Mechanochemistry is a promising green process in which chemical reactions outcome by the use of mechanical constraints. The starting materials are generally under the solid state, and the energy necessary to the creation of the chemical bond is provided by an intense milling in a twin screw extruder or in a ball mill [1]. These mechanochemical reactions have the advantage of being solvent-free and easily implementable in comparison to the traditional wet chemical reactions. In the past 20 years, mechanochemistry received an increasing interest for applications in various fields including inorganic materials synthesis, organic compounds synthesis, metals recycling, crystal engineering, supramolecular aspects, etc [2]. Recently, mechanochemical processes have been explored as an efficient pretreatment prior to lignocellulosic biomass conversion [3], by disrupting the crystalline structure of cellulose and enhancing catalytic accessibility of cellulose and hemicellulose during hydrolysis [4]. Indeed, intense comminution of plant biomass in a ball mill not only significantly affects the crystalinity but also leads to the breakage of covalent bonds linking constitutive macromolecules, generating free radicals that can recombine with other molecules present within the grinder thus modifying the chemical composition of the starting materials [5]. In presence of a reactive, these free radicals could be exploited to graft some specific molecules and functionalize the lignocellulosic biomass for various applications. In previous work we demonstrated that flax fibers can be chemically grafted with a pH-sensitive fluorophore. The fibers, mixed with a polymetric matrix, brought functional properties to the material allowing the design of specific sensor by 3D printing that can react to pH variation [6]. As a continuation of this work, we explore in this study, the possibility to exploit the free radicals formation during ultrafine milling to mechanically graft fluorescein on hemp core.