According to the global trend in the world, many studies are conducted to valorize the plant biomass at its best potential. On one hand, a significant part of these works is focused on the enhancement of thermal and mechanical properties of composites reinforced with lignocellulosic fibres. On the other hand, a huge part of the lignin fraction produced by wood and paper industries should be valorized throughout chemistry for the synthesis of high value-added compound instead of being burnt for the production of energy. In this work, we use ferulic acid, which can be obtained from lignin, and its derivatives, to influence the aspect ratio of lignocellulosic fibres incorporated in biocomposites materials in order to impact the properties. The aspect ratio being one of the key parameters for mechanical thermoplastic's fibre reinforcement. Ferulic acid derivatives are synthesized by enzymatic chemistry following a green process and are afterward pulverized on hemp fibres. These pretreated fibres are incorporated in a polycaprolactone matrix during a single screw extrusion process. Fibres are extracted from the polymer by Soxhlet and analyzed to measure the aspect ratio distribution after process. Tensile test specimens are injected and mechanical properties are measured. Characterizations are also conducted to measure the thermal properties of the composites. Crude products are analyzed by Raman spectroscopy to define their spectral profile. As a result, we have determined by Confocal Raman Imaging the influence of the chemical structure of the ferulic acid derivatives on the aspect ratio of the fibres and on the thermo-mechanical properties of the composites after the extrusion process. Although this imaging technique require an advanced expertise level in image processing and expensive device, the reported method based on confocal Raman allows quantitative analysis and permits high-throughput screening of each individual component within a blend.