Synthesis and Properties of Xerogels Derived from Sulfated Pine Ethanol Lignin.

Organic xerogels based on lignin and tannins isolated from pine bark and wood were for the first time obtained by condensation with formaldehyde and furfuryl alcohol in the presence of hydrochloric acid. Sulfated pine ethanol lignin made it possible to obtain the first sulfur-containing (up to 1.3 wt %) lignin–(tannin)–formaldehyde and lignin–(tannin)–furfuryl xerogels. The gel density increased with the addition of tannins to lignin and ranged 0.13– 0.39 g/cm3. Xerogels synthesized by condensation with furfuryl alcohol were stronger than those obtained using formaldehyde. The presence of sulfur in xerogels was confirmed by elemental and chemical analyses and IR spectroscopy. Scanning electron microscopy showed that lignin–formaldehyde xerogels were formed from large polymer chains, which consisted of interconnected aggregates of micron-sized particles, and had large pores. A more compact, spatially crosslinked gel structure formed when tannins were added to the polycondensation system. The BET method showed that all xerogels had low porosity and that lignin–furfuryl samples had a larger average pore diameter (7.2–14.5 nm) as compared with lignin–formaldehyde samples (3.03–6.80 nm). [ABSTRACT FROM AUTHOR]