Carbon fibers from polypropylene: Structural evolution of precursor fiber during stabilization and carbonization

Utilizing polypropylene (PP) fibers as the precursor material, Polypropylene-based carbon fibers (CFPP) were obtained by carbonization after sulfonation cross-linking with sulfuric acid. First, the mechanism of structural evolution of sulfonated PP fiber (SFPP) during carbonization was investigated at temperatures between 500 °C-1300 °C. According to the results, the chemical structure, as well as the carbon structure transformation of SFPP, depending on the carbonization temperature, i.e., the removal of organic functional groups, the fusion to small aromatic structures, and the transformation to ordered carbon structures. The carbon content of the carbon fibers obtained at 1300 °C was as high as 93.4%. Subsequently, various PP fibers with different diameters and crystalline structures were prepared by melt spinning and subsequent thermal-drawing treatment, and the relationship between their structures and the properties of CFPPs was investigated. The sulfonation reaction rate of PP fibers increased as the sulfonation reaction proceeded and was synergistically regulated by the crystalline structure and fiber diameter. The CFPP with a smaller diameter exhibited a more homogeneous skin-core structure, together with higher overall graphitization, smaller graphite layer spacing, and better graphite microcrystalline structure, and thus its conductivity and mechanical properties of the carbon fiber were significantly improved. The mechanical properties and volume resistivity of the prepared CFPP reached 338.6 MPa and 4.91×10−5 Ω·m, respectively.