Correlation between fibril structures and mechanical properties of polyacrylonitrile fibers during the dry‐jet wet spinning process

Abstract

The high quality polyacrylonitrile (PAN) fibers, which were used to manufacture the high performance carbon fibers, were prepared by the dry‐jet wet spinning process. The fiber samples were treated by using the ultrathin sectioning and solution etching methods. Subsequently, the changes of the fibril structures and mechanical properties were investigated by utilizing scanning electron microscopy, high‐resolution transmission electron microscopy and mechanical tester. The fiber titer and diameters, the amount of the pores decreased during the spinning process. The microfibrils were oriented along the fiber axis to form the fiber backbone in PAN fibers. Furthermore, the microfibrils with small size were incorporated into the large fibrils and some fold chains formed the interfibril transverse joint bridges to reinforce the connection of the fibril elements. The fibrils served as self‐reinforcing element to efficiently resist the cracks propagation and dissipate much energy to increase the tensile strength and initial modulus. Consequently, the PAN precursor fibers with the homogeneous, compact, well‐oriented, and closely interlinked fibrils, presented high tensile strength and initial modulus. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47336.

Enhancing the Interfacial Properties of Composites by Grafting Polyethylene Glycol and Polyvinyl Alcohol Onto a CF Surface

“…As shown in Fig. a, the surface of CFs was smooth and had no groove structure, which is the advantage of the dry‐jet wet spinning process . It can also be seen that there were few bumps on the surface of the CFs, which may have been due to insufficient cleaning of the surface sizing agent.…”

Visualization of microfibrillar elements in cross‐section of polyacrylonitrile fiber along the fiber spinning line

“…Finally, the heat setting process was applied to improve the fiber structures to obtain the sample P6 (precursor fiber). The more details of the spinning conditions could be found in Gao, Jing, Chen, et al (), Gao, Jing, Wang, Chen, Zhao, Qin, et al (), and Gao, Jing, Wang, Chen, Zhao, Wang, et al ().…”

“…The clean PAN fibers were embedded and fixed by epoxy resin at the certain direction. The transverse ultrathin sections (vertical to the fiber axis) and longitudinal section (parallel to the fiber axis) were cut by diamond knife on an ultramicrotome (LKB‐V, BROMMA Ltd., Sweden) and they were controlled within 50 nm in thickness (Gao, Jing, Chen, et al, ; Gao, Jing, Wang, Chen, Zhao, Qin, et al, ; Gao, Jing, Wang, Chen, Zhao, Wang, et al, ). The copper grids with carbon film were adapted to support ultrathin sections for electron microscopic observation.…”

“…Therefore, in order to improve the mechanical performance of the PAN based carbon fibers, there are many efforts to reveal the correlation between the microstructures and strengths. On some fine scale, the microfibrils can be visualized be the element units in PAN fibers (Diefendorf & Tokarsky, ; Gao, Jing, Chen, et al, ; Gao, Jing, Wang, Chen, Zhao, Qin, et al, ; Gao, Jing, Wang, Chen, Zhao, Wang, et al, ; Ko, Ting, Lin, & Chen, ; Perret & Ruland, ). The microfibrils have already formed in the coagulation bath owing to phase separation and crystallization (Cohen & Thomas, ; Gao, Jing, Chen, et al, ; Gao, Jing, Wang, Chen, Zhao, Qin, et al, ; Gao, Jing, Wang, Chen, Zhao, Wang, et al, ), and they would finally develop into oriented fibrils within the PAN precursor fibers during the post‐spinning process (Gao, Jing, Chen, et al, ; Gao, Jing, Wang, Chen, Zhao, Qin, et al, ; Gao, Jing, Wang, Chen, Zhao, Wang, et al, ).…”

“…Along the fiber spinning line, the formation and development of the microfibrillar elements are mainly affected by the stretching fields and heat treatment. Furthermore, the mechanical performance of PAN fiber is relevant to the microfibril structures (Gao, Jing, Chen, et al, ; Gao, Jing, Wang, Chen, Zhao, Qin, et al, ; Gao, Jing, Wang, Chen, Zhao, Wang, et al, ). Therefore, it is important to investigate the microstructural information and the evolution process of the microfibrillar elements in PAN fibers during the spinning process.…”