Isolation and characterization of herbaceous lignins for applications in biomaterials

The imminent industrial production of cellulosic ethanol from annual plants will generate massive amounts of herbaceous lignins that will have to be valorized. However, the chemical and physical properties of herbaceous lignins are much less known than those of wood lignins. In the present study, organosolv lignins were extracted from wheat, triticale, corn, flax, and hemp residues using microwave irradiation under similar conditions. The extracted lignins were extensively analyzed by FT-IR, 31P NMR, gel permeation chromatography, thermogravimetric analysis, and elemental and carbohydrate analysis to determine their applicability in polymers. All lignins were of high purity with low sugar, sulfur, and ash content. Corn, hemp, and flax lignins were found to contain high concentrations of non-methoxylated phenolic groups, syringyl phenolic groups, and aliphatic OH groups, respectively, making them promising candidates for production of phenolic resins, stabilization of polyolefins, and polyurethane synthesis, respectively. Triticale or wheat lignins were less specific, with a balanced content of OH groups, which makes them applicable to polyester synthesis.

► Lignin was extracted from triticale, wheat, corn, flax, and hemp residues. ► Similar microwave-assisted organosolv conditions were applied for all extractions. ► Extracted lignins were characterized by 31P NMR, GPC, TGA, elemental, sugar analyses. ► Measured physico-chemical properties allowed proposing an application for each lignin.