Effect of post-curing on the mechanical properties of carbonized phenolic resins

After curing, phenol-formaldehyde resins were post-cured at 160 degrees C, 230 degrees C, and 300 degrees C in air for several hours, and then those post-cured samples were carbonized at 1000 degrees C. The effect of post-curing on the physical properties and microstructure of the carbonized phenolic resin is reported in this article. The purpose of post-curing was to improve the mechanical properties of the carbonized resins. The post-curing process promoted the crosslinking reaction and the evolution of gases. The cured resin post-cured at a higher post-curing temperature (300 degrees C) had a significantly higher weight loss, greater linear shrinkage and lower density than others samples. During carbonization the post-curing process not only decreased the weight loss but also limited the shrinkage. Post-curing also promoted the formation of carbon basal planes and the chemical densification in structures of the final carbonized resins. The increase in post-curing temperature and time had the effect of reducing the Linear shrinkage of the resin during carbonization. The TGA thermal analysis showed that the post-cured resins improved the total weight loss more than 15 wt% over the unpost-cured resin. The carbonized resins developed from the post-cured resins had a greater flexural modulus by about 10-50% and improved the linear shrinkage by about 10% over that developed from unpost-cured resin.