Fabricating carbon nanofibers from a lignin/r-PET blend: the synergy of mass ratio with the average fiber diameter

Abstract

For the first time, we map the conditions that lead to the successful preparation of carbon nanofibers from a blend of lignin and recycled poly(ethylene terephthalate) (r-PET). Particularly, we describe how their morphology depends on the synergy between the lignin/r-PET mass ratio and the average fiber diameter of the precursor fibers. Electrospun mats consisting of different lignin/r-PET mass ratios (from 50/50 to 90/10) and different average fiber diameters (from 80 to 400 nm) were prepared. After carbonizing them to 600 °C, it was repeatedly observed that the samples having a relatively high mass ratio of r-PET (> 33 wt%) and low average fiber diameters (~ 100 nm) exhibit extensive melting and the fibrous structure collapses. In contrast, samples of the same high mass ratio of r-PET but large average fiber diameters (> 300–400 nm) yield infusible filamentous carbon structures. This nano-dimension phenomenon declines when the r-PET content is low enough (~ 10 wt%). In this case, the nanofibers are practically infusible and carbon nanofibers with average diameters close to 100 nm and a well-formed filamentous structure are produced. Such thin lignin-based carbon nanofibers have scarcely been reported. The reasons leading to the melting of the nanofibrous mats which consist of certain mass ratios and average fiber diameters are related to variations in the decomposition rates of the two precursor polymers and also to differences in their crystallization. These phenomena are explained based on experimental results from thermogravimetry, X-ray diffraction and differential scanning calorimetry. Moreover, BET surface area measurements indicate that the melting of nanofibrous mats compromises the porosity of the activated carbon nanofibers produced from them, while the presence of r-PET has a positive impact on the development of porosity.