Accelerated thermostabilization through electron-beam irradiation for the preparation of cellulose-derived carbon fibers

Abstract

The potential of biobased materials like regenerated celluloses as precursors for carbon fibers (CFs) is long known. However, owing to an intrinsic two pathway pyrolysis mechanism of cellulose its carbonization is accompanied with side reactions under generation of volatiles. In practice, this leads to a reduced char yield, results in inferior mechanical properties of the CFs, and requires time-consuming thermostabilization procedures or wet-chemical pretreatments during production. Thus, their market share currently remains low. In ambitions to circumvent these issues, the potential of electron beam irradiation (EBI) as a dry chemical pretreatment for cellulosic CFs was investigated in this study. The conducted chemical analyses showed that high radiation dosages (2 MGy) lead to a strong depolymerization of the cellulose chains down to oligomers, while the fibrous macrostructure was preserved. Minor oxidation reactions were also evident. Thorough thermostabilization experiments under air in the temperature range from 100 °C to 250 °C revealed that reactions caused by EBI treatment alone were insufficient to increase the char yield. Only when the EBI treated precursor fibers are subjected to heating between 200 and 250 °C the char yield increased significantly to 34.4 % compared to 12.1 % for the untreated fiber. Furthermore, the EBI treatment strongly accelerated the reactions during thermostabilization allowing to collect CFs at heating rates of 2 °C/min compared to 0.5 °C/min needed for pristine fibers. Additionally, cellulose-lignin composite fibers were subjected to EBI treatment, proving that this strategy can also be applied to these emerging biobased CF precursors.