Lignin incorporated polyacrylonitrile has recently come up to be one of the most lucrative precursors owing to its sustainable property coming from natural lignin within the precursor as well as the polymeric phase which is capable of forming highly drawn and oriented carbon fiber precursor. Cyclization reaction is one of the most important classes of stabilization reaction and this kind of reaction is known to be susceptible to the presence of nucleophilic groups in the fiber samples. Although, literature gives us an indication that the presence of lignin has the capability to reduce the activation energy of cyclization, some of the important mechanistic insight is not yet revealed. Based on our understanding of the thermal property of PAN/lignin fibers, we hypothesized that a pre-oxidation step may play a critical role in the cyclization mechanism in PAN/lignin fibers. Here, with the help of differential calorimetric measurements, thermogravimetric measurements, and using isoconversional approach as a tool, we tried to evaluate the activation energy profile for the cyclization reaction in PAN/lignin (2:1) fibers. Consequently, we also tried to deduce mechanistic insights in the fiber systems during the cyclization reactions.

Role of pre-oxidation on cyclization of gel-spun polyacrylonitrile/lignin fiber precursors

ACS Fall 2021

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