Fiber Melt Spinning and Thermo-Stabilization of Para-Rubber Wood Lignin: An Approach for Fully Biomass Precursor Preparation

Abstract

Para-rubber wood (PRW) lignin, extracted from agricultural waste, was successfully melt-spun to fibers and thermo-stabilized without employing auxiliary additives. 31P NMR analysis revealed that PRW-lignin contained mainly a syringyl unit of phenolic C5-substituted OH group, which enabled melt flow during fiber spinning, as well as a guaiacyl unit which offered the ability to cross-link during thermo-stabilization. Thermo-stabilized fibers with no fusion were achieved at 250 °C with the heating rate of 0.1 °C/min. Structural changes in the fibers during stabilization were systematically investigated using FTIR and XPS analyses. From the results, changes in the intensities of characteristic bands relating to C-H stretching, aromatic C-H stretching, and C═O stretching indicated structural changes of lignin toward aromaticity via oxidation reactions. XPS analysis of the fibers carbonized at 900, 1000, and 1200 °C revealed an increase in carbon content from 72 to 87 wt %. and a decrease in oxygen content from 28 to 13 wt %. with the increasing carbonization temperature. The weight loss of carbonized fibers was in the range of 73.6 to 88.7%. The high weight loss of fibers carbonized at 1200 °C was explained partly due to the thermal decomposition of disordered carbon. The tensile strength and modulus of carbonized fibers were 163.0 and 275.1 MPa, respectively. This study demonstrates an approach to prepare a fully biomass precursor fiber and contributes to the exploration of the potential use of lignin from biomass waste.