The Research Of Production Process Of Lignin Based Carbon Fiber And Influence Of Lignin Structure

Development of lignin-based carbon fibers not only can effectively alleviate thesituation of the shortfalls of our country’s carbon fiber, but also can address the rootcauses of pollution in paper industry. This paper studied the methods of preparation oflignin-based carbon fibers, also carried out a detailed analysis of the structure of lignin,In order to research the reaction mechanisms of lignin-based carbon fibers. We came toa conclusion that the functional groups content of the lignin affected the synthesis of thespinning solution.In this experiment, we used the lignin which was liquefied by phenol to prepare thespinning solution of carbon fibers. The preparation process was as follows: liquefied themixture of lignin and phenol2hours in138℃; Incubated for30minutes at a certaintemperature after adding hexamethylenetetramine; The synthesis was removed the smallmolecular by vacuum drying; Then we obtained spinning solution which was porous.We used three kinds of lignin to prepare the spinning solution, only corn alkalilignin could be made of spinning solution. However the other two kinds of lignin werenot suitable for the preparation of the carbon fibers. So we analyzed the lignin structuresby FTIR and³¹P-NMR to research that how contents of functional groups in ligninaffect the synthesis to carbon fibers.Three lignin structures were analyzed by³¹P-NMR, and got the phosphorusspectrum spectrograms. Through the spectrum diagram, we can determine the species ofthe functional groups in the lignin, including the condensed phenolic OH; syringyl OH;aliphatic OH; guaiacyl and demethylate OH; p-hydroxy-phenyl OH. The contents of thehydroxyl and carboxyl groups were calculated according to the amounts of the internalstandard substance and lignin. The conclusions were as follows:（1） The contents of the phenolic hydroxyl groups in the corn stalks alkali ligninwere more than in the other’s, which maked the corn stalks alkali lignin having a goodreaction activity. When we synthesized the spinning solution, more polymerizationreactions occurred in the lignin. And the reactions would produce more phenolicstructure which constituted the carbon fibers.（2） Corn stalks alkali lignin contained more carboxyl groups. The carboxyl groupcould take the acylation reaction with the hydroxyl, which changed molten properties oflignin, so the lignin had a good spinnability. （3） The guaiacyl and p-hydroxy-phenyl hydroxyl groups participated in thepolycondensation reactions, which had an important influence on the synthesis of thespinning solution. However the Syringl hydroxyl groups didn’t participated in thepolycondensation reactions.（4） Corn stalk alkali lignin had higher molecular weight, which dispersion wassmaller. This lignin could more effectively remove small molecular structure duringsynthesis reaction, which was conducive to the synthesis of carbon fiber spinning.