Correlation between the Microstructure and the Mechanical Properties of PAN-based Stabilized/Carbonized Fibers

Abstract

Polyacrylonitrile (PAN) have been regarded as a versatile precursor for high strength carbon fiber. Carbon fiber has been developed 50 years ago, however microstructure developed mechanism and the correlation between microstructure of carbon fiber and mechanical properties has not been clearly established. Using continuous heat-treatment equipment in UNIST, the microstructure of the PAN precursor fiber was defined. In chapter 2, we found optimization conditions on manufacturing process for high strength carbon fiber. The carbonization temperature is the key parameter than another parameter. To determine effect of heat-treatment process, the sample was collected for each temperature zone. In the chapter 3, the cyclization reaction defined in different stage. From 200oC, the cyclization reaction occurred which effect to loss of tensile strength. At 240oC, the crystallite of PAN structure transition to ladder structure. This crystal destroyed effected to the modulus of stabilized. In the fracture morphology image, surface show the tough region. Therefore, the core consist more amorphous PAN structure reacted first, then the crystal phase reacts. In chapter 4, the stabilized fibers were prepared from the chapter 3. As the carbonization temperature increase, the density and the mechanical properties were changed. We defined the four stage of carbonization. At the stage 1, from 400 to 580oC, the residual PAN structure cyclized in the fiber. At the stage 2, from 580 to 900oC, the intermolecular crosslinking by dehydrogenation occurs. At the stage 3, from 900 to 1200oC, the intermolecular crosslinking by denitrogenation with high weight loss in the carbonized fiber. At the stage 4, the structure of graphitic structure growth. The mechanical properties highly increase in carbonization region, stage 3 and 4. With Raman analysis, microstructure of the surface-skin-core region detected. In the stage 2, the high decrease of D-band in core due to the combination of high excess heat. In the stage 3, the amorphous carbon developed in core region due to the shrinkage process. This thesis about tracing of evolution in the PAN fiber and give the key information to manufacturing the carbon fiber. By optimized the carbonization process, the manufacturing cost and time will reduce and might be reduce the cost of final carbon fiber. By high performance carbon fiber in low cost, the application of carbon fiber expands in the industry.