In scientific literature, lignin is usually given a warning sign by being noted as a complex heterogeneous polymer. Further, the complexity of lignin is increased during isolation and recovery processes. Based on its origin that includes species and isolation technique, technical lignin is qualified, providing some insight to its possible structure and degree of contamination with carbohydrates and/or sulfur. From this standpoint, lignin isolated from the black liquor of sulfate processed gymnosperms becomes “softwood kraft lignin”. However, pulping conditions and recovery methods are not considered in this classification, which can influence the structure and performance of the lignin as previously noted in the literature. Moreover, within a single technical lignin source, solvent fractionation has shown that lignin contains a variety of molecular weights with varying functionality. Building from this work, we have investigated the dynamic mechanical properties of acetone fractionated softwood kraft lignin (characterized with GPC and NMR methods) using both tensile and torsional test geometries and have identified significant differences in the thermal behavior, along with large shifts in the glass transition temperature of nearly 80 °C for the soluble and insoluble solvent fractions. As well, physical properties of the lignin vary greatly for the two fractions, such as its degree of hydrophilicity, making technical lignin have at least two categories of performance. Possibilities of the origins of these differences in structure and properties will be discussed along with linking possible polymeric applications. As a result of the differences, technical lignin, even from the same mill, should have a qualifier that it is a complex collection of heterogeneous polymers.<br/>

Distilling the performance of technical softwood lignin with simple solvent fractionation

2019 Spring National Meeting

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