The Investigation Of Carbonization’s Prcoss And Mechanical Properties Of Pan-Based Preoxidized Fibers Under The Constant Elongation Condition

PAN-based carbon fiber has being become the largest amount of carbon’s materials in the market because of its raw material prices are cheaper, good mechanical properties and excellent performance. The carbonization plays a very important role in the carbonization process. The temperature, heating-rate、traction and the purity of protected gas have important impact in the finial fiber structure and properties.We have done a lot of work about the carbonization’s process of PAN-based pre-oxidized-fiber, which includes the relationship with different heating rates and the PAN-based pre-oxidized-fibers’starting carbonization temperature, what is trends of the fiber mechanical properties, surface morphology and lattice parameters of the fiber content and fiber elements when the Temperature, heating rate and elongation rate are changes? Finally, We successfully prepared PAN-based carbon fibers which the intensity is4.27GPa and the modulus is590GPa. The following are the main contents:1、we use thermal gravimetric analysis to investigate the starting carbonization temperature of PAN-based pre-oxygen fibers at heating-rates of5℃/min,10℃/min,15℃/min and20℃/min. We found that there is a linear relationship between starting carbonization temperature and heating-rate, and we also found that the starting carbonization temperature of PAN-based pre-oxygen is382℃when the heating-rates is zero by extrapolation. 2、The fibers’ surface appearance were investigated under different carbonization temperature by SEM, and the content of fibers’ elements also study by XPS and combustion methods. We found that the temperature is the main factor that causing the fiber element content changes. The XRD and Laman spectrum were used to analysis of the structure. It is indicates that in the carbonization process, the content of linear structure chain becomes smaller, and the representatives of the graphite structure d002peak and G peak gradually became more and more. At the same time, the microstructure fiber performance parameters also change accordingly.3、The strength and elongation at break of the fibers were characterized by Single Strands Instrument. It is found that with increasing temperature, heating-rates and elongation-rates increases, there is opposite trend between the modulus, elongation and strength when temperature was changed from300℃～800℃. In the same final carbonization temperature, heating rate and the fixed rate is a major pull factor for carbonization progress. The temperature is still the decisive factor to the mechanical properties of fibers when temperature is more above900℃. But when the temperature is higher than1300℃, the mechanical strength of the fibers was decline in appearance and modulus still maintain growth trend.4、Through compare with the changes of mechanical properties in the low and high temperature carbonization process, we determine to take this process to prepare final PAN-based carbon fiber under constant elongation conditions. It is that the heating rate of10℃/min, was0.70%fixed traction, the final carbonization temperature is600℃is appropriate in low-temperature carbonization process. Through compare with the final properties, it is found that the higher of heating-rate is better, So a heating rate of15℃/min and final carbonization temperature election1300℃is more appropriate in the High temperature carbonization process.