Improvement of Mechanical Properties of Softwood Lignin-Based Carbon Fibers

Abstract

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 (60 g/L) and hydrochloric acid (3 M) at 85°C for 1 h, resulting in the formation of crosslinkages between lignin molecules through methylene groups. These cured fibers were completely thermostabilized upon heating up to 250°C at a heating rate of 2°C/min under an air atmosphere. Finally, the thermostabilized fibers were carbonized to yield CFs, which showed about 1.5 times the tensile strength of our CFs previously prepared.

Keywords:

• Softwood lignin
• chemical curing
• hexamethylenetetramine
• carbon fibers
• mechanical properties

Acknowledgments

This research is financially supported by a grant from the Ministry of Agriculture, Forestry and Fisheries of Japan (Development of Technologies for Biofuel Production Systems in Rural Areas [2012–2015]).