Kraft lignins from different poplar genotypes obtained by selective acid precipitation and their use for the production of electrospun nanostructures

Kraft lignins from different poplar genotypes (Populus alba L. “PO-10-10-20” and Populus x canadensis “Ballotino”) were isolated by selective acid precipitation (pH 5 and 2.5), chemically and structurally characterized and used together with cellulose acetate (CA) for the manufacture of nanostructures by electrospinning. Generally, lignins showed a predominance of β-β´ resinols substructures (4.7–5.3 linkages per 100 aromatic units) followed by β-O-4´ (1.6–3.3 linkages per 100 aromatic units) and β-5´ phenylcoumarans (0.5–2.4 linkages per 100 aromatic units) and a high abundance of S lignin units (S/G 3.0–4.3). Moreover, lignins showed low molecular weight values (between 5.14 and 5.59 KDa) and high phenolic content (529.1 ± 1.0–644.5 ± 5.5 mg GAE/g lignin). Regarding the electrospun nanostructures obtained from Kraft lignins/CA solutions, all of them presented uniform cross-linked nanofibers with a few beaded fibers according to the suitable range values of surface tension (29.18–29.71 mN/cm), electrical conductivity (131.2–158.9 μS/cm) and dynamic viscosity (0.28–0.32 Pa.s) that biopolymer solutions showed. Nevertheless, electrospun Kraft lignins/CA nanostructures with larger mean diameters were generated from lignins at pH 5, which displayed higher phenolic and β-O-4´ contents compared to lignins at pH 2.5. On the other hand, the type of poplar lignin genotype did not exert a significant influence on the mean fiber diameter.