Extrusion‐Drawing Process Coupling With Non‐Solvent Induced Phase Separation for <scp>PAN</scp> Films With Improved Structural Uniformity and Mechanical Properties

ABSTRACT High‐quality polyacrylonitrile (PAN) precursors are crucial for producing high‐performance carbon fibers. While fabricating ribbon‐shaped precursors from PAN films shows great potential, the conventional non‐solvent induced phase separation (NIPS) method does not allow for drawing, resulting in films with inferior quality. To overcome this limitation, an extrusion‐drawing process coupled with NIPS is proposed, in which a PAN solution is extruded through a slit die, traverses an air gap, coagulates into a film in a coagulation bath, and is then drawn. The effects of drawing speed on the structure and properties of the films were investigated. The results indicated that drawing promoted molecular chain disentanglement and orientation in the air gap, as well as shrinkage and densification of the pore network in the coagulation bath, which reduced film porosity by 40.75% and increased crystallinity by 30.76%, ultimately enhancing the tensile strength and modulus by 206.95% and 212.90%, respectively. Furthermore, the establishment of symmetric mass transfer boundary conditions, along with the reduction in film thickness, accelerated phase separation kinetics, promoting the formation of a uniform sponge‐like pore structure. Under optimal conditions, the film achieved a tensile strength of 33.96 MPa, a tensile modulus of 1386 MPa, a thickness of 19.8 μm, and a homogeneous microstructure.