Peeling experiments for hemp retting characterization targeting biocomposites

The control of hemp plant harvesting, in particular the retting process, represents the major step for the development of high-performance hemp biocomposites. In this study, the consequences of hemp retting on the ease of fibre extraction and tensile properties of elementary hemp fibres is explored. Stem peeling experiments are combined with scanning electron microscopy (SEM) to investigate the influence of the retting degree in plants. After studying the evolution of fracture energy at the fibre/woody core interphase within the stem, this work investigates fracture mechanisms during peeling experiments which aims to understand the evolution of fibre bundle cohesion during retting. A drastic drop of fracture energy reveals the impact of retting on the ease of peeling the outer tissue of the stem (containing fibre bundles), leading to less damage of fibres during the extraction process. The positive impact of retting on various fibre defects combined together leads to a 33% increase in the tangent modulus between non-retted and retted fibres, highlighting the importance of understanding the retting process to open up to new markets for biocomposites.