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Summary: A new chemical modification of sugar cane bagasse fibers for phenolic thermoset composites is presented. It consists in creating quinones in the lignin portions of fiber and react them with furfuryl alcohol to create a coating around the fiber more compatible with the phenolic resins used to prepare polymeric matrix. Sodium periodate was used in suitable conditions to oxidize mainly phenolic syringyl and guaiacyl units of the lignin polymer to create quinones, which were characterized by UV‐visible diffuse reflectance spectroscopy by comparison with model compounds. The reactivity of furfuryl alcohol (FA) with fibers was greatly enhanced after they were oxidized: 13% weight percent gain compared to 2% without oxidation. Chemical analysis of unmodified and FA‐modified fibers have shown an important degradation of hemicelluloses and a slight one of cellulose which almost maintains its crystallinity. A 25% decrease of strength and length properties of the fibers after FA chemical treatment was measured by dynamic mechanical analysis. The lignin‐like proportion of the fiber was greatly enhanced after the FA‐treatment. This was confirmed by thermal analysis, DSC, and TGA experiments, on unmodified and FA‐modified fibers. SEM analysis of the fibers and of phenolic composites with modified fibers have confirmed the FA grafting and shown a better compatibility at the interface between the chemically modified fibers and the phenolic matrix. Nevertheless, the chemical treatment of the fibers decreased the impact strength of the composite, which could be caused by the fiber damage suffered during the chemical modification and for the more intense adhesion at the interface, which in some cases decrease somewhat the impact strength.Cross photomicrography of FA‐modified sugar cane bagasse fiber (600×).magnified imageCross photomicrography of FA‐modified sugar cane bagasse fiber (600×).

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