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

Molar masses, Mark-Houwink-Sakurada (MHS) exponents, and refractive index increments (dn/dc) for three lignins were determined without derivatization by multi-detector gel permeation chromatography (GPC) in dimethylformamide (DMF) with 0.05 M lithium bromide (LiBr). The lack of effectiveness of fluorescence filters on molar mass determination by GPC-multi-angle laser light scattering (MALS) was confirmed for softwood kraft lignin (Indulin AT) and revealed for mixed hardwood organosolv lignin (Alcell) as well as soda straw/grass lignin (Protobind 1000). GPC with viscometry detection confirmed that these lignins were present as compact molecules. The MHS exponent alpha for Indulin AT and Alcell was in the order of 0.1. Additionally, the intrinsic viscosity of Protobind 1000 for a given molar mass was much lower than that of either Alcell or Indulin AT. This is the first report of dn/dc values for these three lignins in DMF with 0.05 M LiBr.

Automated summary

Molar masses, MHS exponents, and dn/dc values of three lignins were determined in DMF with 0.05 M LiBr using multi-detector GPC. The ineffectiveness of fluorescence filters on molar mass determination by GPC-MALS was confirmed, and GPC with viscometry detection showed compact molecular structures for the lignins. Intrinsic viscosity of Protobind 1000 was lower than that of Alcell or Indulin AT for a given molar mass.