Mechanically recyclable melt-spun fibers from lignin esters and iron oxide nanoparticles: towards circular lignin materials

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. Melt spinning of lignin C18 fatty acid esters in the presence of magnetite nanoparticles provides a facile and green way to magnetically responsive microfibers for water purification and more.

Automated summary

This study reports on the controlled esterification of softwood kraft lignin (SKL) for the production of scalable, solvent-free melt-spun microfibers. The incorporation of magnetite nanoparticles (MNPs) into lignin oleate fibers improves the thermal stability of the fibers. Adsorption of organic dyes, magnetic recovery, and recycling are achieved through melt spinning of regular and magnetic fibers.