Effects of mass-transfer area on molecular stacking in mesophase pitch during thin-layer evaporation

Abstract

Mesophase pitch is a key precursor for synthesizing high-performance pitch-based carbon fibers. Regulating its microcrystalline structure is crucial for improving the mechanical properties of the carbon fibers obtained through spinning. Here, the large-area thin-layer evaporation (TLE) process was employed to modify the mesophase pitch by adjusting the mass transfer area, thereby improving its spinnability and the mechanical attributes of the subsequently carbonized fibers. Experimental findings reveal that, within a certain range, augmenting the mass transfer area during the TLE process is beneficial for promoting the volatilization of lighter components, enhancing the orderliness of the pitch's microstructure and the degree of molecular stacking, and thus enhancing the mechanical properties of the carbonized fibers. Specifically, the ID/IG value and the number of stacking layers of the mesophase pitch molecules shifted from 0.858 to ∼9 layers without TLE treatment to 0.531 and ∼13 layers after undergoing large-area TLE treatment. The mechanical performance tests further demonstrated that the tensile strength and tensile modulus of the carbonized fibers increased from 1363 MPa to 142.1 GPa (untreated with TLE), to 2044 MPa and 189.8 GPa (treated with large-area TLE), respectively. This research introduces a novel approach for regulating the microstructure of mesophase pitch to elevate the mechanical properties of carbonized fibers.