The influence of post-cure on properties of carbon/phenolic resin cured composites and their final carbon/carbon composites

Two-dimensional (2D) carbon/carbon (C/C) composites were prepared with phenol-formaldehyde resin and graphite fabric. After curing, polymer composites were post-cured in air at 160 degrees C and 230 degrees C for several hows and then all polymer composites were carbonized up to 1500 degrees C. The effect of post-cure on the microstructure and fracture behavior of the resultant carbon/carbon composites was studied. The past-cure process was characterized by weight loss. This process promoted the crosslinking and condensation reactions and led to the formation of long-chain, cross-linked polymeric structures in the matrix. The post-cured composites had a greater density than the unpost-cured composite. This study indicates that a longer post-curing time and higher post-curing temperature would limit the shrinkage for the post-cured composites during carbonization. The improvement in linear shrinkage was 22% to 44%. This process also limited the formation of open pores and decreased the weight loss of the resultant C/C composites. The resultant C/C composites developed from post-cued composites had a greater flexural strength by 7 to 26% over that developed from unpost-cured composite.