However, these melt-spun lignin fibers could not be adequately stabilized due to the presence of thermally stable acetyl groups that would not crosslink, even when the thermo-oxidation heating rate was as low as 0.01 °C/min. Consequently, SKL was reacted with a significantly lower anhydride concentration (0.66 ml Ac2O/g SKL) for only 0.25 h to produce acetylated SKL (Ace-SKL).