Improvement of Mechanical Properties of Softwood Lignin-Based Carbon Fibers

PEG-lignin fibers obtained by a solvolysis pulping of Japanese cedar with polyethylene glycol (PEG) 400 were successfully converted into defective-free, infusible fibers as a precursor for carbon fibers (CFs) by chemical curing followed by oxidative thermostabilization. The curing was performed by immersing PEG-lignin fibers in an aqueous mixed solution of hexamethylenetetramine (60g/L) and hydrochloric acid (3M) at 85 degrees C for 1h, resulting in the formation of crosslinkages between lignin molecules through methylene groups. These cured fibers were completely thermostabilized upon heating up to 250 degrees C at a heating rate of 2 degrees C/min under an air atmosphere. Finally, the thermostabilized fibers were carbonized to yield CFs, which showed about 1.5times the tensile strength of our CFs previously prepared.