Lignin is a cheap material available in large quantities, thus the interest in its valorization is increasing both in industry and academia. A possible approach towards value added applications is using it as a component in plastics. However, blending lignin with polymers is not straightforward because of the polarity of lignin molecules resulting in strong self-interactions. The structure and properties of lignin depend on the extraction technology used for its production. The structure of lignin is complex and its characterization difficult. Lignin has been added to various polymers in the last few decades and the resulting material was sometimes called blend, while in other cases composite. Based on arguments we show that lignin forms blends, and these are classified and discussed according to the interactions developing in them, since competitive interactions determine the structure and properties of the blends. Usually even strong interactions are not sufficient to result in complete miscibility. As a consequence lignin is often modified chemically or by plasticization to improve its dispersion in plastics, or a compatibilizer is added to increase interfacial adhesion. Lignin can be used also as a reactive component in various resins and polymers.

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