carbons via a simple heating mixing, pyrolysis and high temperature graphitization. The results show that the coal tar pitch content and heat treatment temperature can improve the ordered graphite carbon content. As the coal tar pitch content increase, the ordered graphite carbon content of modified epoxy resin carbon increase after 3000 degrees C graphitization for 0.5 h. Particularly, the graphitization degree of epoxy resin carbon and 40 wt% coal tar pitch modified epoxy resin carbon are 8.42 % and 44.21 %, respectively. The grain size (Lc = 13.84 nm) and grain stacking height (La = 7.79 nm) of 40 wt% coal tar pitch modified epoxy resin carbon are bigger than epoxy resin carbon (Lc = 3.44 nm, La = 3.45 nm). The ordered coal tar pitch graphite carbon and disordered epoxy resin amorphous carbon are evenly distributed in the modified epoxy resin carbon, indicating a good comparability of coal tar pitch and epoxy resin. Besides, the entangling carbon ribbon are observed in the epoxy resin carbon after graphitization at 3000 degrees C. With the increase of coal tar pitch content, the content of carbon element, aromatic ring number, the char yield and thermal decomposition temperature of modified epoxy resin increased. Moreover, the char yield of expoxy resion modified by 50 wt% coal tar pitch is 42 wt%, almost two times higher than that of epoxy resin (22 wt%). The increased char yield of modified epoxy resin mainly inherited the high char yield of coal tar pitch (50 wt%) and the chemical crosslinking weight gain. More interesting, the chemical crosslinking weight gain reaches the maximum value of 15 wt% when the content of coal tar pitch is 40wt%. The reason for that is the possible chemical crosslinking reaction can be occured by the epoxy group and hydroxyl group within epoxy resin and carboxyl group and phenolic hydroxyl group within coal tar pitch. This study provides some theory foundation for the future application of epoxy resin carbon composite materials.