Chemical Thermostabilization for the Preparation of Carbon Fibers from Softwood Lignin

A thermally fusible softwood lignin was directly isolated by a solvolysis of cedar wood chips with a mixture of polyethylene glycol 400 (PEG 400) and sulfuric acid. Its fusibility was found to be due to a PEG moiety introduced into the lignin by the solvolysis. The lignin was easily formed into fibers by melt-spinning at temperatures ranging from 145 to 172 o C without any modification. The lignin fibers could be converted into infusible fibers as a precursor for carbon fibers (CFs) by conventional oxidative thermal stabilization processing in air or a stream of oxygen for 2 days. We found that the infusible fibers resulted from the partial cleavage of the PEG moiety from the lignin fibers after treatment with 6 M hydrochloric acid at 100 o C for 2 h. The infusible fibers were converted into CFs with a tensile strength of 450 MPa by carbonization at 1000 o C under a N2 stream.