The inferior thermoplastic properties have limited production of melt-spun fibers from lignin. Here we report on the controlled esterification of softwood kraft lignin (SKL) to enable scalable, solvent-free melt spinning of microfibers using a cotton candy machine. We found that it is crucial to control the esterification process as melt-spun fibers could be produced from lignin oleate and lignin stearate precursors with degrees of esterification (DE) ranging from 20-50%, but not outside this range. To fabricate a functional hybrid material, we incorporated magnetite nanoparticles (MNPs) into the lignin oleate fibers by melt blending and subsequent melt spinning. Thermogravimetric analysis and X-ray diffraction studies revealed that increasing the weight fraction of MNPs led to improved thermal stability of the fibers. Finally, we demonstrated adsorption of organic dyes, magnetic recovery, and recycling via melt spinning of the regular and magnetic fibers with 95% and 83% retention of the respective adsorption capacities over three adsorption cycles. The mechanical recyclability of the microfibers represents a new paradigm in lignin-based circular materials.

Reactive amine compounds are critical for a vast array of useful chemicals in society, yet a limited number of them are derived from renewable resources. This study developed an efficient route to obtain aminated building blocks from phenolic resources derived from nature, such as lignin and tannic acid, for enhancing their utility in applications such as epoxy resins, nylons, polyurethanes, and other polymeric materials. The reaction utilized a carbon storage compound, 2-oxazolidinone as a solvent and as a reagent circumventing the need of hazardous chemistry of conventional amination routes such as those involving formaldehyde. Both free acids and hindered phenolics were readily converted into aminoethyl derivatives resulting in aromatics with primary amine functionality. The aminated compounds, with the potential for enhanced reactivity, can pave the way toward more advanced renewable building blocks.