an aqueous solution of PVA (1 mL, 4.75% w/v) containing 0.1 M HCl was added to the sediments and the mixtures were homogenized by gentle agitation with a spatula. Centrifugation followed by re-suspending of the lignin was repeated twice under the above conditions, each time with a fresh portion of polymer solution. Finally, the suspension of lignin in PVA solution was distributed in equal volumes (2.5 mL) in plastic syringes with removed plungers and closed outlets. The mixtures were cooled in an ice bath for 30 min and a glutaraldehyde solution (40 μL, 25%) was added with gentle mechanical stirring by a spatula. The cross-linking reaction was carried out in a freezer at −14 °C for 20 h,