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Inthis work we report on the preparation, characterization, andproperties of a thermally treated lignin-derived, phenolic-rich fraction(PRF) of wood pyrolysis bio-oil obtained by ethyl acetate extraction.The PRF was characterized for viscoelastic and rheological behaviorusing dynamic mechanical analysis (DMA) and cone and plate rheology.A unique thermoplastic behavior was evidenced. Heat-treated PRFs acquirehigh modulus but show low temperatures of thermal flow which can besystematically manipulated through the thermal pretreatment. Lossof volatiles, changes in molecular weight, and glass transition temperature(Tg) were investigated using thermogravimetricanalysis (TGA), mass spectrometry (MS), and differential scanningcalorimetry (DSC), respectively. Underlying mechanisms for the thermaland rheological behavior are discussed with regard to interactionsbetween pyrolytic lignin nanoparticles present in the system and therole of volatile materials on determining the properties of the materialresembling in several aspects to colloidal suspension systems. Lowthermal flow temperatures and reversible thermal effects can be attributedto association of pyrolytic lignin particles due to intermolecularinteractions that are easily ruptured at higher temperatures. Thethermoplastic behavior of PRF and its low Tgis of particular interest, as it gives opportunities for applicationof this fraction in several melt processing and adhesive technologies. [ABSTRACT FROM AUTHOR]