Evolution of polyacrylonitrile precursor fibers and the effect of stretch profile in wet spinning

Abstract

Wet spinning of polyacrylonitrile‐based polymers is a common technique to manufacture carbon fiber precursors. Understanding the role of stretch profile on structural evolution will support efforts to reduce cost and improve process robustness. Fiber stretch generally occurs in three sequential stages: jet stretch, wet stretch (first draw), and hot draw (second draw). In this study, total fiber stretch was kept constant, but distributed differently across the stretch stages yielding three different fiber variants. Samples were collected and analyzed after each stretch stage in order to correlate process parameters to structural information. For all variants, orientation of the ordered phase increases gradually for each stage of stretch while activation energy for the structural relaxation decreases. Alternatively, crystallite size increases substantially during hot draw, which is shown to have the most pronounced effect on cyclization behavior. Given the process conditions, the variant with the lowest jet stretch and highest hot draw demonstrates the highest tenacity and modulus along with the greatest orientation, crystallite size, and highest peak exotherm temperature.

Intensive and thermally conductive boron nitride/aramid nanofiber composite fibers fabricated via a wet spinning technique

“…It is generally accepted that under the same process conditions, fibers with the lowest jet stretching and the highest thermal stretching have the highest toughness and modulus. 45 During the spinning process, the stretching stress on the fiber between the spinning nozzle and the first collecting roller should be reduced to keep the fiber continuously. Therefore, the fibers are collected using a rotating disc to reduce the fiber tensile stress during the incomplete protonation stage.…”

Polymer-Encapsulated Aerogel Fibers Prepared via Coaxial Wet Spinning with Stepwise Coagulation for Thermal Insulation

“…With increasing the spinneret height, both the stress at break and elongation at break first increased and then decreased. The enhancement of stretching on mechanical properties can be explained by the orientation of polymer chains during stretching. , However, the stretching process will consume part of the deformation capacity of the polymer chains, which results in the drop in the elongation at break. When the stretching is excessive, the reduction in mechanical strength might be due to the existence of defects in the walls caused by the disturbance of the core spinning solution, as evidenced by the tendency of the wet fiber to break when the spinneret height was above 50 cm.…”

Continuous Wet Spinning of Regenerated Silk Fibers from Spinning Dopes Containing 4% Fibroin Protein

“…One method of obtaining a more circular fiber diameter is to decrease the water content in the coagulation bath, which encourages the delayed de-mixing of the polymer dope jet. Thus, little to no skin is formed, and the fiber is allowed to contract uniformly [36,37].…”