Chemical aging mechanism of polyacrylonitrile in different solvents
Polyacrylonitrile spinning dope was used as a raw material for the preparation of polyacrylonitrile precursor in a two-step process under long-term exposure to a minimum of 80℃during preparation,storage and transportation.Thus,long-term heat tracing causes chemical aging of the spinning liquid,which affects the quality of the prepared precursor.Using the most commonly used in the preparation of carbon fiber are N,N-dimethylformamide(DMF),N,N-dimethylacetamide(DMAc)and dimethyl sulfoxide(DMSO)as solvents.The structural changes and viscosity changes of polyacrylonitrile solutions under high temperature conditions were studied by Fourier transform infrared spectroscopy(FTIR)and rotational viscometer,and the corre-sponding chemical aging mechanism was proposed.The results show that the color of PAN solution with DMF,DMAc and DMSO deepen with the increase of aging temperature.In FTIR,the characteristic peak of the—C=N group formed by the cross-linking reaction of acidic nitrile group α-H and similar nitrile group molecules appeare,indicating that an irreversible chemical reaction occurr.The apparent viscosity of the three PAN solutions decrease with the increase of treatment temperature.This is due to the occurrence of nitrile cross-linking reaction within the PAN molecule,which reduces the cohesion energy between the molecules,resulting in a decrease in the viscosity of the solution.The difference is that PAN/DMF solution gels above 180℃.This is due to the fact that the cross-linking reaction between molecular chains is more likely to occur in DMF system at high temperatures,forming a gel network structure.Mastering the chemical aging mechanism of spinning solution can provide a certain reference signif-icance for actual production,such as adjusting parameters to avoid the appearance of chemical gels,or making use of the resulting cross-linked structure.
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