Preparation of Carbon Fibers from Organosolv Lignin Obtained by Aqueous Acetic Acid Pulping

Abstract

Lignin fibers as precursors for carbon fibers were prepared by melt spinning from organosolv lignin (AWL), which was obtained from birch wood by aqueous acetic acid pulping at atmospheric pressure and used without any chemical modification. The spinnability of AWL was attributable to polydispersity of the lignin and to partial acetylation of hydroxyl groups during the pulping. Production of satisfactory lignin fibers was achieved by simple thermal treatment of lignin, followed by continuous spinning at a rate of more than 400m/min. The thermostabilization of thin (less than 30μm in diameter) and thick threads was achieved by heating to 250°C at a rate of 0.5°C/min in air and under oxygen stream, respectively. Carbonization of thermostable fibers was achieved by heating to 1,000°C under nitrogen stream. The mechanical strength of the carbon fibers was found to be related to the diameter of fibers. Typical mechanical properties of carbon fibers from AWL were as follows : fiber diameter 14 ± 1.0 μm ; elongation, 0.98 ± 0.25% ; tensile strength, 355 ± 53 MPa ; modulus of elasticity, 39.1 ± 13.3 GPa. The carbon fibers derived from AWL can be classified as fibers of general performance grade.