Improving preferred orientation and mechanical properties of PAN-based carbon fibers by pretreating precursor fibers in nitrogen

Polyacrylonitrile fibers were heat-treated and stretched appropriately in nitrogen to make the nitrile groups cyclized partially and enhance the molecular orientation. A further reaction in air made the pretreated fibers fully stabilized, showing a higher preferred orientation than those of conventionally stabilized fibers. The resultant carbon fibers had a higher density, smaller interlayer spacing, lower porosity and better preferred orientation, which gave rise to considerable increases in tensile strength and Young’s modulus.