Screening of spinning oils for melt-spun lignin-based carbon fiber precursors

For the improvement of the processing of melt-spun lignin-based fibers, the use of a spinning oil is necessary. The use of spinning oils is standard for the processing of PAN based carbon fiber precursors. Since no commercial spinning preparations for lignin fibers are available on the market, a study on different oils, such as technical oils, food-grade oils or spinning avivages, is performed. A stepwise approach with applied tests (viscosity measurement, fiber etching, melt-spinning, stabilization, carbonization) was developed to eliminate oils which are not suitable. The physical properties of the tested oils are determined and spectroscopic studies of these avivages are performed. Mechanical properties are characterized for as-spun lignin fibers, stabilized lignin-based fibers and lignin-based carbon fibers with and without a spinning preparation. Four of seven tested spinning oils improve the handling during the processing of lignin-based fibers but only two spinning oils lead to good quality carbon fibers and improve even the tensile strength of the resulting carbon fibers.