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.