Light scattering of acetylated lignin

Abstract

SYNOPSISOrganosolv lignin was fractionated on a Sephadex G 75 column with 0.1M aqueous NaOH resulting in 14 fractions. These fractions were acetylated and a high-molecular-weight fraction (F3) was investigated by means of combined static and dynamic light scattering ( LS) in solvents acetone, tetrahydrofuran (THF) , and trifluoroethanol (TFE) . The measurements were found to be reproducible, and recycling of lignin by freeze drying caused slight but unessential changes in solution properties. Depending on the solvent used, weight average molecular weights M , between two and ten million were found. By contrast, M , of the fractions, measured by vapor pressure osmometry (VPO) , was in the range of a few thousands only. Analysis of the angular dependence in static LS by means of a CasassaHoltzer plot and the fractal dimensions showed the presence of chain stiffness, most distinct in TFE. Also, the dynamic light scattering results in TFE are typical for semiflexible chains, while in THF, and to some extent in acetone, the dynamic measurements including viscosity suggest the presence of spherical structures. These findings are being explained by large lignin clusters that consist of stiff subunits.

Getting Closer to Absolute Molar Masses of Technical Lignins

“…The latter point is quite important as lignins fluoresce that might cause extremelyo verestimated values as the fluorescence radiation interferes with the scattered laser light in the MALS detector. [27][28][29][30] Some examples are found in literature presenting lignin weight-average molar masses (M w )u pt o 400 000 gmol À1 in SEC-MALS analysis with the overestimation causedb yt his fluorescenceproblem. [27][28][29][30] If technical lignins from the kraft process are to be analyzed, the errors originating from fluorescence issues become more critical.…”

“…[27][28][29][30] Some examples are found in literature presenting lignin weight-average molar masses (M w )u pt o 400 000 gmol À1 in SEC-MALS analysis with the overestimation causedb yt his fluorescenceproblem. [27][28][29][30] If technical lignins from the kraft process are to be analyzed, the errors originating from fluorescence issues become more critical. The process conditions during kraft pulping result in the formation of variousc hromophores and condensed structures, [31] including ab road range of fluorescing moieties (conjugated aromatica nd quinoids ystems).…”

Molar mass determination of lignins and characterization of their polymeric structures by multi-detector gel permeation chromatography

“…Using a light-scattering detector to determine absolute molar mass of lignins is challenging because fluorescence interferes strongly and leads to overestimation of the molar mass (Cathala et al, 2003;Froment & Pla, 1989;Merkle et al, 1992). However, reports in literature are incongruous regarding the efficiency and role of fluorescence filters and if light scattering provides true molar masses for lignin.…”

Formation of uniform colloidal spheres from lignin, a renewable resource recovered from pulping spent liquor

“…In some studies, alkali lignin is acetylated to improve the solubility in organic solvents. 24 Colloidal spheres formed from the ACL can provide a new approach to exploit the functionality of lignin derivatives, such as drug controlled release and pesticide microencapsulation.…”