Morphological and microstructural development of polyacrylonitrile-based carbon fibers through controlled coagulation conditions

Abstract

Controlling the microstructure of polyacrylonitrile (PAN) precursor fibers is critical for manufacturing highperformance carbon fibers. This study investigates the impact of coagulation conditions, specifically DMF content in methanol bath and temperature, on the structural development and mechanical properties of carbon fibers. Rapid phase separation, achieved in pure methanol at -10 ◦C (MeOH100_-10), produced precursor fibers with a well-developed crystal structure and small, highly-oriented microvoids. In contrast, slower phase separation in a 30 vol% DMF bath at 30 ◦C (MeOH70_30) resulted in a poorly-developed crystal structure with large, misaligned microvoids. Although the crystalline differences minimized after carbonization, the microvoid and radial structural differences were retained. The rapidly phase-separated MeOH100_-10 precursor fiber produced a carbonized structure with well-oriented microvoids. Conversely, the slowly phase-separated MeOH70_30 precursor fiber yielded a carbon fiber with a poor microvoid orientation. These structural differences directly affected the mechanical properties of carbonized fibers. The tensile strength and modulus of MeOH100_-10 carbon fiber were 18% and 11% higher than those of MeOH70_30 carbon fiber, respectively. These findings demonstrate that phase separation behavior under different coagulation conditions significantly affects precursor microstructure and carbon fiber performance.