According to the global trend in the world, many studies are conducted in order to valorize plant biomass at its best potential, in particular as materials. On one hand, plant fibers are used to reinforce composites and to enhance their thermal and mechanical properties. On the other hand, the lignin fraction produced by wood and paper industries, which is burnt now to produce energy, should be valorized through chemistry for the synthesis of high value-added compound. In this work, ferulic acid and its derivatives, which can be obtained from lignin, were used to influence the aspect ratio of lignocellulosic fibers incorporated in biocomposites materials, one of the key parameters for mechanical thermoplastic's fiber reinforcement.<br/><br/>In this work, two ferulic acid derivatives were synthesized by enzymatic chemistry following a green process and subsequently pulverized on hemp fibers. The first ferulic acid derivative was a macrobisphenol while the second one was obtained after the methylation of the phenolic functions of the latter. Then, these pretreated lignocellulosic fibers were incorporated in a polycaprolactone matrix during a single screw extrusion process. Fibers were extracted from the polymer by Soxhlet and analyzed to measure the exact fiber content and the aspect ratio distribution after process. Tensile test specimens were injected and mechanical properties were measured. Chemical analysis were conducted by steric exclusion chromatography to measure the impact of the ferulic acid derivatives on the molar mass of the matrix. Rheological analysis provided information about the plasticizing effect of the ferulic acid derivatives on the materials. Hemp fibers, ferulic acid derivatives and crude polycaprolactone were also analyzed by Raman spectroscopy to define their spectral profile.<br/><br/>As a result, the microstructure of the composites after the extrusion process was determined by Confocal Raman Imaging and was correlated with the mechanical properties measured by tensile tests. We evidenced that the very single methylation of the macrobisphenol led to significant differences on the mechanical properties and the structure of the composites. Two hypothesis were investigated to explain such effects: a stronger interaction between hemp fibers and ferulic acid derivative changing the microstructure and/or an increased plasticizing effect of the ferulic acid derivative on the polymeric matrix.

How can a single methyl group drastically modify the microstructure of a biocomposite and affect its mechanical properties?

253rd National Meeting (2017)

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