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

Abstract After curing, phenol‐formaldehyde resins were post‐cured at 160°C, 230°C, and 300°C in air for several hours, and then those post‐cured samples were carbonized at 1000°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°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.