Abstract. Wheat straw lignin was pre-treated by organic solvents of different polarity: ethylacetate, ethylmethylketone and ethylmethylketone/water mixture, using sequential extraction technique. The total yield of fractions was ~ 40% (w/w). In comparison with non-treated lignin the solvent soluble fractions have lower molecular weights, lower polydispersity and average functionality indices. The low viscosity lignopolyols with lignin substituent content up to 40%, suitable for rigid polyurethane foams obtaining were produced by the oxypropylation of isolated fractions. The non-soluble in organic solvents lignin residue represent a purified natural aromatic amorphous cross-linked polymer. Therefore besides oxypropylation its application as filler of thermostable polymers with enhanced flammable resistance could be beneficial biorefinery approach.
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