Effects of Purification on the Structure and Properties of Hardwood Kraft Lignin

Poor melt spinnability of lignin hinders the development of lignin-based high-value products, which can attribute to the diversity of its component and structure. In this work, hardwood kraft lignin (HKL), which was obtained from paper pulping process, was filtered using a 0.05 μm ceramic membrane followed by the heat-treatment under vacuum to evaluate the effects of different purification on the chemical structure, components, and thermal properties of HKL. Results showed that the contents of ash and lignin-carbohydrate complexes (LCCs), the molecular weight and its distribution were significantly decreased after purification, while the basic structure of HKL did not change. The thermal stability and carbon content increased a lot after the heat-treatment, while the content of methoxy and β-β or β-1 linkages decreased. However, the melt spinnability of HKL decreased significantly and many defects appeared in the obtained carbon fibers after heat-treatment for a long time.