Multistep structure evolution during the coagulation of PAN/DMSO solution studied by in-situ FTIR spectroscopy

Coagulation is the first step in the formation of the aggregation structure during the preparation of polyacrylonitrile (PAN) fiber, which has a significant effect on the mechanical properties of PAN precursor and its based carbon fiber. However, due to the rapid coagulation speed of the PAN/DMSO solution in the coagulation bath, research about the complex matter exchange and structural evolution during this process is still a challenging topic. In the present study, the PAN/DMSO solution was set in an environment with constant humidity to slow down the coagulation rate. In situ FTIR measurements combined with two-dimensional correlation analysis were used for the first time to study the detailed evolution of the intermolecular interaction and PAN chain conformation caused by the change of H2O, DMSO, and PAN content during coagulation. The results indicated that with the diffusion of H2O from the atmosphere to PAN/DMSO solution, hydrogen bonds between H2O and DMSO were gradually generated, which led to a chemical environmental change around PAN chains and promoted the dissociation of PAN and DMSO. After that, the parallel-oriented –CN groups promoted the conformation change of the PAN chains.