*2.5. Milled Wood Lignin (MWL) Isolation*

To compare the lignin recovered by the formosolv process with the pristine lignin in Paulownia wood, the milled wood lignin was prepared according to methods as previously described [21,22]. Milled Paulownia wood from an IKA WERKE MF 10 grinder (particle size < 1 mm) was subjected to several steps, as follows: (i) extraction with acetone for 8 h in Soxhlet and with hot water (100 ◦C) during 3 h, (ii) milling in a Retsch PM 400 centrifugal ball mill with toluene using an agate jar and balls, (iii) three consecutive extractions (12 h) with dioxane:water (9:1, *v*/*v*) (25 mL of solvent/g of milled wood), (iv) the separation of the supernatant by centrifugation and evaporation at 40 ◦C at reduced pressure until dryness, (v) the residue obtained (raw MWL) was redissolved in a mixture of acetic acid:water (9:1, *v*/*v*) (20 mL of solvent/g of raw MWL), (vi) precipitated in water and separated by centrifugation, (vii) milled in an agate mortar, (viii) dissolved in a solution of 1,2-dicloroethane:ethanol (1:2, *v*/*v*), (ix) the mixture was then centrifuged to eliminate the insoluble material, precipitating the supernatant in diethyl ether and separating the residue obtained by centrifugation, (x) this residue was then resuspended in petroleum ether and centrifuged again to obtain the final purified MWL fraction, which was dried under a N<sup>2</sup> current. The final yield was ca. 20% of the original Klason lignin content.
