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a b s t r a c tThe modern biorefinery concept is aimed at the elaboration of sustainable processes with the most profitable utilization of all biomass products obtained at the technological cycle. Lignin separated as byproduct in the lignocellulosic chemical processing is recognized as an important component of polymer systems. The presence of sterically hindered phenolic hydroxyl groups in the lignin macromolecule opens the possibility of its application as antioxidant for composites, e.g. polyurethanes (PU), which are considered as one of the most versatile polymeric materials. In the present work, the object of investigations was lignin obtained as a product, so-called BIOLIGNIN TM , of wheat straw organosolv processing for pulp and fuel ethanol production (CIMV pilot plant, France). However, heterogeneity of the lignin obtained negatively influences its applicability that can be overcome by fractionation. Three soluble fractions were isolated from CIMV lignin by a sequential extraction with dichloromethane (A fraction), methanol (B fraction) and mixture of both the solvents (C fraction) and characterized in terms of their composition, functionality and structure using analytical pyrolysis (Py-GC/MS), 31 P NMR and Size Exclusion Chromatography (SEC) methods. Antioxidant properties of BIOLIGNIN TM fractions were assessed in the tests with free radicals ABTS • + and DPPH • . Application of Py-GC/MS for characterization of the fractions opened an opportunity to found some novel "structure-activity" correlations needed for understanding and tuning of antioxidant properties of lignins. The antioxidant activity of the fractions under investigation was tested by their influence on thermo-oxidative destruction of prepared model PU films. The data of TGA method (oxidative conditions) clearly testified the antioxidant effect of all three fractions with the most prominent activity for C fraction. The shifting of the exothermal maxima connected with oxidizing of volatile products of PU destruction to the higher temperature region by 20-30 K and 30-40 K was registered.

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Rigid polyurethane (PUR) foams with the apparent density in the range of 45-60 kg/m 3 were produced from tall oil polyol (TOP) and organosolv wheat straw lignin as filler. PUR foams were filled with lignin in the amount of 0-6.3 wt %. Mechanical properties, dimensional stability, water absorption and thermal conductivity of prepared foams were investigated. The use of lignin increased the content of renewable materials in the end product, reaching together with TOP the value of 23.6 wt %. The viscosity of polyol system and foaming process parameters (cream time, gel time, tack-free time and full rise time) were determined. The viscosity of polyol system rose exponentially when concentration of lignin in the PUR foam was increased. The maximum value of compressive strength (0.35 MPa parallel to the foaming direction) was reached in the PUR sample where the concentration of lignin in foam was 1.2 wt %. It was concluded that wheat straw lignin can be used as a filler to obtain rigid PUR foams having the characteristics of thermal insulation material.