SYNTHESIS AND STUDY OF THE PROPERTIES OF XEROGELS DERIVED FROM SULFATED PINE ETHANOL LIGNIN

Abstract

Organic xerogels based on lignin and tannins isolated from pine bark and wood were first obtained by condensation with formaldehyde and furfuryl alcohol in the presence of hydrochloric acid. The use of pine sulfated ethanol lignin made it possible for the first time to obtain sulfur-containing (up to 1.3% wt.) lignin-(tannin)-formaldehyde and lignin-(tannin)-furfuryl xerogels. The density of the obtained gels increases with the addition of tannins to lignin and varies in the range 0.13–0.39 g/cm3. Xerogels synthesized by condensation with furfuryl alcohol are stronger than those obtained using formaldehyde. The presence of sulfur in xerogels was confirmed by elemental and chemical analysis and IR spectroscopy. It was shown by scanning electron microscopy, that lignin-formaldehyde xerogels are formed from large polymer chains, consisting of interconnected aggregates of micron-sized particles and have large pores. The addition of tannins to the polycondensation system is accompanied by the formation of a more compact spatially crosslinked gel structure. BET method showed that all xerogels have low porosity, and lignin-furfuryl samples have a larger average pore diameter (7.2–14.5 nm) compared to lignin-formaldehyde samples (3.03–6.80 nm).