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

Abstract

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 °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 °C. With the coal tar pitch content increasing, the carbon element content and aromatic ring number of modified epoxy resin increased. As the coal tar pitch content increase, the char yield and thermal decomposition temperature of modified epoxy resin gradually increase. The char yield of 50 wt% coal tar pitch modified epoxy resin is 42 wt%, almost double that of epoxy resin (22 wt%). The char yield increased values of modified epoxy resin mainly inherited the high char yield of coal tar pitch (50 wt%) and a small portion of char yield increased value is from the chemical crosslinking weight gain. When the coal tar pitch content is 40 wt%, the chemical crosslinking weight gain reaches the maximum value of 15 wt%. Possible chemical crosslinking reaction can be epoxy group and hydroxyl group of epoxy resin and carboxyl group and phenolic hydroxyl group of coal tar pitch. This study provides some theory foundation for the future application of epoxy resin carbon composite materials.