Size‐Exclusion Chromatography and Aggregation Studies of Acetylated Lignins in N,N‐Dimethylacetamide in the Presence of Salts

Abstract

The molar masses of acetylated kraft lignin and organosolv lignin are determined using both dynamic light scattering and size-exclusion chromatography (SEC). Preparative gel fractionation of both lignins is allowed for the further analysis of low-polydispersity lignin fractions. Fundamental information about the aggregation behavior of different molecular weight lignins in different solvent systems is provided. Two different solvent systems are used for SEC. Universal calibration is used for analysis. Applying the Flory-Fox theory, the obtained molecular weights are allowed for determining the maximum glass transition temperature at theoretical infi nite molecular weight, T g ∞ , of both acetylated lignins. from synthetic polymers. First, lignin is structurally quite inhomogeneous. Both the structure and molecular mass depend on the wood species used, and the pulping and subsequent isolation process. In course of its biogenesis, lignin is built up via radical enzymatic coupling reactions out of three monomeric subunits, i.e., cumaryl, coniferyl, and sinapyl alcohol. The coupling of these monomers leads to p -hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units. [ 2 ] On the basis of these subunits, lignin can be divided into three different types which are softwood lignins containing mainly G units, hardwood lignins containing both the G and S units, and lignin from annual plants primarily consisting of H units. [ 2 ] The relative ratio of these subunits determines the degree of branching in lignin. Softwood lignins are more prone to branching due to a lower number of methoxy groups. Vice versa, hardwood lignins have a lower degree of branching and as a consequence a more linear molecular structure.One crucial step that infl uences the properties of lignin and its molecular weight is the pulping process. The main industrial pulping processes are the kraft process, the sulfi te process, and the soda-anthraquinone process. [ 3 ]

Carbon Fibers Prepared from Melt Spun Peracylated Softwood Lignin: an Integrated Approach

“…For a more comprehensive discussion on the resulting structures kindly refer to work by Sakakibara and Nimz . In fact, softwood lignin fractions of different molecular weight have been found to possess Mark–Houwink (α) constants close to zero, which confirms their almost spherical structure. This prevents crystallization and renders these materials virtually 100% amorphous, which in turn facilitates the melt spinning of lignins.…”

Effects of Ethanol Concentration on Organosolv Lignin Precipitation and Aggregation from Miscanthus x giganteus

“…Understanding and interpreting the assembly of lignin macromolecules in solution are relevant and significant, as the heterogeneity and complexity of lignin structure, unique chemical reactivity, and the unknown molecular characteristics of lignin become the greatest bottlenecks in the utilization of lignin in producing various useful and renewable materials in the industry [11][12][13]. Previously, numerous studies on lignin aggregates have been conducted in conjunction with different types of methods and sources of lignin such as the aggregation and assembly of alkali lignin using iodine as probe [14], the impact of lignin source on its self-assembly in d-DMSO solution [10], and the aggregation of acetylated lignins in N,N-dimetylacetamide in the presence of salts [15]. A crucial physicochemical property of organosolv lignin which becomes the subject matter for this work is the higher solubility of organosolv lignin in organic solvents [16].…”

Lignin-Depolymerisation via UV-Photolysis and Titanium Dioxide Photocatalysis

“…Thus, 25 mg of the lignins were weighed into a 1.5 mL reaction vessel and added with 850 µL acetylation reagent. Inspired by Clauss et al [19] and…”